title: Macrocycle breathing in [2]rotaxanes with tetralactam macrocycles.
abstract: The structural dynamics of two pairs of [2]rotaxanes were compared using variable-temperature NMR. Each rotaxane had a surrounding tetralactam macrocycle with either 2,6-pyridine dicarboxamide or isophthalamide bridging units. Differences were observed in two types of rotational processes: spinning of the phenylene wall units in the surrounding macrocycle of squaraine rotaxanes and macrocycle pirouetting in xanthone rotaxanes. The rotaxanes with macrocycles containing 2,6-pyridine dicarboxamide bridges exhibited higher rotational barriers due to a cavity contraction effect, which disfavored macrocycle breathing.
authors.affiliation: Department of Chemistry and Biochemistry, 236 Nieuwland Science Hall, University of Notre Dame, Notre Dame, Indiana 46556, United States.
authors.forename: Ivan
authors.initials: I
authors.lastname: Murgu
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Baumes
authors.forename: Jens
authors.initials: J
authors.lastname: Eberhard
authors.forename: Jeremiah J
authors.initials: JJ
authors.lastname: Gassensmith
authors.forename: Easwaran
authors.initials: E
authors.lastname: Arunkumar
authors.forename: Bradley D
authors.initials: BD
authors.lastname: Smith