Showing papers on "Acetonitrile published in 1994"
270 citations
TL;DR: The crystal structure of the serine protease subtilisin Carlsberg in anhydrous acetonitrile was determined at 2.3 A resolution and was found to be essentially identical to the three-dimensional structure ofThe enzyme in water; the differences observed were smaller than those between two independently determined structures in aqueous solution.
Abstract: The crystal structure of the serine protease subtilisin Carlsberg in anhydrous acetonitrile was determined at 2.3 A resolution. It was found to be essentially identical to the three-dimensional structure of the enzyme in water; the differences observed were smaller than those between two independently determined structures in aqueous solution. The hydrogen bond system of the catalytic triad is intact in acetonitrile. The majority (99 of 119) of enzyme-bound, structural water molecules have such a great affinity to subtilisin that they are not displaced even in anhydrous acetonitrile. Of the 12 enzyme-bound acetonitrile molecules, 4 displace water molecules and 8 bind where no water had been observed before. One-third of all subtilisin-bound acetonitrile molecules reside in the active center, occupying the same region (P1, P2, and P3 binding sites) as the specific protein inhibitor eglin c.
212 citations
TL;DR: In this paper, the flatband potential of a metaloxide semiconductor electrode (titanium dioxide) and the composition of a contiguous electrolyte solution (water, methanol, ethanol, and acetonitrile each containing 0.2 mol dm[sup [minus]3] tetrabutylammonium perchlorate) were investigated.
Abstract: We report studies directed toward a quantitative understanding of the relationship between the flatband potential (V[sub fb]) of a metaloxide semiconductor electrode (titanium dioxide) and the composition of a contiguous electrolyte solution (water, methanol, ethanol, and acetonitrile each containing 0.2 mol dm[sup [minus]3] tetrabutylammonium perchlorate). A relationship between V[sub fb] and the proton-generating ability of the electrolyte solvent, as measured by the autoprotolysis constant of the pure solvent, is demonstrated. Additional studies have examined the dependence of V[sub fb] on the composition of a binary electrolyte solvent mixture (acetonitrile/ethylene carbonate and acetonitrile/water). We conclude that the composition of the acetonitrile/ethylene carbonate mixture at the semiconductor-electrolyte solution interface (SLI) is similar to that of the bulk solution. However, for an acetonitrile/water mixture there is preferential adsorption of water at the SLI. Finally, for aprotic electrolyte solutions, the dependence of V[sub fb] on the electrolytic solute was studied. Cations such as Li[sup +] and Na[sup +] are potential determining. 19 refs., 4 figs., 5 tabs.
200 citations
TL;DR: In this paper, self-assembled monolayers with attached redox centers are characterized by their reversible behavior and their electron transfer kinetics in a range of nonaqueous solvents: methanol, ethanol, propanol, butanol, acetonitrile, N,N-dimethylformamide, dimethylsulfoxide, propylene carbonate, acetone, and tetrahydrofuran.
Abstract: Self-assembled monolayers with attached redox centers are characterized by their reversible behavior and their electron-transfer kinetics in a range of nonaqueous solvents: methanol, ethanol, propanol, butanol, acetonitrile, N,N-dimethylformamide, dimethylsulfoxide, propylene carbonate, acetone, and tetrahydrofuran. The monolayers are formed by coadsorbing the thiols HS(CH 2 ) n CONHCH 2 pyRu(NH 3 ) 5 (PF 6 ) 2 and HS(CH 2 ) n COOH (n= 10 or 15) on gold electrodes. The monolayer-coated electrodes are examined by cyclic voltammetry and chronoamperometry first in the nonaqueous electrolyte and then in an aqueous electrolyte
103 citations
91 citations
TL;DR: In this paper, aqueous perchloric acid medium was used to increase the solubility of thiophene and lower the oxidation potential of the monomer to about 0.9 V vs. 1.6 V in acetonitrile.
83 citations
TL;DR: In this paper, the polysiloxanes with cyclic carbonate side chains were prepared by hydrosilation of poly(hydromethylsiloxane) (PHMS) with vinyl-containing cyclric carbonates in acetonitrile using the divinyltetramethyldisiloxane platinum complex as the catalyst.
