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1.
The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm,
Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of 137Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the
photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other
measured values. 相似文献
2.
3.
Paine TK Weyhermüller T Wieghardt K Chaudhuri P 《Dalton transactions (Cambridge, England : 2003)》2004,(14):2092-2101
Seven copper(II)-complexes 1-7 with the ligand 2,2'-selenobis(4,6-di-tert-butylphenol) providing [O,Se,O]-donor atoms have been isolated and characterized. Three of them 1, 2 and 3 are mononuclear, two 4 and 7 dinuclear and 5, 6 are trinuclear. The crystal structures of the complexes were determined by X-ray diffraction and the electronic structures were established by various physical methods including EPR and variable temperature (2-290 K) susceptibility measurements. The magnetic behaviour of the compounds 4-6 exhibits antiferromagnetic exchange coupling resulting in well-isolated S(t)= 1/2 ground state for 5 and 6 and a diamagnetic spin state for 4. Complexes 5 and 6 belong to the class of asymmetric trinuclear copper(II) complexes modelling the trinuclear copper site in multicopper oxidases. Complex 1 is a catalyst in the presence of a strong base for the aerial oxidation of primary alcohols to the corresponding aldehydes. A dinuclear complex, seemed to be 4, prepared in situ has been found to be a catalyst for the aerial oxidation of primary amines containing alpha-C-H atoms. Primary kinetic isotope effects show that H-abstraction from the alpha-carbon atom of a coordinated substrate (alcoholato or amine) is the rate-determining step in both cases. Two functional models for the metalloenzymes galactose oxidase and amine oxidases are thus described. 相似文献
4.
J.Y. Becker D. Dolphin J.B. Paine T. Wijesekera 《Journal of Electroanalytical Chemistry》1984,164(2):335-346
The interaction between two “spatially close” porphyrins plays important roles in biochemical functions. The present study focuses on the effects of distortion, steric hindrance, distance and orientation exerted by a variety of porphyrin monomers (strapped and capped) and dimers (mono- and doubly-linked) on their redox properties as well as the stability of positively charged intermediates derived from them. Cyclic voltammograms have been conducted in aprotic media on both free bases and their metal complexes (Zn and Mg). The effect of the nature of supporting electrolyte on the anodic peak potentials and wave separation has been studied in the case of conjugated directly-linked bis-zinc and bis-magnesium porphyrins. 相似文献
5.
The reaction of tris(trimethylsilyl)methylboron dihalides (Me3Si)3CBX2 (X = Cl, F) with the lithium phosphides LiPHtBu and LiPHmes leads to the phosphinoboranes (Me3Si)3CBX‐(PHR), (Me3Si)3CB(PHR)2 or the 1,3,2,4‐diphosphadiboretanes [(Me3Si)3CB(PR)]2, depending on the ratio of the reagents, the reaction temperature and concentration. High dilution and low temperatures are required for the synthesis of (Me3Si)3CB(Hal)PHR ( 1–3 ) in order to prevent the formation of (Me3Si)3CB(PHR)2 ( 4 and 5 ). The latter compounds are best prepared in a two step phosphination from (Me3Si)3CBHal2 and LiPHR. At higher temperatures the four‐membered 1,3,2,4‐diphosphadiboretanes [(Me3Si)3CB(PR)]2 6 and 7 are the most stable compounds. On the other hand, compounds of type (Me3Si)3CB(Hal)PR2, 8 and 9 , are thermally more stable than the monophosphinoboranes 1 – 3 . Phosphinoboranes of type (Me3Si)3CB(PR2)2 (R = tBu, mes) could not be prepared. NMR and mass spectral data are in accord with the monomeric nature of compounds 1 to 9 . 相似文献
6.
