title: Subtle "supramolecular buttressing effects" in Cucurbit[7]uril/guest assemblies.
abstract: Biphenyl derivatives bearing a dimethylsulfonium group at position 3 and three different substituents at position 4 (H, F and CH3) have been prepared as probes to test the validity of the "supramolecular buttressing" concept. We define the latter as the alteration, by a neighboring unit, of a substituent effect on intermolecular recognition. In this case, the 4-substituents exert some pressure on the 3-dimethylsulfonium groups and control the ratio of their syn and anti conformations. As free species, biphenyls bearing 4-H and 4-F substituents are present as approximately equimolar mixtures of syn and anti-conformers, while the biphenyl scaffold with a 4-CH3 group adopts the anti-conformation exclusively. The 3-dimethylsulfonium substituents then interact with one of the carbonylated portals of Cucurbit[7]uril (CB[7]), and their conformations affect the position of the guests inside the cavity of the macrocycle, thereby validating our "supramolecular buttressing" model. Surprisingly however, binding affinities towards CB[7] are barely affected by the nature of the 4-substituents and the conformations of the neighboring sulfonium groups, despite very different electronic densities presented to the CB[7] portal in their syn or anti conformations. Solvation was found to dramatically smoothen host-guest Columbic interactions, although the latter remain important in the recognition process. Replacing the positively charged 3-dimethylsulfonium unit with an isopropyl substituent decreases the affinity of the biphenyl guest by 1000-fold.
authors.affiliation: Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701, USA.
authors.forename: Roymon
authors.initials: R
authors.lastname: Joseph
authors.forename: Eric
authors.initials: E
authors.lastname: Masson
mesh_terms: D001952:Bridged-Ring Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D007093:Imidazoles / Q000138:chemical synthesis* / Q000737:chemistry; D046911:Macromolecular Substances / Q000138:chemical synthesis / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D001952:Bridged-Ring Compounds; D007093:Imidazoles; D046911:Macromolecular Substances; C456276:cucurbit(7)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils