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

Abstract

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 [Lys(3)]BN) 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 wavenumber of proper bands upon adsorption on different silver surfaces are consistent with BN and its analogues adsorption primarily through Trp(8). Slightly different adsorption states of these molecules are observed depending upon natural amino 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 N(1)--H bond for all the peptides, except [Phe(12)]BN. This is in contrary to the results obtained for the silver roughen electrode that show direct but not strong N(1)--H/Ag interaction for all peptides except [D-Phe(12),Leu(14)]BN and [Leu(13)-(R)-Leu(14)]BN. For BN only C==O is not involved in the chemical coordination with the colloidal surface. [Lys(3)]BN and BN also adsorb with the C--N bond of NH(2) group normal and horizontal, respectively, to the colloidal surface, whereas C--NH(2) in other peptides is tilted to this surface. Also, the Trp(8) --CH(2)-- moiety of only [Tyr(4)]BN, [Lys(3)]BN, and [Tyr(4),D-Phe(12)]BN coordinates to Ag, whereas the Phe(12) ring of [Phe(12)]BN, [Tyr(4),D-Phe(12)]BN, and [D-Phe(12),Leu(14)]BN assists in the peptides binding only on the colloidal silver.

Binding of Silver Nanoparticles to Bacterial Proteins Depends on Surface Modifications and Inhibits Enzymatic Activity

“…For AgNPs, cysteine (36) and amine-bearing amino acids (37) contain the bond-forming residues. In addition, carboxyls (36,38,39) and aromatics (36)(37)(38)40) were also found to be involved. One study alone identified sulfhydryl, carboxyl, aromatic, and imino groups across a wide range of proteins as responsible for binding to AgNPs (41), suggesting binding may be controlled not by a single amino acid but by specific sequences of amino acids.…”

Structural properties of bombesin‐like peptides revealed by surface‐enhanced Raman scattering on roughened silver electrodes

“…41,43 Although in the case of these peptides adsorbed on the colloidal silver surface their -NH 2 group interacts with the silver nanoparticles. 42,44 …”

“…41,43 In each case, bands associated with Trp 8 dominated the SERS spectra, thus confirming previously obtained results. [41][42][43][44] Therefore, it may be deduced that this residue was involved in substrate binding to the Ag surface, although it occurred in a different manner for each peptide. In addition, the SERS spectra (see Figure 3) differed substantially from the corresponding FT-RS spectra (see Figure 2).…”

Optimization of extinction efficiency of gold‐coated polystyrene bead substrates improves surface‐enhanced Raman scattering effects by post‐growth microwave heating treatment

“…[18,27,28] Weak |E| 2 is also accounted for by the small surface roughness (r of ∼12 nm) due to the ineffective surface plasmon energy radiation. [25,27,29] In contrast, the modified substrate with T MW of 200 s ( Fig. 1(b)) exhibits ∼14- fold improvements in |E| 2 compared to the as-grown substrates (maximum intensity counts of 47 763 in Fig.…”