Local structure analysis of short-lived reaction intermediates by means of a time-resolved stopped-flow extended X-ray absorption fine-structure technique

Three types of time-resolved stopped-flow extended X-ray absorption fine-structure (EXAFS) instruments have been developed by combining an EXAFS spectrometer equipped with the original time-resolved detection system and a stopped-flow unit to analyze the local structure around the metal center in short-lived reaction intermediates. The whole X-ray energy region used to obtain an EXAFS spectrum could be measured simultaneously for the instrument in the dispersive mode, and a. time-resolution on the order of ms has been acheived in the case of die instrument using synchrotron radiation as an X-ray source. By using these time-resolved stopped-flow EXAFS instruments, we have analyzed the local structure around the metal center in some short-lived reaction intermediates, such as a peroxochromium intermediate formed in a reduction reaction of chromate ion by hydrogen peroxide in an acidic aqueous solution; a Cu(II)/Hg(II) heterodinuclear porphyrin intermediate formed in the Cu(II) ion incorporation process into 5,10,15,20-tetrakis (4-sulfonatophenyl) porphyrin in the presence of the Hg(II) ion in water, and a chloride-bridged precursor intermediate formed in the inner-sphere reduction of CoCl(NH3)(5)(2+) by Fe2+ in N,N-dimethylformamide. According to the obtained local structure of the reaction intermediate, the reaction mechanisms and the structural characteristics of the reaction intermediates have been microscopically clarified.