Regularities of reversible radical dissociation in liquid crystals

The effect of liquid-crystalline ordering of alkylcyanobiphenyls on the thermodynamic parameters of reversible dissociation of the dimeric 2,2"-bis[2-(p-dimethylaminophenyl)indane-1,3-dione] to the 2-(p-dimethylaminophenyl)indane-1,3-diyl radicals was found. The angular dependence of the ESR spectra of the radicals in the smectic mesophase is related to their orientation along the liquid crystal director.     

Effect of micelles on the acid hydrolysis of N-phenylbenzohydroxamic acid

The effect of cationic (cetylpyridinium bromide and cetylpyridinium chloride) anionic (sodium dodecyl sulfate and lithium dodecyl sulfate) and non-ionic (Brij-35 and Triton-X-100) micelles on the acid-catalyzed hydrolysis of N-phenylbenzohydroxamic acid in 20 vol.% dioxane medium has been investigated. The kinetic results are explained by both pseudo-phase and Piszkiewicz cooperativity models.     

Spectrophotometric determination of the acid dissociation constants for cacodylic acid and p-Nitrophenol at elevated temperatures

Using 2.5-dinitrophenol as an optical indicator, the pK_a of cacodylic acid were spectrophotometrically determined at elevated temperatures under saturation vapor pressures. The result is pK_a = -26.41 + 1296/T + 4.973 InT whereT is in Kelvin. In a similar way, the pK_a ofp-nitrophenol were obtained up to 200‡C giving pK_a = -24.82 + 2135/T + 4.353 InT From these results, several thermodynamic functions of cacodylic acid andp- nitrophenol were calculated.     

Potentiometric and viscometric study of the alkalization of latex dispersions of ethyl acrylate — methacrylic acid copolymers in the presence of salt

The behavior of latices of ethyl acrylate — methacrylic acid copolymers during alkalization was investigated using potentiometric titration and viscometry. In the presence of NaCl in dispersion medium pH and viscosity were lower compared to salt-free dispersions. Due to strong electrostatic interactions at low salt concentration the apparent dissociation constant of the carboxylic groups is small and the polymer segments bearing these groups are in extended conformations. The screening effect at higher salt concentration increases the apparent dissociation constant and decreases the extension of the polymer segments. The pH and viscosity of latex dispersions alkalized in the presence of salt are thus smaller.     

Spectrophotometric and potentiometric investigations of the H2PO 4 − -HPO 4 2− equilibrium at elevated pressure and temperature

The second dissociation reaction of phosphoric acid has been studied Raman spectrophotometrically and potentiometrically at pressures up to 100 MPa and temperatures up to 473.2 K in solutions with ionic strengths from 0.3 to about 1.0 mol-kg^–1. Molalities, of orthophosphate salts from 0.005 to 0.1 mol-kg^–1 have been used. The changes of the widths at half-height and the Raman shifts for both H₂PO ₄ ^– and HPO ₄ ^2– ions with changing variables of state are reported. Stoichiometric equilibrium constants for the second dissociation reaction are evaluated.     

Acidity measurements at elevated temperatures. VII. Dissociation of water

The self-dissociation of water has been studied over the temperature range from 0 to 300°C and in KCl media from 0.02m to 2.7m. Also, isothermal pressure coefficients of the dissociation quotients have been obtained in these same media up to 250°C. A potentiometric method employing a hydrogen electrode concentration cell with flowing solutions was employed. The estimated accuracy of logQ _w values up to 250°C is 0.02 log units and at 300°C is 0.04 log units. Smoothing functions have been found which fit these data along with the precise potentiometric data of Harned and co-workers at low temperatures, the existing calorimetric data up to 55°C and the recent conductimetric measurements of pure water up to 271°C by Bignoldet al., within about 1.5 times the estimated errors. Thermodynamic quantities for the dissociation reaction have been tabulated for rounded values of temperature and ionic strength at the saturation pressure of water. The isothermal pressure coefficients of log Q_w varies approximately linearly with the square root of the ionic strength. This and the dependence of logK _w on the density of the water is consistent with the assumption that the molal volumes of aqueous ions vary linearly with the compressibility coefficient of water. The heat for the dissociation reaction at infinite dilution is also shown to be strongly dependent on density.     

DSC and PVT measurements

The dissociation of gas and model hydrates was studied using a classical thermodynamic method and a calorimetric method, in various aqueous media including pure water, high concentration calcium chloride solutions and water-in-oil emulsions. Methane hydrate dissociation temperatures vs. pressure curves were determined using pressure vs. temperature measurements in a constant volume cell (PVT), and high pressure differential scanning calorimetry (DSC), at 5 to 10 MPa gas pressure and at temperatures ranging from -10 to +12°C. PVT and DSC results are in good agreement, and concordant with data available in literature. From a thermodynamic point of view, there are no measurable differences between bulk solutions and emulsions. From a kinetic point of view, due to the considerable surface of interface between the two phases, emulsions allow the formation of much greater amounts of hydrate than solutions, without any agitation. Model hydrate of trichlorofluoromethane was studied in 9 to 27 mass% calcium chloride solutions in emulsion in oil, using DSC under atmospheric pressure, at temperatures ranging from -20 to +5°C. A diagram of dissociation temperature vs. salt concentration is proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Gas-phase dissociation pathways of a tetrameric protein complex

The gas-phase dissociation of the tetrameric complex transthyretin (TTR) has been investigated with tandem-mass spectrometry (tandem-MS) using a nanoflow-electrospray interface and a quadrupole time-of-flight (Q-TOF) mass spectrometer. The results show that highly charged monomeric product ions dissociate from the macromolecular complex to form trimeric products. Manipulating the pressure conditions within the mass spectrometer facilitates the formation of metastable ions. These were observed for the transitions from tetrameric to monomeric and trimeric product ions and additionally for losses of small molecules associated with the protein complex in the gas phase. These results are interpreted in the light of recent mechanisms for the electrospray process and provide insight into the composition and factors governing the stability of macromolecular ions in the gas phase.     

邻苯二甲酸二甲酯胶束增溶过程的NMR研究

胶束的增溶作用，可通过X射线，紫外光谱以及核磁共振潜等进行研究.Eriksson等［‘］用NMR法研究了芳香烃在CTAB表面活性剂胶束溶液中的增溶作用.李干佐等问用NMR法研究了件二甲苯和末甲醇在SDS表面活性剂胶束溶液中的增溶作用.然而，关于既非亲油也非亲水的某些小的极性分子的