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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Calculation of vibrational spectra of linear tetrapyrroles. 4. Methine bridge C-H out-of-plane modes
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Calculation of vibrational spectra of linear tetrapyrroles. 4. Methine bridge C-H out-of-plane modes

机译：线性四吡咯的振动光谱计算。 4.蛋氨酸桥C-H面外模式

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Quantum chemical force fields obtained by density functional theory (DFT) calculations systematically overestimate the frequencies of normal modes including ethylenic C-H out-of-plane (HOOP) coordinates. Compensation of this deviation requires a specific scaling factor for this type of coordinate that is distinctly lower than those applicable to out-of-plane coordinates in general. Such a specific scaling factor (0.900) has been optimized for the DFT(B3LYP) level of theory on the basis of vibrational analyses of training molecules including the HOOP coordinate. Thus, the root-mean-square deviation for the calculated frequencies of these modes is reduced from 16 to 8 cm(-1). Although Raman intensities are yet not reproduced in a satisfactory manner, implementation of the HOOP scaling factor into the set of global scaling factors determined previously (Magdo et al. J. Phys. Chem. A 1999, 103, 289-303) allows for a substantially improved reproduction of the experimental (resonance) Raman spectra of test molecules including linear methine-bridged tetrapyrroles. A very good agreement between calculated and experimental spectra is noted for the phycocyanobilin dimethylester dimer as well as for the protein-bound phycocyanobilin in the antenna pigment R-CPC. However, for the phycocyanobilin chromophore in the P-r state of the plant photoreceptor phytochrome phyA, considerable deviations remain in the spectral range between 800 and 500 cm(-1), which are attributed to the effect of specific protein-chromophore interactions. The influence of the protein environment is not considered in the present calculations that refer to the molecule in vacuo.
机译：通过密度泛函理论（DFT）计算获得的量子化学力场系统地高估了包括乙烯C-H面外（HOOP）坐标在内的正常模式的频率。这种偏差的补偿需要针对这种坐标类型的特定比例因子，该比例因子明显低于通常适用于平面外坐标的比例因子。在对包含HOOP坐标的训练分子进行振动分析的基础上，针对DFT（B3LYP）的理论水平优化了这样的特定比例因子（0.900）。因此，这些模式的计算频率的均方根偏差从16减少到8 cm（-1）。尽管拉曼强度尚未以令人满意的方式再现，但将HOOP缩放因子实现为先前确定的全局缩放因子集（Magdo等人，J。Phys。Chem。A 1999，103，289-303）可以实现大大改善了测试分子（包括线性次甲基桥联四吡咯）的实验（共振）拉曼光谱的再现性。对于藻蓝花青素二甲基酯二聚体以及天线色素R-CPC中与蛋白质结合的藻蓝花青素，在计算和实验光谱之间发现了非常好的一致性。但是，对于处于植物光感受器植物色素phyA的P-r状态的藻蓝蛋白生色团，在800至500 cm（-1）的光谱范围内仍存在相当大的偏差，这归因于特定蛋白质-生色团相互作用的影响。在涉及真空中分子的当前计算中，未考虑蛋白质环境的影响。

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