In–out interactions of different guests with the hexameric capsule of resorcin[4]arene

Abstract

Hydrogen-bond molecular capsules of resorcin[4]arenes (1) and pyrogallol[4]arenes (2) attracted much interest in the last decade. It was found, for example, that resorcin[4]arenes form hexameric capsules in non-polar organic solvents that can accommodate both trialkylamines and tetraalkylammonium salts. In search for the bulkiest guest that can be accommodated in the cavity of such capsules we found, with the aid of diffusion NMR, that such guests can interact also with the external surface of the hexameric capsules. Interestingly, monitoring the effect of CD₃OD titration on the diffusion coefficients of the different components in such host–guest systems indicates that the interaction of such guests with the external surface of the hexameric capsule is significant and can be found also in case where guest's encapsulation occurs as in the case of trioctylamine (3) and tetraoctylammonium bromide (6). These CD₃OD titrations showed also that these interactions are disrupted before the hexamer is disrupted and that before observing the free guests one can observe apparently the formation of a 1:1 complex between 1 and the guests.

Keywords:

• supramolecular chemistry
• resorcinarenes
• capsules
• NMR
• diffusion NMR

Acknowledgements

The authors gratefully acknowledge the financial support from the Israel Science Foundation (ISF, Grant No. 301/07), Jerusalem, Israel.

Supporting Information

Experimental section and Figure S1 and S2 showing the ¹H NMR spectra of 1 in the presence of 4 and 5 and mixtures of 1/5 at different ratios; Figure S3 showing the diffusion coefficients of 1, 3 and of mixtures of 1 and 3 and Figure S4 showing the effect of CD₃OD titration on the diffusion coefficient of 1 and 3; Figure S5 and S6 showing the diffusion coefficients of 1, 6, 7 and of mixtures of 1 and 6 and of 1 and 7, are all available to view online.