Effect of an aliphatic spacer group on the adsorption mechanism of phosphonodipeptides containing N-terminal glycine on the colloidal silver surface

摘要

This study presents the complete solid-state vibrational assignments for a series of five zwitterionic phosphonodipeptides containing an N-terminal glycine: L-Gly-L-CH(Me)-PO3H2 (G1), L-Gly-C(Me,Me)-PO3H2 (G2), L-Gly-L-CH(Et)-PO3H2 (G3), L-Gly-C(Me,Et)-PO3H2 (G4), and L-Gly-L-CHGBU)-PO3H2 (G5). The assignments are based primarily on Fourier-transform Raman spectra (FT-RS) and Fourier-transform infrared spectra (FT-IR) spectra, as well as density functional theory (DFT) calculations at the B3LYP; 6-31++G** level of theory. Existing literature data are also taken into consideration. The surface geometry of these molecules on a colloidal silver surface was also determined by observing the wavenumber, width, and relative intensity changes of enhanced bands in their surface-enhanced Raman scattering spectra. It is proposed that G1 mainly adsorbs onto the colloidal silver particles through the phosphonate terminus, whereas the P=O bond in G3 and G5 assists in the interaction of these molecules with the silver surface. G3 interacts with Ag mainly via alpha-methlyalanine and the amide bond. It is also shown that the amide bond and glycine backbone are involved in the adsorption of G3 on the silver nanoparticles. In addition, the differences recorded for G4 and G5 SERS spectra are mainly due to interactions between the silver surface and the amine group and N- and P-terminus, respectively, and are manifestations of the characteristic vibrations of these groups. Copyright (C) 2008 John Wiley & Sons, Ltd.