Isomerization of urocanic acid after ultraviolet radiation is influenced by skin pigmentation

Exposure to ultraviolet (UV) radiation may induce erythema, DNA damage and suppression of immune responses. Melanin pigmentation offers protection against the first two of these effects, but immunosuppression seems to occur irrespective of the subject's pigmentation. Cis-urocanic acid (cis-UCA), produced by isomerization of trans-UCA in the stratum corneum on UV exposure, initiates some of the immunomodulatory effects of UV radiation. In the present study the relationship between skin pigmentation and UCA isomerization has been examined in 28 healthy individuals of skin types I-IV. Pigmentation is measured in five areas of not recently exposed back skin before irradiation with 0, 0.45, 0.9, 1.8 and 3.6 standard erythema dose (SED) of filtered broadband UV-B (1 SED = 10 mJ cm-2 at 298 nm). The concentration of UCA isomers is measured immediately after the irradiation. With 3.6 SED, the relative production of cis-UCA is close to the maximum obtainable, irrespective of skin type. A significant negative correlation is found between pigmentation and relative production of cis-UCA at 0.45 and 1.8 SED, and between pigmentation and absolute production of cis-UCA at 0.45 SED. At doses of 0.45 and 0.9 SED the relative and absolute production of cis-UCA are higher in the group with skin types I and II when compared with the group with skin types III and IV. The higher isomerization in the lightly pigmented subjects than in the more pigmented ones may indicate that people with fair skin are at a relatively higher risk of immunosuppression when exposed to low doses of UV radiation.     

Experimental Evidence for the Existence of Neutral P(6): A New Allotrope of Phosphorus

High-energy collisions of Cp*P(6)(+) cations yield neutral P(6) molecules (see reaction), thus providing the first experimental evidence for the existence of this new allotrope of phosphorus.     

Determination of (13)C natural abundance of amino acid enantiomers in soil: methodological considerations and first results

The application of a combined gas chromatography-combustion/isotope ratio mass spectrometry (GC-C/IRMS) method for stable carbon isotope analysis of amino acid enantiomers in soil samples is presented. Triplicate delta(13)C analyses of pentafluoropropionyl (PFP) isopropyl ester derivatives of 27 amino acid enantiomers revealed that discrimination of (13)C during derivatization is different for different amino acid enantiomers and different amounts. Injection of increasing amounts of amino acid derivatives showed that the isotopic signal varied up to 10 per thousand for D-aspartic acid. Correction for the delta(13)C signal of underivatized amino acid enantiomers is possible for all investigated amino acid enantiomers using logarithmic functions. Operating the GC-C/IRMS system in the split-mode (split ratio 1:12) is possible but resulted in a higher isotopic discrimination. The detection limit approached 3 ng for some amino acid enantiomers in the splitless mode, while the lower limit of routine determination exceeded 10 ng injection amount. The upper limit at which accurate stable isotope values were obtained was 200 ng injection amount. Compound-specific delta(13)C analysis of alanine, valine, aspartic and glutamic acid showed that the D-forms were enriched in (13)C relative to the L-forms, suggesting that microbes significantly contributed to the formation of the D-enantiomers in soil.