Characterization of pH Dependent-Charged Structures of Valine and Aspartic Acid Through Their Partitioning into Imidazol
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RESEARCH PAPER
Characterization of pH Dependent-Charged Structures of Valine and Aspartic Acid Through Their Partitioning into Imidazolium-Based Ionic Liquids Leila Sheikhian1 Received: 1 March 2020 / Accepted: 15 September 2020 Ó Shiraz University 2020
Abstract Imidazolium-based ionic liquids 1-hexyl-3-methylimidazolium hexaflorophosphate, and 1-hexyl-3-methylimidazolium tetrafloroborate were used to determine pH dependent-ionic forms of Valine and Aspartic acid in aqueous solutions. For this purpose, the partitioning behaviors of both compounds between the aqueous phase with different pH values and ionic liquid phase were investigated. The results revealed that due to having different pH-dependent ionic forms, each compound showed different partitioning behavior. Partitioning behaviors of Valine and Aspartic acid depend strongly to aqueous solution acidity and chemical structures of ionic liquids. Water content of ionic liquid phase and charge density of anionic and cationic constituents of ionic liquids are effective parameters for extraction of studied amino acids into ionic liquid phase. This study was considered as a basis for introducing a green technique to realize the real ionic species of different amphoteric compounds such as amino acids in the aqueous solutions. Keywords Valine Aspartic acid Ionic liquid Partition coefficient Aqueous solution
1 Introduction Charge characterization and speciation of amino acids is of interest not only in biological sciences for better understanding of the metabolic processes in tissue membranes but also in analytical chemistry for improving and designing new separation and measurement procedures. Generally, knowing the chemical forms, including the charged structures, of a compound as it really exists in a sample would help revealing its true impact on human or the environment. Speciation analysis plays a unique role in studies of biogeochemical cycles of chemical compound, determination of toxicity as well as ecotoxicity of selected elements, quality control of food products, control of medicines and pharmaceutical products, technological process control, and clinical analysis. For instance, zwitterions, used widely in chemical, biological and medicinal
& Leila Sheikhian [email protected]; [email protected] 1
Young Researchers and Elite Club, Kazerun Branch, Islamic Azad University, Kazerun, Iran
fields, show distinct physicochemical properties relative to ordinary ampholytes, which largely decide their bioavailability and biological activities (Yang et al. 2016). Many studies including computational protocols have been done about charge characterization of peptides and proteins (to interpret their mass spectrometry data) (Marchese et al. 2010) as well as amino acids in gas phase (Wyttenbach et al. 2000; Price et al. 1997; Wu and McMahon 2005, 2007, 2008; Wu et al. 2011). However, few studies about the charged structures of amino acids in aqueous phase are available for checking the studies reported by ma
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