By use of steady photo-irradiation in the system of riboflavin aqueous solution containing methyl-sulf-amino acid and superoxide dismutase (SOD) as competitive scavenger of O2, the rate constant of superoxide anion radi- cal(O2 ·)scavenged by (Amberacid-chitosan-complex with copper (II), ACCC) was determined as 1.26×109, ? 1.11×109 and 4.98×108 mol-1 s-1 dm3 under irradiation of 254nm, 365nm UV lights and sun light, respectively. The results also show that the scavenge rate of O2 · by ACCC reached 91%, which is about the same as with ? natural SOD (93%), and is far more higher than the O2 · scavenge rate with just amberacid or chitosan, which is ? only 2.6% and 5.8%, respectively.
The piperonal electron affinity was studied using pulse radiolysis technique. The electron transfer reaction process between piperonal and anthraquinone-2-sulfate was observed in the pH 7 phosphoric acid salt buffer. The transient absorption spectra of electron transfer re-action between piperonal and anthraquinone-2-sulfate were obtained, and the initial proof of the electron transfer between electron donor and acceptor was provided directly. The one-electron reduction potential of piperonal was determined to be ?0.457 V.
MA Jianhua1, LIN Weizhen2, WANG Wenfeng2 & YAO Side2 1. College of Biology Engineering, Jimei University, Xiamen 361021, China
Indolinonic aminoxyls can effectively scavenge various radicals by directly coupling with them or by imitating superoxide dismutase. To better understand the radical-coupling reactions, DFT method B3LYP/6-31G(d,p) was employed to calculate variations of free energy for the coupling reactions and other physico-chemical parameters. The radical-coupling activity difference between aminoxyls was elucidated to a large extent in terms of electronic properties of substituents.
Density functional theory (DFT) at B3LYP/6-31G(d,p) level was employed to calculate intramolecular hydrogen bond enthalpies (HIHB), O-H charge differences, O-H bond lengths and bond orders for various substituted catechols and their radicals generated after H-abstraction. It was found that although the charge difference between hydrogen-bonded H and O played a role in determining HIHB, HIHB was mainly governed by the hydrogen bond length. As the oxygen-centered radical has great tendency to form a chemical bond with the H atom, hydrogen bond lengths in catecholic radicals are systematically shorter than those in catechols. Hence, the HIHB for the former are higher than those for the latter.
