Interaction of Model Peptides with Water and Lithium Bromide

Abstract

KNOWLEDGE of the interactions between peptide groups and water or denaturing agents is of major importance in understanding proteins. Klotz and Franzen¹ showed recently by infra-red studies that aqueous N-methylacetamide (NMA) forms few inter-peptide hydrogen bonds except at concentrations approaching 12 M. Hydrogen bonds between water and NMA are formed more readily. Harrington and Schellman² proposed that the increased viscosity of proteins in strong lithium bromide solutions is the result of more extensive bonding and more helical coiling than in water, in contrast to the widely held idea that hydrogen bonds are broken in lithium bromide solution. We present viscometric data relating to the interaction of water solutions of lithium bromide with NMA, dimethylacetamide (DMA), acetone, and polysarcosine. The results show that increased viscosities occur in systems where interpeptide hydrogen bonds cannot form.