| Research Abstract |
The purpose of this study was to develop the Variable Rate Flow (VRF) instrument in order to determine the rate constants for the fast thermal reactions with the rate constant of ca. 10^6 s^<-1> (the half-life of ca. 0.5 μs) occurred in solutions. In the VRF instrument, the flow rate of the mixed solution is controlled with the high accuracy and the change in the transmitted light intensity is measured by varying the flow rate.
In order to achieve the purpose, we first modified the commercial VRF instrument to introduce the 10-jet mixing chamber and the piston cylinder which is connected with a high-power servo motor controlled automatically. Then we developed the data reduction system to collect the output signals from the encoder of the servo motor to measure the flow velocity and from the photomultiplier detector to measure the transmitted light intensity.
By using the newly developed VRF instrument, the kinetic measurements for the fast complexation reactions of Cu(II) and Zn(II) ion
… More
s were systematically performed in acetonitrile. It has been too difficult to measure directly the complexation reactions for these metal(II) ions because of their lability. Owing to the development of the VRF instrument, it becomes possible to monitor directly and to determine the rate constants. For the Cu(II) ion, the complexation reactions with some porphyrins were measured, and the formation mechanisms of the Sitting-Atop intermediate, which is existed during the dynamic processes of the metalation reaction, have been clarified. An unique trend of the observed rate constants is interpreted in terms of the axially-elongated distorted octahedral solvation structure of the Cu(II) ion and the limited axial-equatorial interconversions of the substituted Cu(II) species. For the Zn(II) ion, the complexation rate constants with some aromatic amine ligands were successfully determined. Especially in the case of the multidentate ligand, such as 2,2'- bipyridine, an unknown pathway for the complexation reaction was suggested kinetically according to the dependency of the rate constant as a function of the widely-variable concentration of the Zn(II) ion. Less
|
