Perturbing the O–H…O Hydrogen Bond in 1-oxo-3-hydroxy-2-propene

Ab initio MP2/aug’-cc-pVTZ calculations have been carried out to identify and characterize equilibrium structures and transition structures on the 1-oxo-3-hydroxy-2-propene: Lewis acid potential energy surfaces, with the acids LiH, LiF, BeH₂, and BeF₂. Two equilibrium structures, one with the acid interacting with the C=O group and the other with the interaction occurring at the O–H group, exist on all surfaces. These structures are separated by transition structures that present the barriers to the interconversion of the two equilibrium structures. The structures with the acid interacting at the C=O group have the greater binding energies. Since the barriers to convert the structures with interaction occurring at the O–H group are small, only the isomers with interaction occurring at the C=O group could be experimentally observed, even at low temperatures. Charge-transfer energies were computed for equilibrium structures, and EOM-CCSD spin–spin coupling constants ^2hJ(O–O), ^1hJ(H–O), and ¹J(O–H) were computed for equilibrium and transition structures. These coupling constants exhibit a second-order dependence on the corresponding distances, with very high correlation coefficients.     

Twentyfold increase in alkaline phosphatase activity by sequential reversible activation of the enzyme followed by coupling with a copolyme of ethylene and maleic anhydride

Alkaline phosphatase, APase, (EC 3.1.31) from calf intestine, after shifting the equilibrium by effector molecules towards the dimeric form of the enzyme, was coupled (ratio 1:2, protein: copolymer) to a copolymer of ethylene and maleic anhydride, EMA. The water-soluble APase-EMA was separated from APase and the unbound EMA by DEAE-cellulose ion exchange chromatography. The specific activity of the APase-EMA, compared to APase, increased 26-fold at pH 7.1 and 10-fold at pH 8.6. The pH optimum of APase-EMA was shifted down from pH 9.5 (native APase) to 8.6. This change could be interpreted in terms of polyelectrolyte theory. APase-EMA retained 50–70% of its optimum activity in the pH range 7–8, while APase retained only 5–15% of its optimum activity within the same pH range. Its isoelectric point, pI, was 4.2 (APase 6.0) and it migrated on polyacrylamide gel electrophoresis in a single band, anodic movement twice as fast as APase. Parallel with the kinetic measurements, the reactive-enzyme sedimentation method was used to measure S_20,w values. S_20,w values obtained for APase-EMA, activated APase, and APase dialyzed against wafer were 6.56S, 6.46S, and 5.17S, respectively. Molecular weights, M_r, were determined by equilibrium sedimentation: the values obtained were 180,000, 160,000, and 84,500. M_r values of APase-EMA and APase (native) estimated by Sepharose-4B gel filtrations were essentially the same. The above-mentioned values remained unchanged for APase-EMA after intensive dialysis against water, whereas for the activated APase, separation from the effector molecules caused the equilibrium to shift back to the monomeric, very slightly active enzyme with concomitant changes of S_20,w to 5.15 and M_r to 82,000.     

ChemInform Abstract: Vibrational Spectrum and Gas-Phase Structure of Disulfur Dinitride (S2N2)

The first gas-phase high-resolution FTIR spectra of S₂N₂ (D_2h) is presented together with a high-level quantum mechanical and experimental study of its molecular ground-state and equilibrium structures.     

Kinetic regularities of the heat release during the reactions of aliphatic hydrocarbons with aqueous HNO3

The kinetics of the heat release during the reactions of aqueous HNO₃ withn-heptane andn-octadecane was studied. The kinetic regularities of the reactions of hydrocarbons C₇H₁₆−C₁₈H₃₈ with HNO₃ and the heats of the reactions were described. At all stages, except initial, the hydrocarbon reacts with NO₂ and nitric acid reproduces NO₂ in the reaction with NO. The accumulation of NO₂ results in the acceleration of the process. When the pressure of the hydrocarbon vapor is equilibrium, its reaction with NO₂ can also proceed in the gas phase. The contribution of this reaction to the total heat release was estimated. The additives of aromatic and unsaturated hydrocarbons to aliphatic hydrocarbons increase strongly the initial rate of the heat release and changes slightly the subsequent stages of the process. Naphthenic hydrocarbons have almost no effect on the kinetic parameters of the process. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–40, January, 1998.     

