CHARACTERIZATION OF CROWN-ETHERS AS MACROCYCLIC ELEMENTS FOR ROTAXANEPREPARATION - A MONTE-CARLO SIMULATION

Rotaxane synthesis via the statistical method depends upon various geo metric considerations such as the ring size of the macrocyclic compone nts. In this paper, we examine the conformational statistics for a ser ies of crown ethers (18-crown-6, 24-crown-8, 30-crown-10, and 36-crown -12) in terms of their average radius, radius of gyration, and intramo lecular oxygen-oxygen distances. We conduct NPT Monte Carlo simulation s to examine these properties as a function of solvent polarity at 25 degrees C and 1 atmosphere pressure. We find that the crowns are more accessible to statistical threading in water than in carbon tetrachlor ide from the viewpoint of ring size. However, the macrocycles are more distorted (ellipsoidal) in CCl4, thus opening up the possibility of p reparing rotaxanes wherein the macrocycles discriminate between linear chains with differently shaped monomers depending upon the solvent us ed. Results regarding the scaling of the radius of gyration with molec ular weight for the cyclic molecules are also presented.