Time-resolved laser flash photolysis study on transient reaction between excited triplet state of anthraquinone derivatives (AQS) and 2-deoxythymidine

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The transient absorption spectra and kinetics of excited triplet state of anthraquinone derivatives 2-anthraquinonesulfonatesodium (AQS) and 2-deoxythymidine (dT) have been investigated in CH3CN-H2O (97:3) using the time-resolved laser flash
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  Vol.6, No.1, 1-4 (2014)   Natural Science http://dx.doi.org/10.4236/ns.2014.61001  Time-resolved laser flash photolysis study on transient reaction between excited triplet state of anthraquinone derivatives (AQS) and 2-deoxythymidine Jianhua Ma Department of Materials Science and Engineering, Xiamen Institute of Technology, Huaqiao University, Xiamen, China;  jianhuam1957@126.com Received 27 April 2013; revised 27 May 2013; accepted 4 June 2013 Copyright © 2014 Jianhua Ma. This is an open access article distributed under the Creative Commons Attribution License, which  permits unrestricted use, distribution, and reproduction in any medium, provided the srcinal work is properly cited. In accordance of the Creative Commons Attribution License all Copyrights © 2014 are reserved for SCIRP and the owner of the intellectual property Jianhua Ma. All Copyright © 2014 are guarded by law and by SCIRP as a guardian.  ABSTRACT   The transient absorption spectra and kinetics of excited triplet state of anthraquinone derivatives 2-anthraquinonesulfonatesodium (AQS) and 2- deoxythymidine (dT) have been investigated in CH 3 CN-H 2 O (97:3) using the time-resolved laser flash photolysis technique (KrF, 248 nm). The absorption spectra of dT radical cation and the radical anion of AQS have been observed. From dynamic and thermodyrnamic analysis, the me- chanism of this transient reaction has been in-itially analysed. KEYWORDS 2-Anthraquinonesulfonatesodium (AQS); 2-Deoxythymidine; Transient Reaction; Laser Flash Photolysis 1. INTRODUCTION Quinones play central roles in aerobic respiration and energy-yielding photosynthesis [1]. The “strong sensitiz-er” 2-anthraquinonesulfonatesodium (AQS), has received much attention because of its relevance to some impor-tant photosensitizing effects induced by anthraquinones,  phototendering of cellulosic materials. Recently, interest in photobiology area has been heightened by suggestions for utilizing anthraquinones as photonuclease [2]. AQS is a strong sensitizer and for numerous investigations con-cerning on it [3-5], only a few studies have been per-formed on the reaction of AQS with biological sub-stances [5]. Here we report that time-resolved spectros- copic and kinetic evidences for the interaction of AQS with dT in CH 3 CN-H 2 O solvent mixture were investi-gated using KrF laser flash photolysis. The transient ab-sorption spectra and kinetics obtained from electron transfer oxidation of dT by triplet AQS indicated that the  produced radical ion pairs, radical cations of dT and rad-ical anion of AQS, were identified simultaneously. 2. EXPERIMENTAL 2-Anthraquinonesulfonatesodium (AQS) (Fluka, >98%) was recrystallized twice from triply distilled water before use. 2-Deoxythymidine (dT) was purchased from sigma. All the samples were prepared in triply distiled water and deoxygenated by bubbling with high purity nitrogen (99.99%). All experiments were carried at room tem-  perature. Laser flash photolysis experimental methods and the specifications of equipment (KrF excimer laser: 248 nm; pulse wide: 20 ns, 50 mJ) has been described  previously [6]. 