E and Z Secondary Amides in Supramolecular Nanotubes and Nanospheres - Molecular Self-Assembly: Advances and Applications - page 43

When we started our own approach toward such appealing
structuresin2001,broaduseofknownpeptidenanotubeswas
invariably thwarted by their inherent insolubility [62]. We then
reasoned that if a cyclohexapeptide like cyclohexaglycine self-
assembled as tubes whilst assuming a symmetric hexagone

conformation (for the sake of simplicity), each such bracelet-shaped
cyclopeptide would experience as many as 12 hydrogen bonds
withtwoneighbouringrings(Fig.2.6).Thisarrangementwould
result in six hydrogen bonds used to join two consecutive rings. The
corresponding rather huge stacking energy of 36 kcal/mol might
well be seldom responsible for the insolubility of the material since
the equilibrium is likely strongly biased towards the nanotube to the
detriment of the free constitutive cyclopeptides.

S 6

Figure 2.6 (a)Designoftarget( ) from cyclohexaglycine. Hypothetical

stacking of (b) cyclohexaglycine and (c) target (

1

1 ) showing

the hydrogen bonds.

A straightforward way around the insolubility problem could
then be to simply reduce the number of hydrogen bonds involved