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91.
The chromium chemistry of two positional isomers of the ligand 2-[(N-arylamino)phenylazo]pyridine (HL(1)and HL(2)) are described. While the ligand HL(1) coordinates as a bischelating tridentate N,N,N-donor, [L(1)](-), with deprotonation of the amine nitrogen, its isomer HL(2) coordinates as a neutral bidentate N,N-donor. The amine nitrogen in this case remains protonated. Thus the reaction of CrCl(3).nH(2)O with HL(1) produced the brown cationic complex, [Cr(L(1))(2)](+), [1](+). The representative X-ray structure of [1a](ClO(4)) is reported. The two azo nitrogens of the anioinc tridentate ligand approach the metal center closest with Cr(1)-N(azo) av 1.862(6) A. There is a significant degree of ligand backbone conjugation in the coordinated ligands, which resulted in shortening of the C-N distances and also in lengthening of the diazo (N=N) distances. Two synthetic approaches for the synthesis of chromium complexes of HL(2) are investigated. The first approach is based on the substitution reaction, wherein all the coordinated CO ligands of Cr(CO)(6) were completely substituted by the three bidentate HL(2) ligands to produce a violet complex [Cr(HL(2))(3)]. The second approach is based on para-amination reaction of coordinated 2-(phenylazo)pyridine (pap). Thus the reaction of an inert complex, [CrCl(2)(pap)(2)], with ArNH(2) yields a mixed ligand complex, [CrCl(2)(pap)(HL(2))], 3. In this reaction one of the two coordinated pap ligands in [CrCl(2)(pap)(2)] undergoes amination at the para carbon (with respect to the diazo function) to yield HL(2) in situ. This metal-promoted transformation is authenticated by the X-ray structure determination of a representative complex, [CrCl(2)(pap)(HL(2a))], 3a. Notable differences in bond distances along the ligand backbones of the two coordinated ligands in 3a indicate different levels of metal-ligand overlap in this complex. All the chromium complexes of HL(2) are characterized by their intense blue-violet color. The frequencies of the visible range transitions in these complexes linearly correlate with the Hammett's substitution constant. Intraligand charge-transfer transitions in the visible region are believed to be responsible for the intense color. Redox properties of all these complexes are reported. 相似文献
92.
N-Cinnamoyl-L-proline can be used as a template on which beta-substituted phenylalanine and beta-phenylisoserine residues can be synthesized leading to tripeptide derivatives as structural analogues of HIV protease inhibitors. 相似文献
93.
VanNieuwenhze MS Mauldin SC Zia-Ebrahimi M Winger BE Hornback WJ Saha SL Aikins JA Blaszczak LC 《Journal of the American Chemical Society》2002,124(14):3656-3660
Bacterial peptidoglycan is composed of a network of beta-[1,4]-linked glyan strands that are cross-linked through pendant peptide chains. The final product, the murein sacculus, is a single, covalently closed macromolecule that precisely defines the size and shape of the bacterial cell. The recent increase in bacterial resistance to cell wall active agents has led to a resurgence of activity directed toward improving our understanding of the resistance mechanisms at the molecular level. The biosynthetic enzymes and their natural substrates can be invaluable tools in this endeavor. While modern experimental techniques have led to isolation and purification of the biosynthetic enzymes utilized in peptidoglycan biosynthesis, securing useful quantities of their requisite substrates from natural substrates has remained problematic. In an effort to address this issue, we report the first total synthesis of lipid II (4), the final monomeric intermediate utilized by Gram positive bacteria for peptidoglycan biosynthesis. 相似文献
94.
Sandeep Sundriyal Smriti Khanna Rikta Saha Prasad V. Bharatam 《Journal of Physical Organic Chemistry》2008,21(1):30-33
This theoretical study attempts to find out similarity between metformin and glitazone class of antidiabetic drugs. It was found that some tautomeric forms of both metformin and thiazolidinedione ring of glitazones have similar molecular electrostatic potential (MESP) surface and may bind to a common complementary surface. Complexation and docking studies were also carried out in order to support this hypothesis. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
95.
Basudeb Saha Sumana Gangopadhyay Mahammad Ali Pradyot Banerjee 《Journal of Chemical Sciences》1995,107(4):393-402
The kinetics of the reduction of [NiIII(L1)]2+ (where HL1 = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) by sulphur(IV) and selenium (IV) over the regions pH 2.50–8.02
and 2.01–4.00 respectively have been investigated at 30°C. Attempts were made to evaluate the reactivity of all the reacting
species, of sulphur(IV) and selenium(IV) by considering suitable pH ranges. The oxidation of SC2·H2O and HSO
3
−
is proposed to proceed through the formation of a hydrogen-bonded adduct. The reaction with SO
3
2−
seems to follow a direct outer-sphere route which is well supported by Marcus crossrelation calculation. The oxidation of
HSeO
l3
−
is ≈ 103 times slower than that of H2SeO3. The kinetic data indicate that the oxidation of sulphur(IV) by [NiIIIL1)]2+ is much more favourable as compared to the corresponding oxidation of selenium(IV). 相似文献
96.
A. Dey A. C. Kulshreshtha G. M. Saha 《Annals of the Institute of Statistical Mathematics》1972,24(1):525-528
Summary Two methods of construction of partially balanced arrays of strength two and three are presented. 相似文献
97.
In some recent papers, it has been shown that electrovac spacetimes may sometimes be interpreted as space-time filled with a viscous fluid—one such spacetime being the Kerr-Newman metric. Here the possible fluid motion in that case is studied in some detail and some interesting features of the motion in the black hole region are pointed out. 相似文献
98.
Helen?BarbasEmail author Claus?C?Hilgetag Subhash?Saha Caterina?R?Dermon Joanna?L?Suski 《BMC neuroscience》2005,6(1):32
Background
The neocortical commissures have a fundamental role in functional integration across the cerebral hemispheres. We investigated whether commissural projections in prefrontal cortices are organized according to the same or different rules as those within the same hemisphere, by quantitatively comparing density, topography, and laminar origin of contralateral and ipsilateral projections, labeled after unilateral injection of retrograde tracers in prefrontal areas. 相似文献99.
Saha A Mukherjee AK 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(8-9):1731-1737
The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures. 相似文献
100.
A rare asymmetric end-on double azido-bridged copper(II) complex has been synthesized and characterized structurally and magnetically. The Cu-N(azide)-Cu angle in this complex is calculated to be 89.1 degrees. This is unusually low in comparison to the same angle in other end-on azido-bridged binuclear complexes reported so far. Though a strong ferromagnetic interaction between the metal centers is expected in the complex, the coupling has actually been found to be antiferromagnetic, instead. 相似文献