Department of Inorganic and Analytical Chemistry, Faculty of Science and Technology, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary.
J Inorg Biochem. 2013 Oct;127:53-61. doi: 10.1016/j.jinorgbio.2013.06.006. Epub 2013 Jun 18.
Stability constants of the complexes formed between the natural trihydroxamic acids desferrioxamine B (DFB) and desferricoprogen (DFC) with Nd(III), Gd(III) and Yb(III) ions were determined using pH-potentiometry. The equilibrium in these systems can be described by models containing mononuclear protonated (Ln(HL), Ln(H2L) and Ln(H3L)), deprotonated (LnL) and ternary hydroxo Ln(H-1L) complexes, but for both ligands dinuclear complexes of low stability were also detected. The stability constants for the Ln(HDFB)(+) complexes are 11.95 (Nd(III)), 13.16 (Gd(III)) and 14.67 (Yb(III)), while these values of the Ln(DFC) complexes are considerably higher (14.42 (Nd(III)), 15.14 (Gd(III)) and 16.49 (Yb(III))). The stability constants of the complexes of DFB and DFC are much lower than those of the Ln(L)3 complexes formed with some aromatic hydroxamic acids indicating that the relatively long spacer between the hydroxamic acid moieties in DFB and DFC is unfavorable for Ln(III) complexation. The relaxometric study conducted for the Gd(HDFB)(+) species revealed an interesting pH dependence of the relaxivity associated with a large hydration number (bishydrated complex) and fast water exchange (kex=(29.9±0.4)×10(6)s(-1)), which would be favorable for CA use. However the dissociation of Gd(HDFB)(+) is fairly fast (<2ms) under all conditions employed in the present work thus the kinetically labile Gd(HDFB)(+) is not suitable for in vivo CA applications. Some low stability ternary complexes were also detected with K(Gd(HDFB)(HCO3))=17.5±1.9 and K(Gd(HDFB)(Lactate))=8.4±3.2 but in the presence of citrate and phosphate ions the Gd(HDFB)(+) complex was found to dissociate.
使用 pH 电位法测定了天然三羟肟酸去铁胺 B (DFB) 和去铁酮 (DFC) 与 Nd(III)、Gd(III) 和 Yb(III) 离子形成的配合物的稳定常数。这些体系中的平衡可以用包含单核质子化 (Ln(HL)、Ln(H2L) 和 Ln(H3L))、去质子化 (LnL) 和三元羟肟 Ln(H-1L) 配合物的模型来描述，但对于两种配体，还检测到低稳定性的双核配合物。Ln(HDFB)(+)配合物的稳定常数为 11.95(Nd(III))、13.16(Gd(III))和 14.67(Yb(III))，而 Ln(DFC)配合物的这些值要高得多(14.42(Nd(III))、15.14(Gd(III))和 16.49(Yb(III))。DFB 和 DFC 配合物的稳定常数远低于与一些芳香族羟肟酸形成的 Ln(L)3 配合物，表明 DFB 和 DFC 中羟肟酸部分之间相对较长的间隔不利于 Ln(III)配合物的形成。对 Gd(HDFB)(+)物种进行的弛豫研究表明，与大水合数(双水化配合物)和快速水交换(kex=(29.9±0.4)×10(6)s(-1))相关的弛豫率表现出有趣的 pH 依赖性，这有利于 CA 的使用。然而，在本工作中采用的所有条件下，Gd(HDFB)(+)的解离都相当快(<2ms)，因此动力学不稳定的 Gd(HDFB)(+)不适合用于体内 CA 应用。还检测到一些低稳定性的三元配合物，K(Gd(HDFB)(HCO3))=17.5±1.9 和 K(Gd(HDFB)(Lactate))=8.4±3.2，但在柠檬酸根和磷酸根离子的存在下，发现 Gd(HDFB)(+)配合物解离。
