Magnetic and electric studies of a new Co(II) perovskite-like material

Structural phase transitions in the perovskite-like material [(CH₄)₁₂(NH₃)₂]CoCl₄ have been observed using differential thermal scanning. The material shows an order-disorder transition at T ₁ = 396 ± 5 K with entropy, (ΔS ₁) = 12.8 J/mole/K. A "chain melting" transition with a major endothermic peak at T ₂ = 337 ± 3 K and a minor one at T ′ = 316 ± 2 K, has total entropy ΔS = 28 J/mole/K. At low temperatures, the transitions at T ₃ = 288 ± 3 K and at T ₄ = 188 ± 3 K, have entropies of ΔS ₃ = 14.4 J/mole/K and ΔS ₄ = 2.6 J/mole/K respectively. AC magnetic susceptibility in the temperature range 78-290 K, in a magnetic field of 160 A/m and at a frequency of 320 Hz is presented. The results indicate changes in symmetry at 188 K. Dielectric permittivity has been studied as a function of temperature in the range 300-430 K and frequency range (60 Hz-100 kHz), confirming the observed transitions. The dielectric permittivity reflects rotational and conformational transition for the material. The variation of the real part of the conductivity with temperature is thermally activated with different activation energies in the range of ionic hopping. The temperature dependence of the dc conductivity and that of the ions hopping rate have indicated that the concentration of mobile ions is independent of temperature. The dependence of the conductivity on frequency follows the universal power law, <artwork name="GPHT31040ei1"> in the temperature range 340 K<T<390 K. Values 0 <s ₁ <1 dominate at low frequency and correspond to translational hopping motion and values 1<s ₂<2 dominate at high frequencies and correspond to well localized hopping and/or reorientational motion. For T > 396 K, the AC conductivity was fitted to <artwork name="GPHT31040ei2"> with 0<s<1. Comparison with the corresponding Cu-containing material is discussed.     

Complex Formation Reactions of Divinyltin(IV) Complexes with Amino Acids,Peptides, Dicarboxylic acids and Related Compounds

Complex formation equilibria of divinyltin(IV) with amino acids, peptides, and dicarboxylic acids have been investigated. Stoichiometry and stability constants for the complexes formed were determined at 25°C and ionic strength 0.1 M NaNO₃. The results showed the formation of ML, MLH, and ML₂ (organotin : ligand : hydrogen) complexes with amino acids. Peptides form ML complexes and the corresponding deprotonated amide species MLH_?1. In the latter species the binding with divinyltin(IV) occurs through the terminal amino group, carboxylate oxygen, and the amide nitrogen atoms (CO^? ₂, N^? _amide, NH₂). The results showed the formation of ML and ML₂ complexes with dicarboxylic acids. The concentration distribution of the complexes in solution was evaluated. The bonding sites of the divinyltin(IV) complex in solid state with oxalic acid was investigated by means of elemental analyses, FTIR, and mass spectra. Non-isothermal decomposition of the above complex has been studied and the result was statistically analyzed. The main steps were identified for the thermal decomposition reaction and each step proved to be a first order reaction. The kinetic parameters E _a and A were calculated for each step in the reaction. The thermodynamic functions H, G, and S* were calculated for each step of the reaction.     

Melting of columnar hexagonal DNA liquid crystals

The persistence length DNA hexagonal-cholesteric phase transition upon dilution and/or increase in solvent ionic strength is investigated with polarized light microscopy. The ionic strength dependence of the transition follows Lindemann criterion , i.e., the hexagonal lattice melts when the root-mean-square fluctuations in transverse order exceed 10% of the interaxial spacing. The spacings are derived from density and the fluctuations are estimated with a theory of undulation enhanced electrostatic interactions. Additional support for this theory is given by the DNA equation of state and anisotropic neutron radiation scattering from magnetically aligned cholesteric samples just below the phase transition. Received: 17 November 1997 / Revised: 21 January 1998 / Accepted: 25 February 1998     

Synthesis and Study of the Thermal Epimerization of r -2-Ethoxy- cis -4- cis -5-Dimethyl-1,3,2-λ 3 -Dioxaphospholane Using 31 P NMR

The exclusive synthesis of r -2-ethoxy- cis -4- cis -5-dimethyl-1,3,2- u 3 -dioxaphospholane ( cis - 1 ) is reported. The kinetic measurements of the epimerization of cis - 1 to trans - 1 were performed by 31 P NMR from 50 to 80;C in toluene. The energy of activation (E a ) of the epimerization process was calculated from Arrhenius plot. The thermodynamic parameters of the transition state led us to conclude that the activation barrier of the inversion at phosphorus is driven by the enthalpy and by a large and negative entropy of activation.     

