Computational studies of inclusion phenomena and synthesis of a novel and selective molecular receptor for 1,4-disubstituted benzenes and 4,4 '-disubstituted biphenyls

A new tetracationic molecular receptor has been synthesized and studied by semiempirical molecular orbital theory. This novel macrocycle, 1(4+), deriv ed from pentacyclo[5.0.0.0.(2,6)0.(3,10)0(5,9)]undecane-8,11-dione (PCU-8,1 1-dione), structurally resembles cyclobis(paraquat-p-phenylene), 2(4+), in which a xylyl group has been replaced by a PCU unit. This derivatization ef fectively increases the size and flexibility of 1(4+) and changes its elect ronic, dynamical, and binding properties. A conformational search using Osa wa's corner flapping technique and the PM3 semiempirical method identifies eight unique and low-energy 1(4+) conformers. The principal regions of stru ctural variation occur in the bipyridinium torsion and in the ethylene brid ges between PCU and the tetracationic unit. The inclusion complexes of 1(4) with 1,4-disubstituted benzenes and 4,4'-disubstituted biphenyls have bee n studied by PM3. The first shell of solvation is approximated by the expli cit inclusion of 12 acetonitriles in the computed supramolecular complexes. Binding of 1,4-disubstituted benzenes and 4,4'-biphenol is shifted from th e 1(4+) geometric center. From the computations, host 1(4+) is predicted to have an enhanced binding preference for benzidine over 4,4'-biphenol, as c ompared to 2(4+). For all guests computed, 1(4+) binds more strongly than 2 (4+). These properties can be exploited in the future design of supramolecu lar systems with potential applications as nanoscale devices.