Department of Life Sciences, Faculty of Science and Technology, and Center of Neurosciences and Cell Biology, University of Coimbra, 3001-401 Coimbra, Portugal.
Inorg Chem. 2010 Mar 15;49(6):2969-74. doi: 10.1021/ic9025014.
Aqueous suspensions of metal organic frameworks (MOF) containing different Ln(3+) ions, consisting of a series of layered Ln(3+) networks formulated as [Ln(H(2)cmp)(H(2)O)] (where H(5)cmp is (carboxymethyl)iminodi(methylphosphonic acid), with a relatively wide size distribution (400 nm to 1 microm) were studied by relaxometry. The water (1)H longitudinal (r(1)) and transverse (r(2)) relaxivities were obtained for aqueous suspensions of these materials with different lanthanide ions. The values of r(1) are very small and varied only slightly with the effective magnetic moment (mu(eff)) of the lanthanide ions, while r(2) values are larger and proportional to the value of mu(eff)(2). The dependence of R(2) on tau(CP) (the time interval between two consecutive refocusing pulses in the train of 180 degrees pulses applied in a CPMG pulse sequence) was evaluated. The value of R(2) initially increases with tau(CP) and then saturates at higher tau(CP) at a value that is about 3 to 5 times lower than R(2p)*. This can be explained by the static dephasing regime (SDR) theory, in which the diffusion effect is taken into account and where the condition tau(D) > Delta omega(r(p))(-1) holds (tau(D) = r(p)(2)/D, where D is the diffusion coefficient, r(p) is the radius of the particle, and Delta omega(r(p)) is the Larmor frequency shift at the particle's surface). Separation of the particles into two fractions with different particle sizes led to a significant enhancement of the r(2) relaxivity of the smaller particles with a narrow size distribution. Magnetometric measurements performed with the particles containing Dy(III), Ho(III), and Gd(III) showed a typical paramagnetic behavior from 4 to 100 K, used to determine the Curie constants.
水相悬浮液中的金属有机框架（MOF）含有不同的Ln（3+）离子，由一系列层状 Ln（3+）网络组成，其化学式为[Ln（H（2）cmp）（H（2）O）]（其中 H（5）cmp 是（羧甲基）亚氨基二（甲基膦酸），具有相对较宽的尺寸分布（400nm 至 1μm），通过弛豫率进行了研究。对于这些具有不同镧系元素离子的材料的水悬浮液，获得了水（1）H 纵向（r（1））和横向（r（2））弛豫率。r（1）的值非常小，并且仅随镧系元素离子的有效磁矩（μ（eff））略有变化，而 r（2）值较大，并且与μ（eff）（2）的值成正比。评估了 R（2）对 tau（CP）（在应用于 CPMG 脉冲序列的 180 度脉冲序列的连续脉冲串中的两个连续重聚焦脉冲之间的时间间隔）的依赖性。R（2）的值最初随 tau（CP）而增加，然后在较高的 tau（CP）下饱和，其值比 R（2p）*低约 3 到 5 倍。这可以通过静态去相位（SDR）理论来解释，其中考虑了扩散效应，并且满足 tau（D）> Delta omega（r（p））（-1）的条件（tau（D）= r（p）（2）/D，其中 D 是扩散系数，r（p）是粒子的半径，Delta omega（r（p））是粒子表面处的拉莫尔频率偏移）。将粒子分为两个具有不同粒径的分数，导致较小粒径的粒子的 r（2）弛豫率显着提高，且粒径分布较窄。用包含 Dy（III），Ho（III）和 Gd（III）的粒子进行的磁测量显示，从 4 到 100 K 的典型顺磁行为，用于确定居里常数。
