Environment-Friendly Cathodes Using Biopolymer Chitosan with Enhanced Electrochemical Behavior for Use in Lithium Ion Batteries

The biopolymer chitosan has been investigated as a potential binder for the fabrication of LiFePO₄ cathode electrodes in lithium ion batteries. Chitosan is compared to the conventional binder, polyvinylidene fluoride (PVDF). Dispersion of the active material, LiFePO₄, and conductive agent, Super P carbon black, is tested using a viscosity analysis. The enhanced structural and morphological properties of chitosan are compared to the PVDF binder using X-ray diffraction analysis (XRD) and field emission scanning electron microscopy (FE-SEM). Using an electrochemical impedance spectroscopy (EIS) analysis, the LiFePO₄ electrode with the chitosan binder is observed to have a high ionic conductivity and a smaller increase in charge transfer resistance based on time compared to the LiFePO₄ electrode with the PVDF binder. The electrode with the chitosan binder also attains a higher discharge capacity of 159.4 mAh g^–1 with an excellent capacity retention ratio of 98.38% compared to the electrode with the PVDF binder, which had a discharge capacity of 127.9 mAh g^–1 and a capacity retention ratio of 85.13%. Further, the cycling behavior of the chitosan-based electrode is supported by scrutinizing its charge–discharge behavior at specified intervals and by a plot of d<i>Q</i>/d<i>V</i>

Structural comparison between isoliquiritigenin-bound <i>Da</i>CHI1 and liquiritigenin-bound <i>Ms</i>CHI.

<p>(A) Isoliquiritigenin (orange)-bound <i>Da</i>CHI1 and liquiritigenin (yellow)-bound <i>Ms</i>CHI structures are shown. (B) Liquiritigenin-binding mode of <i>Ms</i>CHI. (C) Superposition of isoliquiritigenin (orange)-bound <i>Da</i>CHI1 (dark gray) and liquiritigenin (yellow)-bound <i>Ms</i>CHI (light gray) structures. Overall ligand-binding modes differed markedly between the two complexes; the liquiritigenin-binding position was shifted deep into the active site cavity in <i>Ms</i>CHI as compared to isoliquiritigenin binding in <i>Da</i>CHI1. Conformational differences between the two structures were also observed at the Arg34 position (Arg36 in <i>Ms</i>CHI) and in the β6–β7 loop region.</p

Data collection and refinement statistics.

<p>Data collection and refinement statistics.</p

Crystal structure of <i>Da</i>CHI1 and multiple sequence alignment of CHI proteins.

<p>(A) Overall structure of unliganded <i>Da</i>CHI1, shown as a ribbon diagram. α-Helices and β-strands are colored cyan and orange, respectively. (B) Overall structure of isoliquiritigenin-complexed <i>Da</i>CHI1, shown as a ribbon diagram. The bound ligand is shown as a stick model with a Fo-Fc electron density map (contoured at 3σ). (C) Multiple sequence alignment of <i>Da</i>CHI1, <i>Zm</i>CHI (<i>Zea mays</i>; UniProtKB code Q08704), <i>At</i>CHI (PDB code 4DOI; UniProtKB code P41088), <i>Vv</i>CHI (<i>Vitis vinifera</i>; NCBI reference sequence NP_001268033.1), <i>Ph</i>CHI (<i>Petunia hybrida</i>; UniProtKB code P11651), <i>Ip</i>CHI (<i>Ipomoea purpurea</i>; UniProtKB code O22604), <i>Ms</i>CHI (<i>Medicago sativa</i>; UniProtKB code P28012), <i>Pv</i>CHI (<i>Phaseolus vulgaris</i>; NCBI reference sequence XP_007142690.1), and <i>Ps</i>CHI (<i>Pisum sativum</i>; UniProtKB code P41089). Strictly and partially conserved residues are shaded black and gray, respectively. Two residues for distinguishing between type I and II CHI are indicated by black circles above the sequence alignment. Secondary structures obtained from the crystal structure of <i>Da</i>CHI1 are shown above the aligned sequence. Multiple sequence alignment was performed with ClustalX and was edited with the GeneDoc program.</p

<i>Da</i>CHI1 ligand-binding site.

