Publications

Abstract Ion specific effects on the mutual solubilities between hydrophobic ionic liquids (ELs) and water are complex and not fully understood. The aim of this work is to obtain further evidence about the molecular mechanism behind this phenomenon by evaluating the effect of a large series of inorganic and organic salts on the mutual solubilities of water and the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(4)mim][Tf(2)N]. The magnitudes of the salting-in and salting-out effects were assessed by changing either the cation or the anion, in a series of salts, as well as the salt concentration. It was observed that the influence of the ions on the solubility followed the Hofmeister series. Both salting-in and salting-out effects were observed and they showed to be dependent on both the nature of the salt and its concentration, while the pH had only a marginal effect on the studied solubilities. On the basis of the solubility changes of the ionic liquid in water in the presence of salts and on NMR spectroscopic data, it will be shown that salting-out inducing ions (high charge density) and salting-in inducing ions (low charge density) act through different mechanisms. While the former act mainly through an entropic effect resulting from the formation of water-ion hydration complexes which cause the dehydration of the solute and the increase of the surface tension of the cavity, the salting-in results from a direct ion binding of the low charge density ions to the hydrophobic moieties of the solute.

Abstract Self-assembled monolayers (SAMs), prepared by the immersion method, from ethanolic solutions containing alpha,omega-alkanedithiol, n-alkanethiol or mixed thiol/dithiol solutions, with 6, 9 and 10 carbon atoms in the alkyl chain, have been investigated. The amount of adsorbate and the SAM stability in alkaline medium is evaluated by reductive desorption of the prepared monolayers by cyclic voltammetry. An upright orientation of the dithiol self-assembled molecules and disulfide bonding at the SAM/solution interface are suggested by the higher reductive desorption charge of the dithiol monolayers (relative to thiol SAMs) for n = 6 and 9. The results show that an improvement on the stability of these dithiol SAMs is obtained by the presence of monothiols, resulting in mixed monolayers. Mixed SAMs prepared from longer alkane chain thiols, n = 10, allow to overcome the increased possibility of loop formation and therefore lower surface coverage is obtained for the 1,10-decanedithiol monolayers. Morphological characterisation of the modified electrodes is performed by scanning tunnelling microscopy (STM) ex situ, in air. Typical one atom deep thiol induced depressions are observed in the STM images of the dithiol and mixed SAMs.

Abstract In the title compound, C(16)H(16)N(4)O(4), the dihedral angle between the aromatic rings is 79.04 (8)degrees and an intramolecular N-H center dot center dot center dot O hydrogen bond occurs. In the crystal, weak C-H center dot center dot O and C-H center dot center dot center dot pi interactions link the molecules, forming sheets.

Abstract In the title molecule, C(17)H(12)O(2), the dihedral angle between the mean plane of the benzene ring and that of the naphthalene ring system is 49.09 (6)degrees. In the crystal structure, molecules are linked to form centrosymmetric dimers via intermolecular O-H center dot center dot center dot O hydrogen bonds. The hydroxy H atom is disordered over two sites with refined occupancies of 0.62 (3) and 0.38 (3).

Abstract The innate immunity factor lactoferrin harbours two antimicrobial moieties, lactoferricin and lactoferrampin, situated in close proximity in the NI domain of the molecule. Most likely they cooperate in many of the beneficial activities of lactoferrin. To investigate whether chimerization of both peptides forms a functional unit we designed a chimerical structure containing lactoferricin amino acids 17-30 and lactoferrampin amino acids 265-284. The bactericidal activity of this LFchimera was found to be drastically stronger than that of the constituent peptides, as was demonstrated by the need for lower dose, shorter incubation time and less ionic strength dependency. Likewise, strongly enhanced interaction with negatively charged model membranes was found for the LFchimera relative to the constituent peptides. Thus, chimerization of the two antimicrobial peptides resembling their structural orientation in the native molecule strikingly improves their biological activity.

Abstract A thermochemical and thermophysical study has been carried out for crystalline barbital [5,5'-diethyl-barbituric acid]. The thermochemical study was made by static bomb combustion calorimetry, from which the standard (p degrees = 0.1 MPa) molar enthalpy of formation of the crystalline barbital, at T = 298.15 K, was derived as -(753.0 +/- 1.8) kJ . mol(-1). The thermophysical study was made by differential scanning calorimetry over the temperature interval (265 to 470) K. A solid-solid phase transition was found at T = 413.3 K. The vapour pressures of the crystalline barbital were measured at several temperatures between T = (355 and 377) K, by the Knudsen mass-loss effusion technique, from which the standard molar enthalpy of sublimation, at T = 298.15 K was derived as (117.3 +/- 0.6) kJ . mol(-1). The combination of the experimental results yielded the standard molar enthalpy of formation of barbital in the gaseous phase, at T = 298.15 K, as -(635.8 +/- 1.9) kJ . mol(-1). This value is compared and discussed with our theoretical calculations by several methods (Gaussian-n theories G2 and G3, complete basis set CBS-QB3, density functional B3P86 and B3LYP) by means of atomization and isodesmic reaction schemes.

