This study investigated the mental health problems of university students in Hong Kong and related sociodemographic and psychosocial predictors under the pandemic. A total of 978 undergraduate students (mean age = 20.69 ± 1.61) completed an online questionnaire measuring sociodemographic factors, psychological morbidity, positive well-being, COVID-19 related stress and self-efficacy, and positive psychosocial attributes. Psychosocial risk factors included psychological morbidity, COVID-19 related stress, and difficulties encountered under the pandemic, whereas protective factors comprised pandemic related self-efficacy, positive psychological attributes, positive environmental factors, need satisfaction and positive perception toward service. Results showed that psychological morbidity in the participants was widespread, and it was related to sociodemographic factors, particularly family financial difficulties. While pandemic related stress positively predicted psychological morbidity and negatively predicted well-being indicators, COVID-19 self-efficacy showed an opposite effect. Besides, positive psychological attributes  and environmental factors  negatively predicted psychological morbidity and positively predicted well-being. Furthermore, need satisfaction and positive perception toward service were negatively associated with psychological morbidity and positively associated with well-being, while perceived difficulties showed an opposite effect. In HongN = 1,173) also revealed high levels of depression and anxiety under the pandemic  and student mental health under the pandemic? Based on the literature , we expeResearch Question 5: What are the associations between environmental factors  and student mental health under the pandemic? Based on the existing literature , we expeResearch Question 6: What are the associations between need satisfaction, perceived difficulties, and perceived usefulness of university services and student mental health under the pandemic? Referring to the existing literature , we hypoWith reference to the above research questions, we proposed four separate models to be tested. For Model 1, the predictive effects of factors related to COVID-19  on mental health of university students were examined . For Mod2.2.1.In the summer of 2022 when the fifth wave of COVID-19 (Omicron strain) occurred in Hong Kong, we invited undergraduate students from a public university in Hong Kong to participate in an online survey. Due to the difficulties in conducting random sampling in the pandemic period, quota sampling was used to recruit the participants with faculty and year of study as two stratifying factors. As one type of non-probability sampling, quota sampling selects a sample from a population consisting of subgroups and selects participants from each subgroup  based on a convenient approach . This sa2.2.2.2.1.2.2.1.1.Not at all” to “3” = “Most of the time”). By summing corresponding item scores, the total score of each problem was calculated. Previous studies supported the psychometric properties of the measure  was adopted to assess three mental health problems: depression, anxiety, and stress, with each problem being assessed by seven items . Each pa measure . The inf2.2.1.2.Not at all or less than 1 day” to “4” = “Nearly every day for 2 weeks.” The sum of all item scores was calculated as the score of CESD-R. Previous studies supported the psychometric properties of the measure , a 20-item measure assessing depression based on nine-cluster symptoms developed corresponding to the “American Psychiatric Association Diagnostic and Statistical Manual (DSM-V)” . On each measure .2.2.1.3.Yes” vs. “0” = “No”). The sum score was obtained from all items to indicate IA. A total score ≥ 4 was classified as addicted to the Internet according to Young’s criteria. Previous research provided support for the psychometric properties of the measure (Ten-Item Internet Addiction Test (IAT-10)  was adop measure .2.2.1.4.have not experienced” or “1” = “have experienced”). The sum of all item scores indicates the severity of PTSD symptoms. The psychometric properties of the measure were supported (PTSD was gauged using Trauma Screening Questionnaire (TSQ) . Particiupported .2.2.1.5.Yes” and “0” = “No”)  . The sum = “No”) .2.2.1.6.Strongly disagree” to “6″ = “Strongly agree”). The mean score of all items indicates hopelessness in this study. Previous studies supported the psychometric properties of the study .As psychological morbidity was indicated by the composite scores of the above six mental health problems in the tested structural equation modelling (SEM) models, confirmatory factor analysis (CFA) was conducted to examine the validity of the latent variable. Different model fit indices were adopted to examine the fitness of CFA models, including “Comparative Fit Index (CFI),” “Tucker-Lewis Index (TLI),” “root mean square error of approximation (RMSEA)” and “standardized root mean squared residual (SRMR).” The CFI and TLI values >0.90 together with RMSEA and SRMR values ≤0.08 indicate acceptable model fit . The mod2.2.2.2.2.2.1.Strongly disagree” to “6” = “Strongly agree.” The level of life satisfaction was represented by the item mean score. Previous research supported the psychometric properties of the scale  (five items)  to examihe scale . To exam2.2.2.2.Strongly disagree” to “7” = “Strongly agree”). Flourishing is indicated by the mean score of all items. The good psychometric properties of the scale were supported by previous research  was adopted to assess flourishing. FS has eight items measuring one’s psychological well-being in different life domains  . The parresearch . CFA bas2.2.3.2.2.3.1.Not at all” to “4” = “Always”). The mean score was gained to indicate COVID stress. CFA (three-factor model) was conducted for the scale in this study, which indicated a good model fit: χ2/df = 7.548; CFI = 0.944; TLI = 0.931; RMSEA = 0.082; SRMR = 0.053. Factor loadings ranged between 0.64 and 0.89.As a risk factor, the COVID-19 related stress was evaluated by a modified version of the “COVID Stress Scale” . This sc2.2.3.2.Not at all” to “6″ = “Exactly true”). The mean score was used as the indicator of COVID-19 self-efficacy. CFA (one-factor model) was conducted which indicated good model fit: χ2/df = 5.992; CFI = 0.967; TLI = 0.956; RMSEA = 0.071; SRMR = 0.027. The factor loadings ranged between 0.68 to 0.74.As a protective factor, the COVID-19 related self-efficacy was assessed by a modified measure developed based on the “General Self-Efficacy Scale” (GSE) . The GSE2.2.4.2.2.4.1.Strongly disagree” to “6” = “Strongly agree”). The scale score was gained by averaging all item scores. The psychometric properties of the scale were supported by previous research   to assesresearch . In our research . CFA (on2.2.4.2.Strongly disagree” to “6” = “Strongly agree”). The mean scores of the two subscales were obtained as the indicators of resilience and emotional competence, respectively. CFA was conducted for the two subscales, respectively. As each subscale contains only three items, the two CFA models were saturated models with factor loadings ranging between 0.64 and 0.87.Emotional competence and resilience were measured by two three-item subscales from the Chinese Positive Youth Development Scale (CPYDS) . The CPY2.2.5.2.2.5.1.Very unlike” to “5” = “Very like”). The composite score was indicated by the item mean score. CFA (one-factor model) was conducted, which showed good model fit: χ2/df = 4.354; CFI = 0.993; TLI = 0.985; RMSEA = 0.059; SRMR = 0.016. The factor loadings ranged between 0.55 and 0.85.The Chinese Family Assessment Instrument (C-FAI) is a locally developed measure assessing family process in terms of five dimensions , which d2.2.5.2.strongly disagree” to “5” = “strongly agree”). The item mean score was used to indicate participants’ perceived peer support. CFA (one-factor model) was conducted for the adopted peer support subscale, which indicated desirable model fit: χ2/df = 2.564; CFI = 0.999; TLI = 0.995; RMSEA = 0.040; SRMR = 0.004. The factor loadings ranged between 0.62 and 0.89.The Multidimensional Scale of Perceived Social Support (MSPSS) is a 16-item multidimensional scale assessing social support from three aspects including family, peers, and significant others . The sca2.2.5.3.strongly disagree” to “5” = “strongly agree”). The mean score of the three items was used to indicate participants’ perceived community support. As the measure contains three items, the CFA model was a saturated model with factor loadings ranging from 0.74 to 0.82.Community support was measured by three items selected from the Collective Efficacy Scale (CES) . CES ass2.2.6.2.2.6.1.not met at all” and “6″ representing “fully met.” A mean score was gained as the scale score. The measure showed good reliability in previous research   . A one f2.2.6.2.Never” and “5” being “Always.” An average score was gained as the total score. Previous research showed good internal consistency of the scale  was conducted for the measure, with results indicating acceptable model fit: χ2/df = 3.339; CFI = 0.911; TLI = 0.866; RMSEA = 0.074; SRMR = 0.051, although two items have slightly lower loadings.A measure with 10 items was developed by the research team of this study to assess students’ perceived usefulness of the university services related to the COVID-19. These services include “Counselling and Wellness Section,” “University Health Service,” “Special Funding under COVID-19″, etc. Students needed to rate their perceived usefulness of these services through a measure of six points with “1″ being “2.2.6.4.2/df = 8.278; CFI = 0.959; TLI = 0.945; RMSEA = 0.086; SRMR = 0.030. The factor loadings ranged between 0.72 and 0.84.Another measure with 12 items was developed by the research team of this study to assess students’ satisfaction with the services provided by the university during the COVID-19. Through a six-point rating scale, the students needed to indicate their levels of satisfaction with university service/support in different domains such as teaching and learning, counselling, campus facilities, etc. A mean score was gained as the total score. The results of CFA indicated good model fit: χ2.3.Descriptive and reliability analyses were conducted for all variables. We first investigated the profiles of psychological morbidity  among the participants, particularly those scales with cutoff scores . Then, Pearson’s correlation coefficients were computed to show inter-correlations among different risk and protective factors and the outcome variables . Finally, SEM was run to examine the predictive effects of the COVID-19 related factors (Model 1), positive psychological attributes (Model 2), environmental factors (Model 3), and need satisfaction, difficulties, service usefulness, and service evaluation (Model 4) on psychological morbidity, life satisfaction, and flourishing. The analyses were performed using SPSS (Version 26) and Mplus (Version 8.3).R2 increase in the SEM models. For each SEM model, the Mplus results reported the R2 values indicating the proportion of variance explained by the predictors. Based on the R2 values (ranging between 0.09 and 0.27), the estimated sample size for power = 0.09 for the predictors in the four SEM models ranged between 43 and 161. This showed that our sample size of 978 ensured sufficient statistical power to detect the effect of predictors.We used G*Power to perform power analysis of the study based on 3.3.1.The descriptive and reliability statistics are presented in 3.2.3.3.