Laser Flash Photolysis Mechanism of Anthraquinone-2-Sodium Sulfonate in Pyridine Ionic Liquid/Water Mixed System

The photochemical reaction process of anthraquinone-2-sodium sulfonate （AQS） in the mixture of water （H2O） and N-butylpyridinium tetrafluoroborate （[BPy] [BF4]） was studied using the laser flash photolysis technique. Experimental results show that the excited triplet of AQS （3AQS＊） could react rapidly with H2O and the transient absorption spectra greatly changed by increasing the volume fraction of the ionic liquid （VIL） in [BPy][BF4]/H2O mixtures. The absorbance at 510 nm increased gradually with increasing VIL when 0〈VIL〈0.1. By contrast, the absorbance decreased gradually when VIL〉0.1. Otherwise, the absorbance of the band near 380 nm steadily increased. The apparent kinetic parameters of transient species B and ^3AQS＊ are obtained approximately. 3AQS＊ abstracting hydrogen from [BPy]＋ was also explored. It was deduced that the 350-420 nm band was the superposition of the peaks of 3AQS＊ and AQSH＇. The two reactions of 3AQS＊ with [BPy][BF4] and H2O are a pair of competitive reactions. We also concluded that the entire reaction processes slow down in the case of high [BPy] [BF4] concentrations.

TIME-RESOLVED IR STUDIES OF UV LASER FLASH PHOTOLYSIS OF W(CO)_6 IN C_6H_(12)-CCl_4 AND CCl_4 SOLUTION

Time-resolved IR absorption spectroscopy has been used to atudy the photochemistry of W(CO)_6 in cyclohexane, carbon tetrachloride, and the mixture of carbon tetrachloride and cyelohexane. The reastion of photolytically generated W(CO)_5. C_6H_(12) with CCl_4 was investigated. An intermediate with a lifetime of about 0.5ms, presumably attributed as W(GO)_5.CCl_4, was first observed.

Photophysical Properties and Photoinduced Electron Transfer between [60] Fullerene-Containing Cyclic Sulphoxide [C_(60)-C_6H_8SO] and Tetrathiafulvalene (TTF) by Laser Flash Photolysis

Photoinduced electron transfer (PET) processes between C 60-C 6H 8SO and Tetrathiafulvalene (TTF) have been studied by nanosecond laser photolysis. Quantum yields (Φ et) and rate constants of electron transfer (k et) from TTF to excited triplet state of fullerene-containing cyclic sulphoxide in benzonitrile (BN) have been evaluated by observing the transient absorption bands in the NIR region. With the decay of excited triplet state of fullerene-containing cyclic sulphoxide, the rise of radical anion of fullerene-containing cyclic sulphoxide is observed.

Determination of Astaxanthin and Canthaxanthin Triplet Properties in Different Polarities of the Solvent by Laser Flash Photolysis

Triplet-triplet extinction coefficients for astaxanthin （I） and canthaxanthin （II） in different deaerated polarity solutions of MeCN and benzene were evaluated by laser flash photolysis at 298 K in the spectral region from 350 to 650 nm by energy transfer method, employing 2-acetonaphthone as sensitizer. The triplet-triplet extinction coeffi- cients in MeCN and benzene were different in terms of the carotenoid present. The maximum triplet-triplet extinc- tion coefficient was 0.1-1.7 ×10^5 L·mol^-1·cm^-1 in different solvents. The rate constants of triplet decay were I： 1.25×10^10 L·mol^-1·s^-1, II： 1.12×10^10 L·mol^-1·s^-1 in MeCN; and I： 1.75×10^10 L·mol^-1, II： 3.27×10^10 L·mol^-1·s^-1 in benzene. The bimolecular rate constants of energy transfer from triplet excited 2-acetonaphthone to carotenoids were determined from the linear regression of the decay rate constant of 2-acetonaphthone triplet at varying carotenoid concentrations. The triplet lifetimes of ^3AST^＊ and 3CAN^＊ in different solvents were also determined. The results indicated that triplet energy transfer was nearly diffusion-controlled.

Photosensitized oxidation of tryptophan and tyrosine by aromatic ketones:A laser flash photolysis study

Photochemical processes of benzophenone （BP） and xanthone （XT） with tryptophan （TrpH） and tyrosine （TyrOH） were stud- ied using the laser flash photolysis technique. It has been observed that the triplet state of BP and XT reacted with TrpH and TyrOH by hydrogen transfer with the formation of BP and XT ketyl radicals and oxidized radicals of Trp＂ and TyrO＇. The re- lated rate constants of these reactions were determined in this paper. The free energy changes （AG） of these reactions suggested that the proposed hydrogen transfer mechanism was thermodynamically feasible. These results provide theoretical foundation for further studying structural effects on the photochemical behaviors of proteins with triplet state BP and XT.

