ABSTRACT
Cupric oxide leaf-like nanostructures (CuONSs) (average dimensions: 80-180 nm in width and 400-750 nm in length) were synthesized via anodic electrochemical dissolution of copper in an ethanol solution containing LiCl electrolyte and water. Ultraviolet-visible (UV-Vis), Fourier-transform infrared (FT-IR), and Raman spectroscopies as well as scanning electron microscope (SEM), high-resolution transmission electron microscopy with energy dispersive X-ray (HD-TEM-EDS), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) were used to explore the metal surface plasmon, size, rheology, and structure of CuONSs. Then, pyridine α-aminophosphinic acid isomers (α-, ß-, and γ-NHPy) were synthesized and assembled on the CuONS/air and CuONS/aqueous solution interfaces at the pH level of solution = 7. Differences in adsorption and thus in the spectral response resulting from positional isomerism were examined by surface-enhanced Raman scattering (SERS) with an excitation wavelength of 785 nm. The manner of interaction of the investigated isomers with CuONSs in an aqueous solution was discussed in detail and compared with that at the CuONS/air interface. For γ-NHPy, at the CuONS/water interface, the time-dependent changes in the spectral profile were observed and analyzed. For ß-NHPy at the CuONS/air interface, tip-enhanced Raman scattering (TERS) measurements were performed. These measurements allowed observing single molecule behavior and avoiding interference from the molecule's surrounding environment.
ABSTRACT
The tip-enhanced Raman scattering (TERS) spectra of bradykinin (BK) and its potent B2 BK receptor antagonists, [d-Arg(0),Hyp(3),Thi(5,8),l-Pip(7)]BK and [d-Arg(0),Hyp(3),Thi(5),d-Phe(7),l-Pip(8)]BK, approximately with a size of about 40 nm, adsorbed onto colloidal suspended Ag nanowires with diameter in the range of 350-500 nm and length of 2-50 µm were recorded. The metal surface plasmon resonance and morphology of the Ag nanowires were studied by ultraviolet-visible (UV-Vis) spectroscopy and scanning electron microscopy (SEM). Briefly, it was shown that two C-terminal amino acids of BK and [d-Arg(0),Hyp(3),Thi(5,8),l-Pip(7)]BK are involved in the interaction with the colloidal suspended Ag nanowire surface, whereas three last amino acids of the [d-Arg(0),Hyp(3),Thi(5),d-Phe(7),l-Pip(8)]BK sequence attached the Ag surface. Thus, BK adsorbs on the colloidal suspended Ag nanowires mainly through the Phe(5/8) ring (tilted orientation) and the one oxygen atom of the carboxylate group and the H2N-C-NH-CH2- fragment of Arg(9). In the case of [d-Arg(0),Hyp(3),Thi(5,8),l-Pip(7)]BK, the Thi(8) ring (through the lone electron pair on the sulfur atom) and the both oxygen atoms of the carboxylate group and the amine group of Arg(9) mainly participated in the interaction with the Ag nanowire surface. For [d-Arg(0),Hyp(3),Thi(5),d-Phe(7),l-Pip(8)]BK, the d-Phe(7) ring, the Pip(8) ring, and the Arg(9) side-chain assisted in the peptide interaction with the Ag surface. The obtained results emphasize the importance of the C-terminal part of these peptides in the adsorption process onto the colloidal suspended Ag nanowires.
