Conformational studies of 3,4-dideoxy furanoid sugar amino acid containing analogs of the receptor binding inhibitor of vasoactive intestinal peptide

Conformational analysis of vasoactive intestinal peptide (VIP) receptor binding inhibitor Leu¹-Met²-Tyr³-Pro⁴-Thr⁵-Tyr⁶-Leu⁷-Lys⁸1 by various NMR techniques and constrained molecular dynamics (MD) simulation studies revealed that the molecule had a turn structure involving its Tyr³-Pro⁴-Thr⁵-Tyr⁶ moiety with intramolecular hydrogen bond between Tyr⁶NH→Tyr³CO. In order to mimic the structure of 1, peptidomimetic analogs 2-4 were synthesized using conformationally constrained scaffolds of 3,4-dideoxy furanoid sugar amino acids (2S,5R)-ddSaa1 5 and its enantiomer (2R,5S)-ddSaa2 6. All these analogs displayed well defined three-dimensional structures akin to that found in 1. Peptides 2 and 3, which differed only in the sugar amino acid stereochemistry, show propensity of structures with identical intramolecular hydrogen bonds between ThrNH→MetCO. A similar structure with a hydrogen bond between TyrNH→MetCO was observed in 4.     

Spectroscopic, cyclic voltammetric and biological studies of transition metal complexes with mixed nitrogen-sulphur (NS) donor macrocyclic ligand derived from thiosemicarbazide

The complexation of new mixed thia-aza-oxa macrocycle viz., 2,12-dithio-5,9,14,18-tetraoxo-7,16-dithia-1,3,4,10,11,13-hexaazacyclooctadecane containing thiosemicarba-zone unit with a series of transition metals Co(II), Ni(II) and Cu(II) has been investigated, by different spectroscopic techniques. The structural features of the ligand have been studied by EI-mass, (1)H NMR and IR spectral techniques. Elemental analyses, magnetic moment susceptibility, molar conductance, IR, electronic, and EPR spectral studies characterized the complexes. Electronic absorption and IR spectra of the complexes indicate octahedral geometry for chloro, nitrato, thiocyanato or acetato complexes. The dimeric and neutral nature of the sulphato complexes are confirmed from magnetic susceptibility and low conductance values. Electronic spectra suggests square-planar geometry for all sulphato complexes. The redox behaviour was studied by cyclic voltammetry, show metal-centered reduction processes for all complexes. The complexes of copper show both oxidation and reduction process. The redox potentials depend on the conformation of central atom in the macrocyclic complexes. Newly synthesized macrocyclic ligand and its transition metal complexes show markedly growth inhibitory activity against pathogenic bacterias and plant pathogenic fungi under study. Most of the complexes have higher activity than that of the metal free ligand.     

Spectrophotometric determination of ruthenium(III) and iridium(TV) with 8-hydroxyquinoIine N-oxide

The spectrophotometric characteristics and the stability constants of the yellow to brown 1:1 and 1:2 complexes of platinum metals with oxine N-oxide (existing as chloro mixed-ligand complexes) have been investigated. Oxine N-oxide can be used as a spectrophotometric reagent for ruthenium(III) and iridium(IV).     

Line strengths and transition probabilities for allowed transitions in Fe XXI

Configuration interaction wavefunctions, transition energies, line strengths and transition probabilities for allowed transitions within then=2 complex of C-like Fe XXI have been calculated in the LS coupling scheme. We included internal, semi-internal, and all-external types of correlations. We compare our non-relativistic line strengths values with those of relativistic calculations in the Breit-Pauli approximation. The relativistic effects on line strengths are negligible for all transitions except for the transition¹ D ^e →¹ D ⁰. Experimental wavelengths are used in the calculation of transition probabilities.     

Extractive spectrophotometric determination of nitrite in polluted waters

Nitrite is diazotised with p-nitroaniline in hydrochloric acid and coupled with 8-quinolinol in alkaline medium to give a purple azo dye (λ_max = 550 nm, ? = 3.88 × 10⁴ l mol^-1 cm^-1). Extraction of the dye into 3-methyl-1-butanol shifts the absorption maximum to 570 nm and improves the apparent molar absorptivity to 5.852 × 10⁴ l mol^-1 cm^-1. Beer's law is obeyed for 0.01–0.06 ppm nitrite. The Sandell sensitivity is 0.00078 μg cm^-2. The method is applicable to polluted waters.     

