Vibrational circular dichroism study of solvent- and temperature-induced conformational changes in poly-γ-benzyl-l-glutamate and poly-β-benzyl-l-aspartate

Abstract

Vibrational circular dichroism (VCD) spectroscopy was used to study the effect of the different composition of mixed solvents and temperature on the conformation and aggregation states of two synthetically prepared polypeptides, poly-γ-benzyl-l-glutamate (PBLG) and poly-β-benzyl-l-aspartate (PBLA).Additions of trifluoroacetic acid (TFA) into a solution of heligenic solvents trichloromethane and benzene-d6 caused the conformational change from the α-helical to polyproline II-like for both of the polypeptides, which represented interesting transition previously mostly observed in aqueous solutions rather than in organic solvents. The VCD method proved a lower stability of the α-helical conformation of PBLA than PBLG and the structural differences between these polypeptides.The variation of temperature in the region 13–50°C induced atypical conformational transformations in the PBLG/trichloromethane/TFA and PBLG/benzene-d6/TFA systems. The usually more stable α-helical conformation was observed at higher temperatures than the polyproline II-like conformation.