Hydroxyl radical is the active species in photochemical DNA strand scission by bis(peroxo)vanadium(V) phenanthroline

Bis(peroxo)vanadium(V) complexes are widely investigated as anticancer agents. They exert their antitumor and cyctotoxic effects through inhibition of tyrosine phosphatases and DNA cleavage, respectively. The latter process remains poorly understood. The mechanism of DNA cleavage by NH(4)[(phen)V(O)(eta(2)-O(2))(2)] (phen = 1,10-phenanthroline) was investigated. Kinetic studies on DNA cleavage revealed that the complex is a single-strand nicking agent with no specificity. EPR experiments using 2,2,6,6-tetramethyl-4-piperidone (TMP) and 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) as spin-traps for singlet oxygen and hydroxyl radical, respectively, implicated hydroxyl radical production upon photodecomposition of bis(peroxo)vanadium(V). This was corroborated by benzoate inhibition of DNA strand scission and stoichiometric oxidation of 2-propanol to acetone upon irradiation of bis(peroxo)vanadium(V) phenanthroline. High-resolution polyacrylamide gel analysis of the vanadium cleavage reaction and [Fe(II)EDTA](2)(-)/H(2)O(2) resulted in comigration of "ladder" pattern bands, which superimposed when both reactions were run on the same lane. These findings identify hydroxyl radical produced from the photooxidation of the peroxo ligand on vanadium as the active species in DNA cleavage.     

Formation and structure of a novel enediyne-RNA base covalent adduct

The structure of an unusual covalent adduct formed by thiol-activated neocarzinostatin chromophore (NCS-chrom) and a RNA-DNA hybrid having an overhang of four unpaired residues at the 3'-end of the RNA strand has been elucidated by MS and NMR spectroscopic analyses. Unlike previously characterized adducts formed by NCS-chrom on the sugar residue of the DNA target, this adduct has been found to be on one of the uracil bases in the RNA overhang. Covalent linkage is between C-6 of the post-activated NCS-chrom and C-5 of the uracil. A novel mechanism involving adduction of the NCS-chrom C-6 radical, generated by 2-mercaptoethanol activation, to C-5 of the uracil at the U9 position of the RNA 11-mer, oxidation by dioxygen, reduction by the thiol, and subsequent dehydration is proposed for adduct formation.     

Catalytic combustion of chlorobenzene over V2O5/TiO2 catalysts prepared by the precipitation-deposition method

Catalytic combustion of chlorobenzene over supported vanadium oxides has been investigated. TiO₂ was prepared by the sol-gel method from titanium isopropoxide. The supported vanadium oxide catalysts have been prepared by precipitation-deposition and impregnation method and characterized by XRD, FT-Raman and TPR. In the VO_x/TiO₂catalysts prepared using the impregnation method, when vanadium loading reaches 3 wt.%, the activity shows a maximum. However, in the VO_x/TiO₂catalysts prepared by precipitation-deposition, when vanadium loading reaches 7 wt.%, the activity shows a maximum. This result suggests that the precipitation-deposition can yield a higher metal loading on the support and a high dispersion compared to the impregnation method. This revised version was published online in August 2006 with corrections to the Cover Date.     

Direct observation of an intermediate state for a surface photochemical reaction initiated by hot electron transfer

The photoinduced charge transfer that had been suggested to result in the dissociation of phenol on Ag(111) was investigated by two-photon photoemission spectroscopy. An unoccupied intermediate state was positively identified, which was found to be located 3.22 eV above the Fermi level. From the photoelectron energy dispersion, the effective mass of the intermediate state was determined to be (15 +/- 10)m(e) for a 1 ML coverage of phenol. This implies that the excited electron is localized mainly on the adsorbed phenol, forming a molecular resonance state. Polarization dependence of the photoelectron intensity suggested that the initial photoexcitation of the substrate produces hot electrons that scatter into the molecular resonance state, leading ultimately to the dissociation of the adsorbate. These results are the first two-photon photoemission study to characterize the transient anionic state involved in photodissociation of a molecule adsorbed on a metal surface.     

