Conformational change of glycine trimer alkyl esters in aqueous solution

Abstract

Vibrational spectra of glycine trimer alkyl (propyl, butyl and hexyl) ester hydrochloride have been studied in the solid state and in aqueous solution and compared with those of polyglycine I (PGI; extended β form) and polyglycine II (PGII; helical form). It has been assumed that these oligomers have a PGII-Iike helical structure in the solid state. The concentration and pH dependences of the Fourier transform IR spectra of the aqueous glycine trimer solutions have been investigated. The results are summarized as follows. Below the CMC PGI-Iike extended and PGII-like helical structures coexist in aqueous solution. Above the CMC, the PGII-Iike helical structure is stabilized. In the pH range 3.5–7.0, both the PGI-like extended and the PGII-like helical structures coexist, while the PGII-Iike helical structure is predominantly stabilized in alkaline solution.