Surface-enhanced Raman difference between bombesin and its modified analogues on the colloidal and electrochemically roughen silver surfaces

In this article, surface-enhanced Raman scattering (SERS) spectra of bombesin (BN) and its six modified analogues ([D-Phe(12)]BN, [Tyr(4)]BN, [Tyr(4),D-Phe(12)]BN, [D-Phe(12), Leu(14)]BN, [Leu(13)-(R)-Leu(14)]BN, and [LYS3 JBN) on a colloidal silver surface are reported and compared with SERS spectra of these species immobilized onto an ellectrochemically roughen silver electrode. Changes in enhancement and wavenianber of proper bands upon adsorption on different silver surfaces are consistent ivith BN and its analogues adsorption primarily through TrP8. Slightly different adsorption states of these molecules are observed depending upon natural anzino acids substitution. For example, the indole ring in all the peptides interacts with silver nanoparticles in a edge-on orientation. It is additionally coordinated to the silver through the NI-H bondfor all the peptides, except [Ph e 12]BN. This is in contrary to the results obtainedfor the silver roughen electrode that show direct but not strong NI-HIAg interaction for all peptides except [D-Phe 12 Leu 14]BN and [Leu-@-Leu 14 IBN. For BN only C=O is not involved in the chemical coordination with the colloidal surface. [LyS JBN and BN also adsorb with the C- N bond of NH group normal and horizontal, respectively; to the colloidal sur(ace, whereas C-NH-, in other peptides is tilted to this surface. Also, the Trp8 - CH2- 1110iCtY Of Only [Tyr4]BN, [Lys-]BN, and [Tyr4,D-Phe 12 JBN coordinates to Ag, whereas the Phe 12 ring of [Phe 12 IBN, [Tyr4,D-Phe 12]BN, and [D-Phe 12 Leu 14 JBN assists in the peptides binding only on the colloidal silver. (c) 2008 Wiley Periodicals, Inc.