Ionic Liquids (ILs) are a class of solvents formed by combining an organic cation with a suitable organic or inorganic anion, and they possess fascinating properties such as high thermal-chemical stability, negligible vapor pressure, and tunability. These characteristics make them suitable for various applications, including catalysis, separation, purification, extraction, and electrochemistry1. The diazabicyclo [5.4.0] undec-7-ene (DBU) is a base catalyst commonly used in organic synthesis and polymerization reactions, and it can be utilized to synthesize stable ILs. However, this class of ILs is less explored compared to the commonly studied imidazolium and ammonium based ILs. In this study, we investigate the potential use of DBU-based ILs for various biopolymer-related applications.
The growing demand for lignocelluloses as a renewable bio-feedstock is a result of the depletion of non-renewable resources like coal and oil. Various pretreatment methods have been proposed to effectively utilize lignocellulose as an abundant resource, but none have been proven to be both efficient and environmentally friendly2. To address this issue, we synthesized DBU-based protic ILs with varying basicity and utilized them for the pretreatment of rice straw. The effectively pretreated solid was analyzed using various techniques like PXRD, SEM, FTIR Spectrum, and TGA. Additionally, we investigated physicochemical and viscometric properties of ternary systems consisting of the IL, DMSO, and model compounds of lignin and xylose. By analyzing the ion-solvent interactions using the calculated apparent and partial molar properties, we aimed to design an economically viable large-scale dissolution of biopolymers using ILs. In case of Proteins, biopolymers formed by the condensation of amino acids, maintaining their thermodynamic stability is critical in various fields such as therapeutics, biological processes, and diagnostics3. The stability of globular proteins is dependent on the balance between intermolecular interactions of functional groups and interactions with co-solvent molecules. A novel series of ILs were prepared by pairing DBU with other major base molecules like imidazole, morpholine, and triazole, and used spectroscopic examination techniques such as UV-visible, fluorescence, DLS, and TCSPC to investigate them for protein studies, using hemoglobin. Chitosan, a polysaccharide with biocompatible, low toxicity, and polycationic properties, is another important biomaterial that has gained interest in various applications4. When incorporated with ionic liquids, chitosan-based gels can be used as polymer electrolytes in fuel cells. Protic ILs with mobile protons in the cationic structure show high conductivity, and the membranes with -SO3H functionalized ILs exhibit high thermal stability and electrochemical window. In this study, we have examined the ability of aqueous solutions of protic DBU ILs with -SO3H functional groups, to form chitosan-based gels. Rheological studies were conducted to analyze the strength and stability of the gels, and the electrochemical properties were examined to determine their suitability as polymer electrolytes. So, we propose DBU based ILs as a suitable and ecofriendly solvent media in the biopolymer field in a future perspective.



References

1. T. Welton, Biophys Rev, 2018, 10, 691–706.
2. K.J. Jisha, S. Rajamani, D. Singh, G. Sharma, and R.L. Gardas, J. Ionic Liq., 2022, 2 ,100037.
3. C. Schroder, Top Curr Chem, 2017, 375.
4. G. Santos-Lopez, W. Arguelles-Monal, E. Carvajal-Millan, Y.L. Lopez-Franco, M.T. Recillas-Mota, and J. Lizardi-Mendoza, Polymers (Basel), 2017, 9, 722.