Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands.
Langmuir. 2012 Oct 16;28(41):14672-80. doi: 10.1021/la303143w. Epub 2012 Oct 1.
The dynamic sorption of an organic compound by nanoparticles (NPs) is analyzed by solid-phase microextraction (SPME) for the example case of the pharmaceutical diclofenac in dispersions of impermeable (silica, SiO(2)) and permeable (bovine serum albumin, BSA) NPs. It is shown that only the protonated neutral form of diclofenac is accumulated in the solid phase, and hence this species governs the eventual partition equilibrium. On the other hand, the rate of the solid/water partition equilibration is enhanced in the presence of the sorbing nanoparticles of SiO(2) and BSA. This feature demonstrates that the NPs themselves do not enter the solid phase to any appreciable extent. The enhanced rate of attainment of equilibrium is due to a shuttle-type of contribution from the NP-species to the diffusive supply of diclofenac to the water/solid interface. For both types of nanoparticulate complexes, the rate constant for desorption (k(des)) of bound diclofenac was derived from the measured thermodynamic affinity constant and a diffusion-limited rate of adsorption. The computed k(des) values were found to be sufficiently high to render the NP-bound species labile on the effective time scale of SPME. In agreement with theoretical prediction, the experimental results are quantitatively described by fully labile behavior of the diclofenac/nanoparticle system and an ensuing accumulation rate controlled by the coupled diffusion of neutral, deprotonated, and NP-bound diclofenac species.
以药物双氯芬酸在不可渗透（二氧化硅，SiO2）和可渗透（牛血清白蛋白，BSA）纳米颗粒分散体中的实例，分析了纳米颗粒（NPs）对有机化合物的动态吸附作用。通过固相微萃取（SPME）进行分析。结果表明，只有双氯芬酸的质子化中性形式被积累在固相相中，因此该物质控制最终的分配平衡。另一方面，在存在吸附 SiO2 和 BSA 的纳米颗粒的情况下，固/水分配平衡的速率得到增强。这一特征表明，纳米颗粒本身不会以任何可观的程度进入固相。平衡达到的增强速率是由于来自 NP 物质的穿梭型贡献，将双氯芬酸扩散供应到水/固界面。对于这两种类型的纳米颗粒复合物，从测量的热力学亲和常数和吸附的扩散限制速率导出了结合双氯芬酸的解吸（k(des)）速率常数。计算出的 k(des) 值足够高，使得 NP 结合的物质在 SPME 的有效时间尺度上不稳定。与理论预测一致，实验结果被双氯芬酸/纳米颗粒系统的完全不稳定行为以及中性、去质子化和 NP 结合的双氯芬酸物质的耦合扩散控制的积累速率定量描述。
