Reactions of the anticancer active dirhodium tetraacetate (1), Rh₂(AcO)₄ (AcO⁻ = CH₃COO⁻), with the amino acid histidine (HHis) and human serum albumin (HSA) were monitored over time and different metal: ligand ratios using UV-vis spectroscopy and/or electro-spray ionization mass spectrometry. Initially, histidine formed 1:1 and 1:2 adducts in aqueous solutions. The crystal structure of Rh₂(AcO)₄(L-HHis)₂·2H₂O (2) confirmed the axial coordination of histidine imidazole groups (average Rh-N_axial 2.23 Å). These adducts, however, were found to be unstable in solution over time (24 h). Heating Rh₂(AcO)₄ –histidine solutions to 40 °C (near body temperature) or 95 °C accelerated the formation of Rh^II₂(AcO)₂(His)₂ and Rh^III(His)₂(AcO) complexes. The corresponding pH change from neutral to mildly acid (pH 4–5) indicates deprotonation of histidine NH₃⁺ groups due to coordination to Rh ions, which simultaneously bind to histidine COO⁻ groups, as evidenced by ¹³C NMR spectroscopy. In the case of HSA with 16 histidine and one cysteine residues, UV-vis spectroscopy indicates that mono- and di-histidine HSA adducts with Rh₂(AcO)₄ are formed. X-ray absorption spectroscopy showed almost the same Rh-Rh distance (2.41 ± 0.01 Å) for the Rh₂(AcO)₄ units as in 2, and a contribution from an axial thiol coordination (Rh-S_axial 2.62 ± 0.05 Å). The Rh₂(AcO)₄ – HSA complex was found to decompose partially (~15%) over 24 h at ambient temperature. The partial decomposition of Rh₂(AcO)₄ both through coordination to histidine or to human serum albumin, the most abundant protein in blood plasma, is a factor to consider for its efficacy as a potential anticancer agent.

随着时间的推移和不同的金属监测抗癌活性四乙酸二铑 ( 1 )、Rh ₂ (AcO) ₄ (AcO ^- = CH ₃ COO ^- ) 与氨基酸组氨酸 (HHis) 和人血清白蛋白 (HSA) 的反应：使用紫外-可见光谱法和/或电喷雾电离质谱法测定配体比率。最初，组氨酸在水溶液中形成 1:1 和 1:2 的加合物。_{Rh 2} (AcO) ₄ ( L -HHis) ₂ · 2H ₂ O ( 2 )的晶体结构证实了组氨酸咪唑基团的轴向配位（平均Rh-N_轴向2.23 埃）。然而，发现这些加合物在溶液中随时间（24 小时）不稳定。将Rh ₂ (AcO) ₄ -组氨酸溶液加热到 40 °C（接近体温）或 95 °C 加速了 Rh ^II ₂ (AcO) ₂ (His) ₂和 Rh ^III (His) ₂ (AcO) 复合物的形成。相应的 pH 从中性变为弱酸性（pH 4-5）表明组氨酸 NH ₃ ⁺基团由于与 Rh 离子的配位而去质子化，同时与组氨酸 COO ^-基团结合，如^13所示C 核磁共振波谱。在具有 16 个组氨酸和一个半胱氨酸残基的 HSA 的情况下，UV-vis 光谱表明形成了具有 Rh ₂ (AcO) ₄的单组氨酸和二组氨酸 HSA 加合物。X 射线吸收光谱显示 Rh ₂ (AcO) ₄单元的 Rh-Rh 距离 (2.41 ± 0.01 Å) 与2中的几乎相同，并且来自轴向硫醇配位 (Rh-S_轴向2.62 ± 0.05 Å) . 发现Rh ₂ (AcO) ₄ – HSA 复合物在环境温度下在 24 小时内部分分解（~15%）。_{Rh 2} (AcO) ₄的部分分解通过与组氨酸或人血清白蛋白（血浆中最丰富的蛋白质）的配位，是考虑其作为潜在抗癌剂功效的一个因素。