Wenfeng Wang

The scavenging reactions of nitrogen dioxide radical and carbonate radical by tea polyphenol derivatives: a pulse radiolysis study

Abstract The reactions of tea polyphenol derivatives, including epicatechin (EC) and epigallocatechin gallate (EGCG), with nitrogen dioxide radical (NO 2 ) and carbonate radical (CO 3 − ) have been studied in detail using time-resolved pulse radiolysis technique. In all the cases, the corresponding phenoxyl radical was formed through electron transfer reaction. From the build-up kinetics of the phenoxyl radicals and the decay kinetics of CO 3 − radical, the reaction rate constants of EC, EGCG with NO 2 and CO 3 − were determined to be 9.0×10 7 , 1.2×10 8 and 5.6×10 8 , 6.6×10 8 xa0dm 3 xa0mol −1 xa0s −1 , respectively. Therefore, tea polyphenol derivatives proved to be efficient scavengers of NO 2 and CO 3 − radicals.

Fast repair of deoxythymidine radical anions by two polyphenols: rutin and quercetin

The effects of rutin and quercetin on the repair of the deoxythemindine radical anion (dT*) were studied using the technique of pulse radiolysis. The radical anion of dT was formed by the reaction of hydrated electron with dT. After pulse irradiation of nitrogen-saturated aqueous solutions containing dT, 0.2M t-BuOH and either rutin or quercetin, the initially formed dT*(-), detected spectrophotometrically, rapidly decayed with the concurrent formation of the radical anion of rutin or quercetin. The results indicated that dT*(-) can be rapidly repaired by rutin or quercetin. The rate constants of the repair reactions were determined to be 3.1 and 4.1 x 10(9)M(-1)s(-1) for rutin and quercetin, respectively. With substitution by glycosyl groups at C(3)-OH bond being neighbor to C(4) keto group, which is the active site for electron transfer, rutin has a lower repair reaction rate constant toward dT*(-) than quercetin. Together with findings from our previous studies, the present results demonstrated that nonenzymatic fast repair may be a universal form of repair involving phenolic antioxidants.

Triplet state mechanism for electron transfer oxidation of DNA

The interaction of anthraquinone-2-sulfonate with nucleotides and DNA in acetonitrile and acetonitrile water solvent mixture have been studied using KrF laser photolysis aimed at elucidation of the reaction mechanism. Laser spectroscopy directly demonstrates that the initial species from interaction of anthraquinone-2-sulfonate with nucleotides are radical cations of nucleotides and radical anion of anthraquinone-2-sulfonate. In addition, formation of ion pair from interaction of any of nucleotides with anthraquinone-2-sulfonate is synchronous with decay of triplet anthraquinone-2-sulfonate, which has provided dynamic evidence for initiation of electron transfer from DNA bases to triplet anthraquinone-2-sulfonate. Moreover, direct observation of stabilized DNA guanyl radical cation from interaction of anthraquinone-2-sulfonate with DNA has provided initial evidence for selective cleavage of DNA at guanine moiety. The solvent-separated ion pairs in acetonitrile have evidently dissociated into free ions, thereby enabling independent study of the behavior of guanyl radical cations and radical anion of anthraquinone-2-sulfonate.

Kinetic observation of rapid electron transfer between pyrimidine electron adducts and sensitizers of riboflavin, flavin adenine dinucleotide (FAD) and chloranil: a pulse radiolysis study

Abstract Rapid electron transfer from electron adducts of pyrimidine nucleotides dCMP, TMP and UMP to sensitizers of riboflavin (RF), flavin adenine dinucleotide (FAD) and chloranil (CHL) were studied using the techniques of pulse radiolysis. Both spectroscopic and kinetic analyses showed that the transient absorption spectra of pyrimidine electron adducts formed at first, and then were replaced by those of radical anions of RF, FAD and CHL after several microseconds of electron beam pulse, which indicated that electron transfer from electron adducts of pyrimidines to RF, FAD and CHL occurred. From buildup kinetics of sensitizer radical anions, a series of rate constants for electron transfer are determined respectively. RF and FAD can capture electron from pyrimidine electron adducts induced in irradiated cell, which would reduce possible repair of damaged targets due to the inhibition of charge recombination of radical ion pair. Thereby RF and FAD might play the role of radio-sensitizer in DNA damage process.

Characterization of reactive intermediates in laser photolysis of nucleoside using of sodium salt anthraquinone-2-sulfonic acid as photosensitizer

Abstract The interaction of triplet state of sodium salt of anthraquinone-2-sulfonic acid (AQS) with nucleosides has been investigated in CH 3 CN using KrF(248xa0nm) laser flash photolysis. The transient absorption spectra and kinetics obtained from the interaction of triplet AQS and nucleoside demonstrated that the primary ionic radical pair, radical cation of nucleosides and radical anion of AQS has been detected simultaneously for the first time.

