Title: Probing cations recognized by a crown ether with the 3D-RISM theory. II. 18-crown-6 ether
Author(s):

	Y.Maruyama ( Depament of Theoretical Studies, Institute forMolecular Science, Okazaki, Aichi, 444-8585, Japan ) ,
	M.Matsugami (Chemistry, General Education, Kumamoto National College ofTechnology, 2659-2, Suya, Koshi, Kumamoto, 861-1102, Japan ) ,
	Y.Ikuta ( Depament of Theoretical Studies, Institute forMolecular Science, Okazaki, Aichi, 444-8585, Japan ) ,

In the previous study, we investigated the cation recognition by12-crown-4 ether with the 3D-RISM theory [Ikuta, Y. et al., Chem. Phys. Lett., 2007, 433, 403], and showed the applicability of the theory to the problem. The results show that a 12-crown-4 ether recognizes Li⁺ and Mg²⁺. 18-crown-6 ether is widely used in comparison with 12-crown-4ether. In this study, we calculated three-dimensional distributions of water as well as cations (Li⁺, K⁺, Mg²⁺, Ca²⁺) inside and outside 18-crown-6 ether in aqueous solutions of electrolytes. A 18-crown-6 ether recognizes not only Li⁺ and Mg²⁺ but also K⁺ and Ca²⁺. K⁺ is dehydrated in the host cavity whereas other cations are hydrated. It is found that a hydration structure, as well as cation size, is important for the molecular recognition by crown ether.%

Key words: 3D-RISM theory, molecular recognition, crown ether, cation
PACS: 02.30.Rz, 31.15.Bs, 61.25.Em

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