Mobility of oligopeptides on normal‐phase silica: Effect of positional isomerism

Abstract

SynopsisIsomeric oligopeptides composed of five methionyl residues and one glycyl residue or of five y-methyl-L-glutamyl residues and one glycyl residue all exhibit marked differences in retention on normal-phase silica. When the glycyl residue is at internal positions of hexaor heptapeptides, the peptide elutes most rapidly from the pPorasil column. Comparison of the effect of positional isomerism on retention in short oligopeptides with the effect on retention of hexamers and heptamers suggests that a change in peptide conformation may be responsible for the change in oligopeptide mobility.

Zwitterion polymerization of 2-methyl-2-oxazoline and acrylic acid

“…The multiplet centered at 6. 15 ppm is assigned to olefinic protons of the group OOC-CH=CH2. This assignment is confirmed by the proton NMR of the brominated copolymer.…”

“…Within each of the groups of carbon signals, a number of further assignments were relatively easy to make based on chemical shift values. For example, methylene carbons attached to oxygens (signals [13][14][15] have higher chemical shifts than those attached to amide " Chemical shifts are relative to CHgCN (methyl carbon 1.70 ppm relative to Me4Si). nitrogens (signals [8][9][10][11][12], which, in turn, have higher chemical shifts than those attached to ester or acid carbonyls (signals 6 and 7).…”