Publications

Abstract Freeze-drying has widely been applied to improve the stabilization of colloidal drug carriers. In the present study, the effect of cryoprotectants on the physicochemical characteristics of silica nanoparticles (SiNP) during the freeze-drying process has been extensively investigated. SiNP were synthesized by sol–gel technology and freeze-dried in the presence of sorbitol, trehalose, and/or mannitol at different concentrations and ratios. Dynamic light scattering (DLS), atomic force microscopy (AFM), X-ray diffraction analysis (XRD), and differential scanning calorimetry (DSC) have been used for particle characterization after freeze-drying. Based on the obtained results, SiNP in the presence of mannitol showed a more crystalline behavior in comparison to nanoparticles with sorbitol or trehalose (confirmed by DSC and XRD). SiNP in the presence of trehalose showed a more crystalline structure than SiNP in the presence of sorbitol. However, trehalose was more efficient in preserving the particle size of nanoparticles during the freeze-drying process. The optimal concentration of trehalose for preserving silica nanoparticles was 10 % at a ratio of (1:1). During the freeze-drying process, trehalose is able to replace water molecules due to the strong interaction via hydrogen bounds between silanol groups present in SiNP surface and the sugar, forming a stable layer around the particle and thus preserving the particle physical properties.

Abstract The self-association equilibrium constants, K-ass, for the dimerization of some small oligothiophenes in acetone, acetonitrile and chloroform were measured by H-1 NMR spectroscopy. The gas phase interaction energies for some oligothiophene dimers were determined by computational quantum chemistry. The H-1 NMR results indicate that K-ass generally increases with the chain length (the number of thienyl rings, n) and solvent polarity; however, K-ass for thiophene (n = 1) was found to be higher than for the bithiophenes (n = 2). The linear oligothiophenes 2,2'-bithiophene and 2,2',5',2 ''-terthiophene were found to self-associate less than their corresponding nonlinear isomers 3,30-bithiophene and 3,2',5',3 ''-terthiophene in solution and in the gas phase. For a-quaterthiophene (n = 4) K-ass in solution was found to be smaller than expected. The non-linear dependence of the standard molar Gibbs energy of self-association, Delta(ass)G(m)(0), on the chain length in solution could be nicely reproduced and related to the conformational entropy change of dimerization. It was observed that the melting properties of oligothiophenes correlate well with their tendency to self-associate, with more self-association leading to increased liquid stability, and thus lower melting temperatures. These results highlight the relevance of self-association in isotropic systems for the correct molecular interpretation of phase equilibria.

Abstract An experimental and theoretical study on the phase and molecular stability of Mq(3) (M = Al, Ga, and In; q = 8-hydroxyquinoline) is presented. The results suggest that the energy difference between the meridional and facial isomers of Mq(3) shall be significantly lower than previously though and provide an explanation for the reported mer-fac solid-solid transition. The first accurate vapor pressure measurements for Alq(3), Gaq(3), and Inq(3) are presented, which are of great relevance for the manufacturing of thin films by vacuum deposition. Phase transition thermodynamics indicates higher cohesive energies of the mer-isomers and an entropic differentiation that can be associated with the different molecular symmetry of the mer- and fac-isomers.

