Showing papers on "Acetonitrile published in 1992"

How do organic solvents affect peroxidase structure and function

Abstract: The effect of organic solvents on horseradish peroxidase structure and function has been studied. Some, but not complete, enzyme denaturation occurs even in low volumes of water-miscible organic solvents (e.g., greater than 30% v/v dioxane, greater than 50% v/v methanol, and greater than 20% v/v acetonitrile) as determined by the decreased difference between the fluorescence of peroxidase's sole tryptophan residue and free L-tryptophan in solution. Absorbance and electron paramagnetic resonance spectroscopies indicate exposure of peroxidase's active site to the organic solvent. This reduces the local polarity in the enzyme's active site and results in stronger hydrogen bonding of phenolic substrates to the enzyme. In extreme cases (e.g., 95% v/v dioxane, 90% v/v acetonitrile, and ethyl and butyl acetate containing 2 and 1% v/v aqueous buffer, respectively), the transition state of the enzymic reaction is sufficiently perturbed so as to alter the magnitude of the Hammett rho value. This is most likely the result of the increased strength of hydrogen bonding between electron-donating alkoxyphenols (negative sigma values) and an electrophilic group in the enzyme's active site, thereby reducing catalytic efficiencies for such substrates relative to alkyl- and chlorophenols. Perhaps the most important effect of the organic solvent, however, is the significant ground-state stabilization of phenolic substrates in organic media as opposed to aqueous buffer. This stabilization can account for nearly 4 orders of magnitude in reduction of catalytic efficiency and is manifested in increased Km's. This study indicates that enzymes can maintain much of their native active-site structure in organic media and that the effect of solvent on substrate thermodynamics must be considered.

Bis(carbonyl)gold(I) undecafluorodiantimonate(V), [Au(CO)2][Sb2F11]: synthesis, vibrational, and carbon-13 NMR study and the molecular structure of bis(acetonitrile)gold(I) hexafluoroantimonate(V), [Au(NCCH3)2][SbF6]

Abstract: The synthesis of the bis(carbonyl)gold(I) salt, [Au(CO) 2 ][Sb 2 F 11 ], is achieved in a of gold(III) fluorosulfate, Au(SO 3 F) 3 , in HSO 3 F to give Au(CO)SO 3 F as an intermediate, followed by solvolysis in liquid antimony(V) fluoride in the presence of carbon monoxide. The use of 13 CO or C 18 O permits the synthesis of the corresponding isotopically labeled salts. The compound is thermally stable up to 130 o C.

Stereocomplex formation between enantiomeric poly(lactic acids). 5. Calorimetric and morphological studies on the stereocomplex formed in acetonitrile solution

Abstract: Precipitates from acetonitrile solutions of poly(D-lactic acid) (PDLA)+poly(L-lactic acid) (PLLA) mixtures obtained under various conditions by changing the mixing ratio of the isomers, the polymer concentrations, the molecular weights of the polymers, and the solution temperature were found to contain only racemic crystallites (stereocomplexes) consisting of equimolar amounts of D-monomer and L-monomer units, independent of the PDLA content in the initial acetonitrile solution

Homogeneous catalytic hydrogenation. 6. Synthetic and mechanistic aspects of the regioselective reductions of model coal nitrogen, sulfur, and oxygen heteroaromatic compounds using the (.eta.5-pentamethylcyclopentadienyl)rhodium tris(acetonitrile) dication complex as the catalyst precursor

Abstract: The synthetic and mechanistic aspects of the regioselective hydrogenation of representative mono and polynuclear heteroaromatic nitrogen, sulfur, and oxygen model coal compounds such as 2-methylpyridine (1), N-methylindole (2), benzofuran (3), benzothiophene (4), quinoline (5), 2-methylquinoline (6), 5,6- and 7,8-benzoquinolines (7 and 8), and acridine (9) were studied with a (η 5 -pentamethylcuclopentadienyl)rhodium tris(acetonitrile) dicationic complex, [Cp*Rh(CH 3 CN) 3 ] 2+ , as the catalyst precursor. The order of relative rates as a function of structure was found to be 8>>>9>5>7>6>4>>1-3

Temporary anion states of hydrogen cyanide, methyl cyanide, and methylene dicyanide, selected cyanoethylenes, benzonitrile, and tetracyanoquinodimethane

Abstract: The vertical electron affinities of temporary negative ion states of HCN, CH{sub 3}CN, CH{sub 2}(CN){sub 2}, acrylonitrile, fumaronitrile, benzonitrile, tetracyanoquinodimethane, and tetracyanoethylene are determined using electron transmission spectroscopy and molecular orbital calculations.

