Methodology for the estimation of chlorothalonil and its metabolite in mustard crop by gas liquid chromatography

A simplified method for the determination of chlorothalonil (I) and its metabolite 4-hydroxy-2,5,6-trichloroisophthalonitrile (II) in mustard crop is described. It involves extraction, derivatisation, clean-up on a silica-gel column and gas-liquid chromatography. The retention times and detection limits are 4.49, 5.39 min and 0.01, 0.005 g/g for I and II, respectively.     

Studies on adsorption of 5-amino tetrazole on silver nanoparticles by SERS and DFT calculations

The surface-enhanced Raman scattering (SERS) studies of 5-amino tetrazole (5AT), a tetrazole derivative, in aqueous silver sol at pH approximately 9 and on deposited colloidal silver films were carried out and compared with the normal Raman spectrum of the molecule. The experimentally observed Raman bands along with their corresponding infrared bands were assigned based on the results of density functional theory (DFT) calculations. The significant changes evidenced between the SERS and the normal Raman spectra combined with the theoretical data obtained for Ag-5AT system demonstrated that the molecule is adsorbed on colloidal Ag particles through the lone pair of electrons of the nitrogen atom. The contribution of the chemical mechanism for the SERS enhancement was proved by the behavior of the electronic absorption spectrum of the Ag colloid upon addition of 5AT. This is further supported by the theoretical calculations that show that the favorable interaction of the frontier orbitals localized on Ag(+) and the negatively charged nitrogen from the tetrazole ring leads to the formation of the stable (up to 130 kJ mol(-1)) charge-transfer complex. The orientation of the adsorbed species with respect to the metal surface was also predicted by applying the "surface selection rule". In addition, the feasibility of the formation of the polymeric species has also been discussed.     

Microwave assisted green chemical synthesis of novel spiro[indole-pyrido thiazines]: a system reluctant to be formed under thermal conditions

Spiro [3H-indole-3,2′-[4H] pyrido [3,2-e]-1,3-thiazine]-2,4′ (1H) diones, a class of previously unknown compound which does not form under conventional conditions, can be prepared by treatment of ‘in situ’ generated 3-indolylimine derivatives with 2-mercaptonicotinic acid under microwave irradiation in absence of any solvent or solid support in 85-92% yields in 3-8 min. The facile one pot reaction is generalized for a variety of ketones and amines to give pure pyrido [3,2-e] thiazine derivatives, which do not require further purification processes.     

NS and NSO-Donor ligands and their metal complexes. Synthesis and characterisation of a new low-spin iron(III) complex with 1,2-di(o-aminophenylthio)ethane and iron(III), cobalt(III) and manganese(III) complexes of 1,2-di(o-salicylaldiminophenylthio)ethane

Summary Iron(III) complexes of a quadridentate N₂S₂ donor ligand, 1,2-di(o-aminophenylthio)ethane (DAPTE) and its Schiff Base with salicylaldehyde, a hexadentate N₂S₂O₂ donor ligand,viz. 1,2-di(o-salicylaldiminophenylthio)ethane (H₂DSALPTE) have been synthesised and characterised.The Schiff base ligand (1 mol) gave a dark green tri-iron(III) [Fe₃(DSALPTE)(HDSALPTE)Cl₃]Cl₂ complex when reacted with anhydrous iron(III) chloride (1 mol). The Mössbauer data of this complex suggest the presence of three iron sites, one of which is octahedral and the other two tetrahedral. On the other hand, Fe(ClO₄)₃ reacted smoothly with H₂DSALPTE in ethanol to give a mononuclear pseudo-octahedral complex in which the ligand functions in a dibasic hexadentate fashion. Mössbauer data suggest the presence of a low-spin-high-spin equilibrium in the solid state. The manganese(III) and cobalt(III) complexes of the Schiff base, H₂DSALPTE, are also studied for the sake of comparison with the corresponding iron(III) complex. The N₂S₂ ligand, however, formed a low-spin pseudo-octahedral iron(III) complex. The complexes have been characterised by elemental analysis, molar conductance values, cryomagnetic data and i.r., electronic and Mössbauer spectral data.     

