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931.
A. L. Attwood D. M. Murphy J. L. Edwards T. A. Egerton R. W. Harrison 《Research on Chemical Intermediates》2003,29(5):449-465
The formation of a series of oxygen-centred radicals on different TiO2 samples (P25 and two different rutile materials) under various conditions was investigated using X-band c.w. Electron Paramagnetic Resonance (EPR) spectroscopy. The radicals were formed either on thermally-reduced TiO2, or by UV irradiation of the oxide under an oxygen atmosphere. The nature and stability of the radicals was also explored as a function of surface hydration. On thermally reduced TiO2, containing surface and bulk Ti3+ centres, oxygen adsorption at 300 K results in the preferential formation and stabilisation of O2
- anions on the P25 surface, but O- and O3
- anions are generated on the rutile surfaces. Superoxide anions (O-) and trapped holes (O2
-) were also identified after photo-irradiation of the thoroughly dehydrated TiO2 samples under oxygen. The O- anions were only visible at low temperatures under continuous irradiation, while the O2
- anions were stable for days at 300 K. By comparison, on fully hydrated surfaces, no stable oxygen centred radicals could be detected on P25, while O2
- anions were easily observed on the rutile surfaces. On partially hydrated P25, the O-, O2
- and HO2 anions were detected after UV irradiation at 77 K; all radicals decayed upon warming to 298 K. On partially hydrated rutile, the O- and O2
- anions were detected and, unlike the case for P25, were found to be stable for days under the same conditions. The results illustrate the varied formation and stability of the oxygen centred radicals on TiO2 surfaces depending on the pretreatment conditions. 相似文献
932.
MECHANISM OF PHOTOINACTIVATION OF PLANT PLASMA MEMBRANE ATPASE 总被引:1,自引:0,他引:1
Abstract UV radiation at 290 and 365 nm inactivates two forms of the K+ -stimulated ATPase associated with the plasma membrane of suspension-cultured cells of Rosa damascena . One form is 15 and 36 times more sensitive than the other to 290 and 365 nm, respectively. For both forms, the inactivation requires oxygen, is inhibited by azide and diazobicyclo(2.2.2.2)octane, but not glycerol, and is enhanced up to 7.5 times in deuterium oxide solvent. Inactivation occurs concomitantly with loss of absorbance at 290 nm. Cs+ and NO− 3 , quenchers of tryptophan fluorescence, inhibit inactivation. The results suggest that inactivation involves singlet-oxygen mediated destruction of tryptophans in the ATPases. 相似文献
933.
Michael P. Cava Zakeen Ahmed Nicholas Benfaremo Raymond A. Murphy Gerard J. Omalley 《Tetrahedron》1984,40(22):4767-4776
The commercially available dye intermediates 1-hydroxyanthraquinone, 1-amino-2-methylanthraquinone and 1,8-dihydroxyanthraquinone (chrysazin) have been elaborated in a regiospecific manner into tetracyclic ketonitriles. The latter are potential precursors of the anthracycline aglycone aklavinone and its 4-deoxy analog1 相似文献
934.
[reaction: see text] Aryl epoxyazides undergo efficient electron-deficient reaction cascades mediated by Lewis acids, leading to regiospecific amination of the aromatic ring. 相似文献
935.
Equations are developed to describe the response of Zeeman-modulated spectrometers to a line background-absorption interference. The treatment is used to demonstrate that the analyte sensitivity is identical but the line background-responses are different for source-modulated and atomizer-modulated spectrometers. Two correction procedures are developed, the applicability of which depends on the separation of the zero-field source line and the interfering absorption line. Experimental data are shown for the interference of Co in the determination of Hg and of Pt in the determination of Fe. 相似文献
936.
Mitochondria-derived reactive oxygen species mediate blue light-induced death of retinal pigment epithelial cells 总被引:9,自引:0,他引:9
King A Gottlieb E Brooks DG Murphy MP Dunaief JL 《Photochemistry and photobiology》2004,79(5):470-475
Throughout the lifetime of an individual, light is focused onto the retina. The resulting photooxidative stress can cause acute or chronic retinal damage. The pathogenesis of age-related macular degeneration (AMD), the leading cause of legal blindness in the developed world, involves oxidative stress and death of the retinal pigment epithelium (RPE) followed by death of the overlying photoreceptors. Evidence suggests that damage due to exposure to light plays a role in AMD and other age-related eye diseases. In this work a system for light-induced damage and death of the RPE, based on the human ARPE-19 cell line, was used. Induction of mitochondria-derived reactive oxygen species (ROS) is shown to play a critical role in the death of cells exposed to short-wavelength blue light (425 +/- 20 nm). ROS and cell death are blocked either by inhibiting the mitochondrial electron transport chain or by mitochondria-specific antioxidants. These results show that mitochondria are an important source of toxic oxygen radicals in blue light-exposed RPE cells and may indicate new approaches for treating AMD using mitochondria-targeted antioxidants. 相似文献
937.
