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Environmental chemistry 2020 -Anthraquinone and L-amino Acid Derivatives Schiff Base Cu(II) Complexes as a Mediator between Cathode of Biofuel Cell and Oxygen-reducing Laccase- Yuto Takeuchi- Tokyo University of Science

Yuto Takeuchi

 Abstract:

Background: Cathode materials of biofuel cells sometimes contain mediator (metal complexes) to enhance  electron transfer efficiency between electrode and laccase. Laccase is an enzyme which catalyzes four-electron reduction of oxygen to water.

Methods:

We have synthesized new four anthraquinone and L-amino acid (L-alanine, L-valine, L-leucin, and L-isoleucin) derivatives Schiff base Cu(II) complexes aiming at low cost materials using abundant Cu metal instead of Os or Ru metals employed commonly.

Conclusion:

By means of spectroscopic, electrochemical, and docking simulation studies, the complex of L-valine derivative ligand exhibited the best performance as a mediator among these four complexes in view of low reduction potentials, high current density, and appropriate docking features.

Keywords:

Biofuel cell; Oxygen reduction; Chiral Schiff base; Copper(II); Laccase

Introduction:

Laccase will not form the intermediate water-soluble peroxide, and can catalyze a four-electron reduction of molecular oxygen to water. This electron reduction, in a very  peptide polymer, is because of work by four Cu active sites. Cu sites of laccase are divided into three types largely from their features, called type 1 (S-coordinated blue copper), type 2 (normal), and type 3 (O-bridged dinuclear). The type 1 site is found in electron transport chain proteins, with the coordination of cysteine, because they exhibit a blue color due to the strong charge transfer (CT) transitions, also referred to as “blue copper”

Materials and Methods

General procedures

Chemicals of the highest commercial grade available (solvents from Kanto Chemical, organic compounds from Tokyo Chemical Industry and metal sources and MWCNT from Wako) were used as received without further purification. Laccase from Trametes versicolor was purchased from Sigma-Aldrich (St. Louis, MO USA). Basically, 2-hydroxy-9,10-dioxo-9,10-dihydroanthracene- 1-carbaldehyde was prepared as per the literature method (formylation) with modification of using a Biotage Initiator+ microwave synthesis device in trifluoroacetic acid at 403 K for 90 min .

Preparations of complexes 1-4:

Treatment of 2-hydroxy-9,10-dioxo-9,10-dihydroanthracene- 1-carbaldehyde (0.10 g, 0.40 mmol) and NaHCO3(0.034 g, 0.40 mmol), and L-alanine (0.036 g, 0.40 mmol) in a mixed solution of methanol (50 mL) and water (10 mL) at 333 K for 3 hr, copper(II) acetate monohydrate (0.080 g, 0.400 mmol) were added and stirred for 2 hr to give rise to green precipitates to be filtrated and washed with methanol. Complexes 2-4 were also prepared in similar procedures to 1 using L-valine, L-leucin, L-isoleucin, respectively, rather than of L-alanine. UV-vis and circular dichroism (CD) spectra and cyclic voltammogram (CV) were depicted in Supplementary Figures 1 and 2, respectively.

Docking of complex(1-4)+laccase:

For electrochemical or spectral measurements, hybrid materials of complex(1-4)+laccase to discuss docking of complex and laccase are prepared as complex solutions (6 μM in 70 mL wáter:metanol=9:1 solvent ) after addition of laccase by 1 mg as solutions of a similar  solvent.

Bottom Line: This work is partly presented at Environmental Chemistry and Engineering September 20-22, 2018 Berlin, Germany/ Golden Tulip Berlin – Hotel Hamburg