The trifunctional ligand 2,6-[(C6H5)2P(O)CH2]2 C5H3NO (1), in a mixed EtOH/MeOH solvent system, when combined with an aqueous nitric acid solution of Pu(IV), produces a 2:1 coordination complex, [Pu(1)2(NO3)2](NO3)2. A single crystal of [Pu(NO3)2(2,6-[(C6H5)2P(O)CH2]2C5H3NO)2](NO3)2x1.5H2Ox0.5MeOH was characterized by X-ray diffraction analysis. The crystal is monoclinic, space group P2(1)/n, with a = 19.1011(9) A, b = 18.2873(9) A, c = 21.507(1) A, alpha = gamma = 90 degrees, beta = 108.64(1) degrees, and Z = 4. Two neutral ligands (1) are bonded to the Pu(IV) ion in a tridentate fashion. Two nitrate ions also occupy inner sphere coordination positions, while two additional NO3- ions reside in the outer sphere. Comparison of the solution optical absorbance and solid diffuse reflectance spectra shows the same Pu(IV) chromophore exists in both solid and solution states. 相似文献
7.
Density functional theory calculations employing the B3LYP exchange-correlation functional, as well as Hartree–Fock computations, were performed on 2-hydroxy-2,4,6-cycloheptatrien-1-one (tropolone) and 3,5- and 3,6-cycloheptadiene-1,2-dione in gas and aqueous solution phases in order to determine the equilibrium constant for keto to enol interconversion of the isomers of C7H6O2. Two standard basis sets were used throughout, namely 6-311++G∗∗ and aug-cc-pVDZ. Solvent effects were modelled using two different self-consistent reaction field approaches – the Onsager dipole and the polarizable continuum models (PCM). In addition, the G3 method was used for calculations on species in the gas phase. Molecular geometries were fully optimized at each model chemistry, and it was found that the two keto isomers are always higher in energy than the enol form. From the results of B3LYP/6-311++G∗∗ calculations of the difference in Gibbs free energy in the gas phase and using PCM, the relative pK values for the 2-hydroxy-2,4,6-cycloheptatrien-1-one ? 3,5- and 3,6-cycloheptadiene-1,2-dione system are 13.75 (g), 15.78 (g) and 13.05 (aq) and 13.45 (aq), respectively. That equilibrium is tilted almost exclusively in the direction of tropolone is due to resonance stabilization of the enol as a result of aromaticity, and is most easily understood on the basis of elementary Hückel theory. 相似文献
8.
Robert T. Paine William F. McNamara Jerzy Fr. Janik Eileen N. Duesler 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):241-244
Abstract Aspects of the reactivity of metallophosphanes are presented along with the synthesis and structure determinations for new aluminophosphanes. 相似文献
9.
Lorraine M. Deck Robert T. Paine Elizabeth R. BrightSabrina Ouizem Diane A. Dickie 《Tetrahedron letters》2014
Simple, aqueous-based syntheses of methylpyridine and methylpyridine N-oxide decorated 3,4-dihydro-2H-naphthoxazine and 2,3-dihydro-1H-naphthoxazine monomers, as well as thermally promoted syntheses of 3,4-dihydro-2H-benzoxazine monomers and bisoxazine methylpyridine derivatives of substituted 1,5-, 2,6-, and 2,7-dihydroxynaphthalenes are described. The crystal structures of two derivatives are presented. 相似文献
10.
Oindrila Das Tanmay Malakar Arghya Mandal Dr. Ankan Paul Dr. Tapan Kanti Paine 《化学:亚洲杂志》2013,8(3):623-629
The synthesis and characterization of two pyrazolate‐bridged dicopper(II) complexes, [Cu2(L1)2(H2O)2](ClO4)2 ( 1 , HL1=3,5‐dipyridyl‐4‐(2‐keto‐pyridyl)pyrazole) and [Cu2(L2)2(H2O)2](ClO4)2 ( 2 , HL2=3,5‐dipyridyl‐4‐benzoylpyrazole), are discussed. These copper(II) complexes are formed from the reactions between pyridine‐2‐aldehyde, 2‐acetylpyridine (for compound 1 ) or acetophenone (for compound 2 ), and hydrazine hydrate with copper(II) perchlorate hydrate under ambient conditions. The single‐crystal X‐ray structure of compound 1? 2 H2O establishes the formation of a pyrazole ring from three different carbon centers through C? C bond‐forming reactions, mediated by copper(II) ions. The free pyrazoles (HL1 and HL2) are isolated from their corresponding copper(II) complexes and are characterized by using various analytical and spectroscopic techniques. A mechanism for the pyrazole‐ring synthesis that proceeds through C? C bond‐forming reactions is proposed and supported by theoretical calculations. 相似文献