Adsorption of oligopeptides on silver nanoparticles: Surface-enhanced Raman scattering and theoretical studies

7 pags.; 4 figs.; 2 tabs.The MRKDV peptide structurally associated with an immunomodulatory protein, as well as model peptides ADEDRDA and LGRGISL with common amino acid residues were studied using surface enhanced Raman scattering (SERS) supported by quantum chemical computations. Peptides display different net charges and hydrophobic characteristics, which are related to particular structural aspects of the peptide-metal interaction. Samples were photostable when probed with laser lines at 514, 633 and 785 nm. SERS samples were prepared by coating the solid peptides with metal colloids on a quartz slice. This innovation makes possible to obtain high spectral batch to batch reproducibility. MRKDV SERS spectrum is dominated by signals coming from the guanidinium moiety of the arginine amino acid (R); guanidinium is the intrinsic probe which drives the orientation of the peptide on the metal surface. LGRGISL interacts with the metal surface through the guanidinium group and other amino acid residues; a single structural conformation of the peptide on the surface is proposed. ADEDRDA interacts with the metal surface through various amino acid residues, also including the guanidinium moiety; at least two different structural conformations seem to coexist on the surface. Theoretical calculations performed by using extended Hückel theory and 6-31G methods for a model of arginine interacting with a silver cluster support the observed experimental result. Similar calculations involving the MRKDV peptide are also reported. Copyright © 2010 John Wiley & Sons, Ltd.This work was supported by the CSIC-CONICYT project 2007-145, Fondecyt project 1070078 and 1090074, the Ministerio de Educación y Ciencia of Spain project FIS2007-63065 and the Comunidad de Madrid project S-0505/TIC/0191 MICROSERES. A. E .A. acknowledges AT-24090050 CONICYT and DPP-stay fellowship Universidad de Chile.Peer Reviewe