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

Monitoring the Interfacial Behavior of Selective Y5 Receptor Antagonist on Colloidal Gold Nanoparticle Surfaces: Surface-Enhanced Vibrational Spectroscopy Studies

This report describes the first detailed characterization of the molecular structure of Lu AA33810, a selective Y5 receptor antagonist, and its behavior at the solid/liquid interface after conjugation with gold nanoparticles (GNPs). Physicochemical characterization, including imaging by scanning electron microscopy as well as electrophoretic mobility and dynamic light scattering measurements, was performed to determine the morphology, electrokinetic properties and range of stability of the GNPs. A comprehensive vibrational analysis, employing Raman spectroscopy, Fourier transform infrared absorption, surface-enhanced Raman spectroscopy, and surface-enhanced infrared absorption methods, is reported. The experimental data are supported by density functional theory calculations. It is implied that the Thz and Phe rings determine the adsorption geometry of Lu AA33810 on the studied GNPs and adopt a tilted orientation, exposing the interaction between the Thz free electron pair and the metallic nanosubstrates. The analysis also provides evidence for strong interaction between the free electron pairs located on the oxygen atoms of the SO₂ fragment of methanesulfonamide and the GNPs. The results provide important insight into designing new compounds with agonistic or antagonistic properties toward the Y5 receptor

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