José Vicente García-Ramos

Sensing polycyclic aromatic hydrocarbons with dithiocarbamate-functionalized ag nanoparticles by surface-enhanced Raman scattering.

Trace detection of polycyclic aromatic hydrocarbons is reported in this work on dithiocarbamate calix[4]arene functionalized Ag nanoparticles by using surface-enhanced Raman scattering (SERS). SERS spectra informed about the existence of the pollutant by measuring its characteristic fingerprint vibrational features. In addition, SERS revealed important structural information from both the host and the analyte which was crucial to understand and deduce the host-guest interaction mechanism. The effectiveness of this system was checked for a group of PAHs: pyrene, benzo[c]phenanthrene, triphenylene, and coronene. From the analyzed results, the affinity constants and the limit of detection were deduced for each pollutant.

Nanosensors based on viologen functionalized silver nanoparticles: few molecules surface-enhanced Raman spectroscopy detection of polycyclic aromatic hydrocarbons in interparticle hot spots.

The functionalization of silver nanoparticles (Ag NPs) by viologen dications (VGDs) is reported in this work as well as their applications in the surface-enhanced Raman scattering (SERS) detection of polycyclic aromatic hydrocarbons (PAHs). VGDs are able to form intermolecular cavities at interparticle junctions (SERS hot spots) where the analyte can be allocated. This leads to a giant intensification of the Raman emission of the target molecule. This effect was applied in the detection of PAHs, one of the most widespread and dangerous group of pollutants existing in the atmosphere and waters. A comparison between sensing-systems based on different VGDs (lucigenin, diquat, and paraquat) was done for the detection of two PAHs (pyrene and benzo[c]phenanthrene). The functionalization with lucigenin (LG) provided the most powerful and stable VGD-NPs sensor, which allowed the SERS detection of pyrene (PYR) down to 10(-9) M in the macro setup and in the zeptomole range for spectra obtained by single NPs aggregates (micro setup). Besides, SERS spectra afforded important structural information about the interaction mechanism of VGD and PAHs, revealing the formation of a CT complex between the VGD and PYR and changes in the host conformation. The position of the nu(Ag-Cl) band and the plasmon resonance contribution assigned to Ag dimers were also used as spectral markers to monitor the host-guest interaction.

MICRO-RAMAN SPECTROSCOPY APPLIED TO DEPTH PROFILES OF CARBONATES FORMED IN LIME MORTAR

Abstract Carbonation takes place in building materials when atmospheric CO 2 reacts with Ca 2+ present in the pore solution. Of the three crystallized forms of calcium carbonate, calcite is the most thermodynamically stable. Raman spectroscopy is a very useful technique for distinguishing between calcite, aragonite and vaterite. In the present study, micro-Raman techniques are used for the first time to establish the existence of various forms of calcium carbonate at different depths in fully carbonated lime mortar, in trials conducted at a temperature of 20 °C and 75% relative humidity in a chamber with atmospheric CO 2 . A new model is introduced for samples containing two or three polymorphs. The size of the calcite crystals formed, also determined with this technique, was estimated to be between 25 and 30 μm.

Comparative SERS effectiveness of silver nanoparticles prepared by different methods: A study of the enhancement factor and the interfacial properties

Different Ag nanoparticles were prepared by four different methods (chemical reduction with trisodium citrate, chemical reduction with hydroxylamine hydrochloride, laser ablation and laser in situ photoreduction) to compare their applicability in surface-enhanced Raman scattering (SERS), their stability and other interfacial characteristics such as the pH, surface availability and the surface potential. This study was conducted by using the anthraquinone dye alizarin as a molecular probe since this molecule is able to be adsorbed onto the metal through three different forms, which relative proportions depend on the interfacial properties of the exposed metal surfaces.

Structural and conformational study of diazabicyclanones and diazabicyclanols

Abstract 3-Methyl-7-alkyl-3,7-diazabicyclo [3.3.1] nonan-9-ones and 9-ols have been studied by 1 H, 13 C NMF_IR and Raman spectroscopy and the crystal structure of 3,7-dimethyl-3,7-diazabicyclo[8.3.1] nonan-9-ol has been determined by X-ray diffraction. The ketones studied adopt in CDCl 3 and (CD 3 ) 2 SO solution a flattened chair—chair conformation; however, in the crystalline N -methyl N -benzyl derivative, the bicyclic system adopts a chair—boat conformation. X-ray data for 3,7-dimethyl-3,7-diazabicyclo [3.3.1] nonan-9-ol have revealed that the compound has crystallized in a chair—chair conformation stabilized by water and ethanol molecules. Frc.a IR data the existence of another chair anhydrous crystalline form stabilized by intramolecular hydrogen bonding has been deduced. The preferred conformation in solution of the diazabycyclanols mainly depends on the polarity of the solvent.

Anomalous Raman bands appearing in surface‐enhanced Raman spectra

Surface-enhanced Raman spectroscopy (SERS) is a very sensitive technique which employs rough metallic surfaces to enhance the Raman signal produced by an adsorbate molecule. The interest of this technique has increased very much in the last years, due to its application in several knowledge fields such are analytical, biological and surface sciences. Although SERS has been applied in the study of a great deal of adsorbates, in very few works is carried out a deep characterization of the metallic substrates employed so far.

