Publications

Abstract Electrified double-layer (EDL) of ionic liquids electrode interfaces have been attracting considerable interest both from the fundamental and applied points of view. So far from the large set of ionic liquids synthetized only a very limited number has been electrochemically studied. As a consequence, the effect of complex shape and chemical properties of the ions and surface morphology on the structure and mechanism of formation of EDL is far from being understood. Binary mixtures of ionic liquids with a common cation (1-ethyl-3-methylimidazolium) paired with two different anions (bis(trifuoromethylsulfonyl) imide, [Tf N-2](-) and tris(pentafluoroethyl)trifluorophosphate, [FAP](-)) were prepared and their molecular mixing behavior was followed through the changes in their vibrational structure by Fourier transform infrared (ATR-FT-IR) spectroscopy. The interface at Hg and each of the binary mixture was followed by electrochemical impedance spectroscopy and drop time measurements. Differential capacitance and charge-potential curves were obtained and compared with those corresponding to the pure liquids. The data is interpreted as suggesting the coexistence at the interface of a mixture of two limiting structures each of which containing essentially one of the anions and sharing the common cation in a co-network.

Abstract Hybrid conjugates of graphene with metallic/semiconducting nanostructures can improve the sensitivity of electrochemical sensors due to their combination of well-balanced electrical/electrocatalytic properties and superior surface-to-volume ratio. In this study, the synthesis and physical characterization of a hybrid conjugate of reduced graphene oxide and nickel nanoparticles (rGO-Ni NPs) is presented. The conjugate was further deposited onto a glassy carbon electrode as a nanocomposite film of chitosan and glucose oxidase. The electrochemical response and morphology of the films were investigated using SEM, CV, and EIS, and their applications as a glucose biosensor explored for the first time in proof-of-concept tests. The low operating potential along with the good linearity and sensitivity (up to 129 mu A cm(-2) mM(-1)) found in the sub-millimolar range suggest potential applications in the self-management of hypoglycemia from blood samples or in the development of non-invasive assays for body fluids such as saliva, tears or breath.

Abstract This work describes the state of the art of electrochemical devices for the detection of an important class of neurotransmitters: the catecholamines. This class of biogenic amines includes dopamine, noradrenaline (also called norepinephrine) and adrenaline (also called epinephrine). Researchers have focused on the role of catecholamine molecules within the human body because they are involved in many important biological functions and are commonly associated with several diseases, such as Alzheimer's and Parkinson. Furthermore, the release of catecholamines as a consequence of induced stimulus is an important indicator of reward-related behaviors, such as food, drink, sex and drug addiction. Thus, the development of simple, fast and sensitive electroanalytical methodologies for the determination of catecholamines is currently needed in clinical and biomedical fields, as they have the potential to serve as clinically relevant biomarkers for specific disease states or to monitor treatment efficacy. Currently, three main strategies have used by researchers to detect catecholamine molecules, namely: the use electrochemical materials in combination with, for example, HPLC or FIA, the incorporation of new materials/layers on the sensor surfaces (Tables 1-7) and in vivo detection, manly by using FSCV at CFMEs (Section 10). The developed methodologies were able not only to accurately detect catecholamines at relevant concentration levels, but to do so in the presence of co-existing interferences in samples detected (ascorbate, for example). This review examines the progress made in electrochemical sensors for the selective detection of catecholamines in the last 15 years, with special focus on highly innovative features introduced by nanotechnology. As the literature in rather extensive, we try to simplify this work by summarizing and grouping electrochemical sensors according to the manner their substrates were chemically modified. We also discuss the current and future of electrochemical sensors for catecholamines in terms of the analytical performance of the devices and emerging applications.

Abstract An immobilization scheme, via glycidyloxypropyl-trimethoxysilane sol-gel crosslinking, of chondroitin sulfate (CS) or fucoidan (Fd), inspired by the biological silicate bridge found in CS, is presented here. It revealed to constitute a simple and effective way of producing biopolymer-silicate composites without compromising the carboxylate- and sulfate- groups of the biopolymers, those which play a determinant role in the binding to metal cations. In the case of the Fd composite, the immobilization process resulted in the similar to 4-fold enhancement of the negatively charged sorption sites, probably due to unfolding effects induced by the synthesis conditions. Textural analysis of the composites showed a microporous, low surface area (6-12 m(2)/g), microstructure which did not prevent the observation of relevant sorption features for metal cations, especially for Pb(II) and Cd(II). Rate constants (1-14 g/mg min(-1)) and affinity constants (79-370L/mg) in the same order of magnitude of chitosan-based sorbents were determined, whereas capacities (2-24 mg/g) were smaller than the generality of those same sorbents. Globally, the sorption of metal cations by the Fd composite was superior to that by the CS composite. Furthermore, high stability of the sorbents and acceptable reproducibility of the synthesis was observed. Overall, the developed scheme of immobilization of CS and Fd appears capable of providing an effective way for integrating these biopolymers into metal cation-related applications such as biosorption, sensing or separation.

