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31.
Liu Y Gallo AA Xu W Bajpai R Florián J 《The journal of physical chemistry. A》2011,115(41):11162-11166
The role of the nonbonded CH···π interaction in the hydrogen abstraction from glycerol by the coenzyme B(12)-independent glycerol dehydratase (GDH) was examined using the QM/MM (ONIOM), MP2, and CCSD(T) methods. The studied CH···π interaction included the hydrogen atom of the -C(2)H(OH)- group of the glycerol substrate and the tyrosine-339 residue of the dehydratase. A contribution of this interaction to the stabilization of the transition state for the transfer of a hydrogen atom from the adjacent terminal C(1)H(2)(OH) group to cysteine 433 was determined by ab initio HF, MP2, and CCSD(T) calculations with the aug-cc-pvDZ basis set for the corresponding methane/benzene, methanol/phenol, and glycerol radical/phenol subsystems. The calculated CH···π distance, defined as the distance between the H atom and the center of the phenol ring, shortened from 2.62 to 2.52 ? upon going from the ground- to the transition-state of the GDH-catalyzed reaction. However, this shortening was not accompanied by the expected lowering of the CH···π interaction free energy. Instead, this interaction remained weak (about -1 kcal/mol) along the entire reaction coordinate. Additionally, the mutual orientation of the CH group and the phenol ring did not change significantly during the reaction. These results suggest that the phenol group of the tyrosine-339 does not contribute to lowering the activation barrier in the enzyme, but do not exclude the possibility that tyrosine 339 facilitates proper orientation of glycerol for the electrostatic catalysis, or inhibits side-reactions of the reactive glycerol radical intermediate. 相似文献
32.
The development of an innovative method to access enantiopure 2,4-disubstituted 6-hydroxy-1,6-dihydro-2H-pyridin-3-ones starting from D-glucal via the aza-Achmatowicz transformation has been described. These highly functionalized pyridin-3-ones have been utilized for the synthesis of contiguously substituted pyridines through a rapid and efficient Et(3)N/Ac(2)O promoted cyclo-elimination, aromatization cascade, allowing the facile assembly of important pyridine-based building blocks like 2-substituted 3-acetoxy-4-iodopyridines and enantiopure 2-substituted 3-acetoxy-4-pyridinemethanols possessing benzylic stereogenic centers, whose synthesis otherwise would be tedious. The utilization of commercially available sugars as starting materials, mild reaction conditions, catalytic transfer hydrogen (CTH) of α-furfuryl azide derivatives, transfer of chiral aryl/alkyl methanols from enulosides to pyridin-3-ones and pyridines, high yields, and short reaction times are key features of this method. The utility of the method has been further exemplified by demonstrating the usage of the 2-substituted 3-acetoxy-4-iodopyridine for the construction of biologically significant molecules like 2,7-disubstituted furo[2,3-c]pyridines and 7,7'-disubstituted 2,2'-bifuro[2,3-c]pyridines. 相似文献
33.
Karasch Christian Popovic Milan Qasim Mohamed Bajpai Rakesh K. 《Applied biochemistry and biotechnology》2002,98(1-9):1173-1185
Data for alkali hydrolysis of 2,4,6-trinitrotoluene (TNT) in aqueous solution at pH 12.0 under static (pH-controlled) as well
as dynamic (pH-uncontrolled) conditions are reported. The experiments were conducted at two different molar ratios of TNT
to hydroxyl ions at room temperature. The TNT disappeared rapidly from the solution as a first-order reaction. The complete
disappearance of aromatic structure from the aqueous solution within 24 h was confirmed by the ultraviolet-visible (UV-VIS)
spectra of the samples. Cuvet experiments in a UV-VIS spectrophotometer demonstrated the formation of Meisenheimer complex,
which slowly disappeared via formation of aromatic compounds with fewer nitro groups. The known metabolites of TNT were found
to accumulate only in very small quantities in the liquid phase. 相似文献
34.
