Helical folding of alkanes in a self-assembled, cylindrical capsule.
The reversible encapsulation of a series of normal alkane guests in a cylindrical host was studied by NMR methods. For small hydrocarbons such as n-pentane or n-hexane, two guests enter the host, and they move freely within. With n-heptane no encapsulation takes place. For longer alkanes such as n-decane, a single guest enters and the aromatic walls of the host are seen to twist to avoid empty spaces and increase favorable interactions with the hydrocarbon. The best guest (n-undecane) adopts a conformation with minimal gauche interactions. The longest alkane accommodated, n-tetradecane, adopts a helical conformation to fit in the cavity, a shape that maximizes CH/pi interactions with the aromatic walls of the receptor. These reciprocal conformational changes are discussed in terms of optimal host/guest interactions.
The Skaggs Institute for Chemical Biology and Department of Chemistry, Scripps Research Institute, MB-26, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
Alessandro
A
Scarso
Laurent
L
Trembleau
Julius
J
Rebek
D000473:Alkanes / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry; D003903:Deuterium; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D008968:Molecular Conformation; D013816:Thermodynamics
D000473:Alkanes; D001555:Benzene Derivatives; C010219:mesitylene; D003903:Deuterium; C022884:undecane