Abstract: Polysiloxanes with cyclic carbonate side chains were prepared by hydrosilation of poly(hydromethylsiloxane) (PHMS) with vinyl-containing cyclic carbonates in acetonitrile using the divinyltetramethyldisiloxane platinum complex as the catalyst. This is initially a heterogeneous reaction since the PHMS is insoluble in acetonitrile, but the polymer eventually becomes soluble as the reaction proceeds. Under these conditions, no gelation due to competitive reactions with the carbonate is observed. The polymers are highly viscous liquids (T g 's of ca. -30°C) and have dielectric constants ranging from ca. 22 to 44, to our knowledge the largest for any silicones. These polymers can also dissolve large quantities of lithium triflate and represent new polymer electrolytes
77 citations
TL;DR: The phase separation of 14 water-miscible polar solvents by salting-out using sodium chloride (4mol dm-3) was investigated in this article, where the phase separation properties of the separated organic solvent were determined by measuring ET(30)(=1.196×105/λ (kJmol 1)) and DII.
Abstract: Fourteen water-miscible polar solvents were investigated for the separation from their aqueous solutions by salting-out using sodium chloride (4mol dm-3). The following solvents showed the phase separation: acetone, acetonitrile, 1, 4- dioxane, tetrahydrofuran, 1-propanol, and 2-propanol. The chemical properties of the separated organic solvents were determined by measuring ET(30)(=1.196×105/λ (kJmol 1)) and DII.I(=1.196×105(λII-1-λI-1)(kJ mol-1))values from the spectral change of 2, 6-Biphenyl-4-(2, 4, 6-triphenylpyridinio)phenolate (DTP) and bis(1, 3-propanediolato)vanadium(IV) (VO(acac)2), where λ, λI, and λII denote the absorption maximum wavelengths (nm) of DTP and VO(acac)2. Solvent properties of acetone, acetonitrile, 1, 4-dioxane, and tetrahydrofuran were dramatically altered by the salting- out. Acceptability of the phase-separated solvents increased due to the dissolution of water molecules having large acceptor numbers. The ion-pair complex of tris(1, 10-phenanthroline)iron(II) chloride was easily extracted into the phase-separated acetonitrile by the salting-out. Some metal chelates of 1-(2-pyridylazo)-2-naphthol (Hpan) and 8- quinolinol (Hox), 5, 10, 15, 20-tetraphenylporphyrin (H2tpp), and ionic species (H2ox+, ox-, and H4tpp2+) were also extracted into 1, 4-dioxane. The raised donor and acceptor abilities of the phase-separated solvents allowed application to solvent extraction.
77 citations
TL;DR: In this paper, the authors used FTIR measurements in the region of the C-N stretching mode of the solvent to reveal bands produced by acetonitrile molecules in the solvation shells and bands of ClO 4, NaClO 4 and ClO 2.
Abstract: The IR spectra of alkaline and alkaline earth metal perchlorate and of lithium bromide solutions in acetonitrile, obtained with the help of FTIR measurements in the region of the C-N stretching mode of the solvent, reveal bands produced by acetonitrile molecules in the solvation shells and bands of ClO
4
−
ions in contact and solvent separated ion pairs The shift and the attenuation of the C-N stretching band of acetonitrile at 2254 cm−1 is used for the calculation of cation solvation numbers for Li+(4), Na+(4), Mg2+(6), Ca2+(6), and Ba2+(6) No solvation is assumed for the contact ion pairs of LiClO4, LiBr, NaClO4, Mg(ClO4)2, Ca(ClO4)2, and Ba(ClO4)2 The association constants of the symmetrical electrolytes are compared to those obtained from other methods
70 citations
TL;DR: The cyclic voltammetry of some fullerene-ferrocene derivatives showed that these compounds possess very interesting electrochemical properties as discussed by the authors, and the properties of these compounds can be found in the literature.
Abstract: The cyclic voltammetry of some fullerene–ferrocene derivatives shows that these compounds possess very interesting electrochemical properties.
70 citations
TL;DR: In this paper, the Gibbs energies of transfer were determined from solubility product or potentiometric measurements, and the enthalpies of transfer, ΔtH⊖, have been determined calorimetrically, for 22 monovalent and two divalent ions from water to N,N-dimethylthioformamide.
