Structure of a five-coordinate mononuclear cobalt(II) complex: chlorobis([N,N-(1,1′-biphenyl-2,2′-dimethylene)]-2-aminomethyl) pyridine)cobalt(II) bromide

A penta-coordinate mononuclear cobalt(II) complex, [Co(BP)₂(Cl⁻)](Br⁻), 1 with a novel, biphenyl-appended N,N-bidentate ligand, BP ([N,N-(1,1′-biphenyl-2,2′-dimethylene)]-2-aminomethyl) pyridine) was synthesized and characterized by elemental analysis, UV-Vis, electro-spray ionization mass spectrum and single crystal XRD. The title complex crystallizes in the monoclinic space group C2/c with cell dimensions a = 11.389(2), b = 25.627(3), c = 12.276(3) Å, β = 100.419(18)° and Z = 2. The cobalt atom has a distorted trigonal bipyramidal (tbp) geometry and is surrounded by 4Ns of two BP, and a Cl⁻/Br⁻ at the 5th coordination site. This is the first report of a mononuclear tbp cobalt complex with biphenyl appended bidentate ligand containing amino-pyridyl moiety.     

Structure determination of 3β-acetoxy-cholest-5-ene-7-one—A steroid

The crystal structure of 3β-acetoxy-cholest-5-ene-7-one (C₂₉H₄₆O₃) has been determined by X-ray diffraction methods. The compound crystallizes in the monoclinic crystal system (space group P2₁) with the unit cell parameters a = 9.632(1) Å, b = 12.280(1) Å, c = 23.099(2) Å, β = 99.52(1)°, and Z = 4. The structure has been solved by direct methods and refined to an R-value of 0.065 for 3927 observed reflections [F ₀ > 4σ(F ₀)]. Two crystallographically independent molecules (I and II) in the asymmetric unit have been observed. In both molecules, rings A and C of the steroid nucleus exist in a chair conformation. Ring B of molecule I adopts a 5α,6β half-chair conformation, and ring B of molecule II shows a 6α sofa conformation. Ring D adopts a 13α,14β half-chair conformation in molecule I and a 13α,14β half-chair conformation in molecule II. The crystal structure is stabilized by the intramolecular and intermolecular C-H?O interactions.     

PHOTOCYCLOADDITION OF ACETONE TO URACIL AND CYTOSINE

Abstract— Ultraviolet irradiation (Λ > 280 nm) of uracil in aqueous acetone (1:1) produces cyclobutane uracil dimer and uracil-acetone addition product. The addition product is identified as an oxetane. The same product is also obtained from cytosine irradiated under the same conditions. The cytosine-acetone oxetane apparently undergoes deamination readily. Irradiation (Λ= 265 nm) of the oxetane in aqueous solution produces acetone and uracil with a quantum efficiency of 0–16.     

Intramolecular pi-stacking interaction in a rigid molecular hinge substituted with 1-(pyrenylethynyl) units

Synthesis of a tetrakis(1-pyrenylethynyl)-substituted rigid hinge-like molecule (1) is described. The intramolecular pi-stacking interaction of the pyrene units is studied by 1H NMR and fluorescence spectroscopy. Due to intramolecular pi-stacking interactions, chemical shifts of the pyrene protons in 1 are highly shielded in the NMR spectrum. Fluorescence from the static excimer state is observed due to pi-stacking interactions among the pyrene units in the ground state of 1. Based on the spectroscopic evidence, conformations and dynamics of 1, arising from the hindered rotation of the major axis, are proposed.     

A Convenient Approach to Stereoisomeric Iminocyclitols: Generation of Potent Brain‐Permeable OGA Inhibitors

Pyrrolidine‐based iminocyclitols are a promising class of glycosidase inhibitors. Reported herein is a convenient epimerization strategy that provides direct access to a range of stereoisomeric iminocyclitol inhibitors of O‐GlcNAcase (OGA), the enzyme responsible for catalyzing removal of O‐GlcNAc from nucleocytoplasmic proteins. Structural details regarding the binding of these inhibitors to a bacterial homologue of OGA reveal the basis for potency. These compounds are orally available and permeate into rodent brain to increase O‐GlcNAc, and should prove useful tools for studying the role of OGA in health and disease.     

Electron donor properties and catalytic activity of manganese ferrospinels

The electron donating properties of manganese ferrospinels of various compositions (MnFe₂O₄, Mn_1.2Fe_1.8O₄, Mn₂FeO₄ and Mn_2.5Fe_0.5O₄) were studied from the adsorption of electron acceptors of various electron affinity values from acetonitrile as solvent. The limit of electron transfer from the oxide surface is from 1.77 to 2.40 eV in terms of the electron affinity of the electron acceptor. The data have been correlated with the catalytic activity of these oxides towards autoxidation of sulfites. Both weak and strong electron donor sites catalyze the reaction.     

Correlation analysis of reactivity in the addition of substituted benzylamines to benzylidenemalononitrile

The kinetics of addition of a number of ortho‐, meta‐, and para‐substituted benzylamines to benzylidenemalononitrile (BMN) in acetonitrile have been studied. The reaction is first‐order with respect to BMN. The order with respect to the amine is more than one. It has been shown that the reaction followed two mechanistic pathways, uncatalyzed and catalyzed by the amine. The enthalpy of activation for the catalyzed path is negative indicating the presence of a preequilibrium (k₁, k₋₁) leading to the formation of a zwitterion. The values of rate constant, k₁, for the nucleophilic attack have been determined for twenty‐eight benzylamines. The rate constant, k₁ was subjected to correlation analyses using various single‐ and multi‐parametric equations. The best correlation is obtained in terms of Charton's LDR and LDRS equations. The polar regression coefficients are negative indicating the formation of a cationic species in the transition state. The reaction is subject to steric hindrance by ortho‐substituents. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 245–252, 1999     

Synthesis,structural characterization and catalytic activity study of Mn(II), Fe(III), Ni(II), Cu(II) and Zn(II) complexes of quinoxaline-2-carboxalidine-2-amino-5-methylphenol: Crystal structure of the nickel(II) complex

Five new transition metal complexes [MnL(OAc)]·H₂O (1), [FeLCl₂] (2), [NiL₂]·H₂O (3), [CuLCl] (4) and [ZnL₂]·2H₂O (5) have been synthesized using a tridentate Schiff base ligand, HL (quinoxaline-2-carboxalidine-2-amino-5-methylphenol) and the complexes have been characterized by physicochemical and spectroscopic techniques. The spectral analyses reveal an octahedral geometry for 3, square pyramidal structure for 2 and square planar structure for 4. Analytical and physicochemical data indicate tetrahedral structure for 1 and octahedral structure for 5. The crystallographic study reveals that [NiL₂]·H₂O shows distorted octahedral geometry with a cis arrangement of N₄O₂ donor set of the bis Schiff base and exhibits a two-dimensional polymeric structure parallel to [0 1 0] plane. The complexes were screened for catalytic phenol hydroxylation reaction. Coordinatively unsaturated manganese(II), iron(III) and copper(II) complexes were found to be active catalysts. The poor catalytic activity of the nickel(II) complex is due to coordinatively saturated octahedral nature of the complex. Maximum conversion of phenol was observed for the copper(II) complex and the major product was catechol.