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Using pulse radiolytic techniques, it has been demonstrated that the interactions of oxidizing OH adducts of DNA (ssDNA and dsDNA), polyA and polyG with hydroxycinnamic acid derivatives proceed via an electron transfer process ( k =5–30×10 8 dm 3 mol −1 s −1 ). In addition, the rates for fast repair of OH adducts of dAMP, polyA and DNA (ssDNA and dsDNA) are slower than the corresponding rates for the rest OH adducts of DNA constituents. The slower rates for repair of oxidizing OH adducts of dAMP may be the rate determining step during the interaction of hydroxycinnamic acid derivatives with OH adducts of DNA containing the varieties of OH adducts of DNA constituents.

Transient absorption spectrum of triplet state of 9,10-anthraquinone-2-sulfonate (AQS) in aqueous solution has been investigated using 248 nm (KrF) laser photolysis. A whole transient absorption spectrum with absorption maxim at 380 nm and 580 nm has been assigned to triple AQS from detailed kinetic analysis of decay of 380 nm and 580 nm signals, which is the neat characteristic absorption of triplet AQS reported for the first time. In addition, the difference in feature of the spectrum of triplet AQS in H 2 O and that in CH 3 CN was eliminated by further study using 248 nm laser pulses.

Pulse radiolysis of chlorogenic acid (CGA) as well as CGA and 2′-deoxyguanosine-5′-monophosphate (dGMP) has been carried out in aqueous solution using pulse radiolytic technique. From detailed kinetic analyses, the kinetic parameters have been obtained. Accordingly, the reaction mechanisms are suggested. Previous studies have indicated that CGA can either scavenge OH radical or repair oxidizing OH radical adduct of dGMP effectively.

Fullerols of C60 and of C70 [C60(OH)n, C70(OH)m], water-soluble fullerene derivatives, unlike some other fullerene derivatives (such as C60 (C4H6O), C60 (C3H7N) and C60 [C(COOEt)2]x), do not result in excited triplet state but in ionization via monophotonic process in aqueous solutions with 248 nm laser. The quantum yields of formation of hydrated electron (Φe−) are determined to be 0.08 and 0.11 for fullerols of C60 and of C70 respectively at room temperature (ca. 15°C) with KI solution used as reference. By laser flash photolysis and oxidation of sulfate radical anion SO4−, the fullerol radical cation or neutral radical of C60 is confirmed to be existent and the transient absorption spectra of fullerol radical cation of C70 are observed for the first time.

The kinetics and mechanisms of ultraviolet photochemical transformation of propylparaben (PPB) were studied. Specific kinetics scavenging experiments coupled with quantum yield determinations were used to distinguish the roles of various reactive species induced by self-sensitized and direct photolysis reactions, and the excited triplet state of PPB ((3) PPB*) was identified as the most important species to initiate the photochemical degradation of PPB in aquatic environments. The computational results of time-resolved absorption spectra proved that (3) PPB* is a highly reactive electron acceptor, and a head-to-tail hydrogen transfer mechanism probably occurs through electron coupled with proton transfer. Physical quenching by, or chemical reaction of (3) PPB* with, O2 was confirmed as a key step affecting the initial PPB transformation pathways and degradation mechanisms. The transformation products were identified and the toxicity evolutions of PPB solutions during photochemical degradation under aerobic and anaerobic conditions were compared. The results indicate that anaerobic conditions are more likely than aerobic conditions to lead to the elimination and detoxification of PPB but less likely to lead to PPB mineralization.

