Publications

Abstract Dextran modified with deoxycholic acid (Dex-DCA) was synthesized by grafting DCA along the polymer backbone, with degrees of substitution (DS)-2% and 3%. The thermodynamics of the association processes of the mixed systems is followed by isothermal titration calorimetry for sodium deoxycholate/sodium dodecyl sulfate (NaDCA/NaDS), Dex-DCA with different surfactants-Dex-DCA/NaDS, Dex-DCA/NaDCA, and Dex-DCA/DTAB (dodecyltrimethylammonium bromide). Calorimetric measurements for the micellization processes of the pure surfactants in aqueous solution were also performed for comparison with the results obtained for the mixed systems. We have obtained and herein present the enthalpies of micelle formation and critical micelle concentrations for the referred pure surfactants, as well as the interaction and aggregation enthalpies for the mixed systems-surfactant/polymer. The dependence of the observed aggregation behavior on the surfactant and temperature is discussed in detail. Finally, we should stress that calorimetry allowed us to ascertain a very important fact in polymer/surfactant interaction. From the comparison between NaDCA/NaDS and Dex-DCA/NaDS calorimetric titration curves, we could clearly see that the interaction between Dex-DCA and NaDS is driven by the interaction between the bile acid moiety and the surfactant.

Abstract The interaction between liposomes (1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)) and a hydrophobically modified water-soluble polymer (HMP; a bile acid-modified dextran)has been investigated by isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC), combined with turbidity measurement and cryogenic scanning electron microscopy (cryo-SEM). The thermodynamic information on the association (enthalpy of interaction, enthalpy of transition of mixed vesicles to mixed micelle-like aggregates) was obtained from lit. Further, the phase behavior for the system could be derived from the lit measurements, and be confirmed by turbidity and cryo-SEM. The effect of cholic acid (CA) side groups on the ordered arrangement of DMPC bilayers Was studied by DSC, by following the changes they induce in the gel-to-liquid crystalline liposome phase transition. The DSC results were in excellent agreement. with the interpretation proposed for the ITC results. The morphology of the aggregates; as characterized by cryo-SEM, is in line with the proposed aggregate morphologies.

Abstract Silica based nanostructured composite materials doped with luminol and cobalt(II) ion were synthesized and characterized, resulting in a highly chemiluminescent material in the presence of hydrogen peroxide. A detection system with the CL light guided from the reaction tube to the photomultiplier tube using a one millimeter glass optical fiber was developed and assessed. A linear response was observed using a semi-logarithm calibration between 50-2000M hydrogen peroxide with 1M as the limit of detection.

Abstract Silver nanoparticles (Ag NPs, similar to 5 nm) were prepared, in presence of citrate, by borohydride reduction and characterized by UVvis and TEM images. Different experimental conditions were used in order to induce changes in the size distribution of the Ag NPs and to study the effect of those experimental conditions on the long range stability of the Ag NPs. The stability of the Ag NP solutions was studied for a period of 1 year. The effect of the storage conditions was studied. After preparation, each of the Ag NP solutions was divided and part of it was stored, in dark. at 4.0 +/- 2.0 degrees C and the other part at 23.0 +/- 2.0 degrees C. Both UV-vis and TEM techniques were used to follow the changes observed in the Ag NP solutions. The Ag NP solutions stored at room temperature show more dramatic changes in UV-vis spectra's evolution comparing with those stored at 4.0 +/- 2.0 degrees C. The use of lower BH(4)(-)/Ag(+) ratio promotes the formation of Ag NPs with various shapes and sizes during the storage time.

Abstract Firefly luciferase (Luc) is the most studied of the luciferase enzymes and the mechanism and kinetics of the reactions catalyzed by this enzyme have been relatively well characterized. Luc catalyzes the bioluminescent reaction involving firefly luciferin (D-LH(2)), adenosine triphosphate (ATP), magnesium ion and molecular oxygen with the formation of an electronically excited species (oxyluciferin), inorganic pyrophosphate (PPi), carbon dioxide and adenosine monophosphate (AMP). Luc also catalyzes other non-luminescent reactions, which can interfere with the light production mechanism. Following electronic relaxation, the excited oxyluciferin emits radiation in the visible region of the electromagnetic spectrum (550-570 nm). Among the various possible compounds, several classes of inhibitory substances interfere with the activity of this enzyme: here, we consider substrate-related compounds, intermediates or products of the Luc catalyzed reactions, in addition to anesthetics and, fatty acids. This review summarizes the main inhibitors of Luc and the corresponding inhibition kinetic parameters.

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.