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Roelofs, Theo A.,Lee, Choon-Hwan,Holzwarth, Alfred R. 부산대학교 유전공학연구소 1992 분자생물학 연구보 Vol.8 No.-
In this study, we have used the method of target analysis to analyze the ps fluorescence kinetics of pea chloroplasts with open (F_0) and closed (F_max) photosystem Ⅱ (PS Ⅱ) centers Extending the exciton/radical pair equilibrium model (Schatz G H H Brock, and A R Holzwarth 1988 Biophys J 54 397-405) to allow for PS Ⅱ heterogeneity, we show that two types of PS Ⅱ (labeled α and β) must be accounted for each pool being characterized by its own-set of molecular rate constants within the model. Simultaneous global target analysis of the data at F_0 and F_max results in a detailed description of the molecular kinetics and energetics of the primary processes in both types of PS Ⅱ units This characterization revealed 'that the PS Ⅱα pool accounts for twice as many Chl molecules as PS Ⅱβ, which suggests a PSⅡα/PSⅡβ reaction center stoichiometry of close to unity. By extrapolation it is shown that the primary charge separation in hypothetical "isolated β reaction centers is slower than in isolated α reaction centers in open centers bv a factor of 4 (1/k^int_1 = 11 vs 29 ps), in closed centers by a factor of 2 (1/k^int_1 = 34 vs 19 ps). Despite this slower charge separation process in PS Ⅱβ the quantum efficiency of the charge separation process is hardly affected a charge stabilization yield at F_1 (i e , P^+ IQ_A^-) of 86% (as compared to 90% in PS Ⅱα). Reduction of Q_A (closing PS Ⅱ) has distinctly different effects on the primary kinetics of PS Ⅱβ, as compared to PS Ⅱα. In PS Ⅱα the charge separation rate drops by a factor of 6, whereas the charge recombination process is hardly affected In PS Ⅱβ the charge separation is slowed down by a factor of 3, whereas the charge recombination rate increases by a factor of 5 in terms of charges in standard free energy the reduction to Q_A - lifts the free energy of the radical pair P-I-relative to the excited state (Chl_n/P)^* by 47 meV in PS Ⅱα and by 67 meV in PS Ⅱβ The concomitant increase in fluorescence quantum yield is the same for both types of PS Ⅱ These results snow that PS Ⅱα and PS Ⅱβ exhibit a different molecular functioning with respect lo the primary processes which might have its origin in a different molecular structure of the reaction centers and/or a different local environment of these centers Location in different parts of the thylakoid membrane might be involved We also applied different error analysis procedures to determine the error ranges of the values found for the molecular rate constants. It is shown that the commonly used standard error has very little meaning as it assumes independence of the fit parameters Instead an exhaustive search procedure accounting for all possible correlations between the fit parameters gives a more realistic view on the accuracy of the fit parameters.
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Marian, Christel M.,Kock, Sebastian C.,Hundsdorfer, Claas,Martin, Hans-Dieter,Stahl, Wilhelm,Ostroumov, Evgeny,Muller, Marc G.,Holzwarth, Alfred R. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.2
For the natural carotenoid 3,3'-dihydroxyisorenieratene (DHIR) and two synthetic derivatives, 3,3'-dihydroxy-16,17,18,16',17',18'-hexanor-$\Phi$,$\Phi$-carotene (DHHC) and $\Phi$,$\Phi$-carotene-3,3'-dione (DHIRQ, isorenieratene-3,3'-dione), steady state absorption experiments and combined density functional and multi-reference configuration interaction calculations were carried out. In addition, femtosecond transient absorption spectra were recorded for DHIR. Due to their marked out-of-plane distortion in DHIR, the phenolic end groups participate only partially in the conjugation system. In the low-energy regime its absorption spectrum with the maximum at $21\;700\;cm^{-1}$ in acetone solution therefore closely resembles that of $\beta$-carotene, the same as for the $T_1$ energy. Further similarities are also found for the decay kinetics of the optically bright $1^1{B_u}^+$ state of these compounds. After femtosecond excitation, the $1^1{B_u}^+$ population of DHIR decays with a lifetime of 110 fs to the vibrationally hot $2^1{A_g}^-$,v state which in turn relaxes to the $2^1{A_g}^-$,0 state within 500 fs. Decay of the $2^1{A_g}^-$,0 state to the $S_0$ state occurs at a time scale of 12 ps. Demethylation of the phenolic end groups alleviates the steric repulsion by the polyene chain and causes a small red shift ($1000\;cm^{-1}$) comparing the absorption spectra of DHHC and DHIR. Oxidation of DHIR leads to drastic changes of the electronic and geometric properties. The quinoid end groups of DHIRQ are fully integrated into the conjugation system, shifting the absorption maximum to $17\;800\;cm^{-1}$ in acetone solution which thus takes a blue color. The results of the quantum chemical calculations indicate that, in addition to the $2^1{A_g}^-$ ($S_1$) state, two dark internal charge-transfer singlet states and the $1^1{B_u}^-$ state might be located energetically below the optically bright $1^1{B_u}^+$ ($S_5$) state of DHIRQ.
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