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951.
The parent amido iron complex (dmpe)2Fe(H)(NH2) (dmpe = 1,2-bis(dimethylphosphino)ethane), the first such first-row transition metal complex, has been synthesized and characterized spectroscopically and crystallographically. This complex has been found to insert carbon monoxide into the amide N-H bond (rather than the M-N bond) to give trans-(dmpe)2Fe(H)(NHCHO). The mechanism of this transformation has been studied and is believed to occur through an unusual mechanism in which CO behaves as an apparent electrophile. 相似文献
952.
Porous materials resembling zeolites that are composed of organic and inorganic building units were synthesized and characterized. Control of pore and channel size was achieved by using different-sized cations. The metal-assembled, anionic cage molecule, Co(4)1(2)(8-), with a hydrophobic cavity and four carboxylate rich arms, was used as a structural unit for the formation of materials with pores and channels. When assembled into a solid material with dications (Mg(2+), Ca(2+), Sr(2+), and Ba(2+)), Co(4)1(2)(8-) arranges into sheets of cages linked together by cations. The series of materials based on Co(4)1(2)(8-) and containing alkaline earth cations was characterized using X-ray crystallography. The magnesium material packs with cages close together, has small channels, and has cation-carboxylate linkages in three dimensions. The calcium material has cages packed with voids between them and has 5 x 10 A channels and 10 x 21 A pores. The strontium and barium materials also pack with voids between the cages and similarly to each other. They have 11 x 13 A and 11 x 11 A channels and 10 x 27 A and 9 x 27 A pores, respectively. Each of these materials has many (20-50) solvent water molecules associated with each cage. The associated water can be removed from and adsorbed by the materials. The heat of water binding has been measured to be -52 kJ/mol (Mg(4)Co(4)1(2)); -47 kJ/mol (Ca(4)Co(4)1(2)); -48 kJ/mol (Sr(4)Co(4)1(2)); -49 kJ/mol (Ba(4)Co(4)1(2)). 相似文献
953.
Sension RJ Cole AG Harris AD Fox CC Woodbury NW Lin S Marsh EN 《Journal of the American Chemical Society》2004,126(6):1598-1599
Ultrafast spectroscopic measurements are used to determine the kinetics of homolysis and recombination for adenosylcobalamin bound in the active site of glutamate mutase. These are the first such measurements on an adenosylcobalamin-dependent enzyme. A short-lived intermediate is formed prior to formation of the cob(II)alamin radical. This intermediate was not observed upon photolysis of adenosylcobalamin in free solution. The intrinsic rate constant for geminate recombination for adenosylcobalamin bound to glutamate mutase is 1.08 +/- 0.10 ns-1, only 16% smaller than the rate constant measured in free solution, 1.39 +/- 0.06 ns-1, suggesting the protein does not greatly perturb the stability of the cobalt-carbon bond upon binding the coenzyme. 相似文献
954.
Nanoscaled TiO2 powders with narrow size dispersion were prepared in supercritical carbon dioxide via non-hydrolytic acylation/deacylation of titanium alkoxide precursors with or without tris-fluorination. The microstructures of these powders were characterized by spectroscopic (FTIR, TGA, and XRD), microscopic (SEM or TEM), and surface area (BET) measurements. Photocatalytic oxidation of 1-octanol on these calcined TiO2 powders and on commercial T805 TiO2 suspended in aerated supercritical carbon dioxide revealed relative reactivity controlled by the powder microstructures. Calcined TiO2 prepared from titanium(IV) isopropoxide and trifluoroacetic anhydride was effectively dispersed in aerated supercritical carbon dioxide under stirring and exhibited high photocatalytic oxidation activity. 相似文献
955.
K. Fox 《Journal of Quantitative Spectroscopy & Radiative Transfer》1970,10(12):1335-1342
A rigorous calculation of the quantum-mechanical rotational partition function for tetrahedral XY4 molecules yields Qr = (
)(2IY + 1)4π
-
exp(/4), where IY is the spin of the Y nucleus, and ≡ Bhc/kT. This result is accurate to 1 per cent or better for all values of B and T such that <
. 相似文献
956.
The use of adsorptive chromatography for preparative nucleic acid separations is often limited by low capacity. The possibility that the adsorbent surface area sterically accessible to nucleic acid molecules could be increased by reducing their radius of gyration with compaction agents has been investigated. The equilibrium adsorption capacity of Q Sepharose anion-exchange matrix for plasmid DNA at 600 mM NaCl was enhanced by up to ca. 40% in the presence of 2.5 mM spermine. In addition, compaction agent selectivity has been demonstrated. Spermine, for example, enhances the adsorption of both plasmid and genomic DNA, spermidine enhances binding only of plasmid, and hexamine cobalt enhances only the binding of genomic DNA. Compaction may be generally useful for enhancing adsorptive separations of nucleic acids. 相似文献
957.
