排序方式: 共有48条查询结果,搜索用时 109 毫秒
1.
H Morrison B Mauclair R M Deibel G Pandey W M Baird 《Photochemistry and photobiology》1985,41(3):251-257
Abstract— Urocanic acid (UA) has previously been shown to photochemically react with N, N-dimethylthymine and with phage G4 single-stranded DNA. In this study, E-[ring-2-14C]-U A and calf thymus DNA have been irradiated with UV light (Λ > 270 nm) in buffered, aqueous solutions. Rc-isolation of the DNA indicates covalent binding of UA at levels of up to 80 nmol UA/mg DNA. Binding is observed for both native and heat denatured DNA. Equilibrium dialysis studies give no evidence for complexation of UA to either form of DNA in the dark. Enzymatic cleavage of the UA bound DNA and analysis by HPLC shows peaks for l4C-labelled products with retention volumes identical to those of a marker mixture prepared by irradiating UA with [3H-methyl]thymidine. Photolysis of the DNA before irradiation with U A leads to the formation of a second product with a retention volume corresponding to that for a deoxyadenosine/UA marker. 相似文献
2.
Redox‐Induced Spin‐State Switching and Mixed Valency in Quinonoid‐Bridged Dicobalt Complexes 下载免费PDF全文
David Schweinfurth Yvonne Rechkemmer Stephan Hohloch Naina Deibel Irina Peremykin Jan Fiedler Raphael Marx Dr. Petr Neugebauer Prof. Dr. Joris van Slageren Prof. Dr. Biprajit Sarkar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(12):3475-3486
The complexes [{(tmpa)CoII}2(μ‐L1)2?]2+ ( 12+ ) and [{(tmpa)CoII}2(μ‐L2)2?]2+ ( 22+ ), with tmpa=tris(2‐pyridylmethyl)amine, H2L1=2,5‐di‐[2‐(methoxy)‐anilino]‐1,4‐benzoquinone, and H2L2=2,5‐di‐[2‐(trifluoromethyl)‐anilino]‐1,4‐benzoquinone, were synthesized and characterized. Structural analysis of 22+ revealed a distorted octahedral coordination around the cobalt centers, and cobalt–ligand bond lengths that match with high‐spin CoII centers. Superconducting quantum interference device (SQUID) magnetometric studies on 12+ and 22+ are consistent with the presence of two weakly exchange‐coupled high‐spin cobalt(II) ions, for which the nature of the coupling appears to depend on the substituents on the bridging ligand, being antiferromagnetic for 12+ and ferromagnetic for 22+ . Both complexes exhibit several one‐electron redox steps, and these were investigated with cyclic voltammetry and UV/Vis/near‐IR spectroelectrochemistry. For 12+ , it was possible to chemically isolate the pure forms of both the one‐electron oxidized mixed‐valent 13+ and the two‐electron oxidized isovalent 14+ forms, and characterize them structurally as well as magnetically. This series thus provided an opportunity to investigate the effect of reversible electron transfers on the total spin‐state of the molecule. In contrast to 22+ , for 14+ the metal–ligand distances and the distances within the quinonoid ligand point to the existence of two low‐spin CoIII centers, thus showing the innocence of the quintessential non‐innocent ligands L. Magnetic data corroborate these observations by showing the decrease of the magnetic moment by roughly half (neglecting spin exchange effects) on oxidizing the molecules with one electron, and the disappearance of a paramagnetic response upon two‐electron oxidation, which confirms the change in spin state associated with the electron‐transfer steps. 相似文献
3.
Alcorta M Rehm KE Back BB Bedoor S Bertone PF Deibel CM DiGiovine B Esbensen H Greene JP Hoffmann CR Jiang CL Lighthall JC Marley ST Pardo RC Paul M Rogers AM Ugalde C Wuosmaa AH 《Physical review letters》2011,106(17):172701
The structure of (15)C, with an s(1/2) neutron weakly bound to a closed-neutron shell nucleus (14)C, makes it a prime candidate for a one-neutron halo nucleus. We have for the first time studied the cross section for the fusion-fission reaction (15)C+(232)Th at energies in the vicinity of the Coulomb barrier and compared it to the yield of the neighboring (14)C+(232)Th system measured in the same experiment. At sub-barrier energies, an enhancement of the fusion yield by factors of 2-5 was observed for (15)C, while the cross sections for (14)C match the trends measured for (12,13)C. 相似文献
4.
