Publications

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.

Abstract The present article involves a comparative study of the influence of oxygen or sulfur heteroatoms present in the central ring of polycyclic compounds, in order to clarify the correlation between the respective thermophysical or thermochemical properties and structural characteristics. Considering the importance of these types of compounds for their broad spectrum of application in diverse fields, from pharmacology to the development of new materials, the critical interpretation of such properties for their crucial role in the reactivity of these substances is of great interest. Knowledge on these thermodynamic data for key compounds is also relevant to the prediction and understanding of the properties and behavior of other parent compounds.

Abstract A comprehensive analysis of the thermochemical properties of levoglucosan, using static bomb combustion calorimetry, Knudsen effusion technique, and differential scanning calorimetry, is presented. The experimental results allow us to derive the enthalpy of formation, in the gaseous phase, and thereafter to do a comparison with the same parameter obtained computationally. The good agreement between the experimental,, and computational results gives confidence to our determinations, particularly when they are compared with others already reported in literature. After testing the computational methodology, the ionization energy, electron affinity, proton affinity, gas-phase basicity, gas-phase acidity, and bond dissociation enthalpies of levoglucosan were also obtained. The presence of intramolecular hydrogen bonds in the most stable conformation of levoglucosan was verified by applying Quantum Theory of Atoms in Molecules calculations. Furthermore, a joint differential scanning calorimetry and temperature dynamic Fourier transform infrared (FT-IR) spectroscopic study was used to study the crystalline phase of levoglucosan between 298.15 K and the melting

Abstract Adenosine receptors (ARs) are signaling molecules ubiquitously expressed in a wide variety of tissues in the human body. ARs mediate physiological functions by interacting with four subtypes of G-protein-coupled receptors, namely A(1), A(2A), A(2B) and A(3). The A(3) AR, probably the most studied subtype, is also ubiquitously expressed, with high levels in peripheral organs and low levels in the brain. This type of AR is involved in a variety of important pathophysiological processes, ranging from modulation of cerebral and cardiac ischemic damage to regulation of immunosuppression and inflammation. Consequently, the development of potent and selective A(3) AR ligands as promising therapeutic options for a variety of diseases has been a prime subject of medicinal chemistry research for more than two decades. Among the plethora of approaches applied quantitative structure activity relationships (QSAR) stands out for being largely employed due to their potential to increase the efficiency at initial stages of the drug discovery process. So, we provide a review of the main QSAR studies devoted to the design, discovery and development of agonist and antagonist A(3) adenosine receptor ligands. Common pitfalls of these QSAR applications and the current trends in this area are also analyzed.