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Solveig Kristensen Ruth Edge Hanne Hjorth Tønnesen Roger Hugh Bisby Suppiah Navaratnam 《Journal of photochemistry and photobiology. B, Biology》2009,94(3):147-157
The formation and reactivity of excited states and free radicals from primaquine, a drug used in the treatment of malaria, was studied in order to evaluate the primary photochemical reaction mechanisms. The excited primaquine triplet was not detected, but is likely to be formed with a short lifetime (<50 ns) and with a triplet energy <250 kJ/mol as the drug is an efficient quencher of the fenbufen triplet and the biphenyl triplet, and forms by laser flash photolysis . Primaquine (PQ) exists as the monocation in aqueous solution at physiological pH. photoionises by a biphotonic process and also forms the monoprotonated cation radical by one electron oxidation by (kq = 6.6 × 109 M?1 s?1) and (kq = 4.7 × 109 M?1 s?1) at physiological pH, detected as a long-lived transient decaying essentially by a second order process (k2 = 7.4 × 108 M?1 s?1). is scavenged by O2, although at a limited rate (kq = 1.0 × 106 M?1 s?1). The reduction potential (E°) of is < +1015 mV, as measured versus tryptophan (). Primaquine also forms at pH 2.4, by one electron oxidation by and proton loss (kq = 2.7 × 109 M?1 s?1). The non-protonated cation radical () is formed during one electron oxidation with at alkaline conditions (kq = 4.2 × 109 M?1 s?1 at pH 10.8). The estimated pKa-value of is pKa ~ 7–8. Primaquine is not a scavenger of at physiological pH. Thus self-sensitization by is eliminated as a degradation pathway in the photochemical reactions. Impurities in the raw material and photochemical degradation products initiate photosensitized degradation of primaquine in deuterium oxide, prevented by addition of the quencher sodium azide. Photosensitized degradation by formation of is thus important for the initial photochemical decomposition of primaquine, which also proceeds by free radical reactions. Formation of is expected to play an essential part in the photochemical degradation process in a neutral, aqueous medium. 相似文献
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The two new quaternary cesium copper(I) rare-earth metal(III) tellurides CsCu2Sc3Te6 and CsCuY2Te4 were prepared at 900 °C by reacting the elements copper, scandium or yttrium and tellurium together with CsBr as flux and cesium source for fourteen days in evacuated torch-sealed silica ampoules. Both compounds crystallize in space group C2/m of the monoclinic system with unit cells of the dimensions a = 1777.63(9), b = 414.20(2), c = 1033.51(5) pm, β = 113.032(4)° for CsCu2Sc3Te6 (Z = 2) and a = 3741.90(19), b = 432.73(2), c = 2087.62(11) pm, β = 107.357(4)° for CsCuY2Te4 (Z = 12). The crystal structure of the scandium compound contains [CuTe4]7? tetrahedra, which are cis-edge connected in order to build up chains, and [ScTe6]9? octahedra, which share edges and vertices in forming corrugated layers. These layers are separated from each other by [CuTe4]7? tetrahedra and Cs+ cations in trans-face bicapped square-prismatic Te2? coordination (CN = 10). The yttrium compound has a three-dimensional structure as well built up of [CuTe4]7? tetrahedra and [YTe6]9? octahedra. All three crystallographically independent Cu+ cations reside in an individual infinite chain, in which each [CuTe4]7? tetrahedron shares two vertices with neighbouring ones. The anionic framework and the copper-bearing one consist of sixteen-membered ring channels containing three different types of Cs+ cations (two in each channel) with bicapped trigonal prismatic (CN = 8) and monocapped cubic Te2? coordination (CN = 9). Thus there is no isotypy with the KCuGd2S4-type structure, characteristic for the lighter chalcogens (e. g. ACuM2Ch4; A = K–Cs, M = La–Er, Ch = S and Se). 相似文献
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《The Journal of chemical thermodynamics》2007,39(7):1090-1097
The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone + 2-propanol = cis- and trans-2-substituted cyclohexanol + acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T = 288.15 to 308.05 K. The thermodynamic quantities at T = 298.15 K are: K = (2.13 ± 0.06); ; ; and for the reaction involving cis-2-methylcyclohexanol, and K = (10.7 ± 0.2); ; ; and for the reaction involving trans-2-methylcyclohexanol. The standard molar Gibbs free energy changes for the reactions (trans-2-substituted cyclohexanol = cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereoselective. 相似文献
