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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Vibrational Assignment of Torsional Normal Modes of Rhodopsin: Probing Excited-State Isomerization Dynamics along the Reactive C_(11)=C_(12) Torsion Coordinate
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Vibrational Assignment of Torsional Normal Modes of Rhodopsin: Probing Excited-State Isomerization Dynamics along the Reactive C_(11)=C_(12) Torsion Coordinate

机译：视紫红质的扭转正态模态的振动分配：沿反应C_（11）= C_（12）扭转坐标探索激发态异构化动力学

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摘要

The resonance Raman spectrum of the 11-cis retinal protonated Schiff base chromophore in rhodopsin exhibits low-frequency normal modes at 93, 131, 246, 260, 320, 446, and 569 cm~(-1). Their relatively strong Raman activities reveal that the photoexcited chromophore undergoes rapid nuclear motion along torsional coordinates that may be involved in the 200-fs isomerization about the C_(11)=C_(12) bond. Resonance Raman spectra of rhodopsins regenerated with isotopically labeled retinal derivatives and demethyl retinal analogues were obtained in order to determine the vibrational character of these low-frequency modes and to assign the C_(11)=C_(12) torsional mod. ~(13)C substitutions of atoms in the C_(12)-C_(13) or C_(13)=C_(14) bond cause the 568-cm~(-1) mode to shift by ～8 cm~(-1), and deuteration of the C_(11)=C_(12) bond downshifts the 568- and 260-cm~(-1) modes by ～35 and 5 cm~(-1), respectively. The magnitudes of these shifts are consistent with those calculated for modes containing significant C_(11)=C_(12) torsional character. Thus, we assign the 568-cm~(-1) mode to a localized C_(11)=C_(12) torsion and the 260-cm~(-1) mode to a more delocalized torsional vibration involving coordinates from C_(10) to C_(13). Consistent with these assignments, these two modes are not Raman active in 13-demethyl, 11-cis rhodopsin which has a planar C_(10)…C_(13) geometry. Furthermore, the relative Raman scattering strengths of the 260- and 568-cm~(-1) modes are ～2-fold higher with preresonant excitation. These data quantitate the instantaneous torsional dynamics of the chromophore about its C_(11)=C_(12) bond on the S_1 surface and indicate that the isomerization process is facilitated by vibronic coupling of the S_1 and S_2 surfaces via C_(11)=C_(12) torsional distortion, which reduces the excited-state barrier along the reaction trajectory. We have also examined the low-frequency Raman spectrum of the trans primary photoproduct, bathorhodopsin, and discuss the relevance of its low-frequency torsional modes at ～54, 92, 128, 151, 262, 276, 324, and 376 cm~(-1) to the observed femtosecond photochemical dynamics.
机译：视紫红质中11-顺式视网膜质子化席夫碱生色团的共振拉曼光谱在93、131、246、260、320、446和569 cm〜（-1）处呈现低频正常模式。它们相对较强的拉曼活性表明，光激发的发色团沿扭转坐标进行快速核运动，该扭转坐标可能参与有关C_（11）= C_（12）键的200-fs异构化反应。为了确定这些低频模式的振动特性并指定C_（11）= C_（12）扭转模态，获得了用同位素标记的视网膜衍生物和去甲基视网膜类似物再生的视紫红质的共振拉曼光谱。 C_（12）-C_（13）或C_（13）= C_（14）键中的〜（13）C原子取代导致568-cm〜（-1）模移动约-8 cm〜（- 1），并且C_（11）= C_（12）键的氘化分别将568-和260-cm〜（-1）模式下移约35和5 cm-（-1）。这些偏移的大小与针对包含显着C_（11）= C_（12）扭转特性的模式计算出的大小一致。因此，我们将568-cm〜（-1）模式分配给局部C_（11）= C_（12）扭转，将260-cm〜（-1）模式分配给更局域的扭转振动，其中涉及C_（10）的坐标）到C_（13）。与这些分配一致，这两种模式在具有平面C_（10）…C_（13）几何形状的13-去甲基，11-顺式视紫红质中不具有拉曼活性。此外，在预共振激发下，260和568 cm〜（-1）模式的相对拉曼散射强度大约高2倍。这些数据量化了发色团在S_1表面上关于其C_（11）= C_（12）键的瞬时扭转动力学，并表明通过C_（11）= C_进行S_1和S_2表面的电子耦合有助于异构化过程。 （12）扭转畸变，它减小了沿着反应轨迹的激发态势垒。我们还研究了反式一次光产物红细胞膜视紫红质的低频拉曼光谱，并讨论了其在54、92、128、151、262、276、324和376 cm〜（〜）处的低频扭转模态的相关性。 -1）观察到的飞秒光化学动力学。

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