Carrera Flora, Marcos Enrique Sánchez, Merkling Patrick J, Chaboy Jesús, Muñoz-Páez Adela
Departamento de Quimica Inorganica, ICMSE, Universidad de Sevilla, CSIC, 41012 Sevilla, Spain.
Inorg Chem. 2004 Oct 18;43(21):6674-83. doi: 10.1021/ic049699q.
Knowledge of the complexes formed by N-coordinating ligands and Cu(II) ions is of relevance in understanding the interactions of this ion with biomolecules. Within this framework, we investigated Cu(II) complexation with mono- and polydentate ligands, such as ammonia, ethylenediamine (en), and phthalocyanine (Pc). The obtained Cu-N coordination distances were 2.02 A for Cu(NH(3))(4), 2.01 A for Cu(en)(2), and 1.95 A for CuPc. The shorter bond distance found for CuPc is attributed to the macrocyclic effect. In addition to the structure of the first shell, information on higher coordination shells of the chelate ligands could be extracted by EXAFS, thus allowing discrimination among the different coordination modes. This was possible due to the geometry of the complexes, where the absorbing Cu atoms are coplanar with the four N atoms forming the first coordination shell of the complex. For this reason multiple scattering contributions become relevant, thus allowing determination of higher shells. This knowledge has been used to gain information about the structure of the 1:2 complexes formed by Cu(II) ions with the amino acids histidine and glycine, both showing a high affinity for Cu(II) ions. The in-solution structure of these complexes, particularly that with histidine, is not clear yet, probably due to the various possible coordination modes. In this case the square-planar arrangements glycine-histamine and histamine-histamine as well as tetrahedral coordination modes have been considered. The obtained first-shell Cu-N coordination distance for this complex is 1.99 A. The results of the higher shells EXAFS analysis point to the fact that the predominant coordination mode is the so-called histamine-histamine one in which both histidine molecules coordinate Cu(II) cations through N atoms from the amino group and from the imidazole ring.
了解由氮配位配体与铜（II）离子形成的配合物，对于理解该离子与生物分子的相互作用具有重要意义。在此框架内，我们研究了铜（II）与单齿和多齿配体的络合情况，如氨、乙二胺（en）和酞菁（Pc）。对于[Cu(NH₃)₄]²⁺，得到的铜 - 氮配位距离为2.02 Å；对于[Cu(en)₂]²⁺，为2.01 Å；对于CuPc，为1.95 Å。在CuPc中发现的较短键距归因于大环效应。除了第一配位层的结构外，通过扩展X射线吸收精细结构（EXAFS）还可以提取螯合配体更高配位层的信息，从而区分不同的配位模式。这是由于配合物的几何结构使得吸收的铜原子与形成配合物第一配位层的四个氮原子共面。因此，多重散射贡献变得显著，从而能够确定更高的配位层。这些知识已被用于获取有关铜（II）离子与氨基酸组氨酸和甘氨酸形成的1:2配合物结构的信息，这两种氨基酸对铜（II）离子都具有高亲和力。这些配合物在溶液中的结构，特别是与组氨酸形成的配合物的结构，目前尚不清楚，可能是由于存在多种可能的配位模式。在这种情况下，已经考虑了甘氨酸 - 组胺和组胺 - 组胺的平面正方形排列以及四面体配位模式。该配合物获得的第一配位层铜 - 氮配位距离为1.99 Å。更高配位层EXAFS分析的结果表明，主要的配位模式是所谓的组胺 - 组胺模式，即两个组氨酸分子通过氨基和咪唑环上的氮原子与铜（II）阳离子配位。