Solvent‐derived metal oxides in electrospray mass spectrometry of metal salt solutions

Abstract: The electrospray mass spectra of MX2and MX3salts (where X is typically halide or nitrate) in protic and aprotic solvents, and solvent mixtures were examined. Comparisons of species responses with equilibrium aqueous solution concentrations were made. For MX2salts, a good correlation between MOH+ response and MOH+ solution concentration was observed under conditions where the collision energy was nominally zero. Cu(II) is easily reduced in acetonitrile to Cu(I); Cu(I) was the principal species observed in the electrospray mass spectrum of Cu(II) in acetonitrile whereas Cu(II) was the principal species observed in that of Cu(II) in dimethyl sulphoxide. Gas-phase reactions between solvated clusters produced by electrospray and a second solvent vapour were examined. M3+clusters were the principal ions observed when an aqueous solution of MX3was sprayed in the presence of aprotic solvent vapours.

Reactivities of diarylmethyl and triarylmethyl cations with primary amines in aqueous acetonitrile solutions. The importance of amine hydration

Abstract: By use of the technique of laser flash photolysis, rate constants k(RNH 2 ) have been directly measured for the reactions of primary amines RCH 2 NH 2 (R=CH 3 CH 2 , CH 3 OCH 2 , NCCH 2 , CF 3 ) with diarylmethyl cations (D + ) in acetonitrile/water solutions

Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance studies of buckminsterfullerene (C60) film electrodeposition and tetra-n-butylammonium electrodoping in acetonitrile

Abstract: A simple and efficient method for presented for preparation of insoluble thin films of C 60 and the (TBA + )(C 60 - ) and (TBA + ) 2 (C 60 2- ) salts where TBA + represents the tetra-n-butylammonium cation. The method consists of bulk electroreducing a fine suspension of solid C 60 in acetonitrile solutions under a controlled potential which is sufficiently negative to generate the soluble C 60 3- anion

Synthesis and complexing properties of a double-calix[4]arene crown ether

Abstract: Treatment ofp-tert-butylcalix[4]arene with tetraethyleneglycol ditosylate in the presence of potassium carbonate in acetonitrile afforded the first example of a double-calixcrown (1) in 52% yield. The double-calixcrown (1) was shown to form 1: 1 complexes with potassium and rubidium picrates in the solid state and in solution in chloroform. The stability constants of the alkali complexes have been determined in acetonitrile, as well as the phase transfer parameters from water to dichloromethane.

Trimethyl phosphate: the intrinsic reactivity of carbon versus phosphorus sites with anionic nucleophiles

Abstract: The thermally equilibrated (298±3 K) gas-phase ion-molecule reactions of trimethyl phosphate with a variety of anions in 0.3 Torr of helium buffer gas have been examined using the flowing afterglow technique. Inorganic anions including amide, hydroxide, alkoxides, and fluoride, as well as the hydrogen sulfide anion, and organic anions including benzenide, allyl, and benzyl anions, as well as the conjugate bases of acetonitrile and acetaldehyde, were used as reactant anions

Comparative kinetic studies of polypyrrole electrogeneration from acetonitrile solutions

Abstract: The formation and growth of polypyrrole films on platinum electrodes from acetonitrile media has been followed by microgravimetricex situ determination of the polymer grafted on the electrode. Kinetic parameters were also obtained from the charge consumed during polymerization. The electrogenerated polymer films were checked in the background electrolyte by voltammetry and chronoamperometry. Assuming a constant oxidation or reduction charge per unit of polymer weight, these charges were used to obtain the reaction order during the polymerization processes. The kinetics were found to be dependent on [pyrrole]0.5 [LiClO4]0.5 from gravimetric determination; [pyrrole]0.4 [LiClO4]0.5 from the polymerization charge; [pyrrole]0.4 [LiClO4]0.5 from the anodic charge of the control voltammograms and [pyrrole]0.4 [LiClO4]0.4 from the anodic and cathodic charge of the control chronoamperograms. Good agreement was found between the different methods. The good agreement between order dependence was due to the low water content.