β = −0.11 and – 0.09, p < 0.05 and = 0.05, respectively). In addition, while living status did not predict mental health problems, it negatively predicted life satisfaction and flourishing . With regard to economic factors, CSSA positively predicted CESD-R  but did not predict other mental health problems and well-being indicators; having family financial difficulty positively predicted DASS-Depression and PTSD  but did not predict other indicators; having personal financial difficulty positively predicted Internet addiction  while negatively predicted life satisfaction ; personal or family members’ unemployment positively predicted DASS-Stress, CESD-R, and Internet addiction . The results supported Hypothesis 1a and Hypothesis 1b.Multiple regression analyses were conducted to examine the predictive effects of different sociodemographic factors . Year of3.4.SEM was conducted to test the predictive effects of COVID-19 related risk and protective factors (Model 1), positive psychological attributes (Model 2), environmental factors (Model 3), and need satisfaction, difficulties encountered, service usefulness and service evaluation (Model 4) on negative mental health and well-being factors (life satisfaction and flourishing). β = −0.19, p < 0.001). Higher socio-economic consequences predicted higher psychological morbidity  and lower flourishing . Checking behavior positively predicted psychological morbidity . Therefore, Hypothesis 2a and 2b were partially supported. For self-efficacy related to COVID-19, it predicted lower psychological morbidity  and higher life satisfaction and flourishing . This supports Hypothesis 2c and 2d. The predictive effects are shown in β = −0.16 and − 0.53, p < 0.01 and p < 0.001, respectively) predicted lower psychological morbidity while resilience did not. Hypothesis 3a was partially supported. Besides, beliefs of adversity and resilience  predicted life satisfaction and flourishing in positive direction while emotional competence only predicted flourishing . Therefore, Hypothesis 3b was partially supported.Regarding positive psychological attributes  negatively predicted psychological morbidity, which supported Hypothesis 4a. In addition, these factors all predicted flourishing and life satisfaction in positive direction , which supported Hypothesis 4b.All environmental factors significantly predicted outcome variables , difficulties encountered displayed a positive effect , supporting Hypothesis 5a. Besides, need satisfaction positively predicted two well-being indicators  and perceived usefulness of services and evaluation of services only positively predicted flourishing , while difficulties encountered negatively predicted two well-being indicators . Hypothesis 5b was partially supported.For Model 4 see , while n4.The present study examined the mental health status of university students in Hong Kong under the COVID-19 pandemic. It has significant contribution to the existing research in this area. Although existing research has identified university students as a vulnerable group under the pandemic and attempted to understand related factors to reduce potential mental health problems, some research gaps need to be filled. First, while a substantial body of research on mental health in university students is conducted in the Western context, few studies have been conducted in the Hong Kong context. Due to the unique cultural and social contexts, such as socio-cultural risk factors , mental 4.1.This study revealed a high prevalence of mental health problems among university students in Hong Kong under the pandemic, with over half of them experiencing symptoms of depression and anxiety, and a sizeable proportion showing symptoms of stress, PTSD, and Internet addiction. These findings are consistent with previous research indicating that university students are vulnerable to negative mental health outcomes under the pandemic .th wave of the pandemic  positively predicted negative mental health. This is consistent with findings from some existing studies which showed positive association between the two dimensions of COVID-19 stress and psychological morbidity such as anxiety, depression, and PTSD . HoweverBesides, results of this study showed that pandemic related self-efficacy negatively predicted mental health problems and positively predicted well-being, which is in line with the findings from existing limited research . This in4.3.Results of this study identified that emotional competence negatively predicted mental health problems while positively predicted flourishing. This provides additional support to the extant literature , indicatFor the environmental factors, the present study showed that positive family functioning, peer support, and supportive community atmosphere all negatively predicted mental health problems and positively predicted well-being factors which is consistent with the extant literature . The resFinally, the study contributes to the extant literature showing that need satisfaction and positive evaluation of university services negatively predicted psychological morbidity and positively predicted well-being. One reason for this relationship may be that students rely on universities to provide them with support and resources during this stressful time, and if they perceive those services as inadequate or ineffective, they may feel unsupported and isolated . This ca5.The study has theoretical implications. As for theoretical aspect, the integration of the ecological systems approach and the strength-based perspective is essential for comprehending the intricate interplay of factors affecting university students’ mental health. This combined approach facilitates a more comprehensive and nuanced understanding of the diverse elements that contribute to students’ well-being and resilience. By adopting this framework, results of this study strengthen the argument that various factors within the ecological system play risk and protective roles in shaping the mental health of university students, with a particular emphasis on personal factors as well as the influence of family, peers, and the community . In addiFor practical implication, the study provides important research-based evidence for better intervention and prevention of mental health symptoms in tertiary students. It points to the importance of paying special attention to the mental health status of students with financial or economic difficulties. It also highlights the direction of promoting intrapersonal and ecological protective factors and reducing risk factors in the treatment and intervention programs. Furthermore, the study highlights the important role of attending to need satisfaction and difficulties faced by university students. Also, helping students to gain a positive perception of the usefulness and value of the services received from the university is important.Despite its pioneer nature, this study has several limitations. First, while the study adopted a quota sampling method (as it is difficult to do random sampling under the pandemic), future studies might be conducted based on random sampling to replicate the findings. However, quota sampling is commonly adopted in studies under COVID-19 . Second,To conclude, the present study examined mental health of university students in Hong Kong  under the pandemic and the related risk and protective factors, including financial difficulties encountered, COVID-19 stress and responses, positive psychological attributes, environmental factors and needs and services factors. The present study suggests that pandemic related stress and perceived difficulties are important risk factors whereas positive psychological and environmental attributes are protective factors. It also suggests the positive role of need satisfaction, perceived usefulness, and satisfaction with university services in the mental health of university students. It enriches the existing literature on the mental health of university students under the pandemic by contributing to our understanding of the predictors of mental health in university students and providing important pointers for prevention and intervention.The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.The studies involving human participants were reviewed and approved by Institutional Review Board (or its Delegate) at the Hong Kong Polytechnic University. The patients/participants provided their written informed consent to participate in this study.DS obtained the research grant, conceived the research, contributed to all stages of the research work, and critically revised all versions of the manuscript. WC conducted the data analyses, drafted the manuscript, and conducted the revision and checking. XL revised the discussion section and checked the whole manuscript. DD revised the introduction section of the manuscript.This project was financially supported by a UGC special grant for student support services in response to the COVID-19 pandemic entitled “Promotion of psychological well-being in university students under COVID-19: Needs assessment and mental health survey” (project no.: 89S7). The publication of this paper was financially supported by the Research Grants Council Matching Fund and Wofoo Foundation (R-ZH4Q).The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Background: The ability to perceive two tactile stimuli as asynchronous can be measured using the somatosensory temporal discrimination threshold (STDT). In healthy humans, the execution of a voluntary movement determines an increase in STDT values, while the integration of STDT and movement execution is abnormal in patients with basal ganglia disorders. Sensorimotor integration can be modulated using focal muscle vibration (fMV), a neurophysiological approach that selectively activates proprioceptive afferents from the vibrated muscle. Method: In this study, we investigated whether fMV was able to modulate STDT or STDT–movement integration in healthy subjects by measuring them before, during and after fMV applied over the first dorsalis interosseous, abductor pollicis brevis and flexor radialis carpi muscles. Results: The results showed that fMV modulated STDT–movement integration only when applied over the first dorsalis interosseous, namely, the muscle performing the motor task involved in STDT–movement integration. These changes occurred during and up to 10 min after fMV. Differently, fMV did not influence STDT at rest. We suggest that that fMV interferes with the STDT–movement task processing, possibly disrupting the physiological processing of sensory information. Conclusions: This study showed that FMV is able to modulate STDT–movement integration when applied over the muscle involved in the motor task. This result provides further information on the mechanisms underlying fMV, and has potential future implications in basal ganglia disorders characterized by altered sensorimotor integration. The ability to temporally discriminate tactile stimuli can be measured with the somatosensory temporal discrimination threshold (STDT) technique, defined as the shortest time interval necessary for two sequential tactile stimuli to be perceived as consecutive ,2,3. STDA neurophysiological approach that may potentially modulate sensorimotor integration is muscle vibration ,15,16,17Based on this evidence, it is reasonable to hypothesize that if fMV can modulate sensory afferents, motor