Abstract: The transfer thermodynamic functions for 22 monovalent and two divalent ions from water to N,N-dimethylthioformamide, and for the nitrate, hydrogen sulfate, sulfate, permanganate and dichromate anions from water to methanol, acetonitrile, dimethyl sulfoxide and pyridine, have been reported The Gibbs energies of transfer, ΔtG⊖, have been determined from solubility product or potentiometric measurements, and the enthalpies of transfer, ΔtH⊖, have been determined calorimetrically The entropies of transfer, ΔtS⊖, have been calculated from the experimentally obtained ΔtG⊖ and ΔtH⊖ values The extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption has been applied in order to calculate the contribution from the individual ions Previously determined transfer thermodynamic functions for monovalent ions from water to methanol, acetonitrile, dimethyl sulfoxide, pyridine, tetrahydrothiophene and liquid ammonia are summarized and discussed in this paper The transfer thermodynamic behaviour of the monovalent ions shows that the cations studied can be divided into two groups, metal ions and cations with hydrocarbon groups facing the solvent, and the anions can accordingly be divided into the subgroups inorganic anions and anions with hydrocarbon group(s) facing the solvent The ΔtG⊖ and ΔtH⊖ terms counterbalance each other in such a way that the ΔtS⊖ terms become almost constant for each of these subgroups of ions in a certain solvent The hard alkali-metal ions are as strongly solvated by dimethyl sulfoxide as by any other solvent, while the weakest solvation is found in N,N-dimethylthioformamide among the solvents in this study The soft silver ion is, on the other hand, most strongly solvated in N,N-dimethylthioformamide The strongest solvation of the thallium(I) ion, which is a borderline acceptor, is found in dimethyl sulfoxide and N,N-dimethylthioformamide The transfer thermodynamics of the ammonium and tetraalkylammonium ions display an irregular pattern with the NH4+ ion behaving as the hard monovalent metal ions and the (C4H9)4N+ ion behaves as the tetraphenylarsonium ion The inorganic anions are all more strongly solvated in water than in any other solvent, and the ΔtS⊖ values are pronouncedly negative, while the anions with hydrocarbon groups are more strongly solvated in the non-aqueous solvents and with positive ΔtS⊖ values
TL;DR: A comparison of quantum chemical and FTIR examination of proton transfer energetics, heats of adsorption, and vibrational spectra of acetone and acetonitrile complexes is discussed in this article.
Abstract: A comparison of quantum chemical and FTIR examination of proton-transfer energetics, heats of adsorption, and vibrational spectra of acetone and acetonitrile complexes is discussed. Both of these methods indicate that acetone and acetonitrile form the H-bonded {open_quotes}neutral{close_quotes} complex with bridging hydroxyls of HZSM-5, HY, and HX zeolites. 33 refs., 5 figs., 5 tabs.
TL;DR: In this paper, p-alkylanisoles (1a-h) bearing benzylic protons with hypervalent iodine reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA) and trimethylsilyl azide (TMSN3) in acetonitrile gave arylalkyl azides (3a-H) in considerable yields.
Abstract: Treatment of p-alkylanisoles (1a-h) bearing benzylic protons with hypervalent iodine reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA) and trimethylsilyl azide (TMSN3) in acetonitrile gave arylalkyl azides (3a-h) in considerable yields.
TL;DR: The acid properties of cobalt-and silicon-substituted AlPO-5, 11 and 44 have been characterized by adsorption calorimetry and IR measurements as mentioned in this paper.
Abstract: The acidic properties of cobalt-and silicon-substituted AlPO-5, –11 and –44 have been characterized by adsorption calorimetry and IR measurements. Adsorption calorimetric measurements indicate that the adsorption potential of the samples for acetonitrile is enhanced upon cobalt incorporation. The calorimetrically measured heats of adsorption indicate the formation of strong acid sites, due to this cobalt incorporation, as well as the presence of weaker acid sites, probably terminal P—OH groups. IR measurements of adsorbed ammonia and acetonitrile indicate that some Bronsted-bonded ammonia and acetonitrile are present, in combination with Lewis-bonded species. The Bronsted-bonded species presumably originate from interaction of the base with the weakly acidic P—OH groups. The Lewis-bonded species are due to the coordinative interaction of the lone pair of the base with framework cobalt ions.
