Capillary Electrophoretic Reactor and Microchip Capillary Electrophoretic Reactor: Dissociation Kinetic Analysis Method for "Complexes" Using Capillary Electrophoretic Separation Process

A capillary electrophoresis (CE)-based unique methodology for the dissociation kinetic analysis of metal complexes, capillary electrophoretic reactor (CER), is described. The basic idea of CER is using the following CE separation process as a kind of reactor for the dissociation reaction of metal complexes. In the precapillary derivatization CE of the metal complex employing an electrophoretic buffer solution without chelating reagent, the metal complex, which migrates in its isolated bands along a capillary from those of free ligand and metal ions, is exposed to an overwhelming force causing dissociation by CE resolution because of the absence of the free ligand in the electrophoretic buffer solution. This on-capillary dissociation reaction follows first-order kinetics. In order to determine the dissociation rate constant (kd) of the metal complex, it is therefore necessary to analyze the decay of the residual ratio of the complex with the increase in reaction time as first-order decay reaction. In CER, the migration time of the metal complex is considered to be equal to the reaction time of the on-capillary dissociation reaction, and the residual ratio of the metal complex can be evaluated from the peak height. The dissociation degree-time profiles for the complexes are quantitatively described as the decay of the peak height absorbance of the metal complex with the increase in migration time using the data of a series of electropherograms with different migration times. The kd of the metal complex can be estimated by analyzing it directly, readily, and accurately. An application of CER to the dissociation kinetic analysis of biomolecular complexes was also described. CER proposed here also serves as an experimental approach for such moderately slow decay kinetics with a half-life of "min." CER-related methods for faster dissociation reactions with a half-life of "sec" and slower dissociation reactions with a half-life of "hour," microchip capillary electrophoretic reactor (μCER) and ligand substitution mode CER (LS-CER) are also described.