Changes in ultraviolet absorbance and hence in protective efficacy against lipid peroxidation of organic sunscreens after UVA irradiation

Owing to the spectral distribution of solar UV, the UVA component of sunlight is now believed to be the main cause of photoaging and photocarcinogenesis and is much more effective than UVB in inducing peroxidative damage. Consequently, most skin care cosmetic products now include UVA filters in their formulations along with UVB filters. These modern sunscreens should provide and maintain their initial absorbance, hence protection, throughout the entire period of exposure to sunlight. However, not all UVA and UVB filters are sufficiently photostable. In this study, we examine the correlation between the photochemical degradation of sunscreen agents under UVA irradiation, with particular reference to the UVA-absorber 4-tert-butyl-4'-methoxydibenzoylmethane, alone and in combination with other organic UV filters (2-ethylhexyl 4 methoxycinnamate and 2-ethylhexyl 2-cyano-3,3-diphenylacrylate) and their ability to prevent UVA-induced lipid peroxidation. Since antioxidants are also added to formulations to deactivate free radicals generated during UVA exposure, vitamin E and the synthetic antioxidant, bis(2,2,6,6-tetramethyl-1-oxyl-piperidine-4-yl)sebacate, a nitroxide derivative, were also included in this study. By using simple in vitro tests, the results show that a decrease in spectral absorbance of the UV filters correlates in most cases with increased UVA-induced lipid peroxidation; this depends on the specific UV absorber analysed and also on whether they are alone or in combination. Furthermore, the combined presence or absence of antioxidants has a profound effect on this oxidative event. In particular, the nitroxide appears to be a more efficient photo-antioxidant than vitamin E. Similar experiments were also performed under natural sunlight and the results obtained did not differ substantially from those performed under UVA. The results presented and discussed in this work may help in understanding the effects of UVA/UVB absorbers and antioxidants upon the level of UV-induced ROS generated under UVA exposure and in natural sunlight which could be relevant for improving the photoprotection and efficacy of skin care cosmetic formulations.     

Excited-state properties and emission spectra of nonplanar heterocyclic helicenes

We discuss the electron-vibration coupling in mono-aza-[5]helicenes on the basis of a Franck-Condon analysis and density functional theory (DFT) calculations of the fluorescence and phosphorescence spectra measured in ethanol. The geometries of the initial states were obtained from time-dependent DFT (S(1)) and unrestricted DFT (T(1)) excited-state optimizations. In general, the position of the nitrogen atom has only a minor impact on the vibronic fine-structure in both absorption and emission. The shapes of the emission spectra from the lowest singlet and triplet states are found to be determined by contributions from multiple normal modes. The results of the calculations demonstrate how the interplay among these normal modes results in qualitatively and quantitatively different spectra for fluorescence and phosphorescence.     

Co2+ binding cysteine and selenocysteine: a DFT study

In this paper we report structural and energetic data for cysteine and selenocysteine in the gas phase and the effect of Co(2+) complexation on their properties. Different conformers are analyzed at the DFT/B3LYP level of both bound and unbound species. Geometries, vibrational frequencies, and natural population analysis are reported and used to understand the activity of these species. In particular, we have focused our attention on the role of sulfur and selenium in the metal binding process and on the resulting deprotonation of the thiol and seleniol functions. From the present calculations we are able to explain, both from electronic structure and thermochemical point of views, a metal-induced thiol deprotonation as observed in gas-phase experiments. A similar process is expected in the case of selenocysteine. In fact, cobalt was found to have a preferential affinity with respect to thiolate and selenolate functions. This can be related to the observation that only S and Se are able-in thiolate and selenolate states-to make a partial charge transfer to the cobalt thus forming very stable complexes. Globally, very similar results are found when substituting S with Se, and a very small difference in cobalt binding affinity is found, thus justifying the use of this substitution in X-ray absorption experiments done on biomolecules containing cysteine metal binding pockets.     

The "non-nucleophilic" anion [Tf2N]- competes with the nucleophilic Br-: an unexpected trapping in the dediazoniation reaction in ionic liquids

Imidazolium ionic liquids containing [Tf2N]- anion are not as innocent as they are often considered; [Tf2N]- is more reactive than Br- in heterolytic dediazoniation reactions.     

Synthesis, characterization and olefin/CO exchange reactions of pyrazolylborato complexes of copper(I)

New bis(pyrazolyl)borato olefin complexes of copper(I) of general formula Cu[BH2(3,5-(CF3)2Pz)2](olefin) have been prepared (olefins: coe = cyclooctene, van = 4-vinylanisole, clsty = 4-chlorostyrene, tevs = triethylvinylsilane, fn = fumaronitrile). The structures of Cu[BH2(3,5-(CF3)2Pz)2](L), L = coe, van, tevs, fn, have been determined by X-ray diffraction methods. Considering the two N atoms of the bis(pyrazolyl)borate ligand and the midpoint of the C-C double bond of the coordinated olefin, the compounds with L = coe, van and tevs contain a copper atom in a trigonal planar coordination. A coordination polymer with N-coordinated fumaronitrile and tetrahedral coordination of copper atoms is obtained in the case of L = fn. The carbonylation reactions of Cu[BH(2)(3,5-(CF3)2Pz)2](olefin) (olefin = coe, clsty, van, tevs), Cu[BH2(3,5-(CF3)2Pz)2](olefin) + CO<==>Cu[BH2(3,5-(CF3)2Pz)2](CO) + olefin, have been studied gas volumetrically and the thermodynamical parameters of the equilibria for the displacement of the coordinated olefin by carbon monoxide have been determined. These data for copper(I) are compared with those reported in the literature.     

