Showing papers on "Bromide published in 1973"

The Crystal Structures of Methyl Bromide and Methyl Iodide

Abstract: The crystal structures of methyl bromide and methyl iodide have been determined by the X-ray diffraction method at about −120°C and about −80°C respectively. Both the crystals are isomorphous, with orthorhombic space group D2h16–Pnma. Unit cells containing four molecules have the dimensions: a=4.474(1), b=6.420(2), and c=9.150(1) A for methyl bromide, and: a=4.597(2), b=6.987(1), and c=10.117(1) A for methyl iodide. These structures are quite different from that of methyl chloride, which has a symmetry of C2v12–Cmc21. In the three crystals, all the molecules are found on the mirror planes; the difference lies in the mutual orientations of the molecules.

The interaction between ribonuclease A and surfactants.

Abstract: 1. U.v. difference spectra show that the anionic surfactant sodium n-dodecyl sulphate unfolds ribonuclease A at pH7.3 and 10.3, but that the cationic surfactant n-dodecyltrimethylammonium bromide does not affect the conformation of the enzyme. 2. Equilibrium-dialysis experiments show that sodium n-dodecyl sulphate binds to ribonuclease A, but no binding of n-dodecyltrimethylammonium bromide could be detected at pH7.3. 3. The enzymic activity of ribonuclease A is unaffected by n-dodecyltrimethylammonium bromide up to a concentration of 0.03m at 25°C. 4. Ultracentrifuge studies support the conclusion that n-dodecyltrimethylammonium bromide does not interact significantly with ribonuclease A. 5. The enthalpy change as measured by microcalorimetry on binding of sodium n-dodecyl sulphate to ribonuclease A is consistent with an exothermic enthalpy of binding occurring simultaneously with an endothermic enthalpy of chain unfolding.

Alcohol, barbiturate, and bromide withdrawal syndromes in mice*

Abstract: Most diseases are characterized by a continuous dynamic interaction between the causative agent and the diseased organism. Withdrawal illnesses are unique in that they occur with the partial or complete removal of the causative agent. Apparently the addictive drug has elicited a functional adaptation to its presence in the organism. Upon discontinuation of the drug, this adaptation becomes the disease. The pathogenesis is essentially unknown: However, several working hypotheses are being explored at all levels of biological organization, from the behavioral to the molecular.30~ 37-41 Eventually it will be possible to integrate into a coherent concept of the multitude of observations which now appear isolated and sometimes contradictory. A major obstacle to progress in the field of alcohol withdrawal research has been the lack of suitable animal models to test various pathogenetic hypotheses and empirical therapeutic procedures. Several recently developed animal models are described in this monograph. This report describes the induction of ethanol, barbiturate, and bromide withdrawal syndromes in mice. Some of the data have been presented previously.10

Cross sections for the alkali atom‐Br2 reactions

Abstract: The reaction cross sections of alkali metal atoms with bromine molecules have been obtained by direct measurements of alkali atom decay rates. The alkali atoms were produced in the presence of a known amount of bromine molecules by photodissociating the bromide of the particular alkali atom with a short pulse of uv light. As the alkali atoms reacted with bromine molecules their decay rate was monitored by observing the transmission of alkali atom resonance light through the vapor. The cross sections were computed from the decay rates. They are Na, 116 A2; K, 151 A2, Rb, 197 A2, and Cs, 204 A2. These results are accurate to about 15%. The results are compared with theoretical calculations.

The role of magnesium ions in β-galactosidase-catalysed hydrolyses. Studies on charge and shape of the β-galactopyranosyl-binding site

Abstract: 1. beta-d-Galactopyranosyl trimethylammonium bromide is a competitive inhibitor of beta-galactosidase, K(i)=1.4+/-0.2mm at 25 degrees C. 2. Tetramethylammonium bromide is not an inhibitor (K(i)>0.2m). 3. The kinetics of deactivation of Mg(2+)-saturated, and of inhibitor-and Mg(2+)-saturated, enzyme in 10mm-EDTA are similar. 4. The apparent K(i) for the glycosylammonium salt is approx. 2.2mm in the absence of Mg(2+). 5. It is therefore concluded that Mg(2+) and the inhibitor bind independently, and that the Mg(2+) does not act as an electrophilic catalyst. 6. Complexant fluorescence measurements indicate binding of 1 Mg(2+) ion per 135000-dalton protomer. 7. This stoicheiometry is confirmed by equilibrium dialysis. 8. 1,6-Anhydrogalactopyranose is neither a substrate (k(cat.)/K(m) 0.2m). 9. Considerations of conformations available to the cationic inhibitor and to the anhydrogalactose indicate that the substrate is bound with the pyranose ring in a conformation not greatly different from the normal chair (C1) conformation.

