Mn2+ complexes of 1-oxa-4,7-diazacyclononane based ligands with acetic, phosphonic and phosphinic acid pendant arms: Stability and relaxation studies
Mn2+ complexes of 1-oxa-4,7-diazacyclononane based ligands with acetic, phosphonic and phosphinic acid pendant arms: Stability and relaxation studies
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DOI：
10.1039/c1dt10543d
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发表时间：
2011-01-01
影响因子：
4
通讯作者：
Toth, Eva
中科院分区：
文献类型：
--
作者：
Drahos, Bohuslav;Pniok, Miroslav;Toth, Eva
合成了一类新的基于1-氧杂-4，7-二氮杂环烷的大环配体，并研究了它们与Mn2+的络合物的稳定性和松弛性能。每个配体都有两个悬挂臂，涉及羧酸(H_2L1-1-氧杂-4，7-二乙酸)、膦(H_4L2-1-oxa-4，7-diazacyclononane-4，7-bis(methylenephosphonic酸)、膦(H_2L3-1-oxa-4，7-diazacyclononane-4，7-bis(methylenephosphinic酸)或苯基膦(H_2L4-1-oxa-4，7-diazacyclononane-4，7-bis[methylene(phenyl)膦酸)酸部分。首次合成了H_2L_3和H_2L4。Mn2+与H_2L4形成的络合物的晶体结构确定了Mn2+的配位数为6。用电位法测定了所有配体的质子化常数及其与Mn2+和某些生物或生物医学相关金属离子的络合物的稳定常数。H-1和P-31核磁共振法测定了H_2L_3的质子化顺序，认为质子化的第二步是第二大环氮原子。电位法数据表明，所有配体的Mn2+络合物的热力学稳定性相对较低。对于H_2L_3和H_2L_4，即使有100%的配体过剩，也不能实现对Mn2+的完全络合。在pH为6时，MnL1和MnL2与Zn2+的交换反应速度太快，不能继续进行。用变温H-1NMRD和O-17NMR测量了MnL1和MnL2的水交换和转动动力学信息。O-17化学位移表明，MnL1的单水化物种和双水化物种之间存在水合平衡，而MnL2为单水化物种。水交换在MnL1(k(Ex)(298)=1.2x10(9)S(-1))上比在onMnL(2)(k(Ex)(298)=1.2x10(7)S(-1))上快得多。小的内源性阴离子(磷酸盐、碳酸盐、柠檬酸)不会取代两个络合物中的配位水，但它们会导致它们缓慢分解。所有的Mn2+络合物对空气氧化都是稳定的。
A new class of macrocyclic ligands based on 1-oxa-4,7-diazacyclononane was synthesized and their Mn2+ complexes were investigated with respect to stability and relaxation properties. Each ligand has two pendant arms involving carboxylic (H2L1 - 1-oxa-4,7-diazacyclononane-4,7-diacetic acid), phosphonic (H4L2 - 1-oxa-4,7-diazacyclononane-4,7-bis(methylenephosphonic acid)), phosphinic (H2L3 - 1-oxa-4,7-diazacyclononane-4,7-bis(methylenephosphinic acid)) or phenylphosphinic (H2L4 - 1-oxa-4,7-diazacyclononane-4,7-bis[methylene(phenyl) phosphinic acid]) acid moieties. H2L3 and H2L4 were synthesized for the first time. The crystal structure of the Mn2+ complex with H2L4 confirmed a coordination number of 6 for Mn2+. The protonation constants of all ligands and the stability constants of their complexes with Mn2+ and some biologically or biomedically relevant metal ions were determined by potentiometry. The protonation sequence of H2L3 was followed by H-1 and P-31 NMR titration and the second protonation step was attributed to the second macrocyclic nitrogen atom. The potentiometric data revealed a relatively low thermodynamic stability of the Mn2+ complexes with all ligands investigated. For H2L3 and H2L4, full Mn2+ complexation cannot be achieved even with 100% ligand excess. The transmetallation of MnL1 and MnL2 with Zn2+ was too fast to be followed at pH 6. Variable temperature H-1 NMRD and O-17 NMR measurements have been performed on MnL1 and MnL2 to provide information on water exchange and rotational dynamics. The O-17 chemical shifts indicate hydration equilibrium between mono-and bishydrated species for MnL1, while MnL2 is monohydrated. The water exchange is considerably faster on MnL1 (k(ex)(298) = 1.2 x 10(9) s(-1)) than onMnL(2) (k(ex)(298) = 1.2 10(7) s(-1)). Small endogenous anions (phosphate, carbonate, citrate) do not replace the coordinated water in either of the complexes, but they induce their slow decomposition. All Mn2+ complexes are stable toward air-oxidation.