Conformational mobility of the six-membered ring in 5-oxo-1,3-cyclohexadiene and its derivatives

Molecular mechanics and MNDO calculations showed that the six-membered ring in the molecule of 5-oxo-1,3-cyclohexadiene possesses high conformational mobility. The transition from a planar equilibrium conformation to a distorted sofa conformation in which the C(sp²)-C(=O)-C(sp³)-C(sp²) torsion angle is equal to ±30° increases the energy of the molecule by less than 1 kcal mol^–1. The influence of steric (R = Me, Et, Prⁱ, Bu^t) and electronic (R = NH₂, NO₂) effects of substituents R on the equilibrium conformation and mobility of the carbocycle has been analyzed. Both types of substituents at unsaturated C atoms do not change the equlibrium conformation or flexibility of the six-membered ring. Substituents at saturated C atoms cause the transition of the carbocycle to the distorted sofa conformation and significantly restrict its mobility. The electronic structures of 5-oxo-1,3-cyclohexadiene and its amino and nitro derivatives have been analyzed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 849–854, May, 1995.     

Conformations and electronic properties of alkyl peroxides,alkylperoxy radicals and alkoxy radicals

The equilibrium geometric parameters have been determined for peroxides (H₂O₂, CH₂O₂H, and CH₃O₂CH₃), alkylperoxy radicals (HO₂, CH₃O₂), and C₂H₅O₂), and alkoxy radicals (HO, CH₃O, and C₂H₅O) by means of the semiempirical MINDO/2' method. The predicted bond lengths were found to be more reasonable than those estimated by the CNDO/2 and INDO methods, but the bond angles were predicted too large because of the insufficient parametrizations for such heteroatoms as oxygen. The electronic properties of the above species are also discussed in connection with their physicochemical constants.     

Liquid–liquid equilibrium of (1H,1H,7H-perfluoroheptan-1-ol + perfluoroalkane) binary mixtures

This work presents new liquid–liquid equilibrium data for mixtures of 1H,1H,7H-perfluoroheptan-1-ol and linear perfluoroalkanes from C₆ to C₉. Data were measured at atmospheric pressure by turbidimetry and at pressures up to 5 MPa using a laser light scattering technique. The coexistence curves have been fitted to renormalization group extended-scaling expressions with the critical temperature and molar fraction obtained from the fit.     

Solvent effect on the equilibrium constant of the chain reversible reaction of <Emphasis Type="Italic">N,N</Emphasis>′-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone

The temperature dependences of the equilibrium constant K of the reversible chain reaction of N,N′-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone in benzene, chlorobenzene, anisole, benzonitrile, and CCl₄ were studied. The enthalpies and entropies of the reaction in these solvents were determined, and a linear dependence between them in aromatic solvents was found. The equilibrium constant depends on the solvent nature: the replacement of CCl₄ by benzene at T = 298 K increases K from 13.6 to 140. The solvation effects are caused by several types of intermolecular interactions of participants of equilibrium with the medium. The decrease in K in the benzene-anisole-benzonitrile series is related, to a great extent, to complex formation with hydrogen bonding between 2,5-dichlorohydroquinone and the solvents. In anisole a charge-transfer complex is formed between the solvent and reaction product (2,5-dichloroquinone). The constant and enthalpy of the complexation were estimated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2296–2302, December, 2007.     

Isomerization of monohydroperfluoroalkenes

Isomerization of monohydroperfluoro-1-alkenes HC(CF₂)_nCF=CF₂ (n = 2 to 8) catalyzed by Lewis bases or acids (CsF, KHF₂, and SbF₅) under conditions of thermodynamic control affords equilibrium mixtures of all of the possible isomers resulting from migration of the double bond along the carbon chain. Under conditions of kinetic control, isomerization through the action of SbF₅ gives -H-perfluoro-2-alkenes. The substantially higher proportion ofcis-isomers in the resulting monohydroperfluoroalkenes than in their perfluorinated analogs has been attributed to the effect of an intramolecular hydrogen bond.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1614–1619, September, 1994.     

