Showing papers on "Acetonitrile published in 1995"

Assessing the structural integrity of a lyophilized protein in organic solvents

Abstract: The structure of a model protein, bovine pancreatic trypsin inhibitor (BPTI), in organic solvents has been examined using hydrogen isotope exchange/high-resolution NMR methodology. When lyophilized deuterated BPTI is suspended in acetonitrile, tetrahydrofuran, ethyl acetate, or butanol, each containing 1% {sup 1}H{sub 2}O, several protein amide protons that are buried and strongly hydrogen bonded in aqueous solution are found to exchange with the solvent significantly within 24 h. When solid BPTI is prepared by different methods, such as rotary evaporation, acetone precipitation, or lyophilization from a dimethyl sulfoxide solution, and subsequently suspended in acetonitrile containing 1% water, the exchange intensities of the amide protons vary greatly among the preparations. These data combined suggest that the structure of BPTI in the four aforementioned organic solvents is partially unfolded, but not more so than in lyophilized powder, i.e., that these solvents cause little additional protein denaturation beyond that brought about by lyophilization. Using the same methodology, the BPTI structure also has been studied in several protein-dissolving solvents containing 1% water. In dimethyl sulfoxide, dimethylformamide, or methanol, the same amide protons exchange almost completely within 24 h, while in glycerol they do not. 33 refs., 3 figs., 2 tabs.

Dielectric relaxation of electrolyte solutions in acetonitrile

Abstract: Complex permittivity spectra in the frequency range 0.95≤v (GHz)≤89 for acetonitrile and its solutions of LiBr, NaI, NaClO4, and Bu4NBr at 25°C show one Debye equation for the neat solvent whereas the superposition of a Debye process for the solute and a Cole-Cole distribution for the solvent is necessary to account for the dielectric relaxation behavior of the solutions. The reorientation of bulk acetonitrile is diffusive and only weakly coupled to viscosity. The number of solvent molecules irrotationally bound to the electrolyte is in good agreement with conventional solvation numbers for all electrolytes, when kinetic depolarization is assumed to be negligible. The solute relaxation process is dominated by the formation kinetics and reorientation of contact ion pairs. There is evidence for solvent-shared ion pairs in dilute NaClO4 solutions.

Cationic iroporphyrins as catalyst in comparative oxidation of hydrocarbons: homogeneous and supported on inorganic matrices systems

Abstract: Cationic ironporphyrins in solution and supported on imidazole propyl gel (IPG) and silica gel (SG) as catalyst in cyclohexane hydroxylation using iodosylarene as oxygen donor were studied. FeTM4PyP 5+ , 1 as homogeneous catalyst for cyclohexane hydroxylation, in acetonitrile (CH 3 CN) and ultrasound stirring, gives cyclohexanol (C-ol) yields of 20%. The FeTM2PyP 5+ , 2 as catalyst for cyclohexene oxidation in CH 3 CN and ultrasound stirring is a very efficient system, giving 93% of total yield, with an epoxide:alcohol:ketone selectivity of 77:12:11. The supported systems, 1 -IPG and 1 -SG are particularly efficient in dichloromethane (CH 2 Cl 2 ), giving C-ol yields of 37% and 53%, respectively. These systems consist of polar hemin in isolated sites, which selectively catalyze cyclohexane oxidation in apolar solvent. They represent good cytochrome P-450 model systems. In the same way, the active site of P-450 consists of a polar protohemin in a hydrophobic pocket, promoting selective cyclohexane oxidation. These rigid cationic 1 -IPG, 1 -SG, 2 -IPG, 2 -SG, 3 -IPG and 3 -SG systems can catalyze with very small amounts of ironporphyrins, which correspond to about 30–80 times fewer numbers than the hemin in P-450 catalytic site.

Preferential solvation controlled by clustering conditions of acetonitrile–water mixtures

Abstract: Experimental evidence for the preferential solvation of phenol in a mixed solvent of acetonitrile and water has been obtained by mass spectrometric analysis of the clusters isolated from liquid droplets by the adiabatic expansion. The effect of temperature on the formation of phenol–hydrate clusters, (C6H5OH)(H2O)n : n= 1,2,3, …, showed that phenol molecules are solbated preferentially by acetonitrile molecules at xw(water mole fraction) < 0.85, the phenol–hydrate clusters were hardly observed at temperatures lower than 50 °C but appeared at higher temperatures. On the contrary, at xw 0.85, hydrate formation became preferable at lower temperatures. The observed temperature effect confirmed microscopically inhomogeneous clustering of the solvent and solute molecules in the mixtures. A. similar temperature effect was also observed in the emission spectra of 2-naphthol in the same mixtures.