First systematic investigation of C-H...Cl hydrogen bonding using inorganic supramolecular synthons: lamellar, stitched stair-case, linked-ladder, and helical structures

Using a group of six neutral M(II)Cl(2)-containing coordination compounds as building blocks, the first systematic investigation of C-H...Cl hydrogen-bonding interactions was performed. Single-crystal X-ray structural analyses of four new compounds (pseudo-tetrahedral Co(II) and Zn(II); distorted trigonal bipyramidal Zn(II)) authenticate the metal coordination geometry. To provide a unified view of the presence of noncovalent interactions in this class of compounds, we have re-examined the packing diagram of two previously reported compounds (a distorted square-pyramidal Cu(II) complex and a trans-octahedral Co(II) complex). The organic ligands of our choice comprise bidentate/tridentate pyrazolylmethylpyridines and an unsymmetrical tridentate pyridylalkylamine. This systematic investigation has allowed us to demonstrate the existence of versatile C-H...Cl(2)M interactions and to report the successful application of such units as inorganic supramolecular synthons. Additional noncovalent interactions such as C-H...O and O-H...Cl hydrogen bonding and pi-pi stacking interactions have also been identified. Formation of novel supramolecular architectures has been revealed: 2D lamellar (p-cyclophane) and 3D lamellar, 3D "stitched staircase" (due to additional hydrogen-bonding interactions by water tetramers, with an average O-O bond length in the tetramer unit of 2.926 A, acting as "molecular clips" between staircases), 3D linked ladder, and single-stranded 1D helix.     

Superconvergence error estimates of discontinuous Galerkin time stepping for singularly perturbed parabolic problems

Numerical Algorithms - A parabolic convection-diffusion-reaction problem is discretized by the non-symmetric interior penalty Galerkin (NIPG) method in space and discontinuous Galerkin (DG) method...     

On sparse spanners of weighted graphs

Given a graphG, a subgraphG' is at-spanner ofG if, for everyu,v V, the distance fromu tov inG' is at mostt times longer than the distance inG. In this paper we give a simple algorithm for constructing sparse spanners for arbitrary weighted graphs. We then apply this algorithm to obtain specific results for planar graphs and Euclidean graphs. We discuss the optimality of our results and present several nearly matching lower bounds.The work of G. Das and D. Joseph was supported by NSF PYI Grant DCR-8402375. The work of D. Dobkin was supported by NSF Grant CCR-8700917. The work of J. Soares was supported by CNPq proc 203039/87.4 (Brazil) and NSF Grant CCR-9014562. This research was accomplished while G. Das was a student at the University of Wisconsin-Madison. A preliminary version was presented at the Second Scandinavian Workshop on Algorithm Theory, Bergen, Norway, 1990, under the title Generating Sparse Spanners for Weighted Graphs, and proceedings appear in the series Lecture Notes in Computer Science, Springer-Verlag. The preliminary version also appears as Princeton University Technical Report CS-TR-261-90, and as University of Wisconsin-Madison Computer Sciences Technical Report 882.     

Synthesis of silver nanoprisms in formamide

Polygonal (mainly triangular) silver nanoprisms were prepared by reducing silver perchlorate in formamide in the presence of polyethylene glycol (PEG) at room temperature. The reduction of silver ions by formamide leads to the deposition of arrays of triangular shaped silver nanoparticles on the glass walls of the container, accompanied by evolution of CO2 gas. In the presence of poly(N-vinyl-2-pyrrolidone) (PVP) and PEG (1:1), both nanospheres and nanoprisms are formed.     

A hybrid technique of orthonormality constrained orbital optimization in SCF calculations

A recently proposed orthonormality constrained orbital optimization technique is operationally modified further by coupling it to a gradient biased method, namely the steepest descent procedure of McWeeny. The hybrid technique developed in this way is shown to have better convergence properties in closed and unrestricted open-shell calculations. The technique can be adapted to MCSCF procedures as well. The important role played by "orbital symmetries" in the operation of the method is analysed. Similarities and differences of the present method with the orthogonal gradient method are pointed out. Possible avenues of circumventing convergence difficulty that one may encounter in pathological cases, particularly in ab initio calculations involving extended basis set, are suggested.     

On a new partitioning of the Hamiltonian in many-body calculation of pair-correlation energies in closed-shell systems

We introduce here a new partitioning of the Hamiltonian in calculating pair-correlation energies using many-body perturbation theory, by which we are able to eliminate the off-diagonal particle–hole (p–h) ladders exactly to all orders in the perturbation expansion. In this formulation, the particle states turn out to be different for each distinct pair of hole states in the correlation energy calculation. We have also included the contributions of the diagonal particle–particle (p–p) and hole–hole ladders exactly to all orders. The effect of the off-diagonal p–p ladders has been estimated for each pair by computing the third-, foruth- and fifth-order energies. For highly symmetric systems the present partitioning yields in general symmetry-broken orbitals. Here one may use an average kind of partitioning for all the partners of the degenerate sets, which restores the symmetry and at the same time ensures cancellation of the p–h ladders exactly at the lowest order and approximately at the higher orders. Results are presented for a selection of 6π-electron conjugated systems. The correlation energy for each pair is in excellent agreement with that obtained from a partial CI calculation involving all double excitations from this pair. The advantages of implementing the present scheme in larger systems has been discussed.