Publications

Abstract The purpose of the present study was to evaluate the in vitro antibacterial effects of different classes of important and common dietary phytochemicals (5 simple phenolics - tyrosol, gallic acid, caffeic acid, ferulic acid, and chlorogenic acid; chalcone - phloridzin; flavan-3-ol - (-) epicatechin; seco-iridoid - oleuropein glucoside; 3 glucosinolate hydrolysis products - allylisothiocyanate, benzylisothiocyanate and 2-phenylethylisothiocyanate) against Escherichia coli, Pseudomonas aeruginosa, Listeria monocytogenes and Staphylococcus aureus. Another objective of this study was to evaluate the effects of dual combinations of streptomycin with the different phytochemicals on antibacterial activity. A disc diffusion assay was used to evaluate the antibacterial activity of the phytochemicals and 3 standard antibiotics (ciprofloxacin, gentamicin and streptomycin) against the four bacteria. The antimicrobial activity of single compounds and dual combinations (streptomycin-phytochemicals) were quantitatively assessed by measuring the inhibitory halos. The results showed that all of the isothiocyanates had significant antimicrobial activities, while the phenolics were much less efficient. No antimicrobial activity was observed with phloridzin. In general P. aeruginosa was the most sensitive microorganism and L. monocytogenes the most resistant. The application of dual combinations demonstrated synergy between streptomycin and gallic acid, ferulic acid, chlorogenic acid, allylisothiocyanate and 2-phenylethylisothiocyanate against the Gram-negative bacteria. In conclusion, phytochemical products and more specifically the isothiocyanates were effective inhibitors of the in vitro growth of the Gram-negative and Gram-positive pathogenic bacteria. Moreover, they can act synergistically with less efficient antibiotics to control bacterial growth.

Abstract A novel electroanalytical method for the detection of paraquat using DNA modified gold nanoparticles immobilized at a gold electrode is demonstrated The electrode surface was first modified using the self-assembly of gold nanoparticles (NPs) followed by the simple adsorption of DNA onto the NPs which was straightforward fast and cost effective The DNA-nanoparticle composite sensor was then characterized in terms of electrochemical responses both in the absence and in the presence of paraquat using cyclic voltammetry differential pulse voltammetry and square wave voltammetry The DNA-NPs composite electrode proved to work adequately as a biosensor for the quantitative analysis of paraquat concentrations taking advantage of utilizing both the modified gold nanoparticles and the interaction between DNA with paraquat molecules In addition the NPs modified electrode demonstrated good sensitivity and stability towards the first reversible reduction step of the double charged paraquat ion Good linearity between paraquat concentration and peak current was observed for the concentration range of 50 x 10(-6) to 10 x 10(-3) M when using differential pulse voltammetry The use of modified electrodes improves the performance of the biosensor in the presence of interfering species in particular when square wave voltammetry is used

Abstract The effect of experimental factors [pH and Hg(II)] on the fluorescence excitation emission matrices (EEMs) of nanosensor carbon dots (CDs) was analyzed by multiway decomposition methods based on parallel factor (PARAFAC) analysis. PARAFAC analysis of the EEM structures identifies three components corresponding to two different-sized CDs with the Hg(II) and pH profiles highly correlated plus a background. Parallel profiles with Linear Dependences (PARALIND) model with three components in the excitation-emission spectral modes and two components in the Hg(II) or pH mode gave similar results as PARAFAC, but is more useful from a theoretical point of view because PARALIND shows that the two different-sized CDs have similar chemical reactivity toward Hg(II) and pH. PARAFAC2 was used as a trilinear confirmatory test of the data structures under analysis. Copyright (C) 2010 John Wiley & Sons, Ltd.

