Nitrogen-15 chemical shifts and 1J15N1H of some tripeptides measured at the natural abundance level.

An indirect method combining double-resonance and difference spectroscopy has been used in order to determine 15N chemical shifts and 1J15N1H in glutathione (in H2O at pH 3 and under the same conditions with urea added) and in a series of tripeptides of the type Gly-Gly-L-X (with X = Glu, His, Val, Leu, and Ile) in H2O and at two different pH values. This method has proved to be very efficient as long as the NH proton is not in exchange. The chemical shifts are shown to depend on the considered sequence and especially on the substituent in the gamma position. One-bond couplings show some systematic trends which have been tentatively interpreted in terms of the s character of the N-H bond. Although these latter parameters seem of potential utility in structural determinations, additional data will be needed in order to rationalize their variations.