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61.
Summary The displacement of chloride ligands from -cis-chloro-aquoethylenediamine-N,N-diacetatocobalt(III) in nonacidic aqueous solutions was followed conductimetrically at 30–45° and the products of aquation were characterised by conductance, spectral and ion-exchange techniques. The rate constants for aquation in aqueous media and in 1 : 4 v : v mixed solvents at 25° are: 4.0 × 10–5 s–1 in H2O, 2.71 × 10–5 s–1 in MeOH : H2O, 2.74 × 10–5 s–1 in EtOH: H2,O and 2.58 × 10–5 s–1 n in Me2CO : H2O. The corresponding H* and S* values have also been evaluated. Solvent polarity has a marked influence on the rate of chloride ion release. The aquation rate constants and the activation parameters have been correlated with solvent parameters,e.g. D, Y-values, Dimroth's ET and Kosower's Z-values and, based on these correlations, a dissociative interchange (Id) mechanism is proposed rather than dissociative as observed for some other cobalt(III) complexes.Senior author. 相似文献
62.
Radiationless transitions in lanthanide ions embedded in glassy and crystalline hosts have been briefly reviewed. The correlations
of multiphonon relaxation rates with energy gaps, vibrational frequencies, temperatures and electronic symmetries have been
discussed. The essence of various theories, such as Nth order methods, non-adiabatic Hamiltonian method, dynamic coupling
model has also been presented. 相似文献
63.
S1 nuclease fromAspergillus oryzae (EC 3.1.30.1) was coupled to gelatin-alginate composite matrix using the residual free aldehyde groups on the surface of
glutaraldehyde crosslinked matrix. The immobilized enzyme retained approximately 10% activity of the soluble enzyme. When
partially purified enzyme was bound to the matrix, the immobilized preparation did not show any detectable enzyme activity.
However, the activity could be restored when the coupling was carried out in the presence of a coprotein or substrate. The
optimum pH of the immobilized S1 nuclease shifted to 3.8 from 4.3 for the soluble enzyme. Also, optimum temperature increased
to 65°C after immobilization. Bound S1 nuclease showed increased pH and temperature stabilities. Immobilization brought about
a twofold decrease in the Michaelis-Menton constant (K
m). 相似文献
64.
Spontaneous separation of chiral phases was observed in the monolayers of a racemate of gemini-type twin-tailed, twin-chiral amphiphiles, (2R,3R)-(+)-bis(decyloxy)succinic acid and (2S,3S)-(-)-bis(decyloxy)succinic acid. The pressure-area isotherms of the interfacial monolayers formed at the liquid-air interface, and the 2D lattice structures studied through surface probe measurements revealed that the racemate exhibits a homochiral discrimination of the enantiomers in two dimensions. An enantiomeric excess (e,e) of 20% was sufficient to break the chiral symmetry at the air-water interface for a homochiral interaction. Langmuir monolayers on ZnCl2 and CaCl2 subphases manifested chiral discrimination with Zn2+ evidencing homochiral interaction with a chelate-type complex, whereas Ca2+ resulted in a heterochiral interaction forming an ionic-type complex. For the chiral asymmetric units, oblique and rectangular unit cells of the racemic monolayer had exclusive requirements of homo- and heterochiral recognitions for Zn2+ and Ca2+ ions, respectively. Monolayers transferred from the condensed phase at 25 mN/m onto hydrophilic Si(100) and quartz substrates revealed the formation of bilayers through transfer-induced monolayer buckling. The emergence of homochiral discrimination was explained using the effective-pair-potential (EPP) approach. 相似文献
65.
66.
