摘要
采用混合密度泛涵理论中的B3LYP方法,结合4种基组6-31G(d),6-31G(df,p),6-31+G(d)和6-311+G(2d,2p),系统计算了光合反应中心叶绿素的配位体-组氨酸在空气、四碌化碳、四氢呋喃、水和蛋白质模拟环境中的几何结构、电离能、红外光谱及同位素标记谱。计算及分析结果表明:组氨酸分子的几何参数在不同计算基组和介质中略有不同,且C2—N3,N3—C4的键长在空气中最大;同一介质中,增大计算基组和采用扩散函数,均使计算的单点势能和振动频率降低,电离能增加,对应光谱强度增高;而同一计算方法下,介质的电介常数越高,分子的单点势能越低,电离能越小,对应的振动频率减小强度增加;另外,电离能和主要特征峰位及其15N和13C标记谱的计算结果与文献中的实验结果相吻合。所有计算均显示,高基组和施加扩散函数的计算结果与实验更接近。该研究为深入探索叶绿素与组氨酸配位后在光合反应中心的功能与振动光谱特性提供理论参考依据。
Histidines provide axial ligands to the primary electron donors in photosynthetic reaction centers （RCs） and play an important role in the protein environments of these donors. In this paper the authors present a systematic study of ionization energies and vibrational properties of histidine using hybrid density functional theory （DFT）. All calculations were undertaken by using B3LYP method in combination with four basis sets： 6-31G（d）, 6-31G（df, p）, 6-31＋G（d） and 6-311＋G（2d,2p） with the aim to investigate how the basis sets influence the calculation results. To investigate solvent effects and gain a detailed understanding of marker bands of histidine, the ionization energies of histidine and the vibrational frequencies of histidine which are unlabeled and ^13C, ^15N, and ^2H labeled in the gas phase, CCl4, protein environment, THF and water solution, which span a wide range of dielectric constant, were also calculated. Our results showed that： （1） The main geometry parameters of histidine were impacted by basis sets and mediums, and C2—N3 and N3—C4 bond of imidazole ring of histidine side chain display the maximum bond lengths in the gas phase; （2） single point energies and frequencies calculated were decreased while ionization energies increased with the increasing level of basis sets and diffuse function applied in the same solvent; （3） with the same computational method, the higher the dielectric constant of the solvent used, the lower the ionization energy and vibrational frequency and the higher the intensity obtained. In addition, calculated ionization energy in the gas phase and marker bands of histidine as well as frequency shift upon ^13C and ^15N labeling at the computationally more expensive 6-311＋G（2d,2p） level are in good agreement with experimental observations available in literatures. All calculations indicated that the results calculated by using higher level basis set with diffuse function were more accurate and closer to the experimental value. In conclusion, the results provide useful information for the further studies of the functional and vibrational properties of chlorophyll-a ligated to histidine residue in photosynthetic reaction center.
出处
《光谱学与光谱分析》
SCIE
EI
CAS
CSCD
北大核心
2010年第5期1192-1197,共6页
Spectroscopy and Spectral Analysis
基金
国家自然科学基金项目(10764006)资助
关键词
组氨酸
电离能
红外光谱
密度泛涵理论
基组
Histidine
Ionization energy
Infrared spectrum
Density functional theory
Basis set
