Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands.
Langmuir. 2012 Jan 10;28(1):227-34. doi: 10.1021/la203602y. Epub 2011 Dec 19.
The chemodynamics of metal complexes with nanoparticulate complexants can differ significantly from that for simple ligands. The spatial confinement of charged sites and binding sites to the nanoparticulate body impacts on the time scales of various steps in the overall complex formation process. The greater the charge carried by the nanoparticle, the longer it takes to set up the counterion distribution equilibrium with the medium. A z+ metal ion (z > 1) in a 1:1 background electrolyte will accumulate in the counterionic atmosphere around negatively charged simple ions, as well as within/around the body of a soft nanoparticle with negative structural charge. The rate of accumulation is often governed by diffusion and proceeds until Boltzmann partition equilibrium between the charged entity and the ions in the medium is attained. The electrostatic accumulation proceeds simultaneously with outer-sphere and inner-sphere complex formation. The rate of the eventual inner-sphere complex formation is generally controlled by the rate constant of dehydration of the metal ion, k(w). For common transition metal ions with moderate to fast dehydration rates, e.g., Cu(2+), Pb(2+), and Cd(2+), it is shown that the ionic equilibration with the medium may be the slower step and thus rate-limiting in their overall complexation with nanoparticles.
金属配合物与纳米颗粒配合剂的化学动力学与简单配体有很大的不同。带电荷的位点和结合位点在纳米颗粒主体内的空间限制影响了整个配合物形成过程中各个步骤的时间尺度。纳米颗粒所带的电荷越大，与介质达到抗衡离子分布平衡所需的时间就越长。在 1:1 的背景电解质中，带正电荷 z+的金属离子（z > 1）将在带负电荷的简单离子的反离子气氛中以及带负结构电荷的软纳米颗粒的体内/周围积聚。积累的速度通常由扩散控制，并一直进行，直到达到带电实体与介质中离子之间的 Boltzmann 分配平衡。静电积累与外球和内球配合物的形成同时进行。最终内球配合物形成的速度通常由金属离子的脱水速率常数 k(w)控制。对于具有中等至快速脱水速率的常见过渡金属离子，例如 Cu(2+)、Pb(2+)和 Cd(2+)，可以看出与介质的离子平衡可能是较慢的步骤，因此在它们与纳米颗粒的整体络合中是限速步骤。