Triplet excitation dynamics of β-carotene studied in three solvents by ns flash photolysis spectroscopy

Upon anthracene-sensitizing, triplet excitation dynamics of β-carotene（β-Car） were studied in nhexane, in methanol, and in acetonitrile, respectively, by ns flash photolysis spectroscopy. In n-hexane,only the bleaching of the ground state absorption（GSB） and the excitation triplet（^3Car＊） absorption were observed, and there were no cationic species detected. In both methanol and acetonitrile, similar excitation dynamics were observed, i.e.,^3Car＊ having a similar lifetime to that in n-hexane, and the immediate generation of the cation dehydrodimer（^#[Car]2^＋） upon excitation following transformation into the radical cation Car＊^＋, since Car＊^＋ has much longer lifetime in acetonitrile than in methanol. The results prove that both solvent and carotenoid structure determine the triplet excitation mechanism.

Photochemical Hydrogen Abstraction and Electron Transfer Reactions of Tetrachlorobenzoquinone with Pyrimidine Nucleobases

Pentachlorophenol, a widespread environmental pollutant that is possibly carcinogenic to humans, is metabolically oxidized to tetrachloroquinone （TCBQ） which can result in DNA damage. We have investigated the photochemical reaction dynamics of TCBQ with two pyrimidine type nucleobases （thymine and uracil） upon UVA （355 ran） excitation using the technique of nanosecond time-resolved laser flash photolysis. It has been found that 355 nm excitation populates TCBQ molecules to their triplet state 3TCBQ＊, which are highly reactive towards thymine or uracil and undergo two parallel reactions, the hydrogen abstraction and electron transfer, leading to the observed photoproducts of TCBQH. and TCBQ.- in transient absorption spectra. The concomitantly produced nucleobase radicals and radical cations are expected to induce a series of oxidative or strand cleavage damage to DNA afterwards. By characterizing the photochemical hydrogen abstraction and electron transfer reactions, our results provide potentially important molecular reaction mechanisms for understanding the carcinogenic effects of pentachlorophenol and its metabolites TCBQ.

Degradation characteristic of 4-bromdiphenyl ether in mixed solutions by electron beam irradiation

The degradation characteristic of 4-bromdiphenyl ether （BDE-4） was investigated in different solutions.The study indicates that the process of direct degradation of this compound is dependent upon the bromine and the ether bond connected to diphenyl by electron beam.laser flash photolysis was employed to determine the degradation of each species （cationic,neutral,and anionic）.From these data,intermediate products of BDE-4 degradation were shown for direct irradiationdegradation.The neutral radical was formed during the photolysis of these compounds.For all the compounds,diphenyl ether and hydroxybiphenyl were observed as common products.Reaction of the BDE-4 under electron beam was debromide.The debromide rate of BDE-4 at pH=5.5 is somewhat lower than that of BDE-4 at pH=10.0.The decomposition rate for BDE-4 is 99.8% at pH=10.0 on the dose of 14 kGy.BDE-4 from its radical could provide bromine ion into water and the cation radical of BDE-4 formed quickly recombine with hydrogen radical and formed phenyl ether.

Comparison of ligand migration and binding in heme proteins of the globin family

The binding of small diatomic ligands such as carbon monoxide or dioxygen to heme proteins is among the simplest biological processes known. Still, it has taken many decades to understand the mechanistic aspects of this process in full detail. Here, we compare ligand binding in three heme proteins of the globin family, myoglobin, a dimeric hemoglobin, and neuroglobin. The combination of structural, spectroscopic, and kinetic experiments over many years by many laboratories has revealed common properties of globins and a clear mechanistic picture of ligand binding at the molecular level. In addition to the ligand binding site at the heme iron, a primary ligand docking site exists that ensures efficient ligand binding to and release from the heme iron. Additional, secondary docking sites can greatly facilitate ligand escape after its dissociation from the heme. Although there is only indirect evidence at present, a preformed histidine gate appears to exist that allows ligand entry to and exit from the active site. The importance of these features can be assessed by studies involving modified proteins（via site-directed mutagenesis） and comparison with heme proteins not belonging to the globin family.

H-Atom Transfer Reaction of Photoinduced Excited Triplet Duroquinone with Tryptophan and Tyrosine in Acetonitrile-Water and Ethylene Glycol-Water Homogeneous Solutions