Reaction of 2-formyl-2-(2,3-O-isopropylidene-5-O-trityl-D-ribofuranosyl)acetonitrile (VII) with semicarbazide hydrochloride followed by sodium ethoxide treatment afforded an α,β-mixture of 3-amino-2N-carbamoyl-4-(2,3-O-isopropylidene-5-O-trityl-D-ribofuranosyl)pyrazole (IX). Conversion of IX to 4-oxo-8-(2,3-O-isopropylidene-5-O-trityl-D-ribofuranosyl)-3H-pyrazolo[1,5-a]-1,3,5-triazine (XIII) was achieved by treatment of IX with ethylorthoformate. The β-isomer IXb gave only the β-isomer XIIIb, and the α-isomer IXa was converted exclusively into the α-isomer XIIIa. Upon deprotection with 3% n-butanolic hydrogen chloride, both IXa and IXb gave the same mixture of the α- and β-isomers of 3-amino-2N-carbamoyl-4-(D-ribosyl)pyrazole, which were separated by chromatography. The syntheses of the hitherto unknown compounds, 3-amino-2N-carbamoylpyrazole (IVa) and its 4-methyl analog (IVb) are also reported. Experimental details of the synthesis of 3-amino-4-(2,3-O-isopropylidene-5-O-trityl-β-D-ribofuranosyl)pyrazole (XIIb), an important intermediate for “purine-like” C-nucleosides, are also described. 相似文献
958.
Electrical-conductance measurements have been made at 25° C up to concentrations of 0.06M in aqueous solutions of Na2SO4 at atmospheric pressure and as a function of pressure up to 2000 atm. Calculations of the change of the dissociation constant for the NaSO 4 ? ion pair with pressure indicate that the difference in partial molal volumes between products and reactants at infinite dilution is \(\Delta \bar V^ \circ \tilde = - 8.25{\text{ }}cm^3 /mole\) . Using the equation of Davies, Otter, and Prue, we found the average dissociation constants for five concentrations between 0.005 and 0.06 moles/liter to be 0.097, 0.131, and 0.165 at 1, 1000, and 2000 atm, respectively, with a standard deviation of ±0.003. The atmospheric-pressure value is 0.080±0.016 over the entire concentration range from 0.00005 to 0.06 moles/liter, about half that obtained by Jenkins and Monk. This is consistent with a value ofK=0.077±0.006 recalculated from the limited-concentration-conductance work of Jenkins and Monk, with a value ofK=0.073 obtained by Fisher from data of Kurtze and Tamm on ultrasonic absorption in MgSO4?NaCl solutions, and withK=0.067 calculated by Fisher from the potentiometric data of Pytkowicz and Kester at high ionic strength. The relationship of this work to sound absorption and ion pairing in seawater is discussed. The predicted pressure dependence of the NaSO 4 ? ion pair in seawater from this work differs substantially from earlier work by Kester and Pytkowicz and by Millero. 相似文献
959.
The proteinoid cells are assembled of thermal polymers of amino acids. Typically, an appropriate mixture of amino acids containing
aspartic or glutamic acid is heated at 190°C for 6 h, stirred with water for 2 h, dialyzed during 2 d, and lyophilized. Spheroidal
cells are made from such polymer by dissolving it in the water by boiling, and then cooling. Many of them can be made by sonication
at room temperature.
These artificial cells, ranging from microns to tens of microns in diameter (depending on composition and preparation), have
double membranes and various internal compositions. The spherules can microencapsulate dyes, oxidant-reductant compounds or
acceptor-donor substances, and can be packed together.
Such spherules display electrical polarization and electrical discharges and respond to intra- and extracellular ionic and
electric influence upon membrane and action potential. These properties arise from the double membrane structure, asymmetric
membrane permeability, and channeling phenomena.
Such features as exponential dependence of the steady-state conductance and capacitance as well as negative resistance of
the membrane seem to be responsible for the flip-flop alternations of the membrane polarization, rhythmic electric oscillations,
and all-or-none action potentials.
The presence of such chromophores as pteridine and flavin in polymers constituting these cells is responsible for their photosensitivity. 相似文献
960.
M. Anpo T. Nomura T. Kitao E. Giamello D. Murphy M. Che M. A. Fox 《Research on Chemical Intermediates》1991,15(3):225-237
Cu2+ ions supported on SiO2 (Cm2+ /SiO2) prepared by an ion-exchange method are reduced to Cu+ when Cu2+/SiO2 samples are evacuated at temperatures higher than 573 K Reduced Cu2+ ions on SiO2 (Cu+/SiO2 catalyst) decomposes NO molecules photocatalytically and stoichiometrically into N2 and O2 at 275 K. The physicochemical and photochemical properties of copper ions anchored onto SiO2 have been investigated by means of ESR and dynamic photoluminescence spectroscopies, as well as the analysis of photoreaction
products. These results indicate that the excited state of the copper ions (Cu+ species) plays a significant role in the photocatalytic decomposition of NO molecules and the photoreaction involves an electron
transfer from the excited state of the Cu+ ion into an anti-bonding π orbital of NO molecule within the lifetime of its excited state. Thus, the present results obtained
with the Cu+/SiO2 catalysts imply the possibility of their utilization as a potentially promising type of photocatalysts in gas-solid systems. 相似文献