RESUMO
SERS spectroscopy is successfully employed in this work to reveal different components integrating the cochineal colorant employed for dying archaeological textile samples from the Arica Region in North Chile. This analysis was done by in-situ experiments that does not imply the material (colorant and biomolecules) extraction. The spectroscopic analysis of the archaeological textiles by SERS reveals the presence of bands attributed to carminic acid and nucleobases, mainly adenine and guanine. The identification of these biomolecules was also verified in raw cochineal extract and in cochineal dyed replica wool fibers fabricated by us following ancient receipts. The effect of Al on the complexation of carminic acid and other biomolecules was also tested in order to understand the changes induced by the metal interaction on the colorant structure. This study revealed that Al can also complex biomolecules existing in the cochineal extract. In particular, guanine residue seems to interact strongly with the metal, since SERS bands of this residue are enhanced. Furthermore, a theoretical analysis on the interaction of carminic acid and a silver surface was also performed in order to better understand the interaction mechanism between carminic acid and a metal surface that leads to the final SERS spectrum. The results of the present work will be very useful in the identification of different molecules and metal complexes that may be forming part of the cochineal colorant found in archaeological materials.
RESUMO
In a previous work we demonstrated that toxic aggregates of the protein ß-amyloid (ATAß) involved in the Alzheimer's disease (AD) can be destabilized upon electromagnetic irradiation of the peptide Cys-Leu-Pro-Phe-Phe-Asp (CLPFFD) adsorbed on gold nanospheres (AuNSs). For a selective recognition of the therapeutic target (i.e. ATAß) of AD by the conjugates peptide-nanoparticle it is relevant to understand how the interaction between attached ligands and nanoparticles occurs. In this work a surface enhanced Raman scattering spectroscopy (SERS) study of the interactions of CLPFFD with AuNSs of 10nm average diameter was carried out. The SERS data suggest that phenylalanine displays its aromatic ring coplanar to the surface which is supported by theoretical data obtained from molecular mechanics (MM) and Extended Hückel Theory (EHT) calculations.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Ouro/química , Nanosferas/química , Peptídeos/química , Ácido Aspártico/química , Cisteína/química , Concentração de Íons de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Nanopartículas Metálicas/química , Modelos Moleculares , Peptídeos/farmacologia , Fenilalanina/química , Conformação Proteica , Espectrofotometria Ultravioleta , Análise Espectral Raman/métodosRESUMO
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).
Assuntos
Antioxidantes/química , Aporfinas/química , Nanopartículas Metálicas/química , Prata/química , Análise Espectral Raman/métodos , Modelos MolecularesRESUMO
Raman and surface-enhanced Raman scattering (SERS) spectra of the synthetic carboxy terminal peptide of human chorionic gonadatropin ß-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
Assuntos
Gonadotropina Coriônica Humana Subunidade beta/química , Sequência de Aminoácidos , Gonadotropina Coriônica Humana Subunidade beta/genética , Humanos , Interações Hidrofóbicas e Hidrofílicas , Técnicas In Vitro , Nanopartículas Metálicas , Modelos Moleculares , Oligopeptídeos/química , Oligopeptídeos/genética , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/genética , Análise Espectral Raman/métodos , Eletricidade EstáticaRESUMO
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.
Assuntos
Arginina/química , Análise Espectral Raman/métodos , Nanopartículas Metálicas/química , Modelos Moleculares , Modelos Teóricos , Estrutura Molecular , Prata/químicaRESUMO
In this work surface-enhanced resonance Raman spectroscopic experiments have demonstrated that metallic single-walled carbon nanotubes can be used as chemical assemblies between the pyrene analyte and the silver colloidal surface. Pyrene has been detected at concentrations lower than 10(-9) M by use of the 514.5 nm excitation laser line. A charge transfer from the surface to the nanotube characterizes the nanotube-silver surface interaction. The pyrene-nanotube interaction occurs through a pi-pi electronic stacking. Extended Hückel calculations based on a simplified molecular model for the analyte/nanotube/surface system support the experimental conclusions. The nanotube-pyrene distance is 3.4 A, and the most probable orientation for pyrene is confirmed to be plane parallel to the nanotube surface. An energy transfer from the silver surface to the nanotube/analyte system is verified.