Abstract The electrochemical Interfaces of several deep eutectic solvents based on choline chloride mixtures with 1 2-ethanediol 1 2-propanediol 1,3-propanediol urea or thiourea and mixtures of acetylcholine chloride with urea were studied at a Hg electrode The cyclic voltammetric results identified the potential domains of electrochemical stability and illustrated their dependence on the deep eutectic solvents composition The differential capacitance-potentials C(E) curves for the electrical double layers were obtained from electrochemical impedance data by adjusting the appropriate equivalent circuits The structure of the interfaces is proposed to be dominated by adsorption of choline cations at large negative polarizations while at less negative or positive polarizations the structure is dominated by the adsorption of the anion The temperature coefficients of capacitance were found to be nearly zero for Hg

Abstract The crystal structure of 1,3‐diphenyl‐propan‐2‐one oxime, C15H15NO, is described. The compound crystallises in the monoclinic space group C2/c. Centrosymmetrically related molecules are linked to form R22 (6) dimers. An update, since 2003, of a systematic analysis of the hydrogen bonding patterns in oxime structures with and without competitive O‐H...A type acceptors (an acceptor other than the nitrogen of the oxime) functional group is made, taking into account their moieties. The majority of these oximes form dimeric, R22 (6), structures but R33 (8) and R44 (12) were also found. C3 chains which were classically claimed as the usual oxime H‐bond pattern were rarely observed. They are mostly found in aldoxime structures.

Abstract Biomembrane models built at the interface between two immiscible electrolytes (ITIES) are useful systems to study phenomena of biological relevance by means of their electrochemical processes: The unique properties of ITIES allow one either to control or-measure the potential difference across the biomimetic membranes. Herein we focus on phospholipid monolayers adsorbed at liquid-liquid interfaces; and besides discussing recent developments on the subject, we deseribe electrochemical techniques that can be used to get insight on the interfacial processes and electrostatic properties of phospholipid membranes at the ITIES. In particular, we examine the electrochemical and physicochemical properties of (modified) phospholipid monolayers and their interaction with other biologically relevant compounds. The use of liquid-liquid electrochemistry as a powerful tool to characterize drug properties is outlined. Although this review is not a survey of all the work in the field, it provides a comprehensive referencing to current research.

Abstract A new cost-effective amperometric proton selective sensor utilizing a single microhole interface between two immiscible electrolyte solutions (ITIES) is developed. The sensing methodology is based on measuring currents associated with proton transfer across the interface assisted by a proton selective ionophore. The ellipse shaped micro-interface was first fabricated by simple mechanical punching with a sharp needle on a thin PVC film (12 mu m thick) commercially available as a food wrapping material. The microhole was then filled up with a gellified polyvinylchloride (PVC)-2-nitrophenyloctylether (NPOE) to create a single microhole liquid/liquid interface. Direct ion transfer reactions across the polarized interface serving as ion sensing platforms were studied using cyclic voltammetry. In order to enhance the selectivity of proton sensing, a proton selective ionophore, octadecyl isonicotinate (ETH1778), was incorporated into the organic gel layer and their electrochemical sensing characteristics were investigated using cyclic voltammetry and differential pulse stripping voltammetry. As an example, we employed the proton selective sensor for the determination of glucose concentrations. The detection scheme involves two steps: (i) protons are first generated by the oxidation of glucose with glucose oxidase in the aqueous phase; and (ii) the current associated with the proton transfer across the interface is then measured for correlating the concentration of glucose.

Abstract Pure 1,10-decanedithiol (C(10)-SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled monolayers (SAMs) prepared from ethanolic solution on Au(111) surfaces have been used in order to investigate the effect of the SAM organization and the availability of free -SH groups at the SAM/solution interface on the development of layer-by-layer architectures containing SAMs and gold nanoparticles (Au-NPs). The SAM modified electrodes have been electrochemically characterized by cyclic voltammetry in alkaline medium (reductive desorption) and in the presence of an electroactive species, Fe(CN)(6)(3-), in KNO(3) solution, enabling the evaluation of the stability and organization of the SAMs. Enhanced stability, organization, and hindrance to the electron transfer were found for the mixed SAMs with increasing thiol content, when compared with the pure dithiol SAM. The mixed SAM prepared from solution containing the thiol to dithiol proportion of (50:1) and pure C(10)-SH SAMs have been selected for further modification; the electrochemical quartz crystal microbalance (EQCM) enables the detection of different amount of citrate stabilized Au-NPs attachment to the selected SAMs modified electrodes due to distinct availability of free -SH groups at the SAM/solution interface and the electrochemical characterization of the layer-by-layer assemblies (based on pure C(10)-SH and mixed SAMs) showed that the electron transfer (ET) properties of the such architectures strongly depend on the nature of the base SAM and amount of immobilized Au-NPs. Atomic force microscopy (AFM) morphological characterization of the C(10)-SH SAM upon layer-by-layer modification was performed ex situ in air.