Fast repair activities of quercetin and rutin toward dGMP hydroxyl radical adducts

Abstract The repair activities and mechanisms of both quercetin and rutin towards the oxidizing deoxyguanosine monophosphate (dGMP) hydroxyl radical adduct were investigated with pulse radiolytic technique. On pulse irradiation of nitrous oxide saturated 2xa0mM dGMP aqueous solution containing 0.1xa0mM quercetin, the transient absorption spectrum of the dGMP hydroxyl radical adduct decays with the formation of phenoxyl radical of quercetin within tens of microseconds. It indicates that there is a repair reaction between dGMP hydroxyl radical adduct and quercetin. The repair activity of rutin towards hydroxyl radical adducts of dGMP was also observed. The rate constants of the repair reactions were calculated to be 3.05×10 8 and 1.31×10 8 xa0M −1 xa0s −1 for quercetin and rutin, respectively. This result together with our previous studies demonstrated that non-enzymatic, fast repair is a universal repair mechanism of phenolic antioxidants.

Terahertz Time-Domain Spectroscopy of Four Hydroxycinnamic Acid Derivatives

The well-resolved absorption spectra of the hydroxycinnamic acid (HCA) derivatives, caffeic acid, ferulic acid, sinapic acid and chlorogenic acid, were measured over the frequency region from 0.3 to 2.0xa0THz at 294xa0K with terahertz time-domain spectroscopy (THz-TDS). Theoretical calculation was applied to assist the analysis and assignment of the individual THz absorption spectra of the HCA derivatives with density functional theory (DFT). The distinctive spectral features were originated from the collective motion of molecules held together by hydrogen bonds. The real and imaginary parts of dielectric function of the four HCA derivatives were also obtained.

Effects of pH and polarity on the excited states of norfloxacin and its 4’- N -acetyl derivative：a steady-state and time-resolved study

The properties of norfloxacin (NFX) and its 4′-N-acetyl derivative (ANFX) are investigated in different pH aqueous solutions and H2O-CH3CN mixed solutions, to determine the effects of pH and polarity on their ground and excited states. The triplet states of NFX and ANFX are affected more by pH than by polarity. The pH dependence of the NFX and ANFX triplet states is likely due to the different quantum yields of different protonated forms. Steady-state fluorescence, time-resolved fluorescence, and laser flash photolysis experiments at different pH values provide clear evidence of the involvement of different intramolecular charge-transfer pathways in the singlet states of NFX and ANFX. The different electron-donating capacities of 1-N, 1′-N, and 4′-N under different conditions determine the major pathway.

Fast repair of dAMP hydroxyl radical adduct by verbascoside via electron transfer

DNA damaged by oxygen radicals has been implicated as a causative event in a number of degenerative diseases, including cancer and aging. So it is very impotant to look for ways in which either oxygen radicals are scavenged prior to DNA damage or damaged DNA is repaired to supplement the cells’ inadequate repair capacity. The repair activity and its mechanism of verbascoside, isolated fromPedicularis species, towards dAMP-OH · was studied with pulse radiolytic technique. On pulse irradiation of nitrous oxide saturated 2 mmol/L dAMP aqueous solution containing verbascoside, the transient absorption spectrum of the hydroxyl adduct of dAMP decayed with the formation of that of the phenoxyl radical of verbascoside well under 100 microseconds after electron pulse irradiation. The result indicated that dAMP hydroxyl adducts can be repaired by verbascoside. The rate constants of the repair reaction was deduced to be 5.9 × 108 dm3 · mol-1 · s-1. A deeper understanding of this new repair mechanism will undoubtedly help researchers explore new prevent and/or intervening medicine.

Photoreactions of 1,4-naphthoquinone with lysozyme studied by laser flash photolysis and steady-state analysis

Photoprocesses of 1,4-naphthoquinone (NQ) and its photoreactions with lysozyme in acetonitrile/water (3:1, v/v) solution were studied using 355 nm laser flash photolysis technique combined with electrophoresis and turbidimetric assay. The transient spectra of NQ were observed and the transient species were assigned. The electron transfer process from N,N,N,N-tetramethyl-p-phenylenediamine (TMPD) to NQ triplet state ((3)NQ) was investigated and the rate constant was determined to be k(t1)=2.0 x 10(10)M(-1)s(-1). It has been found that (3)NQ can abstract hydrogen atom from lysozyme with a rate constant of k(t2)=2.4 x10(10)M(-1)s(-1). Furthermore, the results of steady-state analysis suggested that lysozyme can be damaged by NQ irradiated with UVA light influenced by the concentration of NQ and the gas saturated in the solution. The mechanisms of photosensitized damage of lysozyme were discussed.