Browsing by Author "S. Kashyap"

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Antarctic cyanobacteria as a source of phycocyanin: An assessment
(2008) S.P. Shukia; Jay S. Singh; S. Kashyap; D.D. Giri; A.K. Kashyap
The growth characteristics and phycocyanin contents were examined in antarctic and tropical isolates of three cyanobacterial genera Anabaena, Nostoc and Phormidium in batch cultures, and in indoor and outdoor mass-culture units under varying conditions of temperature, light and nutrients. The Antarctic isolates showed 54-62% higher phycocyanin content than the tropical ones. The contents recorded in Antarctic isolates were 1.8 to 3.3 folds higher than the reported values for one of the commercially used strain of Spirulina maxima. The study proves that Antarctic cyanobacteria can yield higher amount of phycocyanin by manipulating growth conditions. The information will serve as a base line data for future biotechnological applications of antarctic cyanobacterial strains within the preview of the Antarctic treaty.
Computational tridimensional protein modeling of CrylAb19 toxin from Bacillus thuringiensis BtX-2
(Korean Society for Microbiolog and Biotechnology, 2012) S. Kashyap; B.D. Singh; D.V. Amla
We report the computational structural simulation of the Cry1Ab19 toxin molecule from B. thuringiensis BtX-2 based on the structure of Cry1Aa1 deduced by x-ray diffraction. Validation results showed that 93.5% of modeled residues are folded in a favorable orientation with a total energy Z-score of -8.32, and the constructed model has an RMSD of only 1.13Å. The major differences in the presented model are longer loop lengths and shortened sheet components. The overall result supports the hierarchical three-domain structural hypothesis of Cry toxins and will help in better understanding the structural variation within the Cry toxin family along with facilitating the design of domain-swapping experiments aimed at improving the toxicity of native toxins. © The Korean Society for Microbiology and Biotechnology.
Cu(II), Zn(II) and Mn(II) complexes of NNS tridentate and Pd(II) complex of NN(μ-S) tetradentate thiobenzyl esters: Synthesis, spectral and X-ray characterization
(Elsevier Ltd, 2015) Pooja Bharati; A. Bharti; M.K. Bharty; N.K. Singh; S. Kashyap; Udai P. Singh; R.J. Butcher
A new type of NNS tridentate ligand, N′-[bis(benzylsulfanyl)methylene]-picolinoyl hydrazide (Hbsmph) (1), and N′-(pyridine 2-carbonyl) hydrazine carbodithioic acid benzyl ester (H2pchcbe), together with their Cu(II), Zn(II)/Mn(II) and tetranuclear Pd(II) complexes, have been synthesized. The reactions of N′-[bis(benzylsulfanyl)methylene]-picolinoyl hydrazide (Hbsmph) (1) with CuCl2·2H2O, CuBr2 and CuCl gave [Cu(bsmph)X·CH3OH] {X = Cl (2), Br (3)} and [Cu(bsmph)(μ-Cl)]2·2H2O (4), respectively. The reactions of N′-(pyridine 2-carbonyl) hydrazine carbodithioic acid benzyl ester (Hpchcbe) with ZnCl2·2H2O, MnCl2·4H2O and ZnBr2 yielded [M(Hpchcbe)2]·CHCl3 {M = Zn (5), Mn (7)} and [Zn(Hpchcbe)2] (6), which possess a distorted octahedral geometry. A tetranuclear [Pd4(μ-pchcbe)4]·4H2O complex (8) has also been prepared by the reaction of Hpchcbe with PdCl2, which has a square planar geometry around each Pd(II) centre. An interesting feature of the Pd(II) complex is the formation of an eight membered twisted boat-like arrangement of alternate palladium and sulfur atoms, with Pd-Pd distances of 3.317(5) and 3.280(5) Å. In [Pd4(μ-pchcbe)4]·4H2O, the ligand behaves as NN(μ-S) dinegative tetradentate, whereas in the Zn(II) and Mn(II) complexes it acts as mononegative NNS tridentate. The thermal degradation of complexes 4 and 8 has been investigated by TGA, which indicates that the final residues are CuS and PdS, respectively. © 2015 Elsevier Ltd. © 2015 Elsevier Ltd. All rights reserved.