outputs and their integration, then it may also induce changes in mechanisms of sensorimotor integration such as those involved in the STDT–movement integration task.Therefore, the aim of the present study was to assess whether fMV, applied over the first dorsalis interosseous (FDI) muscle, would modulate STDT values tested during and after voluntary movement execution in healthy subjects. It has been also tested whether fMV applied on FDI can induce changes in the STDT–movement integration. In order to better clarify whether the effect of fMV on STDT–movement integration depended on the vibrated muscle, in a control experiment, fMV was applied over the abductor pollicis brevis (APB) or the flexor radialis carpi (FRC) muscles. Finally, in order to investigate the effect of the amplitude of the vibratory stimulus on the STDT–movement integration changes, fMV was used to generate a different displacement in a separate control experiment. These data may clarify the mechanism of action of the fMV in physiological conditions, and whether fMV might have therapeutic applications in movement disorders that are known to underlie abnormal sensorimotor integration.In the following sections, the methodological approach used in the study, including details on the experimental procedure, will first be described; afterwards, results will be reported, explained and discussed in the following “results” and “discussion” sessions.The effects of FMV on STDT and STDT–movement integration were investigated in a sample of healthy volunteers. To follow, demographic features of the volunteers, inclusion and exclusion criteria and methodological details for each experimental procedure will be detailed.A total of 17 healthy volunteers were enrolled in the study .The sample size was based on an a priori analysis with G*Power 3.1 software, assuming an expected effect size (Cohen’s d) of 0.85 and a statistical power of 0.80 at a 0.05 alpha level, with the number of measurement set as 4 for experiment 1 and as 3 for experiments 2 and 3. This resulted in a total sample size of 17 subjects for experiment 1 and 15 subjects for experiments 2 and 3.Accordingly, all participants took part in experiment 1, while only fifteen of them took part in experiments 2 and 3.Exclusion criteria were a history of neuropsychiatric disorders or symptoms of focal upper limb nerve entrapment, cervical brachialgia, polyneuropathy or central nervous system (CNS)-acting drug intake at the time of the experiments. Volunteers were asked to avoid the intake of caffeine, nicotine or any other substances interfering with CNS at least 6 h before the experimental session.All participants except two were right-handed, as evaluated by the Edinburgh Handedness Inventory . All expSTDT–movement integration paradigm paragraph).EMG activity was recorded through a pair of surface electrodes placed over the FDI muscle of the dominant hand, in a belly–tendon configuration. The EMG signal was recorded (×1000) and filtered (5–5000 Hz) with a Digitimer D360 , and then analyzed offline with a personal computer through a 1401 plus analog–digital (A/D) laboratory interface  [STDT was investigated according to previous studies ,3,4, usiSimilarly to previous studies ,9, paireFocal muscle vibration was applied to the FDI muscle using a specific device consisting of an electromechanical transducer, a mechanical support and an electronic control .The instrument consisted of an electromechanical transducer, a specific mechanical support and an electronic control device. The transducer was positioned over the FDI muscle at a point approximately corresponding to its maximal transversal size. The FDI was chosen as it is feasible for the fMV protocol and it is involved in the motor task used for the STDT–movement integration paradigm.The vibration was applied by means of a small probe 10 mm in diameter directly over the FDI muscle belly. The transducer was driven to produce sinusoidally modulated forces. Soft tissues were compressed to ensure better transmission of the vibrations into the muscle ,24,25.The vibration frequency was set at 100 Hz and vibration amplitude ranged from 0.1 to 0.2 mm peak-to-peak, which was sufficient to drive Ia spindle afferents, to avoid muscle fiber injury and as a subthreshold for the tonic vibration reflex. Each instance of stimulation consisted of two blocks lasting 10 min (‘), with an interblock interval of 1 min.The design of the study included a main experiment (experiment 1) and two control experiments (experiments 2 and 3), which took place one week apart from the main experiment to avoid interference due to possible long term effects of each fMV session. The order of the experimental sessions was randomized across the participants.Experiment 1: Effects of fMV applied over the FDI muscle on STDT and STDT–movement integrationAll subjects participated at this experiment. STDT and the STDT–movement paradigm were tested prior to, during and after the application of fMV over the FDI muscle, which was involved in the motor task underlying STDT–movement integration. In particular, the STDT at rest and the STDT–movement paradigm were tested at the beginning of each experimental session (T0), during the second block of fMV (T1) and 5′ (T2) and 10′ (T3) after fMV. FMV was applied to generate a 0.1 mm peak-to-peak sinusoidal displacement. For the STDT–movement paradigm, the different intervals  between movement onset and the STDT testing were selected in a randomized order for each subject .Experiment 2 (fMV topographic specificity): effects of fMV applied over the abductor pollicis brevis (APB) or the flexor radialis carpi (FRC) muscles on STDT and STDT–movement integrationIn order to investigate whether the possible effects of fMV on STDT or STDT–movement changes were specific to the stimulated muscular district, STDT and STDT–movement integration were tested prior to, during and after the application of fMV on different muscles of the upper limbs that were not involved in the movement execution. To this aim, in 14 out of 17 participants enrolled in experiment 1, the STDT and the STDT–movement paradigm were tested “before”, “during” and “after” fMV was applied over the APB, as well as over the FRC, in separate experimental sessions. The stimulation parameters and time points were the same as those used for experiment 1.Experiment 3: Effects of fMV applied over the APB generating a 0.2 mm muscle displacementIn order to investigate whether possible effects of fMV on STDT or STDT–movement integration depended on vibration parameters, STDT and STDT–movement integration were tested prior to, during and after the application of fMV, which generated a 0.2 mm displacement of the APB muscle. To this aim, in 14 out of 17 participants enrolled in experiment 1, the STDT and the STDT–movement paradigm were tested “before”, “during” and “after” fMV was applied, generating a 0.2 mm displacement of the APB muscle. The stimulation parameters and time points were the same as those used for experiment 1.t-tests with Bonferroni’s correction for multiple comparisons. Compound symmetry was calculated with Mauchly’s test, and the Greenhouse–Geisser correction was applied when required. All variables were first tested for normality using the Kolmogorov–Smirnov test. Significance was set at p value < 0.05. Unless otherwise stated, values are expressed as means ± standard error of the mean (SEM). To quantify the magnitude of effect for the observed differences, the partial eta-squared effect size (ηp2) was computed.Statistical analysis was performed using SPSS 20 software . Repeated measures (RM) analysis of variance (ANOVA) and post hoc analyses were conducted by means of For all the experiments, to evaluate changes in STDT value due to fMV, a one-way RM-ANOVA was used, with time (before (T0), during (T1) and 5′ (T2) and 10′ (T3) after fMV) as a within-subject factor. For the STDT–movement integration, to evaluate changes in STDT values during movement execution as determined by fMV, a two-way RM-ANOVA was performed with time (before (T0), during (T1) and 5′ (T2) and 10′ after (T3) fMV for experiment 1; and only T0, T1 and T2 for experiments 2 and 3) and ISI  as within-subject factors.In the following section, the results obtained from each experimental session will be described. All the results are summarized in Experiment 1: Effects of fMV applied over the FDI muscle on STDT and STDT–movement integration3,39) = 1.239; p = 0.299, ηp2 = 0.072), showing no differences in STDT values measured at rest before, during or after fMV  = 57.739; p < 0.001, ηp2 = 0.783), time  = 34.894; p < 0.001, ηp2 = 0.686) and interaction between factors  = 8.69; p < 0.001, ηp2 = 0.352) , during  and after  fMV. Moreover, the post hoc analysis showed that STDT–movement integration at T1 (during fMV) significantly differed from that at T0 (before fMV) (p = 0.001). Similarly, STDT–movement at T2 (5 ‘ after fMV) (p < 0.001), as well as at T3 (10′ after fMV), was significantly different from that at T1 (during fMV) (p < 0.001). Finally, the post hoc analysis showed a significant effect of fMV on STDT modulation only “during” fMV at all the ISIs  after index finger abduction .The one-way RM-ANOVA performed to investigate changes in STDT values while fMV was applied over the FDI failed to detect a significant effect of the time factor (F(fter fMV . The two= 0.352) . First, Experiment 2: fMV topographic specificity effects of fMV applied over the APB or the FRC muscles on STDT–movement integration task = 2.199; p = 0.139, ηp2 = 0.136). The two-way RM-ANOVA performed to compare STDT–movement integration before, during and after fMV’s application over the FDI showed a significant effect of ISI  = 23.517; p < 0.001, ηp2 = 0.681), but a non-significant effect of time  = 1.885; p = 0.179, ηp2 = 0.146) and of interaction between factors  = 0.917; p = 0.459, ηp2 = 0.077). Post hoc analysis showed a significant difference between the baseline and 0 ms, 100 and 200 ms (p < 0.05). Similarly, in the experimental session in which fMV was applied over the FRC muscle, the one-way RM-ANOVA showed a non-significant effect of time  = 0.043; p = 0.956; ηp2 = 0.003) for STDT values. In addition, the two-way RM-ANOVA on STDT–movement integration showed a significant effect of ISI  = 30.851; p < 0.001, ηp2 = 0.720), but a non-significant effect of time  = 0.811; p = 0.411, ηp2 = 0.063) and of interaction between factors  = 0.517; p = 0.738, ηp2 = 0.041). Post hoc analysis still showed a difference between baseline, 0 ms and 100 ms .The one-way RM-ANOVA performed to investigate changes in STDT values at rest when fMV was applied over the FDI muscle showed a non-significant effect of time  = 2.199; p = 0.139, ηp2 = 0.136). The two-way RM-ANOVA performed to compare STDT–movement integration before, during and after the application of fMV, generating a 0.2 mm displacement of the APB muscle, showed a significant effect of ISI  = 23.517; p < 0.001, ηp2 = 0.681), but a non-significant effect of time  = 1.885; p = 0.179, ηp2 = 146) and of interaction between factors  = 0.917; p = 0.459, ηp2 = 0.077). Post hoc analysis showed significant differences between the baseline, 0 ms, 100 ms and 200 ms (p < 0.05).The one-way RM-ANOVA performed to investigate changes in STDT values at rest during the application of fMV, generating a 0.2 mm displacement of the APB muscle, showed a non-significant effect of time (FThe present study demonstrates that fMV does not influence STDT