State-to-state reaction dynamics of CH3I photodissociation at 304 nm

The detailed reaction dynamics of CH(3)I photodissociation at 304 nm were studied by using high-resolution long time-delayed core-sampling photofragment translation spectroscopy. The vibrational state distributions of the photofragment, i.e., CH(3), are directly resolved due to the high kinetic resolution of this experiment for the first time. CH(3) radicals produced from I((3)Q(0+)), I((1)Q(1) <--( 3)Q(0+)), and I((3)Q(1)) channels are populated in different vibrational state distributions. The I((3)Q(0+)) and I((3)Q(1)) channels show only progressions in the nu2'(a2") umbrella bending mode, and the I((1)Q(1) <-- (3)Q(0+)) channel shows both progression in the nu2' umbrella bending mode and a small amount of excitation in the nu1'(a1') C-H stretching mode. The photodissociation processes from the vibrational hot band of CH(3)I (upsilon3 = 1, upsilon3 = 2) were also detected, primarily because of the absorption probability from the vibrational excited states, i.e., hot bands are relatively enhanced. Photofragments from the hot bands of CH(3)I show a cold vibrational distribution compared to that from the vibrational ground state of CH(3)I. The I* quantum yield and the curve crossing possibility were also studied for the ground vibrational state of CH(3)I. The potential energy at the curve crossing point was calculated to be 32 790 cm(-1) by using the one-dimensional Landau-Zener model.     

Studies of the Factors Controlling Regioselective Nucleophilic Addition to Dienylium-Iron Complexes

Tricarbonyl(4-alkoxyl-1-alkylcyclohexadienylium)iron complexes (I) react with metal-cation enolate nucleophiles to give in most cases a mixture of products (II) and (III), resulting from attack at the C-1 and C-5 termini of the dienylium ring. Factors that control the regioselectivity of nucleophilic addition, including the steric and electronic effects of the 4-alkoxyl and 1-alkyl substituents, the degree of association between the enolate nucleophiles and their counterions, and the polarity of the solvents, were investigated.     

Studies on diacetylenic vinyl compounds. VI. ESR studies on the polymerization of diacetylene containing acrylate and methacrylates

A number of diacetylene containing acrylate and methacrylates have been synthesized and the interaction between their propagating radicals and the diacetylene groups was studied by ESR spectroscopy. In the case of polymerization at 70°C using AIBN as an initiator, the propagating radicals of methacrylates are temporarily trapped with the diacetylenes with rapid exchange of the electron, thus showing strong signals of the propagating radicals. Gamma irradiation of the frozen state produces a blue color in samples, and the ESR signals were found to be those of uninteracted acrylate and methacrylates. From a comparison of spectral widths, there seems to exist an intramolecular interaction between the radicals and the diacetylene group at the frozen state. © 1992 John Wiley & Sons, Inc.     

The transport of condensible vapors through a microporous vycor glass membrane

The flow of condensible vapors through microporous Vycor glass was investigated experimentally as well as theoretically. In porous materials, adsorbable gases frequently exhibit higher permeability than predicted from the flow of nonadsorbable gases. This enhanced flow has been attributed to the surface diffusion of adsorbed molecules along the surface of the porous media or to the viscous flow of capillary condensate at high relative pressures. In the present investigation, a new flow model of condensible vapors through microporous material was developed by considering the blocking effect of the adsorbed phase on the basis of a cylindrical capillary structure. Six different flow modes were considered depending on the pressure distribution and the film thickness of the adsorbed layer. Experimental measurements were also conducted on the transport of condensible vapors (Freon-113 and water) through microporous Vycor glass at steady state in the entire range of relative pressure. The maximum peak and scattering phenomena of permeabilities were observed. The estimated values of permeability from the developed model were compared with the experimental results. Also, it was attempted to explain the maximum peak and scattering phenomena of the experimentally observed permeabilities.     

Friedel-crafts acylation of 2-methoxynaphthalene over h-beta catalysts: effect of Si/Al ratio

The acylation of 2-methoxynaphthalene with acetic anhydride was carried out over zeolite beta catalysts having various Si/Al ratios. It was found that the reaction performance is strongly dependent on the Si/Al ratio of the catalyst. The catalytic reaction features were elucidated in terms of the acidic properties of the catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

1,3,4-oxadiazolin-2-ones from carbo-t-butoxyhydrazones

5-Substituted-1,3,4-oxadiazolin-2-ones 2 were synthesized by the oxidation of carbo-t-butoxyhydrazones 1 of aromatic aldehydes with lead tetraacetate or, preferably, iodosobenzene diacetate. In some instances 5-acetoxy-1,3,4-oxadiazoles 3 were obtained along with 2 . The oxidation of carboethoxyhydrazones 4 gave 2-ethoxy-1,3,4-oxadiazoles 5 .