Thermodynamic properties of LiZr2(PO4)3 crystal phosphate

The temperature dependence of the heat capacity of LiZr₂(PO₄)₃ crystal phosphate is studied in an adiabatic vacuum calorimeter in the temperature range of 6 to 358 K. A phase transition caused by the transition of a low-temperature (triclinic) modification to a high-temperature (rhombohedral) modification is observed in the temperature range of 290–338 K and its standard thermodynamic characteristics are estimated and analyzed. Standard thermodynamic functions are calculated from experimental data: heat capacity, enthalpy, entropy, and Gibbs function in the range of T → 0 to 358 K. Fractal dimensionality D is calculated from the data on low-temperature (20 K ≤ T ≤ 50 K) heat capacity and the topology of the phosphate’s structure is estimated.     

Interaction of sodium fullerene derivatives with trimethylchlorosilane

Soluble dimer compounds of the general formula [C₆₀(Me ₃Si)_n]₂ (where n = 3, 5, 7, or 9 and M _e = CH₃) and a soluble monomer compound, C₆₀(Me ₃Si)₁₂, are synthesized by the reaction of the compound C₆₀Na_n(THF)_x (where n = 4, 6, 8, 10, or 12 and THF = tetrahydrofuran) with trimethylchlorosilane Me ₃SiCl. The compounds synthesized are identified using IR and NMR spectroscopy and mass spectrometry. An irreversible endothermic effect exhibited by the [C₆₀(Me ₃Si)₇]₂ compound in the temperature range 448–570 K is revealed by dynamic adiabatic calorimetry. From analyzing the experimental results, it becomes possible for the first time to demonstrate the structural flexibility of the fullerene in the following sequence of reactions: $\begin{array}{*{20}c} {C_{60} \xrightarrow[{ - 12C_{10} H_8 }]{{ + 12NaC_{10} H_8 }}C_{60} Na_{12} \xrightarrow[{ - 12NaCl}]{{ + excess Me_3 SiCl}}C_{60} (Me_3 Si)_{12} \xrightarrow[{ - 12Me_3 SiCl}]{{ + HCl(gas)}}[C_{60} H_n ]\xrightarrow[{ - 1/2nH_2 }]{{hv}}C_{60} } \\ {C_{60} \xrightarrow[{ - 8C_{10} H_8 }]{{ + 8NaC_{10} H_8 }}C_{60} Na_8 \xrightarrow[{ - 8NaCl}]{{ + excess Me_3 SiCl}}[C_{60} (Me_3 Si)_7 ]_2 \xrightarrow{{573K}}\begin{array}{*{20}c} {products of the} \\ {transformation of + } \\ {Me_3 Si groups} \\ \end{array} C_{60^ - } } \\ \end{array} $      

Discrete-continuum model of symmetric separation of a material

A problem of the beginning of motion of a finite-width cut in a linearly elastic plane under the action of symmetric external loading is formulated. The material on the way of cut propagation forms a layer (interaction layer). The stress-strain state of the material is postulated to be homogeneous across this layer. A system of integral boundary equations is obtained for determining the stress-strain state. Based on this system of equations, a discrete model of separation of the layer material is constructed under the assumption of a constant stress-strain state in an element of the interaction layer. The stress distribution in the pre-fracture zone is determined. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 134–140, January–February, 2009.     

Models of strain and separation process

We consider models of strain and separation processes of rigid bodies, which are based on the use of the well-known scheme of mathematical cut [1, 2] and the concept of interaction layer developed in [3, 4].     

Thermodynamic characteristics of triphenylantimony diacrylate

The heat capacity of triphenylantimony diacrylate Ph₃Sb(O₂CCH=CH₂)₂ was studied in an adiabatic vacuum calorimeter at 6?C350 K and differential scanning calorimeter at 330?C450 K. Melting was revealed at these temperatures; the melting point was estimated at 428.4 ± 0.5 K. It was accompanied by the partial decomposition of the substance. The low-temperature (20 K ?? T ?? 50 K) heat capacity was treated using the Debye theory of the heat capacity of solids and its multifractal model. The type of the structure topology was determined. The standard thermodynamic functions C _p ^o (T), H ^o(T) ? H ^o(0), S ^o(T), and G ^o(T) ? H ^o(0) of the compound in the crystal state were calculated from the obtained experimental data in the range from T ?? 0 to 428 K. The standard entropy of the formation of the crystalline compound Ph₃Sb(O₂CCH=CH₂)₂ at T = 298.15 K was determined.     

