DETECTION OF DNA-PSORALEN PHOTOADDUCTS in situ

Abstract— An immunological method, with the use of specific immune serum, has been developed for detection of 8-methoxypsoralen (8-MOP) photoadducts to DNA, formed in situ in cell nuclei, after combined treatment with 8MOP and UV-A irradiation (Zarçbska et al. , 1978). Lymphocytes fixed on slides or in suspension, and cryostat sections of different mammalian tissues, served as antigenic substrate, after treatment with 8-MOP and UV-A in vitro. Specific fluorescence in these substrates was detected in the nuclei after treatment with 30 ˜ 140 kJ/m² UV-A in the presence of 0.1-0.3 μg/cm² 8-MOP. PHA-stimulated-lymphocytes appeared to be the most sensitive substrate.
However, hairless mice treated with high doses of UV-A in vivo , 70 ˜ 360 kJ/m² did not reveal a specific fluorescence of epidermal nuclei, unless a high local concentration of 8-MOP was attained.
The apparent discrepancy in the level of photoadduct detection between the in vitro and in vivo treated specimens was explained by the low number of DNA-8-MOP-photoadducts formed in vivo under these experimental conditions. The relevance of these findings to the role of DNA-8-MOP-photoadducts formed during PUVA photochemotherapy is discussed.     

Investigation of polarisation effects in injection locked lasers

Received: 14 June 1996/Revised version: 6 November 1996     

Investigation of the Montmorillonite clay-catalyzed [1,3] shift reaction of 3-methyl-2-butenyl phenyl ether

The [1,3] shift reaction of 3-methyl-2-butenyl phenyl ether was catalyzed more effectively by Montmorillonite K10 clay than Montmorillonite KSF clay, and proceeded with greatest ortho-selectivity in carbon tetrachloride at room temperature.     

A Reinvestigation of the Structure and Torsional Potential of N2O5 by Gas‐Phase Electron Diffraction Augmented by Ab Initio Theoretical Calculations

Gaseous N₂O₅ consists of two NO₂ groups bonded to a bridging O‐atom to form a nonlinear N−O−N moiety. The NO₂ groups undergo slightly hindered internal rotation around the bonds to the bridge so that instantaneous composition of the gaseous system is characterized by molecules with all combinations of torsion angles. In an earlier investigation, an attempt was made to determine the coefficients for an empirical form of the double‐rotor torsional potential, and the bond lengths and bond angles measured subject to assumptions that the structure of the O−NO₂ groups was invariant to torsion angle and that these groups had C_2v symmetry. The system has now been reinvestigated in terms of a more realistic model in which this symmetry restriction was relaxed, account was taken of structural changes in the NO₂ groups with torsion angle as predicted by ab initio theory at the B3LYP/6‐311+G* level, and a more convenient form of the torsional potential was assumed. The most stable conformation has C₂ symmetry with torsion angles τ₁ (defined as ∢(N−O−N=O₄)) equal to τ₂ (defined as ∢(N−O−N=O₆)) equal to 33.7°; because of the broad potential minimum in this region, the uncertainty in these angles is difficult to estimate, but is probably 3 – 4°. The results for the bond lengths and bond angles for the most stable conformation are r_g(N−O)=1.505(4) Å, r_g(N=O)=1.188(2) Å, ∢_α(N−O−N)=112.3(17)°, ∢_α(O=N=O)=134.2(4)°, 〈∢_α(O−N=O)〉=112.8(2)°. The difference between the symmetry‐nonequivalent O−N=O angles is estimated to be ca. 6.7° with the larger angle positioning the two N=O bonds on different NO₂ groups nearest each other. These average values are similar to those obtained in the original study. The main difference is found in the shape of the torsional potential, which at τ₁/τ₂=0/0 has a saddle point in the present work and a substantial peak in the earlier. The implication of the torsion‐angle findings for electron‐diffraction investigations of this type is discussed.     

Finite element analysis of flow,heat transfer,and free interfaces in an electron-beam vaporization system for metals

A numerical analysis is made of the liquid flow and energy transport in a system to evaporate metals. The energy from an electron-beam heats an axisymmetric metal disk supported by a water-cooled platform. Metal evaporates from the surface of a hot pool of liquid which is surrounded by a shell of its own solid. Flow in the pool is strongly driven by temperature-induced buoyancy and capillary forces, and is located in the transition region between laminar and turbulent flow. The evaporation rate is strongly influenced by the locations of the free boundaries. A modified finite element method is used to calculate the steady state flow and temperature fields coupled with the interface locations. The mesh is structured with spines that stretch and pivot as the interfaces move. The discretized equations are arranged in an ‘arrow’ matrix and are solved using the Newton–Raphson method. The electron-beam power and platform contact resistance are varied for cases involving the evaporation of aluminum. The results reveal the interaction of liquid flow, heat transfer and free interfaces. © 1998 John Wiley & Sons, Ltd.     

Novel,Monomeric Cyanine Dyes as Reporters for DNA Helicase Activity

The dimeric cyanine dyes, YOYO-1 and TOTO-1, are widely used as DNA probes because of their excellent fluorescent properties. They have a higher fluorescence quantum yield than ethidium homodimer, DAPI and Hoechst dyes and bind to double-stranded DNA with high affinity. However, these dyes are limited by heterogeneous staining at high dye loading, photocleavage of DNA under extended illumination, nicking of DNA, and inhibition of the activity of DNA binding enzymes. To overcome these limitations, seven novel cyanine dyes (Cyan-2, DC-21, DM, DM-1, DMB-2OH, SH-0367, SH1015-OH) were synthesized and tested for fluorescence emission, resistance to displacement by Mg²⁺, and the ability to function as reporters for DNA unwinding. Results show that Cyan-2, DM-1, SH-0367 and SH1015-OH formed highly fluorescent complexes with dsDNA. Of these, only Cyan-2 and DM-1 exhibited a large fluorescence enhancement in buffers, and were resistant to displacement by Mg²⁺. The potential of these two dyes to function as reporter molecules was evaluated using continuous fluorescence, DNA helicase assays. The rate of DNA unwinding was not significantly affected by either of these two dyes. Therefore, Cyan-2 and DM-1 form the basis for the synthesis of novel cyanine dyes with the potential to overcome the limitations of YOYO-1 and TOTO-1.     

Direct bound-free photodesorption of physisorbed molecules

Because light, weakly adsorbed atoms and molecules have very few bound states, the harmonic oscillator Δv = 1 optical selection rule is invalid for vibrational transitions of the physisorption bond. For such systems, we show that very low power (50 mW) infrared radiation should be sufficient to cause a direct one-photon optical transition from the ground state to continuum translational levels, resulting in photodesorption. Using a simple one-dimensional model, we present computations of the photodesorption rate as a function of photon energy for the Morse potential and several dipole moment functions. The threshold behavior at long wavelengths is analyzed.