Chemistry Department, Case Western Reserve University, Cleveland, Ohio 44106, USA.
J Phys Chem A. 2013 Feb 14;117(6):1094-101. doi: 10.1021/jp304256f. Epub 2012 Sep 18.
Ion-neutral complexes of pentaalalanine with several singly- and doubly charged metal ions are examined using conformation analysis by infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) computations. The infrared spectroscopy in the 1500-1800 cm(-1) region is found to be conformationally informative; in particular, the frequency of the C═O stretching mode of the terminal carboxyl group is diagnostic for hydrogen bonding of the terminal hydroxyl. The doubly charged alkaline earth metal ions (Ca(2+) and Ba(2+)) enforce a highly structured chelation shell around the metal ion, with six strongly bound Lewis-basic chelation sites, and no hydroxyl hydrogen bonding. With the more weakly binding alkali metal ions (Na(+), K(+), and Cs(+)), structures with intramolecular hydrogen bonds are more favorable, leading to dominance of conformations with lower degrees of metal ion chelation. The favored coordination mode correlates with ionic charge and binding strength but is not related to the ionic radius of the metal ion.
采用红外多光子解离（IRMPD）光谱和密度泛函理论（DFT）计算研究了五丙氨酸与几种单价和二价金属离子的离子中性配合物。在 1500-1800 cm(-1) 区域的红外光谱具有构象信息；特别是，末端羧基的 C═O 伸缩模式的频率可用于氢键的末端羟基的诊断。带两个电荷的碱土金属离子（Ca(2+)和 Ba(2+)）在金属离子周围强制形成高度结构化的螯合壳，具有六个强结合的路易斯碱性螯合位点，没有羟基氢键。对于结合力较弱的碱金属离子（Na(+)、K(+)和 Cs(+)），具有分子内氢键的结构更有利，导致具有较低金属离子螯合程度的构象占主导地位。首选的配位模式与离子电荷和结合强度相关，但与金属离子的离子半径无关。
