Chrysophanol glycosides from callus cultures of monocotyledonous Kniphofia spp. (Asphodelaceae)

We established callus cultures of the monocotyledonous plants Kniphofia foliosa and K. tuckii (Asphodelaceae), which produce the anthraquinone derivatives chrysophanol and its glycosides. The minor product chrysophanol 8-O-beta-gentiobioside was fully characterized by spectroscopic analysis and synthesis.     

Comparison of the aerobic photoreactivity of A2E with its precursor retinal

A2E (2-[2,6-dimethyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E, 3E,5E,7E-octatetraenyl]-1-(2-hydroxyethyl)-4-[4-methyl-6(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E,5E-hexatrienyl]pyridinium) is a blue-absorbing molecular constituent of human ocular lipofuscin and contributes to the golden-yellow emission of this pigment. Lipofuscin photoproduces toxic reactive oxygen intermediates (ROI), but the specific molecular components responsible for this phototoxicity remain unidentified. In this article the aerobic photoreactivity of A2E is quantified by comparison with its biosynthetic precursor, all-trans-retinal, and with other appropriate standards. Under blue-light exposure the efficacies for formation of cholesterol (Ch) hydroperoxides and the superoxide radical anion (O2*-) were determined using high-pressure liquid chromatography with electrochemical detection and electron spin resonance oximetry and spin trapping, respectively. Photogeneration of singlet oxygen after blue-light excitation of A2E was demonstrated unambiguously by the Ch peroxidation assay. After blue-light irradiation of A2E, O2*- were detected, but the concentration was insufficient to account for the measured production of O2*- by the solvent extract of lipofuscin granules. The collective data support the conclusion that A2E does not produce sufficient concentrations of ROI to be the primary phototoxic constituent of lipofuscin.     

Solution versus solid-state electropolymerization of regioregular conjugated fluorenone–thienylene vinylene macromonomers—voltammetric and spectroelectrochemical investigations

We present detailed voltammetric and spectroelectrochemical studies of poly(2,7-bis(5-[(E)-1,2-bis(3-octylthien-2-yl)ethylene])-fluoren-9-one) (PTVF)—a conjugated polymer consisting of thienylene, vinylene, and fluorenone subunits. PTVF can be easily obtained either by electropolymerization of its monomer ((2,7-bis(5-[(E)-1,2-bis(3-octylthien-2-yl)ethylene])-fluoren-9-one) [TVF]) dissolved in the electrolytic solution or via solid-state electropolymerization of a thin film of the monomer deposited on the electrode. UV-vis-NIR spectroscopic data indicate that the latter method leads to a polymer of a smaller degree of polymerization (DP). The possibility of the formation of a polymeric conductor on a transparent conductive substrate such as indium tin oxide, in situ, via solid-state electropolymerization, combined with its postpolymerization transformation into an organic semiconductor by electrochemical dedoping, is technologically very attractive and makes TVF and its polymer very promising materials for applications in organic electronics. Contribution to the International Workshop on Electrochemistry of Electroactive Materials (WEEM-2006), Repino, Russia, 24–29 June 2006.     

Interactions in open-shell clusters: ab initio study of pre-reactive complex O(3P) + HCl

Van der Waals interactions between the ground-state triplet O(3P) atom and the closed-shell HCl molecule are investigated in the pre-reactive region. Three adiabatic (two of A' symmetry and one of A' symmetry) and four non-relativistic diabatic potential energy surfaces are obtained by combining a restricted open-shell coupled cluster approach with the multireference configuration interaction method. The lower A' adiabatic potential surface has a single minimum (D(e) = 589 cm(-1)) for a linear O...HCl configuration. The upper A' potential has a weak (D(e) = 65 cm(-1)) minimum for a linear HCl...O configuration. The A' adiabatic potential has a weak (124 cm(-1)) T-shaped minimum. Adiabatic potentials intersect once in the O...HCl linear configuration and twice in the linear HCl...O geometry. The role of electrostatic interactions in shaping these potentials is discussed. The effects of spin-orbit coupling on this interaction are also investigated assuming a constant value of the SO parameter.     

Electrochemical charging and electrocatalysis at hybrid films of polymer-interconnected polyoxometallate-stabilized carbon submicroparticles

Using the layer-by-layer technique, carbon submicroparticles, that have been modified and stabilized with monolayers of Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻), can be dispersed in multilayer films of organic polymers, poly(3,4-ethylenedioxythiophene), i.e., PEDOT, or poly(diallyldimethylammonium) chloride, i.e., PDDA, deposited on glassy carbon or indium-tin oxide conductive glass electrodes. The approach involves alternate treatments in the colloidal suspension of PMo₁₂O₄₀³⁻-covered carbon submicroparticles in the solution of monomer, 3,4-ethylenedioxythiophene or in solution of PDDA polymer. Electrostatic attractive interactions between anionic phosphomolybdate-modified carbon submicroparticles and cationic polymer layers permit not only uniform and controlled growth of the hybrid organic–inorganic film but also contribute to its overall stability. The system composed of PMo₁₂O₄₀³⁻-covered carbon submicroparticles dispersed in PEDOT is characterized by fast dynamics of charge transport and has been used to construct symmetric microelectrochemical redox capacitor. The PDDA-based system has occurred to be attractive for electrocatalytic reduction of hydrogen peroxide.     

Enantiomeric differentiation of amino acids by a chiral crown ether derived fromd-mannose studied by the liquid membrane technique

Chiral 18-crown-6 incorporating ad-mannopyranoside unit displays noticeable enantioselectivity in the recognition of amino acids and their sodium and potassium salts in transport experiments across a liquid membrane containing the carrier.d-phenylalanine andd-phenylglycine were transported faster than their correspondingl-enantiomers, whereas the enantioselectivity was reversed with tryptophan.