Reversible organogels triggered by dynamic K+ binding and release.

In this study, a new lipophilic guanosine derivative was synthesized as an organogelator. The self-aggregation behavior of this organogelator was investigated by NMR, XRD and AFM. In solution, the lipophilic guanosine derivative can form a stable ribbon-like structure through NH(1)-N(7) and NH(2)-O(6) hydrogen bonds. However, gelation would occur in some aprotic solvents after the concentration reached a definite value. More interesting, the ribbon-like structure was able to change to G-quartets in the presence of K(+), which led to the transformation from a gel to a sol. Upon the addition of the cryptand [2.2.2], which can efficiently complex with K(+), G-quartets reverted to the original ribbon-like structure and the gel recovered. Subsequently, upon the addition of acids, K(+) was released from the cryptate with the transformation of gel-to-sol simultaneously. Finally, upon the addition of bases which deprotonated [H(+) ⊂ 2.2.2], the liberated cryptand [2.2.2] recaptured K(+) and the gel was regenerated again. This process of interconversion between G-ribbon 1(n) and octamer 1(8)·K(+) was well monitored by circular dichroism spectra.