Vibrational characterization of L‐valine phosphonate dipeptides: FT‐IR, FT‐RS, and SERS spectroscopy studies and DFT calculations

Abstract

AbstractFour L‐valine (L‐Val) phosphonate dipeptides that are potent inhibitors of zinc metalloproteases, namely, L‐Val‐C(Me)2‐PO3H2 (V1), L‐Val‐CH(iP)‐PO3H2 (V2), L‐Val‐CH(iB)‐PO3H2 (V3), and L‐Val‐C(Me)(iP)‐PO3H2 (V4), are studied by Fourier‐transform infrared (FT‐IR) spectroscopy, Fourier‐transform Raman spectroscopy (FT‐RS), and surface‐enhanced Raman scattering (SERS). The band assignment (wavenumbers and intensities) is made based on (B3LYP/6‐311 + + G**) calculations. Comparison of theoretical FT‐IR and FT‐RS spectra with those of SERS allows to obtain information on the orientation of these dipeptides as well as specific‐competitive interactions of their functionalities with the silver substrate. More specifically, V1 and V4 appear to interact with the silver substrate mainly via a CsgCH3 moiety localized at the NamideCsg(CH3)Pmolecular fragment. In addition, the POH and isopropyl units of V4 assist in the adsorption process of this molecule. In contrast, the CαNH2 and PO3H− groups of V2 and V3 interact with the silver nanoparticles, whereas their isopropyl and isobutyl fragments seem to be repelled by the silver substrate (except for the CH2  of V3), similar to the Cβ(CH3)2 fragment of L‐Val for all L‐Val phosphonate dipeptides investigated in this work. The adsorption mechanism of these molecules onto the colloidal silver surface is also affected by amide bond behavior. Copyright © 2010 John Wiley & Sons, Ltd.