Abstract
The adsorption of certain chiral amino acids from aqueous solution onto β-cyclodextrin silica particles (CDS) had been investigated with the aim of in-depth understanding of the host-guest interaction. The adsorption intensity was found to be strongly dependent on the aqueous phase pH and this dependence could be interpreted from a model for neutral species adsorption in all cases. Adsorption equilibrium data fitted well to the Freundlich isotherm. The adsorption efficiencies of L-amino acids were found to be higher compared to the corresponding D-isomers. Hydrogen bonding and hydrophocities of amino acids were responsible for the differences in adsorption, by influencing the strength of interactions between the amino acid and CDS. The adsorption rate curves for all the molecules appeared to be typical of the pseudo second-order kinetics. Infrared spectral analysis has been performed to characterize adsorptive interaction. The porous structure of CDS as revealed by scanning electron micrograph thus shown to be promising materials for enantioselective separation of amino acids. In addition, molecular modeling studies performed on such molecules were found to correlate very well to the experimental results obtained.
Highlights
Chiral amino acids are one of the most important biomolecules because of their relevance in nature and their chemical richness
Tang et al [24] have studied the application of cross-linked β-CD polymer for adsorption of aromatic amino acids. We report both experimental and theoretical results on adsorption behaviour of certain chiral amino acids on β-CD bonded to silica gel with emphasis on understanding the host-guest interaction and such a study will be useful for better understanding of the chiral recognition mechanism of amino acids by β-CD bonded silica gel as a selective sorbent
The results of the investigation revealed some important insights for the adsorption mechanism of certain amino acid enantiomers on β-CD bonded to silica particles
Summary
Chiral amino acids are one of the most important biomolecules because of their relevance in nature and their chemical richness. Methods based on chiral ligandexchange [7,8,9,10] and on the formation of inclusion complexes with cyclodextrins have received the most attention [11,12,13]. Β-Cyclodextrin (β-CD) is a cyclic oligosaccharide with seven glucose units, with its cavity structure, and can form an inclusion complex with certain molecules through a host-guest interaction. The chiral nature of the cavity in these molecules makes them useful for enantiomeric separation applications. We report both experimental and theoretical results on adsorption behaviour of certain chiral amino acids on β-CD bonded to silica gel with emphasis on understanding the host-guest interaction and such a study will be useful for better understanding of the chiral recognition mechanism of amino acids by β-CD bonded silica gel as a selective sorbent. Ized the amino acid-β-CD complex by UV-Visible (UVVis) spectroscopy
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