Quadruply hydrogen bonded cytosine modules for supramolecular applications.

In view of the range of properties required from supramolecular materials, there is clearly a need for new strong quadruple hydrogen bonded modules, which can be used in polymer or copolymer synthesis via the self- or hetero-association of complimentary units. A cytosine-based module has been prepared for supramolecular applications using a straightforward synthetic approach. The cytosine module was designed such that it does not undergo tautomeric changes observed with ureidopyrimidinones. The cytosine module was capable of forming quadruple hydrogen bonded assemblies both in solution and in the solid state, and the structure of the dimeric self-assembled unit was confirmed by single-crystal X-ray and solution NMR techniques. The dimerization constant was estimated to be greater than 9 x 106 M-1 in deuterated benzene. The capacity of the cytosine-based module to strongly hetero-associate with the ureidopyrimidinone module was demonstrated, and a supramolecular polymer of a bifunctional unit incorporating the cytosine module and PEG-based linker was described.