A study of ion pairing in acetonitrile solutions containing magnesium perchlorate using attenuated total reflection FTIR spectroscopy

Abstract: A study of ion pairing for Mg(ClO 4 ) 2 dissolved in acetonitrile has been carried out using attenuated total reflection FTIR spectroscopy. The present results indicate that the coordination number for ligands around the Mg 2+ ion is approximately four, and not six as previously reported. Ion pairing is relatively strong with 70% of the Mg 2+ ions forming contact ion pairs with one perchlorate ion. The spectral characteristics of acetonitrile associated with Mg 2+ have been clearly distinguished from those of the free molecule

Complex Formation of Hydronium Ion with Several Crown Ethers in 1,2-Dichloroethane, Acetonitrile, and Nitrobenzene Solutions

Abstract: A conductance study concerning the interaction between hydronium ion and several crown ethers in acetonitrile, nitrobenzene and 1,2-dichloroethane solutions has been carried out at 25°C. The stability constants of the resulting 1:1 complexes in acetonitrile and nitrobenzene solutions were determined from the molar conductance-mole ratio data and found to vary in the order 18C6>DB30C10>DC18C6>DB18C6>DB21C7>DB24C8>B15C5. In 1,2-dichloroethane solution, the complexation process results in the dissociation of ion pairs. There is an inverse relationship between the stabilities of the complexes and the Gutmann donicity of the solvents. In nitrobenzene solution, some evidence for the formation of a 2:1 sandwich adduct between the smaller crowns (i.e., B15C5 and 18-crowns) are observed from the molar conductance-mole ratio data which is supported by the1H NMR data.

Preparation and characterization of crystalline N-acylammonium salts

Abstract: The reaction of a tertiary amine with an acid chloride or chloroformate followed by anion exchange with either sodium tetraphenylborate or silver tetrafluoroborate provides stable, nonhygroscopic, crystalline acylammonium salts

New Applications of Weak Donor Atoms to Coordination, Organometallic and Materials Chemistry

Abstract: Non-aqueous solvated transition metal cations are enjoying renewed popularity as precursors for new applications in molecular and materials chemistry. In two related projects, we are engaged in a general investigation of the syntheses, structures and reactivity of new compounds containing nitrile and ether ligands. A major effort is underway to synthesize homoleptic metal-metal bonded acetonitrile cations of second and third row metals for use in coordination and organometallic chemistry, photochemistry and materials chemistry. Dinuclear carboxylate, halide and halide-phosphine complexes are used to synthesize the metal-metal bonded acetonitrile cations [M2(MeCN)10]4+ (M = Re, Rh). The unusual partially solvated species [Mo2 IV,IV(μ-F)(MeCN)8O2]3+ was prepared from MoCl3(THF)3 in CH3CN. Reactions of the bulky ether-phosphine ligand tris(2,4,6-trimethoxyphenyl)phosphine (TMPP) with the dinuclear cation [Rh2(MeCN)10]4+ and with acetonitrile cations of 3d metals [M(MeCN)6]2+ (M = Co, Ni) produce bis...

Preferential solvation of 6-propionyl(N,N-dimethylamino)naphthalene in binary, polar solvent mixtures

Abstract: Using fluorescence spectroscopy, we have determined the extent of preferential solvation of the dye PRODAN (6-propionyl(N,N-dimethylamino)naphthalene) in binary mixture where one component is capable of hydrogen bonding. In mixtures of methanol with acetone, acetonitrile, or pyridine the spectroscopically determined mole fraction of the PRO-DAN-methanol complex was much higher than the methanol mole fraction. The amount of preferential solvation followed the trend acetonitrile>acetone>pyridine with corresponding stoichiometries of 1.1, 1.2, and 0.93 and equilibrium constant of 12.0, 7.9, and 1.7

Enzymatic polymerization: The first in vitro synthesis of cellulose via nonbiosynthetic path catalyzed by cellulase

Abstract: The in vitro synthesis of cellulose via a nonbiosynthetic path has been achieved for the first time by condensation of β-D-cellobiosyl fluoride as substrate for cellulase in a mixed solvent of acetonitrile/acetate buffer (pH 5,5:1) (enzymatic polymerization). Under reaction condition of a higher substrate concentration or higher acetonitrile concentration, cellooligosaccharides were produced predominantly. The present method of using a glycosyl fluoride as substrate for a hydrolytic enzyme in an organic/water mixed solvent has successfully been applied to synthesis of maltooligosaccharides and unnatural oligosaccharides.

Anion exchange activity of electrochemically bonded ethylene diamine on carbon fibres

Abstract: Carbon fibre based anion exchangers were prepared through electrochemical oxidation and bonding of ethylene diamine on fibre electrodes in acetonitrile and subsequent formation of the chloride salts of the ammonium groups.