Abstract The present work reports an experimental thermochemical study supported by state of the art calculations of two heterocyclic compounds containing oxygen in the ring: xanthone and tetrahydro-gamma-pyrone. The standard (pA(0)A = 0.1 MPa) molar enthalpies of formation in the condensed phase, at T = 298.15 K, were derived from the measurements of the standard molar energies of combustion in oxygen atmosphere, using a static bomb calorimeter. The standard molar enthalpies of sublimation or vaporization, at T = 298.15 K, of the title compounds were obtained from Calvet microcalorimetry measurements. These values were used to derive the standard enthalpies of formation of the compounds in the gas-phase at the same temperature, which were compared with estimated data from G3(MP2)//B3LYP computations.

Abstract The molecular stability of thioxanthene, a key species from which very important compounds with industrial relevance are derived, has been studied by a combination of several experimental techniques and computational approaches, The standard (p(o) = 0.1 MPa) molar enthalpy of formation of crystalline thioxanthene (117.4 +/- 4.1 kJ . mol(-1)) was determined from the experimental standard molar energy of combustion, in oxygen, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The enthalpy of sublimation was determined by a direct method, using the vacuum drop microcalorimetric technique, and also by an indirect method, using a static apparatus, where the vapor pressures at different temperatures were measured. The latter technique was used for both crystalline and undercooled liquid samples, and the phase diagram of thioxanthene near the triple point was obtained (triple point coordinates T = 402.71 K and p = 144.7 Pa). From the two methods, a mean value for the standard (p(o) = 0.1 MPa) molar enthalpy of sublimation, at T = 298.15 K (101.3 +/- 0.8 kJ . mol(-1)), was derived. From the latter value and from the enthalpy of formation of the solid, the standard (p(o) = 0.1 MPa) enthalpy of formation of gaseous thioxanthene was calculated as 218.7 +/- 4.2 kJ . mol(-1). Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several homodesmotic reactions in order to derive the standard molar enthalpy of formation of thioxanthene. The ab initio results are in excellent agreement with the experimental data.

Abstract The structure and temperature behaviour of the DNA+dipalmitoylphosphatidylcholine (DPPC) bilayer as a function of ZnCl(2) concentration were examined using differential scanning calorimetry (DSC), small-angle neutron scattering (SANS) and small-angle X-ray diffraction (SAXD). Experiments revealed the coexistence of two lamellar phases in the mixture: the L(PC) phase, formed due to Zn(2+) binding to the DPPC bilayers, and the condensed lamellar phase L(DNA+PC) with DNA strands packed between the DPPC bilayers. With increasing concentration of zinc, the temperature of the gel - liquid-crystal phase transition of DPPC increases in both phases, and the volume fraction of LDNA+PC phase decreases. In the gel state (at 20 degrees C), the repeat distance of LDNA+PC phase is constant, d(DNA+PC) similar to 8.3 nm, up to 20 mmol/l of ZnCl(2), and increases for higher concentrations of the salt. The periodicity of the L(PC) lamellar phase decreases substantially with the increasing concentration of the salt in the mixture. In the liquid-crystalline state, concentrations above 20 mmol/l ZnCl(2) promote the dissolution of the LDNA+PC phase into DPPC + Zn(2+) unilamellar vesicles and DNA is neutralized by Zn(2+) ions. The screening of Zn(2+) charge and the formation of a diffuse double layer due to increasing ionic strength of solution are responsible for the observed changes.

Abstract One of the possible approaches for the development of novel solid-phase microextraction (SPME)fibers is the physical deposition of porous materials Oil to a support using high-temperature epoxy glue. However, a major drawback arises from decomposition of epoxy glue at temperatures below 300 degrees C and instability in some organic solvents. This limitation motivated us to explore the possibility of replacing the epoxy glue with a sol-gel film, thermally more stable and resistant to organic solvents. We found that functionalised silica particles could be successfully attached to a robust Ni-Ti wire by using a UV-curable sol-gel film. The particles were found to be more important than the sol-gel layer during the microextraction process, as shown by competitive extraction trials and by the different extraction profiles observed with differently functionalised particles. If a quality control microscopic-check aiming at the rejection of fibers exhibiting unacceptably low particle load was conducted, acceptable (6-14%) reproducibility of preparation of C(18)-silica fibers was observed, and a strong indication of the durability of the fibers was also obtained. A cyclohexyldiol-silica fiber was used, as a simple example of applicability, for the successful determination of benzaldehyde. acetophenone and dimethyl phenol at trace level in spiked tap water. Recoveries: 95-109%; limits of detection: 2-7 mu g/L; no competition effects within the studied range (<= 125 mu g/L).