A novel photochromic compound, 3,4-bis[2,5-dimethylthiophene-3-yl]-2,5-dihydrothiophene (BT), has been synthesized. The photochromic reactions of BT in a polar solvent (acetonitrile) and a non-polar solvent (cyclohexane) were investigated by means of steady state absorption spectra and time-resolved transient absorption spectra. The maximum absorption wavelengths of BT in acetonitrile and cyclohexane are at 232 and 233 nm, respectively, and the maximum absorption wavelengths of the photocyclization product (CBT) in acetonitrile and cyclohexane are 445 and 453 nm, respectively. Upon irradiation with ultraviolet light, BT is first excited to the excited singlet state, and then to the excited triplet state via inter-system crossing. Only the excited singlet state generates CBT. The excited triplet state, which has a maximum absorption wavelength at 390 nm, decays rapidly to the starting compound (BT) alone.

The results of pulse radiolytical research on the · OH radical-induced oxidation of NDM in aqueous solution demonstrate that pH value has a great influence on the radiolytical mechanism of NDM. At low pH value, the product is mainly stabilization of the oxidizing sulfur centre in the three-electron-bonded cation radical NDM2 ·+ [S]; with the increase of pH value, NDM2 ·+ [S] gradually decays to become the reducing α-amino radical which was verified by the chemical method and whose yield was also calculated. Compared with Met2 ·+ [S] produced by the · OH radical-induced oxidation in aqueous solution [1], the stability of NDM2·+ [S] increases and the yield of α-amino radical decreases. This suggests that the introduction of phosphoryl group has a coordinating effect on the radioprotection of methionine to biological systems, and provides the essentially theoretical foundation for the thorough clarification of the reversible phosphorylation of proteins.

Photochromic reactions of 17 spiro[indolineoxazine] derivatives were investigated using nanosecond laser flash photolysis techniques. The substituent in the 2′-position of the oxazine moiety plays a decisive role in the formation of photoproducts. When the 2′-substituent is hydrogen, photoexcitation of spirooxazine only yielded long-lived photomerocyanine (PMC); however, with other substituents, a short-lived charge separation twisted species (CT) was formed as the predominant product. This observation is attributed to the steric hindrance effect of the substituent in the 2′-position of the oxazine moiety and methyl groups in the 1- and 3-positions of the indoline moiety. In addition, the substituent on nitrogen atom of the indoline moiety also affects the structural characteristics of the CT intermediate. The substituents in the 5-position of the indoline moiety and 9′-position of the naphthooxazine moiety affect the system mainly through electronic effects. A substituent effect on the λmax of the absorption spectra of PMC is also observed. A potential energy surface is proposed to explain these substituent effects. The structural characteristics of PMC and CT intermediates are discussed.

Ultrasmall superparamagnetic iron oxide (USPIO) with synthetic polymer, based on magnetite core, was synthesized via facile photochemical in situ polymerization. A possible mechanism of photochemical in situ polymerization was proposed. The obtained polymer-enveloped UPSIO was characterized by transmission electron microscopy (TEM), photo-correlation spectroscopy (PCS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric (TG) analysis and vibrating sampling magnetometer (VSM) measurement. Properties such as ultrasmall particle size, hydrophilicity, strong magnetization and surface characteristics, which are desirable for magnetic resonance imaging (MRI) contrast agents, were evaluated in detail. The resultant USPIO-based MRI contrast agent holds considerable promise in molecular MR tracking, MR immune imaging, cell tracking and targeted intracellular hyperthermia, etc.

Photochromic reactions of 17 spiro[indolineoxazine] derivatives were investigated using nanosecond laser flash photolysis techniques. The substituent in the 2′-position of the oxazine moiety plays a decisive role in the formation of photoproducts. When the 2′-substituent is hydrogen, photoexcitation of spirooxazine only yielded long-lived photomerocyanine (PMC); however, with other substituents, a short-lived charge separation twisted species (CT) was formed as the predominant product. This observation is attributed to the steric hindrance effect of the substituent in the 2′-position of the oxazine moiety and methyl groups in the 1- and 3-positions of the indoline moiety. In addition, the substituent on nitrogen atom of the indoline moiety also affects the structural characteristics of the CT intermediate. The substituents in the 5-position of the indoline moiety and 9′-position of the naphthooxazine moiety affect the system mainly through electronic effects. A substituent effect on the λmax of the absorption spectra of PMC is also observed. A potential energy surface is proposed to explain these substituent effects. The structural characteristics of PMC and CT intermediates are discussed.

