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首页> 外文期刊>Inorganic Chemistry: A Research Journal that Includes Bioinorganic, Catalytic, Organometallic, Solid-State, and Synthetic Chemistry and Reaction Dynamics >Synthesis, structure, and DNA cleavage properties of copper(II) complexes of 1,4,7-triazacyclononane ligands featuring pairs of guanidine pendants
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Synthesis, structure, and DNA cleavage properties of copper(II) complexes of 1,4,7-triazacyclononane ligands featuring pairs of guanidine pendants

机译：1,4,7-三氮杂环壬烷配体与胍基悬垂对的铜（II）配合物的合成，结构和DNA裂解特性

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摘要

Two new ligands, L~1 and L~2, have been prepared via N-functionalization of 1,4,7-triazacyclononane (tacn) with pairs of ethyl- or propyl-guanidine pendants, respectively. The X-ray crystal structure of [CuL~1](ClO_4)_2 (C1) isolated from basic solution (pH 9) indicates that a secondary amine nitrogen from each guanidine pendants coordinates to the copper(II) center in addition to the nitrogen atoms in the tacn macrocycle, resulting In a five-coordinate complex with intermediate square-pyramidal/trigonal bipyramidal geometry. The guanidines adopt an unusual coordination mode in that their amine nitrogen nearest to the tacn macrocycle binds to the copper(II) center, forming very stable five-membered chelate rings. A spectrophotometry pH titration established the pK_(app) for the deprotonation and coordination of each guanidine group to be 3.98 and 5.72, and revealed that [CuL~1]~(2+) Is the only detectable species present in solution above pH ～8. The solution speciation of the CuL ~2 complex (C2) is more complex, with at least 5 deprotonation steps over the pH range 4-12.5, and mononuclear and binuclear complexes coexisting. Analysis of the spectrophotometric data provided apparent deprotonation constants, and suggests that solutions at pH ～7.5 contain the maximum proportion of polynuclear complexes. Complex C1 exhibits virtually no cleavage activity toward the model phosphate diesters, bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenyl phosphate (HPNPP), while C2 exhibits moderate activity. For C2, the respective k_(obs) values measured at pH 7.0 (7.24 (±0.08) × 10~(-5)S~(-1) (BNPP at 50°C) and 3.2 (±0.3) × 10~(-5) s~(-1) (HPNPP at 25°C)) are 40- and 10-times faster than [Cu(tacn)(OH_2) _2]~(2+) complex. Both complexes cleave supercoiled pBR 322 plasmid DNA, indicating that the guanidine pendants of [CuL~1] ~(2+) may have been displaced from the copper coordination sphere to allow for DNA binding and subsequent cleavage. The rate of DNA cleavage by C2 Is twice that measured for [Cu(tacn)(OH_2)_2]~(2+), suggesting some degree of cooperativity between the copper center and guanidinium pendants In the hydrolysis of the phosphate ester linkages of DNA. A predominantly hydrolytic cleavage mechanism was confirmed through experiments performed either in the presence of various radical scavengers or under anaerobic conditions.
机译：通过分别用成对的乙基或丙基胍基侧基对1,4,7-三氮杂环壬烷（tacn）进行N-官能化，制备了两个新的配体L-1和L-2。从碱性溶液（pH 9）中分离的[CuL〜1]（ClO_4）_2（C1）的X射线晶体结构表明，除氮原子外，每个胍侧基上的仲胺氮还与铜（II）中心配位tacn大环中的原子，形成具有中间正方形-金字塔形/三角形双金字塔形几何结构的五坐标复合物。胍采用不寻常的配位模式，因为它们最接近tacn大环的胺氮与铜（II）中心结合，形成非常稳定的五元螯合环。用分光光度法pH滴定法确定了每个胍基的去质子和配位的pK_（app）分别为3.98和5.72，并发现[CuL〜1]〜（2+）是pH〜8以上溶液中唯一可检测到的物种。 。 CuL〜2配合物（C2）的溶液形态更为复杂，在pH范围4-12.5内具有至少5个去质子化步骤，并且单核和双核配合物共存。分光光度数据的分析提供了明显的去质子常数，表明在pH〜7.5的溶液中含有最大比例的多核配合物。复合物C1对模型磷酸二酯，双（对硝基苯基）磷酸酯（BNPP）和2-羟丙基-对硝基苯基磷酸酯（HPNPP）几乎没有裂解活性，而C2具有中等活性。对于C2，各自的k_（obs）值在pH 7.0（7.24（±0.08）×10〜（-5）S〜（-1）（50°C下的BNPP）和3.2（±0.3）×10〜（ -5）s〜（-1）（25°C下的HPNPP）比[Cu（tacn）（OH_2）_2]〜（2+）络合物快40倍和10倍。两种复合物均切割超螺旋的pBR 322质粒DNA，表明[CuL〜1]〜（2+）的胍基侧基可能已从铜配位球上移开，以允许DNA结合和随后的切割。 C2对DNA的切割速率是[Cu（tacn）（OH_2）_2]〜（2+）的两倍，表明铜中心和胍基侧基之间存在一定程度的协同作用。 。通过在各种自由基清除剂的存在下或在厌氧条件下进行的实验，证实了主要的水解裂解机理。

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