Complexation properties of N,N′,N",N′"-[1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayltetrakis(1-oxoethane-2,1-diyl)]tetrakis[glycine] (H4dotagl).: Equilibrium, kinetic, and relaxation behavior of the lanthanide(III) complexes
Complexation properties of N,N′,N",N′"-[1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayltetrakis(1-oxoethane-2,1-diyl)]tetrakis[glycine] (H4dotagl).: Equilibrium, kinetic, and relaxation behavior of the lanthanide(III) complexes
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DOI：
10.1002/hlca.200590042
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发表时间：
2005-01-01
影响因子：
1.8
通讯作者：
Zékány, L
中科院分区：
文献类型：
--
作者：
Baranyai, Z;Brücher, E;Zékány, L
Eu ~（3+）、Dy ~（3+）和Yb ~（3+）的四酰亚胺N，N '，N "，N“-[1，4，7，10-四氮杂环十二烷-1，4，7，10-四基四（1-氧代乙烷-2，1-二基）]四[甘氨酸]（H（4）dotagl）配合物是MRI中潜在的CEST造影剂。在[Ln（dotagl）]配合物中，Ln（3+）离子处于四个环N原子和酰胺O原子给体原子形成的笼中，H2O分子占据第九个配位。[Ln（dotagl）]配合物的稳定常数约为。比[Ln（dota）]类似物（H（4）dota = 1，4，7，10-四氮杂环十二烷-1，4，7，10-四乙酸）低10个数量级。[Ln（dotagl）]中的游离羧酸根基团在pH 1-5范围内质子化，产生单质子化、二质子化、三质子化和四质子化物质。与二价金属（Mg 2+、Ca 2+和Cu 2+）的络合物也具有相对低的稳定性。在pH > 8时，Cu 2+形成羟基络合物;然而，由于不存在锚N-原子，酰胺H-原子不会解离，这是环的刚性结构的结果。[Gd（dotagl）]的弛豫率从10度到25度减小，然后在30度到50度之间增加。这一不寻常的趋势与低H2O交换率解释。[Ln（dotagl）]络合物缓慢形成，通过平衡形成单质子化中间体，其在缓慢的OH-催化反应中去质子化并重排为产物。形成速率低于相应的Ln（dota）配合物。[Eu（dotagl）]的解离速率与[H+]（0.1 - 1.0mHClO_4）成正比，[Eu（H（4）dotagl）]的质子辅助解离速率较低（k（1）= 8.1（.）10（-6）m（-1）s（-1））比[Eu（dota）]（k（1）= 1.4（.）10（-5）m（-1）s（-1））。
Eu3+,Dy3+, and Yb3+ complexes of the dota-derived tetramide N,N ',N '',N '''-[1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayltetrakis(1-oxoethane-2,1-diyl)]tetrakis[glycine] (H(4)dotagl) are potential CEST contrast agents in MRI. In the [Ln(dotagl)] complexes, the Ln(3+) ion is in the cage formed by the four ring N-atoms and the amide O-atom donor atoms, and a H2O molecule occupies the ninth coordination site. The stability constants of the [Ln(dotagl)] complexes are ca. 10 orders of magnitude lower than those of the [Ln(dota)] analogues (H(4)dota = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). The free carboxylate groups in [Ln(dotagl)] are protonated in the pH range 1-5, resulting in mono-, di-, tri-, and tetraprotonated species. Complexes with divalent metals (Mg2+, Ca2+, and Cu2+) are also of relatively low stability. At pH > 8, Cu2+ forms a hydroxo complex; however, the amide H-atom(s) does not dissociate due to the absence of anchor N-atom(s), which is the result of the rigid structure of the ring. The relaxivities of [Gd(dotagl)] decrease from 10 to 25 degrees, then increase between 30-50 degrees. This unusual trend is interpreted with the low H2O-exchange rate. The [Ln(dotagl)] complexes form slowly, via the equilibrium formation of a monoprotonated intermediate, which deprotonates and rearranges to the product in a slow, OH--catalyzed reaction. The formation rates are lower than those for the corresponding Ln(dota) complexes. The dissociation rate of [Eu(dotagl)] is directly proportional to [H+] (0.1 - 1.0m HClO4); the proton-assisted dissociation rate is lower for [Eu(H(4)dotagl)] (k(1) = 8.1 (.) 10(-6) m(-1) s(-1)) than for [Eu(dota)] (k(1) = 1.4 (.) 10(-5) m(-1) s(-1)).