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

Abstract

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.