Publications

Abstract An electrochemical sensor has been developed for the determination of the herbicide bentazone, based on a GC electrode modified by a combination of multiwalled carbon nanotubes (MWCNT) with β-cyclodextrin (β-CD) incorporated in a polyaniline film. The results indicate that the β-CD/MWCNT modified GC electrode exhibits efficient electrocatalytic oxidation of bentazone with high sensitivity and stability. A cyclic voltammetric method to determine bentazone in phosphate buffer solution at pH6.0, was developed, without any previous extraction, clean-up, or derivatization steps, in the range of 10-80μmolL-1, with a detection limit of 1.6μmolL-1 in water. The results were compared with those obtained by an established HPLC technique. No statistically significant differences being found between both methods. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract In the present work we bridge neutron scattering and calorimetry in the study of a low-hydration sample of a 15-residue hybrid peptide from cecropin and mellitin CA(1-7)M(2-9) of proven antimicrobial activity. Quasielastic and low-frequency inelastic neutron spectra were measured at defined hydration levels a nominally 'dry' sample (specific residual hydration h = 0.060 g/g), a H2O-hydrated (h = 0.49) and a D2O-hydrated one (h = 0.51). Averaged mean square proton mobilities were derived over a large temperature range (50-300 K) and the vibrational density of states (VDOS) were evaluated for the hydrated samples. The heat capacity of the H2O-hydrated CA(1-7) M(2-9) peptide was measured by adiabatic calorimetry in the temperature range 5-300 K, for different hydration levels. The glass transition and water crystallization temperatures were derived in each case. The existence of different types of water was inferred and their amounts calculated. The heat capacities as obtained from direct calorimetric measurements were compared to the values derived from the neutron spectroscopy by way of integrating appropriately normalized VDOS functions. While there is remarkable agreement with respect to both temperature dependence and glass transition temperatures, the results also show that the VDOS derived part represents only a fraction of the total heat capacity obtained from calorimetry. Finally our results indicate that both hydration water and the peptide are involved in the experimentally observed transitions.

Abstract COSMO-RS, the Conductor-like Screening Model for Real Solvents, has been used to predict a set of basic partition coefficients of 22 (alkylated) naphthalenes. To validate the approach, methyl-, dimethyl-, and ethylnaphthalenes have been chosen, according to the availability of experimental data. Then, predictions have been extended to diisopropylnaphthalenes. Given the model's expected uncertainty intervals, COSMO-RS predictions of aqueous solubilities, (subcooled) vapor pressures, Henry's law constants, as well as octanol-water partition coefficients, are in agreement with available literature data. Simultaneous overestimation of aqueous solubilities and vapor pressures of comparable magnitude leads to partial error cancellation in the Henry's law constants. Based on physico-chemical property data obtained with COSMO-RS, the Mackay Level III fugacity model, a steady-state, non equilibrium, and regional-scale model, has been applied to exemplary evaluate the tendency of 2,6-diisopropylnaphthalene to migrate between media by modelling emissions to each individual medium and calculating the amount present at steady state.

Abstract A thermodynamic study of important biogenic compounds, (-)-alpha-pinene, (-)-beta-pinene, (-)-cis-verbenol, and (-)-verbenone, is presented in this work. The vapor pressure measurements were performed using the static method over the environmentally important temperature range from 238 to 313 K. The sublimation and vaporization enthalpies were derived from these measurements as well as directly determined by a Calvet high temperature microcalorimeter. Heat capacities of condensed phases were measured by Calvet and drop calorimetry in the temperature interval from 273 to 355 K. The thermodynamic properties of the ideal-gas state were calculated by combining statistical thermodynamics and density functional theory (DFT) calculations. The trends in thermodynamic properties within the group of compounds possessing similar molecular structures are discussed.

Abstract A structural study of three synthesized stereoisomeric oximes, (-)-8-phenylmenthyl glyoxylate oxime (8-PMGO), (+)-8-phenylneomenthyl glyoxylate oxime (8-PnMGO), and (-)-8-phenylisoneomenthyl glyoxylate oxime (8-PinMGO), was performed by means of variable temperature H-1 NMR spectroscopy, X-ray crystallography, and ab initio calculations. It was found that in 8-PMGO a conformation where the phenyl and oxime moieties are stacked is significantly favored, whereas in the other stereoisomers this preference was not so evident. The conformational differences found between the isomers were used to rationalize the outcome of the reaction (simultaneous 1,3-cycloaddition and aza-Diels Alder reaction) between the referred oximes and cyclopentadiene, in which the stereoselectivity was evaluated and found to be nicely reproduced by a simple conformational analysis. The global results indicate that the stereoselectivity of the studied oximes, a bit higher for 8-PMGO, originates from their particular conformational distribution, in which the phenyl. oxime aromatic interaction plays a decisive role.