Hg(II) complexes of 4-phenyl-5-(3-pyridyl)-1,2,4-triazole-3-thione and 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione and a Ni(II) complex of 5-(thiophen-2-yl)-1,3,4-oxadiazole-2-thione: Synthesis and X-ray structural studies
(Elsevier Ltd, 2013) A. Bharti; M.K. Bharty; S. Kashyap; U.P. Singh; R.J. Butcher; N.K. Singh
Three new mixed ligand complexes, [Hg(en)(4-pptt)2] (2) {4-pptt = 4-phenyl-5(3-pyridyl)-1,2,4-triazole-3-thione}, [Hg(en)(4-pot)2] (3) {4-pot = 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione} and [Ni(en) 2(5-thot)2] (4) {5-thot = 5-(thiophen-2-yl)-1,3,4- oxadiazole-2-thione}, have been prepared containing en as a co-ligand. It is observed that 5-(pyridine-4-carbonyl) hydrazine carbodithioic acid methyl ester undergoes cyclization during complexation with Hg(II) in the presence of ethylenediamine and formed complex 3 containing 5-(4-pyridyl)-1,3,4-oxadiazole- 2-thione. The metal complexes have been characterized with the aid of elemental analyses, IR, magnetic susceptibility and single crystal X-ray studies. The ligand 4-pptt (1) and complexes 2, 3 and 4 crystallize in the monoclinic system, space group P21/n, P21/c, P121/c1 and P21/n respectively. The ligand is present in the deprotonated thiol form in complexes 2 and 3, and is bonded covalently through sulfur, while in complex 4 the ligand 5-(thiophen-2-yl)-1,3,4- oxadiazole-2-thione is present as the thione form and is bonded to Ni(II) through the oxadiazole nitrogen. Complex 4 shows quasi-reversible redox behavior assignable to a Ni2+/Ni3+ one electron transfer. The photoluminescence properties indicate that the complexes are fluorescent materials with maximum emissions at 433, 376 and 465 nm for complexes 2, 3 and 4 at excitation wavelengths of 293, 273 and 327 nm, respectively. All the complexes contain extended hydrogen bonding that provides a supramolecular framework. © 2012 Elsevier Ltd. All rights reserved.
Homology modeling deduced 3D structure of the Cry1Ab22 toxin
(2011) S. Kashyap; B.D. Singh; D.V. Amla
δ-Endotoxin Cry1Ab22 is produced by Bacillus thuringiensis BtS2491Ab. The toxic spectrum of this protein is reported to span Lepidopteron and Dipteran. Here, we predict the theoretical structural model of newly reported Cry1Ab22 toxin by homology modeling method on the structure of the Cry1Aa toxin. Proposed model resembles the target by sharing common three dimensional, three domain structure. The main differences being located in the length of loops, absence of helixes (α7b, α10a, α10b, α11a) and presence of additional components (β21, α9b). Few of the components like α9a, α9b and α12a are positioned spatially at different locations. A better understanding of the 3D structure will be helpful in designing the domain swapping and mutagenesis experiments aimed at improving toxicity, and will lead to a deeper understanding of the common mechanism of toxins.
Homology modelling deduced 3-D structure of Bacillus thuringiensis Cry1Ab17 toxin
(Science Society of Thailand under Royal Patronage, 2010) S. Kashyap; B.D. Singh; D.V. Amla
We predict the first theoretical structural model of the newly reported Cry1Ab17 δ-endotoxin produced by Bacillus thuringiensis using homology modelling. Both Cry1Abl7 and Cry1Aa share a common structure; both contain three flexible domains that participate in the formation of a pore and determine the receptor binding specificity. The main differences between the two is in the length of loops, and in Cry1Ab17, the absence of α7b, α10a, α10b, α12a, β19, β20 and presence of additional β0 β1b, α9b components. A few of the components such as α8a, α8b, α9a, α9b, and α11a differ in their locations. A better understanding of the 3-D structure of Cry1Ab17 will be helpful in designing the domain swapping experiments to improve its insecticidal toxicity.
Prediction of three-dimensional structure of Cry1Ab21 toxin from bacillus thuringiensis Bt IS5056
(2011) S. Kashyap; B.D. Singh; D.V. Amla
Cry1Ab21 is a δ-endotoxin produced by Bacillus thuringiensis Bt IS5056. The toxic spectrum of this protein is reported to span Lepidopteran, Dipteran and nematodes. Here, we predict the theoretical structural model of newly reported Cry1Ab21 toxin by homology modeling on the structure of the Cry1Aa toxin (2.5Å). Cry1Ab21 resembles the Cry1Aa toxin structure by sharing a common 3D structure with three domains along with few structural deviations. The main differences being located in the length of loops, absence of α7b, α9b, β10, β11, β12 and presence of additional β0 component. Some of the components like α10a, α10b, α11a are spatially positioned at different locations. A better understanding of 3D structure will be helpful in the design of efficient biopecticides. © Society for Plant Biochemistry and Biotechnology 2011.
