The natural flavonoid compounds quercetin (3,3',4',5,7-pentahydroxyflavone) and luteolin (3',4',5,7-tetrahydroxyflavone) are important bioactive compounds with antioxidative, anti-allergic, and anti-inflammatory properties. However, both are unstable when exposed to atmospheric oxygen, which causes degradation and complicates their analytical determinations. The oxidative change of these flavonoids was observed and followed by UV-visible spectrophotometry, both in aqueous and ethanolic solutions. The distribution of the degradation products in aqueous media was monitored by LC-MS and LC-DAD analysis. The amounts of oxidative reaction products increase with the exposure time. The oxidative degradation reduces the pharmacological efficiency of these antioxidants and renders analytical determination inaccurate. The oxidative changes in flavonoid test solutions can explain the inconsistent dissociation constants reported in the literature. Dissociation constants of quercetin and luteolin were determined both by alkalimetric titration and by UV-visible spectrophotometry under deaerated conditions. The values pK(1) = 5.87 ± 0.14 and pK(2) = 8.48 ± 0.09 for quercetin, and pK(1) = 5.99 ± 0.32 and pK(2) = 8.40 ± 0.42 for luteolin were found.

Single-molecule conductance in a series of extended viologen molecules was measured at room temperature using a gold-molecule-gold scanning tunneling microscopy break junction arrangement. Conductance values for individual molecules change from 4.8 ± 1.2 nS for the shortest compound to 2.9 ± 1.0 nS for the compound with six repeating units and length of 11 nm. The latter value is almost 3 orders of magnitude higher than that reported for all-carbon-based aromatic molecular wires of comparable length. On the basis of the length of the molecules, an attenuation factor of only 0.06 ± 0.004 nm(-1) (0.006 ± 0.0004 Å(-1)) was obtained. To the best of our knowledge, this is the smallest value reported for the conductance attenuation in a series of molecular wires.

A transfer of fullerene C(60) to water was achieved by sonication of a two-phase system of water and C(60) in organic solvents, namely, benzene and toluene. Resulting aqueous dispersions were analyzed electrochemically, spectroscopically, by MALDI-MS and AFM methods. Samples prepared from benzene yield the formal redox potential very close to a value expected from the correlation of redox potentials and solvent donor numbers. However, these samples are not stable and C(60) precipitates out of the aqueous dispersion. Sonication of the toluene/water system produces stable system, in which the measured formal redox potential of C(60) is less negative. Stabilization of C(60) clusters in water is achieved by the presence of an organic amphiphile and spectroscopic methods indicate the presence of benzoate formed during sonication of a toluene/water mixture.

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We report on an electrochemical conversion of N2 to NH3 at ambient pressure and 60 degrees C, which is mediated by reduced C(60) inside the molecular cavity of gamma-cyclodextrin.