Ruthenium is a platinoid that exhibits a range of unique chemical properties in solution, which are exploited in a variety of applications, including luminescent probes, anticancer therapies, and artificial photosynthesis. This paper focuses on a recently demonstrated ability of this metal in its +3 oxidation state to form highly stable complexes with tris (hydroxymethyl)aminomethane (H2 NC(CH2 OH)3 , Tris-base or T) and imidazole (Im) ligands, where a single RuIII cation is coordinated by two molecules of each T and Im. High-resolution electrospray ionization mass spectrometry (ESI MS) is used to characterize RuIII complexes formed by placing a RuII complex [(NH3 )5 RuII Cl]Cl in a Tris buffer under aerobic conditions. The most abundant ionic species in ESI MS represent mononuclear complexes containing an oxidized form of the metal, ie, [Xn RuIII T2 - 2H]+ , where X could be an additional T (n = 1) or NH3 (n = 0-2). Di- and tri-metal complexes also give rise to a series of abundant ions, with the highest mass ion representing a metal complex with an empirical formula Ru3 C24 O21 N6 H66 (interpreted as cyclo(T2 RuO)3 , a cyclic oxo-bridged structure, where the coordination sphere of each metal is completed by two T ligands). The empirical formulae of the binuclear species are consistent with the structures representing acyclic fragments of cyclo(T2 RuO)3 with addition of various combinations of ammonia and dioxygen as ligands. Addition of histidine in large molar excess to this solution results in complete disassembly of poly-nuclear complexes and gives rise to a variety of ionic species in the ESI mass spectrum with a general formula [RuIII Hisk Tm (NH3 )n - 2H]+ , where k = 0 to 2, m = 0 to 3, and n = 0 to 4. Ammonia adducts are present for all observed combinations of k and m, except k = m = 2, suggesting that [His2 RuIII T2 - 2H]+ represents a complex with a fully completed coordination sphere. The observed cornucopia of RuIII complexes formed in the presence of histidine is in stark contrast to the previously reported selective reactivity of imidazole, which interacts with the metal by preserving the RuT2 core and giving rise to a single abundant ruthenium complex (represented by [Im2 RuIII T2 - 2H]+ in ESI mass spectra). Surprisingly, the behavior of a hexa-histidine peptide (HHHHHH) is similar to that of a single imidazole, rather than a single histidine amino acid: The RuT2 core is preserved, with the following ionic species observed in ESI mass spectra: [HHHHHH·(RuIII T2 )m - (3m-1)H]+ (m = 1-3). The remarkable selectivity of the imidazole interaction with the RuIII T2 core is rationalized using energetic considerations at the quantum mechanical level of theory.

中文翻译：

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通过电喷雾电离质谱和分子建模揭示了含咪唑体系中钌的配位偏爱：钌（III）/三（羟甲基）-氨基甲烷/咪唑配合物具有令人惊讶的稳定性的可能线索。

钌是类铂盐，在溶液中表现出一系列独特的化学性质，可在多种应用中加以利用，包括发光探针，抗癌疗法和人工光合作用。本文重点研究了这种金属在+3氧化态下与三（羟甲基）氨基甲烷（H2 NC（CH2 OH）3，Tris-base或T）和咪唑（Im）配体形成高度稳定的配合物的能力，其中单个RuIII阳离子由T和Im的两个分子配位。高分辨率电喷雾电离质谱（ESI MS）用于表征通过在有氧条件下将RuII配合物[（NH3）5 RuII Cl] Cl放在Tris缓冲液中形成的RuIII配合物。ESI MS中最丰富的离子种类表示包含金属氧化形式的单核络合物，即 [Xn RuIII T2-2H] +，其中X可以是一个附加的T（n = 1）或NH3（n = 0-2）。二金属和三金属络合物还会产生一系列丰富的离子，其中质量最高的离子代表具有经验式Ru3 C24 O21 N6 H66（解释为环（T2 RuO）3，环状氧桥联结）的金属络合物结构，其中每种金属的配位球由两个T配体完成）。双核物种的经验公式与代表环（T2 RuO）3的无环片段并添加氨和双氧的各种组合作为配体的结构一致。向该溶液中加入大摩尔过量的组氨酸会导致多核络合物的完全分解，并在ESI质谱图中产生具有通式[RuIII Hisk Tm（NH3）n-2H] +的各种离子物种，其中k = 0至2，m = 0至3，n = 0至4。除k = m = 2之外，所有观察到的k和m组合均存在氨加合物，表明[His2 RuIII T2-2H] +代表具有完整完成的协调范围的综合体。观察到的在组氨酸存在下形成的RuIII络合物的聚宝盆与先前报道的咪唑的选择性反应形成了鲜明的对比，后者通过保留RuT2核与金属相互作用并生成了一个丰富的钌络合物（由[Im2 RuIII在ESI质谱中为T2-2H] +。令人惊讶的是，六组氨酸肽（HHHHHH）的行为类似于单个咪唑，而不是单个组氨酸氨基酸：保留了RuT2核，在ESI质谱图中观察到以下离子种类：[HHHHHH· （RuIII T2）m-（3m-1）H] +（m = 1-3）。