Ambar Sengupta 《Communications in Mathematical Physics》1997,183(3):661-705
The quantum field measure for gauge fields over a compact surface with boundary, with holonomy around the boundary components
specified, is constructed. Loop expectation values for general loop configurations are computed. For a compact oriented surface
with one boundary component, let be the moduli space of flat connections with boundary holonomy lying in a conjugacy class in the gauge group G. We prove that a certain natural closed 2-form on , introduced in an earlier work by C. King and the author, is a symplectic structure on the generic stratum of for generic . We then prove that the quantum Yang-Mills measure, with the boundary holonomy constrained to lie in , converges in a natural sense to the corresponding symplectic volume measure in the classical limit. We conclude with a
detailed treatment of the case , and determine the symplectic volume of this moduli space.
Received: 30 June 1996 / Accepted: 22 July 1996 相似文献
35.
S. D. Bajpai 《Proceedings Mathematical Sciences》1968,68(6):285-290
In this paper we have derived some expansions for G-function involving Bessel functions with the help of the orthogonality property of Bessel functions. 相似文献
36.
Summary Mixed valence (thiosemicarbazone)2CuII-CuI complexes were prepared and their e.p.r. spectra in the polycrystalline state studied. Complexes derived from acetophenone- and propiophenonethiosemicarbazones exhibit strong copper(II)-copper(II) and copper(II)-copper(I) interactions, whereas those derived from benzyl methyl ketone and cyclohexanone show strong copper(II)-copper(I) interaction but almost no copper(II)-copper(II) interaction. 相似文献
37.
The reduction mechanism of speckles appearing in laser-microscope images is studied theoretically and experimentally when an object is illuminated by laser light through a rotating multimode optical fiber. The principle of the speckle reduction is based on independent addition of microscope images with boiling-like speckles as a result of the rotational motion of the optical fiber used for illumination. Especially, the speckle reduction is evaluated from first-order statistics of the speckle intensity in which its saturation effect is taken into consideration. 相似文献
38.
Manisha Bajpai Kusum Kumari Ritu Srivastava M.N. Kamalasanan R.S. Tiwari Suresh Chand 《Solid State Communications》2010,150(13-14):581-584
The current density–voltage () behavior of polymer PDY 132 thin films has been investigated in hole-only device configuration, viz., ITO/poly(ethylene-dioxthiophene):polystyrenesulphonate (PEDOT:PSS)/PDY 132/Au, as a function of polymer (PDY) film thickness (150 nm and 200 nm) and temperature (290–90 K). Hole current density was found to follow two distinct modes of conduction, (i) low electric field region I: ohmic conduction where slope , and (ii) intermediate and high electric field region II: non ohmic conduction where slope . Region I has been attributed to the transport of intrinsic background charge carriers while region II has been found to be governed by space charge limited currents (SCLC) with hole mobility strongly dependent on electric field and temperature. The respective hole transport parameters determined from the SCLC regime, is , is , and zero field activation energy () of 0.48 eV is obtained. 相似文献
39.
M. E. O. Hughes A. C. Bajpai 《International Journal of Mathematical Education in Science & Technology》2013,44(2):131-134
For a long time schools have been finding it difficult to appoint sufficient numbers of teachers of mathematics of the quality they would like. Qualifications of the teachers of arts subjects in a school are usually a good deal higher than those teaching sciences or mathematics. At the same time a revolution in the syllabus is taking place, and although the ‘Modern’ Syllabus is being encouraged there are very few competent teachers of it available. In many schools the choice of a new textbook is handicapped by a lack of knowledge. This project, under the auspices of CAMET, is an attempt to provide a remedy. 相似文献
40.
Isahak Wan Nor Roslam Wan Hasan Siti Zubaidah Ramli Zatil Amali Che Ba-Abbad Muneer M. Yarmo Mohd Ambar 《Research on Chemical Intermediates》2019,45(3):951-953
Research on Chemical Intermediates - 相似文献