5.
Schiffer JP Hoffman CR Kay BP Clark JA Deibel CM Freeman SJ Howard AM Mitchell AJ Parker PD Sharp DK Thomas JS 《Physical review letters》2012,108(2):022501
The quantitative consistency of nucleon transfer reactions as a probe of the occupancy of valence orbits in nuclei is tested. Neutron-adding, neutron-removal, and proton-adding transfer reactions were measured on the four stable even Ni isotopes, with particular attention to the cross section determinations. The data were analyzed consistently in terms of the distorted wave Born approximation to yield spectroscopic factors. Valence-orbit occupancies were extracted, utilizing the Macfarlane-French sum rules. The deduced occupancies are consistent with the changing number of valence neutrons, as are the vacancies for protons, both at the level of <5%. While there has been some debate regarding the true "observability" of spectroscopic factors, the present results indicate that empirically they yield self-consistent results. 相似文献
6.
M. A. Deibel J. M. Savage J. D. Robertson W. D. Ehmann W. R. Markesbery 《Journal of Radioanalytical and Nuclear Chemistry》1995,195(1):83-89
Chronic lead (Pb) intoxication has been linked to Alzheimer's disease (AD). Lead, like many heavy elements, tends to accumulate in bone. PIXE is a powerful analytical tool which permits the determination of Pb at the g/g level without requiring sample digestion. GFAAS is one of the most sensitive methods for the determination of Pb and is capable of determining ng/g levels in solution. For bone analyses by GFAAS, sample dissolution and a matrix modifier are required. Rib bone samples were analyzed for Pb by PIXE and GFAAS. IAEA Animal Bone (H-5) was used as a secondary standard for Pb with both methods to ensure accuracy. The range of Pb concentrations in human rib bone was 1.4–11.5 g/g for the trabecular surface by PIXE, 1.3–45 g/g for the cortical surface by PIXE, and 1.54–11.75 g/g for whole bone by GFAAS. No significant difference (p>0.05) was found for AD versus control for either surface or for whole bone. 相似文献
7.
INFLUENCE OF HYDRATION ON THE INTERNAL DYNAMICS OF HEN EGG WHITE LYSOZYME IN THE DRY STATE 总被引:1,自引:0,他引:1
Abstract— Proteins exist in a predominately aqueous solvent environment. Hydration of the protein surface significantly affects many aspects of the protein's structure and function; these effects may be related to the molecular dynamics of the protein. We have examined the influence of hydration on the internal dynamics of hen egg white lysozyme using room-temperature phosphorescence from the intrinsic tryptophan residues. Powders of lyophilized lysozyme were hydrated in a phosphorimeter using a flow system that allowed for continuous manipulation of relative humidity over the range 0–92%; this system allowed us to directly compare intensity differences that result from changes in hydration. Lysozyme phosphorescence intensity decreased as a function of hydration over the entire relative humidity range; the decrease was not linear but appeared to occur in distinct phases. The phosphorescence intensity decays were multiexponential over the hydration range studied, and hydration had the largest influence on the long lifetime component. These data suggest that the protein exists in multiple, static conformations in the dry state and that water binding to polar (as opposed to charged) sites on the protein surface induces local and/or global softening of the protein structure. 相似文献
8.