Laser flash photolysis was used to investigate the photoinduced reactions of excited triplet bioquinone molecule duroquinone(DQ)with tryptophan(Trp)and tyrosine(Tyr)in acetonitrile-water(Me CN-H_(2)O)and ethylene glycol-water(EG-H_(2)O)solutions.The reaction mechanisms were analyzed and the reaction rate constants were measured based on Stern-Volmer equation.The H-atom transfer reaction from Trp(Tyr)to ^(3)DQ^(*)is dominant after the formation of^(3)DQ^(*)during the laser photolysis.For DQ and Trp in MeCN-H_(2)O and EG-H_(2)O solutions,^(3)DQ^(*)captures H-atom from Trp to generate duroquinone neutral radical DQH^(·),carboncentered tryptophan neutral radical Trp^(·)/NH and nitrogen-centered tryptophan neutral radical Trp/N^(·).For DQ and Tyr in Me CN-H_(2)O and EG-H_(2)O solutions,^(3)DQ^(*)captures H-atom from Tyr to generate duroquinone neutral radical DQH^(·) and tyrosine neutral radical Tyr/O^(·).The H-atom transfer reaction rate constant of^(3)DQ^(*)with Trp(Tyr)is on the level of 109 L·mol^(-1)·s^(-1),nearly controlled by diffusion.The reaction rate constant of^(3)DQ^(*)with Trp(Tyr)in Me CN/H_(2)O solution is larger than that in EG/H2O solution,which agrees with Stokes-Einstein relationship qualitatively.

Photophysical and photochemical processes of riboflavin (vitamin B_2) by means of the transient absorption spectra in aqueous solution

Using time-resolved techniques of 337 and 248 nm laser flash photolysis, the photo physical and photochemical processes of riboflavin (RF, vitamin B2) were studied in detail in aqueous solution. The excited triplet state of riboflavin (3RF*) was produced with 337 nm laser, while under 248 nm irradiation, both3RF* and hydrated electron (eaq) formed from photoionization could be detected. Photobiological implications have been inferred on the basis of reactivity of3RF* including energy transfer, electron transfer and hydrogen abstraction. The RF·+ was generated by oxidation of SO4 ·-radical with the aim of confirming the results of photolysis.

Photosensitive damage of lysozyme caused by pazufloxacin and the protective effect of ferulic acid

Laser flash photolysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE) experiments were carried out to study the photosensitive damage induced by pazufloxacin(PAX) and the protection of lysozyme(Lyso) by ferulic acid(FCA), an active antioxidant. Transient absorption spectra revealed electron transfer from Lyso and FCA to 3PAX*, with respective bimolecular reaction rate constants of 6.3×107 and 1.4×1010 dm3/(mol s). A pulse radiolysis study was also performed to investigate the formation of Lyso radical cations. Results showed that FCA effectively inhibited the cross-linking of protein induced by fluoroquinolones. Finally, a mechanism of the protective effect of FCA on Lyso was proposed.

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.

Kinetics and mechanisms of reactions for hydrated electron with chlorinated benzenes in aqueous solution

The reactions between chlorinated benzenes （CBzs） and hydrated electron （eaq^-） were investigated by the electron beam （EB） and laser flash photolysis （LFP） experiments. Under the EB irradiation, the effects of irradiation dose, initial concentration and the number of Cl atoms on the removal efficiencies were further examined. At 10 kGy, the removal efficiencies of mono-CB, 1,3-diCB, 1,2-diCB and 1,4-diCB were 41.2%, 87.2%, 84.0%, and 84.1%, respectively. While irradiation dose was 50 kGy, the removal efficiencies increased to 47.4%, 95.8%, 95.0%, and 95.2%, respectively. Irradiation of CBzs solutions has shown that the higher the initial concentration, the lower the percentage of CBzs removal. In addition to this, the dechlorination efficiencies of 1,2-dichlorobenzene （1,2-diCB）, 1,3-dichlorobenzene （1,3-diCB） and 1,4-dichlorobenzene （1,4-diCB） were much higher than that of chlorobenzene （mono-CB）. The kinetics of the reactions was achieved with nanosecond LFP. The rate constants of second-order reaction between eaq^- with mono-CB, 1,2-diCB, 1,3-diCB and 1,4-diCB were （5.3±0.4） × 10^8, （4.76±0.1） × 10^9, （1.01±0.1） × 1010 and （3.29±0.2） × 10^9 L·mol^-1·s^-1, respectively. Density functional theory （DFT） calculations were performed to determine the optical properties of unstable CBzs anion radicals, and the main absorption peaks lied in the range of 300–550 nm. The primary reaction pathway of CBzs with eaq^- was gradual dechlorination, and the major products were Cl^- and benzene （CBzs（-Cl^-））. Furthermore, biphenyl （or chlorobiphenyl） was observed during the LFP, which was probably formed by recombination of benzene radicals.

Two-photon Dissociation Study of Carbon Disulfide in Acetonitrile at 266 nm

Using laser flash photolysis/transient absorption technique for the study of two photon photodissociation of carbon disulfide in acetonitrile solution at 266 nm, the transient UV-Vis absorption spectrum of Rydberg state CS2 （6sσg） within 240-370 nm and subsequent dissociation product CS （α^3П） with the maximum absorption at 260 nm were directly observed. The lifetime of CS （α^3П） in the nitrogen and oxygen saturated solution is also studied in our experiment.