Reaction between vicinal diols and hydrogen bromide in acetic acid; synthesis of chiral propylene oxide

Abstract: Several vicinal diols react rapidly with 6M-hydrogen bromide in acetic acid to afford vicinal acetoxy-bromides in excellent yield. The mechanism, scope, and limitations of this reaction have been explored. Its mechanism involves monoacetylation of the diol, cyclisation to a 1,3-dioxolan-2-ylium ion, and capture of this intermediate by bromide ion. This has been established by kinetic studies, determination of substrate stereospecificity, and observation of intermediate 1,3-dioxolan-2-ylium ions by n.m.r. spectroscopy. The preparative value of the reaction is illustrated by its application in a simple three-stage synthesis of optically pure (S)-propylene oxide from readily available (S)-ethyl lactate.

Preparation of alkyl bromides from the corresponding alcohols and Me2SBr2

Abstract: On treating various alcohols with dimethyl-bromosulphonium bromide the corresponding bromide is obtained in high yield, the reaction proceeding mainly through an inversion process.

Crystal structure of dibromodiadeniniumcopper(II) dibromide: a complex with unidentate adenine

Abstract: The crystal structure of the title compound has been determined from three-dimensional X-ray diffractometer data by Patterson and Fourier methods. Crystals are monoclinic with unit-cell dimensions a= 18·649. b= 8·731, c= 12·028 A, β= 113·14°, space group C2/c, and Z= 4. Full-matrix least-squares refinement by use of 1657 independent reflections has reached R 0·056.The structure contains complex cations [Cu(adenineH)2Br2]2+ and bromide ions. In the complex cation the central copper atom lies on a diad and is co-ordinated to two N(9) atoms of unidentate adeninium ligands and to two terminal bromide atoms. The copper atom has a co-ordination intermediate between tetrahedral and square planar, with Cu–N 2·013 and Cu–Br 2·361 A. The adenine molecule is protonated at N(1), and atoms N(1) and N(7) are involved in hydrogen bonding of the type N–H ⋯ Br–.

Structural Properties of the Creatine-Kinase Active Site Studied by Chromophoric-Reagent Labelling

Abstract: The environment of the active site of creatine kinase has been investigated by means of three chromophoric reagents: 2-hydroxy-5-nitrobenzyl bromide, 2-methoxy-5-nitrobenzyl bromide and 2-(dansylamino)ethyl monophosphate. 1 The first two reagents are incorporated at the essential thiol groups. The effect of pH on the spectra of the 2-hydroxy-5-nitrobenzyl-labelled creatine kinase suggests that this reagent lies inside the active site near an ionized residue, while the 2-methoxy-5-nitrobenzyl group is apparently exposed to the medium. Conformational changes induced by the binding of different ligands, including nucleotide substrates or anions, produce only perturbations of the 2-hydroxy-5-nitro-benzyl chromophore. 2 The 2-(dansylamino)ethyl monophosphate (which is really an analogue of the nucleotide substrate) interacts with the nucleotide site of creatine and arginine kinases in a relatively hydrophobic environment.

Zinc-bromide secondary cell

Abstract: A zinc-bromine secondary cell is divided into two compartments by an ion exchange diaphragm. The electrolyte system includes an essentially bromide ion free, aqueous solution containing a zinc ion as an anolyte and a bromide ion containing catholyte. A method of operating the cell is disclosed.

Selective isomerization of pentenenitriles

Abstract: A process of isomerizing geometric isomers of 2-pentenenitrile or 3-pentenenitrile by contacting the isomers at a temperature in the range of 100*-200*C. with a catalyst of the general formula R3CX, such as triphenylmethyl bromide. By this process trans-2pentenenitrile can be separated from a mixture containing mainly 3-pentenenitrile by isomerizing the trans-2-pentenenitrile to cis-2-pentenenitrile and removing the more volatile cis isomer by fractional distillation.

Unstable intermediates. Part CXXIV. Alkyl radical–halide ion adducts

Abstract: A recent suggestion that methyl bromide in methyl cyanide when exposed to γ-rays at 77 K gives methyl radicals which are loosely associated with their parent bromide ions has been examined, the previous e.s.r. results have been confirmed, and the bromine hyperfine tensor components obtained. These show that transfer of spin to bromine is small, and indeed it may well be that spin density is acquired mainly by spin polarisation. Similar results were obtained from methyl iodide and ethyl bromide. t-Butyl bromide gave only Me3C· radicals. The same compounds in methyl alcohol gave only the corresponding alkyl radicals with no halide interaction. This difference is explained in terms of the far greater anion solvating power of the alcohol. Methylene bromide in both solvents gave Br2– and HĊBr2 but no species corresponding to the bromide ion adducts. The pure compounds on irradiation at 77 K gave dihalide anions and other products, but no halide ion adducts. In contrast, N-chloro- and N-bromo-amides gave σ* radical anions without loss of halide ion, both in methyl cyanide and in methyl alcohol. These differences are explained in terms of the different structures of the organic radicals formed by loss of halide ions.