Ruiz C Parikh A José J Buchmann L Caggiano JA Chen AA Clark JA Crawford H Davids B D'Auria JM Davis C Deibel C Erikson L Fogarty L Frekers D Greife U Hussein A Hutcheon DA Huyse M Jewett C Laird AM Lewis R Mumby-Croft P Olin A Ottewell DF Ouellet CV Parker P Pearson J Ruprecht G Trinczek M Vockenhuber C Wrede C 《Physical review letters》2006,96(25):252501
The strength of the Ec.m. = 184 keV resonance in the 26gAl(p, gamma)27 reaction has been measured in inverse kinematics using the DRAGON recoil separator at TRIUMF's ISAC facility. We measure a value of omega gamma = 35 +/- 7 microeV and a resonance energy of Ec.m. = 184 +/- 1 keV, consistent with p-wave proton capture into the 7652(3) keV state in 27Si, and discuss the implications of these values for 26GAl nucleosynthesis in typical oxygen-neon white-dwarf novae. 相似文献
9.
Silbernagel K Jechorek R Barbour WM Mrozinski P Alejo W Aleo V Andaloro B Beacorn F Benzinger J Bogar S Brayman C Broom J Carson M Carver C Cheng C Centrella B Clayborn J Collins C Deibel C Divine M Eliasberg S Farmer D Frye S Gatesy T Goodstein E Halker C Hall G Hanson P Hartman G Heddaeus K Hembree J Hutchins J Istafanos P Jechorek R Jenkins J Kerdahi K Kremer S Lal A Leighton S Lester D Lewis J Lin J Martin J Maselli M McCarthy P McGovern B Mills M Mohnke F Moon B Moss D Plaza M Robeson S 《Journal of AOAC International》2004,87(2):395-410
A multilaboratory study was conducted to compare the automated BAX system and the standard cultural methods for detection of Listeria monocytogenes in foods. Six food types (frankfurters, soft cheese, smoked salmon, raw, ground beef, fresh radishes, and frozen peas) were analyzed by each method. For each food type, 3 inoculation levels were tested: high (average of 2 CFU/g), low (average of 0.2 CFU/g) and uninoculated controls. A total of 25 laboratories representing government and industry participated. Of the 2335 samples analyzed, 1109 were positive by the BAX system and 1115 were positive by the standard method. A Chi square analysis of each of the 6 food types, at the 3 inoculation levels tested, was performed. For all foods, except radishes, the BAX system performed as well as or better than the standard reference methods based on the Chi square results. 相似文献
10.
PHOTODESTRUCTION OF PHAEOMELANIN 总被引:2,自引:0,他引:2
M. R. Chedekel ‡ P. W. Post † ‡ R. M. Deibel M. Kalus 《Photochemistry and photobiology》1977,26(6):651-653
Abstract. Phaeomelanin readily decomposes by the action of UV light and oxygen. This finding may explain many of the abnormal reactions of the skin of redheads and blondes to sunlight, including their high susceptibility to skin cancer. In aqueous solution, phaeomelanin displays an EPR signal rich in hyperfine splitting, consistent with structural information.
Phaeomelanin readily, decomposes by the action of UV light and oxygen. This finding may explain many of the abnormal reactions of the skin of redheads and blondes to sunlight, including their high susceptibility to skin cancer. We have yet to identify any of the fragmentation products. Chromatographic analysis of the photolysate indicates at least 17 different compounds. Work on the reactions of phaeomelanin with superoxide, and the identification, synthesis, and physiological evaluation of these photoproducts as etiological factors in sunburn and carcinogenesis is in progress. In aqueous solutions, phaeomelanin displays an air stable EPR signal rich in hyperfine splitting. Complete analysis of this signal will provide a better understanding of the structure of the pigment. 相似文献
SUMMARY
Phaeomelanin readily, decomposes by the action of UV light and oxygen. This finding may explain many of the abnormal reactions of the skin of redheads and blondes to sunlight, including their high susceptibility to skin cancer. We have yet to identify any of the fragmentation products. Chromatographic analysis of the photolysate indicates at least 17 different compounds. Work on the reactions of phaeomelanin with superoxide, and the identification, synthesis, and physiological evaluation of these photoproducts as etiological factors in sunburn and carcinogenesis is in progress. In aqueous solutions, phaeomelanin displays an air stable EPR signal rich in hyperfine splitting. Complete analysis of this signal will provide a better understanding of the structure of the pigment. 相似文献