Phe-MetNH₂ Terminal Bombesin Subfamily Peptides: Potential Induced Changes in Adsorption on Ag, Au, and Cu Electrodes Monitored by SERS

Surface-enhanced Raman scattering, electrochemistry, and generalized two-dimensional correlation analysis methods were used to characterize phyllolitorin and a peptide derived from <i>Pseudophryne guntheri</i> (PG-L). Phyllolitorin and PG-L were deposited onto Ag, Au, and Cu electrode surfaces at different applied electrode potentials in an aqueous solution at physiological pH, and the orientations and adsorption mechanisms of peptides were determined based on the enhancement, broadening, and shifts in the wavenumbers of specific bands. On the basis of these analyses, specific conclusions were drawn regarding the peptide geometry and changes in the geometry that occurred when the electrode type and applied electrode potential were varied. The phyllolitorin and PG-L 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 and Trp rings, the sulfur atom of Met, and the amide bond. Variations in the arrangement of these fragments were observed with changes in the metal surface and the applied electrode potential

Vibrational and Theoretical Studies of the Structure and Adsorption Mode of <i>m</i>‑Nitrophenyl α‑Guanidinomethylphosphonic Acid Analogues on Silver Surfaces

This work presents Fourier transform Raman (FT-Raman), Fourier transform absorption infrared (FT-IR), and surface-enhanced Raman scattering (SERS) spectroscopic investigations of three <i>m</i>-nitrophenyl α-guanidinomethylphonic acids, including <i>m</i>-NO₂PhG­(cHex)­P, <i>m</i>-NO₂PhG­(Morf)­P, and <i>m</i>-NO₂PhG­(An)­P, adsorbed onto colloidal and roughened silver surfaces. The SERS spectra were deconvoluted to determine the overlapped bands from which the specific molecular orientation can be deducted. The vibrational wavenumbers are calculated through density functional theory (DFT) at the B3LYP/6-31++G** level with the Gaussian 03, Raint, GaussSum 0.8, and GAR2PED software packages. The experimental and calculated vibrational bands are compared to those from SERS for the investigated compounds adsorbed on colloidal and roughened silver surfaces. The geometry of these molecules on the SERS-active silver surfaces is deduced from the observed changes in both the intensity and width of the Raman bands in the spectra of the bound species relative to the free species

Raman, Surface-Enhanced Raman, and Density Functional Theory Characterization of (Diphenylphosphoryl)(pyridin-2‑, -3‑, and -4-yl)methanol

This work presents near-infrared Raman spectroscopy (FT-RS) and surface-enhanced Raman scattering (SERS) studies of three pyridine-α-hydroxymethyl biphenyl phosphine oxide isomers: (diphenylphosphoryl)­(pyridin-2-yl)­methanol (α-Py), (diphenylphosphoryl)­(pyridin-3-yl)­methanol (β-Py), and (diphenylphosphoryl)­(pyridin-4-yl)­methanol (γ-Py) adsorbed onto colloidal and roughened in oxidation–reduction cycles silver surfaces. The molecular geometries in the equilibrium state and vibrational frequencies were calculated by density functional theory (DFT) at the B3LYP 6-311G­(df,p) level of theory. The results imply that the most stable structure of the investigated molecules is a dimer created by two intermolecular hydrogen bonds between the H atom of the α-hydroxyl group (in up (HO_U) or down (HO_D) stereo bonds position) and the O atom of tertiary phosphine oxide (O) of the two monomers. Comparison the FT-RS spectra with the respective SERS spectra allowed us to predict the orientation of the hydroxyphosphonate derivatives of pyridine that depends upon both the position of the substituent relative to the ring N atom (in α-, β-, and γ-position, respectively) and the type of silver substrate