Abstract This work reports experimental vapour pressures at different temperatures of four halogenated acetophenones. The liquid phase vapour pressures of p-fluoro and p-chloro acetophenones were measured, respectively, across the temperatures ranges (255.1 to 310.2) K and (271.6 to 335.0) K, using a static method based on capacitance diaphragm manometers. This experimental technique was also used to measure the vapour pressures of both (crystalline and liquid) condensed phases of p-bromo-and p-iodoacetophenones, respectively, through the temperature intervals (295.3 to 378.4) K and (313.1 to 402.0) K. The temperatures and molar enthalpies and entropies of fusion of the four p-halogenated acetophenones were determined using differential scanning calorimetry. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporisation, at selected reference temperatures, were derived from the experimental results. The contributions of the acetyl group and of the constituent halogen atoms to these thermodynamic properties were also predicted through correlation equations.

Abstract In the present study, aqueous solutions of a thermo-responsive negatively charged triblock copolymer methoxy-poly(ethylene glycol)-block-poly(N-isopropylacrylamide)-block-poly (2-succinic acid-propyloxyl methacrylate) (MPEG(45)-b-PNIPAAM(48)-b-PSAPMA(10)), have been characterized in the presence of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) surfactant, at a constant concentration of polymer and various levels of surfactant addition. For this purpose, dynamic light scattering (DLS) was used to probe the effect of the ionic surfactants on the size of the block copolymer species, and small angle neutron scattering (SANS) was applied as a complementary technique to probe the structure on a mesoscopic length scale. The results obtained revealed that the addition of a surfactant to the copolymer solution leads to a decrease of the particle size, due to electrostatic repulsions and solubilization of the hydrophobic microdomains. By zeta potential analysis it was shown that the charge density of the surfactant-coated polymer moieties increases with increasing surfactant concentration. The turbidities of the polymer-surfactant mixtures were measured using a cloud point analyzer. Our data revealed that the behavior not only depends on the surfactant concentration, but it is also affected in some cases by temperature. In addition, cytotoxicity studies were carried out on mouse fibroblasts cells NIH-3T3 to evaluate the potential of the systems as drug delivery carriers. Results showed that the cytotoxicity of the polymer changes with surfactant addition, rising as the concentration of SDS increases but falling off with increasing DTAB concentration.

Abstract Glioblastoma (GBM), the highest grade astrocytoma, is one of the most aggressive and challenging cancers to treat. The standard treatment is usually limited due to the intrinsic resistance of GBM to chemotherapy and drug non-specific effects. Therefore, new therapeutic strategies need to be developed to target tumor cells, sparing healthy tissues. In this context, the inhibitor-of-apoptosis protein (IAP) survivin emerges as an ideal target for a gene silencing approach, since it is sharply differentially expressed in cancer tissues. In this work, two different families of cationic gemini surfactants (bis-quat conventional and serine-derived) were tested regarding their efficiency to deliver small interfering RNAs (siRNAs) in a human GBM cell line (U87), in order to select an effective siRNA anti-survivin carrier. Importantly, survivin downregulation combined with administration of the chemotherapeutic agents temozolomide or etoposide resulted in a synergistic cytotoxic effect, thus revealing to be a promising strategy to reduce the chemotherapeutic doses for GBM treatment.

Abstract This paper reports experimental vapor pressures of condensed phases of methyl p-cyano, p-formyl, p-nitro, and p-(methylamino) benzoates measured over the temperature ranges (303.9 to 393.0) K, (303.1 to 388.2) K, (319.0 to 415.8) K, and (332.9 to 392.4) K, respectively, using a static method based on capacitance diaphragm manometers. The Knudsen mass-loss effusion technique was also used to measure the vapor pressures of crystalline methyl p-(methylamino)benzoate in the temperature range (317.1 to 339.2)" K. These results enabled the calculation of the standard molar enthalpies and entropies of sublimation and of vaporization, at reference temperatures as well as the (p,T) values of the triple point of each compound. The temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the values derived indirectly from the vapor pressure measurements. The enthalpies of the intermolecular hydrogen bonds O-H center dot center dot center dot O in the crystalline phase of the parent benzoic acids were determined.

Abstract This work reports the experimental determination of relevant thermodynamic properties and the characterization of luminescence properties of the following polycyclic aromatic hydrocarbons (PAHs): 2,6-diethylnaphthalene, 2,6-diisopropylnaphthalene and 2,6-di-tert-butylnaphthalene. The standard (p(o) = 0.1 MPa) molar enthalpies of combustion, Delta H-c(m)o, of the three compounds were determined using static bomb combustion calorimetry. The vapor pressures of the crystalline phase of 2,6-diisopropylnaphthalene and 2,6-di-tert-butylnaphthalene were measured at different temperatures using the Knudsen effusion method and the vapor pressures of both liquid and crystalline phases of 2,6-diethylnaphthalene were measured by means of a static method. The temperatures and the molar enthalpies of fusion of the three compounds were determined using differential scanning calorimetry. The gas-phase molar heat capacities and absolute entropies of the three 2,6-dialkylnaphthalenes studied were determined computationally. The thermodynamic stability of the compounds in both the crystalline and gaseous phases was evaluated by the determination of the Gibbs energies of formation and compared with the ones reported in the literature for 2,6-dimethylnaphthalene. From fluorescence spectroscopy measurements, the optical properties of the compounds studied and of naphthalene were evaluated in solution and in the solid state.