Photochemical and photobiological properties of 4,8-dimethyl-5'-acetylpsoralen

The photochemical and photobiological properties of 4,8-dimethyl-5'-acetylpsoralen (AcPso), proposed for the photochemotherapy of some skin diseases, were investigated. The photoreaction of AcPso with DNA is weaker in the presence of air than in a nitrogen atmosphere, in terms of total photobinding and DNA cross-linking; when UVA irradiation is performed in air, AcPso behaves as a monofunctional reagent. The quenching effect of oxygen is related to the high capacity of AcPso to produce singlet oxygen. Furthermore, it is demonstrated that AcPso photoadducts are better producers of singlet oxygen than free AcPso in solution. Using DNA sequencing methodology, two modes of DNA photosensitization by AcPso are shown, these lead to the formation of photoadducts mainly at T residues (and at C to a lesser extent) and to photo-oxidized G residues probably via singlet oxygen. Chemical or enzymatic cleavage were used as probes in these experiments. A rapid assay for the detection of the photodynamic effect of a photosensitizer on DNA, involving oxygen, is also described. Finally, the cytotoxicity and genotoxicity of AcPso on E. coli WP2 cells appear to be related to its ability to form photoadducts, in particular cross-links, rather than to its capacity to produce singlet oxygen.     

Photoreaction of New Psoralen Analogs with DNA: Sequence and Mutation Specificity in the Escherichia coli lacZ Gene

New thio- and seleno-analogs of psoralen were synthesized and analyzed for their photoreactivity toward DNA. Using oligonucleotides of denned sequence, we first showed that these derivatives predominantly generated interstrand crosslinks at 5′-TpA sites. We also observed a surprisingly high reactivity of 7H-thiopyrano[3,2-f][l]benzofuran-7-one (PSO[0-S]) with the BamHl and PstI oligomers, giving rise to the formation of crosslinks at 5′-ApT sites and of the thymidine-psoralen-cytosine type. Next, the sequence specificity in the photochemical binding of all the compounds was investigated in two DNA fragments encompassing the lacZ gene of Escherichia coli, using the T₄ DNA polymerase sequencing methodology. Resulting maps demonstrated that thio-and seleno-analogs of psoralen preferentially photoreact-ed with thymine and cytosine residues. The AT-rich sequences proved to be particularly reactive sites as did adjacent thymines, especially at C-surrounding residues. Likewise, photoaddition at cytosines in CA/AC context was observed. It was highly significant that all of the derivatives exhibited similar sequence specificities with only minor differences. However, PSO(O-S) differed from the other heteropsoralens. Photoadducts occurred with a higher frequency at AC and CA dinucleotides, and new sites were detected. A comparison with 8-methoxypsor-alen photobinding is also reported. Finally, the mutagenic consequences of photoadducts induced in M13mp19 DNA by PSO(O-S) were determined in a forward system that detects all classes of mutagenic events. The high phototoxicity exhibited by PSO(O-S) could be attributed to crosslinks, and the comparison of the observed mutational specificity with the photoadduct distribution within the same gene showed that mutations were targeted at potential monoadduct sites where photolesions were detected in our footprinting experiments     

High-performance liquid chromatography-UV diode array,inductively coupled plasma mass spectrometry (ICMPS) and orthogonal acceleration time-of-flight mass spectrometry (oa-TOFMS) applied to the simultaneous detection and identification of metabolites of 4-bromoaniline in rat urine

Summary The paper describes the role and tasks of environmental analysis and monitoring. It emphasises the leading role played by gas chromatography, especially when coupled with suitable sample preparation. This is demonstrated by some literature evidence and mainly by the author's original work on the design of sample preparation apparatus and development of GC-based methods of determination of a wide variety of organic pollutants in environmental samples. A typical example is the physical speciation of PAHs and PCBs in river environment with the use of a home-made filtration vessel coupled with SPE cartridges to prepare samples for GC-MS analysis; thin layer head space with self-generation of aqueous concentrate to prepare humane urine samples for DAI (direct aqueous injection)-GC-ECD analysis for the content of volatile chloro-organic compounds; studies on capillary denuders in sampling organic air pollutants; passive dosimeters in indoor air quality measurements; design and application of thermal desorbers for the introduction of analytes into GC columns and modification of a speciation analyser for organometalic environmental pollutants. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Electrically controllable multiple, active, computer-generated hologram

The multiple, active, computer-generated hologram (MACH) is a novel device combining the attributes of electrically controllable diffraction gratings and computer-generated holograms. The version discussed here consists of a surface relief transmitting structure immersed in a nematic liquid crystal and sandwiched between two, planar indium tin oxide electrodes. Under control of a single applied voltage, the device can selectively generate any one of a number of desired, uncorrelated optical wave fronts. The device principles are discussed and experimental results presented. There is a brief discussion of the relative merits of the MACH and electrically addressed spatial light modulators.     

Fission fragment angular distributions in 16O+181Ta

Time of flight and energy of fission fragments were measured using pulsed beam. Fission fragment mass and energy integrated angular distributions were extracted. Fission fragment anisotropy was explained in the framework of saddle point model.     

Vibrational dynamics of biological molecules: Multi-quantum contributions

High-resolution X-ray measurements near a nuclear resonance reveal the complete vibrational spectrum of the probe nucleus. Because of this, nuclear resonance vibrational spectroscopy (NRVS) is a uniquely quantitative probe of the vibrational dynamics of reactive iron sites in proteins and other complex molecules. Our measurements of vibrational fundamentals have revealed both frequencies and amplitudes of ⁵⁷Fe vibrations in proteins and model compounds. Information on the direction of Fe motion has also been obtained from measurements on oriented single crystals, and provides an essential test of normal mode predictions. Here, we report the observation of weaker two-quantum vibrational excitations (overtones and combinations) for compounds that mimic the active site of heme proteins. The predicted intensities depend strongly on the direction of Fe motion. We compare the observed features with predictions based on the observed fundamentals, using information on the direction of Fe motion obtained either from DFT predictions or from single crystal measurements. Two-quantum excitations may become a useful tool to identify the directions of the Fe oscillations when single crystals are not available.     

Mössbauer studies of two-iron centers in biomolecules

We report slow-relaxation Mössbauer spectra for a nitric oxide and a sulfide derivative of hemerythrin and for reduced purple acid phosphatase. Anomalous hyperfine tensors derived from simulations of the latter two systems and the unusual EPR spectrum of the former one are explained in terms of a single spin Hamiltonian model.