J. C. Otero

Vibrational study of the metal-adsorbate interaction of phenylacetic acid and α-phenylglycine on silver surfaces

Raman and SERS spectra of phenylacetic acid and alpha-phenylglycine on silver sols have been recorded at several concentrations and pH values. The alpha-phenylglycine has been also studied in D(2)O. The respective vibrational assignments have been proposed and the analysis of the SERS spectra has made it possible to conclude that phenylacetic acid links to the metal through its carboxylate group only, while alpha-phenylglycine links also through its amino group. In both cases the aromatic ring seems to be almost perpendicular to the metal surface. On the other hand, the contribution of the charge transfer (CT) mechanism to the enhancement of the SERS spectra has been calculated as well and it is found to be very important in both molecules. The band most enhanced by this mechanism is that of vibration 8a, mainly in alpha-phenylglycine.

Phase II study of gemcitabine plus cisplatin in metastatic breast cancer.

Our objectives were to assess the efficacy and toxicity of gemcitabine plus cisplatin as first-line therapy in metastatic breast cancer (MBC). Patients with stage IV MBC and no prior chemotherapy for metastatic disease were treated with gemcitabine 1200 mg/m2 on days 1 and 8, and cisplatin 75 mg/m2 on day 1 every 21 days. Up to 6 cycles were given. A total of 46 patients with a median age of 49 years (range 24–77) and Karnofsky performance status of 80 or above were enrolled. In total, 238 cycles were administered. Of the 42 patients evaluable for response, seven (17%) achieved a complete response and 27 (64%) a partial response, for an overall response rate of 81% [95% confidence interval (CI) 69–93%]. Median time to progression was 14.9 months (95% CI 0–30.2 months). Median duration of response was 24.2 months (95% CI 11.2–37.3 months). The median survival was 27.9 months (95% CI 23.1–32.7 months), and the 1- and 2-year survival probabilities were 71.4 and 61.4%, respectively. All patients were evaluable for toxicity, and grade 3/4 WHO toxicities included neutropenia (41.3%), anemia (8.7%), thrombocytopenia (8.7%), alopecia (26.1%) and nausea/vomiting (32.6%). We conclude that gemcitabine plus cisplatin is a highly effective and safe first-line treatment for patients with MBC. The time to progression of 14.9 months compares favorably with other standard treatments (anthracyclines, taxanes). A randomized study is required to further investigate the role of this combination as first-line treatment for MBC.

How a resonant charge transfer mechanism determines the relative intensities in the SERS spectra of 4-methylpyridine

Abstract The surface-enhanced Raman scattering (SERS) spectra of 4-methylpyridine (4-MP) have been recorded at different electrode potential versus saturated Ag/AgCl/KCl reference electrode. By comparing the relative intensity of the SERS with the Raman spectrum of the aqueous solution it is possible to determine that 12, 6a, δ(CH) and especially 8a modes are strongly enhanced. In this work, it is demonstrated that these vibrations are closely related to Franck–Condon factors of a resonant photoinduced charge transfer (CT) mechanism similar to a resonance Raman (RR) process. The theoretically calculated ΔQ displacements represent the differences between geometries of the potential energy minima of the states involved in the resonant process, allowing to calculate the relative intensities in RR from the Peticolas’ equation. These calculated intensities are in a perfect agreement with the experimental behavior.

Evidences for the contribution of a resonant charge transfer process to the surface-enhanced Raman scattering of 2,6-dimethylpyridine

The surface-enhanced Raman scattering spectra of 2,6-dimethylpyridine have been recorded on silver at different electrode potentials. The main feature of these spectra is the strong enhancement of the band corresponding to the 8a mode when the electrode potential becomes more negative. This enhancement has been discussed on the basis of a resonant charge transfer (CT) mechanism by using a methodology based on the analysis of the ab initio optimized equilibrium structures of the electronic states involved in the CT resonant process namely: the ground electronic states of the neutral molecule and its radical anion.

Surface-enhanced Raman scattering of hydroxybenzoic acids adsorbed on silver nanoparticles.

