Studies On Photolysis Of Coenzyme B₁₂ And Its Model Compouds Using Photoacoustic Calorimetry

Coenzyme B12 (5'-deoxyladenosylcobalamin, AdoCbl), the only organo-metallic compound with biological activity in nature, serves as a cofactor for various enzymatic reactions related to metabolism and DNA synthesis. And in addition, it plays an important role in intramolecular rearrangement and nucleotide reduction. The homolytic cleavage of the Co-C bond is the essential step in the enzymatic catalysis. Accordingly, in order to provide insight into the function of coenzyme B12 and the mechanism of enzymatic catalysis, it is necessary to investigate the conformational change of corrin ring accompa-nying the Co-C bond homolysis, the Co-C bond dissociation energy, and the factors influencing the Co-C bond strength. With the development of techniques of laser and signal detection in the past decade, the photoacoustic method has been applied in various research fields, such as chemistry, physics, medicine and biology. Time-resolved photoacoustic calorimetry (PAC), also called laser-induced optoacoustic calorimetry (LIOAC), is a new method that quantitatively determines the energetics and conformational changes accom-panying laser-induced photochemical reactions and photo-biochemical reactions in nanosecond to microsecond timescales. We study the photolysis of coenzyme B12 and its model compounds using photoacoustic calorimetry to obtain dynamic and kinetic information and to give evidence of biological function and enzymatic mechanism for coenzyme B12 in organism.Based on PAC experiments and data analysis, the main works of this thesis are shown as follows:(1) Photoacoustic calorimetric investigations on photolysis of coenzyme B12 and alkyl cobalt-Schiff base complexes...