Lanthanides such as cerium(III), europium(III), and gadolinium(III) are widely used for designing fluorescent probes or magnetic resonance imaging contrasting agents for biological systems. The synthesis and study of lanthanide complexes in buffer solutions imitating biological fluids are often complicated because of a lack of data on the lanthanide interactions with buffer solution components. Therefore, Ln(III) [where Ln(III) = La(III), Ce(III), Gd(III), Eu(III)] complexation with a widely used buffer agent, tris(hydroxymethyl)aminomethane (Tris), in aqueous solution is studied using potentiometry, spectrofluorimetry, and ¹³⁹La NMR spectroscopy. The stoichiometric composition of complexes is determined using mass spectrometry. The thermodynamic stability constants of Ln(III)-Tris complexes are calculated from potentiometric and spectral data; the difficulties in the study of these systems, reliability, and accuracy of the obtained constants are discussed. The possible structures of free Tris and its complexes with lanthanides(III) are optimized on the density functional theory/PBE0 level; the peculiarities of metal–ligand bonds were studied by Quantum Theory Atoms in Molecules analysis.

中文翻译：

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La（III），Ce（III），Gd（III）和Eu（III）与三（羟甲基）氨基甲烷的水溶液络合

镧系元素如铈（III），euro（III）和g（III）被广泛用于设计用于生物系统的荧光探针或磁共振成像造影剂。由于缺乏有关镧系元素与缓冲溶液成分相互作用的数据，在模拟生物流体的缓冲溶液中镧系元素络合物的合成和研究通常很复杂。因此，Ln（III）[其中Ln（III）= La（III），Ce（III），Gd（III），Eu（III）]与广泛使用的缓冲剂三（羟甲基）氨基甲烷（Tris）络合，使用电位计，分光荧光法和¹³⁹研究水溶液中的La NMR光谱。使用质谱法测定复合物的化学计量组成。Ln（III）-Tris配合物的热力学稳定性常数由电位和光谱数据计算得出；讨论了这些系统的研究困难，所获得常数的可靠性和准确性。在密度泛函理论/ PBE0水平上优化了游离Tris及其与镧系元素（III）配合物的可能结构；通过分子理论中的量子理论原子研究了金属-配体键的特殊性。