Surface-enhanced Raman scattering (SERS) of hydroxybenzoic acids has been studied on silver sols in H(2)O and D(2)O solutions. The adsorption behavior of 4-hydroxybenzoic acid (4HBA) is different from that of salicylic (2HBA) and 3-hydroxybenzoic (3HBA) acids. It was concluded that 4HBA is adsorbed on silver nanoparticles (Ag(n)) as either oxidobenzoate (A(2-)) or hydroxybenzoate (A(-)), depending on the pH of the solution, given rise to a flat orientation. Both 2HBA and 3HBA acids are always adsorbed as hydroxybenzoates anions (A(-)) at pH >or=5 and link to the metal through the carboxylate group (Ag(n)--A(-)), standing more or less perpendicular to the metal surface. In the case of these monoanions, the selective enhancement of the bands is due mainly to a resonant electron or charge transfer process (ET or CT) from the metallic nanoparticles to the adsorbates, yielding the transient formation of the respective radical dianions (Ag(+)(n)--A(2-)). It is found that the enhanced bands, and especially the mode 8a;nu(ring), are related to the difference between the equilibrium structures of the adsorbate in its ground (A(-)) and CT-excited (A(2-)) states. In the SERS spectrum of 4HBA dianion, the contribution of CT mechanism is not observed.

Adsorption of carbendazim pesticide on plasmonic nanoparticles studied by surface-enhanced Raman scattering.

Surface-Enhanced Raman Spectra (SERS) of methyl N-(1H-benzimidazol-2-yl)carbamate (MBC), usually named carbendazim, have been recorded on silver colloids at different pH values. In order to identify the neutral, protonated or deprotonated species of MBC that originate the SERS, the vibrational wavenumbers of these three isolated forms and linked to a silver atom have been predicted by carrying out DFT calculations. The results indicate that the active SERS species in the studied pH range correspond to the neutral MBC and its deprotonated ion in the amidate form. According to theoretical calculations, neutral MBC is linked to the metal through the imidazolic nitrogen atom, while the deprotonated MBC could be linked through the imidazolic nitrogen together with the amidic nitrogen atom or the carbonyl oxygen atom. Both adsorbed species, neutral and deprotonated, have the benzimidazolic ring orientated almost perpendicular to the silver surface and no molecular reorientation has been detected. pH of the bulk controls the relative abundance of the neutral MBC and its amidate anion which can be monitored through the intensities of the SERS bands recorded at about 1230 and 1270cm(-1). These two key bands correspond to the in-plane NH deformation of amidic and imidazolic groups, respectively.

Surface enhanced Raman spectra of benzene tricarboxylate anions on silver sols

Abstract Surface enhanced Raman spectra of hemimellitate, trimesate and trimellitate anions adsorbed on aqueous silver sols have been investigated. For each one, the results obtained at different pH values have been interpreted in terms of the degree of dissociation. Some conclusions concerning how the ions bond to the metal surface were obtained. The hemimellitate ion was found to bond to the metal through at least two carboxylate groups in an upright orientation, whereas the trimellitate ion seems to orientate face-on with respect to the surface. No unambiguous conclusion has been established for trimesate ion.

Vibrational spectra of phenylacetate and phenylglycinate ions

The force fields of phenylacetate (PAC) and phenylglycinate (PGLY) ions have been calculated at B3LYP/6-31 þ G* level of theory and improved by using Pulay’s scaling methodology by directly transferring scale factors from related molecules. On this basis, a general assignment of the Raman spectra of these ions has been proposed. q 2003 Elsevier Science B.V. All rights reserved.

Characterization of electronic properties of charge-transfer states of biological molecules by Surface-Enhanced Raman Scattering

One of the most important chemical transformations which a molecule can undergo is the transfer of an electron, this process playing a foremost role in biological reactions. Charge transfer intermediates, as for instance radical ions of organic molecules, are originated in such processes which require sophisticated instrumentation to be studied experimentally. In this contribution, the keys to detect the presence of the charge-transfer (CT) mechanism in Surface-enhanced Raman scattering (SERS) are presented, which allows for the use of these kind of spectroscopy to characterize such short lived chemical species.