Potential Induced Changes in Neuromedin B Adsorption on Ag, Au, and Cu Electrodes Monitored by Surface-Enhanced Raman Scattering

Interaction of 4-imidazolemethanol with a copper electrode revealed by isotope-edited SERS and theoretical modeling

Adsorption of 4-imidazolemethanol (ImMeOH) on a copper electrode has been investigated by in situ isotope-edited (H/D and (63)Cu/(65)Cu) surface enhanced Raman spectroscopy (SERS) in aqueous solutions at physiological pH (7.0) in a potential window from -0.500 to -1.100 V. Theoretical modeling by DFT calculations at the B3LYP/6-311++G(d,p) level for light atoms and LANL2DZ with ECP for copper atoms have been employed for the interpretation of experimental data. The copper surface was modeled by a cluster of 6 atoms. It was found that the imidazole ring adopts Tautomer-I form in the adsorbed state and coordinates with the Cu surface through the N3 atom. Linear potential-dependence of ν(C4=C5) mode with the slope of (15 ± 1) cm(-1) V(-1) was experimentally observed. The imidazole ring mode near 1492 cm(-1) primarily due to ν(C2-N3) + β(C2H) vibration has also showed a considerable decrease in frequency at more negative electrode potentials with the slope of (9 ± 2) cm(-1) V(-1). Both modes can be used as sensitive probes for analysis of interaction of the imidazole ring with the metal surface. In agreement with experimental data theoretical modeling has predicted higher stability of surface bound Tautomer-I compared with Tautomer-II. The formation of a covalent bond between the metal and adsorbate was experimentally evidenced by metal isotopic ((63)Cu/(65)Cu) frequency shift of ν(Cu-N) mode at 222 cm(-1), combined with theoretical modeling of the surface complex.

Effect of potential on temperature-dependent SERS spectra of neuromedin B on Cu electrode

Adsorption of decapeptide neuromedin B (NMB) on copper electrode has been investigated by in situ surface-enhanced Raman scattering (SERS) spectroelectrochemistry in the temperature interval from 12 to 72 °C at -0.600 and -1.000 V potentials. It was found that intensities of peptide bands decrease at temperatures above 30 °C with higher decrease slope at -1.000 V. Frequency of F12 mode (1004 cm(-1)) of non-surface-interactive phenylalanine residue was found to be insensitive to temperature variation at both studied electrode potentials, while frequency-temperature curves for surface-interactive groups (Amide-III, methylene) were found to be controlled by the potential. In particular, opposite frequency-temperature trends were detected for Amide-III (Am-III) mode indicating decrease in H-bonding interaction strength of amide C[double bond, length as m-dash]O and N-H groups above 38 °C for -0.600 V, and increase in H-bonding interaction strength between 12 and 72 °C for -1.000 V. Anomalous Am-III temperature-dependence of the frequency at -1.000 V was explained by temperature-induced transformation of a disordered secondary structure to a helix-like conformation. The potential-difference spectrum revealed interaction of methylene groups with Cu surface at sufficiently negative potential values because of the appearance of a soft C-H stretching band near 2825 cm(-1) and a broad band near 2904 cm(-1) assigned to vibration of a distal C-H bond of the surface-confined methylene group. Consequently, a rapid decrease in frequency of CH(2)-stretching band with temperature was observed at -1.000 V, while no essential frequency changes were detected for this mode at -0.600 V. The results show that electrode potential controls the temperature-dependence of the frequency for vibrations associated with surface-interactive molecular groups.

Influence of applied potential on bradykinin adsorption onto Ag, Au, and Cu electrodes

Surface‐enhanced Raman scattering, electrochemistry, and generalized two‐dimensional correlation analysis (G2DCA) methods were used to characterize bradykinin (BK), a hormone which is known to be involved in small‐cell and non‐small‐cell lung carcinoma and prostate cancer. BK was deposited onto Ag, Au, and Cu electrode surfaces under different applied electrode potentials (−1.000 V to 0.200 V) in aqueous solutions. Based on the analysis of the enhancement, the broadening, and the shifts in the wavenumbers of individual bands, specific conclusions were drawn regarding the peptide geometry and changes in this geometry that occurred when the electrode type and applied electrode potential were varied. Briefly, BK deposited onto the Ag, Au, and Cu electrode surfaces showed bands that were due to the vibrations of moieties in contact with or in close proximity to the electrode surfaces and were thus located on the same side of the polypeptide backbone. These moieties included the Phe, Arg, and Pro residues. The findings for adsorbed BK were fully supported by G2DCA, which also allowed us to determine the order in which changes occurred when the electrode potential was changed. In addition, it was found that at negative electrode potentials, the Phe rings and methylene groups interact with Ag electrode surface. No such interaction was observed for Au and Cu electrodes. Copyright © 2013 John Wiley & Sons, Ltd.

Characterization of adsorption mode of new B2 bradykinin receptor antagonists onto colloidal Ag substrate

In this paper, the surface‐enhanced Raman scattering (SERS) spectra of the potent B2 bradykinin receptor antagonists, [D‐Arg0,Hyp3,Thi5,8,L‐Pip7]BK, Aaa[D‐Arg0,Hyp3,Thi5,8,L‐Pip7]BK, [D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK, and Aaa[D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK, were measured when immobilized onto a colloidal assembly of apparently randomly adhering Ag spheres with diameters of approximately 20 – 25 nm. The observed SERS bands corresponding to different vibrational modes of the molecule, attached to or near Ag, and the variations in these bands resulting from competitive interactions of the functional groups of the peptides with the SERS‐active Ag surfaces were analyzed in this study. Briefly, it was shown that Pip, in generally in vertical orientation, and Thi, in the edge‐on position, relative to the colloidal Ag surface interacted with this surface through their lone electron pairs on the nitrogen and sulfur atoms, respectively. The imide bond of the X‐Pro peptide linkage and the guanidine group of Arg were involved in the adsorption process. In addition, it was demonstrated that the specific differences in the amino acid sequences slightly influenced the mode of adsorption. For example, Aaa in Aaa[D‐Arg0,Hyp3,Thi5,8,L‐Pip7]BK and Aaa[D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK and D‐Phe (vertical with respect to the colloidal Ag surface) in [D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK, and Aaa[D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK assisted in the adsorption of these peptides onto the colloidal Ag particles. To discuss these spectral alterations due to the different surface adsorption mechanisms of these peptides, the spectral changes were analyzed according to the adsorption process and Fourier‐transform‐Raman spectra. Copyright © 2013 John Wiley & Sons, Ltd.

B2 bradykinin receptor antagonists: adsorption mechanism on electrochemically roughened Ag substrate

In this paper, the surface‐enhanced Raman scattering (SERS) spectra of the potent B2 bradykinin receptor antagonists, [D‐Arg0,Hyp3,Thi5,8,L‐Pip7]BK, Aaa[D‐Arg0,Hyp3,Thi5,8,L‐Pip7]BK, [D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK, and Aaa[D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK, were measured when immobilized onto a highly specific electrochemically roughened SERS‐active Ag substrate characterized by the formation of a 50 – 150 nm Ag islands on its surface. The observed SERS bands corresponding to different vibrational modes of the molecule, attached to or near Ag, and the variations in these bands resulting from competitive interactions of the functional groups of the peptides with the SERS‐active Ag surfaces and reorientation occurring over time of adsorption were analyzed in this study. Copyright © 2012 John Wiley & Sons, Ltd.