at rest, but significantly modulates STDT–motor integration. FMV-induced modulation was observed only during fMV administration, and was specific to the muscle involved in the motor task performed to evaluate STDT–motor integration.To rule out the possibility that movement-induced STDT modulation evaluated before, during and after fMV was due to changes in attention, the ISIs for the STDT–movement protocol were tested in a randomized order, except for the STDT measurement at rest, which was performed as the first assessment in all trials. In addition, the order of the experimental sessions was randomized across the participants. The fMV protocol used in our study was selected in order to obtain the highest muscle–tendon complex displacement without evoking reflex muscular contractions, i.e., the tonic vibration reflex, or selectively stimulating the Ia afferents . As the The observation that fMV modified STDT in healthy subjects only when tested during movement, but not at rest, suggests that the fMV is able to interfere with mechanisms of sensorimotor integration, but not with pure sensory processing in the temporal domain. The modulation of STDT–movement integration observed during fMV may possibly reflect an interaction between the neural circuits involved in the STDT–movement integration task and the proprioceptive circuits activated by fMV in physiological conditions.One possible explanation for our findings is that vibratory stimulation may affect cortical processing of sensorimotor information related to movement execution. However, the observation that fMV left STDT values unchanged tentatively rules out that changes in STDT–movement integration during fMV rely on inhibitory circuits in S1 ,5. MoreoAnother possible explanation is that fMV interferes with mechanisms of STDT–movement integration by altering M1 excitability. According to previous studies, fMV selectively increases the excitability of the representation of the vibrated muscle in M1 . Our obsStudies on monkeys showed that the putamen and globus pallidus process Ia afferent inputs ,30. MoreThe muscle spindle input activation determined by fMV, as well as subsequent changes in sensory gating at the subcortical level, could also potentially have an influence on the sensorimotor integration processes underlying STDT–movement integration at the cortical level . FMV-indFinally, a further relevant observation of this study was that the effects observed in the present study on STDT–movement integration only lasted for the duration of the stimulation, without inducing plasticity. This is apparently in contrast with a previous study which demonstrated that fMV can induce long-term depression-like plasticity in healthy subjects . HoweverWe acknowledge some limitations of this study. First, we did not measure kinematic features of movement, which would have clarified whether fMV induced changes in motor performance. A further limitation is that we did not test M1 excitability ; thus, cNevertheless, our results have potential implication for future studies aiming to investigate the effects of fMV in patients with dystonia, a movement disorder characterized by altered sensorimotor integration and gating of sensory processing ,35. In c


Finally, we prospect the semiconductor technology roadmap by summarizing the technological development of 2D semiconductors over the past decade.Over the past 60 years, the semiconductor industry has been the core driver for the development of information technology, contributing to the birth of integrated circuits, Internet, artificial intelligence, and Internet of Things. Semiconductor technology has been evolving in structure and material with co-optimization of performance–power–area–cost until the state-of-the-art sub-5-nm node. Two-dimensional (2D) semiconductors are recognized by the industry and academia as a hopeful solution to break through the quantum confinement for the future technology nodes. In the recent 10 years, the key issues on 2D semiconductors regarding material, processing, and integration have been overcome in sequence, making 2D semiconductors already on the verge of application. In this paper, the evolution of transistors is reviewed by outlining the potential of 2D semiconductors as a technological option beyond the scaled metal oxide semiconductor field-effect transistors. We mainly focus on the optimization strategies of mobility ( EOT, oxε, sε, and st are the equivalent oxide thickness of gate oxide, the dielectric constant of gate oxide, the dielectric constant, and the thickness of channel materials, respectively. Therefore, transistors demand larger gate capacitances (high dielectric constant and thinner oxide thickness) and thinner channel thicknesses to maintain ideal switching characteristics at sufficiently small dimensions.In 1965, Gordon Moore, the cofounder of Intel, extrapolated an observation and projection through historical trend that the number of transistors in a dense integrated circuit (IC) doubles about every 2 years, which has become an indestructible economic driver for the exponential growth of the semiconductor industry. It is important to note that Moore's Law [ddV of the new-generation devices are reduced by 30% to ensure a constant electric field, which, in turn, leads to a 30% lower circuit delay τ. Crucially, after the 130-nm node, Dennard Scaling [ddV that comes with shrinking channel dimensions. In the following 45-nm node, the severe short-channel effect caused leakage current and degradation of the subthreshold slope . In fact, the industry has employed oxynitride instead of pure SiO2 as a gate dielectric since the 1990s to raise the dielectric constant and to offer other advantages against dopant diffusion. By the 65-nm node, the thickness of oxynitride has been reduced to 1.2 nm [κ metal gate abbreviated as HKMG) to enhance gate modulation while suppressing tunneling current [Figure  Scaling  is out o Scaling ,5. Durin current .SS improvements have been achieved by vertically stacking multibridge channel (MBC) FET [An even bigger technological leap occurred at 22 nm, and since then, semiconductor devices embraced the biggest structural revolution since complementary metal oxide semiconductor, with Fin-FET and ultrathin body silicon on insulator (UTB-SOI) replacing the planar devices and bulk silicon technologies, respectively . For morMBC) FET .2, exhibit atomically thin thickness and provide perfect gate modulation on an extremely scaled planar or MBC-FET structure [For device structure, both Fin-FET and MBC-FET are approaching quasi-2-dimensional (2D) nanosheets, and a better solution is the thinner semiconductor layer. 2D semiconductors, especially transition metal dichalcogenides (TMDs) with a general chemical formula of MXtructure –21. TMD tructure –24, layetructure ,26, and tructure , which atructure ,29. Thertructure –32.In this paper, we will review the development of TMD logic devices, especially the key technologies to achieve high-performance, low-power transistors through systematic optimizations of mobility, dielectric, and contact. First, we expound the characteristics of ideal 2D metal oxide semiconductor field-effect transistors. Next, we start with key device metrics and summarize the most important progresses published in the literature. Finally, we discuss the optimal device performance data reported to date and prospect the requirements for future industrial applications.CR) and the channel resistance (chR). The latter can be expressed as:L, W, N, oxC, μ, gsV, and dsV are the effective channel length and width, the stacking layer number, the areal capacitance of the gate oxide, the mobility, the gate voltage, and the drain voltage, respectively. Therefore, for a specific node, lower cR, higher mobility, and greater areal capacitance are critical for better drive capability. Figure SS and low off-state current are essential for low power consumption (dynamic and static). On the other hand, a large on-state current is also highly desired, as seen in both the output and transfer curves, which points to good contact and high mobility. Furthermore, a well-controlled threshold voltage (thV) that can serve as an indicator of process variation is especially important for large-scale integration. Next, we will systematically discuss the principal performance metrics at the device level.Benefiting from van der Waals (vdW) stacking of 2D semiconductors, it is more feasible to realize MBC-FET and complementary FET (CFET) structures compared to bulk materials, and thus to obtain superior device characteristics. Figure mτ) and the effective mass (m∗). For a specific semiconductor, scattering determines mτ and thus its mobility. Compared with that in Si, the charge transport in TMD is more susceptible to scattering (intrinsic and extrinsic). According to Matthiessen's Law, in a TMD containing multiple scattering mechanisms, the free carrier mobility can be evaluated by [phμ, SOμ, CIμ, and DEμ are the mobilities associated with the intrinsic phonons, the surface optical phonons (SOs), the Coulomb impurities (CIs), and the defects, respectively. Therefore, quantitatively determining the contributions of the various scatterings to the resistivity poses an enormous challenge, which invokes collaboration between the experimental study with precisely controlled parameters and the numerical modeling so as to interpret the relevant mobility variations with scattering.Carrier mobility represents the drift velocity per unit electric field, and is a key parameter to characterize the charge transport. Mobility can be expressed as uated by ,34μT−1=μ2 as an example, the μ − T−1 relationship under different scattering mechanisms is qualitatively plotted in Fig. 2 V−1 s−1 for monolayer MoS2 at room temperature should signify a transport mode dominated by the intrinsic phonon scattering, which consists of longitudinal acoustic , and thus the intrinsic phonon-limited mobility varies as μ ∝ T−1. When the temperature is greater than 100 K, the optical wave phonons become the major contributor, and then the intrinsic phonon-limited mobility varies as μ ∝ T−1.69 [κ dielectric [2 FETs using high-κ dielectric may be as low as 200 cm2 V−1 s−1 [2 could be much lower than the theoretical value. The nature of the charge transport in MoS2, however, remains poorly understood despite the extensive theoretical and experimental studies performed to date. In the early days, the mobility of monolayer MoS2 was around 10 cm2 V−1 s−1, and the μ − T−1 relationship exhibited obvious insulating behaviors [2 lattice. These vacancies acted as localized states, giving rise to hopping transport at low carrier concentration (nD2) [2 devices [boxε and ε0 are the permittivity of the substrate and vacuum; elε(q) corresponds to the electronic part of the dielectric function and depends on the carrier density n. As n and boxε increase, screening gets stronger, reducing the scattering potential and thus increasing the CI-limited mobility.Take MoS∝ T−1.69 . Apart f∝ T−1.69 . SO scat∝ T−1.69 . Differielectric . Under t V−1 s−1 ,39. Evenehaviors –42  . Besides devices . The int devices ,46 ϕqscrκ with high carrier concentration to suppress CI scattering and realized a phonon-limited mobility of ~150 cm2 V−1 s−1 at room temperature in monolayer MoS2 [2 channel in-between boron nitride (BN) layers, CI scattering can be considerably suppressed, leading to high mobility at room temperature and at low temperatures [To obtain higher