RESEARCH NOTE

Fluorescence microscopy has been utilized to investigate the effects of UV irradiation on the organization of keratin intermediate filaments in normal human epidermal keratinocytes. Sun lamp irradiation induced the condensation of keratin intermediate filaments into the perinuclear region and inhibited the reorganization of keratin filaments normally induced by Ca2+. Exposure to UVC appeared to disrupt keratin filaments similarly, whereas UVA had no discernible effect.     

RESEARCH NOTE

Energies and lifetimes of triplet states of a series of 2-cyclohexenones have been measured in solution under ambient conditions by time-resolved photoacoustic calorimetry (PAC). The PAC triplet lifetimes are in excellent agreement with lifetimes measured by kinetic absorption spectrophotometry (KAS) using nanosecond flash techniques, indicating that the present data indeed pertain to the enone triplets previously studied using KAS. The data demonstrate that, as previously proposed, the pi pi triplet energies in these systems are indeed correlated with triplet lifetimes, and vary sensibly with the anticipated extent of conformational flexibility of the C = C bond. No evidence supporting formation of metastable trans-cyclohexenones was obtained. The data also demonstrate greater precision and, for lifetimes, greater accuracy than has hitherto been claimed for the PAC technique for study of transients with lifetimes in the 25 ns range.     

RESEARCH NOTE

A previous report [Freeman et al. (1986) Photochem. Photobiol. 43S, 93S] indicated that irradiation of human skin in situ with 385 or 405 nm radiation produced detectable levels of pyrimidine dimers in DNA. Since these wavelengths are absorbed poorly by DNA, these results suggested that DNA damage was sensitized by other absorbing molecules present in skin. Examination of two experimental aspects of the previous work indicates that (1) the static gel electrophoresis method for DNA dispersion used in lesion determination gave accurate values of the levels of induced dimers, and (2) the DNA damage apparently induced by 385 nm was actually induced by shorter wavelength UV present in the 20 nm bandpass beam of the monochromator. The current results indicate that monochromatic 385 and 405 nm radiation are ineffective in dimer production in human skin in situ.     

RESEARCH NOTE

Two mutants of Escherichia coli unable to synthesize riboflavin were grown with limiting (2 micrograms ml-1) and non-limiting (10 micrograms ml-1) concentrations of riboflavin. These riboflavin auxotrophs when grown to exponential phase with non-limiting riboflavin are more sensitive to broad spectrum near-ultraviolet light (NUV, 320-400 nm) inactivation than when they are grown with limiting riboflavin. Exponential phase cells of the riboflavin auxotrophs grown with limiting riboflavin are sensitized when irradiated in saline supplemented with riboflavin. This suggests that extracellular riboflavin is important as a NUV sensitizer when intracellular levels of riboflavin are reduced. The concentration of riboflavin in crude extracts from exponentially growing cells correlates well with the sensitivity of these mutants to NUV inactivation. The level of riboflavin supplementation has little effect on the NUV sensitivity of the parental strain.     

RESEARCH NOTE: PHOTOREACTION OF 4', 5'-DIHYDROPSORALEN WITH THYMINE

Abstract— The photocycloaddition reaction of 4',5'-dihydropsoralen with thymine was carried out in solution and in the frozen state. A major photoadduct was isolated and characterized by elemental analysis and physical methods. The photoadduct was proven to be the 1:1 C₄-cycloaddition product, an analogue of furocoumarin-DNA biadduct, with the stereochemistry of anti -head-to-head formed through 2+2 addition reaction between the pyrone double bond of 4', 5'-dihydropsoralenand 5,6-double bond of thymine.     

RESEARCH NOTE ON THE CHARGE-TRANSFER PATHWAY IN THE MEROCYANINE 540 TRIPLET STATE QUENCHING BY NITROXYL RADICAL

Abstract— Quenching of merocyanine 540 triplet state by nitroxyl radical has been investigated by flash photolysis. An increase of solvent polarity leads to an increase of the quenching rate. This polarity effect shows that merocyanine 540 triplet state is able to react with nitroxyl radical via a charge-transfer process. The data presented in this work are shown to be consistent with previous results obtained in micelles and liposomes.     