The degradation mechanism of p-nitrophenol (p-NP) exposed to 254 nm UV light was studied in the presence and the absence of oxygen respectively via both steady-state photolysis and time-resolved laser flash photolysis (LFP) experiments. It has been confirmed that p-NP can be photo-ionized to produce its radical cation (p-NP(+center dot)) and hydrated electron (e(aq)(-)) with a quantum yield of 0.52. In neutral solution p-NP(+center dot) will be quickly deprotonated to form its phenoxyl radical (p-NP(center dot)) which will react with oxygen to promote the breakage of benzene ring of p-NP. The degradation efficiency of p-NP exposed to 254 nm UV is as low as commonly reported. However, oxygen could improve the photo-degradation efficiency, which is due to the reaction of oxygen with p-NP(center dot). The reaction between oxygen and p-NP(center dot) has been experimentally confirmed both in LFP and in pulse radiolysis. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Using 266 nm laser flash photolysis it has been demonstrated that Berberine (BBR) in aqueous solution is ionized via a mono-photonic process giving a hydrated electron, anion radical that formed by hydrated electron react with steady state of BBR, and neutral radical that formed from rapid deprotonation of the radical cation of BBR. The quantum yield of photoionization is determined to be 0.03 at room temperature with KI solution used as a reference. Furthermore utilizing pH changing method and the SO(4.)(-) radical oxidation method, the assignment of radical cation of BBR was further confirmed, the pK(a) value of it was calculated, and the related set up rate constant was also determined.

Successfully systemic gene therapy has been hindered by vector-related limitations, including toxicity and inefficient gene delivery to tumor cells after intravenous administration. In this study, we evaluated the potential of spherical polyethylenimine nanogels (M-PEIs) as a novel vector for intravenous delivery of plasmids to tumor cells. M-PEIs provided a sustained release of plasmids up to 14 days and were also effective in protecting plasmids from enzymatic degradation in serum-conditioned media. M-PEIs showed no obvious cytotoxicity to mammalian cells in vitro as well as to liver, heart and kidney in mice after intravenous injection. Importantly, following intravenous administration of M-PEIs/plasmid complexes into human hepatocellular carcinoma xenograft-bearing mice, green fluorescence protein reporter gene expression was predominantly found in the tumor. This study indicates that M-PEIs may be a candidate for systemic delivery of plasmids into tumors.

The property of the excited triplet state of berberine (BBR) was investigated by using time-resolved laser flash photolysis of 355 nm in acetonitrile. The transient absorption spectra of the excited triplet BBR were obtained in acetonitrile, which have an absorption maximum at 420 nm. And the ratio of excitation to ionization of BBR in acetonitrile solvent was calculated. The self-decay and self-quenching rate constants, and the absorption coefficient of (3)BBR* were investigated and the excited state quantum yield was determined. Furthermore utilizing the benzophenone (BEN) as a triplet sensitizer, and the beta-carotene (Car) as an excited energy transfer acceptor, the assignment of (3)BBR* was further confirmed and the related energy transfer rate constants were also determined.

Thermal oxidation process of styrene-butadiene-styrene (SBS) copolymer was studied by using a variety of analytical and spectroscopic methods including thermal analysis, dynamic mechanical analysis and FTIR spectroscopy. The experimental results indicate that the thermal oxidation process of SBS is a free radical self-catalyzed reaction containing four steps (initiation, growth, transfer, and termination of the chain) with both crosslinking and scission and the latter is confirmed to be the main process. The antioxidants 1010 as scavenger of free radicals and 168 acting decomposition of hydroperoxides were used to improve the oxidation aging resistance of SBS copolymer. It has been found that synergic effect of 1010 and 168 may be the best in practice and 0.2 wt % 1010 + 0.4 wt % 168 can effectively prevent SBS from the thermal oxidation at certain temperature. Furthermore, the aging resistance of the SBS-modified asphalt was improved by addition of complex antioxidants. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 754-761, 2010

