Potential energy surface of thionylimide

The potential energy surface (PES) of thionylimide has been searched using ab initio MO and density functional calculations. The electronic structures of the isomers of HNSO have been studied using the HF/6‐31+G*, MP2(full)/6‐31+G*, and B3LYP/6‐31+G* levels. Final energies of these molecules have been calculated at the high‐accuracy G2 and CBS‐Q levels. The probable pathways of isomerization of thionylimide to its isomers (e.g., thiocyanic acid, HONS, nitrosothiols) have been explored by studying the three‐ or four‐membered transition states. This study identified total eight possible isomers ( 1–8 ) of HNSO, of which four ( 1–4 ) have already been realized experimentally. Of the remaining four ( 5–8 ), at least two ( 5, 7 ) can be generated experimentally. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Solvolytic behaviour and the solubilities of various inorganic compounds, lewis acids and bases in fused monobromo acetic acid solvent system—II

Solubilities and the solvolytic behaviour of various inorganic compounds, Lewis acids and bases in fused monobromoacetic acid at 60 ± 0.5°C are discussed. Ionic compounds are fairly soluble, iodides and thiocyanates being comparatively more soluble than chlorides and bromides. Tetraalkyl ammonium halides are highly soluble in this solvent. Conductometric and spectroscopic studies of various Lewis acids and bases in fused monobromoacetic acid indicate their solvolytic behaviour and their subsequent ionization. The solvolyses products BBr₃·CH₂BrCOOH and SbCl₅·CH₂BrCOOH have been observed to be the strongest Bronsted acids. Auto-ionization of this solvent has been supported by acid/base titrations.     

Synthesis of N-substituted piperazinyl carbamoyl and acetyl derivatives of tetrahydropapaverine: potent antispasmodic agents

The synthesis and structure-activity-relationship (SAR) for a series of N-substituted piperazinyl carbamoyl 7-15 and piperazinyl acetyl 18-26 derivatives of tetrahydropapaverine have been carried out. The general synthetic methods of carbamoyl tetrahydropapaverine analogues involve N-substituted piperazines and carbamoyl imidazole tetrahydropapaverine as starting materials. Another route for synthesizing these compounds, involving the formation of carbamoyl imidazole piperazine has also been explored. Acylation of tetrahydropapaverine followed by substitution with various piperazinyl moities afforded the acetyl tetrahydropapaverine derivatives. Variously substituted piperazines have been used to monitor the effect of electron releasing and electron withdrawing substituents upon the antispasmodic activity of the molecules. Effect of varying electron densities on the antispasmodic activity, by altering the position of these groups on the benzene ring has also been monitored. Pharmacological methods involve the in vitro antispasmodic activity studies on a freshly removed guinea pig ileum using a force displacement transducer amplifier connected to a physiograph. Among the analogues synthesized in the present study, a promising compound 7, a potent muscle relaxant as compared to papaverine has been obtained.     

Dibromosilylene: Determination of the absolute rate constants for its gas-phase reactions with oxygen and nitric oxide

Following the newly-discovered UV absorption spectrum of Br₂Si, its reactions with oxygen and nitric oxide in the gas phase have been quantitatively investigated using the flash photolysis-kinetic absorption spectroscopy technique. The room temperature bimolecular rate constants are:      

Complexes of metal ions with phosphorus or arsenic containing ligands. Part XVIII. Chelates ofo-phenylenebis(diarylarsines) with cobalt(II) and nickel(II) halides and pseudohalides

Summary Ten complexes of nickel(II) and cobalt(II) witho-phenylenebis(diphenylarsine), (pdpa) ando-phenylenebis(di-p-tolylarsine), (pdta) have been synthesised. The stoichiometry of complexes is markedly dependent upon the reaction temperature, thus reaction atca. 0° gives the M(A-A)₂X₂ chelates, [M = Ni, X = Br, (A-A) = pdpa; M = Ni, X = I, (A-A) = pdpa, pdta; M = Co, X = CNS, (A-A) = pdpa] whereas at higher temperatures the M(A-A)X₂ chelates [M = Ni, X = Br, I, (A-A) = pdpa, pdta; M = Co, X = CNS, (A-A) = pdpa or pdta] are obtained. The Ni(A-A)₂I₂ compounds can be converted into Ni(A-A)I₂ by boiling under reflux in n-BuOH; the conversion can be reversed by cooling a CH₂Cl₂ solution of the latter at or below 0°. Stereochemical assignments of all the new complexes have been made on the basis of room temperature _eff values, molar conductance, i.r. and u.v. data.     