Catalytic proficiency of ubiquitin conjugation enzymes: balancing pK(a) suppression, entropy, and electrostatics

Biological organisms orchestrate coordinated responses to external stimuli through temporal fluctuations in protein-protein interaction networks using molecular mechanisms such as the synthesis and recognition of polyubiquitin (polyUb) chains on signaling adaptor proteins. One of the pivotal chemical steps in ubiquitination involves reaction of a lysine amino group with a thioester group on an activated E2, or ubiquitin conjugation enzyme, to form an amide bond between Ub and a target protein. In this study, we demonstrate a nominal 14-fold range for the rate of the chemical step, k(cat), catalyzed by different E2 enzymes using non-steady-state, single-turnover assays. However, the observed range for k(cat) is as large as ～100-fold for steady-state, single-turnover assays. Biochemical assays were used in combination with measurement of the underlying protein-protein interaction kinetics using NMR line-shape and ZZ-exchange analyses to determine the rate of polyUb chain synthesis catalyzed by the heterodimeric E2 enzyme Ubc13-Mms2. Modest variations in substrate affinity and k(cat) can achieve functional diversity in E2 mechanism, thereby influencing the biological outcomes of polyubiquitination. E2 enzymes achieve reaction rate enhancements through electrostatic effects such as suppression of substrate lysine pK(a) and stabilization of transition states by the preorganized, polar enzyme active site as well as the entropic effects of binding. Importantly, modestly proficient enzymes such as E2s maintain the ability to tune reaction rates; this may confer a biological advantage for achieving specificity in the diverse cellular roles for which these enzymes are involved.     

Simultaneous quantitation of IC87114, roflumilast and its active metabolite roflumilast N‐oxide in plasma by LC‐MS/MS: application for a pharmacokinetic study

A sensitive and reliable high‐performance liquid chromatography–mass spectrometry (LC–MS/MS) was developed and validated for simultaneous quantification IC87114, roflumilast (RFM), and its active metabolite roflumilast N‐oxide (RFN) using tolbutamide as an internal standard. The analytes were extracted by using liquid–liquid extraction and separated on a reverse phase C₁₈ column (50 mm × 3 mm i.d., 4.6 µ) using methanol: 2 mM ammonium acetate buffer, pH 4.0 as mobile phase at a flow rate 1 mL/min in gradient mode. Selective reaction monitoring was performed using the transitions m/z 398.3 > 145.9, 403.1 >186.9, 419.1 > 187.0 and 271.1 > 155.0 to quantify quantification IC87114, RFM, RFN and tolbutamide, respectively. The method was validated over the concentration range of 0.1–60 ng.mL^?1 for RFM and RFN and 6 to 2980 ng.mL^?1 for IC87114. Intra‐ and inter‐day accuracy and precision of validated method were within the acceptable limits of <15% at all concentrations. Coefficients of correlation (r²) for the calibration curves were >0.99 for all analytes. The quantitation method was successfully applied for simultaneous estimation of IC87114, RFM and RFN in a pharmacokinetic drug–drug interaction study in Wistar rats. Copyright © 2012 John Wiley & Sons, Ltd.     

Crystalline complexes of fullerene with anisole derivatives

For the first time, bis(anisole)chromium fulleride (PhOMe)₂Cr^+·[C₆₀]^−· and a crystalline complex of fullerene with ortho-butoxyanisole have been obtained. The temperature dependence of the parameters of the EPR spectrum of bis(anisole)chromium fulleride (PhOMe)₂Cr^+·[C₆₀]^−· has been studied. The molecular structure of the complex of fullerene with ortho-butoxyanisole has been established.     

Structure of nonpolarizable water/nitrobenzene interface: potential distribution, ion adsorption, and interfacial tension

Adsorption of hydrophobic and hydrophilic ions at the nonpolarizable interface between two immiscible electrolyte solutions was investigated. The results were analyzed in three different models: (i) Gouy-Chapman model, (ii) ions as hard spheres, and (iii) ion pair formation at the interface. In the Gouy-Chapman model, an analytical expression for the interfacial tension was obtained. It predicts that interfacial tension should be proportional to the square root of the electrolyte concentration, which does not agree with experimental data. Modeling ions as hard spheres only slightly improves the agreement. The third model of interfacial ion pairing as the main origin of adsorption was analyzed using the amphiphilic isotherm (Markin-Volkov isotherm). A good agreement between ion-pairing theory and experimental values was achieved. The MV isotherm takes into account the limited number of adsorption sites, final size of molecules, complex formation at the interface, and interaction between adsorbed particles. The analysis revealed repulsion between adsorbed tetraalkylammonium ions at the nitrobenzene/water interface and demonstrated linear dependence between adsorption site area and the size of a molecule.     

Thermodynamic Study of Formamidinium Lead Iodide (CH5N2PbI3) from 5 to 357 K

In the present study, the molar heat capacity of solid formamidinium lead iodide (CH₅N₂PbI₃) was measured over the temperature range from 5 to 357 K using a precise automated adiabatic calorimeter. In the above temperature interval, three distinct phase transitions were found in ranges from 49 to 56 K, from 110 to 178 K, and from 264 to 277 K. The standard thermodynamic functions of the studied perovskite, namely the heat capacity C°_p(T), enthalpy [H⁰(T) − H⁰(0)], entropy S⁰(T), and [G°(T) − H°(0)]/T, were calculated for the temperature range from 0 to 345 K based on the experimental data. Herein, the results are discussed and compared with those available in the literature as measured by nonclassical methods.