TL;DR: The use of an enzyme tyrosinase sensor capable of being employed in non aqueous media represents a good opportunity to investigate the effects of the organic solvent on enzyme activity.
TL;DR: In this paper, a cis-trans Isomerism was proposed for [Ni(β-dik)(diam)L2]-+ complexes in an extended CNDO/2 framework, due to the mechanism of stepwise co-ordination.
Abstract: Equilibria between four-, five- and six-co-ordinated substituted and unsubstituted [Ni(β-dik)(diam)]+ complexes associated with various solvents like acetonitrile, acetone, n-butanol, formamide dimethylformamide, dimethyl sulfoxide and pyridine have been investigated in nitroethane solution at 293 K. Increasing donor strength of the donor solvents (L) as well as increasing electron-withdrawing properties of the substituents at the β-diketonate (β-dik) and the diamine (diam) ligands favours the formation of six-co-ordinated species. The results are interpreted using correlations with IR, Hammett and electrochemical data, and results of semiempirical quantum-mechanical calculations carried out within an extended CNDO/2 framework, cis–trans Isomerism is proposed for [Ni(β-dik)(diam)L2]+ due to the mechanism of stepwise co-ordination.
TL;DR: Iodoetherification of all isomers of the 3-methylalk-4-en-2-ols proceed with excellent levels of stereoselectivity, leading to tetrasubstituted tetrahydrofurans [18∼22] via overall anti-addition to the alkene function.
TL;DR: In this article, the effects of solvents and media on the antioxidant activity of alpha-tocopherol were studied, and the results showed that hydrogen bonding between the protic solvent and either oxygen is not important but that the hydrogen binding between protic and phenolic group reduces the activity of α-tocopheroxyl radical.
TL;DR: In this article, the authors investigated the surface specificity of polycrystalline Pt surfaces at the (111, (110) and (100) planes, together with the (311) stepped plane, in the absence of adsorbed acetonitrile.
TL;DR: In this article, a non-aqueous mobile phase consisting of ammonium acetate and a mixture of organic solvents, namely, methanol and acetonitrile, was used to separate tamoxifen and its metabolites.
Abstract: Tamoxifen and its metabolites were separated using a non-aqueous mobile phase consisting of ammonium acetate and a mixture of organic solvents, namely, methanol and acetonitrile. The effects of using other organic salts as the conducting medium and varying the composition of the mixture of acetonitrile and methanol on the separation were also investigated. Optimum separation was obtained by using 25 mM ammonium acetate in a 50:50 acetonitrile/ methanol mixture. High efficiency separations and short analysis times of less than 8 min were obtained. The reproducibility of migration time was better than 0.4%. The detection limits of tamoxifen and its metabolites were less than 40 pg.
TL;DR: The first integral equation study of molecular correlations in a real nonaqueous electrolyte solution was performed in this article, where a 0.39 M acetonitrile solution of cryptate K+ 222, ClO−4 was analyzed.
Abstract: Hypernetted chain calculations are reported for pure liquid acetonitrile and for a 0.39 M acetonitrile solution of cryptate K+ 222, ClO−4. The obtained molecular correlations between solvent and solute particles are discussed in detail. It is found that the acetonitrile correlations are very similar in the pure liquid and in the solution. The solvation geometries around the cations and the anions are surprisingly unsymmetric and hence far from the picture which chemists currently use to describe ionic solvation. The theoretical results are compared to available wide‐angle neutron scattering data for the pure liquid and to small‐angle neutron scattering data for the cryptate solution. To our knowledge, this is the first integral equation study of molecular correlations in a real nonaqueous electrolyte solution.
TL;DR: In this article, a preparative method for the synthesis of (ω-1), ω-dioxocarboxylic acids and (ω -1)-oxoalkanedioic acids monoesters by respective oxidative cleavage of 2-substituted cycloalkane-1,3-diones and cyclic β-ketoesters, by copper perchlorate in acetonitrile in an oxygen atmosphere, is reported.
