title: Acceleration of amide bond rotation by encapsulation in the hydrophobic interior of a water-soluble supramolecular assembly.
abstract: The hydrophobic interior cavity of a self-assembled supramolecular assembly exploits the hydrophobic effect for the encapsulation of tertiary amides. Variable-temperature (1)H NMR experiments reveal that the free energy barrier for rotation around the C-N amide bond is lowered by up to 3.6 kcal/mol upon encapsulation. The hydrophobic cavity of the assembly is able to stabilize the less polar transition state of the amide rotation process. Carbon-13 labeling studies showed that the (13)C NMR chemical shift of the carbonyl resonance increases with temperature for the encapsulated amides, which suggests that the assembly is able to favor a twisted form of the amide.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Pluth
authors.forename: Robert G
authors.initials: RG
authors.lastname: Bergman
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Raymond
mesh_terms: D000577:Amides / Q000737:chemistry*; D002247:Carbon Isotopes; D057927:Hydrophobic and Hydrophilic Interactions; D007553:Isotope Labeling; D046911:Macromolecular Substances / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D015394:Molecular Structure; D012399:Rotation; D012995:Solubility; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D000577:Amides; D002247:Carbon Isotopes; D046911:Macromolecular Substances; D014867:Water