mobility, numerous interface and defect engineering designs have been proposed for TMD. Yu et al.  developeyer MoS2 . It was eratures ,47,48. Meratures ,32,49–732, MoSe2, WS2, and WSe2. The conventional Si is subject to the repeated thinning and etching processes, and its mobility drops sharply as the SOI thickness reduces below 3 nm. This will severely restrict the device performance at the advanced nodes. By contrast, the thickness of monolayer TMDs is only 0.7 nm. Although the experimental mobility is far lower than the theoretical prediction, it still holds distinct advantage against SOI to provide one-decade higher mobility at similar thickness. In future, an ultraclean, nondestructive manufacturing environment and the delicate design of device structures are vital to the development of 2D-FETs.Figure SS and high transconductance) and for lower leakage. As native oxide, SiO2 benefits from the nearly perfect interface with Si and has transformed from an ideal dielectric layer to an ideal interface layer in the high-κ era  suitD. Furthermore, introduction of these interfacial defects further increases the source of CI scattering, resulting in irreversible degradation of mobility. Huang et al. [2O3 through water plasma treatment and the corresponding itD reached 2.1 × 1012 cm−2 eV−1, which is more than 2 orders of magnitude higher than that at SiO2/Si [EOT requirements of advanced node. As a result of combining the advantages of the aforementioned methods, a more advanced interface layer—2D native oxide—was invented recently. Typical examples are HfS2 [2O2Se [itD of 6 × 1011 cm−2 eV−1 between HfS2 channel and converted HfO2 dielectric. Li et al. [EOT dielectric layers of Bi2SeO5 through layer-by-layer oxidation of the underlying 2D Bi2O2Se semiconductor. The corresponding leakage current was lower than 1 × 10−7 A·cm−2 under an external field strength of 1 MV·cm−1. This method is expected to meet both of the requirements for interface quality and EOT under precise control. However, the problem is also obvious: only a few specific 2D semiconductors can form dense native oxide, especially Mo-based and W-based TMD with the greatest application potential, for which this methodology is completely infeasible. Hence, another strategy, viz., vdW heterogeneous interface layer, is more friendly to 2D materials owing to ultrasmooth interface and damage-free vdW interaction. Wang et al. [EOT was made for 2D materials [2/Si. The noncovalent monolayer of organic crystal has excellent interface quality, versatility, and reliability for 2D devices, but is restricted by the intrinsic low dielectric constant. Therefore, it is still very challenging to achieve a more aggressive EOT of sub-1 nm by means of this technique. More recently, Liu et al. employed a 2D inorganic molecular crystal of Sb2O3 as an ALD interface layer. Benefiting from its ultrahigh dielectric constant of 11.5 and the equally perfect interfacial quality to PTCDA, inorganic molecular crystals demonstrated great potential to become a new candidate of interfacial layer [The purpose of surface treatment is to create uniform point defects and dangling-bonds on 2D surface, which assist the adsorption and the nucleation of ALD precursors. Typical treatment methods include plasma –80, ozong et al.  achieved SiO2/Si . Another SiO2/Si –87, magn SiO2/Si , and ytt SiO2/Si ,88,89).  SiO2/Si  and orga SiO2/Si . The sel SiO2/Si . The fatare HfS2  and Bi2O2 [2O2Se . Lai et 2 [2O2Se  fabricati et al.  achievedg et al.  used orgaterials . In furtaterials  proved tal layer .h-BN). Yet, its dielectric constant is only 4 [h-BN almost impossible to be applied for larger-scale integration. A new generation of layered dielectric has been reported in recent years. For example, layered calcium fluoride [EOT down to 0.6 nm with excellent interface between high-κ and 2D semiconductors. However, such technologies are still in demonstration for back-gate devices. Future development of top-gate integration will be essential for CFETs and MBC-FETs.In addition to the traditional ALD oxide, 2D layered dielectrics have also been considered to be a unique solution for their 2D vdW properties. The representative, first-generation layered dielectric should be hexagonal BN , and itD of high-quality dielectric/semiconductor systems must be strictly controlled to be lower than 1 nm, 10−2 A·cm−2 [10 cm−2 eV−1 [κ dielectrics onto 2D semiconductors, while satisfying the needs of EOT, gI, and itD. Of course, the premise is to find a high-κ 2D dielectric material suitable for 2D semiconductors.In principle, 2 A·cm−2 , and 101m−2 eV−1 ,105, resCR contributes mostly to the total resistance [CR. According to the Schottky–Mott limit, the SB height of metal–semiconductor (M–S) contact can be manipulated by adjusting metal’s WF. However, SB height is usually insensitive to WF. In reality, the Fermi level is often pinned by interface states, known as Bardeen limit [2 as example ballistic transport within mean free path dominates . Consequsistance . The Schen limit ,109. Feren limit –113 and en limit –116. OwicR, 2 strategies can be utilized: (a) contact doping to make metallic contact or tunneling barrier and (2) MIGS suppression to minimize the SB height. The mainstream strategies for CR optimization are summarized in Fig. CR for whatever n-type and p-type devices [CR of few-layer WS2 and MoS2 were decreased to 0.7 kΩ·μm and 0.5 kΩ·μm, respectively. Gao et al. [2 channel for the first time, where the specified MoS2 was treated by electronegative materials such as MoO3 or MoO2. Metallic phase 2D materials are another effective strategy [2 can be locally induced by alkali metal intercalation on semiconducting 2H phase, thus decreasing cR to 200 to 300 Ω·μm at zero gate voltage [CR as low as 250 Ω·μm through atomically ultraclean vdW vanadium diselenide contacts [h-BN intercalated interfaces to form metal–insulator–semiconductor contacts, effectively reducing the SB height to be around 35 meV  between metal and 2D semiconductor , where MIGS were considerably suppressed and degenerate states were spontaneously generated in the TMD  was discovered by Intel, TSMC, etc. [Therefore, in order to satisfactorily obtain  devices –134. Yan devices  reportedo et al.  achievedstrategy –138. The voltage . Also, t voltage , laser b voltage , and argcontacts . A schemtt limit . Other rectively ,147. Comectively  reportedMC, etc. , which sCR in a vdW system. Theoretically, the quantum limit of CR can be expressed by [mW is the metal’s WF, sn is 2D sheet carrier density, h is the Planck constant, vg is the valley degeneracy , d is the effective tunneling gap, and χD2 is the affinity energy of the 2D semiconductor. According to CR is linearly dependent on the tunneling gap induced by the vdW gap. As depicted in Fig. cR at different vdW gaps  all display a strong dependency on the channel’s carrier concentration. It implies that, in addition to designing a perfect vdW interface with the matched WF, enhancing the coupling between 2D semiconductor and contact metal is crucial to reduce the cR further, approaching the quantum limit.Finally, one can explore what are the critical factors of essed by Rc,minW=honI, which can be approximated as onI = dsV/totR. Figure onI as a function of the channel length (chL) for monolayer 2D-FETs reported in the literature, where onI is extracted at DV equal to 1 V with maximum gsV. The dashed line illustrates prediction using totR = chRshL + 2CR, where the average sheet resistance of the channel shR = (eμnD2)−1 ≈ 1,524 Ω·sq−1 with nD2 = 1013 cm−2, μ = 125 cm2 V−1 s−1 (IRDS 2021), dsV = 0.75 V (IRDS 2021), and CR = 100 Ω·μm. Apparently, onI is significantly limited by the channel mobility for long-channel devices, but becomes strongly dependent on CR for short-channel devices. As shown in Fig. chL < 100 nm. In the past decade, the onI of short-channel 2D-FET has been successively improved through contact and material optimizations. Nowadays, n-type MoS2-FETs demonstrated onI up to 1,135 μA/μm at chL = 35 nm for monolayer [chL = 50 nm for bilayer [2-FET has been reduced to 3.3kΩ·μm [2-FET, an onI of 1,720 μA/μm and a contact resistance of 250 Ω·μm have been achieved by employing the vdW–epitaxy VSe2 contact [chL = 18 nm [After going through the optimizations discussed above, we then focus on the most important performance parameter for IC application—onolayer  and 1,27 bilayer , respect3.3kΩ·μm . Besides contact , showing = 18 nm , which mκ/2D semiconductor interface and then to realize low EOT. The surface modification strategy or the selection of interfacial layer should take low itD, low EOT, and low gI all into account. For contact engineering, the key is to reduce the height and the width of SB and suppress MIGS, and then to realize stable ohmic contacts with ultralow CR. Controllable contact-localized doping and suitable contact (semi)metal selection are 2 major strategies. Now, the special semimetal (Sb and Bi) contacts show great potential in this regard [To extend the relentless downscaling, Fin-FET, nanosheet FET, and envisaged Fork-sheet and CFET have been developed  epitaxy with large-area homogeneity would further boost the performance of 2D TMD devices . Also, teμ = 410 cm2 V−1 s−1, hμ = 219 cm2 V−1 s−1, CR < 100 Ω·μm at nD2 = 1013 cm−2, itD < 1010 cm−2 eV−1, EOT < 1 nm, and gI < 10−2 A·cm-2, where eμ (hμ) is the electron (hole) mobility of n-type (p-type) 2D transistors. Achieving these performance merits actually implies the maturity of 2D-FET technology. From another point of view, the operating frequency of 2D transistors is also a recognized indicator and should be considered to systematically evaluate device performance. At present, the oscillating frequency of the reported ring oscillator based on 2D transistors is still far below 1 GHz, which hardly meets the requirement for commercial ICs. This means that, despite impressive progresses made in laboratory, more effort should be dedicated to device array and integration, i.e., not just a single transistor. Hence, more attention should be paid to their uniformity, reliability, and yield. Moreover, the CFET is the mainstream development direction for 2D transistors. Although the performance of p-type 2D-FET has made great breakthrough, its process compatibility with n-type device remains to be solved.At the device level, as discussed before, the comprehensive optimization, including mobility, dielectric, and contact, should continue uninterruptedly until the expected target for 2D-FETs is satisfied, i.e., 2 transistors offered a persuasive example [At the application level, although 2D-FET technology is considered to be one of the most promising candidates in the post-Moore era, it is still implausible that silicon will be fully replaced by 2D semiconductors in the foreseeable future, because of the enormous investment and the immature technology to commercialize 2D transistors. For constant development, some specific “killer application” is necessary. As transferring vdW materials to arbitrary substrates is feasible under room-temperature conditions, monolithic 3D integration of 2D transistors with mainstream semiconductor technologies is a promising way, even being able to substitute the existing amorphous silicon or oxide thin-film transistor technologies. A recent demonstration of fully 3D monolithic, 1270-PPI active-matrix micro-LED displays driven by monolayer MoS example . Moreove


