Rill Christoph, Kolar Zvonimir I, Kickelbick Guido, Wolterbeek Hubert Th, Peters Joop A
Institute of Materials Chemistry, Vienna University of Technology, A-1060 Vienna, Austria.
Langmuir. 2009 Feb 17;25(4):2294-301. doi: 10.1021/la803562e.
The temperature-dependent adsorption on hydroxyapatite (HAP) of the Tb complexes of two macrocyclic DOTA-like ligands containing HAP-binding phosphonate groups was studied by a radiotracer method using 160Tb as the label. One ligand (DOTP) contains four separate phosphonate groups, while the second ligand (BPPED) contains a single bisphosphonate group coupled via a phosphinate spacer group. The equilibrium isotherms were fitted by models according to Langmuir, Freundlich, Langmuir-Freundlich, Toth, and Dubinin-Radushkevich, with the Langmuir-Freundlich and the Toth models resulting in the best fits. These models take into account the energetic surface heterogeneity of HAP for the binding of the complexes, which was confirmed by the dependence of the reversibility of the adsorption on the complex concentration. The affinity of the Tb-BPPED complex toward the HAP surface was substantially higher than that of the Tb-DOTP complex. Thermodynamic parameters obtained from the temperature-dependence of the adsorption and the Van't Hoff relation showed that the adsorption of both complex types is endothermic and entropy-driven, due to dehydration of the complex and the HAP surface during adsorption. The kinetics of the adsorption were very fast, and of the tested models (pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich) only the Elovich model described the experimental data suitably. The activation energy of the adsorption was calculated by application of an Arrhenius-type relation, showing chemisorption for both complex types. Adsorption rates were reduced when HAP with larger particle size was used.
采用放射性示踪法，以(^{160}Tb)为标记，研究了两种含HAP结合膦酸酯基团的大环类DOTA配体的Tb配合物在羟基磷灰石（HAP）上的温度依赖性吸附。一种配体（DOTP）含有四个独立的膦酸酯基团，而第二种配体（BPPED）含有一个通过次膦酸酯间隔基团连接的双膦酸酯基团。根据朗缪尔、弗伦德利希、朗缪尔 - 弗伦德利希、托特和杜比宁 - 拉杜舍维奇模型对平衡等温线进行拟合，其中朗缪尔 - 弗伦德利希模型和托特模型拟合效果最佳。这些模型考虑了HAP表面对于配合物结合的能量表面非均质性，吸附可逆性对配合物浓度的依赖性证实了这一点。Tb - BPPED配合物对HAP表面的亲和力明显高于Tb - DOTP配合物。从吸附的温度依赖性和范特霍夫关系式获得的热力学参数表明，由于吸附过程中配合物和HAP表面的脱水，两种配合物类型的吸附都是吸热的且由熵驱动。吸附动力学非常快，在所测试的模型（伪一级、伪二级、颗粒内扩散和埃洛维奇）中，只有埃洛维奇模型能较好地描述实验数据。通过应用阿伦尼乌斯型关系式计算吸附活化能，表明两种配合物类型均为化学吸附。使用较大粒径的HAP时，吸附速率降低。