With the development of nano material industry, more and more attention has been paid on the biological effect of nano materials. However, little research focused on the effect of nano TiO2 on protein level. In this study, we detected the toxic effect of nano TiO2 (50~60 nm) on DNA and functional proteinase. The oxidative damage of nano TiO2 on DNA was detected by gel electrophoresis and HPLC. Anson method was used to study the inhibition of nano TiO2 on pepsin, and the mechanism of the reaction was further researched by the method of UV-Vis scan and TEM. The results showed that the ratio of super-coiled DNA decreased significantly both under UV radiation and visible light. Levels of 8-OHdG generated from DNA increased from 27.66 8- OHdG/104 dG to 296.69 8-OHdG/104 dG after treated with nano TiO2. After water incubated with nano TiO2 at 37degC, the activity of pepsin decreased with the increase of the concentration of particels, UV-Vis scan and TEM detection proved the binding effect of nano TiO2 on pepsin, which indicated potential usage for oral drug delivery of nano TiO2.

Titanium dioxide (TiO 2 ) has been considered as non-toxic mineral particles widely used in the fields like cosmetics, food and drug. When the scale come to nanometer, TiO 2 nanoparticles (nano-TiO 2 ) exhibits multiple specific characteristics coupled with unknown risks on health. The purpose of this study was to systematically research the influence of nano-TiO 2 on erythrocyte. The results indicated that the erythrocytes treated with nano-TiO 2 underwent abnormal sedimentation, hemagglutination and dose dependent hemolysis, totally differing from those treated with micro-TiO 2 . The ghost cells were firstly investigated by using ultra-thin cell section in the case under nano-TiO 2 . The mechanism of such adverse effects is (1) the attachment around erythrocyte change the surface native properties and ultimately lead to hemoagglutination; (2) the content leak to the outside of erythrocyte through the breakage induced by both the nano-TiO 2 trans-membrane and the oxidative stress under nano-TiO 2 . Our findings imply that nano-TiO 2 may have potential toxicity to human being health.

Photochemical properties of the ionic liquid (RTIL) 1-butyl-3-methylimidazoliumhexafluorophosphate [bmim][PF6] and its binary mixed solutions with organic solvent(DMF and MeCN) were investigated by laser photolysis at an excitation wavelength of 355nm, using anthraquinone (AQ) as a probe molecule. It was indicated that the triplet excitedstate of AQ (3AQ*) can abstract hydrogen from [bmim][PF6]. Moreover, along with thechange of the ratio of RTIL and organic solvent, the reaction rate constant changes regularly.Critical points were observed at volume fraction VRTIL = 0.2 for RTIL/MeCN and VRTIL =0.05 for RTIL/DMF. For both systems, before the critical point, the rate constant increasesrapidly with increasing VRTIL, however, it decreases obviously with VRTIL after the criticalpoint. We conclude that the concentration dependence is dominant at lower VRTIL, while theviscosity and phase transformation are dominant at higher VRTIL for the effect of ionic liquidon the decay of rate constant.

Radiation-induced degradation of Congo Red (an azo dye) in aqueous solution was studied both with steady-state radiolysis and time-resolve techniques of pulse radiolysis and laser flash photolysis. Decomposition and mineralization of Congo Red by gamma-rays was investigated with the changes of absorption spectra, degradation efficiency, TOC removal and pH changes of the solutions in different irradiation systems. The main radiolytic products resulting from steady-state radiolysis of Congo Red were examined by HPLC and LC-MS. Complete degradation of Congo Red was observed at different absorbed doses under diverse irradiation condition. The TOC removal of the solutions saturated with O2 or N2O reached 76% and 86% at the absorbed dose of 11.9 kGy, respectively. Pulse radiolysis and laser flash photolysis experiments were carried out to study the reaction of Congo Red with e(aq)- and ()OH. The reaction rate constants were determined.

