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Title:
Several physical properties of hybrid materials of laccase and chiral azo-amino acid Schiff base copper complexes |
Abstract:
Laccase is an enzyme that catalyzes the four-electron reduction of oxygen to water. Taking advantage of this property, laccase is used as a cathode catalyst in enzymatic biofuel cells. Azo-Schiff base copper(II) is known to act as an excellent mediator between biofuel cell electrodes and laccase. Azobenzene is one of the most used optical switches because it has a high quantum yield, is stable, and easy to synthesize derivatives. In this study, we newly synthesized some amino-acid derivative Schiff base copper(II) complexes containing an azobenzene moiety (Figure) [1], and while comparing it with other amino acid derivative complexes, we investigated cis-trans photoisomerization or pH and temperature dependence of the redox potential and the associated mediator effects.
DFT calculations suggested that the orbital energy level and maximum light absorption wavelength change due to cis-trans photoisomerization of the azobenzene moiety; the azobenzene moiety is in the stable trans form and in the (unstable) cis form after UV light irradiation. The cyclic voltamgram (CV) of the redox behavior of the threonine derivative complex proved the effect of isomerization. In the CV experimental results, the change in the amount of current of the oxidation wave was remarkable. Furthermore, we modified the laccase electrode with the complex, irradiated it with visible/ultraviolet light, and evaluated it as a mediator.
In the CV experiment results for phosphate buffer solutions containing the complex alone (pH 6.5, 7.5, 8.0), the change in current amount was significant. The arginine moiety of the ligand has a guanidine group that easily protonates under acidic conditions and is sensitive to pH changes. For this reason, it is thought that on the basic side, the amount of current tended to increase, although the change in redox potential was small, due to changes in the molecular structure associated with the elimination of protons. On the other hand, on the acidic side, which approaches the optimum pH of laccase at 4, guanidine hydrochloride is known to work as a protein refolding agent (denaturing agent) and as a solubilizing agent for poorly soluble organic compounds in water. These properties are rather expected to disadvantage the oxygen reduction catalytic function of laccase.
For CV measurement, phenylalanine derivative copper(II) complex + carbon nanotubes + ultrapure water), 25% glutaraldehyde, and (laccase + Nafion) were sequentially dropped onto the surface of the working electrode and dried to form a modified electrode. It was carried out in a buffer solution (pH 7.0). CV measurements were performed at 0 ˚C, 25 ˚C, 40 ˚C, and 60 ˚C to evaluate the reducing ability of mediator oxygen. Details will be presented at the conference.
References
Y. Kuroda, R. Miyazaki, D. Shimonishi, D. Nakane, T. Akitsu, "Coordination and Photoisomerization of Azobenzene-Amino Acid Schiff Base Copper(II) Complexes to Lysozyme", Journal of Materials Science and Chemical Engineering, 11, 34-44 (2023). DOI: 10.4236/msce.2023.113003
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Biography:
Takashiro Akitsu is Professor of Chemistry at Department of Chemistry, Faculty of Science Division II, Tokyo University of Science, Japan since 2016. He graduated from Department of Chemistry, Osaka University in 1995. By studying crystal and electronic structures of chiral copper complexes, he obtained his Ph.D. from from Osaka University in 2000. Dr. Akitsu studied at the Institute for Protein Research (metalloproteins), Department of Chemistry, Keio University (photo and magnetic functional organic/inorganic hybrid compounds), and Department of Chemistry at Stanford University (physical and bioinorganic chemistry) before moving to Tokyo University of Science. He has published about 220 articles and book chapters. He has also served as an editorial board member and peer reviewer for many journals and was involved in the organizing committees for international conferences. His research field is inorganic coordination chemistry and crystalography. His research interest is hybrid materials of (Schiff base) metal complexes and other (photo-)funtional materials such as polymers, dyes or proteins.
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