Synthesis of atomically ordered AuCu and AuCu(3) nanocrystals from bimetallic nanoparticle precursors

A new multistep approach was developed to synthesize atomically ordered intermetallic nanocrystals, using AuCu and AuCu(3) as model systems. Bimetallic nanoparticle aggregates are used as precursors to atomically ordered nanocrystals, both to precisely define the stoichiometry of the final product and to ensure that atomic-scale diffusion distances lower the reaction temperatures to prevent sintering. In a typical synthesis, PVP-stabilized Au-Cu nanoparticle aggregates synthesized by borohydride reduction are collected by centrifugation and annealed in powder form. At temperatures below 175 degrees C, diffusion of Cu into Au occurs, and the atomically disordered solid solution Cu(x)Au(1)(-)(x) exists. For AuCu, nucleation occurs by 200 degrees C, and atomically ordered AuCu exists between 200 and 400 degrees C. For AuCu(3), an AuCu intermediate nucleates at 200 degrees C, and further diffusion of Cu into the AuCu intermediate at 300 degrees C nucleates AuCu(3). Atomically ordered AuCu and AuCu(3) nanocrystals can be redispersed as discrete colloids in solution after annealing between 200 and 300 degrees C.     

Ag-mediated synthesis of six-membered N-heterocycles

Abstract

One of the highly emerging and an important aspect of organic chemistry is the metal catalyzed synthesis of heterocycles. The methods used earlier for the synthesis of heterocycles were significant in the organic synthesis and developing cost-effective, improved and facial methods were beneficial to construct the complex architectures. For the both stereoselective and regioselective synthesis of six-membered nitrogen containing heterocycles, cyclic reactions that are Ag-mediated have known to be very efficient. The present review covers the applications of Ag in the formation of six-membered nitrogen containing heterocycles.     

Folding, conformational changes, and dynamics of cytochromes C probed by NMR spectroscopy

NMR spectroscopy has become a vital tool for studies of protein conformational changes and dynamics. Oxidized Fe(III)cytochromes c are a particularly attractive target for NMR analysis because their paramagnetism (S = (1)/(2)) leads to high (1)H chemical shift dispersion, even for unfolded or otherwise disordered states. In addition, analysis of shifts induced by the hyperfine interaction reveals details of the structure of the heme and its ligands for native and nonnative protein conformational states. The use of NMR spectroscopy to investigate the folding and dynamics of paramagnetic cytochromes c is reviewed here. Studies of nonnative conformations formed by denaturation and by anomalous in vivo maturation (heme attachment) are facilitated by the paramagnetic, low-spin nature of native and nonnative forms of cytochromes c. Investigation of the dynamics of folded cytochromes c also are aided by their paramagnetism. As an example of this analysis, the expression in Escherichia coli of cytochrome c(552) from Nitrosomonas europaea is reported here, along with analysis of its unusual heme hyperfine shifts. The results are suggestive of heme axial methionine fluxion in N. europaea ferricytochrome c(552). The application of NMR spectroscopy to investigate paramagnetic cytochrome c folding and dynamics has advanced our understanding of the structure and dynamics of both native and nonnative states of heme proteins.     

Mössbauer study on thermal decomposition of ammonium tris (malonato) ferrate (III) tetrahydrate

Thermal decomposition of ammonium tris (malonato) ferrate (III) tetrahydrate, i. e. (NH₄)₃[Fe(CH₂C₂O₄)₃]·4H₂O has been studied up to 973 K in static air atmosphere employing Mössbauer and infrared spectroscopies, and non-isothermal techniques (TG, DTG, DTA). The anhydrous complex decomposes into an iron (II) intermediate at 453 K. The iron (II) species on further heating is reoxidized to -Fe₂O₃ as the final thermolysis product. An increase in particle size of -Fe₂O₃ with increasing decomposition temperature has been observed. The results are compared with the analogous oxalate complex.