Catechol polymerization in the presence of silver surface

Abstract Polymerization of catechol (o-diphenol) was studied by UV–visible absorption and surface-enhanced Raman spectroscopies. Catechol was found to polymerize in solution, both in ethanol and in water, leading to a browning of the solution. This process may take place in nature for o-diphenols similar to catechol, either by enzymatic or by abiotic mechanisms implying inorganic catalysts, leading to the formation of humic substances in soils. Catechol is an excellent molecular model for studying oxidative polymerization processes since it is the simplest molecule containing the very reactive o-diphenol group, like other polyphenols existing in nature. The results found in this study reveal that the oxidative condensation of catechol is remarkably enhanced in the presence of the silver colloids employed to enhance the Raman signal. The possible polymerization mechanism that catechol may follow can be (i) formation of CC and ether COC bonds between aromatic rings, which is the predominant mechanism at neutral pH, (ii) the creation of benzofuran and benzodioxane moieties, also probable, although this mechanism seems to be less important than in the case of caffeic acid, and (iii) a ring opening mechanism yielding aliphatic chains with carboxylic acids, mainly induced at alkaline pH in the absence of light. The influence of pH, light irradiation and storage time on the catechol condensation was investigated in relation to the above mechanisms.

Adsorption of Beta-Adrenergic Agonists Used in Sport Doping on Metal Nanoparticles: A Detection Study Based on Surface-Enhanced Raman Scattering

The adsorption of beta(2)-adrenergic agonist (βAA) drugs clenbuterol, salbutamol, and terbutaline on metal surfaces has been investigated in this work by means of surface-enhanced Raman scattering (SERS). To assist in this investigation, a previous vibrational (IR and normal Raman) characterization of these drugs was performed, supported by ab initio density functional theory calculations. The application of SERS was aimed to apply this highly sensitive technique, based on localized surface plasmon resonance, in the detection of βAA at trace concentrations and as a possible alternative method which can be postulated in routine antidoping analysis. The adsorption of these drugs was studied in depth at different experimental conditions: on Au and Ag, at different pHs, and with varying adsorbate concentration. Moreover, plasmon resonance spectroscopy was employed to investigate the adsorption of these drugs on the metal nanoparticles as well as their aggregation. It was found that the adsorption of these molecules is more effective on gold nanoparticles and at acidic pH, based on the direct interaction of the aromatic or aliphatic moieties through ionic or coordination bonds with the metal. These drugs followed a Langmuir adsorption model from which the adsorption constant and the limit of detection can be determined.

Multicomponent Direct Detection of Polycyclic Aromatic Hydrocarbons by Surface-Enhanced Raman Spectroscopy Using Silver Nanoparticles Functionalized with the Viologen Host Lucigenin

Silver nanoparticles (NPs) functionalized with the molecular assembler bis-acridinium dication lucigenin (LG) have been used as a chemical sensor system to detect a group of polycyclic aromatic hydrocarbon (PAH) pollutants in a multicomponent mixture by means of surface-enhanced raman scattering (SERS). The effectiveness of this system was checked for a group of PAHs with different numbers of fused benzene rings, namely anthracene, pyrene, triphenylene, benzo[c]phenanthrene, chrysene, and coronene. In order to determine the host capacity of this sensor system, the self-assembly of the LG viologen on a metallic surface has been checked by analyzing SERS intensities of PAH bands at different LG concentrations. The NP-LG-analyte affinity is derived from the analysis of PAH band intensities at different concentrations of pollutants, the adsorption isotherm of each PAH on NP-LG cavities has been studied, and the corresponding adsorption constants have been evaluated. The limit of detection at trace-level concentration is confirmed by the presence of their characteristic fingerprint vibrational bands. The SERS spectra of PAH mixtures confirm that LG viologen dication shows a higher analytical selectivity to PAHs constituted by four fused benzene rings, mainly pyrene and benzo[c]phenanthrene, in agreement with their higher affinity which is also related to their better fit into the intermolecular LG cavities. As a conclusion, SERS spectra recorded on modified NP-LG surfaces are a powerful chemical tool to detect organic pollutants.

Calculations of the direct electromagnetic enhancement in surface enhanced Raman scattering on random self-affine fractal metal surfaces

We study the classical electromagnetic enhancement at the excitation wavelength related to surface enhanced Raman scattering (SERS) experimental configurations in the vicinity of random rough metal surfaces possessing self-affine scaling behavior. The scattered electromagnetic intensity is obtained by means of numerical calculations based on the rigorous integral equations formulation of the electromagnetic wave scattering, free from the limitations of electrostatic and/or dipolar approximations. From the enhancement of the scattered field intensity in the immediate vicinity of the surface, originated in the excitation of transversal-magnetic surface plasmon polaritons, the SERS electromagnetic mechanism on substrates of Ag, Au, and Cu is explored as a function of the surface fractal dimension, rms height, and excitation wavelength. It is found that fractality favors the occurrence of large electromagnetic enhancements, which in turn appear to be maximum at an optimum wavelength as a result of the comprom...