Study of the effect of triarylphosphine ligands on chemical hardness of triarylphosphinegold cations

Exchange reactions with the participation of triarylphosphinegold and phenylmercury 4-fluorothiophenoxides, 4-nitrophenoxides, and acetates were studied by¹⁹F NMR spectroscopy. The data on the comparative chemical hardness of Ar³PAu⁺ and PhHg⁺ cations were obtained based on the data on the equilibrium constants. The chemical hardness of Ar₃PAu⁺ cations increases as the electron-donating ability of triarylphosphine ligands increases. The effect of these ligands is described by the or ° constants of substituted phenyl groups and by ionization potentials of their electron pairs or the pK _a values.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 10, pp. 2568–2572, October, 1996.     

Improvement of hydrogen isotope exchange reactions on Li4SiO4 ceramic pebble by catalytic metals

Li4SiO4 ceramic pebble is considered as a candidate tritium breeding material of Chinese Helium Cooled Solid Breeder Test Blanket Module(CH HCSB TBM) for the International Thermonuclear Experimental Reactor(ITER).In this paper,Li4SiO4 ceramic pebbles deposited with catalytic metals,including Pt,Pd,Ru and Ir,were prepared by wet impregnation method.The metal particles on Li4SiO4 pebble exhibit a good promotion of hydrogen isotope exchange reactions in H 2-D 2 O gas system,with conversion equilibrium temperature reduction of 200-300 8C.The out-of-pile tritium release experiments were performed using 1.0 wt% Pt/Li4SiO4 and Li 4 SiO 4 pebbles irradiated in a thermal neutron reactor.The thermal desorption spectroscopy shows that Pt was effective to increase the tritium release rate at lower temperatures,and the ratio of tritium molecule(HT) to tritiated water(HTO) of 1.0 wt% Pt/Li4SiO4 was much more than that of Li4SiO4,which released mainly as HTO.Thus,catalytic metals deposited on Li4SiO4 pebble may help to accelerate the recovery of bred tritium particularly in low temperature region,and increase the tritium molecule form released from the tritium breeding materials.     

Kinetic scheme of homogeneous acid-catalyzed transformation of isopentenols

The reactions occurring in an equilibrium mixture of 3-methyl-1-buten-3-ol and 3-methyl-2-buten-1-ol in 24–49 % aqueous solutions of H₂SO₄ yield isoprene, 3-methyl-3-buten-1-ol, isobutylene, formaldehyde, 3-methylbutane-1,3-diol. Isobutylene is rapidly hydrated to give 2-methylpropan-2-ol. The presence of formaldehyde in the reaction mixture indicates that the transformations involve the reverse Prins reaction. On the basis of experimental and literature data, two most probable reaction schemes were suggested.Translated fromIzvestiya Akademii Nauk. Sertya Khimicheskaya, No. 5, pp. 867–870, May, 1995.     

New method for calculating the adsorption of noble gases on amorphous surfaces

A new approach to calculating the equilibrium characteristics of the adsorption of noble gases on the amorphous surfaces of adsorbents was developed and applied to the Ar−TiO₂(rutile) system. Intermolecular adsorbate-adsorbate interactions are taken into account for the nearest neighbors in the quasi-chemical approximation. The lattice energy parameters of all interactions of the model are determined from the Lennard-Jones potential (12-6). The formation of amorphous TiO₂(rutile) surface includes completion of the surface layers and partial removal of the surface oxygen ions. The quality of the amorphization procedure was confirmed by the experimentally measured heats and isotherms of adsorption of the system under study. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1109–1118, June, 1997.     

Separation and characterisation of beta2-microglobulin folding conformers by ion-exchange liquid chromatography and ion-exchange liquid chromatography–mass spectrometry

In this work we present for the first time the use of ion-exchange liquid chromatography to separate the native form and a partially structured intermediate of the folding of the amyloidogenic protein beta₂-microglobulin. Using a strong anion-exchange column that accounts for the differences in charge exposure of the two conformers, a LC–UV method is initially optimised in terms of mobile phase pH, composition and temperature. The preferred mobile phase conditions that afford useful information were found to be 35 mM ammonium formate, pH 7.4 at 25 °C. The dynamic equilibrium of the two species is demonstrated upon increasing the concentration of acetonitrile in the protein sample. Then, the chromatographic method is transferred to MS detection and the respective charge state distributions of the separated conformers are identified. The LC–MS results demonstrate that one of the conformers is partially unfolded, compared with the native and more compact species. The correspondence with previous results obtained in free solution by capillary electrophoresis suggest that strong ion exchange LC–MS does not alter beta₂-microglobulin conformation and maintains the dynamic equilibrium already observed between the native protein and its folding intermediate.     

