Effects of intramolecular hydrogen bonding on the ionization energies of proline.
Effects of intramolecular hydrogen bonding on the ionization energies of proline.
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DOI：
10.1002/anie.200504039
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发表时间：
2006-02
影响因子：
--
通讯作者：
S. Tian;Jinlong Yang
中科院分区：
文献类型：
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作者：
S. Tian;Jinlong Yang
了解分子间和分子内氢键的性质是化学和生物化学领域广泛研究的重点，因为许多化学和生物化学系统的热力学和动力学在很大程度上是由氢键决定的关于配合物中分子间氢键的结构信息可以从各种光谱实验中获得，[1]和能量学可以在超分子，高水平从头算方法中预测。虽然分子内氢键的性质与分子间氢键相同，但由于分子内氢键是所涉及分子的固有特征，因此分子内氢键能量的评估在实验和理论上都具有挑战性。[1,2]电离能（IEs）是理解电荷转移、亲电性和修饰生物分子各种反应模式的重要数据实验研究表明，氢键分子的孤对轨道的IE (n)通常高于没有（或具有非常弱的）分子内氢键的分子，并且溶剂化分子的孤对轨道的激发跃迁能经常与气相自由分子的激发跃迁能不同由于多种构象共存，分子内氢键对IEs的影响难以用紫外光电子能谱（UPS）测定。[5,6]对于氨基酸来说，分子内氢键和分子间相互作用都在蛋白质折叠和肽组装中发挥作用通过气相UPS实验获得了分离氨基酸及其衍生物的IE值本文基于从头算电子传播子理论[7]结合自然键轨道（NBO）[8]分析，首次对脯氨酸[5]的UP谱进行了赋值，并证明了分子内氢键具有很强的
Understanding the nature of inter-and intramolecular H-bonding is the focus of extensive research in the fields of chemistry and biochemistry because the thermodynamics and kinetics of many chemical and biochemical systems are determined to a large degree by H-bonding.[1] Structural information regarding the intermolecular H-bonding in complexes can be obtained from various spectroscopic experiments,[1] and the energetics can be predicted within a supermolecular, high-level ab initio approach. Although the nature of the intramolecular H-bonding is the same as for the intermolecular H-bonding, the evaluation of the intramolecular H-bonding energy has been challenging both experimentally and theoretically because intramolecular H-bonding is an intrinsic feature of the molecule involved.[1, 2] Ionization energies (IEs) are important data for understanding the charge transfer, electrophilicity, and for modification of the diverse reactivity patterns of biological molecules.[1] Experimental studies indicate that the IE of a lone-pair orbital (n) of the H-bonding molecule is usually higher than that of the molecule without (or with very weak) intramolecular H-bonds,[3] and the excitation transition energy of the lone-pair orbital for the solvated molecule frequently differs from that for the free molecule in the gas-phase.[4] The effects of intramolecular H-bonding on the IEs are difficult to determine by ultraviolet photoelectron spectroscopy (UPS) because of the coexistence of several conformers.[5, 6] For amino acids, both intramolecular H-bonding and intermolecular interactions play a role in protein folding and peptide assembly.[1] The IE values of isolated amino acids and their derivatives have been obtained by gas-phase UPS experiments.[5] Herein, we provide the first assignment of the UP spectrum of proline [5] based on ab initio electron-propagator theory [7] combined with natural bond orbital (NBO)[8] analyses and show that intramolecular H-bonding has a strong