C. Garrido

SERS and theoretical studies of arginine.

Arginine amino acid (Arg) has been vibrationally studied through its infrared, Raman and surface-enhanced Raman scattering (SERS) spectra, and theoretical calculations. Net charge is used to predict the possibility to obtain the SERS spectrum of Arg in colloidal solution. The interpretation of the SERS spectral data suggests that the Arg-Ag nanoparticles interaction in a colloidal solution and in the case of the Arg coated by Ag is mainly verified through the guanidinium moiety. Theoretical calculations performed by using extended Hückel theory method for a model of Arg interacting with an Ag cluster support the observed SERS experimental result.

Surface-enhanced Raman scattering and theoretical studies of the C-terminal peptide of the β-subunit human chorionic gonadotropin without linked carbohydrates.

Raman and surface-enhanced Raman scattering (SERS) spectra of the synthetic carboxy terminal peptide of human chorionic gonadatropin β-subunit free of carbohydrate moieties(P37) are reported. The spectral analysis is performed on the basis of our reported Raman spectrum and SERS data of oligopeptides displaying selected amino acids sequences MRKDV, ADEDRDA, and LGRGISL. SERS samples of P37 were prepared by coating the solid peptide with metal colloids on a quartz slide. This treatment makes possible to obtain high spectral batch to batch reproducibility. Amino acids components of P37 display net charges and hydrophobic characteristics, which are related to particular structural aspects of the adsorbate-substrate interaction. The spectroscopic results are supported by quantum chemical calculations performed by using extended Hückel theory method for a model of P37 interacting with an Ag surface. The P37-metal interaction is drove by positively charged fragments of selected amino acids,mainly threonine 109, lysine 122, and arginine in positions 114 and 133. Data here reported intend to contribute to the knowledge about the antigen-antibody interaction and to the drugs delivery research area

SERS spectrum of gallic acid obtained from a modified silver colloid

Two different crystals of the gallic acid were microscopically separated from a p.a. commercial product. The Raman spectra analysis allowed distinguishing monomeric and dimeric structures. The vibrational wave numbers were computed using DFT quantum chemical calculations. The data obtained from wave number calculations are used to assign vibrational bands obtained in the Raman spectrum. The dimer, characterized as ellagic acid, involves the carboxyl and hydroxyl moieties. The Raman spectrum in water solution of each species is dominated by the monomeric form. A low negatively charged Ag colloid allowed obtain to the best of our knowledge, the first surface enhanced Raman scattering (SERS) spectrum of the gallic acid. The possible electrophilic attacking sites of the title molecule are identified using MEP surface plot study and the orientation of the analyte on the metal surface is proposed tilted to the surface.

Surface-enhanced Raman scattering activity of negatively charged bio-analytes from a modified silver colloid

ABSTRACT A modification to the traditional synthesis of reduced silver metal nanoparticles with hydroxylamine hydrochloride is proposed. The new colloid, obtained by decreasing the concentration of hydroxide and chloride ions, is stable in a large pH range. The low negative surface charge density of the nanoparticles allowed to obtain surface-enhanced Raman scattering (SERS) spectral activity of bio-analytes containing negatively charged groups in aqueous solution. The new colloidal system, characterized by electronic spectroscopy, atomic force microscopy, and zeta potential measurements, was used in the SERS study of the bio-analytes aspartic acid, four oligopeptides, one polypeptide and a probe, the organic dye fluorescein.

Surface enhanced Raman scattering study of the antioxidant alkaloid boldine using prismatic silver nanoparticles.

Prismatic silver nanoparticles (PNps) were used in the surface enhanced Raman scattering (SERS) study of the antioxidant alkaloid boldine (5,6,6a,7-tetrahydro-1,10-dimethoxy-6-methyl-4H-dibenzo[de,g]quinoline-2,9-diol). Prismatic and quasi-spherical (QsNps) silver nanoparticles were synthesized and characterized by UV-Vis spectra, topographic profile (AFM) and zeta potential measurements. Raman and infrared (IR) spectra of the boldine were registered. Theoretical model calculations of the boldine onto the Ag surface predict a nearly coplanar orientation of the benzo[de]quinoline moiety and non-bonded interactions (electrostatic).

Surface-enhanced Raman scattering and theoretical study of the bilichromes biliverdin and bilirubin

ABSTRACT The surface-enhanced Raman scattering spectra of biliverdin and bilirubin were obtained and analyzed; a physical silver ligand interaction was inferred. The structural conformation of biliverdin is practically the same when passing from the dry to solution relative to that observed in Raman solid. However, the surface effect induces a different molecular orientation on the surface in dry and in solution. The conformational structure of bilirubin is modified when passing from dry to solution conditions; the orientation of the analyte on the surface is different in both media. The carboxylate groups interact with the surface more closely in bilirubin than in biliverdin. The unsaturated methine bridge in biliverdin confers an additional stability by delocalizing the π-electronic cloud. Both sides of the molecule could be in the same plane. On contrary, bilirubin with a tetrahedric carbon (methylene bridge) confers the whole system a rather free rotation of each side of the whole molecule. Theoretical model calculations of the biliverdin and bilirubin onto the silver surface predict a nearly coplanar orientation of the whole molecules and non-bonded interaction.