Polyethyleneimine nanogels (named as M-PEIs) with different sizes were prepared by photo-Fenton reaction in aqueous solution from which samples of 38, 75, 87, 121, 132 and 167nm were selected for in vitro transfection. The homogeneous structure and the same component made it possible to study the size effect of M-PEIs nanogels on gene transfection efficiency when loading the same quantity of plasmid DNA (pLEGFP-C1) into A549, Bel7402, BGC-823 and Hela cells. M-PEIs and its DNA complexes were characterized by photo correlation spectroscopy and atomic force microscopy. The protein expression was observed by flow cytometry and fluorescence microscopy. All of the DNA complexes had no obvious cytotoxicity and the surface charges were positive charged at the optimum weight ratio. Therefore, the expressed protein was affected by the size of M-PEIs when the same quantity of DNA was used to transfect cells. In addition, the samples of 75 and 87nm yielded the highest transfection efficiency about 30% in all of the four cell lines which were also cell line independent.

α-Chymotrypsin (CT) as model enzyme was conjugated onto the novel carboxyl-functionalized superparamagnetic nanogels, prepared via facile photochemical in situ polymerization, by using 1-ethyl-3-(3-dimethylaminepropyl) carbodiimide (EDC) as coupling reagent. The obtained magnetic immobilized enzyme was characterized by use of photo correlation spectroscopy (PCS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) measurement, thermogravimetric (TG) analysis and vibrating sample magnetometer (VSM) measurement. PCS result showed that the immobilized enzyme was 68 nm in diameter while the magnetic nanogels with carboxyl groups were only 38 nm; enzyme immobilization led to pronounced change in size. Superparamagnetic properties were retained for Fe 3 O 4 after enzyme immobilization while slightly reducing its value of saturation magnetization. Immobilization and surface coating did not induce phase change of Fe 3 O 4 by XRD analysis. The binding capacity was 30 mg enzyme/g and 37.5 mg enzyme/g nanogel determined by TG analysis and BCA protein assay, respectively. Specific activity of the immobilized CT was calculated to be 0.77 U/(mg min), 82.7% as that of the free form.

Oxidative damage to protein has been implicated in a number of diseases. Much interest has been focused on preventing oxidative damage to protein. Here we showed that hydroxycinnamic acid derivatives (HCA) were able to inhibit the cross-linking of protein induced by riboflavin-mediated photooxidation. HCA were also found to strongly protect lysozyme from gamma rays irradiation. The antioxidative properties of HCA were further studied by laser flash photolysis. Mechanism of antioxidant activities of HCA on lysozyme oxidation was discussed. HCA were found to protect protein against oxidation by scavenging oxidizing species and repairing the damaged protein.

In a study of the mechanism of UV-induced cationic polymerization of divinylether-onium salt systems, UV laser photolysis was performed. The transient absorption of cationic species was recorded in the range of 330–420 nm at room temperature. The decay rate constant of cationic species was found to be 0.1 μs −1 .

Direct EPR evidence of the photo-generation of superoxide radicals (O(2) (-.)) was obtained by using a novel spin trapping probe in spinach Photosystem II (PS II) membrane fragments. The production of O(2) (-.) was detected by following the formation of 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) superoxide adducts (DEPMPO-OOH). The inhibition of O(2) (-.) formation by 3-(3,4-dichlorophenyl) -1,1-dimethylurea (DCMU) and the 77 K fluorescence spectrum indicated that O(2) (-.) were generated from PS II, not from PS I. The inhibition of O(2) (-.) formation by DCMU also suggested that O(2) (-.) were generated from the Q(B)binding site, not at a site prior to DCMU blockage. The extrinsic proteins and Mn are very important to eliminate O(2) (-.), showing that the oxygen-evolving system is involved in O(2) (-.) removal rather than production.

