Dipartimento di Chimica, Università di Roma La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy.
Phys Chem Chem Phys. 2010 Feb 21;12(7):1525-34. doi: 10.1039/b921769j. Epub 2010 Jan 6.
In this study copper(ii) complexes with the tridentate nitrogen ligand bis[2-(1-methylbenzimidazol-2-yl)ethyl]amine (2-BB) are considered as model compounds for the Cu-tris(imidazole) array found in several copper proteins. 2-BB chelates copper(ii) forming two six-membered rings and the complexes contain methanol, nitrite, azide and water as ancillary ligands; both the coordination numbers and stereochemistries differ in these complexes. Their key structural features were investigated by using full multiple-scattering theoretical analysis of the copper K-edge X-ray absorption spectrum with the MXAN code. We showed that using cluster sizes large enough to include all atoms of the ligand, the analysis of the XANES region can give both a structural model of the metal centre and map the structure of the 2-BB complexes. Complex Cu(2-BB)(N(3)) provided a critical test through the comparison of the XANES simulation results with crystallographic data, thus permitting the extension of the method to the complex Cu(2-BB)(H(2)O)(n) (n = 1 or 2), for which crystallographic data are not available but is expected to bear a five-coordinated Cu(3N)(2O) core (n = 2). The structural data of Cu(2-BB)(MeOH)(ClO(4)) and Cu(2-BB)(NO(2)), both with a Cu(3N)(2O) core but with a different stereochemistry, were used as the starting parameters for two independent simulations of the XANES region of the Cu(2-BB)(H(2)O)(2) cation. The two structural models generated by simulation converge towards a structure for the aqua-cation with a lower coordination number. New calculations, where four-coordinated Cu(3N)(O) cores were considered as the starting structures, validated that the structure of the aqua-complex in the powder state has a copper(ii) centre with a four-coordinated Cu(3N)(O) core and a molecular formula Cu(2-BB)(H(2)O).(H(2)O). A water solvation molecule, presumed to be disordered from the simulations with the two Cu(3N)(2O) cores, is present. The successful treatment of this Cu-2-BB complex system allows the extension of the method to other biomimetic compounds when a structural characterization is lacking.
在这项研究中，铜（ii）配合物与三齿氮配体双[2-（1-甲基苯并咪唑-2-基）乙基]胺（2-BB）一起被视为在几种铜蛋白中发现的 Cu-三（咪唑）阵列的模型化合物。2-BB 螯合铜（ii）形成两个六元环，配合物含有甲醇、亚硝酸盐、叠氮化物和水作为辅助配体；这些配合物的配位数和立体化学性质不同。使用 MXAN 代码对铜 K 边 X 射线吸收光谱进行全多次散射理论分析，研究了它们的关键结构特征。我们表明，通过使用足够大的簇大小来包含配体的所有原子，可以对 XANES 区域进行分析，从而为金属中心提供结构模型，并绘制 2-BB 配合物的结构。Cu(2-BB)(N(3)) 配合物通过将 XANES 模拟结果与晶体数据进行比较提供了一个关键测试，从而允许将该方法扩展到晶体数据不可用但预计具有五配位 Cu(3N)(2O)核心（n = 2）的Cu(2-BB)(H(2)O)(n)（n = 1 或 2）。Cu(2-BB)(MeOH)(ClO(4)) 和 Cu(2-BB)(NO(2)) 的结构数据，均具有 Cu(3N)(2O)核心，但具有不同的立体化学，用作 Cu(2-BB)(H(2)O)(2)阳离子 XANES 区域两个独立模拟的起始参数。通过模拟生成的两个结构模型收敛到具有较低配位数的水合阳离子的结构。新的计算，其中考虑四配位 Cu(3N)(O)核作为起始结构，验证了在粉末状态下水合配合物的结构具有四配位 Cu(3N)(O)核的铜（ii）中心和分子式Cu(2-BB)(H(2)O)。(H(2)O)。一个假定为无序的水分子处于溶剂化状态。从两个 Cu(3N)(2O)核的模拟中推断出该水合配合物在水溶液中具有四配位 Cu(3N)(O)核的铜（ii）中心和分子式Cu(2-BB)(H(2)O)。(H(2)O)。一个假定为无序的水分子处于溶剂化状态。从两个 Cu(3N)(2O)核的模拟中推断出该水合配合物在水溶液中具有四配位 Cu(3N)(O)核的铜（ii）中心和分子式Cu(2-BB)(H(2)O)。(H(2)O)。一个假定为无序的水分子处于溶剂化状态。从两个 Cu(3N)(2O)核的模拟中推断出该水合配合物在水溶液中具有四配位 Cu(3N)(O)核的铜（ii）中心和分子式Cu(2-BB)(H(2)O)。(H(2)O)。