3. RESULTS AND DISCUSSION 3.1. The Characteristic Transient Absorption Spectra of the H-Abstraction Radicals of Deoxyribonucledeotide Bases Figure 1  shows the transient absorption spectra at 1 μs after laser photolysis of N 2  saturate CH 3 CN-H 2 O (97:3) solution containing 1 × 10 − 4  mol·dm − 3  deoxyribonuc- ledeotide bases (TMP, dCMP, dGMP, dAMP) and 2 × 10 2  mol·dm − 3  K  2 S 2 O 8  and 2 × 10 − 2  mol·dm − 3  t-BuOH, respectively. These characterized transient absorption  peaks are very similarity that reported previously [5-7], Copyright © 2014 SciRes. OPEN ACCESS  J. H. Ma / Natural Science 6 (2014) 1-4   2 300 350 400 450 500 550 600-0.050.000.050.100.150.200.250.30        A       b     s     o     r       b     a     n     c     e Wavelength[nm]   Figure 1.   N 2  saturate CH 3 CN-H 2 O (97:3) solution containing 1 × 10 − 4  mol·dm − 3  deoxyribonucledeotide bases (TMP, dCMP, dGMP, dAMP) and 2 × 10 2  mol·dm − 3  K  2 S 2 O 8  and 2 × 10 − 2  mol·dm − 3  t-BuOH. ( ◇ ) TMP, ( ▼ ) dCMP, ( △ ) dAMP, (○) dGMP, respectively. Recorded at 40 μs after laser excitetiam.   should be reasonably ascribed to the radical cation of H- abstraction radicals of deoxyribonucledeotide bases. It is clear that the same radical cation species were produced in different experiments. For example, the one of genera-tion of dT cation radical can be illustrated as below: t-BuOH + ·OH →  CH 2 C(CH 3 ) 2 OH + H 2 O (1) e -aq   + 22 8 S O  −   → 4 SO −   + 24 SO  −  (2) dT + 4 SO −   → dT +  + 24 SO  −  + H +  (3) 3.2. The Transient Absorption Spectra of the Interaction of AQS with dT In our present paper, the characteristic transient ab-sorption spectra of radical anion of AQS (AQS − ) and triplet AQS ( 3 AQS * ) are from laser photolysis in deae-rated CH 3 CN-H 2 O (97:3) solution have been repored, and the spectrum characterized at 510 nm and 380 nm, 470 nm, 580 nm have assigned to radical anion of AQS (AQS − ) and triplet AQS ( 3 AQS * ), respectively [8]. Figure 2  shows transient absorption spectra from laser  photolysis of 0.028AQS mmol·dm − 3  and 0.05 mmol·dm − 3  dT in CH 3 CN-H 2 O (97:3) solution, saturated with N 2 O. After the pulse , an absorption band characterized at ~510 nm and decays by second order kinetics, which is similar to that of the radical anion of AQS reported previously [8], and should be assigned to AQS − . The late transient absorption characterized rang 350 nm - 450 nm , should  be reasonably ascribed to the radical cation of dT-H due to its similarity to that the radical cation of dT in  Figure 1  and photoinization of deoxyribonucleotide [8,9]. The growth trace of transient species at 510 nm was occurred exactly in the same time interval as did the AQS triplet decay at 580 nm ( Figure 3 ), which decayed following first-order kinetics, and it is the net contribution of triplet AQS ( 3 AQS * ), as shown  Figure 4 . So we implying that the AQS triplet state is the pre-cursor of the radical anion and transient species at 350 nm - 450 nm, revealing the feature of dT +  characterized. It is evident that 3 AQS *  was quenched by dT via electron transfer producing long lived dT +  species. 3.3. The kinetic Parameters of Transient Species and Free Energy Change (ΔG)  of Electron Transfer between AQS and dT In the reaction of electron transfer between AQS and dT, the formation trace of dT +  at 360 nm can be obtained  by subtracting the absorbance at 580 nm multiplied by A 360 /A 580  from that at 360 nm. At mean time, the forma-tion trace of AQS −  at 510 nm can be obtained by sub-tracting the absorbance at 580 nm multiplied by A 510 / A 580  from that at 510 nm too. The corresponding kinetic  parameters of transient species growth at 360 nm, 510 nm and triplet AQS decay at 580 nm are 1.2 × 10 9  dm 3 ·mol − 1 ·s − 1 , 1.6 × 10 9  dm 3 ·mol − 1 ·s − 1  and 1.5 × 10 9  dm 3 ·mol − 1 ·s − 1 , respectively. Obviously, the formation rate constants of radical cations of dT and radical anion of AQS are nearly equal to that of decay of triplet AQS respectively. On the other hand, The Δ G (free energy changes) for the electron transfer of between triplet AQS and dT can be calculated according to the Rehm-Weller equation and the E ox  values of dT was calculated via an Copyright © 2014 SciRes. OPEN ACCESS    J. H. Ma / Natural Science 6 (2014) 1-4   3   Figure 2.  