title: Impact of long-range van der Waals forces on chiral recognition in a Cinchona alkaloid chiral selector system.
abstract: Singly-charged complexes of (8S,9R)-tert-butylcarbamoylquinine (tBuCQN), N-3,5-dinitrobenzoyl-(S,R)-leucine (DNB-S/R-leucine), and alkali metal counter ions (Li(+), Na(+), K(+)) were investigated by density-functional theory. It is shown that the cations prefer formation of an ionic pair with the carboxylate group of DNB-Leu over the formation of a cation-π interaction. The [tBuCQN·DNB-S/R-Leu·Na](+) complex is bound by a coulombic attraction, a hydrogen bond, a π-π interaction and van der Waals forces. The tBuCQN chiral selector preferentially complexes with the DNB-S-Leu enantiomer, because the favourable stereochemistry allows the stabilization of the complex by at least one binding mode more compared to the complex containing the DNB-R-Leu molecule. Weakening of the binding modes is observed using the lithium counter ion compared to the sodium one. The weakening is more pronounced in [tBuCQN·DNB-R-Leu·Li](+) than in [tBuCQN·DNB-S-Leu·Li](+). The exact opposite effect is observed using the potassium counter ion. Hence, the lithium counter ion enhances the enantioselectivity of tBuCQN while the potassium counter ion reduces the enantioselectivity of tBuCQN.
authors.affiliation: Charles University in Prague, Faculty of Science, Department of Organic Chemistry, Hlavova 8, 12843 Prague 2, Czech Republic. petr.milko@weizmann.ac.il
authors.forename: Petr
authors.initials: P
authors.lastname: Milko
authors.forename: Jana
authors.initials: J
authors.lastname: Roithová
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Schug
authors.forename: Karel
authors.initials: K
authors.lastname: Lemr
mesh_terms: D002929:Cinchona / Q000737:chemistry*; D002930:Cinchona Alkaloids / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry; D006860:Hydrogen Bonding; D008094:Lithium / Q000737:chemistry; D008968:Molecular Conformation; D012964:Sodium / Q000737:chemistry; D055672:Static Electricity; D013237:Stereoisomerism
chemical_list: D002930:Cinchona Alkaloids; D056831:Coordination Complexes; D008094:Lithium; D012964:Sodium