Plasma-ghrelin, -motilin, -insulin and blood-glucose concentrations were determined every 10 min before and 30 min after feeding; appetite was scored every 10 min. Hunger scores were investigated with a special interest 50–60 min after the ingestion of hydroxychloroquine sulfate, right before a rewarding chocolate milkshake was offered to drink ad libitum. Compared with the placebo, hydroxychloroquine sulfate tended to reduce hunger at the time of interest (p = 0.10). No effect was found upon subsequent milkshake intake. Motilin plasma concentrations were unaltered, but acyl-ghrelin plasma concentrations decreased after the ingestion of hydroxychloroquine sulfate . These data suggest that the oral intake of hydroxychloroquine sulfate tablets reduces subjective hunger via a ghrelin-dependent mechanism but does not affect motilin release, hedonic food intake or insulin levels in healthy women.The direct infusion of bitter solutions in the gastrointestinal tract can reduce the secretion of orexigenic hormones and influence appetite and food intake. We aimed to explore whether oral ingestion of the bitter tastant hydroxychloroquine sulfate can exert similar effects. Ten lean adult women were included in this double-blind, randomized, two-visit, crossover study. After an overnight fast, each volunteer received film-coated tablets containing 400 mg of hydroxychloroquine sulfate (Plaquenil Bitter flavors are frequently associated with spoiled or toxic substances . As a reThe reaction caused by bitter tastants in the GI tract is, at least in part, linked to the altered secretion of appetite-regulating hormones. Both in vivo studies on animals and humans and in vitro studies on cell lines and human primary gastric crypt preparations have shown that bitter agonists can affect the secretion of appetite-regulating hormones ,14,15,16®. It has anti-parasitic and anti-inflammatory properties used to prevent and treat malaria and to treat autoimmune diseases [Although the direct infusion of bitter solutions in the GI tract shows promising effects, the expansion of its use is hampered by the need for nasogastric intubation. Replacement with a so-called “bitter pill” that releases its content in the stomach could offer a solution to overcome this barrier. Such a pill is already commercially available under the name Plaquenildiseases . The maidiseases . HCQS, cdiseases , which dThis study aims to investigate whether the intake of a pill comprising HCQS can have similar effects on hunger sensations, hedonic food intake and orexigenic gut hormone release compared with previously reported ,27 intraclinicaltrials.gov as NCT04005768. All study procedures were performed in full accordance with the Declaration of Helsinki. All participants approved and signed the informed consent before being included in the study and were allowed to withdraw at any time for any reason.The trial was approved by the Leuven University Hospital Medical Ethics Committee (S61870 11/12/2018) and registered at 2. The volunteers were not dieting and had a stable body weight for at least 3 months. In order not to exceed the maximal dose of 6.5 mg HCQS per kg body weight after the intake of two tablets of Plaquenil®, the volunteers needed to have a minimal body weight of 62 kg. Volunteers needed to use a highly effective method of birth control. Finally, volunteers had to score 60 or higher on a 100 mm visual analogue scale (VAS) for liking a chocolate milkshake to ensure its rewarding nature. Potential subjects were excluded if they met any of the following criteria: history of GI or other significant somatic or psychiatric diseases; known drug allergies; diabetes; significant heart, lung, liver or kidney diseases; a prolonged QT-interval > 450 ms or other symptoms that HCQS can worsen during long-term use; food allergies or lactose intolerance. Ten healthy lean female volunteers between the ages of 18 and 65 were included in this proof-of-concept study . Their B® tablet compared to a previously reported study where a QHCL solution was administered in the stomach [As reported in a previous study , fourtee stomach . Only fe stomach ,30. ®  or two placebo tablets , administered in a double-blinded, crossover fashion. In total, the two Plaquenil® tablets contained 400 mg of HCQS, which equals 310 mg of hydroxychloroquine (HCQ). Participants received two tablets of PlaquenilDuring the screening visit, the study protocol was explained; the informed consent form was signed; and in- and exclusion criteria were checked. Weight, height, waist–hip ratio and body composition were measured. The latter was determined using a Bodystat1500 . Subjects tasted the chocolate milkshake for “liking” and were only included when they rated a score of 60 or higher on a 100 mm VAS to ensure the rewarding nature of the milkshake. An electrocardiography (ECG) confirmed the absence of a prolonged QT interval. Volunteers filled in the online screening questionnaires, including the Dutch version of the Rome IV criteria questionnaire to confirm the absence of functional GI disorders. ®  or placebo were administered orally with 240 mL of water (time = 0). Then, blood samples were collected for one hour, every 10 min. Thereafter, volunteers were instructed to a drink chocolate milkshake ad libitum until they felt fully satisfied (time = 60). After 30 min, the last blood sample was taken and volunteers returned home (time = 90). For the duration of the whole study, volunteers were requested to score appetite-related sensations  and symptoms  every 10 min on a 100 mm VAS. Hunger was rated as “How hungry do you feel?”, prospective food intake as “How much do you think you can eat?” and satiety as “How satisfied do you feel?”. A rating of 0 mm meant “Not at all”, and 100 mm meant “Very much”. A 2-week washout period between the study visits was respected to avoid any potential carryover effects. This study was a placebo-controlled, double-blind, randomized, two-visit crossover study . VolunteBefore each study visit, a fresh chocolate milkshake was prepared by combining 8 scoops of vanilla ice cream , 710 mL of 2% milk  and 4 tablespoons of Imperial’s Chocolate Topping . Volunteers drank from a 200 mL beaker that was repeatedly refilled with chocolate milkshake until the volunteers expressed that they felt comfortably full. The milkshake was weighed before and after ad libitum consumption, taking into account that each ingested gram of chocolate milkshake equaled 1 kcal. This approach to measuring hedonic food intake is based on a publication from Iven et al. , who adag, after which, plasma was collected. Plasma for acyl-ghrelin was further acidified to a final concentration of 0.1 N HCl, extracted using a Sep-Pak C18 column  and vacuum-dried. All samples were stored at −80 °C until further analysis. Insulin concentration was measured using the EK-035-06 kit , while motilin and acyl-ghrelin were measured using an in-house radio-immuno-assay (RIA), as described before [Blood samples for hormone analysis were collected in lithium–heparin-coated tubes  for motilin analysis and ethylenediaminetetraacetic acid (EDTA)-coated tubes  for ghrelin and insulin analysis. Blood was supplemented with 500 kIU aprotinin/mL of blood. Blood collected for ghrelin measurements was additionally supplemented with 0.57 mM of phenylmethylsulfonyl fluoride solution . Samples were centrifuged at 4 °C for 10 min at 1400× d before ,33. p < 0.05, and the data were presented as mean ± SEM. First, baseline values (t = −10) were compared between conditions using a two-tailed paired t-test. Because no significant baseline differences between conditions were found, appetite-related sensations , gut hormone concentrations (insulin) and blood glucose levels were analyzed as absolute changes from baseline (∆). For appetite-related sensations and blood glucose levels, the effect of treatment on these ∆variables over time was analyzed using marginal linear mixed models for the fasted (t = 10–60) and fed state (t = 70–90 for appetite-related sensations and t = 90 for hormones and glucose) separately. For these variables and for plasma hormone concentrations, a planned contrast analysis was performed to see if there was a difference between treatments 50–60 min after administration. ANCOVA mixed models were performed to better account for the effect of treatment over time on orexigenic hormone concentrations  and the correlation of gut peptide concentrations within patients. The “time” and “treatment by time interaction” effects were set as linear and quadratic covariance parameters. The treatments  and distinct study phases  were included as fixed effects. To account for the correlation between the timepoints in each volunteer, time and treatment were treated as random effects with the patient set as the random variable with an autoregressive order 1 (AR1) covariance structure specified. To state the model’s degrees of freedom, the Satthertwaite method was chosen. LRT tests were performed to test the linear and quadratic covariance parameters “time” and “treatment by time interaction” for significance at the 5% level. Milkshake intake and taste were analyzed using a one-tailed paired t-test. Symptom scores below a cut-off of 10 out of 100 mm VAS were not considered in this study design. The area under the curve (AUC) of symptom severity above the 10 mm cut-off was calculated for the fasted and fed states separately and compared between the placebo and HCQS condition with a Wilcoxon matched-pairs test. Data are presented as interquartile range (IQR). For the statistical analysis, the SAS University Edition software v9.4  was used. To ensure that all the assumptions were met, logarithmic boxcox transformations were applied if data were not normally distributed. These data were presented as the transformed values. Significance was set at 2; age 24 ± 1 years) were included in the study. These volunteers had a waist-hip ratio of 0.73 ± 0.01; a fat percentage of 23.4 ± 0.9%; a lean mass of 51 ± 1 kg; a dry lean mass of 16 ± 0.4 kg; and a water percentage of 53 ± 0.7%.Fifteen volunteers signed the informed consent form. Five were excluded because of a rating lower than 60 out of 100 for liking the milkshake or because they did not meet other inclusion criteria. Ten volunteers (BMI of 22.8 ± 0.3 kg/mp = 0.42). After placebo administration, hunger increased by 5 ± 3 mm; conversely, a reduction of −6 ± 4 mm was found after the HCQS treatment. The ∆change in hunger scores from baseline was maximal after 50–60 min but did not reach statistical significance  without a difference between conditions (p = 0.35). Mean changes from baseline (∆) in VAS ratings for appetite-related sensations  are shown in p = 0.67). Prospective food intake values decreased by −7 ± 3 mm from baseline for the placebo and −5 ± 4 mm for HCQS at the time of interest (p = 0.53). Drinking the milkshake strongly affected the volunteer’s prospect of food intake (p < 0.0001), but this was not condition-dependent (p = 0.70). Baseline values of prospective food intake were 69 ± 2 mm for the placebo group and 66 ± 7 mm for the HCQS group (interest B. The dep = 0.11). The original baseline scores were 19 ± 7 mm for the placebo and 12 ± 7 mm for HCQS. The satiety scores increased by 5 ± 6 mm from baseline 50–60 min after the administration of HCQS and decreased by −3 ± 2 mm after placebo administration (p = 0.18) (p < 0.0001), but this increase was similar across conditions (p = 0.33). Absolute satiety baseline values were not normally distributed and