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.

To show the effects of growth inhibitory factor (Cu4Zn3MT-III) involved in the scavenging of reactive oxygen species (ROS), a pulse radiolytic study was employed using N2O-saturated Cu4Zn3MT-III aqueous solutions. It was demonstrated that the oxidizing OH* radical efficiently reacted with Cu4Zn3MT-III by forming a thiyl radical RS* with a second-order constant of 1.46 x 10(11) mol l(-1) s(-1), which was determined by competition kinetics against KSCN. The thiyl radical RS* reacted rapidly and reversibly with a thiolate in Cu4Zn3MT-III to form radical anion RSSR*- with a constant of 1.65 x 10(9) mol lL(-1) s(-1) per thiolate, while the constant of the decay of this radical anion was 2.72 x 10(5) s(-1), and the equilibrium constant of the formation for RSSR*- was 6.08 x 10(3) mol(-1) l. These values were close to those of Cd5Zn2MT-II. The SOD activity of Cu4Zn3MT-III to quench O2(*-) was assayed by the riboflavine-methionine-nitrobluetetrazolium (NBT) method which catalyzed the dismutation of superoxide (O2(*-)) at pH 7.8 with an IC50 value of 1.50 x 10(-6) M for Cu4Zn3MT-III and 1.62 x 10(-6) M for Cd5Zn2MT-II. Additionally, the down-regulation of GIF may be a main factor in the decrease of the scavenging ability for the free OH* and O2(*-) radicals, which is possibly associated with the pathogenesis of neurodegenerative disease.

Riboflavin, suggested to be a radiosensitizer, was studied in murine thymocytes and human hepatoma L02 cell line in vitro with MTT method and fluorescence microscopy. When the murine thymocytes treated with 5-400 mumol/L riboflavin were irradiated by 5 Gy (60)Co gamma ionizing radiation, the low concentration groups, i.e. treated with 5-50 mumol/L riboflavin, showed a different surviving fractions-time relating correlation compared with the high concentration groups, i.e. treated with 100-400 mumol/L riboflavin. The former had a high survival level at the end of irradiation, but which, after 4-h incubation, decreased rapidly to a low level. On the contrary, the high concentration groups showed a low survival level at the end of irradiation, and a poor correlation was found between the surviving fraction and the incubation time, after 4 h a little difference was observed. The results of fluorescence microscopy indicated that under low concentration conditions, the riboflavin localized mainly in nucleus (both perinuclear area and inside of nuclear membrane), while under high concentration conditions, intensive riboflavin also localized around cytoplasmic membranes. Thus we can conclude: the riboflavin had radiosensitivity effect on DNA under low concentration conditions, and enhanced the damage to cytoplasmic membrane under high concentration conditions. Also the most effective concentration of riboflavin can be evaluated to be approximate 100 mumol/L.

Repair effects of rutin and quercetin on purine deoxynucleotide radical cations were studied using pulse radiolysis technique. On electron pulse irradiation of N(2) saturated deoxynucleotide aqueous solution containing 20 mmol/L K(2)S(2)O(8), 200 mmol/L t-BuOH and rutin or quercetin, the transient absorption spectra of the deoxynucleotide radical cations decayed quickly. At the same time, the spectra of flavonoid phenoxyl radicals formed within several dozen microseconds. The results indicated that deoxynucleotide radical cations can be repaired by flavonoids. The rate constants of the repair reactions were 3.8 x10(8)-4.4 x10(8) mol(-1) * L * s(-1) and 1.3x10(8)-1.8x10(8) mol(-1) * L * s(-1) for dAMP and dGMP radical cations, respectively.

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 mucleotides 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 tripler 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. (C) 2000 Elsevier Science S.A. All rights reserved.