Electrochemistry of iodine and iodide in chloroaluminate melts

The electrochemical behavior of iodine and iodide has been studied in AlCl₃+NaCl mixtures with compositions ranging from NaCl saturated melts to AlCl₃+NaCl (63+37 mol %) at platinum and tungsten electrodes. Iodide is oxidized in two steps to iodine and I(I); a reduction wave to iodide and an oxidation wave to I(I) are obtained in iodine solutions. The equilibrium constant for the reaction, I^?+I(I)=I₂, is 6×10⁸ l mol^?1 in molten chloroaluminate melts at 175°C.     

Notes on notation of sodium oxofluoroaluminate anions

The chemical notation of the reaction products in the system NaF—AlF₃—Al₂O₃ was reevaluated and its modifications were suggested. Based on these modifications, the equilibrium constants of selected reactions were calculated. Some of the equilibrium constants differed by one or two orders of magnitude from the values of the corresponding original equilibrium constants.     

Parameters estimation and VLE calculation in asymmetric binary mixtures containing carbon dioxide + n-alkanols

In the present work, the estimation of the parameters for asymmetric binary mixtures of carbon dioxide + n-alkanols has been developed. The binary interaction parameter k₁₂ of the second virial coefficient and non-random two liquid model parameters τ₁₂ and τ₂₁ were obtained using Peng–Robinson equation of state coupled with the Wong–Sandler mixing rules. In all cases, Levenberg–Marquardt minimization algorithm was used for the parameters optimization employing an objective function based on the calculation of the distribution coefficients for each component. Vapor–liquid equilibrium for binary asymmetric mixtures (CO₂ + n-alkanol, from methanol to 1-decanol) was calculated using the obtained values of the mentioned parameters. The agreement between calculated and experimental values was satisfactory.     

Swelling behaviors of polyelectrolyte hydrogels containing sulfonate groups

Series of maleate monoester and diester monomers based on poly(ethylene glycol) monomethyl ether (MPEG) were copolymerized using the ionizable 2‐acrylamido‐2–methyl propane sulfonic acid (AMPS) via different dose rate of electron‐beam irradiation (40–150 kGy). The crosslinking of the copolymers were carried out in aqueous acidic solutions at pH 1 or in the presence of 1% N,N‐methylene bisacrylamide (MBA) as crosslinking agent. The final equilibrium water content and swelling capacities for the prepared hydrogels were determined in aqueous solutions at pH 1, 6.8, and 12 and in aqueous salt solutions at 298 K. Swelling equilibria for prepared hydrogels were determined in different molar salt solutions of NaCl, KCl, CaCl₂, Na₂SO₄, K₂SO₄, and CaSO₄. The swelling ratios of gels in pure water and in the salt solutions were found to depend on the counterion species in the increasing sequence of Ca²⁺, Na⁺ and K⁺. Copyright © 2002 John Wiley & Sons, Ltd.     

Comparison of temperature measurements in ICP and MIP with Ar and He as plasma gas

Various temperature measurements have been carried out in microwave induced plasmas (MIP) generated with a surfatron and inductivcly coupled plasmas (ICP) both with argon and helium as plasma gas. Iron has been used for the determination of excitation temperature, and OH and N⁺₂ for rotational temperatures. In the case of the Ar ICP, equilibrium is attained between the various temperatures (4500 K), as previously described. On the other hand, in the He ICP and the MIPs, iron provides the highest temperature (4500 K) but discrepancies are obtained with results from N⁺₂ and OH. These two species show lower values, especially OH (2000 K).     

Study of protein association and micelle formation in surfactants by microcolumn exclusion chromatography

The application of microcolumn exclusion chromatography to the determination of equilibrium and kinetic association constants for proteins is described. Taking phospholipase A₂ as an example, the relationship between association and enzymatic activity was investigated. A procedure for determination of the critical concentration of micelle formation (CCM) in surfactants was developed.