Electrochemical oxidation of 6-hydroxy-1,2,3,4-tetrahydro-β-carboline in aqueous solution

The electrochemical oxidation of 6-hydroxy-1,2,3,4-tetrahydro-β-carboline (1), an alkaloid which occurs naturally in the mammalian brain, has been studied in aqueous solution particularly at physiological pH. The first voltammetric oxidation peak of 1 observed at the pyrolytic graphite electrode generates a radical intermediate which dimerizes to give 5,5′-bi-(6-hydroxy-1,2,3,4-tetrahydro-β-carboline) (3). However, the putative radical intermediate can also be further oxidized (1e) to give a C(5)-centered carbocation which can either dimerize in an ion-substrate reaction to give 3 or be attacked by water to give 5,6-dihydroxy-1,2,3,4-tetrahydro-β-carboline (8) which is rapidly oxidized further to 1,2,3,4-tetrahydro-β-carboline-5,6-dione (9). In the presence of glutathione dione 9 forms the 8-S-glutathionyl conjugate of 8 which is easily oxidized to the 8-S-glutathionyl conjugate of 9. It is suggested that 1 might be an alkaloid which is elevated in the brain as a result of chronic alcoholism, and the roles of the oxidative transformations of this compound in some of the addictive and neurophathological consequences of ethanol consumption are discussed.     

The formation of dimetallocycles from reactions of alkynes with (η-C5Me5)2Rh2(CO)2; X-ray structure of [(η-C5Me5)2Rh2(η-CO) {μ-η2,η2-C(O)C2-(CF3)2}]

The complexes (η-C₅Me₅)₂Rh₂(μ-CO) {μ-η²,η²-C(O)CRCR} are obtained from reactions between (η-C₅Me₅)₂Rh₂(CO)₂ and the alkynes RCCR (R  CF₃, CO₂Me, or Ph) at 25°C. The molecular geometry of the complex with R  CF₃ has been established by X-ray diffraction; the bridging 'ene-one' unit adopts a μ-η²,η² conformation. Other complexes isolated from these reactions include (η-C₅Me₅)Rh(C₆R₆) (R  CF₃, CO₂Me), (η-C₅Me)₂Rh₂(C₄R₄) (R  CO₂Me) and (η-C₅Me₅)₂Rh₂(CO₂C₂R₂) (R  Ph). The reaction between (η-C₅Me₅)₂Rh₂(CO)₂ and C₆F₅CCC₆F₅ gives (η-C₅Me₅)₂Rh₂(CO)₂(C₆F₅C₂C₆F₅). Mononuclear complexes such as (η-C₅Me₅)Co(C₄R₄CO) are the major products isolated from reactions between (η-C₅Me₅)₂CO₂(CO)₂ and alkynes at 25°C.     

1,3-Oxazolidin-4-ones. Synthesis and configuration of cis and trans isomers

Mixtures of cis and trans 1,3-oxazolidin-4-ones were obtained by cyclodehydration, in the presence of p-toluenesulfonic acid or boron trifluoride etherate, of lactamide and N-methyl-lactamide with aromatic and aliphatic aldehydes. The products were separated by column (silica) chromatography and their configurations were determined.     

Zdanovskii’s Rule and Isopiestic Measurements Applied to Synthetic Bayer Liquors

Isopiestic measurements of mixed electrolyte solutions involving sodium hydroxide and other components of Bayer liquors were performed at 50?°C and 100?°C. Most of the systems studied obey Zdanovskii’s rule exactly or very closely. However, those with sodium chloride as one of their components show deviations from Zdanovskii’s rule, which are well predicted by our thermodynamic modelling software based on Pitzer’s equations.     

Enzymatic and electrochemical oxidation of uric acid: A mechanism for the peroxidase catalyzed oxidation of uric acid

The oxidation of uric acid has been studied by thin-layer spectroelectrochemistry using an optically transparent gold minigrid electrode and enzymatically using peroxidase. Under both enzymatic and electrochemical conditions a u.v.-absorbing intermediate (λ_max=302–304 nm between pH 7–9.3) is observed. This intermediate is proposed to be an imine-alcohol species formed by rapid hydration of the primary reaction product which is a diimine. Under the conditions employed in both the enzymatic electrochemical studies the imine-alcohol intermediate is hydrated in a first order reaction with an observed rate constant of 3.5×10^?3s^?1 between pH 7–9.3. This study establishes the similarity between the electrochemical and enzymatic oxidation of uric acid and indicates that electrochemical investigations of the redox behavior of purines can provide unique insights into their biological redox properties.     

