Publications

Abstract An amperometric ion sensor featuring a microhole supported water/organic gel interface was developed for the quantitative analysis of a water-soluble anticancer drug species, namely, topotecan, which has been used for ovarian and lung cancer treatments. Voltammetric responses associated with topotecan transfer across a polarized water/1,2-dichloroethane (1,2-DCE) interface were first investigated at different aqueous pH values to provide information on a topotecan partition diagram for understanding the lipophilicity of the topotecan drug species. The well-defined voltammetric characteristics for topotecan transfer in pH 4.0 buffer was then employed in conjunction with a microhole supported water/polyvinyl chloride-2-nitrophenyloctyl ether (PVC-NPOE) gel interface to develop a topotecan sensor. Current responses due to the direct transfer of topotecan molecules across the microhole interface increased linearly with respect to topotecan concentration when using cyclic voltammetry and differential pulse stripping voltammetry (DPSV). Improvements in sensitivity were obtained using DPSV and preconcentrating topotecan in the gel layer by holding the transferring potential at 1 V (vs Ag/AgCl) for 30 s followed by stripping of the drug. The topotecan drug sensor shows a low detectable concentration of 0.1 mu M with a good selectivity over other anticancer drug molecules and interfering reagents. As a practical demonstration, the sensing platform was applied for the analysis of topotecan in a diluted serum sample. The results were also compared to those using high performance liquid chromatography (HPLC).

Abstract The results of a. systematic molecular dynamics study of the interfacial structure between the gold (100) surface and two room-temperature ionic liquids, namely, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]) and 1-butyl-3-methylimadazolium bis(trifluoromethylsulfonyl)imide ([BMIm][NTf2]), are herein reported. It is found that near an uncharged surface the IL structure differs from its bulk, having an enhanced density extended until the two first layers. Interfacial layering is clearly observed at the gold surface, with a higher effect for the [BMIm][NTf2] IL but a higher packing for [BMIm][PF6]. In both ILs the alkyl side chains are oriented parallel to the interface while the imidazolium rings tend to be parallel to the interface in about 60% of the cases. The presence of the interface has a higher impact on the orientation of the cations than on the chemical properties of the counterion. The surface potential drop across the interface is more pronounced toward a negative value for ([BMIm][PF6]) than for ([BMIm][NTf2]), due to relatively larger local density of the anions for ([BMIm][PF6]) near the gold surface.

Abstract MK2 (or MAPKAPK2) was already known for its role in the inflammatory response, however recent studies indicate the involvement of this protein kinase in the DNA damage response mechanism. Within its kinase family the enzyme MK3 shows the highest identity with MK2. Here we report a theoretical study on the binding of two molecules, 05B and P4O, to the proteins MK2 and MK3. The data here obtained may shed light on the contribution of individual residues and binding site water molecules for the binding of potential inhibitors to these two kinases.

Abstract Atmospheric gaseous pollutants can induce qualitative and quantitative changes in airborne pollen characteristics. In this work, it was investigated the effects of carbon dioxide (CO2) on Acer negundo pollen fertility, protein content, allergenic properties, and carbohydrates. Pollen was collected directly from the anthers and in vitro exposed to three CO2 levels (500, 1000, and 3000 ppm) for 6 and 24 h in an environmental chamber. Pollen fertility was determined using viability and germination assays, total soluble protein was determined with Coomassie Protein Assay Reagent, and the antigenic and allergenic properties were investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunological techniques using patients' sera. Also, pollen fructose, sucrose, and glucose values were determined. Carbon dioxide exposure affected negatively pollen fertility, total soluble protein content, and fructose content. The patient sera revealed increased IgE reactivity to proteins of A. negundo pollen exposed to increasing levels of the pollutant. No changes were detected in the SDS-PAGE protein profiles and in sucrose and glucose levels. Our results indicate that increase in atmospheric CO2 concentrations can have a negative influence of some features of A. negundo airborne pollen that can influence the reproductive processes as well as respiratory pollen allergies in the future.

Abstract Conducting polymers directly grown on a supporting substrate through electrochemical methods present improved electrical contact and adherence compared to those deposited from solution. This paper explores different potentiostatic approaches for the electropolymerization of triphenylamine and the prospects of application of the resulting films as inexpensive cathodes for solid-state solar cells. To this end, solid films of the monomer were deposited onto transparent conducting glass and electrochemically cross-linked to different extents. The polymer films were characterized by CV, in situ UV-Vis Spectroscopy, in situ Electrochemical Quartz Crystal Microbalance, and, then, tested as cathodes in an all-solid-state hybrid mesoscopic solar cell based on TiO2 sensitized with CdSe quantum dots. The results indicate that, through the control of the doping state of the p-semiconductor, the Fermi level of the cathode can be tuned to raise the open-circuit voltage of the cells up to values near +0.8 V.

Abstract We describe here a voltammetric method based on the ion transfer at a water/oil interface for the electrochemical study of the interaction between high molecular weight dsDNA and two molecules of biological interest: the anthracycline drug daunorubicin (DNR) and the neurotransmitter dopamine (DA). The binding constants of the complexes were determined by performing an amperometric titration, following the decrease of ion transfer currents upon addition of dsDNA, using differential pulse voltammetry (DPV) technique. Binding constants were interpreted in terms of the main interaction mode of the molecules with DNA. A binding constant of 1.7 x 10(4) M-1 was obtained for the intercalation complex of DNR into DNA base pairs (bp), while a binding constant of 1.8 x 10(3) M-1 was obtained for the electrostatic interaction between positively charged DA and negatively charged dsDNA, using a non-linear binding model. The binding site size, in terms of base pairs, for the interaction between the two molecules and DNA was also estimated using non-linear regression analysis. Two binding site models were tested and compared in this work.