A survey of sampling-based Bayesian analysis of financial data

The capability of implementing a complete Bayesian analysis of experimental data has emerged over recent years due to computational advances developed within the statistical community. The objective of this paper is to provide a practical exposition of these methods in the illustrative context of a financial event study. The customary assumption of Gaussian errors underlying development of the model is later supplemented by considering Student-t errors, thus permitting a Bayesian sensitivity analysis. The supplied data analysis illustrates the advantages of the sampling-based Bayesian approach in allowing investigation of quantities beyond the scope of classical methods.     

Effect of dialkyldimethylammonium vesicles on the thiolysis of p-nitrophenyl acetate

Cationic surfactant vesicles, prepared by an alcohol injection technique and characterized by gel filtration, are extremely effective at increasing the rate of ester thiolysis at near neutral pH.     

Structure of the K0.8-(KCl)0.2 liquid mixture

Summary The structure of liquid solutions of potassium chloride in potassium, at a concentrationx=0.2 of the salt component, is examined in an electron-ion model against multipattern neutron diffraction data. Electronic screening of long-wave-length ionic-density fluctuations and the nature of short-range ionic order are discussed. Further diffraction experiments in the small-angle scattering region and at higher concentrations of the salt component are suggested.

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Riassunto Il lavoro discuta la struttura di soluzioni di cloruro di potassio in potassio liquido a concentrazionex=0.2, contrastando i risultati di un modello teorico con dati di diffrazione neutronica. Si esaminano, in particolare, lo schermo elettronico di fluttuazioni ioniche di grande lunghezza d'onda e la natura dell'ordine ionico a corto raggio. Si suggeriscono ulteriori esperimenti di diffrazione nella regione di piccoli angoli di diffusione e a concentrazioni maggiori della componente salina.

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Резюме В рамках теотической модели, вклющей данные по дифракции нейтронов, исследуется структура Ъидких растворов K_0.8-(KCl)_0.2. Обсуждаются электронное зкранирование длинноволновых флуктуаций плотности ионов и природа коротковолоовой упорядоченности ионов. Предлагаются дифракционные эксперименты по малоугловому рассеянию и при более высоких концентрациях (KCl).

     

Heterocyclo-Substituted Sulfa Drugs: Part XII. Mercapto-S-Azo-Benzothiazol Dyes and Their Metal Complexes

New azo sulfadrugs of 2-mercapto-S-azo ( p '-heterocyclo-substituted benzene-sulfonyl) benzothiazole derivatives (L 1 and L 2 ) were synthesized by coupling of p '-heterocyclo-substituted-benzene-sulphonyl diazonium salts with 2-mercapto-benzothiazole in acid medium. The corresponding iron(III), cobalt(II), nickel(II), copper(II), and mercury(II) chelates were prepared in a 1:1 metal to ligand molar ratio. The ligands and their chelates were characterized on the basis of microanalysis, UV, IR, and H 1 -NMR spectrometry. Thermal decomposition of the complexes was studied in static air. On the basis of the thermogravimetric curves some decomposition steps could be correlated with the proper decomposition products. The photochemical behavior of the ligands and their complexes were investigated. The photosensitivity shown by the complexes was attributed to the photoreactivity of their free ligands. The ligands and their chelates were screened in vitro for their antimicrobial activities (antibacterial and antifungal). The complexes induce a remarkable increase in the antimicrobial activity compared to the corresponding ligands.     

Synthesis of Novel Derivatives of 1,5-Benzothiazepines (Part 1)

Synthesis of 2,4-disubstituted 1,5-benzothiazepines 3a-3i is reported by the condensation of 2-aminothiophenol 1 with 1,3-diones in pyridine. The structures of the compounds have been established by elemental, IR, 1 H NMR, 13 C NMR, and mass spectral analyses.