Synthesis, spectral and structural characterization of Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes with 2-mercapto-5-methyl-1,3,4-thiadiazole: A Zn(II) complex acting as a new sensitive and selective fluorescent probe for the detection of Hg2+ in H2O-MeOH medium
(Elsevier Ltd, 2013) Pooja Bharati; A. Bharti; M.K. Bharty; S. Kashyap; U.P. Singh; N.K. Singh
Five new complexes, [Ni(mthd)2(py)2] (1), [Cu(en)2](mthd)2 (2), [H2en][Hg(mthd) 3]2·2H2O (3), [Cd (mthd) 2(o-phen)2]2·H2O (4) and [Zn(mthd)2(bpy)] (5) (Hmthd = 2-mercapto-5-methyl-1,3,4-thiadiazole), have been synthesized. All the complexes have been fully characterized by various techniques: elemental analyses, IR, electronic and fluorescent spectral data. The ligand is present in the deprotonated thiol form in the complexes [Cu(en)2](mthd)2(2)and [Cd(mthd)2(o-phen) 2]2·H2O(4). In complex 2, the ligand isionically bonded, whereas it is covalently bonded through the sulfur in complex 4. In [Ni(mthd)2(py)2] (1) the ligand is N, S chelating bidentate bonded through the thiol sulfur and the thiadiazole ring nitrogen adjacent to it, forming a four membered chelate ring. The ligand is covalently bonded through the deprotonated thiadiazole ring nitrogen adjacent to the thiol sulfur in [Zn(mthd)2(bpy)] (5). The complex anion in [H2en][Hg(mthd)3]2·2H2O (3) has a triangular planar geometry, with bonding through the deprotonated thiolato sulfur atoms from the three ligands. [Zn(mthd)2(bpy)] (5) is highly fluorescent as compared to the other complexes and has been further used as a metal probe for sensing of Hg2+ in H2O-MeOH solution. Complex 5, upon interaction with Hg2+, shows a hypochromic shift in the absorption spectra whereas the emission spectra exhibited 75% quenching fluorescence behavior. The electrochemical studies also suggest the interaction of Hg(II) with the Zn(II) complex, probably via the free thione sulfur. © 2013 Elsevier Ltd. All rights reserved.
Trinuclear supramolecular Zn(II) complexes derived from N′-(pyridine carbonyl) hydrazine carboperthioates: Synthesis, structural characterization, luminescent properties and metalloaromaticity
(Elsevier S.A., 2015) Pooja Bharati; A. Bharti; U.K. Chaudhari; M.K. Bharty; S. Kashyap; Udai P. Singh; N.K. Singh
Novel trinuclear Zn(II) complexes [Zn3(μ-4-pchcp)2(py)4] (1) and [Zn3(μ-3-pchcp)2(py)4] (2) have been isolated containing N′-(pyridine-4-carbonyl) and (N′-pyridine-3-carbonyl) hydrazine carboperthioate ligands which have been generated from potassium N′-(pyridine-4-carbonyl) and (N′-pyridine-3-carbonyl) hydrazine carbodithioates by in situ S-S coupling. In both complexes, the middle Zn(II) center has four coordinate tetrahedral arrangement bonded through two hydrazinic nitrogens and two sulfur atoms from two perthio ligands. This center mimic structurally a model compound for the zinc finger protein in which zinc is coordinated by two nitrogen atoms of the histidine and two sulfur atoms of the cysteine of the amino acid residue arranged in a tetrahedral fashion. Both terminal Zn(II) centers have five coordination with τ = 0.57, characteristic of a geometry close to trigonal bipyramidal coordinated by one carbonyl oxygen, one hydrazinic nitrogen, one sulfur from perthio ligand and two nitrogens of pyridine which act as secondary ligand. In both complexes, ortho-CH bonds from the pyridine or pyridyl part of the ligand produce CH⋯π interactions with the metal chelate rings. The molecular geometry of complexes is symmetrical, which is a consequence of the four CH⋯π (chelate ring) interactions working cooperatively. We report here the self-assembly of two supramolecular structures based on similar trimeric Zn(II) units that are built from 4 and 3-substituted pyridyl ligands coordinated to Zn(II) ions. In the solid state, the supramolecular structures can be controlled by the pyridyl substituent via intermolecular interaction such as CH⋯S, π⋯π stacking and CH⋯π interactions. Complex 1 is a fluorescent material with maximum emission at 470 nm at an excitation wavelength of 347 nm. © 2014 Elsevier B.V. All rights reserved.