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61.
Chakravarty C 《Physical review letters》1995,75(9):1727-1730
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The synthesis, X-ray data, and electronic structures of two manganese(III) 1D polymers ligated by tetrachlorocatechol, [Mn(2)(III)(H(2)L(1))(Cl(4)Cat)(4).2H(2)O](infinity) (1) and [Mn(2)(III)(H(2)L(2))(Cl(4)Cat)(4).2CH(3)CN.2H(2)O](infinity) (2), are reported. The electronic structures of the complexes have been determined by UV-vis-near-IR, IR, electron paramagnetic resonance (EPR), and magnetic susceptibility measurements. Both 1 and 2 are air stable in the solid state and in solution, unlike most of the previously reported o-quinone-chelated transition-metal complexes. Electronic spectroscopy exhibits a strong near-IR band near 1900 nm for both, suggesting the presence of a mixed-valence semiquinone-catecholate oxidation state of the catechol ligands, Mn(2)(III)(Cl(4)Cat)(2)(Cl(4)SQ)(2), together with the pure catecholate forms. The presence of this isomer was further supported by EPR and magnetic susceptibility measurements. The complexes undergo intramolecular electron transfer (valence tautomerism) upon an increase of the temperature involving the equilibrium Mn(2)(III)(Cl(4)Cat)(2)(Cl(4)SQ)(2) <==> Mn(2)(II)(Cl(4)SQ)(4). This phenomenon is reversible and is studied in solution using UV-vis-near-IR spectroscopy. 相似文献
64.
Patra AK Dhar S Nethaji M Chakravarty AR 《Chemical communications (Cambridge, England)》2003,(13):1562-1563
Ternary copper(II) complex, structurally characterized as [Cu(phen)(met)(MeOH)](ClO4) (1) by X-ray crystallography, has 1,10-phenanthroline (phen) as an intercalator/binder to supercoiled pUC19 DNA and L-methionine (met) as a photosensitizer, and the complex displays efficient photonuclease activity on irradiation with UV (312 nm) or visible (436, 532 nm) light through a mechanistic pathway involving singlet oxygen. 相似文献
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Gupta T Dhar S Nethaji M Chakravarty AR 《Dalton transactions (Cambridge, England : 2003)》2004,(12):1896-1900
The copper(II) complex [Cu(dppz)(2)Cl]Cl () has been prepared, structurally characterized and its DNA binding and cleavage properties studied (dppz, dipyridophenazine). Crystal structure of 1xdppzxH(2)O shows the presence of the monocationic copper(II) complex containing two dppz ligands and one chloride in the five coordinate structure. While one bidentate chelating dppz ligand occupies the basal plane, the other dppz ligand shows an axial/equatorial mode of bonding. The chloride ligand binds at the basal plane. The complex crystallizes with dppz and water as lattice molecules. The dppz moieties in the metal-bound and free forms are involved in pi-pi stacking interactions. The one-electron paramagnetic complex shows a visible spectral d-d band at 707 nm in DMF and displays quasireversible cyclic voltammetric response for the Cu(II)/Cu(I) couple near 0.1 V vs. SCE in DMF-0.1 M TBAP. The complex which is an avid binder to calf thymus DNA giving a binding constant (K(b)) value of 2.0 x 10(4) M(-1) in DMF-Tris buffer, cleaves supercoiled pUC19 DNA in an oxidative manner in the presence of mercaptopropionic acid (MPA) as a reducing agent or on photo irradiation at 312 nm. Control experiments show major groove binding and DNA cleavage via the formation of hydroxyl radical in the presence of MPA and by singlet oxygen in the photocleavage reaction. The complex exhibits significant hydrolytic cleavage of DNA in the dark in the absence of any additives at a rate of approximately 3.0 h(-1). The hydrolytic nature of the DNA cleavage is evidenced from the T4 ligase experiments converting the nicked circular form to its original supercoiled form quantitatively. Complex presents a rare example of copper-based major groove directing efficient synthetic hydrolase. 相似文献
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Summary The kinetics of the aquation of four selenitoaquobisdiamine)cobalt(III) complexes to their respective diaquabis-(diamine)complexes (diamine=ethylenediamine en, propylenediamine pn, dimethylethylenediamine me2en and trimethylenediamine tmd) have been carried out conductimetrically in the 25–45 °C range. All reactions exhibit simple first order kinetics, and the rates increase with increasing temperature. In aqueous solution, the complex species exist in equilibrium with their respective hydroxo species, but only the hydroxo species are involved in the aquation process. This result is also reflected in the linear Arrhenius plot. The rates are higher in a 10% alcoholic solution than in water, but then decrease with increase in the alcohol content. A Grunwald-Winstein plot of rates in methanol yields slopes of 0.18 ± 0.04, 0.27±0.03, 0.43±0.03 and 0.34±0.02 for the four amines respectively. A dissociation mechanism is proposed for the aquation of all these complexes. 相似文献
67.
Mark J. Ablowitz Sarbarish Chakravarty Leon A. Takhtajan 《Communications in Mathematical Physics》1993,158(2):289-314
The self-dual Yang-Mills equations play a central role in the study of integrable systems. In this paper we develop a formalism for deriving a four dimensional integrable hierarchy of commuting nonlinear flows containing the self-dual Yang-Mills flow as the first member. We show that upon appropriate reduction and suitable choice of gauge group it produces virtually all well known hierarchies of soliton equations in 1+1 and 2+1 dimensions and can be considered as a universal integrable hierarchy. Prototypical examples of reductions to classical soliton equations are presented and related issues such as recursion operators, symmetries, and conservation laws are discussed. 相似文献
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Chakravarty PK Tyagarajan S Shih TL Salva S Snedden C Wyvratt MJ Fisher MH Meinke PT 《Organic letters》2002,4(8):1291-1294
An efficient synthesis of the truncated 3"-aldehyde (3) from nodulisporic acid A (1) under mild conditions is described. Further oxidation of 3 to 3"-carboxylic acid (4) and its subsequent oxidative degradation produced 1"-aldehyde (5). These new derivatives are versatile intermediates for the preparation of new, side chain modified derivatives of nodulisporic acid A. [reaction: see text] 相似文献