Investigation of molecular structure of bombesin and its modified analogues nonadsorbed and adsorbed on electrochemically roughened silver surface

This work describes the molecular structure of bombesin (BN) and its analogs on the basis of the absorption infrared and Raman results described below. In these analogues is replaced one (D-Phe12]BN, Tyr4]BN, and Lys3]BN) or two (Tyr4,D-Phe12]BN, D-Phe12,Leu14]BN, and Leu13-(R)-Leu14]BN) amino acid residues within the peptide chain with a synthetic amino acid, creating antagonists to bombesin, which are useful in the treatment of cancer. It is also used surface enhanced Raman scattering (SERS) to study the differences and changes in the vibrational spectra of BN and its analogs, which were attached to an electrochemically roughened silver surface as these peptides interacted with target proteins. This work explores the use of SERS for molecules anchored to a macroscopic silver surface to interrogate the interaction of these peptides with protein receptors. The results presented here show that all peptides coordinate to the macroscopic silver surface through an indole ring and the methylene group of Trp8, the C==O fragment, and an amide bond; however, the orientation of these fragments on the electrochemically roughened silver surface and the strength of the interactions with this surface is slightly different for each peptide. For example, the interaction of --CH2-- of D-Phe12]BN, Tyr4,D-Phe12]BN, D-Phe12,Leu14]BN, Leu13-(R)-Leu14]BN, and Lys3]BN with the silver surface perturbed the vertical orientation of the Trp8 indole ring on this surface. Hence, the indole ring adopted a close to perpendicular orientation on the silver surface for BN and Tyr4]BN, only.