Heats of formation of isomeric [C, H4, O], [C, H3, N] and [C, H5, N] radical cations

The heats of formation of six radical cations have been calculated using ab initio MO methods at the MP4/6-31 + G(2df, p) level with MP2/6-31G(d, p)-optimized geometries. The theoretical values for ΔH⁰_f,298 (kJ/mol) of the radical ions considered are (experimental values in parentheses): methanol CH₃OH^+√: 854 (845); methyleneoxonium CH₂OH^+√₂: 815 (816); methyleneimine CH₂NH^+√: 1076 (1054); aminomethylene HCNH^+√₂: 1040 (1079); methylamine CH₃NH^+√₂: 863 (843) and methyleneammonium CH₂NH^+√₃: 855 (958). The calculated results thus confirm the discrepancy between experiment and theory on the heats of formation of nitrogen-containing radical cations. In the latter, the distonic species are calculated to be more stable than their classical isomers. The higher stability of the distonic ions has also been discussed. The recommended heat of formation of the methyleneiminium cation CH₂NH⁺₂ is 754 kJ/mol.     

Etude theorique de la cycloaddition de la nitrone sur l'ethylene

A theoretical study of the concerted 1,3-dipolar cycloaddition of nitrone on ethylene has been carried out by the LCAO-SCF-MO method. The potential energy hypersurface for the reaction has been investigated and the characteristics of the transition state have been determined.     

Characterization of Copper(II), nickel(II), cobalt(II) and palladium(II) complexes of vicinal oxime-imine ligands; induced chelate isomerism in the same molecule of the nickel(II) complex

Summary Metal complexes of the title ligands were characterized in order to determine the factors influencing the stability of chelate isomerism in the same molecule. The ligands were prepared by 1:1 condensation of isonitrosoacetylacetone (Hiso) with eithero-aminophenol (H₂ isoaph),p-aminophenol (H₂ isopph), or aniline (Hisoanil). The following complexes have been synthesized: [(isoaph)Cu]₄, (Hisoaph)₂Co, (Hisopph)₂ M·nH₂O (M=Ni(II), n=2;M=Pd(II), n=0;M=Co(II), n=2), [(isopph) Cu·H₂O]₂, and (isoanil)₂ M (M=Ni(II), Cu(II), Co(II), or Pd(II)). Both chelate rings in these metal complexes are five-membered. Transimination of one –C=N–C₆H₅ group to –C=NH in (isoanil)₂Ni produced a six-membered chelate ring in (isoim)Ni(isoanil). The induced chelate isomerism is ascribed to intermolecular hydrogen bonding of the imino-hydrogen and the basic nitrogen of the same six-membered chelate ring of an adjacent square planar molecule. Other types of hydrogen bondings with the oximato oxygen (intra- or intermolecular) favour the formation of five-membered chelate rings. Analytical, spectroscopic, and magnetic moment data are in accordance with the suggested formulations.Part of the Ph.D. thesis of Sana M. Imam     

Enantio- and diastereocontrol in intermolecular cyclopropanation reaction of styrene catalyzed by dirhodium(II) complexes with bulky ortho-metalated aryl phosphines

Enantiomerically pure dirhodium(II) complexes with ortho-metalated p-substituted aryl phosphines have been shown to be enantio- and diastereoselective in the cyclopropanation of styrene by ethyl diazoacetate. Enantioselectivities up to 91% and diastereoselectivities up to 90% are observed for ethyl cis-2-phenylcyclopropanecarboxylate.     

Synthesis and reactivity of new chelate-N-heterocyclic biscarbene complexes of ruthenium

The carbene-ligand precursors methylenebis(N-alkylimidazolium) iodide (alkyl = methyl, neo-pentyl) and ethylenebis(N-methylimidazolium) chloride have been used in the preparation of several new Ru(II)-p-cymene complexes where the ligand behaves as mono- and bidentate. The molecular structures of the two biscarbene-complexes are reported. From the data reported, we can conclude that steric reasons (mainly the bisimidazolium linkers, methylene/ethylene) are the main factors determining both reactivity and synthetic difficulties of the products reported.     

Experimental designs for finding stationary points and for computing force constant matrix

We use an experimental design method for computing a local quadratic form which is adequate to find stationary points and to evaluate the force constant matrix on a k-dimensional potential energy hypersurface. Two types of designs are particularly discussed: the composite and the Doehiert's plane. We give examples for illustrating the methodology. Some thermodynamical properties are deduced from our results. Such a method may be used with every type of theoretical calculations (SCF or CI ) and with any program without modification.     

Theoretical study of the borane and diborane positive ions

Summary We describe the geometric, electronic and energetic (H _f) properties of B₂H ₆ ⁺ and BH ₃ ⁺ . Comparisons with experimental measurements have also been made with borane, diborane, BH, BH⁺ and BH ₂ ⁺ . All the theoretical calculations have been performed with various basis sets: 6-31G, 6-31G and 6-31⁺G (2d,f). The geometry optimizations are done at the SCF (RHF or UHF), MP2 and MP4 levels.     

Role of monovalent alkali ions in the Yb3+ centers of CaF2 laser crystals

Yb³⁺ and M⁺ monovalent alkali ions (M⁺ = Li⁺, Na⁺, K⁺)-co-doped CaF₂ cubic laser crystals were grown by the micro-pulling-down method (μ-PD) under CF₄ atmosphere. Structural and spectroscopic characterizations of Yb³⁺ in substitution of Ca²⁺ (absorption, emission and decay curves) were carried out to study the effect of M⁺ ions as charge compensators.     

Synthesis of Novel N-Methylmorpholine-Substituted Benzimidazolium Salts as Potential α-Glucosidase Inhibitors

The α-glucosidase enzyme, located in the brush border of the small intestine, is responsible for overall glycemic control in the body. It hydrolyses the 1,4-linkage in the carbohydrates to form blood-absorbable monosaccharides that ultimately increase the blood glucose level. α-Glucosidase inhibitors (AGIs) can reduce hydrolytic activity and help to control type 2 diabetes. Aiming to achieve this, a novel series of 1-benzyl-3-((2-substitutedphenyl)amino)-2-oxoethyl)-2-(morpholinomethyl)-1H-benzimidazol-3-ium chloride was synthesized and screened for its α-glucosidase inhibitory potential. Compounds 5d, 5f, 5g, 5h and 5k exhibited better α-glucosidase inhibitions compared to the standard drug (acarbose IC₅₀ = 58.8 ± 0.012 µM) with IC₅₀ values of 15 ± 0.030, 19 ± 0.060, 25 ± 0.106, 21 ± 0.07 and 26 ± 0.035 µM, respectively. Furthermore, the molecular docking studies explored the mechanism of enzyme inhibitions by different 1,2,3-trisubstituted benzimidazolium salts via significant ligand–receptor interactions.