TECHNICAL NOTE

Abstract— –The use of a proximity type 12 µm microchannel plate photomultiplier (Hamamatsu R1564U) is demonstrated for the accurate determination of picosecond lifetimes of xanthione, stiff stilbene, cryptocyanine, pinacyanol chloride, erythrosin and l, l'-diethyl-2,2'-dicarbocyanine iodide in solution at room temperature. Single curve and global analyses with reference convolution give statistically acceptable mono-exponential fits to all obtained decays. The count rate and wavelength dependence of the measured excitation pulse profile are discussed. Matching the count rates of sample and reference is recommended for reliable picosecond lifetime determinations.     

RESEARCH NOTE PHOTOTOXICITY OF CITRAL TO Trichoplusia ni (LEPIDOPTERA: NOCTUIDAE) AND ITS AMELIORATION BY VITAMIN A

Abstract Citral, a monoterpene aldehyde synthesized by several plant families, was recently shown to exhibit ultraviolet A light (320–400 nm) (UVA)-enhanced oxygen-dependent toxicity against bacteria and fungi ( Escherichia coli and Fusarium species). In this study, we report for the first time that citral is phototoxic to insects; at concentrations of 300 ppm in artificial diet, mortality of first instar Trichoplusia ni (cabbage loopers) approached 30% after 120 h of UVA exposure, approximately double the mortality level in the absence of UVA. At 300 ppm, the antioxidant vitamin A reduces citral phototoxicity by about 50% in this species, suggesting that citral phototoxicity against insects is oxygen dependent.     

RESEARCH NOTE: THIOPYRONINE-AND 8-METHOXYPSORALEN-SENSITIZED PHOTODYNAMIC EFFECT ON CELL GROWTH, COLONY FORMING ABILITY AND RNA SYNTHESIS IN Saccharomyces MUTANTS DEFICIENT IN DNA REPAIR

Abstract: We compared the photodynamic effects of thiopyronine (TP) and visible light, and 8-methoxypsoralen (8-MOP) and ultraviolet A (UV-A) light, on growth, colony forming ability and RNA synthesis in a repair-proficient Saccharomyces strain and three mutants deficient in DNA repair mechanisms (DNA repair assays). With 8-MOP and UV-A repair-deficient mutants were significantly more sensitive than the repair-proficient strain indicating that the system is sensitive for the detection of DNA damage. With TP and visible light, the photodynamic effects were comparable in the mutants and the control, indicating no DNA damage. These results support previous work showing that the main target of TP photosensitization in eukaryotes is not nuclear DNA.     

RESEARCH NOTE: TRIPLET RADICAL ION PAIR STATE OF THE Zn-PORPHYRIN-VIOLOGEN DYAD AS A MAGNETIC FIELD SENSITIVE PROBE OF PHASE TRANSITIONS IN SMALL UNILAMELLAR VESICLES

The magnetic field effect on the recombination kinetics of the triplet radical ion pair state (RIPS) of the Zn-porphyrin-viologen dyad (P-Ph-Vi2+) in the small unilamellar vesicles (SUV) of D,L-dipalmitoyl-alpha-phosphatidylcholine has been studied by the nanosecond laser flash photolysis technique at 5-60 degrees C. The increase in temperature from 25 to 40 degrees C enhances the rate constant (kr) of the RIPS recombination in zero magnetic field from 0.9 x 10(6) to 1.6 x 10(6) s-1, while kr is temperature insensitive at 5-25 and 40-60 degrees C. The typical break in the kr temperature dependence is observed in the temperature range of the phase transition of the SUV bilayers from the solid to the fluid state. The kr value in a strong magnetic field (B = 0.24 T) is equal to 2.7 x 10(5) s-1 and it is independent of temperature at 5-60 degrees C. The shape of the magnetic field dependence of kr is unaffected by the phase transition of the SUV bilayers and is characterized by the existence of an initial plateau of kr at B = 0 to 0.5 mT.     

NOTE: Polymerization of Cyclic Esters Using Aminoacid Initiators

The low-molecular weight poly(? -caprolactone) and polylactide were obtained by the polymerization of cyclic esters in the presence of amino acid initiators. The polymer structures were elucidated by means of MALDI TOF, NMR and IR studies. Effects of temperature, reaction time and initiator dosage on the polymerization process were examined.