Gas phase hydrogenation of acetonitrile on Raney nickel catalysts: reactive hydrogen

Abstract: Catalytic hydrogenation of acetonitrile on Raney nickel has been studied in gas phase. The chemisorption of hydrogen has been followed by TPD and inelastic neutron scattering; these techniques indicate the presence of both weakly and strongly adsorbed hydrogen. Kinetic studies and pulse experiments show that only weakly adsorbed hydrogen, localised on top of the nickel atoms and on C 3 v symmetry sites, is active for the hydrogenation. Acetonitrile and reactive hydrogen are weakly adsorbed on Raney nickel, and compete for the same site. Conversely, amines more strongly adsorbed than acetonitrile, but on different sites, do not constitute a poison for the reaction.

Characterization of simple photoresponsive systems and their applications to metal ion transport

Abstract: Some new photoresponsive azobenzenes (1–5) have been synthesized and characterized. On irradiation at 330 nm these systems undergo conversion from the E to the Z form to a varying extent which depends upon the nature and position of substitution on the azobenzene rings. They revert back to the E form on thermal isomerization in the dark. Photochemical equilibria have been studied and compared in acetonitrile and o-dichlorobenzene; E forms are stabilized more in o-dichlorobenzene than in acetonitrile. Two of the molecules (1 and 4) show enhanced transport of Cu2+ ions across a liquid membrane on irradiation.

IR study of acetonitrile adsorption on hydroxylated zirconium dioxide: mechanism of acetonitrile hydrolysis

Abstract: In situ FTIR spectroscopy has been used to investigate the adsorption of acetonitrile at room temperature onto zirconia activated at various temperatures (423, 723 and 873 K), attention being focussed on the sample pretreated at 423 K. Two acetamide monoanions (CH3CONH–), called α and β species, were spectroscopically evidenced with main bands, respectively, at 1169, 1432, 1590, 3320 cm–1 and at 1196, 1471, 1557, 3340 cm–1. The use of 18O- or D-labelled compounds gave poor results as far as the vibrational mode description was concerned, except for the δ(NH) mode. However, the H → D substitution was very useful for determining mechanisms. It was proposed that the β-type acetamide species results from H2O displacement from the surface and CH3CN adsorption in acidic Lewis sites, followed by a hydroxylation of this latter species by H2O readsorption. The formation of the α-type acetamide species was thought to be due to a direct interaction of acetonitrile with basic OH groups. Upon heating at a temperature higher than 373 K and in the presence of water vapour, acetamide species were hydrolysed into acetate species.

Novel metal imido calixarene complexes

Abstract: Treatment of [Mo(NR)2(OBut)2](R = C6H3Pri2-2,6) with calix-4-arene (H4L1) and calix-8-arene (H8L2) affords novel mono- and di-metallocalixarene complexes; the crystal structures of [Mo(NR) L1(NCMe)]1 and [{Mo(NR)(NCMe)}2L2]2, both incorporating additional acetonitrile solvent of crystallisation, are reported.

Conducting neutral radical crystals of axially substituted phthalocyanine: crystal structures, dimensionality and electrical conductivity

Abstract: Electrocrystallization of the dicyanophthalocyaninatocobalt(III) anion, [Co(Pc)(CN)2]–, in a mixed solvent of acetonitrile and chloroform gives conducting neutral radical crystals of Co(Pc)(CN)2·2CHCl3. Similarly, that in a mixed solvent of acetonitrile or benzonitrile and water yields crystals of Co(Pc)(CN)2·2H2O. Since the molecule has two axial projections at the centre, a simple one-dimensional columnar structure cannot be formed. Instead, the crystal containing chloroform has two-dimensional sheets of phthalocyanines, and that containing water has a three-dimensional network of phthalocyanines. Their electrical resistivities are remarkably low as neutral radical crystals: that of Co(Pc)(CN)2·2H2O is the lowest of the π-based neutral radical crystals reported to date.

Pseudomonas marginalis: its degradative capability on organic nitriles and amides.