Abstract Vapor pressures of 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide, ([C(1)C(1)im][NTf2]) and 1ethyl-3-propylimidazolium bis(trifluoromethylsulfonyl) imide, ([C(2)C(3)im][NTf2]) ionic liquids were measured as a function of temperature using a Knudsen effusion apparatus combined with a quartz crystal microbalance. Enthalpies and entropies of vaporization were derived from the fitting of vapor pressure and temperature results to the Clarke and Glew equation. [C(1)C(1)im][NTf2] presents a higher enthalpy and entropy of vaporization than the neighboring members of the series. The enthalpy of vaporization of [C(2)C(3)im][NTf2] lies in between the asymmetric and symmetric ionic liquid series, reflecting a decrease in the electrostatic interactions due to a decrease of the charge accessibility between the ionic pairs when the methyl group is replaced by an ethyl group. The obtained higher volatility of [C(2)C(3)im][NTf2] arises from its asymmetric character, leading to an higher entropic contribution that compensates the enthalpic penalty. The border conditions ([C(1)C(1)im][NTf2], [C(2)C(1)im][NTf2] and [C(2)C(2)im][NTf2]), topology ([C(2)C(3)im][NTf2]) and symmetry/asymmetry of the ILs effect were evaluated and rationalized based on a comparative analysis of the thermodynamic properties, enthalpies and entropies of vaporization.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpy of formation of 6-propyl-2-thiouracil was derived from its standard molar energy of combustion, in oxygen, to yield CO2 (g), N-2 (g) and H2SO4 center dot 115H(2)O (I), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapor pressures as function of temperature were measured by the Knudsen effusion technique and the standard molar enthalpy of sublimation, Delta H-g(cr)m(o). at T = 298.15 K, was derived by the Clausius-Clapeyron equation. These two thermodynamic parameters yielded the standard molar enthalpy of formation, in the gaseous phase, at T= 298.15 K: -(142.5 +/- 1.9) kJ mol(-1). This value was compared with estimates obtained from very accurate computational calculations using the G3 and G4 composite methods.

Abstract Biofilms are a problem to food industries, causing equipment damage, increased energy costs, and food spoilage, and they are a potential harbour of pathogenic microorganisms. Their extreme antimicrobial resistance means that novel control strategies are necessary. Plant secondary metabolites (phyto-chemicals) have demonstrated promising antimicrobial properties when applied against planktonic cells and biofilms. The aim of this study was to test the effectiveness of two phenolic acids: ferulic (FA) and sali-cylic (SA), alone and in combination (FSA) on the prevention and control of Bacillus cereus and Pseudomonas fluorescens biofilms. Additional tests were performed to ascertain the effects of FA and SA on bacterial motility, surface properties (physicochemical properties and surface charge), and quorum sensing inhibition (QSI). The effects of a concentration two times the minimum inhibitory concentration (500 mu g mL(-1)) were assessed on single- and dual-species biofilms. The results demonstrated that only swimming was affected by FA and SA and no clear relationship was obtained between the effects of phenolic acids on motility and biofilm prevention. The bacterial physicochemical surface properties and charge were affected by the phenolic acids. Salicylic acid demonstrated capacity for QSI. However, both bacteria were able to form single- and dual-species biofilms in the presence of the phenolic acids. The application of FA and SA (single and combined) to biofilms caused low to moderate inactivation and removal. However, dual-species biofilms formed in the presence of phenolic acids were highly susceptible to a second exposure to the chemicals. The continuous exposure of dual-species biofilms to the phenolic acids decreased their resilience and resistance to inactivation and removal. This study clarifies the role of FA and SA in the prevention and control of biofilms formed by two important food spoilage bacteria.

Abstract The purpose of the present study was to assess the antibacterial activity of phenyl isothiocyanate (PITC), a synthetic isothiocyanate, on biofilms of Escherichia coli and Staphylococcus aureus. The effects of PITC on bacterial free energy of adhesion and motility were also investigated. Biofilm formation in 96-well polystyrene microtiter plates was quantified by crystal violet staining and the metabolic activity of those biofilms was assessed with alamar blue. The viability and culturability of the biofilm bacteria after exposure to PITC were determined. The highest removal and metabolic activity reduction of biofilms with PITC was around 90% for both bacteria. Treatment with PITC enabled 4.5 and 4.0 log(10) reductions of the number of viable cells for E. coli and S. aureus, respectively; and no colony forming units (CFUs) were detected. PITC also affected the adhesion process and motility of bacteria, greatly preventing biofilm formation. In conclusion, PITC enabled both biofilm prevention and control, promoting high biofilm removal and inactivation activities, suggesting that this compound is a promising disinfectant.

