Hydrothermal Synthesis, Crystal Structure and Electrochemical Properties of the Complex Cu(o-Methylbenzoic acid)2(2,2''-bipy)·(H2O)

The title complex (C26H24CuN2O5, Mr = 508.01) has been synthesized by o-methylbenzoic acid, 2,2'-bipyridine (bipy) and copper perchlorate in the mixed solvent of water and methanol. It crystallizes in orthorhombic, space group P212121 with a = 0.70814(10), b = 1.6953(3),c = 1.9539(3) nm, V= 2.3457(6) nm3, Dc= 1.439 g/cm3, Z= 4,μ = 0.971 mm-1, F(000) = 1052, R= 0.0432 and wR = 0.0860. The structural determination shows that the copper atom is coordinated by three oxygen atoms from two o-methylbenzoic acids and one water molecule together with two nitrogen atoms from 2,2'-bipyridine, giving a distorted square-pyramidal coordination geometry.The cyclic voltammetric behavior of the complex is also discussed.     

Computer-aided determination of relative stereochemistry and 3D models of complex organic molecules from 2D NMR spectra

A method for elucidation of the relative stereoconfiguration of natural product molecular structures and their 3D models based on NOE data and the application of a genetic algorithm is described. The method is applicable mainly for rigid polycyclic structures commonly encountered in natural products. It is demonstrated that the technique of simulated annealing cannot be easily used when dealing with low-weight fused ring molecules but the application of a genetic algorithm is proven successful. Examples of a typical genetic algorithm workflow and the optimization of the algorithmic parameters are discussed. The efficiency of the approach developed here is demonstrated on the complex natural products of both Taxol^® (C₄₇H₅₁NO₁₄) and brevetoxin B (C₅₀H₇₀O₁₄).     

A Novel Spectrometer for Simultaneous Chemical Analyses

A novel spectrometer incorporating a multichannel detector for simultaneous multi-element atomic emission spectrometry (AES) is described. The spectrometer consists of a multi-bandpass optical filter comprised of a concave and a fiat grating in substractive mode, and a high resolution stage which utilizes an echelle grating and an one inch 1024-channel photodiode array as the detector. Characterization with respect to the spectral resolution, the spectral response, and the capability of multi-element detection demonstrated the systems's potential for simultaneous chemical analyses without moving any mechanical parts. To adjust the system for the analyses of different sets of elements, the corresponding mask is simply placed in position.     

The near uv vapour absorption spectra of 1-hydroxynaphthalene and 2-hydroxynaphthalene

Vibrational analyses, of the electronic bands of 1-hydroxynaphthalene and 2-hydroxynaphthalene corresponding to the 312 nm electronic transition in naphthalene, have been carried out from the vapour phase absorption spectra recorded under high resolution. It is found that the prominent vibronic bands owe their large intensities to a different vibronic interaction than that in naphthalene. On leave from Pt. Jawaharlal Nehru College, Banda 210 001, India.     

Structure elucidation of dicarboxylate complex of Sn porphyrin with a ring current effect model

A new simple model of porphyrin ring current effect was proposed based on a line current approximation. It can reproduce the porphyrin-induced shifts for several Sn(IV)(tpp) and Sn(IV)(oep) dicarboxylate complexes quite satisfactorily. Perpendicular arrangement of the aromatic rings in the diaromatic-carboxylate complexes of Sn(IV)(tpp) and Sn(IV)(oep) was clarified with this porphyrin ring current effect model. There are two structures, exo and endo, in solution in dinaphthalene-1- and 2- carboxylate complexes of Sn(IV)(tpp) and Sn(IV)(oep). The exo conformer is in dynamic equilibrium with the endo form in solution. Thermodynamic data of these conformational equilibria are given.     

Analyses without calibration curve for determination of indium in sediment and geochemical samples

Influences of atomization temperatures on the characteristic mass and the atomic absorption coefficient of indium were studied. The results show that the values of characteristic mass obtained from the wall, using the platform and the V-shaped boat have appeared to be stable to better than 10, 6 and 12% in the range of 1600–2400 °C, respectively. The determination of indium without calibration curve by furnace with the V-shaped boat using palladium and ammonium salt of EDTA as a matrix modifier are described. The proposed method was applied to the determination of indium in standard sediment and geochemical reference samples and satisfactory results were obtained.     