Abstract: Pseudomonas marginalis, capable of utilizing acetonitrile as the sole source of carbon and nitrogen, was isolated from an industrial waste site. P. marginalis metabolized acetonitrile into ammonia and acetate. The minimal inhibitory concentration values of different nitriles and amides for P. marginalis were in the range 5–300 mM. The bacterium was able to transform high-molecular-mass nitrile compounds and their respective amides into ammonia. The data from substrate-dependent kinetics showed that the Km and Vmax values of P. marginalis for acetonitrile were 33 mM and 67 nmol oxygen consumed min−1 (ml cell suspension)−1 respectively. The study with [14C]acetonitrile indicated that nearly 66% of the carbon was released as 14CO2 and 12% was associated with the biomass. The enzyme system involved in the hydrolysis of acetonitrile was shown to be intracellular and inducible. The specific activities of the enzymes nitrile aminohydrolase and amidase were determined in the cell-free extracts of P. marginalis. Both the enzymes could hydrolyze a wide range of nitriles and amides. The present study suggests that the biodegradation of organic nitriles and the bioproduction of organic acids may be achieved with the cells of P. marginalis.

Rhodium(I)- and Palladium(0)-Catalyzed Carbonylation of Triarylbismuthines with Carbon Monoxide via a Possible Oxidative Addition of a Carbon–Bismuth Bond to Rhodium(I) and Palladium(0)

Abstract: Triarylbismuthines react with carbon monoxide (CO) at atmospheric pressure in acetonitrile at 25 °C in the presence of a catalytic amount of a rhodium compound such as [RhCl(CO)2]2, RhCl3·3H2O, and [RhCl(COD)]2 to give the corresponding diaryl ketones in high yields. If methanol is used as the solvent, methyl benzoates are also produced. When similar reactions are carried out in methanol in the presence of a catalytic amount of palladium(II) acetate together with potassium carbonate in place of the rhodium compound, methyl benzoates are formed as the sole carbonylation products. The oxidative addition of a carbon–bismuth bond to rhodium(I) and palladium(0) is proposed as the key step of these carbonylation reactions.

Chemistry of Organo Halogenic Molecules. 140. Role of the Reagent Structure on the Transformations of Hydroxy Substituted Organic Molecules with the N-Fluoro Class of Fluorinating Reagents

Abstract: Hydroxy-substituted organic molecules were used as target molecules in investigations of the role of the reagent structure on the reactivity of three types of N–F class fluorinating reagents: 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) F-TEDA (1a), N-fluorobis(phenylsulfonyl)amine NSF (1b), and N-fluoropyridinium heptafluorodiborate–pyridine (1/1) NFP (1c). Methanol is stable, but hydroquinone is very quickly transformed in acetonitrile to quinone with F-TEDA at room temperature; on the other hand, NSF is less reactive, while oxidation with NFP is achieved only at an elevated temperature; a structure variation of the hydroquinone derivatives did not influence oxidation. Fluorination was achieved with monohydroxy-substituted aromatic compounds; a similar trend concerning the reactivity of N–F reagent (1) was also observed in reactions with 1- and 2-naphthol, while 9-phenanthrol gave 10,10-difluoro-9-(10H)-phenanthrenone with F-TEDA in acetonitrile and 9,10-phenanthrenequ...

Solvent effects on intermolecular electron transfer processes

Abstract: The solvent effects on the rate constants and activation parameters of several intermolecular electron transfer reactions were investigated. The studies were carried out in protic (methanol, ethanol) and aprotic (acetonitrile, propionitrile) solvents. It was found that rate constants are generally higher in the protic solvents and that activation enthalpies are generally small and in some cases negative. The negative values were found in acetonitrile, while for the same reaction positive values are observed in alcoholic solvents. Large negative values of activation entropies were observed. They are more negative in the aprotic solvents. These observations can be explained by considering the entropy changes caused by the solvent reorganization on forming the transition state. The solvent effect on the quantum yield of the charge separation process was also investigated. For the system pyrene-indole the free-ions quantum yield changes in accordance with the trend of the cage escape rate constant. On the other hand, in the triplet quenching of dibenz-anthracene by nitrobenzenes the charge separation process is much less efficient in acetonitrile than in methanol. These results cannot be explained if the solvent is considered as a dielectric continuum.