Abstract The activity of two selected isothiocyanates (ITCs), allylisothiocyanate (AITC) and 2-phenylethylisothiocyanate (PEITC) was evaluated on the prevention and control of biofilms formed by Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes. In addition, the effect of ITCs was also tested on planktonic cell susceptibility, bacterial motility and adhesion. Biofilm prevention and control were tested using a microtiter plate assay and the effect of ITCs was assessed on biofilm mass and metabolic activity. The minimum bactericidal concentration for E. coli and P. aeruginosa was 1000 mu g mL(-1) (AITC) and >1000 mu g mL(-1) (PEITC), for S. aureus and L. monocytogenes was >1000 mu g mL(-1) (for both ITCs). AITC caused total inhibition of swimming (R aeruginosa) and swarming (E. coli) motilities. PEITC caused total inhibition of swimming (E. coli, P. aeruginosa and L. monocytogenes) and swarming (E. coil and P. aeruginosa) motilities. Colony spreading of S. aureus was completely inhibited with PEITC. Adhesion assessed in terms of free energy was less favorable when bacteria were exposed to AITC for E. coli and P. aeruginosa and PEITC for P. aeruginosa. Both ITCs had preventive action on biofilm formation and showed a higher potential to reduce the mass of biofilms formed by the Gram-negative bacteria. AITC and PEITC promoted reductions in biofilm activity higher than 60% for all the biofilms tested. The overall study emphasizes the potential of ITCs as emergent products to inhibit bacterial motility and prevent/control biofilms of important human pathogenic bacteria.

Abstract As the prostate cancer (PCa) progresses, sarcosine levels increase both in tumor cells and urine samples, suggesting that this metabolite measurements can help in the creation of non-invasive diagnostic methods for this disease. In this work, a biosensor device was developed for the quantification of sarcosine via electrochemical detection of H2O2 (at 0.6 V) generated from the catalyzed oxidation of sarcosine. The detection was carried out after the modification of carbon screen printed electrodes (SPEs) by immobilization of sarcosine oxidase (SOX) on the electrode surface. The strategies used herein included the activation of the carbon films by an electrochemical step and the formation of an NHS/EDAC layer to bond the enzyme to the electrode, the use of metallic or semiconductor nanoparticles layer previously or during the enzyme immobilization. In order to improve the sensor stability and selectivity a polymeric layer with extra enzyme content was further added. The proposed methodology for the detection of sarcosine allowed obtaining a limit of detection (LOD) of 16 nM, using a linear concentration range between 10 and 100 nM. The biosensor was successfully applied to the analysis of sarcosine in urine samples.

Abstract Dioctadecyldimethylammonium bromide (DODAB):Monoolein (MO) lipoplexes have mainly been studied within the range of high molar ratios of DODAB, with noticeable transfection efficiencies in the Human Embryonic Kidney (HEK, a.k.a. 293T) cell line. In this work, we intend to study the effect of high MO content on the structure and physicochemical properties of pDNA/DODAB:MO lipoplexes to achieve some correlation with their transfection efficiency. Static/Dynamic Light Scattering and Cryo-TEM imaging were used to characterize the size/morphology of DNA/DODAB:MO lipoplexes at different DODAB:MO contents (2:1, 1:1, 1:2) and charge ratios (CRs) (+/-). Nile Red fluorescence emission was performed to detect changes in microviscosity, hydration and polarity of DNA/DODAB:MO systems. Lipoplexes stability at physiological pH values and in the presence of anionic lipids was evaluated by Forster Resonance Energy Transfer (FRET). Physicochemical/structural data were complemented with transfection studies in HEK cells using the beta-galactosidase reporter gene activity assay. This work reports the coexistence of multilamellar and non-lamellar inverted phases in MO-richer lipoplexes (DODAB:MO 1:2 and 1:4), leading to transfection efficiencies comparable to those of multilamellar (DODAB-richer) lipoplexes, but at higher charge ratios [CR (+/-) = 6.0] and without dose-effect response. These results may be related to the structural changes of lipoplexes promoted by high MO content.