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

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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.

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