Synthesis and structure of complex compound Rh(III) of (NH4)2[Rh(NO2)3(NH3)(µ-OH)]2 composition

The crystalline structure of a new compound Rh(III) of (NH₄)₂[Rh(NO₂)₃(NH₃)(μ-OH)]₂ composition has been determined. The crystallographic characteristics are H₁₆N₁₀O₁₄Rh₂: a = 6.3963(2) Å, b = 9.3701(4) Å, c = 13.6646(5) Å, β = 102.266(1)°, V = 800.28(5) ų, Z = 2, d _calc = 2.432 g/cm³. The distance Rh...Rh in the dimer is 3.200 Å. Original Russian Text Copyright ? 2006 by S. P. Khranenko, I. A. Baidina, and S. A. Gromilov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No. 2, pp. 380–384, March–April, 2006.     

Koexistenzbeziehungen,Darstellung und Eigenschaften ternärer Phasen im System Cu/Mo/O

Coexistence Relations, Preparation and Properties of Ternary Compounds in the System Cu/Mo/O The phase diagram of the ternary system Cu/Mo/O is presented at 773 K. The compounds CuMoO₄, Cu₃Mo₂O₉, Cu₄Mo₅O₁₇, Cu₆Mo₅O₁₈, Cu_4–xMo₃O₁₂, and Cu_xMoO₃ are found to be thermodynamical stable. The homogeneity range of Cu_4–xMo₃O₁₂ runs to x = 0.1–0.2. Single crystals of CuMoO₄ and Cu₃Mo₂O₉ were grown by chemical transport reactions with TeCl₄, Cl₂, HCl, and Br₂ as transport agent. The results were compared with thermochemical calculations. The decomposition of CuMoO₄ and Cu₃Mo₂O₉ was investigated with thermal analysis and decompositon pressure measurements.     

Multipeak distributions of first passage times in bistable dynamics in a model of a thermochemical system.

A master equation is used to study transitions between the stable limit cycle and stable focus in the two-variable bistable system. The distribution function of the mean first passage time between these attractors and the relative dispersion of the mean first return time from the stable focus to itself as a function of the intensity of fluctuations are calculated and discussed. A coherence resonance is observed for the return time from the focus to itself.     

New aspects of thermal analysis,Part I. Resolution of DSC and means for its optimization

The definitions of the temperature resolution, the so-called resolution of DSC instruments given in literature are discussed. A new definition of the resolution for DSC instruments is presented and outlined. The main characteristic introduced in this new definition is a minimum between two caloric events as a prerequisite of an existing resolution. Possible candidates of test substances have been evaluated. The oligomer n-hexatriacontane is revealing an interesting phenomenon, namely a lambda transition which is in the peak temperature only 2 K lower than the melting temperature of 76°C. The substance was selected as an ideal test substance for the quantification of the resolution of DSC instruments. The lambda transition is a second order process which may reach under certain conditions the saturation of the occurring molecular dislocation within 0.2 K, and after saturation the heat flow rate drops sharply down. Investigations concerning the main characteristics of n-hexatriacontane in respect to the temperatures of transition (lambda transition and melting), to the involved enthalpies, and to the resolution factors were performed as functions of the sample mass and the heating rate. The importance of relevant evaluation procedures increasing the resolution factors of DSC curves are discussed and these procedures are integrated into the testing of the resolution. The necessity for widening the experimental scope from instruments to evaluation procedures is forced by the existence of instruments with built-in signal treatments based on electronic devices and software procedures. A comparison with literature data is outlined for all of the mentioned characteristic values of n-hexatriacontane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Concentrated electrolyte solutions at high temperatures and pressures

A survey is given of recent experimental results obtained from high-temperature, high-pressure investigations with water, aqueous solutions, and ionic fluids. Data on the static dielectric constant of water to 550°C and 5 kbar are given and discussed with respect to their relation to water structure. Infrared and Raman spectra of HDO in pure water have been obtained to 400°C and 4 kbar, which give information on hydrogen bonding. Xe–H₂O and CO₂–H₂O mixtures were investigated in the infrared. Ni(II) and Cu(II) complexes were investigated by absorption spectroscopy in aqueous solutions of high chloride content to 350°C and 2–6 kbar. The gas-liquid critical point of ammonium chloride was found at 880°C and 1635 bars. This fluid appears to be predominantly ionic even in the critical region. The possibility of converting pure polar fluids such as ammonia and water into concentrated ionic solutions by self-ionization at very high pressures is mentioned.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

