Takashi Matsuo's Research Interests
|Top page|Profile|Publication List|

　　Takashi Matsuo has been interested in the reactivities of porphyrinoids both in solvent bulk and in protein matrices. Especially, porphyrinoids with different arrangements of pyrroles rings from that of porphyrin (e.g. porphycene) are attractive from the aspect of molecular design including the development of new catalysts and protein engineering. 　He has investigated the syntheses and the reactivities of porphyrin and its isomers, based on bioinorganic chemistry, coordination chemistry and physical organic chemistry.

1. Porphyrinoid Chemistry in Protein Matrices
　Metal complexes included in protein matrices show us unique reactivities because of the special reaction environments and steric protection by protein matrices, which are difficult to see for the corresponding model compounds in organic solvents. For example, horseradish peroxidase (HRP), a heme-containing oxidase, has the remarkable catalytic oxidation activity, where the observable high-valent species(Fe(IV)=O) are generated. We successfully detected the Fe(IV)=O species of an iron porphycene, a structural isomer of porphyrin, by incorporating it into HRP and characterized by UV-vis spectroscopy. The reactivities of these high-valent species were also investigated by kinetic measurements.
　【in detail】　J. Am. Chem. Soc. 2007, 129, 12906-12907

2. Non-aromatic Porphyrinoids
　Porphyrin is a typical 18-pi conjugated macrocycle, and could, in theoretical, form the corresponding 20-pi conjugated form by injecting 2 electrons and 2 protons. However, such 20-pi conjugated form is extremely unstable and difficult to isolate. Recently, we found that the 20-pi conjugated porphycene with trifluoromethyl groups in the periphery of the framework is isolable and possible to be characterized by X-ray crystallography. This result is explained by positively shifted reduction potential of the macrocycle.
　【in detail】　Org. Lett. 2007, 9, 5303-5306

　

3. Ligand Binding Properties of Reconstituted Myoglobin with Iron Porphycene: Extremely High O2Affinity
　Myoglobin is an oxygen-storage hemoprotein and plays an important role in our bodies. To enhancement O2 of myoglobin is one of the challenging subject from the viewpoint of protein engineering and bioinorganic chemistry. Recently, we successfully prepared a reconstituted myoglobin having the extremely high O2 affinity by using an iron porphycene as a prosthetic group. The O2 affinity of the reconstituted myoglobin is 2,600-fold higher than that of the native myoglobin. Surprisingly, unusual O2 selectivity against CO was also found. Some physicochemical measurements have disclosed that the iron porphycene has very unique characteristics in the protein matrix.
　【in detail】　J. Am. Chem. Soc. 2007, 129, 12906-12907


4. Construction of Myoglobin Having a Mediator of Electron Transfer
　Myoglobin and cytochrome P450 are hemoproteins having the same prosthetic group, protoheme IX and play significant roles in vivo. However their functions are quite different: Myoglobin reversibly binds a dioxygen, whereas cytochrome P450 reductively activates a dioxyen into a highly reactive oxidant (Fe(IV)=O porphyrin pi-cation radical) by using the unique system for electron transmittance. One reason for the inability of dioxygen activation in myoglobin is that myoglobin has no efficient electron pathway. Then, we attempted to convert myoglobin into a dioxygen-activating protein like P450 by introducing an artificial electron pathway. Concretely, we prepared a myoglobin having a flavin, a mediator of electron transfer, (namely "flavomyoglobin") by the reconstitutional method. The reconstituted myoglobin can catalyze deformylation, one of the typical reaction catalyzed by P450, by receiving electrons from NADH, which stems from the smooth electron transmittance from NADH to the hemin via flavin. To the best of our knowledge, this is the first example that shows reductive activation of dioxygen by myoglobin.
　【in detail】　J. Am. Chem. Soc. 2002, 124, 11234-11235



5. Clarification of the Role of Heme-propionates in the Function of Myoglobin
　Protoheme IX, the prosthetic group of myoglobin, is composed of a porphyrin framework and two propionates (6-propionate and 7-propionate). It has been recognized that the propionates play a role of an "anchor" in the heme pocket by hydrogen bondings with some amino acid residues (vide infra), resulting in the stabilization of myoglobin structure. These hydrogen bondings are expected to affect not only thermal stability of myoglobin but also FUNCTION (dioxygen binding) of myoglobin. Then, in order to investigate the role of the propionates in the function of myoglobin not by mutagenesis but by organic synthesis, we prepared the reconstituted myoglobin having propionate-truncated hemes synthesized. The results of kinetic measurements for ligand bindings to the reconstituted myoglobins indicate that the existence of the heme-propionates is essential to the function of myoglobin. The structural analysis by paramagnetic 1H NMR shows that the hydrogen bondings between the heme-propionates and the protein matrix control the structure of the active site of myoglobin, which is correlated with ligand affinity of myoglobin.
　【in detail】　J. Inorg. Biochem. 91, 94-100 (2002)



6. Study on Reaction Mechanism of Serine Proteases from the Viewpoint of Enzyme Fluctuation
　It has been proposed that extraordinary acceleration of a chemical reaction by an enzyme is achieved not only by chemical catalysis at the active site but also by such physical actions as conformational fluctuations of an enzyme. According to induced-fit theory, multi-point interactions between an enzyme and a suitable substrate induce the conformational change of an enzyme during thermal fluctuation so that reactive groups at the active site are forced to take the optimal position for the catalysis. The fluctuations of an enzyme is regarded as Brownian motions and affected by medium viscosity. Then, we investigated effects of medium viscosity on kinetic parameters of serine proteases (e.g. alpha-chymotrypsin etc.) and elucidated the significance of conformational fluctuation of the enzyme for their catalytic activity. Based upon the experimental data, we proposed the novel reaction mechanism of serine proteases from the viewpoint of enzyme fluctuations. In a fluctuation-controlled reaction, the thermal equilibrium between the ground state and the transition state, the assumption in Eyring's transition state theory (TST), fails. Therefore, the experimental data in this research were applied to Sumi-Marcus theory in which the two-dimensional potential is proposed.
　【in detail】　J. Chem. Soc. PerkinTrans 2 887-891 (2000)
　　　　　　　　　Bull. Chem. Soc. Jpn 71, 2187-2196 (1998)



7. Electronic Properties of Alternative Fluorocarbon Refrigerants under High Pressure
　Since 90's, the electronic properties of environmentally acceptable refrigerants (alternative Freon) are necessary to give operational values for some of the design parameters of machinery used in the air-conditioning and refrigeration industry. Then, relative permittivity and resistivity of some HFCs (Hydrofluorocarbons), the candidate of alternative Freon, were measured under high pressure (up to 50 MPa) in 1996. The apparatus employed for the measurements was designed and constructed by us. Based upon the experimental data, the apparent dipole moments of the HFCs under high density were calculated by Kirkwood equation. (Unfortunately, HFCs are now proposed to be an origin of green effect and to be unacceptable materials as an alternative Freon.)