Planar bilayer studies reveal multiple conductance states for synthetic anion transporters

Compounds of the general type R(1)(2)NCOCH(2)OCH(2)CO-(Gly)(3)-Pro-(Gly)(3)-OCH(2)Ph insert in phospholipid bilayers and conduct ions. Different levels of activity were observed when R(1) was either decyl or octadecyl, as judged either by Cl(-) release, detected by ion selective electrodes, or carboxyfluorescein dequenching, detected by fluorescence. Either method reports average behavior for all ionophores over all liposomes. These methods also show that at least two ionophores are involved in the formation of each pore. Planar bilayer experiments reported here confirm pore formation by these compounds but identify more than one conductance state for each. The pseudo-dimer, in which two molecules of the type shown above are covalently linked, shows only two conductance states, of which one is dominant. This state has been characterized by use of a current-voltage plot.     

Electronic and structural shell closure in AgCu and AuCu nanoclusters

The structures of AgCu clusters containing 40 atoms are investigated. The most promising structural families (fcc clusters, capped decahedra, and two types of capped polyicosahedra) are singled out by means of global optimization techniques within an atom-atom potential model. Then, representative clusters of each family are relaxed by means of density-functional methods. It is shown that, for a large majority of compositions, a complex interplay of geometric and electronic shell-closure effects stabilizes a specific polyicosahedral family, whose clusters are much lower in energy and present large HOMO-LUMO gaps. Within this family, geometric and quantum effects concur to favor magic structures associated with core-shell chemical ordering and high symmetry, so that these clusters are very promising from the point of view of their optical properties. Our results also suggest a natural growth pathway of AgCu clusters through high-stability polyicosahedral structures. Results for AuCu clusters of the same size are reported for comparison, showing that the interplay of the different effects is highly material specific.     

On the interplay between CH...O and OH...O interactions in determining crystal packing and molecular conformation: an experimental and theoretical charge density study of the fungal secondary metabolite austdiol (C12H12O5)

The total experimental electron density rho(r), its Laplacian inverted delta(2)rho(r), the molecular dipole moment, the electrostatic potential phi(r), and the intermolecular interaction energies have been obtained from an extensive set of single-crystal X-ray diffracted intensities, collected at T = 70(1) K, for the fungal metabolite austdiol (1). The experimental results have been compared with theoretical densities from DFT calculations on the isolated molecule and with fully periodic calculations. The crystal structure of (1) consists of zigzag ribbons extended along one cell axis and formed by molecules connected by both OH...O and CH...O interactions, while in a perpendicular direction, adjacent molecules are linked by short CH...O intermolecular contacts. An extensive, quantitative study of all the intra- and intermolecular H...O interactions, based not only on geometrical criteria, but also on the topological analysis of rho(r), as well as on the evaluation of the pertinent energetics, allowed us (i) to assess the mutual role of OH...O and CH...O interactions in determining molecular conformation and crystal packing; (ii) to identify those CH...O contacts which are true hydrogen bonds (HBs); (iii) to determine the relative hydrogen bond strengths. An experimental, quantitative evidence is given that CH...O HBs are very similar to the conventional OH...O HBs, albeit generally weaker. The comparison between experimental and theoretical electric dipole moments indicates that a noticeable charge rearrangement occurs upon crystallization and shows the effects of the mutual cooperation of HBs in the crystal. The total intermolecular interaction energies and the electrostatic energy contribution obtained through different theoretical methods are reported and compared with the experimental results. It is found that the new approach proposed by Spackman, based on the use of the promolecular charge density to approximate the penetration contribution to intermolecular electrostatic energies, predicts the correct relative electrostatic interaction energies in most of the cases.     

Separation of molecular constituents from a humic acid by solid-phase extraction following a transesterification reaction

A selective removal of humic constituents involved in ester groups was conducted by a boron trifluoride-methanol transesterification reaction after removal of structurally unbound lipids. An analytical separation of subfractions containing specific classes of compound liberated from the humic matrix simplifies their identification by gas chromatography-mass spectrometry. We compared the traditional liquid-liquid separation into phenolic and aliphatic fractions with the modern and versatile fractionation technique using solid-phase extraction (SPE) on aminopropyl-bonded phases. Our results showed that both methods ensured separation of the same compounds, such as di- and tri-hydroxyalkanoic acids, α-, β- and ω-hydroxy fatty acids, alkanoic acids, α,ω-alkanedioic acids, n-alkanols, phenolic acids and sterols. Moreover, the SPE method not only provided a larger recovery of compounds, but involved smaller sample and solvent requirements, and larger ease and rapidity of sample handling than the traditional liquid-liquid separation. The SPE method should be thus recommended in structural studies of natural organic matter.     

Order parameters of alpha,omega-diphenylpolyenes in a nematic liquid crystal from an integrated computational and 13C NMR spectroscopic approach

The orientational order parameters and conformational behavior of five relatively large rodlike molecules, biphenyl, trans-stilbene, 1,3-diphenyl-butadiene, 1,3,5-diphenyl-hexatriene, and 1,3,5,7-diphenyl-octatetraene, dissolved in the thermotropic liquid crystal ZLI-1167, have been studied using an integrated approach combining (13)C NMR measurements and quantum mechanical computations of carbon chemical shift tensors. Besides biphenyl, the phenyl moiety of all structures has been found to have a high rotational mobility in the temperature range of the present experiments. The rank-two order parameter in the nematic phase is found to increase steadily from the shortest to the longest term of the series at any temperature within the nematic range. The molecular biaxiality order parameter is found to be small and essentially constant with temperature, giving further support to the common assumption of effective uniaxiality for these probes.