Publications

Abstract The addition of surfactants to lipid bilayers is important for the modulation of lipid bilayer properties (e.g., in protein reconstitution and development of nonviral gene delivery vehicles) and to provide insight on the properties of natural biomembranes. In this work, the thermal behavior, organization, and nanomechanical stability of model cationic lipid-surfactant bilayers have been investigated. Two different cationic surfactants, hexadecyltrimethylammonium bromide (CTAB) and a novel derivative of the amino acid serine (Ser16TFAc), have been added (up to 50 mol %) to both liposomes and supported lipid bilayers (SLBs) composed by the zwitterionic phospholipid DPPC. The thermal phase behavior of mixed liposomes has been probed by differential scanning calorimetry (DSC), and the morphology and nanomechanical properties of mixed SLBs by atomic force microscopy based force spectroscopy (AFM-FS). Although DSC thermograms show different results for the two mixed liposomes, when both are deposited on mica substrates similar trends on the morphology and the mechanical response of the lipid-surfactant bilayers are observed. DSC thermograms indicate microdomain formation in both systems, but while CTAB decreases the degree of organization on the liposome bilayer, Ser16TFAc ultimately induces the opposite effect. Regarding the AFM-FS studies, they show that microphase segregation occurs for these systems and that the effect is dependent on the surfactant content. In both SLB systems, different microdomains characterized by their height and breakthrough force F-b are formed. The molecular organization and composition is critically discussed in the light of our experimental results and literature data on similar lipid-surfactant systems.

Abstract Betula pendula pollen, under laboratory conditions, was exposed to three atmospheric pollutants: carbon monoxide (CO), ozone (O-3) and sulphur dioxide (SO2). Two levels of each pollutant were used; the first level corresponds to a concentration on the atmospheric hour-limit value acceptable for human health protection in Europe, the second level to a higher, at least more than double of the first, concentration level. Experiments were done under artificial solar light with controlled temperature and relative humidity. Our results indicate that, in urban areas, concentrations of CO, O-3 and SO2 on the limits established for human protection, can affect pollen fertility. We verified a decrease in the viability and germination of the pollen, indicating damage to the pollen membrane system. Also, a general decreasing trend in the total protein content of the exposed samples when compared with the control samples was observed, which suggests alterations in the antigenic characteristics of pollen.

Abstract This work describes that the conventional analysis by Fourier transform infrared spectroscopy of a set of coals grouped by means of multivariate analysis (nonlinear mapping and hierarchical cluster analysis) obtained results that show this methodology is a good approach to summarize and classify coals by their structural relationships and the geochemical processes of their origin.

Abstract The vapour pressures of the condensed phases of the methyl esters of p-halobenzoic acids were measured over wide temperature ranges. The results enabled the determination of the standard molar entropies and enthalpies of sublimation and of vapourisation, at T = 298.15 K, of these four compounds. The temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the values derived from the vapour pressure measurements. Temperature and enthalpy of fusion of p-chlorobenzoic acid were also measured using DSC. The enthalpies of the intermolecular hydrogen bonds O-H center dot center dot center dot O formed in the crystals of the parent halobenzoic acids were calculated. From the available results for these compounds and from the ones determined in this work, several correlations involving thermodynamic properties of sublimation and fusion as well as the volume of the halogen substituent were derived.

Abstract Vapour pressures of condensed phases of p-monohalophenols were measured over the temperature ranges (265.6 to 342.8) K, (273.5 to 331.0) K, (285.3 to 370.5) K and (307.2 to 380.4) K, respectively for p-fluoro, p-chloro, p-bromo and p-iodophenol, using a static method based on diaphragm capacitance gauges. The results obtained for each compound, enabled the determination of the standard molar enthalpies, Gibbs energies and entropies of sublimation and of vaporisation, at T = 298.15 K as well as phase diagram representations of the (p,T) experimental results. The temperatures and molar enthalpies of fusion were determined using DSC and were compared with the values derived from the vapour pressure measurements. Correlations involving thermodynamic properties and also the volume of the halogen substituent of p-halophenols are presented and compared to the ones derived before for related methyl p-halobenzoates and p-halobenzoic acids. Vapour pressures, at T = 298.15 K, of the compounds included in the three families are well described by a single correlation based on the temperature of fusion and on the volume of the halogen atom.