transformed to 2.5 ± 0.4 mm for the placebo and 1.6 ± 0.4 mm for HCQS, which showed no significant difference ( = 0.18) C. Howevep-values were only obtained for the fullness symptom, which was the only non-zero comparison. No significant differences between treatments were observed in fullness in the fasted state (p > 0.99) or the fed state (p = 0.20). The results of symptoms  reported during the study visits are presented in p < 0.001; Absolute motilin plasma levels did not differ significantly between conditions at baseline (+887 ± 30 pg/mL for the placebo and 845 ± 27 pg/mL for HCQS). For both conditions, the motilin plasma concentration fluctuated over time during the fasted state (p < 0.05), which was lost after correcting for multiple comparisons. At the prespecified timepoint 50–60 min after ingestion, the average ∆acyl-ghrelin values were 9 ± 7 pg/mL for the placebo and −7 ± 6 pg/mL for HCQS (p = 0.11). Thirty minutes after drinking the milkshake, acyl-ghrelin concentrations dropped to −70 ± 18 pg/mL for the placebo and −92 ± 12 pg/mL for HCQS, which was not significantly different.The baseline values of acyl-ghrelin were not significantly different between conditions, with concentrations of 171 ± 13 pg/mL and 178 ± 14 pg/mL for the placebo and HCQS, respectively. Overall, the ∆acyl-ghrelin values tended to be lower after the ingestion of HCQS compared with the placebo B. ANCOVAp = 0.75). ∆Insulin plasma concentrations increased strongly after chocolate milkshake intake by 31.5 ± 5.9 µIU/mL for the placebo and 27.8 ± 4.3 µIU/mL for HCQS, but the difference was also not significant. The absolute insulin baseline values for the placebo and HCQS were 2.3 ± 1.0 and 2.2 ± 1.1 µIU/mL, respectively . These dp = 0.59). Glucose values increased by 17 ± 3 mg/dL from baseline for the placebo and by 8 ± 4 mg/dL for HCQS 50–60 min after administration (p = 0.32). Similarly, glucose levels did not differ significantly between treatments 30 min after milkshake consumption. Whole-blood glucose levels were not significantly different at baseline  after the intake of the placebo (348 ± 29 mL) or HCQS tablets (322 ± 42 mL). The administration of the placebo or HCQS did not affect the taste of the milkshake (p = 0.19). The volume intake of the rewarding chocolate milkshake did not differ significantly (®) is unlikely to reduce food intake. The oral ingestion of HCQS tablets may be capable of reducing subjective hunger sensations in the fasted state one hour after intake, but this does not translate into a reduction in milkshake intake. The hunger-suppressive action is most likely mediated by a ghrelin-dependent mechanism that does not involve changes in plasma motilin concentrations.The direct infusion of bitter solutions in the stomach or duodenum has been the subject of investigation in previous studies for its reported action on appetite-regulating gut peptides, appetite-related sensations and food intake via the gut–brain axis ,23,27,34p = 0.10) in this pilot study, a convincing hunger-lowering trend was still observed. This is in agreement with the formerly reported effect of bitter tastants on hunger sensations [Motilin is a gut peptide that has been, up until now, insufficiently studied for its role in hunger signaling. mainly because of its absence in rodents . Conversnsations ,16,27,39We previously showed that the intragastric administration of quinine decreases hedonic food intake, as measured with an ad libitum drinking test at the end of each test visit using a rewarding chocolate milkshake . In contSurprisingly, we found that the oral intake of HCQS did not affect plasma motilin levels, indicating a different mechanism of action compared with intragastric QHCl administration. Instead, our results showed that the intake of HCQS tended to lower plasma acyl-ghrelin concentrations over the course of the study visit with significant differences reached at timepoints consistent with reduced hunger rating. For the interpretation of differences in acyl-ghrelin and motilin values, as evaluated by ANCOVA mixed models, we opted to not correct for multiple comparisons. Because of the exploratory nature of this pilot study, we accept the increased risk of erroneously deducing a significant effect for this variable. However, the observed effect on acyl-ghrelin is in agreement with results reported previously by Iven et al. and Deloose et al., which showed that, besides an effect on motilin, altered acyl-ghrelin plasma concentrations after QHCl administration in the stomach may contribute to lowered hunger sensations ,27. AddiOne limitation of this study is that we cannot determine the moment that hedonic hunger took over from homeostatic hunger because the volunteers fasted before starting the ad libitum drink test. Ideally, we would offer an ad libitum buffet with rewarding food items and without time restrictions after a standardized breakfast to investigate hedonic food intake after the intake of a bitter pill. However, this would complicate the interpretation of hormone levels, increase the inter-subject variability and make the comparison with previously reported results difficult. Therefore, by only including volunteers who scored liking the chocolate milkshake at 60 mm or more on a 100 mm VAS, our study design ensured the rewarding nature of this beverage and allowed us to pick up changes in hedonic food intake on top of changes in homeostatic food intake in a more reproducible manner. Still, we found no evidence that the reduction in hunger elicited by HCQS translated into a reduction in intake of a rewarding chocolate milkshake. Therefore, we expect limited therapeutic applicability for HCQS-containing bitter pills in weight-loss therapies that focus on dietary intake restriction. Whether pills based on other bitter compounds such as QHCl are able to influence food intake, as seen when QHCl solution was administered directly in the stomach , is a suFinally, we hypothesized a hypoglycemic effect of HCQS through the elevation of insulin levels, as has been reported previously ,29. HoweIn conclusion, our data show that the oral intake of a pill containing HCQS tends to reduce subjective hunger via a ghrelin-dependent mechanism but does not appear to have a hypoglycemic effect, nor does it affect motilin release or feeding behavior in healthy women.


We found that nonpolar local domains formed by 14-carbonalkyl chains are crucial in obtaining two supercooled states of differentdynamics within a single ionic liquid. Although the nano-ordering,confirmed by Raman spectroscopy, still occurs for shorter alkyl chains, it does notbring calorimetric evidence of LLT. Instead, it results in peculiarbehavior of ion dynamics near the liquid-glass transition and 20-timessmaller size of the dynamic heterogeneity compared to imidazoliumionic liquids. These results represent a crucial step toward understandingthe nature of the LLT phenomenon and offer insight into the designof efficient electrolytes based on ionic liquids revealing self-assemblybehavior.The existence of more than one liquid state in a single-componentsystem remains the most intriguing physical phenomenon. Herein, weexplore the effect of cation self-assembly on ion dynamics in thevicinity of liquid–liquid and liquid-glass transition of tetraalkylphosphonium ([P Among others, ILs meet the needs of electrochemistry,energy storage, catalysis, engineering, and pharmacy.6Within 100 years since the discoveryof ethylammonium nitrate by Paul Walden,Tg.7 Amongthe factors controlling the glass-forming ability of ILs, one canmention the symmetry of ionic species, charge delocalization, sizeof ions, and competing for interionic interactions .9 For example,incorporating a small chloride anion into the IL structure increases Tg.11 The same is achieved by introducing strong H-bonding interactionsor elongating the alkyl chain in the cation.14 However, thelatter can also lead to various short-range ordering structures, e.g.,clusters or mesoscopic agglomerates,17 which might dramaticallyinfluence the properties of ILs.20 Therefore, understandingthe molecular-level interactions within ILs is crucial for their industrialapplications.A key advantage of ILs over molecular fluids is their excellentability to exhibit vitrification. Under cooling, low-viscosity liquidbecomes a supercooled equilibrium fluid that transforms to a nonequilibriumamorphous solid at the glass transition temperature 22 Specifically, on cooling,[BH4] was transformed from one supercooledliquid state to another of different local structures, static dielectricpermittivity, and thermodynamic properties. Compared to nonionic systems,including water,24 atomic elements ,26 triphenyl phosphite (TPP),28 water–trehalosemixtures,29 or metallic glasses,30 the LLT in [BH4] can be classified as a genuine transition where both supercooledliquids can flow. It has also been shown that the exchange of borohydrideanion to [TFSI]−, [TCM]−, [SCN]−, or taurine keeps both liquid phases and does notaffect the temperature of LLT substantially. Furthermore, independentlyon anion, LLT was observed at a similar time scale of ionic motions(from 0.3 to 13 ms).22 All these factssuggest that the tendency of amphiphilic phosphonium cations to formlocal structures is responsible for LLT. In this context, the questionnaturally arises, what is the critical length of alkyl chainsto create nonpolar local domains and consequently to observe two differentsupercooled states within a single-component system? In general,longer alkyl chains favor nano-organization. However, it has beenreported that increasing the volume fraction of alkyl groups in thephosphonium ILs does not necessarily promote mesoscale aggregation.31 A detailed analysis of [TFSI]and [TFSI] has shown disruption of the mesoscaleaggregates with increasing lengths of the shorter alkyl chains. Atthe same time, the LLT has not been observed in these materials. Therefore,a thorough understanding of the formation of heterogeneous microstructuresby phosphonium ILs characterized by different combinations of alkylchain lengths seems essential for the precise control of LLT.Recently, the self-organization of ions in quaternaryphosphopnium-basedILs has been considered an origin of the first-order liquid–liquidphase transition (LLT).Supporting Information for details). The former contains ILs with trialkyltetradecyl phosphoniumcation +, specifically[TFSI]− and chloride salts of  and , while the ILs from the second group arecharacterized by trihexyl alkylphosphonium cations, + ,combined again with [Cl]− and [TFSI]− anions. The chemical structures of investigated ILs are shown in To address this issue, we have synthesized two different sets ofphosphonium ILs  exhibit a clear signature of liquid-glass transitionand no signs of the LLT, even if n = 12. Hence, the14-carbon chain seems necessary to induce a transition between twosupercooled states. At the same time, modification of three othersubstituents while keeping the −[CH2]13–CH3 structure of the fourth one brings substantialdifferences in temperature and enthalpy of LLT, as well as affectsthe crystallization tendency of ILs. In particular, the shorteningof three cation side chains from hexyl to butyl increases the enthalpyof LLT  and shifts its onset to highertemperatures. TLL risesby 11 K for ILs with [TFSI]− anion and 20 K forchloride salts. The values of TLL and ΔH are listed in Table S1. High enthalpy of LLT found for -ILs indicates that the alkyl chains self-assembly