Study on the Structure of Host-Guest Supramolecular Polymers

Claudia Leggio, Massimiliano Anselmi, Alfredo Di Nola, Luciano Galantini,* Aida Jover, Francisco Meijide, Nicolae Viorel Pavel, Victor Hugo Soto Tellini, and José Vzquez Tato

Dipartimento di Chimica, Università di Roma "La Sapienza", P.le A. Moro 5, 00185 Roma, Italy; Research Center SOFT-INFM-CNR, Università di Roma "La Sapienza", P.le A. Moro 5, 00185 Roma, Italy; and Departamento de Química Física, Facultad de Ciencias, Universidad de Santiago de Compostela, Avda. Alfonso X El Sabio s/n, 27002 Lugo, Spain

Received March 22, 2007

Revised Manuscript Received May 22, 2007

FULL TEXT

Abstract:

A detailed characterization of a host-guest supramolecular copolymer, formed by adamantane and -cyclodextrin dimers (Ad₂ and CD₂, respectively) in aqueous solution, has been carried out by combining small-angle X-ray scattering and light scattering experiments with molecular dynamics (MD) and Monte Carlo (MC) simulations. First, the solutions of the monomers were studied by a straightforward analysis of the scattering data. Afterward, the complex given by Ad₂ and two -cyclodextrin molecules was investigated by correlating scattering results and MD simulations, to characterize the host-guest linkage. Finally, a detailed interpretation of the polymer scattering data was achieved by MC simulations. These simulations were performed on a single supramolecular aggregate and, in view of its peculiar shape, the complete polymer structure was considered without resorting to more general but simplified chain models. The comparison between simulations with and without excluded volume interaction points out that, at our ionic strength (sodium azide 150 mM), the polymer is close to the theta condition. Fits by reverse MC methods show that the polymer presents a shrunk conformation in solution, but it does not close in stable cyclic structures, as generally hypothesized for this kind of small oligomer. However, a polymerization degree of about 8 (4 Ad₂ and 4 CD₂) was estimated which does not show any concentration dependence.