FTIR study of the protonation of a schiff base in chloroform-methanol mixtures

Abstract

FTIR spectroscopic measurements were carried out to study the protonation of a non-conjugated Schiff base by HBr and by a number of carboxylic acids and amino acids in chloroform and in chloroform-methanol mixtures. It is shown that the presence of methanol always promotes protonation. It is suggested that the mechanism that makes it possible for the weak acids present in rhodopsin to protonate the Schiff base chromophore may be similar to Blatz's levelling effect.