The Self-Assembly of Lipophilic Guanosine Derivatives - Molecular Self-Assembly: Advances and Applications - page 106

the solid state and is detected in solution in (anhydrous) chloroform
soon after dissolving the polycrystalline powder, is held together by
an intramolecular N hydrogen bond network. In

solution, the ribbon A may slowly undergo a structural transition
toward a thermodynamically more stable form (ribbon B, Fig. 4.12B)
characterized by N

2

H-O

6

and N

1

H-N

7

1 6 2 3

intermolecular cyclic hydrogen
bonds: this is normally observed for dialkanoyl derivatives of type
1a

H-O and N H-N

. Upon adsorption at the solid-liquid interface, the guanosine
supramolecular ribbons B undergo a back rearrangement to the
A-type ribbons. In both ribbon-like polymers the glycosydic bonds
adopt an anti conformation.

Figure 4.12 H-bond pattern of ribbon-like assemblies. A) Ribbon A, solid

state; B) ribbon B, in solution. Arrows indicate molecular
dipoles.

In the absence of templating cations, the formation of ribbon-
like polymers seems to be a quite general behavior for LGs, as long as
the molecules can adopt an anti conformation around the glycosidic

bond.
It should be noted that the two ribbons posses a different
symmetry. As a consequence, while in ribbon B (solution) molecular
dipoles cancel each other, ribbon A structure (solid state) has a
permanent dipole moment and, remarkably, in the crystal structure
ribbons are arranged in a parallel fashion, thus making polar the
whole bulk [25b].