<p>(A) Empty ligand-binding site and (B) active site residues of the unliganded <i>Da</i>CHI1 structure. The isoliquiritigenin binding mode of <i>Da</i>CHI1 is shown. The ligand is depicted as a stick figure with green carbon atoms; interacting residues of <i>Da</i>CHI1 are shown as bright orange sticks. Hydrogen bonds with bound isoliquiritigenin are indicated by a red dotted line. (C) Structural superposition of the ligand-binding regions of unliganded <i>Da</i>CHI1 (cyan) and isoliquiritigenin (green)-bound <i>Da</i>CHI1 (bright orange) showing the closing of the β3–β4 region by ligand binding. Hydrophobic interactions are indicated by yellow dotted lines.</p

<i>DaCHI1</i> transcription under cold and UV irradiation treatments.

<p>Plants grown at 16°C and 30 μmol m⁻² s⁻¹ light were subjected to cold and UV-B stress. Plants were exposed to a temperature of 0°C for 2 days or UV-B irradiation (2 kJ m⁻² day⁻¹) for 1 day after 1-day dark adaptation. RNAs extracted from leaves of stress-treated plants were used for RT-PCR of the <i>DaCHI1</i> gene, with 18S rRNA as an internal control.</p

Steady-state kinetic parameters of wild-type and mutant <i>Da</i>CHI1.

<p>Steady-state kinetic parameters of wild-type and mutant <i>Da</i>CHI1.</p

Activity and stability of <i>Da</i>CHI1.

<p>(A) Effects of temperature on <i>Da</i>CHI1 activity. Enzymatic activity was evaluated in the temperature range of 0–70°C in 50 mM potassium phosphate buffer (pH 7.6). Activity is expressed as a percentage of the maximum activity (100%). (B) Effects of temperature on the stability of <i>Da</i>CHI1. The enzyme was pre-incubated for 30 min at temperatures ranging from 0–60°C. Residual activity was measured at 25°C. (C) pH dependence of <i>Da</i>CHI1 activity. The reaction was carried out at 25°C in buffers with pH ranging from 3.0 to 10.0. The following buffers were used: pH 3.0–6.0, 50 mM citrate; pH 6.0–8.0, 50 mM potassium phosphate; and pH 8.0–10.0, 50 mM Tris-HCl. All measurements were made in triplicate.</p

Antioxidant flavonoids produced by <i>Da</i>CHI1 in response to various types of oxidative stresses.

<p>Substrate structures and specificities of type I and II CHIs are shown. CHS, chalcone synthase; PKR, NADPH-dependent chalcone reductase.</p

Crystal structure and enzymatic properties of chalcone isomerase from the Antarctic vascular plant <i>Deschampsia antarctica</i> Desv.

<div><p>Chalcone isomerase (CHI) is an important enzyme for flavonoid biosynthesis that catalyzes the intramolecular cyclization of chalcones into (S)-flavanones. CHIs have been classified into two types based on their substrate specificity. Type I CHIs use naringenin chalcone as a substrate and are found in most of plants besides legumes, whereas type II CHIs in leguminous plants can also utilize isoliquiritigenin. In this study, we found that the CHI from the Antarctic plant <i>Deschampsia antarctica</i> (<i>Da</i>CHI1) is of type I based on sequence homology but can use type II CHI substrates. To clarify the enzymatic mechanism of <i>Da</i>CHI1 at the molecular level, the crystal structures of unliganded <i>Da</i>CHI1 and isoliquiritigenin-bound <i>Da</i>CHI1 were determined at 2.7 and 2.1 Å resolutions, respectively. The structures revealed that isoliquiritigenin binds to the active site of <i>Da</i>CHI1 and induces conformational changes. Additionally, the activity assay showed that while <i>Da</i>CHI1 exhibits substrate preference for naringenin chalcone, it can also utilize isoliquiritigenin although the catalytic activity was relatively low. Based on these results, we propose that <i>Da</i>CHI1 uses various substrates to produce antioxidant flavonoids as an adaptation to oxidative stresses associated with harsh environmental conditions.</p></div