Adsorption Isotherms of Limonene Enantiomers on the Surfaces of Cyanuric Acid, Cytosine, Ionol, and Adenine Dinitrate Cr
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ICAL CHEMISTRY OF SURFACE PHENOMENA
Adsorption Isotherms of Limonene Enantiomers on the Surfaces of Cyanuric Acid, Cytosine, Ionol, and Adenine Dinitrate Crystals V. Yu. Guskova, G. A. Ramazanovaa, D. A. Allayarovaa,*, A. Z. Arslanovaa, G. R. Yakshibaevaa, G. Kh. Khamzinaa, and E. A. Dolbintsevaa aBashkir
State University, Ufa, 450076 Russia *е-mail: [email protected]
Received January 21, 2020; revised March 17, 2020; accepted March 17, 2020
Abstract—Adsorption isotherms are obtained for limonene enantiomers on the surfaces of ionol and adenine dinitrate crystals, and for the crystalline structures of cytosine and cyanuric acid deposited on surfaces of graphitized thermal carbon black. Viedma ripening conditions are used to induce chirality in the crystals. It is found that the isotherms of limonene enantiomers differ from one another during adsorption on all four samples. The shape of the adsorption isotherms also differs for cytosine and cyanuric acid, indicating different mechanisms of adsorption. It is assumed that one enantiomer is partially adsorbed in the cavity of the supramolecular structure of cytosine and cyanuric acid, while the second is not. The degree of surface filling at which different adsorption isotherms are observed shows that the stability of the layers of enantiomers on the topologically chiral surface of the crystals differs. Keywords: adsorption isotherms, gas chromatography, Viedma ripening, chiral recognition DOI: 10.1134/S0036024420110102
INTRODUCTION The development and the study of new surfaces capable of chiral recognition are relevant in modern chemistry [1]. Enantiomers have different rotations of plane-polarized light and interact differently with other chiral molecules. As a result, the recognition of optical isomers during adsorption is possible with a chiral surface or chiral selectors on a surface [2]. Since the first separation of enantiomers via gas [3] and ligand exchange chromatography [4, 5], the chiral recognition of enantiomers with stationary phases has been based on enantiomer molecule–chiral selector diastereomeric complexes that required asymmetric carbon atoms or other chirality centers. In addition, the successful separation of enantiomers requires three-point contact of molecules separated with a chiral selector [6] or two-point contact with an achiral surface providing a third point [7]. There are axial, planar, spiral, and topological types of chirality used rarely in adsorption and chromatography in addition to chirality centers. However, such types of chirality are often observed in supramolecular chemistry [8–10]. Supramolecular chirality appears when there is an asymmetric spatial arrangement of monomer molecules during their self-assembly [11]. Axial or spiral chiralities are more often observed for one-dimensional (1D) tape suprastructures. Two-dimensional (2D) supramolecular layers and three-dimensional (3D) organic crystals, for
which planar (plane) or topological chiralities are observed, are of primary interest when the adsorbents are developed.
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