Publication details
Complexation of Ferrocene Derivatives by the Cucurbit[7]uril Host: A Comparative Study of the Cucurbituril and Cyclodextrin Host Families
| Authors | |
|---|---|
| Year of publication | 2005 |
| Type | Article in Periodical |
| Magazine / Source | Journal of the American Chemical Society |
| MU Faculty or unit | |
| Citation | |
| Field | Macromolecular chemistry |
| Keywords | cucurbiturils; self-assembly |
| Description | The formation of inclusion complexes between cucurbit[7]uril (CB[7]) and ferrocene and its derivs. has been investigated. The x-ray crystal structure of the 1:1 inclusion complex between ferrocene and CB[7] revealed that the guest mol. resides in the host cavity with two different orientations. Inclusion of a set of five water-sol. ferrocene derivs. in CB[7] was investigated by 1H NMR spectroscopy and calorimetric and voltammetric techniques. Data indicate that all neutral and cationic guests form highly stable inclusion complexes with CB[7], with binding consts. in the 109-1010 M-1 and 1012-1013 M-1 ranges, resp. However, the anionic ferrocenecarboxylate, the only neg. charged guest among those surveyed, was not bound by CB[7] at all. These results are in sharp contrast to the known binding behavior of the same guests to b-cyclodextrin (b-CD), since all the guests form stable inclusion complexes with b-CD, with binding consts. in the range 103-104 M-1. The electrostatic surface potentials of CB[6], CB[7], and CB[8] and their size-equiv. CDs were calcd. and compared. The CD portals and cavities exhibit low surface potential values, whereas the regions around the carbonyl oxygens in CBs are significantly neg., which explains the strong affinity of CBs for pos. charged guests and also provides a rationalization for the rejection of anionic guests. Taken together, our data suggest that cucurbiturils may form very stable complexes. However, the host-guest interactions are very sensitive to some structural features, such as a neg. charged carboxylate group attached to the ferrocene residue, which may completely disrupt the stability of the complexes. |