Methyleneation of Peptides by XXXX (TEMED) under Conditions Used for Free Radical Polymerization: A Mechanistic Study.

@entity2574 @entity462 @entity845 @entity36808 @entity1160 @entity1521 @entity3793 @entity2340 @entity376 @entity71725 @entity4389 @entity669 @entity9881 @entity369
UNASSIGNED: Free radical polymerization is often used to prepare protein and peptide-loaded hydrogels for the design of controlled release systems and molecular imprinting materials. Peroxodisulfates (ammonium peroxodisulfates (APS) or potassium peroxodisulfates (KPS)) with @entity71725 ( @entity71725 ) are frequently used as initiator and catalyst. However, exposure to these free radical polymerization reagents may lead to modification of the protein and peptide. In this work, we show the modification of @entity376 residues by ammonium peroxodisulfate (APS)/TEMED of the immunostimulant @entity36808 (TP5). Parallel studies on a decapeptide and a library of 15 @entity9881 were performed to reveal the mechanism of modification. LC-MS of APS/TEMED-exposed TP5 revealed a major reaction product with an increased mass (+12 Da) with respect to TP5. LC-MS(2) and LC-MS(3) were performed to obtain structural information on the modified peptide and localize the actual modification site. Interpretation of the obtained data demonstrates the formation of a @entity845 bridge between the @entity376 and @entity369 residue in the presence of TEMED, while replacing TEMED with a @entity4389 catalyst did not show this modification. Studies with the other peptides showed that the TEMED radical can induce methyleneation on peptides when @entity376 is next to @entity369 , @entity1521 , @entity462 , aspargine, @entity1160 , @entity3793 , @entity669 , @entity2340 , and @entity2574 residues. Stability of peptides and protein needs to be considered when using APS/TEMED in in situ polymerization systems. The use of an alternative catalyst such as @entity4389 may preserve the chemical integrity of peptides during in situ polymerization.