Pure Organic Phase Phenol Biosensor Based on Tyrosinase Entrapped in a Vapor Deposited Titania Sol‐Gel Membrane

A novel amperometric biosensor was constructed for the determination of phenols in pure organic phase. This biosensor was fabricated by immobilizing tyrosinase in a titania sol‐gel membrane which was obtained with a vapor deposition method. This method was facile and avoided the calcination step needed in conventional titania sol‐gel process. The titania sol‐gel membrane could effectively retain the essential water layer around the enzyme molecule needed for maintaining its activity in organic phase. The experimental parameters such as solvent and operating potential were optimized. At ?100 mV this biosensor showed a good amperometric response to phenols in pure chloroform without any mediator and rehydration of the enzyme. For catechol determination the sensor exhibited a fast response of less than 5 seconds. The sensitivity of different phenols was as follows: catechol > phenol > p‐cresol. Additionally, the apparent Michaelis‐Menten constants of the encapsulated tyrosinase to catechol, phenol and p‐cresol were found to be 0.15±0.003, 0.17±0.008 and 0.21±0.004 mM, respectively. The biosensor had also good reproducibility and stability. This work provided a promising platform for the construction of pure organic phase biosensors and the determination of substrates with poor water solubility.     

Ground-state energy of a quantum chain with competing interactions

We show rigorously that the ground state of a quantum chain with competing ferromagnetic nearest and antiferromagnetic next nearest interactions undergoes a transition from ferromagnetic to helical type, in the isotropic case, for a certain value of the relevant ratio of coupling constants. Boundaries of the phase diagram are also determined in the anisotropic case. The stability of a special quantum state (corresponding to a classical modulated phase of =/3) is analyzed by an extension of Holstein-Primakoff arguments, along a line of constant ratio of couplings, showing in particular a sequence of (instability) gaps. Finally, a natural adaptation of a variational wave function due to Huse and Elser is used to study several portions of the phase diagram, with very good agreement with previous theoretical results.     

Description of the turbidity measurements near the phase transition temperature of poly(N-isopropyl acrylamide) copolymers: the effect of pH, concentration, hydrophilic and hydrophobic content on the turbidity

Absorbance values between 300 and 800 nm of aqueous solutions of poly(N-isopropyl acrylamide-co-itaconic acid-9.80), poly(N-isopropyl acrylamide-co-itaconic acid-52.05) and poly(N-isopropyl acrylamide)s containing Tegomer H-Si 2111 end groups and/or blocks were measured using a Shimadzu 160-A UV-visible spectrometer. Turbidities obtained from these absorbance values were used to interpret the macromolecular phase transition from a hydrophilic to a hydrophobic structure of the polymers. The effects of comonomer type and content, concentration of the solutions, pH and temperature on the coil-globule transition were discussed in terms of turbidity form factor, β related to size and shapes of particles and calculated by using the simplified form of Debye equation.The results presented in this work show that the presence of Tegomer H-Si 2111 (Si containing end groups and/or blocks) or high amount of itaconic acid (IA) in the chains prevent a collapse transition from hydrated extended coils to hydrophobic globules, which aggregate and form a separate phase (β<2). Furthermore, it was observed that in the case of concentrated solutions intermolecular hydrophobic interactions between isopropyl groups overcame the repulsive forces resulting from the ionized carboxylic acid groups of IA or surface active nature of Si containing hydrophobic groups (β>2). This stage of the transition corresponds to macroscopic phase separation after an intramolecular process.     

Theoretical studies on the reaction path and dynamics of the reaction CH_3+H_2O→CH_4+OH

The reaction path, the dynamical properties along the reaction path and CVT rate constants are computed by the ab initio MO method, the reaction path Hamiltonian theory and the variational transition state theory. The results show that the effect of the electron correlation energy on activation barrier is large, the recrossing and tunneling effects exist in the reaction.