Synthesis of monofluorinated analogues of lysophosphatidic acid

Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycerol 3-phosphate) displays an intriguing cell biology that is mediated via interactions both with G-protein coupled seven transmembrane receptors and with the nuclear hormone receptor PPARgamma. Synthesis and biological activities of fluorinated analogues of LPA are still relatively unknown. In an effort to identify receptor-selective LPA analogues and to document in detail the structure-activity relationships of fluorinated LPA isosteres, we describe a series of monofluorinated LPA analogues in which either the sn-1 or the sn-2 hydroxy group was replaced by fluorine, or the bridging oxygen in the monophosphate was replaced by an alpha-monofluoromethylene (-CHF-) moiety. The sn-1 or sn-2 monofluorinated LPA analogues were enantiospecifically prepared from chiral protected glycerol synthons, and the alpha-monofluoromethylene-substituted LPA analogues were prepared from a racemic epoxide with use of a hydrolytic kinetic resolution. The sn-2 and sn-1 fluoro LPA analogues were unable to undergo acyl migration, effectively "freezing" them in the sn-1-O-acyl or sn-2-O-acyl forms, respectively. The alpha-monofluoromethylene LPA analogues were unique new nonhydrolyzable ligands with surprising enantiospecific and receptor-specific biological readouts, with one compound showing a 1000-fold higher activity than native LPA for one receptor subtype.     

Structure and dynamics of ND3BF3 in the solid and gas phases: a combined NMR,neutron diffraction,and Ab initio study

The decrease in D-->A bond lengths, previously reported for some Lewis acid/base complexes, in going from the gas to the solid phases is investigated by obtaining an accurate crystal structure of solid ND(3)BF(3) by powder neutron diffraction. The B-N internuclear distance is 1.554(3) A, 0.118 A shorter than the most recent gas-phase microwave value and 0.121 A shorter than the single molecule geometry optimized (1.672 A, CISD/6-311++G(d,p)) bond length. The crystal structure also shows N-D.F-B hydrogen bonds. The effects of this change in structure and of intermolecular hydrogen-bonding on nuclear magnetic shielding (i.e., chemical shifts) and the nuclear quadrupolar coupling constants (QCC) are investigated by ab initio molecular orbital and density functional theory calculations. These calculations show that the nitrogen ((15)N and (14)N) and boron ((11)B and (10)B) chemical shifts should be rather insensitive to changes in r(BN) and that the concomitant changes in molecular structure. Calculations on hydrogen-bonded clusters, based on the crystal structure, indicate that H-bonding should also have very little effect on the chemical shifts. On the other hand, the (11)B and (14)N QCCs show large changes because of both effects. An analysis of the (10)B[(19)F] line shape in solid ND(3)(10)BF(3) yields a (11)B QCC of +/-0.130 MHz. This is reasonably close an earlier value of +/-0.080 MHz and the value of +/-0.050 MHz calculated for a [NH(3)BF(3)](4) cluster. The gas-phase value is 1.20 MHz. Temperature-dependent deuterium T(1) measurements yield an activation energy for rotation of the ND(3) group in solid ND(3)BF(3) of 9.5 +/- 0.1 kJ/mol. Simulations of the temperature-dependent T(1) anisotropy gave an E(a) of 9.5 +/- 0.2 kJ/mol and a preexponential factor, A, of 3.0 +/- 0.1 x 10(12) s(-)(1). Our calculated value for a [NH(3)BF(3)](4) cluster is 16.4 kJ/mol. Both are much higher than the previous value of 3.9 kJ/mol, from solid-state proton T(1) measurements.     

Self aggregation of binary mixtures of sodium dodecyl sulfate and polyoxyethylene alkyl ethers in aqueous solution

The mixed micelles of sodium dodecyl sulphate (SDS) with Brij35 and Brij 97 were studied separately by fluorescence measurement using pyrene as fluorescent probe. In the range of 0–1.0 mole fraction (X) of added SDS to Brij solutions, the cmc value of the mixed micelles varies from 0.085 to 8 mmol with Brij 35 and 0.04 to 8 mmol with Brij 97. The aggregation number also changes. A measure of the stability of mixed micelles is also presented. The interaction parameter ₁₂ and the chain–chain contribution parameter (B₁) are extracted from the analysis of the results. This parameter B₁ is related to the standard free energy change associated with the introduction of one ionic species into a nonionic micelle coupled with the release of one nonionic species from the micelle. The clouding behaviour of Brij 97 in the presence of SDS was investigated and the associated thermodynamic parameters of clouding were generated and discussed.