Anion selective polymeric membrane electrodes based on cyclopalladated amine complexes

The potentiometric anion selectivity of two polymer membrane based electrodes (I and II) formulated with two new cyclopalladated amine complexes as the active components are examined. The electrodes exhibit a non-Hofmeister selectivity pattern with a significantly enhanced response towards thiocyanate, iodide and nitrite. The graph potential versus log c is linear over the concentration range 10(-6)-6x10(-2) M thiocyanate with electrode I and 10(-6)-10(-3) M with electrode II; 10(-5)-10(-2) M iodide with electrode I and 10(-3)-6x10(-2) M with electrode II; and 10(-3)-6x10(-2) M nitrite with both electrodes. The influence of the plasticizer and pH are studied. The potentiometric selectivity coefficients for I, II and blank membrane electrodes are reported. The selective interaction between Pd(II) thiocyanate, iodide and nitrite is postulated to be the reason for its higher response.     

Divergent routes to chiral cyclobutane synthons from (-)-alpha-pinene and their use in the stereoselective synthesis of dehydro amino acids

Several polyfunctionalized cyclobutane derivatives have been synthesized using commercial (-)-alpha-pinene and (-)-verbenone as chiral precursors. Thus, oxidative cleavage of these compounds by using ruthenium trichloride afforded quantitatively (-)-cis-pinonic and (-)-cis-pinononic acids, respectively, without epimerization. These products were converted into several types of aldehydes, which are the key intermediates in the synthesis of cyclobutane dehydro amino acids via Wittig-Horner condensations with suitable phosphonates. These reactions are highly stereoselective, affording exclusively (Z) isomers, stereochemistry being assessed by NMR experiments. The obtained dehydro amino acids are polyfunctionalized molecules useful for the synthesis of other alpha-amino acids, with additional chiral centers, whose configuration must be induced by the chirality of the terpene employed as a precursor.     

Isolation of a stable 1-iridabicyclo[3.2.0]hepta-1,3,6-triene and its reversible transformation into an iridacycloheptatriene

Reaction of the iridacyclopentadiene complex 2 with 2-butyne yields a mixture in equilibrium of the iridacycloheptatriene 3 and a novel 1-iridabicyclo[3.2.0]hepta-1,3,6-triene, 4.     

Pyridazines. Part 31: synthesis and antiplatelet activity of 4,5-disubstituted-6-phenyl-3(2H)-pyridazinones

This paper describes the synthesis and the antiplatelet activity of a series of 4,5-disubstituted-6-phenyl-3(2H)-pyridazinones. Some of these compounds show a dose-dependent activity and were found to be more active than their 5-substituted analogues.     

Intercalation Compounds between Ethyl 2-oxocyclopentanecarboxylate and Saponite

The retention of ethyl 2-oxocyclopentanecarboxylate by a saponite has been studied. Intercalation compounds were prepared by two different methods: 1) in repose at room temperature and 2) heating at 60 °C under reflux. Contact times between 2 and 12 days were considered for each method. The intercalation compounds obtained were characterized by X-ray diffraction, infrared spectroscopy, chemical analyses and thermal analyses. This characterization indicates that the organic compound is retained both in the interlayer region and at the edge of the clay particles. The amount retained outside of the interlayer space is eliminated by careful washing with benzene and cyclohexane. The results obtained when using acid-activated saponite -obtained by treatment of the clay with dilute HCl solutions- in the intercalation experiments were similar to those obtained when using non-activated saponite.     

Theoretical study of the photochemical [2 + 2]-cycloadditions of cyclic and acyclic alpha,beta-unsaturated carbonyl compounds to ethylene

The ground and first triplet excited-state potential energy surfaces of the [2 + 2]-cycloadditions of 2-cyclohexenone, methyl acrylate, and methyl crotonate to ethylene have been studied by means of CASSCF and DFT-B3LYP calculations. The attack of ethylene to the (3)(pi-pi) alpha,beta-unsaturated carbonyl compound leads to the formation of a triplet 1,4-biradical intermediate that evolves to the ground-state potential energy surface. The outcome of the reaction is governed by the competition between the deactivation of the (3)(pi-pi) alpha,beta-unsaturated carbonyl compound itself and its reaction with ethylene to form the triplet 1,4-biradical. For 2-cyclohexenone, the potential energy barrier corresponding to the formation of the biradical intermediate is lower than for the acyclic systems. On the other hand, the energy necessary to reach the crossing point between the (3)(pi-pi) and the ground-state potential energy surfaces is lower for the acyclic systems than for 2-cyclohexenone. For methyl acrylate and methyl crotonate, the decay of the (3)(pi-pi) state of the isolated molecule is therefore expected to be faster than the formation of the 1,4-biradical, so that the [2 + 2]-cycloaddition will not take place. However, for 2-cyclohexenone the formation of the triplet 1,4-biradical is favorable, and the process will lead to the formation of the corresponding cyclobutane derivative.