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The structure of dolomite, CaMg(CO3)2, was determined from 298 to 1466 K at a constant pressure of about 3 GPa using in situ synchrotron X-ray diffraction data to investigate the state of disorder. An order parameter s, defined as 2 xca - 1, varies from s = 1 (where xca = 1) for a completely ordered dolomite to s = 0 (where xca = 0.5) for a completely disordered dolomite. On heating, there is no measured change in s until the temperature is high enough to cause exchange of Ca2+ and Mg2+ cations. Significant disorder began to occur at about 1234 K [s = 0.83(1)] and increases along a smooth pathway to T = 1466 K [s = 0.12(5)]. The R3 ↔ R3c transition in dolomite is described by a modified Bragg-Williams thermodynamic model with the following molar free energy of disorder, Gd (T; s) = RTc[1 - s² + ½ a(s4- 1) - (T/Tc) {2 ln2 - (l+s) ln(1 + s) - (1 - s) ln(1 - s)}]. Using Tc = 1466 K and a = -0.29, this model provides an excellent agreement with experimental data. Moreover, the maximum enthalpy of disorder, Hd(s = 0) = RTc(1 - ½ a) ∼ 14 kJ/mol, agrees with published calorimetric data. A thermodynamic description of the aragonite + magnesite ↔ dolomite reaction boundary is also presented and it reproduces the main qualitative features correctly. [ABSTRACT FROM AUTHOR]

Abstract: The reaction between ZnCl2 and di-2-pyridyl ketone benzoyl hydrazone (dpkbh) in acetonitrile under ultrasonic or reflux conditions gave [ZnCl2(η3-N,N,O-dpkbh)] in good yield. The identity of the compound was established from the results of its elemental analysis and a number of spectroscopic measurements. Solid-state infrared spectra of [ZnCl2(η3-N,N,O-dpkbh)] reveal the coordination of dpkbh, the presence of the amide proton and binding of the oxygen atom of dpkbh. 1H NMR spectra of [ZnCl2(η3-N,N,O-dpkbh)] show sensitivity to solvent and temperature variations and confirm the coordination of dpkbh. The electronic absorption spectra of [ZnCl2(η3-N,N,O-dpkbh)] in non-aqueous media show high sensitivity to changes in their surroundings and divulge two interlocked intra-ligand-charge transfer (ILCT) transitions of the donor–acceptor type between 300 and 500nm. Optical measurements show reversible inter-conversion between two forms of [ZnCl2(η3-N,N,O-dpkbh)] that may be due to complex–substrate interactions and thermodynamic analysis gave changes in enthalpy (ΔH θ ) of −23.3 and +14.1kJmol−1, entropy (ΔS θ ) of −51 and +31Jmol−1K−1, and free energy (ΔG θ ) of −8.16 and +4.54kJmol−1 at 298.15K in DMF and DMSO, respectively. Substrates in concentrations as low as 10−5 M can be detected and determined using [ZnCl2(η3-N,N,O-dpkbh)] in polar solvents. A provisional model for the binding of substrate to [ZnCl2(η3-N,N,O-dpkbh)] is developed and a binding constant in the range 6000–8000M−1 is obtained in the case of ZnCl2 in DMSO. Electrochemical measurements on [ZnCl2(η3-N,N,O-dpkbh)] in DMF show irreversible metal and ligand-based redox processes, and electrochemical reactions of dpkbh with ZnCl2 show facile coordination of ZnCl2 and formation of [ZnCl2(η3-N,N,O-dpkbh)]. X-ray structural analysis done on a crystal grown from a DMF solution of [ZnCl2(η3-N,N,O-dpkbh)] confirmed the identity of [ZnCl2(η3-N,N,O-dpkbh)] and shows an extensive network of non-covalent interactions that connects all molecules. [Copyright &y& Elsevier]

The article presents information on the structure of 7-Acetyl-12-methoxyhorminone. A horminone derivative with the systematic name 7-acetyl-12-methoxyabieta-8,12-diene-11,14- dione, C23H32O5, was isolated from Hyptis verticillata from Jamaica. The Hyptis genus has approximately 400 species and is a member of the Labiatae family growing mostly in the tropical Americas. A number of these species possess significant biological activities, including mycotoxinic, phytotoxinic, teratogenic, and antifertility properties. Hyptis verticillata is widely used in folklore medicine as a treatment for itching, insect stings and rheumatoid arthritis.

The interface between an electrolyte solution and a metal electrode coated with an oxidatively adsorbed, redox-active monolayer of long-chain thiols has been examined from a thermodynamic point of view. The electrode potential is assumed to vary within the region where no reductive desorption of the thiol occurs, so that the interface may formally be regarded as ideally polarizable. The analysis leads to an expression describing the potential dependence of interfacial tension in terms of the charge density on the metal, salt concentration, dielectric properties of the organic film, and the redox properties of the active terminal groups, which vary with the (average) distance from the electrode surface. This result generalizes the classical Lippmann equation to modified electrodes of the type considered.