Synthesis of novel proline-based imidazolium ionic liquids
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ORIGINAL PAPER
Synthesis of novel proline‑based imidazolium ionic liquids Snehkrishn A. Chaubey1 · Niranjan Patra1 · Roli Mishra1 Received: 28 April 2020 / Accepted: 10 August 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract A series of eight novel proline functionalized dipeptide imidazolium ionic liquids (DPILs), i.e. Boc-[Pro-Pro-EMIM], Boc[Pro-Val-EMIM], Boc-[Pro-Ala-EMIM], Boc-[Pro-Phe-EMIM] containing [Cl] and [NTf2] anions were synthesized via a facile reaction of 2-chloroethylamine with four different dipeptides (Boc-Pro-Pro-OH, Boc-Pro-Val-OH, Boc-Pro-Ala-OH, and Boc-Pro-Phe-OH) followed by reaction with 1-methylimidazole and subsequent anion exchange. The synthesized ILs revealed similar characteristics of a conventional imidazolium ILs. The synthesized ILs were investigated by 1H NMR, 13C NMR, FT-IR, mass spectroscopy, TGA, and DSC. TGA revealed an improved thermal stability for NTf2 over chloride ion. DSC revealed a melting temperature less than 100 °C. Graphic abstract Boc-[Pro-AA-EMIM][Cl]/NTf2] Cation Boc N
O N H
H N
A A
N
O
N
Anion Cl NTf2
AA = Proline Valine Alanine Phenyl Alanine
Keywords Proline · Dipeptide ionic liquids · Imidazolium · Amino acid-based ionic liquids · Physicochemical properties
Introduction Amino acid-based ionic liquids (AAILs) have drawn tremendous attention of researchers due to their potential structural and biocompatible properties [1–5]. Amino acids (AAs) can be easily converted into cations and anions in ILs since they have side chains/functional groups as well as chiral properties which can define their wide range of physicochemical and biological properties. These properties make them suitable to find applications as electrochemical Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00706-020-02670-x) contains supplementary material, which is available to authorized users. * Roli Mishra [email protected]; [email protected] 1
Department of Engineering and Physical Sciences, Institute of Advanced Research, Gandhinagar 382426, India
sensors, super capacitors, biocatalytic reactions, biosensors, bio preservation as well as protein solubilization, stabilization and crystallization [6], miscibility with water and/or organic solvents [7], melting point [8–12]. AAILs have also been shown to have excellent C O2 absorption and membrane transport properties [13–18]. There are quite a few reports in which amino acids have been used as cations [19]. Amino acids and their ester salts [AAE] [NO 3/Sac] based ionic liquids have been reported by Kou et al. [20]. In most cases, synthesized AAILs and amino acids are used as anions [21, 22]. Various imidazolium-based AAILs have been synthesized using 20 natural amino acids and imidazole. All the synthesized [EMIM][AA] ILs are stable up to 200 °C except the [EMIM][CYS]. Recently, AAILs with amino acids as the anions and phosphonium, choline, ammonium, and imidazolium as the cations have been reported [23, 24] to have interesting physicoc
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