Transient absorption spectra from laser photolysis of 0.028 mmol·dm − 3  AQS and 0.05 mmol·dm − 3  dT in CH 3 CN- H 2 O (97:3) solution, saturated with N 2 O. (□) 1   μs, (■) 25 μs.   Figure 3. Decay and growth curves of mixed solution of 0.028 mmol·dm − 3  AQS and 0.05 mmol·dm − 3  dT at 580 nm, 510 nm and 360 nm. 0.020.040.060.080.1002468    k   o   b  s   x   1   0    4    /   [   M   L   ] [AQS] (mM)   Figure 4.  Plot of the apparent decay rate constant of 3 AQS * . empirical equation E ox  = 0.89IP - 6.04 [10], and the E red   (AQS, vs. SCE), Δ E 0,0 , Δ G (energy of 3 AQS * ), e 2 / ε d and the coulombic term are published results [11-14], respec-tively. From these, free energy change ( Δ G) value (KJ/ mol) was calculated as dT—68.3 KJ/mol. It means that the electron transfer oxidation reactions between triplet AQS and dT is exothermic. From the above results, these experimental findings  provide reliable evidence for the electron transfer oxida-tion reactions between triplet AQS and dT. The predo-minant initial species from electron transfer oxidation of dT is dT radical cation. The proposed reaction mechan-ism of generation of the dT radical cation and the radical anion of AQS can be presented as follows: hv ISC AQS → AQS *   → 3 AQS *   3 AQS *   + dT → AQS −  + dT + 4. CONCLUSION The transient absorption spectra of interaction of trip-let AQS with dT were observed and the rate constants for formation of radical cation of dT and those of radical anion of AQS and the decay of triplet AQS were also determined. The time resolved evidence of dynamic and thermo-dynamic of laser spectra and kinetics of radical ion pairs from electron transfer oxidation of dT by triplet AQS were provided.    ACKNOWLEDGEMENTS This project was supported by the Education Committee of Fujian Province, China (JA13593S). REFERENCES [1]   Zhang, S.M., Han, S.T. and Liu, Y.H. (2004) Progress of study on photonuclease-anthraquinone derivatives.  Jour-nal Hebei Normal University , 3 , 27-30. [2]   David, T., Breslin, D.T., Coury, J.R., et al . (1997) Anthr-quinone photonuclease structure determines its mode of  binding to DNA and the cleavage chemistry observed.  Journal of America Chemistry Society , 119 , 5043-5045. http://dx.doi.org/10.1021/ja963607h [3]   Ma, J.H., Lin, W.Z., Wang, W.F., Han, Z.H., Yao, S.D. and Lin, N.Y. (1999) Characterization of reactive inter-mediates in laser photolysis of nucleoside using sodium salt of 9,10-anthrax-quinone-2-sulfonate as photosensi-tizer.  Radiation Physics and Chemistry , 54 , 337-340. http://dx.doi.org/10.1016/S0969-806X(98)00300-4 [4]   Loeff, A., Treinin, H. and Linsckitz H. (1983) Photoche-mistry of 9,10-anthraquinone-2-sulfonate in solution. 1. Intermediates and mechanism.  Journal of Physics and Chemistry , 87 , 2536-2540. http://dx.doi.org/10.1021/j100237a017 [5]   Loeff, J., Rabani, A., Treinin, H. and Linschitz H. (1993) Charge transfer and reactivity of n π * and ππ * organic Copyright © 2014 SciRes. OPEN ACCESS    J. H. Ma / Natural Science 6 (2014) 1-4   4 triplets, including anthraquinonesulfonates, in interac-tions with inorganic anion: A comparative study based on classical Marcus theory.  Journal of America Chemistry Society , 115 , 8933-8937. http://dx.doi.org/10.1021/ja00073a007 [6]   Ma, J.H., Lin, W.Z., Wang, W.F., Han, Z.H., Yao, S.D. and Lin, N.Y. (2002) Laser photolysis of interaction of  poly-guanylic acid (5’) with anthraquinone-2-sulfonate. Science in China , 45 , 384-387. [7]   Candeias, L.P. and Steenken, S. (1993) Electron transfer in di(deoxy)nucleoside phosphates in aqueous solution: Rapid migration of oxidation damage (via adenine) to guanine.  Journal of America Chemistry Society , 115 , 2437- 2441. http://dx.doi.org/10.1021/ja00059a044  [8]   Ma, J.H., Lin, W.Z., Han, Z.H., Yao, S.D. and Lin, N.Y. (2006) Electron transfer reaction between desoxyadeno-sine and triplet 2-methyl-1,4-naphthaquinone: A laser  photolysis study. 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