George L. Murphy 《Foundations of Physics》1984,14(4):351-357
Two problems connected with Dirac quantization of relativistic cosmological models are considered. The difficulties with this approach have been the lack of physical interpretation of the spinor wave functions and the difficulty in extracting the spinor square root with a variable mass term in the classical Hamiltonian. It is suggested here that the spinor wave functions may be connected with the temporal irreversibility of physical processes in the universe. The analytical difficulty of extracting the spinor square root suggests a modification of the classical theory, in analogy with the theory of the Dirac electron in an electromagnetic field. 相似文献
938.
Chen J Murphy AR Esteve J Ogletree DF Salmeron M Fréchet JM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7703-7710
The oligothiophene derivative 4-(5' " '-decyl-[2,2';5',2' ';5' ',2' ";5' ",2' " '] pentathiophen-5-yl)-butyric acid (D5TBA) was synthesized by Stille cross-coupling methods using functionalized thiophene monomers. The structural and mechanical properties of D5TBA self-assembled monolayers on mica have been studied by atomic force microscopy (AFM). The self-assembled films were prepared by immersing the mica in dilute chloroform or tetrahydrofuran (THF) solutions. The films were predominantly of monolayer thickness with molecules packed in nearly upright orientations. In regions covered with multilayers, the molecules in each monolayer were oriented opposite to those in the neighboring ones, that is, with COOH-COOH and CH3-CH3 contact. The nature of the end group in contact with the substrate depended on the solvent used and the degree of hydration of the substrate, with hydrophobic chloroform solvent favoring the methyl end down and hydrophilic THF favoring the acid group end down. The orientation could also be controlled by dipping using the Langmuir-Blodgett technique. 相似文献
939.
Kaminski GA Stern HA Berne BJ Friesner RA Cao YX Murphy RB Zhou R Halgren TA 《Journal of computational chemistry》2002,23(16):1515-1531
We present results of developing a methodology suitable for producing molecular mechanics force fields with explicit treatment of electrostatic polarization for proteins and other molecular system of biological interest. The technique allows simulation of realistic-size systems. Employing high-level ab initio data as a target for fitting allows us to avoid the problem of the lack of detailed experimental data. Using the fast and reliable quantum mechanical methods supplies robust fitting data for the resulting parameter sets. As a result, gas-phase many-body effects for dipeptides are captured within the average RMSD of 0.22 kcal/mol from their ab initio values, and conformational energies for the di- and tetrapeptides are reproduced within the average RMSD of 0.43 kcal/mol from their quantum mechanical counterparts. The latter is achieved in part because of application of a novel torsional fitting technique recently developed in our group, which has already been used to greatly improve accuracy of the peptide conformational equilibrium prediction with the OPLS-AA force field.1 Finally, we have employed the newly developed first-generation model in computing gas-phase conformations of real proteins, as well as in molecular dynamics studies of the systems. The results show that, although the overall accuracy is no better than what can be achieved with a fixed-charges model, the methodology produces robust results, permits reasonably low computational cost, and avoids other computational problems typical for polarizable force fields. It can be considered as a solid basis for building a more accurate and complete second-generation model. 相似文献
940.
Bioinspired growth of crystalline carbonate apatite on biodegradable polymer substrata 总被引:12,自引:0,他引:12
Mineralization in biological systems is a widespread, yet incompletely understood phenomenon involving complex interactions at the biomacromolecule-mineral nucleus interface. This study was aimed at understanding and controlling mineral formation in a poly(alpha-hydroxy ester) model system, to gain insight into biological mineralization processes and to develop biomaterials for orthopaedic tissue regeneration. We specifically hypothesized that providing a high surface density of anionic functional groups would enhance nucleation and growth of bonelike mineral following exposure to simulated body fluids (SBF). Polymer surface functionalization was achieved via hydrolysis of 85:15 poly(lactide-co-glycolide) (PLG) films. This treatment led to an increase in surface carboxylic acid and hydroxyl groups, resulting in a substantial increase in polymer surface energy from 42 to 49 dynes/cm2. Treated polymers exhibited a 3-fold increase in heterogeneous mineral grown and growth of a continuous mineral film on the polymer surface. The mineral grown on PLG surfaces is a carbonate apatite, the major mineral component of vertebrate bone tissue. Mineral crystal size and morphology were dependent on the solution characteristics but unaffected by the degree of surface prehydrolysis. The mechanism of heterogeneous carbonate apatite growth was examined via ion binding assays, which indicated that calcium binding is mediated independently by the presence of soluble phosphate counterions and surface functional groups. These findings indicate that poly(alpha-hydroxy ester) materials can be readily mineralized using a biomimetic process, and that the impetus for mineral nucleation in this system appears more complicated than the simple electrostatic interactions proposed in previous biomineralization theory. 相似文献