Two-photon and fluorescence spectroscopy and the effect of environment on the photochemical properties of peridinin in solution and in the peridinin-chlorophyll-protein from Amphidinium carterae
Two-photon and fluorescence spectroscopy and the effect of environment on the photochemical properties of peridinin in solution and in the peridinin-chlorophyll-protein from Amphidinium carterae
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DOI：
10.1021/jp022648z
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发表时间：
2003-10-09
影响因子：
2.9
通讯作者：
Birge, RR
中科院分区：
文献类型：
--
作者：
Shima, S;Ilagan, RP;Birge, RR
利用单光子和双光子光谱、溶剂效应和量子理论研究了多甲藻素在溶液和多甲藻素-叶绿素-蛋白质（PCP）复合物中的基态和激发态性质。CS2中的双光子激发光谱、双光子偏振数据和荧光光谱揭示了多甲藻素中的三种低激发单重态：最低激发态（1）类A（g）（*-）态，其系统原点约为16 200 cm（-1），类1B（u）（*+）S-2态，其系统原点约为19 300 cm（-1），和一个类B-1（u）* 的S-3态，其系统原点在22000 cm（-1）附近。B-1（u）*+-like S-2态在溶液和PCP中的多甲藻素的双光子激发光谱中占主导地位，因为与大振子强度（f近似为1.6）相关联的11型增强与激发时偶极矩的变化（Deltamu近似为3D）相耦合。因此，双光子光谱看起来非常像单光子光谱，尽管在CS2中的多甲藻素的双光子光谱中，在类似于17、类似于18.1和类似于19.2 kK处观察到（1）A（g）（*-）-类态的弱电子振动带。MNDO-PSDCI理论和溶剂效应研究表明，S-1（Ag-1（*-）-like）态在极性和非极性环境中都具有较大的偶极矩（mu（aa）约为16 D，Deltamu约为8 D），远大于基态偶极矩[mu（00）约为6（非极性介质）-8（极性介质）D].因此，（1）A（g）（*-）-like态被指定为在先前研究中观察到的电荷转移态。这些研究不支持在极性溶剂中诱导电荷转移特性的建议。我们的结论是，一些研究表明，增加的电荷转移字符的S，溶剂极性是基于实验，更敏感的（mu（aa）- mu（00））mu（00）比（mu（aa）- mu（00））。在室温己烷溶液中，多甲素以全反式和14-顺式（单键连到丙二烯部分）构象的混合物形式存在，其中前者占优势。极性溶剂如甲醇和高介电溶剂如CS2优先稳定相对于14-s-顺式的全反式构象。MNDO-PSDCI计算最小化的多甲藻素分子内PCP表明，大多数的发色团具有激发态性质类似于孤立的全反式发色团所观察到的。然而，占据位点612和622的发色团不仅蓝移，而且具有反转的S-1和S-2单重态。我们的研究为Damjanovic等人提出的PCP能量转移模型提供了支持和额外的观点。（Biophys. J. 2000，79，1695-1705），其中这些位点中的多甲藻素分子将能量转移到其他多甲藻素发色团，而不是直接转移到叶绿素。我们的结论是，612和622位点通过增加最低激发态B-1（u）*+样态的数量来优化能量转移，这提供了增强的偶极耦合到剩余的多甲藻素组。的分析，PCP复合光谱的色素组分光谱方面表明，两个多甲藻素分子。独特的蓝移光谱
The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll-protein (PCP) complex are studied by using one-photon and two-photon spectroscopy, solvent effects, and quantum theory. Two-photon excitation spectra, two-photon polarization data, and fluorescence spectra in CS2 reveal three low-lying excited singlet states in peridinin: a lowest-excited(1)A(g)(*-)-like state with a system origin at similar to16 200 cm(-1), a 1B(u)(*+)-like S-2 state with a system origin at similar to19 300 cm(-1), and a B-1(u)*--like S-3 state with a system origin at similar to22 000 cm(-1). The B-1(u)*+-like S-2 state dominates the two-photon excitation spectrum of peridinin in solution and in PCP because of type 11 enhancement associated with a large oscillator strength (f approximate to 1.6) coupled with a change in dipole moment upon excitation (Deltamu approximate to 3 D). Thus, the two-photon spectrum looks very much like the one-photon spectrum although weak vibronic bands of the (1)A(g)(*-)-like state are observed at similar to17, similar to18.1, and similar to19.2 kK in the two-photon spectrum of peridinin in CS2. MNDO-PSDCI theory and solvent effect studies indicate that the S-1 (Ag-1(*-)-like) state has a large dipole moment (mu(aa) approximate to 16 D, Deltamu approximate to 8 D) in both polar and nonpolar environments, much larger than the ground-state dipole moment [mu(00) approximate to 6 (non polar media) - 8 (polar media) D]. Thus, the (1)A(g)(*-)-like state is assigned as the charge-transfer state observed in previous studies. The suggestion that the charge-transfer character is induced in polar solvent is not supported by these studies. We conclude that some of the studies that have suggested an increase in the charge-transfer character of S, with solvent polarity are based on experiments that are more sensitive to (mu(aa) - mu(00))mu(00) than (mu(aa) - mu(00)). Peridinin exists as a mixture of all-trans and 14-s-cis (single bond to allene moiety) conformers in ambient temperature hexane solution, with a predominance of the former. Polar solvents such as methanol and high-dielectric solvents such as CS2 preferentially stabilize the all-trans conformer relative to the 14-s-cis. MNDO-PSDCI calculations on the minimized peridinin molecules within PCP indicate that most of the chromophores have excited state properties similar to those observed for the isolated all-trans chromophore. However, the chromophores occupying sites 612 and 622 are not only blue shifted but have inverted S-1 and S-2 singlet states. Our studies provide both support and additional perspective on the PCP energy transfer model proposed by Damjanovic et al. (Biophys. J. 2000, 79, 1695-1705) in which the peridinin molecules in these sites transfer energy to other peridinin chromophores rather than directly to chlorophyll. We conclude that the 612 and 622 sites optimize energy transfer by increasing the population of the lowest-excited B-1(u)*+-like state, which provides enhanced dipolar coupling to the remaining peridinin set. An analysis of the, PCP complex spectrum in terms of component spectra of the pigments indicates that two peridinin molecules have. unique, blue-shifted spectra.