SWITCHING BETWEEN SUPRAMOLECULAR ASSEMBLIES OF LIPOPHILIC GUANOSINE DERIVATIVES TRIGGERED BY EXTERNAL STIMULI

Depending on the experimental conditions, lipophilic guanosines (LipoG’s) can undergo different self-assembly pathways based on different H-bonded motifs, e.g. the cyclic discrete G-quartet and the “infinite” tape-like G-ribbon. The switching between different supramolecular motifs have been obtained by a variety of external stimuli. In this article we will discuss after a general presentation of the LipoG self-assembly, the case of three different stimuli. A first example is represented by chemical stimuli: addition of an alkali metal ion stabilizes the Gquartet while its removal shifts the equilibrium toward the G-ribbon. A second type of stimuli is represented by light: the photocontrolled self-assembly of a modified guanosine nucleobase with a photoactive unit at C8 is obtained selecting the appropriate wavelength. Finally, a lipoG armed with a terthiophene unit undergoes a pronounced variation of its supramolecular organisation by changing the polarity of the solvent: in chloroform the derivative assembles via H-bonding in a Guanosine directed structure, while in the more polar (and H-bond competing) acetonitrile different aggregates are observed, where the terthiophene chains are π-π stacked in a helicoidal arrangement.