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+), derived from pentacyclo5.0.0.0.(2,6)0.(3,10)0(5,9)]undecane-8,11-dione (PCU-8,11-dione), structurally resembles cyclobis(paraquat-p-phenylene), 2(4+), in which a xylyl group has been replaced by a PCU unit. This derivatization effectively increases the size and flexibility of 1(4+) and changes its electronic, dynamical, and binding properties. A conformational search using Osawa's corner flapping technique and the PM3 semiempirical method identifies eight unique and low-energy 1(4+) conformers. The principal regions of structural variation occur in the bipyridinium torsion and in the ethylene bridges between PCU and the tetracationic unit. The inclusion complexes of 1(4+) with 1,4-disubstituted benzenes and 4,4'-disubstituted biphenyls have been studied by PM3. The first shell of solvation is approximated by the explicit inclusion of 12 acetonitriles in the computed supramolecular complexes. Binding of 1,4-disubstituted benzenes and 4,4'-biphenol is shifted from the 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 compared 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 supramolecular systems with potential applications as nanoscale devices.