Role of Rim Functions in Recognition and Selectivity of Small‐Molecule Guests in Water‐Soluble Cavitand Hosts

• Published in: Chemistry, an Asian journal Vol. 17; no. 15; pp. e202200466 - n/a
• Main Authors: Tang, Min‐Min, Kanagaraj, Kuppusamy, Rebek, Julius, Yu, Yang
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.08.2022
• Subjects: Alcohols; Bromides; cavitand; Chemistry; Coiling; Competition; Cycloalkanes; Halides; Imidazole; Iodides; Organic chemistry; Recognition; rim function; Selectivity; Ureas; Water chemistry; water-coordination; selectivity; recognition; rim function; imidazole; cavitand; water-coordination
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.202200466

Groups on the upper rim of cavitands can play major roles in the recognition of small molecules. Water‐soluble deep cavitands 1, 2 or 3 bearing the walls upper rim of imidazole, urea, and methyl urea, respectively, were synthesized and characterized as hosts of small‐molecule guests. The vase forms of 1 or 2 are stabilized through H‐bonding to solvent water molecules between adjacent walls. Various small alkyl organic molecules – alcohols, halides, cycloalkane derivatives and heterocycles – are efficiently bound in 1. For n‐alcohols (C5 to C12), the −OH end is fixed at the upper rim and the alkyl parts are in the hydrophobic cavity. The longer alcohol guests (C7–C12) show coiling. Cycloalkane guests rotate rapidly on all 3 axes within the host cavity, while heterocycles show orientations placing their heteroatoms near the cavitand rim. Competition studies between alkyl chlorides, bromides and iodides showed preference for binding of iodides in 1. Competition between cavitands for hexyl halide guests halide showed the order 2>1>3. Groups near the upper rim of a cavitand play major roles in the recognition of small molecules. Water‐soluble deep cavitands bearing the upper rim of imidazole, urea, and methyl urea, were studied regarding their differences in recognition of various guests. H‐bonding with water co‐ordination between four walls controls the upper‐rim opening and binding pattern of amphiphilic molecules.