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721.
de Groot FM Glatzel P Bergmann U van Aken PA Barrea RA Klemme S Hävecker M Knop-Gericke A Heijboer WM Weckhuysen BM 《The journal of physical chemistry. B》2005,109(44):20751-20762
1s2p resonant inelastic X-ray scattering (RIXS) spectroscopy has been measured for a series of iron oxides, including octahedral and tetrahedral Fe(II) and Fe(III) systems. Their spectral shapes have been analyzed and explained using crystal-field multiplet simulations. The RIXS planes and the K-edge and L-edge X-ray absorption spectra related to these RIXS planes will be discussed with respect to their analytical opportunities. It is concluded that the full power and possibilities of 1s2p RIXS needs an overall resolution of 0.3 eV. This will yield a technique with more detailed information than K-edge and L-edge X-ray absorption combined, obtained in a single experiment. Another major advantage is that 1s2p RIXS involves only hard X-rays, and experiments under essentially any condition and on any system are feasible. 相似文献
722.
Carravetta M Zhao X Johannessen OG Lai WC Verhoeven MA Bovee-Geurts PH Verdegem PJ Kiihne S Luthman H de Groot HJ deGrip WJ Lugtenburg J Levitt MH 《Journal of the American Chemical Society》2004,126(12):3948-3953
We have obtained carbon-carbon bond length data for the functional retinylidene chromophore of rhodopsin, with a spatial resolution of 3 pm. The very high resolution was obtained by performing double-quantum solid-state NMR on a set of noncrystalline isotopically labelled bovine rhodopsin samples. We detected localized perturbations of the carbon-carbon bond lengths of the retinylidene chromophore. The observations are consistent with a model in which the positive charge of the protonated Schiff base penetrates into the polyene chain and partially concentrates around the C13 position. This coincides with the proximity of a water molecule located between the glutamate-181 and serine-186 residues of the second extracellular loop, which is folded back into the transmembrane region. These measurements support the hypothesis that the polar residues of the second extracellular loop and the associated water molecule assist the rapid selective photoisomerization of the retinylidene chromophore by stabilizing a partial positive charge in the center of the polyene chain. 相似文献
723.
An upper-rim-substituted calix[4]arene tetracarboxylic acid forms hydrogen-bonded duplexes with lower-rim-substituted tetra(4-pyridyl)- and tetra(3-pyridyl)calix[4]arenes in chloroform. The formation of these adducts was studied by extraction experiments. The association constants determined via (1)H NMR dilution experiments in CDCl(3) are 7.6 x 10(3) and 1.3 x 10(3) M(-1) for the 4-pyridyl and the 3-pyridyl derivative, respectively. IR studies in the solid state and in solution indicate that the interaction is based on hydrogen bonding and that the degree of proton transfer is negligible. VPO measurements support the formation of 1:1 adducts. 相似文献
724.
Gamez P de Hoog P Roubeau O Lutz M Driessen WL Spek AL Reedijk J 《Chemical communications (Cambridge, England)》2002,(14):1488-1489
Copper(II) nitrate reacts with the rigid polydentate triple-connecting dpyatriz ligand in acetonitrile to an unprecedented infinite molecular ladder in which five-coordinated copper pseudo-dimer are bridged by nitrate anions and the coordination polymer chains are linked by hexacoordinated copper ions leading to the formation of large guest cavities. 相似文献
725.
Powell KA Ramer SW Del Cardayré SB Stemmer WP Tobin MB Longchamp PF Huisman GW 《Angewandte Chemie (International ed. in English)》2001,40(21):3948-3959
This review describes the current state of biocatalysis in the chemical industry. Although we recognize the advantages of chemical approaches, we suggest that the use of biological catalysis is about to expand dramatically because of the recent developments in the artificial evolution of genes that code for enzymes. For the first time it is possible to consider the rapid development of an enzyme that is designed for a specific chemical reaction. This technology offers the opportunity to adapt the enzyme to the needs of the process. We describe herein the development of enzyme evolution technology and particularly DNA shuffling. We also consider several classes of enzymes, their current applications, and the limitations that should be addressed. In a review of this length it is impossible to describe all the enzymes with potential for industrial exploitation; there are other classes, which given appropriate activity, selectivity, and robustness, could become useful tools for the industrial chemist. This is an exciting era for biocatalysis and we expect great progress in the future. 相似文献
726.
Charles B. de Koning Joseph P. Michael Rakhi Pathak Willem A.L. van Otterlo 《Tetrahedron letters》2004,45(6):1117-1119
The synthesis of fused isoquinolines from N-benzyl protected indoles and pyrroles is described. For example, treatment of t-butyl-2-(2-formyl-3,4-dihydro-1-naphthalenyl)-3-methyl-1H-indole-1-carboxylate with KOBut in DMF provided 14-methyl-8-phenylbenzo[h]indolo[2,1-a]isoquinoline in good yield. Analogous N-benzylpyrrole precursors could similarly be cyclized to give pyrrolo[2,1-a]isoquinolines. 相似文献
727.
