Temperature and pH dependence of proton N.M.R. of glutamine in peptides

Abstract

The proton n.m.r. spectra of the peptides Ala-Glu-Gly-Gln-Gly and Gly- Gln-Gly as measured in dimethyl sulfoxide over a range of temperatures yielded kinetic parameters for rotation about the carbon-nitrogen bonds of the glutamine side chains of ΔH^‡ 71.6 kJ mol^-1, ΔS^‡ 2.1 J mol^-1 K^-1, and ΔH^‡/70.6 kJ mol^-1, ΔS^‡ -0.5 J mol^-1 K^-1, respectively, at 298 K. On pH titration in dimethyl sulfoxide/water solutions, the chemical shifts of the cis protons of the glutamine amide remained constant whereas those of the trans protons were altered with a pK corresponding to that of the terminal glycine.