causing LLT isbetter constituted compared to -ILs, and therefore,they crystallize above TLL. This is visible as a sharp exotherm followed by an endotherm, revealinga subsequent melting process on DSC thermograms. Due to the stericalhindrance provided by the [TFSI]− anion, liquid1 of [TFSI] shows a slightly weaker tendency tocrystallize than it does for [Cl].Calorimetric experiments show that all studied ILs could be vitrifiedon cooling; however, they reveal different behaviors during the heatingprocess. In particular, tributyl- and trihexyl tetradecyl phosphoniumILs show well-resolved endothermic peaks identified with the liquid–liquidphase transition. At the same time, the DSC traces of studied + cation by the CH2–CH2–group, i.e., from 14 to 12 carbons, inhibits theability of IL to undergo LLT and markedly decreases the temperatureof the liquid-glass transition. Note that the Tg of ILs with LLT was identified on DSC scansby the time-dependent annealing (aging) experiments performed at T < Tg.Then the liquid-glass transition becomes visible as a step-like changeof heat capacity at T < TLL . Interestingly,a further shortening of alkyl chain length in [TFSI] systems from n = 12 to n = 2 does not change the thermal properties. Namely, Tg remains constant, and none of themshows a crystallization tendency. That is at odds with the behaviorof imidazolium-based ILs, where Tg was found to decrease for material with a shorter alkyl substituent.13 At the same time, in the case of [Cl], Tg plotted asa function of alkyl chain length reveals a nonmonotonic behavior;i.e., it decreases with the elongation of the alkyl chain from 6 to12 carbons and gets higher for C14. Furthermore, amongall studied  +-systems,only [Cl] reveals the crystallization tendencyabove Tg.As mentionedabove, the shortening of a single alkyl chain in +-containing ILs (n =2–12) reveals a substantial broadening of the glass transitionstep compared to classical ILs. Such a result is commonly identifiedwith a broad distribution of structural relaxation times (larger dynamicheterogeneities) within the material and characterizes rather polymerizedionic liquids and multicomponent systems than simple low-molecularILs.34 Therefore, one might expect the formation of someheterogeneous microstructures in +-based IL, although there is no evidence of LLT. Toexplore this issue thoroughly, the Donth36 approach defining the number of dynamically correlated particles, NαD, in the Tg regionhas been employed for +-ILs, (see Supporting Information fordetails). Interestingly, the obtained values of NαD(Tg) are exceptionally low (lessthan ten) for all examined here +-ILs (see Table S1). It meansthat only several particles move cooperatively close to the glassystate. This indicates the existence of some aggregates with strongvan der Waals interactions and short intermolecular distances betweenthe alkyl chains of +-ILs. Such a conclusion is supported by recent reports where NαD(Tg) was stronglycorrelated with the length of alkyl chain attached to the cation .11 However, so far, the lowest reported value of NαD(Tg) was equalto 20, and interestingly, it was found for IL with the phosphate anion,i.e., [C1C2Im][DBP]. Further dielectric studieswere performed to verify whether such exceptionally small regionsof dynamic heterogeneity affect the ion dynamics in +-ILs and how much their relaxation behavioris different from +-ILs that reveal a clear LLT.A closerinspection of thermograms obtained for [TFSI] and [TFSI].To avoid cold crystallizationand maintain the same thermal history,all examined herein ILs were initially quenched to the glass state,and the dielectric data were recorded during the heating scan. Partsa and b of − anion. As the temperature increases,another relaxation mode, the so-called conductivity relaxation process(σ-process), related to the translational mobility of ions,becomes the main feature in the dielectric spectra. Similarly to otherionic glass formers, the M″-peak of each + and +-based ILs shifts toward higher frequencieson heating. However, in the latter cases, the temperature sensitivityof σ-mode changes substantially from liquid 2 to liquid 1. Furthermore,from the data normalization presented in panels c and d of M″(f) spectra are gettingnarrower when the temperature increases above TLLDSC. Meanwhile, the M″(f) peak of +-ILs keeps the same shape at various T valuesover the supercooled state and for different lengths of fourth alkylchain (n = 2–12) (see Table S1).A single secondary relaxation (labeled as β-process)is visiblein the glassy state of all studied ILs. The only difference is inthe secondary process’s amplitude, which is more pronouncedin ILs with [TFSI]Tg. The characteristic of localdynamics (β-processes) is presented in Figure S2 in the Supporting Information. One can note that the glassydynamics of +-ILs and+-ILs are very similar.Namely, there is a single β-process with the activation energyoscillating around 35 ± 2 kJ/mol for ILs with [TFSI]− anion and Ea = 28 ±3 kJ/mol for chloride salts of tetraalkyl phosphonium liquids. However,when we consider a given T < Tg, the dependence between the alkyl chainlength and the time scale of β-relaxation occurs. In particular,the local dynamics slows down with the elongation of alkyl substituentfrom 2 to 14 carbons; however, at the same time, it is insensitiveto structural changes arising from LLT. Considering the relativelylow energy consumption of β-relaxation, some intramolecularmotions within phosphate cation are expected for the occurrence ofthis mode in the M″(f) spectra.In the next step, we have constructed therelaxation maps to highlightthe effect of IL morphology on ion dynamics above and below τσ = 1/2πfmax) determined for ILs containing + and + cations. As canbe seen, the dynamics of both examined +-systems follows the Vogel–Fulcher–Tammann (VFT) inliquid 1 state and markedly changes the behavior at TLLDSC. At the same time, the τσ(T) data of +-ILs are unavailable abovetheir TLL due to thestrong crystallization tendency. Therefore, the temperature dependenceof dc-conductivity log σdc (T–1) determined in thevicinity of Tm has beenemployed to characterize their ion dynamics in the liquid 1 state.As can be seen, around calorimetric LLT, the VFT fit, representingthe behavior of τσ in liquid 1, meets the experimentally determined τσ (T–1) in liquid 2 state. This procedure enables us to estimate the timescale of conductivity relaxation at TLL for [TFSI] and [Cl]. From a direct comparison of τσ (T–1) dependencesfor both examined [Cl]− salts, one can note that τσ (TLL) is almost the same (∼0.1 s).However, an exchange of [Cl]− anion to [TFSI]− shifts τσ(LLT) almost three decades toward shorter relaxation times. Interestingly, the time scale of charge transport at Tg also differs for +-based ILs, and it is much shorterthan 100 s (log τσ(Tg) = 2) commonlyidentified with the freezing of ions mobility at Tg. Specifically, log τσ(Tg) = 0.5 and −1.5 for [Cl]and [TFSI], respectively. It means that the chargetransport still occurs when the structural dynamics become arrested.Such a decoupling between charge transport and structural relaxationin aprotic ionic liquids needs further examination. An exchange to makes the ILs more coupled (log τσ(Tg) = 1.5 and 0 for [Cl] and [TFSI]) compared to +-ILs. The liquid–liquid and liquid-glass transitions are alsoclearly detectable when the Stickel analysis (d[log10τσ]/d[1000/T])−0.5 is performed. For conventionalILs with single VFT behavior, the Stickel operator transforms theVFT function into a linear dependence. On the other hand, when twoVFT equations are required to parametrize the experimental data, twolinear regions intersect at certain temperatures, usually called Tb. In the latter case, the Stickel plot indicatesa fragility change when passing the crossover temperature. As seenin the bottom panel of TLL and reveal a minimum at Tg. Note that at TLL, the slope of (d[log10τσ-/d[1000/T])−0.5 dependence is getting larger, which is in contrast to the Stickelgraph of any other glass-forming liquid,37 and therefore, it can be treated as a dynamic signature of LLT.n=2–12666,]+-ILs resembles classical ILs with the single VFT-typetemperature dependence of τσ and Tg = T (τσ = 100 s). However, a derivative analysis reveals again a uniquecurvature of the Stickel plot, similar to that found for +-ILs undergoing LLT. Namely, at a specific temperature(d[log10τσ]/d[1000/T])−0.5 data of+-ILs (n = 2–12) depart from the high-temperature linear regime (R1)with a deviation degree being to some extent dependent on anion andalkyl-chain length. Precisely, the slope change of Stickel plot isalmost negligible for [TFSI] and [Cl], while three regions of different grades can be detected for[TFSI], n = 6–12 and (ii) deformational modes of CHx  (1275–1525 cm–1) as well as (iii) the stretching vibration of CHx (2800–3050 cm–1).38 The first region is sensitive tothe conformational order, the second corresponds to the degree ofcoupling, and the latter provides information about the ordering ofalkyl chains. As can be seen in 444,14][TFSI] from liquid1 to liquid 2 brings a slight upshift (∼3 cm–1) of ν(C–C)-related bands -modes at 1306 cm–1) and downshifting of CHx-bands (∼3cm–1) within the 2800–3050 cm–1 range. All these spectral changes point to a molecular reorganization,which in analogy to data described recently for [P666.14][BH4], confirmed chain coupling and a more ordered arrangementof alkyl tails in liquid 2 of [TFSI]. Note thatthe Raman spectra recorded for supercooled 1 and 2 states markedlydiffer from that of crystalline [P444.14][TFSI] (see agray line in 2 vibrationsin [TFSI]− anion and ν(C–C), τ(CH2), and δ(CH3) in the + cation. Furthermore, the stretching-related modes, including vs(CH2) and νas(CH2) are shifted to 2853 and 2883 cm–1, respectively.Such changes result from an increase in molecular packing relatedto crystal-like ordering.40As a structurally sensitive technique, Ramanmeasurements havebeen performed for [TFSI]and [TFSI]. In analogy to [TFSI], cooling brings higher intensity and downshift (∼2–3cm–1) of ν(C–C) (from 1071 cm–1) and τ(C–C) (at 1310 cm–1) bands.At the same time, these related to the stretching of ν(CH2) and ν(CH3) are oppositely shifted . Additionally, a slightshift of the δ(CH2) up to 1447 cm–1 suggests a slowing down alkyl chains’ local motions. Allthese facts are clear evidence of aliphatic chain coupling due totheir mutual ordering, which is similar to that accompanying LLT  from VFT behavior. High enthalpyof LLT found for +-ILs compared to+-ILs indicates that the alkyl chainsself-assembly is better constituted in the former case, and thereforebrings spontaneous crystallization just above TLL. On the other hand, for +-based ILs, there is no sign of LLTshown in thermodynamic and dynamic properties. However, an analysisof dielectric data in terms of the Stickel operator gave the resultsto some extent similar to that observed for ILs with LLT; that is,negative deviation from the high-temperature linear regime. Thus,shortening the aliphatic chain reduces the possibility of LLT butkeeps the potential of ILs for partial nanorganization. In turn, thelatter brings peculiar ion dynamics behavior near Tg and exceptionally small regions ofdynamic heterogeneity Nα(Tg) (below 10)determined from Donth analysis of calorimetric measurements.In summary, our experimental Raman studies revealed the local arrangementsof alkyl chains in all examined herein tetraalkyl phosphonium ILs;however, only [P