摘要:

AbstractA novel route for the synthesis of 3‐toluenesulfonylglutarimides on a solid support is described. The cyclization step involves stepwise [3+3] strategy of Rink Amide resin bound onto an α‐toluenesulfonyl group with various α,β‐unsaturate

ISSN:0009-4536    

DOI:10.1002/jccs.200300111

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractThe stability and unfolding mechanism of the N‐terminal β‐hairpin of the [2Fe‐2S] ferredoxin I from the blue‐green algaAphanothece sacrumin pure methanol, 40% (v/v) methanol‐water, and pure water systems were investigated by 10 ns molecular dynamics simulations under periodic boundary conditions. The β‐hairpin was mostly in its native‐like state in pure methanol, whereas it unfolds dramatically following the ‘zip‐up’ mechanism when it was placed in pure water. Both interstrand and inside‐turn hydrogen bonds account for the stability of the β‐hairpin in its native‐like conformation, whereas hydrophobic interactions among nonpolar side chains are responsible for maintaining its stable loop‐like intermediate structures in 40% (v/v) methanol‐water. Reducing solvent polarity seems to increase the stability of the β‐hairpin in its native‐like structure. Methanol is likely to mimic the partially hydrophobic environment around the N‐termi

ISSN:0009-4536    

DOI:10.1002/jccs.200300112

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractThe solubility property of the ternary of Cr(NO3)3‐Met‐H2O has been investigated in the whole concentration by the phase equilibrium method, and the phase diagram has been constructed. From the phase diagram, the congruently soluble complexes Cr(Met)(NO3)3·2H2O (D) and Cr(Met)2(NO3)3·2H2O (E) have been prepared and characterized by chemical analysis, elemental analysis, IR and TG‐DTG. Their combustion energies have been determined by a RBC‐type I precision rotating‐bomb calorimeter, and their standard enthalpies of formation, Δf, Hθm, have been calculated as (‐1842.01 ± 2.13) kJ·mol−1and (‐1136.16 ± 4.45)

ISSN:0009-4536    

DOI:10.1002/jccs.200300113

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractA large class of stereochemcial and related interactions in organic chemistry are repulsive and others are attractive, but the relative orientation of two methyl groups and the amount of energy required to twist one relative to the other (the hindered rotation energy barriers), or the alignment of such a group with respect to a conjugated ring to which it is attached (widely attributed to a mechanism called “hyperconjugation”) are estimated to be small in compared with the total energy of the molecule.We used theories of both isotropic and anisotropic proton hyperfine interactions in the π‐electron systems developed in the early sixties. They are approximated by the magnetic dipole nteractions between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals center on carbon atoms. We have extended these theories to the non‐planar olefinic cation radicals, which are very important in biochemistry as well as in petroleum catalysis. A three dimensional electron spin density equation has been developed in this paper to handle some Jahn‐Teller vibronic molecules. The new electron spin density equation related the observed proton hyperfine splittings to the non‐planar structures of the open‐chain alkene cation radicals generated by radiolysis and various chemical oxidation methods. The spin densities and the conformational calculations based on valence bond theory and symmetry principles are compared with some more elaborated molecular orbital calculations in the literature. The localized valence bond approaches are better in accord with our experimental results. The anomalous line‐width effect of the four methyl groups observed in the 2,3‐dimethyl‐2‐butene cation radicals also confirmed the positive sign of the electron‐proton hyperfine constant of hyper‐conjugation mechanism.A methyl substituent attached to a conjugated molecule often behaves as if it formed part of the region of conjugation; the charge appears to flow from the methyl group into the π electron system and it may also give rise to an appreciable dipole moment. Methylation also gives rise to an appreciable dipole moment, and the resultant red shift of electronic absorption bands is of some importance in

ISSN:0009-4536    

DOI:10.1002/jccs.200300114

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractComplexes equilibrium of (BHPAP) with proton and Sm+3ion has been measured in various mixed aqueous solvents, viz.; methanol‐water, ethanol‐water, acetone‐water and dioxane‐water. Based on potentiometric equilibrium measurements of hydrogen ion concentration at 30 °C, ionic strength 0.1 M KNO3and in the above various mixed solvents, the values of protonation constant of BHPAP‐Sm+3complex have been evaluated. The variation of protonation and stability constants with the inverse of dielectric constant or mole fraction of solvent was studied. Application of Fuoss expression and consideration of electrostatic and non‐electrostatic effects are made to explain the above constants.The solid complexes were isolated for each Pr+3and Nd+3‐BHPAP. Elemental analysis, conductance, infrared spectra, and electronic spectra for these solutions and TG, DTG and DTA measurements characterized these solids. The ligand behaves towards the metal ion as a dibasic tetra

