title: How Small Can a Catenane Be?
abstract: Catenanes are playing an increasingly important role in supramolecular chemistry. In attempting to identify the minimum number of carbon atoms in a viable catenane, the B3LYP, BP86, M06-2X, MM3, and MM4 methods were applied to study representative [2]catenane models, which consist of two mechanically interlocked saturated n-cycloalkanes ([CnH2n]2). The structures, energy variations, and electron density differences vary nearly monotonically from n = 18 to 11. For example, the B3LYP/DZP++ dissociation energies [CnH2n]2 → 2CnH2n are 101, 121, 159, 191, 222, 252, 290, and 323 kcal/mol from n = 18 to 11, respectively. However, there is much variation among the energetic predictions with the B3LYP, BP86, M06-2X, MM3, and MM4 methods. The distances of the longest C-C single bond in each catenane are 1.593 (n = 18), 1.604 (n = 17), 1.631 (n = 16), 1.640 (n = 15), 1.667 (n = 14), 1.669 (n = 13), 1.680 (n = 12), and 1.689 Å (n = 11). These results display something of a shoulder in the vicinity of n = 14. This may suggest that [C15H30]2 is the smallest catenane that will resist fragmentation under specified laboratory conditions.
authors.affiliation: School of Petrochemical Engineering, Changzhou University , Changzhou 213164, China.
authors.forename: Xuejun
authors.initials: X
authors.lastname: Feng
authors.affiliation: Drug Design & Discovery Center, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica Chinese Academy of Science , Shanghai 201203, China.
authors.forename: Jiande
authors.initials: J
authors.lastname: Gu
authors.affiliation: School of Petrochemical Engineering, Changzhou University , Changzhou 213164, China.
authors.forename: Qun
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Department of Chemistry, National Changhua University of Education , No. 1, Jin-De Road, Changhua City 50058, Taiwan.
authors.forename: Jenn-Huei
authors.initials: JH
authors.lastname: Lii
authors.affiliation: Center for Computational Chemistry, University of Georgia , Athens, Georgia 30602-2525, United States.
authors.forename: Norman L
authors.initials: NL
authors.lastname: Allinger
authors.affiliation: Center for Computational Chemistry, University of Georgia , Athens, Georgia 30602-2525, United States.
authors.forename: Yaoming
authors.initials: Y
authors.lastname: Xie
authors.affiliation: Center for Computational Chemistry, University of Georgia , Athens, Georgia 30602-2525, United States.
authors.forename: Henry F
authors.initials: HF
authors.lastname: Schaefer