Repair effect on 2'-deoxyadenosine-5'-monophosphate (dAMP) radical anions by phenylpropanoid glycosides (PPGs) and their analogs, isolated from Chinese folk medicinal herb, was studied using pulse radiolysis technique. The radical anion of dAMP was formed by the reaction of hydrated electron with dAMP. On pulse irradiation of nitrogen-saturated dAMP aqueous solution containing 0.2 M t-BuOH and one of PPGs or their analogs, the transient absorption spectrum of the radical anion of dAMP decayed with the formation of that of the radical anion of PPGs or their analogs within several decades of microseconds after electron pulse irradiation. The results indicated that dAMP radical anions can be repaired by PPGs or their analogs. The rate constants of the repair reactions were deduced to be 1.6-4.5 x 10(8) M(-1) s(-1).

The repair effects on deoxynucleotide radical cations of phenylpropanoid glycosides (PPGs) and their analogs, isolated from a Chinese folk medicinal herb, were studied using the pulse radiolysis technique. The radical cations of deoxynucleotides were formed by the reaction of SO4*- with deoxynucleotides. On pulse irradiation of a nitrogen saturated deoxynucleotide aqueous solution containing 20 mM K2S2O8, 200 mM t-BuOH and one of the PPGs or their analogs, the transient absorption spectra of the radical cations of nucleotide decayed with the formation of those of the radical cation of PPGs or their analogs within several tens of microseconds after electron pulse irradiation. The result indicates that deoxynucleotide radical cations can be repaired by PPGs or their analogs. The rate constants of the repair reactions were determined to be 0.48-1.1 x 10(9), 0.64-1.80 x 10(9) and 2.12-4.4 x 10(9) M(-1) s(-1) for dAMP, dGMP and dCMP radical cations respectively. It is obvious that the rate constants of the repair reaction depend on the number of phenolic hydroxyl groups contained in the PPGs and their analogs. A deeper understanding of this new repair mechanism will undoubtedly help researchers design strategies to prevent and/or intervene more effective in free radical related diseases.

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 important 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 from Pedicularis 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 x 10(8) dm(3) * mol(-1) * s(-1). A deeper understanding of this new repair mechanism will undoubtedly help researchers explore new prevent and/or intervening medicine.

2,4,4'-Tribromodiphenyl ether (BDE-28) was selected as a typical congener of polybrominated diphenyl ethers (PBDEs) to examine its fate both in the atmosphere and in water solution. All the calculations were obtained at the ground state. The mechanism result shows that the oxidations between BDE-28 and OH radicals are highly feasible especially at the less-brominated phenyl ring. Hydroxylated dibrominated diphenyl ethers (OH-PBDEs) are formed through direct bromine-substitution reactions (P1 similar to P3) or secondary reactions of OH-adducts (P4 similar to P8). Polybrominated dibenzo-p-dioxins (PBDDs) resulting from o-OH-PBDEs are favored products compared with polybrominated dibenzofurans (PBDFs) generated by bromophenols and their radicals. The complete degradation of OH adducts in the presence of O-2/NO, which generates unsaturated ketones and aldehydes, is less feasible compared with the H-abstraction pathways by O. Aqueous solution reduces the feasibility between BDE-28 and the OH radical. The rate constant of BDE-28 and the OH radical is determined to be 1.79 X 10(-12) cm(3) molecule(-1) s(-1) with an atmospheric lifetime of 6.7 days.

The reaction of OH radicals with baicalin was studied by pulse and gamma radiolysis in N2O-saturated aqueous solutions. The addition of an OH radical to baicalin produced an intermediate species that shows a maximum UV absorbance band at 420 nm and decays with a unimolecular rate constant of 1.25 x 10(4) s-1 and a bimolecular rate constant of 6.1 x 10(8) mol-1 dm3 s-1. Four major final products were obtained by gamma irradiation, and their structures were identified. Two of them (P1 and P2) are suggested to originate from the unimolecular reaction and the other two (P3 and P4) from the bimolecular reaction of the radicals.

