Infrared spectroscopic studies of vancomycin and its interactions with N-acetyl-D-Ala-D-Ala and N,N′-diacetyl-L-Lys-D-Ala-D-Ala

The infrared (IR) spectrum of vancomycin, in D2O solution, has been assigned by recording spectra at different pD values and by comparing them with the spectrum in H2O at pH 5. The effects of self association on the spectrum of vancomycin at pD 5 have also been investigated. Details of underlying components of the broad bands in the spectra were revealed using resolution enhancement and second derivatives. The IR spectra of two peptide models, N-Ac-D-Ala-D-Ala and N, N′-Ac2-L-Lys-D-Ala-D-Ala, have also been assigned in D2O solution. The interactions of these peptides with vancomycin, in pD 5 solution, have been studied by infrared spectroscopy and the above assignments used to interpret the observed spectral changes; the solubilities of the vancomycin-peptide complexes at pD 5 were determined to facilitate these studies. The IR spectra of the complexes show substantial increases in intensity of a component at about 1588 cm 1. Using 13C labelled N-Ac-D-Ala-D-Ala this was found to be due to the asymmetric stretch of the carboxylate group of the peptide, showing that this group undergoes a substantial perturbation on binding to vancomycin.