ISSN:0009-4536    

DOI:10.1002/jccs.200300115

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractThe addition of reactive carbanions to (η4‐1,3‐diene)Fe(CO)3complexes at −78 °C and 25 °C produced putative homoallyl and allyl anion complexes, respectively. Reaction of the reactive intermediates with 2‐(phenylsulfonyl)‐3‐phenyloxaziridine afforded nucleophilic substituted (η4‐1,3‐die

ISSN:0009-4536    

DOI:10.1002/jccs.200300116

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractA novel method has been developed for the solvent extraction of tin(IV) from 8 M hydrochloric acid with 4% N‐n‐octylaniline. Tin(IV) from the organic phase was determined spectrophotometrically with pyrocatechol violet at 550 nm. Extraction was found to be quantitative in the range of 7–10 M hydrochloric acid. When the concentration of N‐n‐octylaniline was varied from 0.05–20% in xylene, it showed that optimum concentration was>3%. Amongst diluents like benzene and xylene, toluene was found to be an effective diluent. Effect of shaking time, concentration of metal ion, and salting out agents was studied.Tolerance limits of various diverse ions were determined by masking interfering cations. Tin(IV) was separated from associated elements in its binary mixture with Se(IV), Sb(III), Bi(III), Pb(II), Au(III), Cu(II) and Zn(II) and from its ternary mixtures with Sb(III), Bi(III) and Cu(II), Au(III). The proposed method was applied for separation and determination of tin(IV) in tin bearing alloys and

ISSN:0009-4536    

DOI:10.1002/jccs.200300117

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractTi(IV) as TiCl3(O3SCF3) and TiO(O2CCF3)2are used as efficient catalysts for oxidative coupling of aliphatic, aromatic and heteroaromatic thiols to their disulfides in the presence of NaI under air atmosphere.

ISSN:0009-4536    

DOI:10.1002/jccs.200300118

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractThe vapor‐phase reaction of citronellal (CTN) at 220 °C and atmospheric pressure has been studied using mesoporous molecular sieves and zeolites in a fixed‐bed reactor. The primary products included isopulegol (IPG), menthone, and pulegol with subsequent reactions to form cyclic hydrocarbons. The CTN conversion and the product selectivity depend on the acidity and the textural property of catalysts. Lewis and/or Brönsted acid sites are essential for catalyzing this reaction. An increase of SiO2/Al2O3mol ratio diminishes the acid amount of all catalysts and enhances both the surface area and the structural order of MCM‐41. The catalytic activity follows the order of MCM‐41>HZSM‐5>Hβ>USY, in accordance with the relative total acid amount except that of MCM‐41. Despite its low acidity, Si‐MCM‐41 exhibits the best catalytic performance due to its uniform mesopores, large surface area and good stability; the CTN conversion and the IPG yield attain 91.9% and 58.6%, respectively, after at least 2

ISSN:0009-4536    

DOI:10.1002/jccs.200300119

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractMacrocyclic polyethers containing a cholesteryl moiety, e.g., cholesteryl benzo‐15‐crown‐5 (C27H45OOC‐B15C5) and cholesteryl cryptand22 (C27H45OOC‐Cryptand22), were synthesized. The cholesteryl crown ether C27H45OOC‐B15C5 showed liquid crystal characteristics which were observed by polarizing microscopy. In contrast, the cholesteryl cryptand C27H45OOC‐Cryptand22 showed no liquid crystal characteristics. The doping effect of inorganic salts on the liquid crystal formation of cholesteryl benzo‐15‐crown‐5 was also investigated, revealing that the addition of salts resulted in narrower liquid crystal temperature ranges. Both cholesteryl cryptand C27H45OOC‐Cryptand22 and cholesteryl crown ether C27H45OOC‐B15C5 also exhibited the distinctive characteristics of surfactants in solutions. Fluorescence probe of pyrene and surface tension measurement were applied as sensitive tools to study the formation of the micelles and determine the critical micellar concentration (CMC) of the cholesteryl cryptand and crown ether surfactants. The salt effect on the CMC of the cholesteryl cryptand surfactant was also investigated and is discussed. Furthermore, the cholesteryl benzo‐15‐crown‐5 was successfully employed as a quite good phase transfer catalyst for the oxidation of alcohols, e.g., benzhydrol, with NaMnO4as an oxidant. Effects of temperature, solvent and concentration of the crown ether catalyst on the oxidation of benz

ISSN:0009-4536    

DOI:10.1002/jccs.200300120

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY