Zhang S, Wu K, Biewer M C, Sherry A D
Department of Chemistry, University of Texas at Dallas, P.O. Box 830688, Richardson, Texas 75083, USA.
Inorg Chem. 2001 Aug 13;40(17):4284-90. doi: 10.1021/ic0003877.
Lanthanide complexes of a tetra-amide derivative of DOTA (structure 4 in text) with four extended carboxymethyl esters have been characterized by X-ray crystallography and multinuclear NMR spectroscopy. Eu(4)(H(2)O)(3) crystallized from water in the monoclinic, P(21/)(c) space group (a = 10.366 A, b = 22.504 A, c = 23.975 A, and beta = 97.05 degrees ). The Eu(3+) cation is bound to four macrocyclic nitrogen atoms (mean Eu-N = 2.627 A) and four amide oxygen atoms (mean Eu-O(amide) = 2.335 A) in a square antiprismatic geometry with a twist angle of 38.5 degrees between the N4 and O4 planes. A single bound water molecule (Eu-O(W) = 2.414 A) occupies a typical monocapped position on the O4 surface. In pure water, resonances corresponding to a single Eu(3+)-bound water molecule were observed in the (1)H (53 ppm) and (17)O (-897 ppm) NMR spectra of Eu(4)(H(2)O)(3) at 25 degrees C. A fit of the temperature-dependent Eu(3+)-bound (1)H and (17)O water resonance line widths in acetonitrile-d(3) (containing 4% v/v (17)O enriched water) gave identical lifetimes (tau(m)(298)) of 789 +/- 50 micros (in water as solvent; a line shape analysis of the Eu(3+)-bound water resonance gave a tau(m)(298) = 382 +/- 5 micros). Slow water exchange was also evidenced by the water proton relaxivity of Gd(4) (R(1) = 2.2 mM(-1) s(-1), a value characteristic of pure outer-sphere relaxation at 25 degrees C). With increasing temperature, the inner-sphere contribution gradually increased due to accelerated chemical exchange between bound water and bulk water protons. A fitting of the relaxation data (T(1)) to standard SBM theory gave a water proton lifetime (tau(m)(298)) of 159 micros, somewhat shorter than the value determined by high-resolution (1)H and (17)O NMR of Eu(4). Exchange of the bound water protons in Gd(4) with bulk water protons was catalyzed by addition of exogenous phosphate at 25 degrees C (R(1) increased to 10.0 mM(-1) s(-1) in the presence of 1500-fold excess HPO(4)(2-)).
一种具有四个延伸羧甲基酯的DOTA四酰胺衍生物（文中结构4）的镧系元素配合物已通过X射线晶体学和多核NMR光谱进行了表征。Eu(4)(H₂O)₃从水中结晶，属于单斜晶系，P(21/)(c)空间群（a = 10.366 Å，b = 22.504 Å，c = 23.975 Å，β = 97.05°）。Eu(3+)阳离子以方形反棱柱几何构型与四个大环氮原子（平均Eu-N = 2.627 Å）和四个酰胺氧原子（平均Eu-O(酰胺) = 2.335 Å）配位，N4和O4平面之间的扭转角为38.5°。一个单键合水分子（Eu-O(W) = 2.414 Å）占据O4表面上一个典型的单帽位置。在纯水中，在25℃下Eu(4)(H₂O)₃的¹H（53 ppm）和¹⁷O（-897 ppm）NMR光谱中观察到与单个Eu(3+)键合水分子相对应的共振信号。对乙腈-d₃（含有4% v/v富集¹⁷O的水）中温度依赖性的Eu(3+)键合¹H和¹⁷O水共振线宽进行拟合，得到相同的寿命（τm(298)）为789±50微秒（以水为溶剂；对Eu(3+)键合水共振的线形分析给出τm(298) = 382±5微秒）。Gd(4)的水质子弛豫率（R₁ = 2.2 mM⁻¹ s⁻¹，这是25℃下纯外层弛豫的特征值）也证明了水交换缓慢。随着温度升高，由于键合水与大量水质子之间的化学交换加速，内层贡献逐渐增加。将弛豫数据（T₁）拟合到标准SBM理论得到水质子寿命（τm(298)）为159微秒，略短于通过Eu(4)的高分辨率¹H和¹⁷O NMR测定的值。在25℃下加入外源磷酸盐催化了Gd(4)中键合水质子与大量水质子的交换（在存在1500倍过量HPO₄²⁻的情况下，R₁增加到10.0 mM⁻¹ s⁻¹）。
