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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Cation-pi interactions with a model for the side chain of tryptophan: Structures and absolute binding energies of alkali metal cation-indole complexes
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Cation-pi interactions with a model for the side chain of tryptophan: Structures and absolute binding energies of alkali metal cation-indole complexes

机译：阳离子-π相互作用与色氨酸侧链的模型：碱金属阳离子-吲哚配合物的结构和绝对结合能

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Threshold collision-induced dissociation techniques are employed to determine bond dissociation energies (BDEs) of mono- and bis-complexes of alkali metal cations, Li+, Na+, K+, Rb+, and Cs+, with indole, C8H7N. The primary and lowest energy dissociation pathway in all cases is endothermic loss of an intact indole ligand. Sequential loss of a second indole ligand is observed at elevated energies for the bis-complexes. Density functional theory calculations at the B3LYP/6-31G* level of theory are used to determine the structures, vibrational frequencies, and rotational constants of these complexes. Theoretical BDEs are determined from single point energy calculations at the MP2(full)/6-311+G(2d,2) level using the B3LYP/6-31G* geometries. The agreement between theory and experiment is very good for all complexes except Li+(C8H7N), where theory underestimates the strength of the binding. The trends in the BDEs of these alkali metal cation-indole complexes are compared with the analogous benzene and naphthalene complexes to examine the influence of the extended pi network and heteroatom on the strength of the cation-pi interaction. The Na+ and K+ binding affinities of benzene, phenol, and indole are also compared to those of the aromatic amino acids, phenylalanine, tyrosine, and tryptophan to elucidate the factors that contribute to the binding in complexes to the aromatic amino acids. The nature of the binding and trends in the BDEs of cation-pi complexes between alkali metal cations and benzene, phenol, and indole are examined to help understand nature's preference for engaging tryptophan over phenylalanine and tyrosine in cation-pi interactions in biological systems.
机译：阈值碰撞诱导解离技术用于确定碱金属阳离子Li +，Na +，K +，Rb +和Cs +与吲哚C8H7N的单和双配合物的键解离能（BDE）。在所有情况下，主要和最低的能量解离途径是完整吲哚配体的吸热损失。在双配合物的能量升高时观察到第二个吲​​哚配体的顺序损失。在B3LYP / 6-31G *理论水平上的密度泛函理论计算用于确定这些配合物的结构，振动频率和旋转常数。理论BDE是使用B3LYP / 6-31G *几何结构从MP2（full）/ 6-311 + G（2d，2）级别的单点能量计算确定的。除了Li +（C8H7N）（理论上低估了结合强度）外，所有配合物的理论与实验之间的一致性都很好。将这些碱金属阳离子-吲哚配合物的BDEs趋势与类似的苯和萘配合物进行比较，以检验扩展的π网络和杂原子对阳离子-π相互作用强度的影响。还将苯，苯酚和吲哚的Na +和K +结合亲和力与芳香族氨基酸，苯丙氨酸，酪氨酸和色氨酸的Na +和K +结合亲和力进行比较，以阐明有助于复合物与芳香族氨基酸结合的因素。考察了碱金属阳离子与苯，苯酚和吲哚之间阳离子-π配合物的结合性质和BDEs的趋势，以帮助理解自然界对于在生物系统中阳离子-π相互作用中色氨酸胜于苯丙氨酸和酪氨酸的偏好。

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