Formation of stable vesicles from N- or 3-alkylindoles: Possible evidence for tryptophan as a membrane anchor in proteins

Twelve indole derivatives have been prepared and studied. Five were 1-subst ituted: 1, methyl; 2, n-hexyl; 3, n-octyl; 4, n-octadecyl; and 5, cholestan yloxycarbonylmethyl. Four were 3-substituted: 6, methyl; 7, n-hexyl; 8, n-o ctyl; and 9, n-octadecyl. Three were disubstituted as follows: 10, 1-n-decy l-3-n-decyl; ii, 1-methyl-3-n-decyl; and 12, 1,3-bis(n-octadecyl)indole. So nication of aqueous suspensions afforded stable aggregates from 3-5 and 8-1 2. Laser light scattering, dye entrapment, and electron microscopy were use d to characterize the aggregates. Aggregates formed from N-substituted indo les proved to be more robust than those formed from 3-alkylindoles. A stabl e monolayer formed from 3-n-octadecylindole but not from N- or 1,3-disubsti tuted analogues by using a Langmuir-Blodgett trough. The formation of aggre gates was explained in terms of stacking by the relatively polar indole hea dgroup. In the monolayer experiment, this force was apparently overwhelmed by II-bonding interactions with the aqueous phase.