The efficient, regioselective synthesis of functionalized/annulated quinolines was achieved by the coupling of 2‐aminoaryl ketones with alkynes/active methylenes/α‐oxoketene dithioacetals promoted by InCl3 in refluxing acetonitrile as well as under solvent‐free conditions in excellent yields. This transformation presumably proceeded through the hydroamination–hydroarylation of alkynes, and the Friedländer annulation of active methylene compounds and α‐oxoketene dithioacetals with 2‐aminoarylketones. In addition, simple reductive and oxidative cyclization of 2‐nitrobenzaldehyde and 2‐aminobenzylalcohol, respectively, afforded substituted quinolines. Systematic optimization of the reaction parameters allowed us to identify two‐component coupling (2CC) conditions that were tolerant of a wide range of functional groups, thereby providing densely functionalized/annulated quinolines. This approach tolerates the synthesis of various bioactive quinoline frameworks from the same 2‐aminoarylketones under mild conditions, thus making this strategy highly useful in diversity‐oriented synthesis (DOS). The scope and limitations of the alkyne‐, activated methylene‐, and α‐oxoketene dithioacetal components on the reaction were also investigated. 相似文献
67.
Prabuddha Bhattacharya Monisha Singha Eshani Das Arundhoti Mandal Manasi Maji Amit Basak 《Tetrahedron letters》2018,59(32):3033-3051
Garratt-Braverman cyclization has emerged as one of the simplest synthetic tool to construct two consecutive CC bonds leading to the formation of various important structural scaffolds having significance in the field of therapeutics and material science. The strategic design of suitable precursor for this cycloaromatization reaction involves the deep understanding of reaction pathways involving diradicals and ions. On the other hand, the reaction offers an unprecedented mechanistic paradox for the chemists to solve. This report aims at outlining the recent mechanistic and synthetic developments with special emphasis on the research outcomes from our laboratory. 相似文献
68.
QSAR modeling of flotation collectors using principal components extracted from topological indices 总被引:1,自引:0,他引:1
Natarajan R Nirdosh I Basak SC Mills DR 《Journal of chemical information and computer sciences》2002,42(6):1425-1430
Several topological indices were calculated for substituted-cupferrons that were tested as collectors for the froth flotation of uranium. The principal component analysis (PCA) was used for data reduction. Seven principal components (PC) were found to account for 98.6% of the variance among the computed indices. The principal components thus extracted were used in stepwise regression analyses to construct regression models for the prediction of separation efficiencies (Es) of the collectors. A two-parameter model with a correlation coefficient of 0.889 and a three-parameter model with a correlation coefficient of 0.913 were formed. PCs were found to be better than partition coefficient to form regression equations, and inclusion of an electronic parameter such as Hammett sigma or quantum mechanically derived electronic charges on the chelating atoms did not improve the correlation coefficient significantly. The method was extended to model the separation efficiencies of mercaptobenzothiazoles (MBT) and aminothiophenols (ATP) used in the flotation of lead and zinc ores, respectively. Five principal components were found to explain 99% of the data variability in each series. A three-parameter equation with correlation coefficient of 0.985 and a two-parameter equation with correlation coefficient of 0.926 were obtained for MBT and ATP, respectively. The amenability of separation efficiencies of chelating collectors to QSAR modeling using PCs based on topological indices might lead to the selection of collectors for synthesis and testing from a virtual database. 相似文献
69.
Horsey I Krishnan-Ghosh Y Balasubramanian S 《Chemical communications (Cambridge, England)》2002,(17):1950-1951
Metal chelating iminodiacetic acid moieties were appended to abutting ends of two 9-mer oligonucleotides designed to hybridize contiguously on an 18-mer target. Chelation of 1 equivalent of Gd3+ cooperatively increases affinities of the oligonucleotides to the single stranded DNA target as evidenced by a 15 degrees C increase in Tm of the complex. 相似文献
70.
[reaction: see text] Lanthanide triflates along with proline-derived ligands have been found to be efficient catalysts for enantioselective conjugate addition of nucleophilic radicals to enoates. N-Acyl oxazolidinones, when used as achiral additives, gave meaningful enhancements in the ees for the product. 相似文献