Non-radical synthesis of chitosan-quercetin polysaccharide: Properties, bioactivity and applications.

Quercetin-chitosan (QCS) polysaccharide was synthesized via non-radical reaction using L-valine-quercetin as the precursor. QCS was systematically characterized and demonstrated amphiphilic properties with self-assembling ability. In-vitro activity studies confirmed that quercetin grafting does not diminish but rather increases antimicrobial activity of the original chitosan (CS) and provided the modified polysaccharide with antioxidative properties. QCS applied as a coating on fresh-cut fruit reduced microbial spoilage and oxidative browning of coated melon and apple, respectively. Notably, QCS-based coatings prevented moisture loss, a major problem with fresh produce (2%, 12% and 18% moisture loss for the QCS-coated, CS-coated and uncoated fruit, respectively). The prepared QCS polysaccharide provides advanced bioactivity and does not involve radical reactions during its synthesis, therefore, it has good potential for use as a nature-sourced biocompatible active material for foods and other safety-sensitive applications.

Activation of molecular oxygen by a dioxygenase pathway by a ruthenium bis-bipyridine compound with a proximal selenium site.

A ruthenium(II) bipyridine complex with proximal phenylselenium tethers, [Ru](H(2)O)(2), reacted intramolecularly with O(2) in a protic slightly acidic solvent, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), to yield an O-O bond cleaved product, [Ru](O)(2), with formation of two Ru-O-Se moieties. This stable compound was isolated, and its structure was determined by X-ray diffraction. The identification of the compound in solution was confirmed by ESI-MS and the (1)H NMR with the associated Curie plot that showed that [Ru](O)(2) was paramagnetic. The magnetic susceptibility was 2.8 mu(B) by Evan's method suggesting a ground state triplet or biradical. DFT calculations, however, predicted a ground state singlet and an oxidized Se atom. Further it was shown that [Ru](O)(2) is a potent oxygen transfer species of both O(2)-derived atoms to triphenylphosphine and a nucleophilic alkene such as 2,3-dimethyl-2-butene in both HFIP and acetonitrile. UV-vis spectroscopy combined with the measured stoichiometry of PPh(3):O(2) = approximately 2 in a catalytic oxidation of PPh(3) suggests a dioxygenase type activation of O(2) with structural identification of the O-O bond cleavage reaction step, formation of [Ru](O)(2) as an intermediate, and the proof that [Ru](O)(2) is a donor of both oxygen atoms.