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《Journal of organometallic chemistry》2007,692(1-3):111-121
New hexadentate dinucleating ligands having a xylyl linker, X–L–R, were synthesized, where X–L–R = 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl]-2,4,6-trimethybenzene (Me2–L–Me) and 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl]-2-fluorobenzene (H–L–F). They form dinuclear copper(I) complexes, [Cu2(X–L–R)]2+ (Me2–L–Me (1) and H–L–F (2)). The copper(I) complexes in acetone at −78 °C react with O2 to produce intra- and intermolecular (μ-η2:η2-peroxo)dicopper(II) species depending on the concentrations of the complexes: both complexes generate intramolecular (μ-η2:η2-peroxo)dicopper(II) species [Cu2(O2)(X–L–R)]2+ (1-O2 and 2-O2) at the concentrations below ∼5 mM, whereas at ∼60 mM, both complexes produce intermolecular (μ-η2:η2-peroxo)dicopper(II) species, which were confirmed by the electronic and resonance Raman spectroscopies. The electronic spectrum of 1-O2 in acetone at concentrations below ∼5 mM showed an absorption band at (λmax = 442 nm, ε = 5600 M−1 cm−1) assignable to the (O–O)-to-Cu(II) ( component) LMCT transition in addition to an intense band attributable to the (O–O)-to-Cu(II) ( component) LMCT transition (λmax = 359 nm, ε = 21000 M−1 cm−1), indicating that the (μ-η2:η2-peroxo)Cu(II)2 core of 1-O2 takes a butterfly structure. Decomposition of 1-O2 resulted in hydroxylation of the 2-position of the xylyl linker with 1,2-methyl migration (NIH shift), suggesting that the hydroxylation reaction proceeds via a cationic intermediate as proposed for closely related (μ-η2:η2-peroxo)Cu(II)2 complexes having a xylyl linker. Kinetic study of the decomposition (hydroxylation of the xylyl linker) of 1-O2 suggests that a stereochemical effect of the methyl group in the 2-position of the xylyl linker has a significant influence on a transition state for decomposition (hydroxylation of the xylyl linker). 相似文献
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Phase relations in the system (chromium + rhodium + oxygen) at T = 1273 K have been determined by examination of equilibrated samples by optical and scanning electron microscopy, powder X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Only one ternary oxide, CrRhO3 with rhombohedral structure (, a = 0.5031, and c = 1.3767 nm) has been identified. Alloys and the intermetallics along the (chromium + rhodium) binary were in equilibrium with Cr2O3. The thermodynamic properties of the CrRhO3 have been determined in the temperature range (900 to 1300) K by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the electrolyte. For the reaction,where Cr2O3 has the corundum structure and Rh2O3 has the orthorhombic structure. Thermodynamic properties of CrRhO3 at T = 298.15 K have been evaluated. The compound decomposes on heating to a mixture of Cr2O3-rich sesquioxide solid solution, Rh, and O2. The calculated decomposition temperatures are T = 1567 ± 5 K in pure O2 and T = 1470 ± 5 K in air at a total pressure p° = 0.1 MPa. The temperature-composition phase diagrams for the system (chromium + rhodium + oxygen) at different partial pressures of oxygen and an oxygen potential diagram at T = 1273 K are calculated from the thermodynamic information. 相似文献
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Essmaiil Djamali Keith Chen James W. Cobble 《The Journal of chemical thermodynamics》2009,41(9):1035-1041
Standard state thermodynamic properties for aqueous sodium perrhenate at temperature in the range of (298.15 to 598.15) K and at psat were determined by high dilution solution calorimetry down to 10?4 m. Standard state partial molar heat capacities, , of aqueous sodium perrhenate calculated from present study are compared to literature values up to T = 398.15 K. The differences between of and Cl?(aq) at lower temperature is much greater than that due to their internal molecular motions. Consequently, the perrhenate ion appears to have an ionic incomplete primary hydration shell as compared to the chloride ion. The difference in thermodynamic functions has now been well defined up to T = 598.15 K for other important high temperature calculations. 相似文献
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