TL;DR: In this article, the authors examined the dynamics of diphenylmethyl cation produced upon the 266-nm photolysis in acetonitrile and revealed that a contact ion pair is formed with a lifetime of 150 ps which decays by collapse of the ion pair to form dipylmethyl chloride, k 1 =3.81×10 9 s -1, and ion pair separation to the solvent-separated ion pair, k 2 =2.87×10 nine s - 1.
Abstract: Picosecond absorption spectroscopy is used to examine the dynamics of the diphenylmethyl cation produced upon the 266-nm photolysis of diphenylmethyl chloride in acetonitrile. The experiments reveal that a contact ion pair is formed with a lifetime of 150 ps which decays by collapse of the ion pair to form diphenylmethyl chloride, k 1 =3.81×10 9 s -1 , and ion pair separation to the solvent-separated ion pair, k 2 =2.87×10 9 s -1 . The solvent-separated ion pair decays by return to the contact ion pair, k 3 =1.31×10 8 s -1 , and diffusional separation to the free ion, k 4 =7.84×10 8 s -1
TL;DR: A modification to the solid phase extraction (SPE) clean-up step in Quilliam's HPLC-UV method allows for an improved and more versatile domoic acid analysis.
Abstract: Domoic acid (DA) was first reported in mussels from Prince Edward Island, Canada, in 1987 It reappeared in anchovies and pelicans from Monterey Bay, California, in 1991 Later that year, domoic acid was found in razor clams and Dungeness crabs along the Washington and Oregon coasts Since the initial outbreak, a variety of analytical methods for the detection of this neurotoxin have been developed Here, we describe a modification to the solid phase extraction (SPE) clean-up step in Quilliam's HPLC-UV method (1991: NRCC No 33001) The standard 10% acetonitrile (MeCN) wash and 05M ammonium citrate buffer (ACB) in 10% MeCN (pH = 45) eluting solution have been replaced with a 01 M sodium chloride (NaCI) in 10% MeCN wash and a 05M NaCI in 10% MeCN eluting solution This modification allows the analysis to work equally well on both clam and crab viscera and meat Chromatograms of visceral samples no longer contain interfering or late eluting peaks; and all Chromatograms are free of the large solvent peak tailing associated with the ACB eluent The newly modified method allows for an improved and more versatile domoic acid analysis © 1994 Wiley-liss, Inc
TL;DR: Aqueous and acetonitrile solutions of uranyl-triflate-crown systems have been studied by EXAFS and compared to the corresponding solids in this paper.
TL;DR: In this article, the effect of experimental parameters on electroosmotic mobility and electrophoretic mobility of non-ionic organic compounds has been investigated using a tetrahep-tylammonium salt as an additive in aqueous acetonitrile as solvent.
Abstract: Very good separations of non-ionic organic compounds have been achieved by capillary zone electrophoresis (CZE) using a tetrahep-tylammonium salt as an additive in aqueous acetonitrile as solvent. A systematic study was undertaken to determine the effect of experimental parameters on electroosmotic mobility and electro-phoretic mobility. It was found that pH, acetonitrile concentration, and the type and concentration of quaternary ammonium salt are important experimental variables. Under appropriate conditions, the separation window was enlarged and a broad range of electrically neutral organics, including very hydrophobic compounds (e. g. poly-cyclic aromatic hydrocarbons) and fairly hydrophilic compounds were separated in a relatively short time. By adjusting the separation conditions, high resolution CZE of a specific group of neutral organic compounds could be achieved. A method for calculation of capacity factor was proposed and capacity factors for a variety of non-lonic organic compounds were calculated.
TL;DR: Fluoroionophores consisting of coumarin-153 linked to mono- and diaza-crown ethers are able to complex transition metal cations (Ni2+, Zn2+, Cd2+) and Pb2+, with concomitant large changes in photophysical properties.
Abstract: Fluoroionophores consisting of coumarin-153 linked to mono- and diaza-crown ethers are able to complex transition metal cations (Ni2+, Zn2+, Cd2+) and Pb2+, with concomitant large changes in photophysical properties. The stability constants in acetonitrile are higher than 3×106 M −1 except for Ni2+.