Synthesis of 2- and 4-substituted 5,12-dihydroxy-6,11-dioxo-1-azanaphthacenes from 2-aminoquinizarine

The reaction of 2-aminoquinizarine with α,β-unsaturated carbonyl compounds in presence of 10N-hydrochloric acid gives 2- and 4-substituted 5,12-dihydroxy-6,11-dioxo-1-azanaphthacenes.     

Palladium(II) inhibition during cerium(IV) oxidation of aldoses: a kinetic study

Summary The kinetics of oxidation of aldoses, namely xylose, arabinose, galactose and glucose, by Ce^IV have been studied in HClO₄ + H₂SO₄ medium and in the presence of Pd^II. The reactions exhibit a first order rate dependence with respect to oxidant. The rate is inversely dependent on the [HSO _inf4 ^sup– ][H⁺] ratio. The order of reaction with respect to aldose decreases at higher [aldose]. Due to the formation of a complex between Ce^IV and Pd^II, a retarding effect of [Pd^II] on the rate of disappearance of [Ce^IV] has been observed. A mechanism consistent with the observed kinetic data is proposed.     

Effect of methylene blue on the capacity of the dropping mercury electrode

Summary The effect of methylene blue under different conditions of p_H, concentration and frequency of the a. c. ripple used has been investigated on the capacity of the dropping mercury electrode. All the peaks caused by methylene blue at different p_H values have been interpreted as due to the reduction of the methylene blue, as indicated by the comprehensive study of the peaks. The halt at about 0.58 Volt at p_H 5.8 is due to desorption which develops into a satellite peak if potassium nitrate is used as indifferent electrolyte. It is found that the peak at 1.35 Volt at p_H 12.3, first increases with increase in concentration and then diminishes at still higher concentrations. The causes of this have been discussed. The effect of frequency reveals that the reduction reactions involved are rather slow.

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Zusammenfassung Der Effekt von Methylenblau unter verschiedenen Verh?ltnissen von Wasserstoff-Ionen-Konzentration, Konzentration und Frequenz des überlagerten Wechselstroms auf die Kapazit?t der Quecksilbertropfelektrode war Gegenstand der Untersuchung. Alle dem Methylenblau zuzuschreibenden Maxima bei verschiedenen p_H- Werten lassen sich interpretieren durch eine Reduktion des Methylenblau, wie die eingehende Untersuchung der Maxima zeigt. Der Konstanzbereich bei etwa 0,58 Volt und p_H 5,8 ist einer Desorption zuzuschreiben, die ein Begleitmaximum entwickelt, wenn Kaliumnitrat als indifferenter Elektrolyt verwendet wird. Das Maximum bei 1,35 Volt und p_H 12,3 w?chst zun?chst bei Steigerung der Konzentration und nimmt dann bei noch h?heren Konzentrationen wieder ab. Die Gründe hierfür werden diskutiert. Der Frequenzeffekt zeigt an, da? die Reduktionsreaktionen ziemlich niedrig sind.

     

Rotational spectroscopy and equilibrium structures of S3 and S4

The sulfur molecules thiozone S3 and tetrasulfur S4 have been observed in a supersonic molecular beam in the centimeter-wave band by Fourier transform microwave spectroscopy, and in the millimeter- and submillimeter-wave bands in a low-pressure glow discharge. For S3 over 150 rotational transitions between 10 and 458 GHz were measured, and for S4 a comparable number between 6 and 271 GHz. The spectrum of S3 is reproduced to within the measurement uncertainties by an asymmetric top Hamiltonian with three rotational and 12 centrifugal distortion constants; ten distortion constants, but an additional term to account for very small level shifts caused by interchange tunneling, are required to reproduce to comparable accuracy the spectrum of S4. Empirical equilibrium (r(e)(emp)) structures of S3 and S4 were derived from experimental rotational constants of the normal and sulfur-34 species and vibrational corrections from coupled-cluster theory calculations. Quantum chemical calculations show that interchange tunneling occurs because S4 automerizes through a transition state with D2h symmetry which lies about 500 cm(-1) above the two equivalent C2upsilon minima on the potential energy surface.