The structure of liquid alcohols and the temperature dependence of vibrational bandwidth

To obtain the information about the structure peculiarities of liquid alcohols the temperature dependence of Raman profiles widths for these objects was studied. The results of these investigations have shown that in the region 150–340 K the widths of Raman bands in liquid methanol and ethanol are constant. From the data on the constancy of the number of hydrogen bonds per one molecule (in the same temperature range) the conclusion on the dynamic stability of the cluster structure of alcohols was made. The broadening of vibrational bands is determined by inhomogeneous broadening and by the dephasing of intramolecular vibrations due to the hydrogen bond dissociation.     

Synthesis,Biological Evaluation,and Crystallographic Studies of Extended Guanine‐Based (lin‐Benzoguanine) Inhibitors for tRNA‐Guanine Transglycosylase (TGT)

This paper describes the rational design, synthesis, and biological evaluation of a new generation of inhibitors of the bacterial enzyme tRNA‐guanine transglycosylase (TGT), which has been identified as a new target in the fight against bacillary dysentery (Shigellosis). The enzyme catalyzes the exchange of guanine in the anticodon wobble position of tRNA by the modified base preQ₁, a guanine derivative, according to a ping‐pong mechanism involving a covalent TGT‐tRNA intermediate (Fig. 2). Based on computer modeling (Fig. 3), lin‐benzoguanine (6‐aminoimidazol[4,5‐g]quinazolin‐8(7H)‐one ( 2 )) was selected as an extended central scaffold, to form up to seven in‐plane intermolecular H‐bonds with the protein while sandwiching between Tyr106 and Met260. Versatile synthetic protocols were developed for the synthesis of 2 , and derivatives with phenyl, benzyl, and 2‐phenylethyl side chains (i.e., 16, 17a , and 12a, 12b, 13, 17 , resp.) to reach into the lipophilic pocket lined by Val282, Val45, and Leu68 (Schemes 1–3). To account for the limited solubility of the new ligands and in consequence of a recently developed detailed understanding of the mechanism of TGT catalysis (Fig. 2), the enzyme kinetic assay was completely redesigned, providing competitive (K_ic) and uncompetitive (K_iu) inhibition constants with respect to tRNA binding by TGT. The modifications of the various parameters in the new assay are described in detail. Binding affinities of the new inhibitors were found to be in the single‐digit micromolar range (K_ic values, Fig. 8). Decoration of the lin‐benzoguanine scaffold with lipophilic residues only gave a modest improvement in biological activity which was explained on structural grounds with the help of four crystal structures (Fig. 10) obtained by soaking the protein with inhibitors 2 and 12a – 12c . Both biochemical and biostructural analyses reported in this paper provide a fertile basis for the development of more potent future generations of TGT inhibitors.     

EuCN2 — The First,but Not Quite Unexpected Ternary Rare Earth Metal Cyanamide

Red‐orange, transparent single crystals of EuCN₂ (Pnma (62), a = 1232.41(9), b = 395.26(3) and c = 539.43(4) pm, Z = 4) are obtained by the reaction of EuN, C and NaN₃ in arc‐welded Ta ampoules at 1300 K. The first ternary rare earth metal cyanamide is isotypic to α‐SrCN₂ and shows the characteristic frequencies for the CN₂^2— unit in the optical spectra (ν_s = 1244; ν_as = 1969 and 2087; δ = 655 / 666 cm^—1).     

Synthesis and structure of tetrakis(isopropylimino)bis-[tris(dimethylamino)silylamino]alane

A novel cage-type compound tetrakis(isopropylimino)bis[tris(dimethylamino)silylamino]alane, H₆Al₆(NⁱPr)₄[NSi(NMe₂)₃]₂, (1), was prepared by reaction of tris(dimethylamino)silylamine H₂NSi(NMe₂)₃ with poly(isopropyliminoalane) (HAlNⁱPr)₆. The molecular structure of 1 was determined and discussed on the basis of FTIR, NMR and X-ray crystallographic analysis.