Vibronic effects in the spectroscopy and dynamics of C-phycocyanin
Vibronic effects in the spectroscopy and dynamics of C-phycocyanin
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DOI：
10.1088/0953-4075/45/15/154016
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发表时间：
2012-07
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影响因子：
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通讯作者：
J. M. Womick;B. A. West;N. Scherer;Andrew M. Moran
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文献类型：
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作者：
J. M. Womick;B. A. West;N. Scherer;Andrew M. Moran
飞秒激光光谱用于研究分子内核模式对蓝藻光捕获蛋白 C-藻蓝蛋白 (CPC) 电子弛豫的影响。特别令人感兴趣的是位于紧密间隔的藻蓝蛋白色素对（即二聚体）上的亚 ps 动力学。在不同极化条件下进行的实验用于区分二聚体内的各向同性和各向异性振动模式。使用二维光子回波光谱法在 185 和 260 cm−1 附近检测到两种各向同性核模式。此外，瞬态吸收各向异性测量揭示了与 640 和 815 cm−1 附近的（面外）各向异性核模式相关的振动共振。我们研究了各向异性重现的两个可能来源。通过将激子的势能面与波包运动的方向进行比较，排除了康登近似中涉及基态核相干性的机制。电子结构计算表明，非康顿效应是各向异性中观察到的节拍最可能的解释。这种非康顿效应对于 CPC 的振动激子电子结构也具有有趣的意义。我们计算了二聚体中高达 10 cm−1 的非康顿分子间耦合，这表明这些影响不可忽略，值得进一步考虑。我们的研究结果为密切相关的蛋白质别藻蓝蛋白中发现的亚 100 fs 振动弛豫通道提供了更多见解，其色素二聚体具有与 CPC 几乎相同的几何形状和分子间库仑相互作用。这项研究强调了光合光收集中分子内振动耦合和位点能量调节的复杂相互作用。
Femtosecond laser spectroscopies are used to investigate the influence of intramolecular nuclear modes on electronic relaxation in the cyanobacterial light harvesting protein, C-phycocyanin (CPC). Of particular interest are sub-ps dynamics localized on pairs of closely spaced phycocyanobilin pigments (i.e. dimers). Experiments conducted under different polarization conditions are used to distinguish isotropic and anisotropic vibrational modes within the dimers. Two isotropic nuclear modes are detected near 185 and 260 cm−1 using two-dimensional photon echo spectroscopy. In addition, a transient absorption anisotropy measurement reveals vibrational resonances associated with (out-of-plane) anisotropic nuclear modes near 640 and 815 cm−1. We investigate two possible origins for the recurrences in the anisotropy. A mechanism involving ground state nuclear coherences in the Condon approximation is ruled out by comparing the potential energy surfaces of the excitons to the direction of wavepacket motion. Electronic structure calculations suggest that non-Condon effects are the most likely explanation for the beats observed in the anisotropy. Such non-Condon effects also hold interesting implications for the vibronic exciton electronic structure of CPC. We calculate non-Condon intermolecular couplings in the dimer as large as 10 cm−1, which suggests that these effects are not negligible and deserve further consideration. Our findings provide additional insights into the sub-100 fs vibronic relaxation channel found in the closely related protein, allophycocyanin, whose pigment dimers possess nearly the same geometry and intermolecular Coulombic interactions as CPC. This study underscores the complex interplay of intramolecular vibronic coupling and site energy tuning in photosynthetic light harvesting.