New strategies of photoprotection

Adequate photoprotection is essential to control UV-related disorders, including sunburn, photoaging and photocarcinogenisis. Sun avoidance, protection of skin with clothing, and sunscreens are presently the best way of photoprotection, assuming that they are used properly. However, new strategies, which are based on or make use of the endogenous protective response to UV light, may further improve currently used photoprotective means. The addition of repair enzymes and/or antioxidants has a positive effect on skin's recovery from UV-induced DNA-damage. Several botanical agents, mainly vitamins and polyphenols, have shown to influence signal transduction pathways leading to photoprotective effects. Also stimulation of endogenous UV-response pathways via irradiation with a low UV dose or via simulation of UV-induced DNA-damage results in photoprotective effects. Future research in this field and combination of different photoprotective strategies will hopefully lead to improved photoprotection.     

Determination of polycyclic aromatic hydrocarbons in olive oil by a completely automated headspace technique coupled to gas chromatography-mass spectrometry

A new and completely automated method for the determination of ten relevant polycyclic aromatic hydrocarbons (PAHs) in olive oil is proposed using an extraction by the headspace (HS) technique. Quantification and confirmation steps are carried out by gas chromatography-mass spectrometry (GC-MS) combining simultaneously selected-ion monitoring (SIM) and tandem mass spectrometry (MS/MS). This combination offers on one hand an increased sensitivity and on the other hand, selective and reliable qualitative information. Sample pretreatment or clean-up are not necessary because the olive oil sample is put directly into an HS vial, automatically processed by HS and introduced into the GC-MS instrument for analysis. Because of its high selectivity and sensitivity, a triple-quadrupole (QqQ) detector coupled with the gas chromatograph allows us to limit handling. Each sample is completely processed in approximately 63 min (45 min for HS isolation and 18 min for GC-MS determination), a reduced time compared with previously published methods. The chemical and instrumental variables were preliminarily optimized using uncontaminated olive oil samples spiked with 25 microg kg(-1) of each target compound. The final method was validated to ensure the quality of the results. The precision was satisfactory, with relative standard deviation (RSD) values in the range 3-9%. Recovery rates ranged from 96 to 99%. Limits of detection (LOD) were calculated as 0.02-0.06 microg kg(-1) and the limits of quantification (LOQ) were obtained as 0.07-0.26 microg kg(-1). It must be mentioned that the LOD and LOQ are much lower than the maximum levels established by the European Union (EU) in oils and fats intended for direct human consumption or for use as an ingredient in foods, which are set at 2 microg kg(-1). All the figures of merit are completely in accordance with the latest EU legislation. This fact makes it possible to consider the proposed method as a useful tool for the control of PAHs in olive oils.     

Chemisorption of isocyanate (NCO) on the Pd(1 0 0) surface at different coverages

The chemisorption of isocyanate (NCO) species on Pd(1 0 0) was studied within the density functional formalism (DFT) using a periodic slab model. The NCO was adsorbed on top, bridge and hollow sites of the metal surface at different coverages. At low coverages, the adsorption energies are in the range of ?2.5/?3.0 eV, indicating an important adsorbate–substrate interaction for the three sites studied. The lateral repulsive interaction between neighboring NCO species is almost negligible or weak at lower and intermediate coverages, and very strong at complete monolayer. At low coverages, both bridge and hollow sites are energetically preferred; yet the bridge site becomes the only favoured site at intermediate and complete coverages. Work function and dipole moment calculations can be interpreted by an important charge transfer from the metal surface to NCO. Interestingly, while on hollow site the charge taken by NCO is essentially the same over all the range of coverage, an increasing depolarization is observed on bridge and top sites as the coverage increases. Symmetric and asymmetric NCO stretching modes were also calculated and compared with recent infrared spectroscopy measurements.     

Constant-sign solutions of systems of higher order boundary value problems with integrable singularities

We consider some systems of boundary value problems where the nonlinearities may be singular in the independent variable and may also be singular in the dependent arguments. Using the Schauder fixed point theorem, we establish criteria such that the systems of boundary value problems have at least one constant-sign solution.     

Mycosporine-like Amino Acids in Freshwater Copepods: Potential Sources and Some Factors That Affect Their Bioaccumulation

Mycosporine-like amino acids (MAAs) are ubiquitous photoprotective compounds in aquatic environments. MAAs are synthesized by a wide variety of organisms (i.e. bacteria, fungi and algae) and their production is photoinducible by ultraviolet radiation (UVR) (280–400 nm) and/or photosynthetically active radiation (400–750 nm). Most animals however, are unable to synthesize MAAs and must acquire these compounds through their diet or from symbiotic organisms. In this paper, we investigate the possible sources of MAAs and factors (temperature and initial MAA concentration) that may affect their bioaccumulation in freshwater copepods. We found that MAA accumulation may occur even if the copepods are cultured on a MAA-free diet. In addition, we found that the bacteriostatic antibiotic, chloramphenicol, inhibits the bioaccumulation of MAAs. These two pieces of evidence suggest that the source of MAAs in these copepods may be prokaryotic organisms in close association with the animals. The two factors investigated in this study, temperature and initial MAA concentrations, were found to affect the rates at which MAAs are accumulated. Temperature had positive effects on both uptake and elimination rates. On the other hand, the rate of uptake decreased at the highest assayed initial MAA concentration, probably because the concentration of MAAs was already close to saturation.     

Synthesis and photophysical properties of novel amphiphilic ruthenium (II) complexes containing 4,4′‐dialkylaminomethyl‐2,2′‐bipyridyl ligands

The synthesis of a number of new 2,2′‐bipyridine ligands functionalized with bulky amino side groups is reported. Three homoleptic polypyridyl ruthenium (II) complexes, [Ru(L)₃]²⁺ 2(PF₆^?), where L is 4,4′‐dioctylaminomethyl‐2,2′‐bipyridine (Ru4a), 4,4′‐didodecylaminomethyl‐2,2′‐bipyridine (Ru4b) and 4,4′‐dioctadodecylaminomethyl‐2,2′‐bipyridine (Ru4c), have been synthesized. These compounds were characterized and their photophysical properties examined. The electronic spectra of three complexes show pyridyl π → π* transitions in the UV region and metal‐to‐ligand charge transfer bands in the visible region. Copyright © 2005 John Wiley & Sons, Ltd.     

Flow injection determination of diesters as ferric hydroxamate complexes

Diesters such as succinylcholine chloride (SCC) and dioctylsulfosuccinate (DOSS) can be converted to hydroxamic acids which are found to react with Fe³⁺ in methanol to form a purple chelate complex having an useful absorption band at 520 nm with a molar absorptivity of about 171 L/mole*cm, and a detection limit of 1.5 × 10^–4 M. To adapt this method for flow injection, a methanol-water solvent and acidification of the sample were required to reduce the large blank peak. The reproducibility of the flow injection method was a factor of two better than standard spectrophotometry but the detection limit of the former method was two times higher. This colorimetric method can permit analysis of pharmaceutical products containing either SCC or DOSS. Phosphatidylcholine (lecithin) can also be determined using this method.