S. Brochsztain et Mj. Politi, Solubilization of 1,4,5,8-naphthalenediimides and 1,8-naphthalimides through the formation of novel host-guest complexes with alpha-cyclodextrin, LANGMUIR, 15(13), 1999, pp. 4486-4494
Solubility studies were performed in aqueous solutions of 1,8-naphthalimide
s and 1,4,5,8-naphthalenediimides (Scheme 1). A large solubility increase w
as found for N-butyl-1,8-naphthalimide (MBN) and N,N'-dibutyl-1,4,5,8-napht
halenediimide (DBN) in the presence of a-cyclodextrin (alpha-CD), indicatin
g the formation of inclusion complexes. The presence of the N-butyl group i
s required for complex formation, leading to the conclusion that the butyl
groups are the binding sites for alpha-CD. Accordingly, the analysis of sol
ubility isotherms for the systems MBN/alpha-CD and DBN/alpha-CD showed the
presence of 1:1 complexes for the former and of both 1:1 and 1:2 complexes
for the latter. Association constants for the two systems were estimated, g
iving K = 470 M-1 for the MBN/alpha-CD complex and K-11 = 1316 M-1 and Kit
= 329 M-1 for the stepwise association constants in the DBN/alpha-CD system
. MBN undergoes hydrolysis in water, but the reaction is inhibited upon com
plexation with alpha-CD. The remarkable solubilization in water and stabili
zation toward hydrolysis makes these novel complexes of imides and diimides
with alpha-CD potentially useful in the pharmaceutical applications known
for these imides, as well as in the preparation of new materials, like poly
imide-based polyrotaxanes.