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11.
The subject of proton transfer between carbon acids and nitrogen bases in aprotic solvents is reviewed. Equilibrium and rate constants that characterize such reactions are most often determined utilizing UV-visible spectrophotometry. At ambient temperature reaction rates are sufficiently rapid that fast reaction methods, for example, the stopped-flow and temperature-jump techniques are required in many cases. Variation of the properties of the donor and acceptor reaction pairs enables electronic and steric effects upon thermodynamic and kinetic parameters of proton transfer to be assessed. Determination of the kinetic isotope effect (KIE), i.e. k(protium)/k(deuterium) led to the conclusion that, under certain circumstances and when the KIE is greater than seven, the proton undergoes reaction with a significant degree of quantum mechanical tunneling, consistent with a theoretical prediction advanced several decades earlier. In fact this aspect may be one of the most significant outgrowths of these studies. Many reactions have been characterized (by tunneling) but rarely are the reacting systems experimentally amenable to obtaining all the experimental criteria that support tunneling. Controversy that has arisen regarding treatment of experimental data and resulting conclusions from them is visited in this review. The structural nature of the product state of reaction is formulated based on spectroscopic evidence, in favorable cases, and probable structures of the transition state can be inferred. 相似文献
12.
Sarah C. Hubbard 《Tetrahedron》2005,61(31):7425-7430
The preparation and investigation of triplet photosensitizers designed to be preferentially soluble in room-temperature ionic liquids are reported. Photosensitizers prepared by covalent attachment of 1-methylimidazole to aryl ketones are soluble in ionic liquids and remain in the ionic liquid layer when the solution is extracted with an organic solvent. The photosensitized isomerization of trans-β-ionol to cis-β-ionol was efficiently carried out in ionic liquid solution with the product ionol being extracted and the sensitizer/ionic liquid mixture being re-used in additional photosensitization reactions. The scope and utility of the sensitizers in sensitizing other reactions are discussed. 相似文献
13.
Peter J. Stiles Michael Kagan Joseph B. Hubbard 《Journal of colloid and interface science》1987,120(2)
A theory for the stabilizing influence of an axial external magnetic field on a magnetic colloid engaged in cylindrical Couette flow is presented. For the case of a narrow gap, analytical expressions which predict the magnetic field dependences of the critical wavelength and the critical Taylor number at the onset of cellular Taylor flow are obtained. 相似文献
14.
Recently we characterised a novel 29 kDa endoplasmic reticulum protein that is widely expressed in rat tissues, and named it ERp29. Several ERp29-like gene products have been reported in human tissues but uncertainty surrounds their relationships with each other and rat ERp29. To clarify these issues, ERp29 was isolated from human liver and characterised by primary structural analysis and two-dimensional gel mapping. Comparisons with rat ERp29 revealed striking homologies both in sequence and physical properties. Characterisation of the isoelectric heterogeneity and anomalous mass on two-dimensional gels enabled two reported homologues (UL35 and ERp31) to be identified as ERp29. Resolution of a sequence discrepancy led to unequivocal correlation of human ERp29 with the cognate cDNA previously named ERp31 and ERp28. Consequent links established to human genome and proteome projects showed that ERp29 is encoded by a gene on chromosome 12 that is expressed universally in human tissues. Together, these findings unified various ERp29 homologues as products of a single gene orthologous to rat ERp29 and established ERp29 as the only known member of a new protein class. Investigations of ERp29 function in human health and disease should benefit from the integrated links between genome, proteome and murine model organisms established here. 相似文献
15.
The Iteraltive Extended Hückel Molecular Orbital method has been adapted to calculation of the properties of an electrode and compact layer. Predictions of the stablest orientations, on the Pt(111) surface of species such as H2O, Pt, OH?, H, and the halides, F?, Cl?, Br? and I?, based upon calculation of the total energy corresponding to various internuclear distances, are reported. The calculations correctly predict self-adsorption of Pt on the Pt(111) surface at the face-centered cubic closest-packing position. The H2O molecule is predicted to locate itself above three adjoining Pt atoms, with the O atom closest to the surface and the H atoms opposite the O. Similar results were obtained for OH? and the halides. Atomic H, however, is predicted to drop into the plane of centers of the Pt surface atoms, where it would lie between, three adjacent Pt atoms. Application of the method to electrode studies requires only modest amounts of computer time but produces surprisingly reliable qualitative predictions. Compulation of electrochemical quantities such as charge, differential capacitance, surface tension and potential energy as a function of electrode potential will be described in future work. 相似文献
16.
Straub PB Jaffe DE Glass HD Adams MR Brown CN Charpak G Cooper WE Crittenden JA Finley DA Gray R Hemmi Y Hsiung YB Hubbard JR Jonckheere AM Jöstlein H Kaplan DM Lederman LM Luk KB Maki A Mangeot P McCarthy RL Miyake K Plaag RE Rutherfoord JP Sakai Y Santiard JC Sauli F Smith SR Yoshida T Young KK 《Physical review letters》1992,68(4):452-455
17.
Microwave transitions up to J = 53 in the ground vibrational state of deuterothioformaldehyde, CD2S, were studied between 8 and 40 GHz. A detailed centrifugal distortion analysis yields accurate constants for comparison with force field values. The isotopic species 13CH2S, CH234S, CH233S, 13CD2S, CD234S, and CD233S were studied in natural abundance. Accurate average zero-point structures were determined for both CD2S and CH2S: Changes in the zero-point geometry for deuterium substitution were established. Quadrupole fine structure arising from the 33S nucleus has been measured in CH233S and CD233S. Analysis gives the following coupling constants (for both molecules) as χaa = ?11.7 and χbb - χcc = 88.1 MHz. The dipole moment of CD2S was measured to be 1.6588(8)D and an accurate comparison with CH2S was made; the ratio of dipole moments was found to be 1.0062(4). The spectroscopic and bonding properties of CH2S will be compared with formaldehyde and other molecules. 相似文献
18.
Björn C.G. Söderberg Jeremiah W. Hubbard Stacey R. Rector Shannon N. O'Neil 《Tetrahedron》2005,61(15):3637-3649
A route to 3,4-fused indoles via two consecutive palladium-catalyzed reactions; an intramolecular Heck reaction followed by a reductive N-heteroannulation is described. Using this route, a number of indoles have been prepared having a variety of ring sizes anchored to the 3- and 4-position of the indole nucleus. Furthermore, a number of functional groups, both carbon and heteroatom substituents can be introduced in (and on) the additional ring without any detrimental effects on the two reactions. 相似文献
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