Laccase-Catalyzed Heterocoupling of Dihydroquercetin and p-Aminobenzoic Acid: Effect of the Reaction Product on Cultured Cells.

Derivatization of the natural flavonoid dihydroquercetin with p-aminobenzoic acid was carried out in an ethyl acetate/citric buffer biphasic system using laccase from the fungus Trametes hirsuta. The main reaction product yield was ~68 mol %. The product was characterized by H NMR, C NMR, and liquid chromatography-mass spectroscopy, and its structure was elucidated.

Synthesis of Siloxyalumoxanes and Alumosiloxanes Based on Organosilicon Diols.

We have drawn a few interesting conclusions while studying reaction products of Ph₂Si(OH)₂ with Al(Bu)₃ and tetraisobutylalumoxane. In the first place, this is the production (at a Ph₂Si(OH)₂ and Al(Bu)₃ equimolar ratio) of an oligomer siloxyalumoxane structure with alternating four- and six-member rings. In addition, it shows isobutyl and phenyl group migration between aluminum and silicon due to the formation of an intramolecular four-member cyclic complex [Ph₂(OH)SiO]Al(Bu)₂ → [(Bu)Ph(OH)SiO]Al(Bu)Ph.

Enzymatic polymerization of dihydroquercetin using bilirubin oxidase.

Dihydroquercetin (or taxifolin) is one of the most famous flavonoids and is abundant in Siberian larch (Larix sibirica). The oxidative polymerization of dihydroquercetin (DHQ) using bilirubin oxidase as a biocatalyst was investigated and some physicochemical properties of the products were studied. DHQ oligomers (oligoDHQ) with molecular mass of 2800 and polydispersity of 8.

Structural trends of 29Si-1H spin-spin coupling constants across double bond.

The calculations of geminal and vicinal (29)Si-(1)H spin-spin coupling constants across double bond in 15 alkenylmethylsilanes and alkenylchlorosilanes were carried out at the second-order polarization propagator approach level in a good agreement with experiment. Two structural trends, namely, (i) the geometry of the coupling pathway and (ii) the effect of the electrowithdrawing substituent, have been interpreted in terms of the natural J-coupling analysis within the framework of the natural bond orbital approach. Thus, the marked difference between cisoidal and transoidal (29)Si-(1)H spin-spin coupling constants across double bond was accounted for the delocalization contributions including bonding and antibonding Si-C and C-H orbitals, whereas the chlorine effect was explained in terms of the steric contributions including bonding Si-Cl orbitals.

Benchmark calculations of (29) Si-(1) H spin-spin coupling constants across double bond.

Benchmark calculations of geminal and vicinal (29) Si-(1) H spin-spin coupling constants across double bond in three reference alkenylsilanes have been carried out at both DFT and SOPPA levels in comparison with experiment. At the former, four density functionals, B3LYP, B3PW91, PBE0 and KT3, were tested in combination with five representative basis sets. At the latter, three main SOPPA-based methods, SOPPA, SOPPA(CC2) and SOPPA(CCSD), were examined in combination with the same series of basis sets.