No abstract

Chitosans, derived from the abundant natural resource chitin, are among the most versatile and promising functional biopolymers due to their unique physicochemical properties and biological activities. These can be further improved or modified by various functionalizations, targeting both the hydroxy and amino groups. However, the chemical routes used for functionalization typically use harsh chemicals, increasing the ecological footprint of the products, tend to yield low degrees of substitution, and often lack chemoselectivity. We here report on an alternative, biocatalytic route of chitosan N-acylation using a recombinant chitin deacetylase (CDA). These enzymes are known for their ability to chemo- and regioselectively N-acetylate glucosamine oligomers, and they were recently shown to also exhibit this reverse activity toward polyglucosamine, yielding partially acetylated chitosan polymers with a nonrandom pattern of acetylation. As chitin deacetylases can possess a certain cosubstrate promiscuity, we explored the ability of a CDA from the fungus Colletotrichum lindemuthianum (ClCDA) to N-acylate glucosamine tetramers and polyglucosamines using a range of small carboxylic acids as cosubstrates. The resulting tetramers were analyzed using ultra-high-performance hydrophilic liquid chromatography-tandem mass spectrometry (UHPLC-HILIC-MS), and the kinetic parameters of the acylation reactions thus determined gave deeper insight into the limitation of the cosubstrate scope of ClCDA. Using polyglucosamines as substrates, we obtained N-propiolated chitosan polymers with high fractions of substitution of 0.7. Copper-catalyzed azide–alkyne cycloaddition (CuAAC) then yielded a fluorescence-labeled polymer, providing proof-of-principle for click functionalization of chitosans using this chemoenzymatic approach. Given the known regioselectivity of chitin deacetylases, which is retained during reverse N-acetylation, this process might give access to a broad variety of functionalized chitosans with nonrandom substitution patterns.

The increasing demand for lithium ion batteries consequently involves research on environmentally benign materials and processing routes. Environmentally friendly cobalt‐free, and fluorine‐free electrodes processed without organic solvents were targeted as this approach combines high work safety and sustainability with good electrochemical performance. In this study, chitosan‐based biopolymers were synthesized and systematically investigated for the first time as “green” binders for positive electrodes utilizing LiMn2O4 (LMO). In particular, chitosans with different specifically designed low and high degrees of polymerization (DP), each with comparable degree of acetylation (DA), revealed insights into the impact on the mechanical and electrochemical performance of LMO positive electrodes. Herein, low DP chitosan provided twice the adhesion strength compared to the state‐of‐the‐art binder polyvinylidene difluoride (PVdF) in LMO electrodes, thus, showing the opportunity to reduce the binder content and increase the specific energy. Electrodes with DA<16 % chitosan‐based binder could deliver higher discharge capacities than cathodes using PVdF or chitosans with DA>16 % in LMO||Li metal cells. Cross‐linking of chitosans with citric acid (CA) was demonstrated to significantly increase the discharge capacity up to 80 mAh g−1 at 10 C charge/discharge rate.

Hybrid electrolytes are developed to meet the requirements of safety, performance, and manufacturing for electrolytes suitable for Li-ion batteries with Li-anodes. Recent challenges-in addition to these key properties-emphasize the importance of sustainability. While compromising between these three objectives, the currently available materials are still well below the targeted goals. Three important issues for the design of hybrid electrolytes are (i) the role of the morphology and surface state of the ceramic particles in the polymer matrix, (ii) the dependence of salt concentration and ionic conductivity and, (iii) the effects of substituting part of the polyethylene oxide (PEO), with biopolymers. Electrolyte films were prepared from PEO, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZO:Ta), and biopolymers with varying contents of these components by a solution casting method. The films were analyzed with respect to structural and microstructural characteristics by DSC, Raman spectroscopy, and SEM. Ionic conductivity was evaluated by electrochemical impedance spectroscopy. Most interesting, when comparing films with LLZO:Ta versus without, the content of LiTFSI required for the maximum conductivity in the respective systems is different: a higher LiTFSI concentration is required for the former type. Overall, addition of LLZO:Ta as well as partial substitution of PEO by chitosan mesylate or cellulose acetate decrease the ionic conductivity. Thus-at least in the present approaches-a loss in performance is the drawback from attempts to enhance the safety by LLZO:Ta additions and sustainability by biopolymer blending of hybrid electrolytes.