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 reaction 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.

The electron transfer reaction of triplet menadione (3MQ*) with polyguanylic acid (polyG) in CH3CN rich (97%) solution was investigated by 248 nm(KrF) laser flash photolysis. The transient absorption spectra and kinetics obtained from the interaction of 3MQ* with polyG demonstrated that the primary radical ion pair, radical cation of polyG and radical anion of menadione can be detected simultaneously. The results demonstrated that the reaction rate constant of 3MQ* with polyG is almost equal to that of 3MQ* with dGMP.

Time-resolved laser flash photolysis and pulse radiolysis have been used to study the chemical activity of podophyllotoxin(PPT) and etoposide(VP-16). The mechanism of photoionization of etoposide and podophyllotoxin has been confirmed and illustrated. It is demonstrated that VP-16 and PPT in aqueous solution can be photoionized at 248 nm to give hydrated electron and neutral radical resulting from rapid deprotonation of radical cation of VP-16 and PPT. The quantum yield for the photoionization of VP-16 and PPT with single-photo is 0.21 and 0.61, respectively. In addition, they can react with hydrated electron, hydrogen radical and hydroxyl radical. This will give chemists some advice on synthesizing new derivatives of podophyllotoxin in cancer treatment.

The electron transfer reaction between triplet anthraquinone-2-sulfonate and polyguanylic acid (5′) in CH3CN-H2O (97?3) has been investigated by 248 nm (KrF) laser flash photolysis. The transient absorption spectra and kinetics obtained from the interaction of triplet anthraquinone-2-sulfonate and poly[G] demonstrate that the primary ionic radical pair, radical ation of poly[G] and radical anion of anthraquinone-2-sulfonate have been detected simultaneously. The free energy changes in the process of the electron transfer were also calculated.

The antitumor mechanism of etoposide (VP-16) is investigated using pulse radiolysis technology. The oxidizing mechanism of VP-16 is studied by sodium persulfate, and the reaction rate constant is 4.04×109 L·mol−1·s −1. The electron-transfer between VP-16 and tyrosine is observed and the reaction rate constant is 1.1×108 L·mol −1·s −1.

By using time-resolved kinetic spectrophotometry and pulse radiolysis technique, the oxidation of Phe by SO4 - radical has been investigated both in aqueous and water/acetonitrile mixed solutions. The results reveal that attack of the oxidizing SO4 - radical on Phe leads directly to the formation of Phe cation radical 3 with a strong absorption peak at 310 nm, then it proceeds in three competitive reactions via either hydroxylation, deprotonation or decarboxylation, which were found to be strongly dependent upon the ionization state of the substitutes —COOH and —NH2 and the nature of the solvents. Decarboxylation takes place only when the carboxyl group is deprotonated. At high pH deprotonation of Phe cation radical 3 is much easier to occur than that in neutral or acid solutions. Moreover, with addition of acetonitrile, deprotonation is more predominant than hydroxylation, whereas in aqueous solutions hydroxylation is much easier to occur.

Actinomycin D (AMD) is an anticancer antibiotic that can bind selectively to both double-stranded and single-stranded DNA, and this binding greatly enhances DNA photosensitization. Using electron paramagnetic resonance (EPR) in combination with spin trapping techniques, a systematic study was carried out on the reactive oxygen species generated in the photosensitization process of AMD. It was found that 1O2 and $$O_2^{ - \cdot } $$ are important reactive intermediates either in solution or in DNA complexes, and the generation of these species is in competition. This finding suggests that the photodynamic action of AMD proceeds via two pathways: energy transfer (type I mechanism) and electron transfer (type II mechanism). 1O2 is the main product formed via energy transfer reaction in solution while electron transfer between the excited states of AMD and DNA becomes the predominant pathway in DNA complexes.