Abstract The purpose of this study was to determine the ability and the safety of a series of alkylammonium C12-gemini surfactants to act as permeation enhancers for three model drugs, namely lidocaine HCl, caffeine, and ketoprofen. In vitro permeation studies across dermatomed porcine skin were performed over 24 h, after pretreating the skin for 1 h with an enhancer solution 0.16 M dissolved in propylene glycol. The highest enhancement ratio (enhancement ratio (ER) = 5.1) was obtained using G12-6-12, resulting in a cumulative amount of permeated lidocaine HCl of 156.5 mu g cm(-2). The studies with caffeine and ketoprofen revealed that the most effective gemini surfactant was the one with the shorter spacer, G12-2-12. The use of the latter resulted in an ER of 2.4 and 2.2 in the passive permeation of caffeine and ketoprofen, respectively. However, Azone was found to be the most effective permeation enhancer for ketoprofen, attaining a total of 138.4 mu g cm(-2) permeated, 2.7-fold over controls. This work demonstrates that gemini surfactants are effective in terms of increasing the permeation of drugs, especially in the case of hydrophilic ionized compounds, that do not easily cross the stratum corneum. Skin integrity evaluation studies did not indicate the existence of relevant changes in the skin structure after the use of the permeation enhancers, while the cytotoxicity studies allowed establishing a relative cytotoxicity profile including this class of compounds, single chain surfactants, and Azone. A dependence of the toxicity to HEK and to HDF cell lines on the spacer length of the various gemini molecules was found.

Abstract The title compound, C17H13NO4, crystallizes in two polymorphic forms, each with two molecules in the asymmetric unit and in the monoclinic space group P2(1)/c. All of the molecules have intramolecular hydrogen bonds involving the amide group. The amide N atoms act as donors to the carbonyl group of the pyrone and also to the methoxy group of the benzene ring. The carbonyl O atom of the amide group acts as an acceptor of the beta and beta' C atoms belonging to the aromatic rings. These intramolecular hydrogen bonds have a profound effect on the molecular conformation. In one polymorph, the molecules in the asymmetric unit are linked to form dimers by weak C-H center dot center dot center dot O interactions. In the other, the molecules in the asymmetric unit are linked by a single weak C-H center dot center dot center dot O hydrogen bond. Two of these units are linked to form centrosymmetric tetramers by a second weak C-H center dot center dot center dot O interaction. Further interactions of this type link the molecules into chains, so forming a three-dimensional network. These interactions in both polymorphs are supplemented by pi-pi interactions between the chromone rings and between the chromone and methoxyphenyl rings.

Abstract In the face of a growing human population and increased urbanization, the demand for pesticides will simply rise. Farmers must escalate yields on increasingly fewer farm acres. However, the risks of pesticides, whether real or perceived, may force changes in the way these chemicals are used. Scientists are working toward pest control plans that are environmentally sound, effective, and profitable. In this context the development of new pesticide formulations which may improve application effectiveness, safety, handling, and storage can be pointed out as a solution. As a contribution to the area, the microencapsulation of the herbicide oxadiargyl (OXA) in (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CD) was performed. The study was conducted in different aqueous media (ultrapure water and in different pH buffer solutions). In all cases an increment of the oxadiargyl solubility as a function of the HP-beta-CD concentration that has been related to the formation of an inclusion complex was verified. UV-Vis and NMR experiments allowed concluding that the stoichiometry of the OXA/HP-beta-CD complex formed is 1:1. The gathered results can be regarded as an important step for its removal from industrial effluents and/or to increase the stabilizing action, encapsulation, and adsorption in water treatment plants.