Measuring reaction kinetics in a lab-on-a-chip by microcoil NMR 总被引:5,自引:0,他引:5
Wensink H Benito-Lopez F Hermes DC Verboom W Gardeniers HJ Reinhoudt DN van den Berg A 《Lab on a chip》2005,5(3):280-284
A microfluidic chip with an integrated planar microcoil was developed for Nuclear Magnetic Resonance (NMR) spectroscopy on samples with volumes of less than a microliter. Real-time monitoring of imine formation from benzaldehyde and aniline in the microreactor chip by NMR was demonstrated. The reaction times in the chip can be set from 30 min down to ca. 2 s, the latter being the mixing time in the microfluidic chip. Design rules will be described to optimize the microreactor and detection coil in order to deal with the inherent sensitivity of NMR and to minimize magnetic field inhomogeneities and obtain sufficient spectral resolution. 相似文献
728.
Bert Vanhaecht Bart Rimez Rudolph Willem Monique Biesemans Cor E. Koning 《Journal of polymer science. Part A, Polymer chemistry》2002,40(12):1962-1971
The effects of the partial substitution of 1,4‐disubstituted cyclohexane monomers for linear aliphatic monomers in polyamides are discussed. More specifically, the relation between the stereochemistry of the cycloaliphatic residues and the thermal properties [melting temperature (Tm) and crystallization temperature (Tcr)] was investigated. For this purpose, two different types of copolyamides were synthesized: in polyamides 12.6, the adipic acid residues were partially replaced by cis/trans‐1,4‐cyclohexanedicarboxylic acid (1,4‐CHDA), whereas in polyamides 4.14, the 1,4‐diaminobutane residues were partially substituted with cis/trans‐1,4‐diaminocyclohexane (1,4‐DACH). For both systems, increasing the degree of substitution of cycloaliphatic residues for linear aliphatic residues resulted in a rise of both Tm and Tcr. This points to the isomorphous crystallization of the linear and cycloaliphatic residues. In contrast to the use of 1,4‐DACH as a comonomer, 1,4‐CHDA residues showed isomerization upon thermal treatment of the polyamides. This isomerization of the cyclohexane residues influenced the thermal properties of the copolyamides. The use of a nonisomerizing cis–trans mixture of 1,4‐DACH exhibited the large influence of the stereochemistry of the cycloaliphatic residues on the Tm of the copolyamides. For both the 1,4‐CHDA‐ and 1,4‐DACH‐based copolyamides, differential scanning calorimetry analysis revealed that recrystallization occurs during melting. This exothermal effect becomes less pronounced with an increasing content of rigid cycloaliphatic residues. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1962–1971, 2002 相似文献
729.
Ion cyclotron resonance studies using deuterium labelled substrates have revealed a more complex mechanism than previously proposed for the structure-specific ion/molecule reaction of the [C2H4O]+˙ and [C3H6O]+˙ enol ions with neutral cyclobutanol. This requires the intermediacy of a species in which all of the methylene groups present in both the reactant ion and neutral can become equivalent. 相似文献
730.
The pyrazole derivatives of aminoethane N,N-bis(3,5-dimethyl-1-pyrazolyl- methyl)aminoethane (aebd) and N,N-bis(1-pyrazolylmethyl)aminoethane (aebp) form co- ordination compounds with copper(I) of stoichiometry [Cu(L)X], with X = Cl, Br, I and SCN, and [Cu(L)2X], with X = CF3SO3 and BF4. The ligands chelate in a bidentate manner, with only the pyrazole groups coordinating. The crystal structures of two representative examples have been determined: [Cu(aebp)Cl]2 is triclinic, space group P
, with a = 8.711(2), b = 9.351(1) and c = 9.528(1) Å, = 68.57(1)°, β = 61.47(1)° and γ = 77.82(1)°, and Z = 2. Standard least-squares refinement gave R = 0.029 (Rw = 0.038) for 1804 reflections. [Cu(aebp)2]CF3SO3 is monoclinic, space group P21/n, with a = 13.352(5), b = 14.663(3) and c = 15.752(4) Å, β = 117.49(3)°, and Z = 4. Standard least-squares refinement gave R = 0.029 (Rw = 0.032) for 1786 reflections. In both cases the copper environment is slightly-distorted tetrahedral. The chloride compound is dimeric with one ligand molecule (Cu---N distances of 2.011(2) and 2.047(2) Å) and two bridging chlorides per copper (Cu---Cl distances of 2.3874(8) and 2.4094(8) Å). With the non- coordinating triflate anion, a monomeric compound with two ligand molecules per copper was obtained (Cu---N distances of 2.018(4), 2.028(4), 2.049(4) and 2.050(4) Å). 相似文献