Communication Association of model peptides and dehydropeptides: N-acetyl-l-bu- tyrine and (Z)-dehydrobutyrine N’,N’-dimethylamides*

These comparative studies on the aggregation behaviour of Ac-(Z)-∆Abu-NMe2 and Ac-L-AbuNMe2 in carbon tetrachloride were performed by the analysis of their FTIR spectra and by theoretical calculations. The percentage of the monomeric form (α) decreased as concentration increased and this occurred to a higher degree for the (Z)-∆Abu derivative than for its saturated analogue. The dimerization constant KD, calculated on the basis of the intensity of the monomer and associate bands in the νs(N-H) vibration region, is by three orders of magnitude larger for Ac-(Z)-∆Abu-NMe2 than for Ac-L-Abu-NMe2. The obtained dimer geometries of the dehydrocompound were calculated by the B3LYP/6-31+G** method.