(Amino acid + silica) adsorption thermodynamics: Effects of temperature |
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| Affiliation: | 1. Universidade Federal do Rio Grande do Norte, Laboratório de Peneiras Moleculares, Natal 59078-970, RN, Brazil;2. Instituto de Tecnología Química, Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas, Valencia 4602, Spain;1. Interdisciplinary Center for Nanotoxicity, Jackson State University, 1400 J. R. Lynch Street, Jackson, MS 39217, USA;2. Department of Chemical Engineering, The University of Mississippi, P.O. Box 1848, University, MS 38677, USA;1. Department of Environmental Health Sciences, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422-8526, Japan;2. Department of Environmental and Life Sciences, School of Food and Nutritional Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422-8526, Japan;3. Department of Biological Environment, Akita Prefectural University, Shimoshinjo-Nakano, Akita 010-0195, Japan;4. National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Japan |
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| Abstract: | 
A thorough understanding of amino acid adsorption by mineral and oxide surfaces has a major impact on a variety of industrial and biomedical applications. Little information currently exists regarding temperature effects on most of these adsorption processes. Deeper thermodynamic analyses of their multiple temperature adsorption isotherms would aid the interpretation of the interfacial interactions. Low solution concentration adsorption isotherms for glycine, lysine and glutamic acid on a silica adsorbent were generated for T = (291, 298 and 310) K. Data analysis via the Clausius–Clapeyron method yielded the isosteric heat of adsorption as a function of fractional monolayer coverage for each adsorptive. Each amino acid showed an exothermic adsorption response. Glycine and lysine experienced a greater negative effect of increased temperature compared with glutamic acid, indicating a greater number of adsorbed molecules than glutamic acid, with the former undergoing intermolecular clustering within the adsorbed phase. Isosteric heat analyses suggest ionic interactions for lysine and hydrogen bonding for glutamic acid, both weakening with increased coverage. In contrast, initial hydrogen bonding led to ionic bonding for glycine with increasing coverage. |
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| Keywords: | Amino acids Glycine Lysine Glutamic acid Adsorption Silica Temperature dependence Isosteric heat Clausius–Clapeyron |
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