Abstract The energetic study of benzoxazole, 5-chloro-2-methylbenzoxazole, and 2-chlorobenzoxazole, in condensed and gaseous states, has been developed using experimental techniques and computational approaches. The values of the standard (p degrees = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, of crystalline benzoxazole (36.0 +/- 2.0) kJ . mol(-1) and 5-chloro-2-methylbenzoxazole (145.6 +/- 2.2) kJ . mol(-1) and liquid 2-chlorobenzoxazole (52.5 +/- 3.0) kJ . mol(-1) were determined from the corresponding experimental standard molar energy of combustion in oxygen, -(3432.1 +/- 1.7) kJ . mol(-1), -(3883.0 2.0) kJ . mol(-1), and -(3298.0 +/- 2.8) kJ . mol(-1), respectively, measured by static or rotating-bomb combustion calorimetry. At T = 298.15 K, the standard (p degrees = 0.1 MPa) molar enthalpy of sublimation of benzoxazole and 5-chloro-2-methylbenzoxazole and of vaporization of 2-chlorobenzoxazole, (69.2 +/- 0.8) kJ . mol(-1), (82.4 +/- 2.2) kJ . mol(-1), and (56.3 +/- 1.6) kJ . mol(-1) respectively, were determined by a direct method, using the vacuum drop microcalorimetric technique. From the latter values and from the enthalpies of formation of the condensed compounds, the standard (p degrees = 0.1 MPa) enthalpies of formation of the gaseous compounds have been calculated. Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several working reactions in order to derive the standard molar enthalpy of formation of the three compounds. There exists a good agreement between the experimental and the computational data.

Abstract New strategies to reduce the environmental and economic costs of pesticides use are currently under study. Microencapsulation has been used as a versatile tool for the production of controlled release agricultural formulations. In this study, the photochemical degradation of the herbicides MCPA and mecoprop has been investigated in different aqueous media such as ultrapure and river water under simulated solar irradiation. To explore the possibility of introducing cyclodextrins in the herbicide formulations, the photodegradation study of the inclusion complexes of MCPA and mecoprop with (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CD) was also performed. The half-lives of MCPA and mecoprop inclusion complexes were increased approximately by a factor of three related to the free molecules. Additionally, it has been shown that the photodegradation of MCPA and mecoprop is influenced by their structural features. The additional methyl group existing in mecoprop molecular structure has a positive influence on the stabilization of the radical intermediate formed in the first stage of photodegradation of both herbicides. The results found indicated that MCPA and mecoprop form inclusion complexes with HP-beta-CD showing higher photostability compared to free herbicides indicating that HP-beta-CD may serve as ingredient in these herbicide formulations.

Abstract The standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of sarcosine, -(388.0 +/- 1.0) kJ . mol(-1), and sarcosine anhydride, -(334.5 +/- 1.6) kJ . mol(-1), were calculated by combining, for each compound, the standard molar enthalpy of formation, in the crystalline phase, and the standard molar enthalpy of sublimation, derived from measurements of the standard massic energies of combustion by static bomb combustion calorimetry, and from measurements of vapour pressures by the Knudsen mass-loss effusion method, respectively. The standard (p(o) = 0.1 MPa) molar enthalpies, entropies and Gibbs functions of sublimation, at T = 298.15 K, were also calculated. A theoretical study at the G3 and G4 levels has been carried out, and the calculated enthalpies of formation have been compared with the experimental ones.

Abstract Numerous studies in humans, animal models and cell lines have suggested the potential benefits from the consumption of green tea polyphenols, including prevention of cancer and heart diseases. However these potential effects have been strongly limited by green tea catechins low bioavailability, which hinders the development of therapeutic applications. In this review formulations that are being proposed for delivery of green tea catechins are discussed. New delivery systems are presented as valid alternatives to overcome the limitations such as green tea catechins poor stability or intestinal absorption.

Abstract In recent years, much attention has been given to dietary antioxidants, especially polyphenols. Several peptides derived from protein molecules have also been found to show antioxidant capacity along with other biological properties and thus there is an increasing interest in these compounds as health promoters. This review summarizes and discusses the main sources of antioxidative peptides with focus on food-derived peptides (animal, plant and marine sources), methods of preparation, antioxidant capacity evaluation as well as their proposed mechanisms of action. A discussion of the potential health effects and comments on the different applications for these antioxidants and their potential research interest are also subject of this review.