The thermodynamics of adsorption of some substituted 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from water–acetonitrile solutions with acetonitrile volume fraction varying within a range of 0.35–0.90 on chemically modified Luna C18 and Discovery C18 silica gels has been studied within a temperature range of 313.15–333.15 K. The thermodynamic characteristics of the adsorption of these compounds on Luna C18 and Discovery C18 silica gels have been determined as depending on solution composition. In the case of Discovery C18, the character of the dependences of different thermodynamic characteristics of the adsorption on liquid phase composition is similar to that of the corresponding dependences previously observed for modified Ascentis®Phenyl silica gel. A similarity has also been found for the dependences of the thermodynamic characteristics of the adsorption on Luna C18 and modified Diasfer-110-C18 silica gel studied previously. The mechanism of the liquid-phase adsorption of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines on Luna C18 is changed within a range of acetonitrile volume fractions of 0.60–0.75, as it is in the case of Diasfer-110-C18. At acetonitrile volume fractions of higher than 0.75, the studied heterocycles are adsorbed on Luna C18 surface dynamically modified with acetonitrile without a direct interaction with the grafted layer of the chemically modified silica gel. At the same time, the mechanism of their adsorption on Discovery C18 remains unchanged while acetonitrile concentration is increased in the liquid phase.
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We are grateful to Ass. Prof. of the Department of Organic Chemistry of Samara State Technical University, Candidate of Sciences in Chemistry, A.V. Yudashkin, for giving us the possibility to use heterocycles 1–5, which he has synthesized, and the Center for Collective Use of the Frumkin Institute Physical Chemistry and Electrochemistry, Russian Academy of Sciences, for allowing us to use experimental equipment.
This work was carried out within the framework of a state order to the Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences.
B.R. Saifutdinov is grateful to the Russian Foundation for Basic Research (project no. 17-03-01308-a), the Council for Grants of the President of the Russian Federation for State Support of Young Russian Scientists and State Support of Leading Scientific Schools of the Russian Federation (project no. MK-5757.2018.3), and the Ministry of Science and Higher Education of the Russian Federation (project no. 4.7150.2017/8.9) for partial financial support of the performed investigations.
The authors declare that they have no conflict of interest.
Translated by E. Khozina
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Saifutdinov, B.R., Buryak, A.K. The Influence of Water–Acetonitrile Solvent Composition on Thermodynamic Characteristics of Adsorption of Aromatic Heterocycles on Octadecyl-Bonded Silica Gels. Colloid J 81, 754–761 (2019) doi:10.1134/S1061933X19060176