Cleft Formation upon Polymerization of Surfactant Vesicles

Article abstract of DOI:10.1021/ja00338a014

Morphological consequences of the photopolymerization of vesicles prepared from (C18H37)2N⁺(CH3)CH2C6H4-p-CH-=CH2*Cl^-, 1, have been investigated by using 8-hydroxy-1,3,6-pyrenetrisulfonate (POH) as a reporter group.Static and dynamic laser light scattering established the hydrodynamic radius and the molecular weight of 1 vesicles to be 425 +/-25 Angstroem and 2.3E7.Neither of these values changed upon polymerization.POH was shown to bind appreciably to 1 vesicles.Excitation of POH, following immediately its addition to nonpolymerized 1 vesicles, resulted in fluorescence emission with maxima at 440 and 520 nm.Incubation led to time-dependent changes of this spectra.Increasing incubation time of POH containing nonpolymerized 1 vesicles resulted in the gradual disappearance of the emission band at 520 nm and in the concomitant increase of the emission band at 440 nm.Fluorescence spectra of POH did not show any time-dependent changes following its addition to polymeryzed 1 vesicles.These results were interpreted in terms of the gradual penetration of POH into nonpolymerized 1 vesicles and in terms of long-term stabilization of POH in the clefts formed on the vesicle surface upon pulling the surfactant head groups together by photopolymerization.Differences between nonpolymerized and polymerized vesicles also manifested in the excited state protonation equilibria (POH)^* <*> (PO^-)^* + H⁺.A k_off⁸ value of 4.3E9 s^-1 was obtained in nonpolymerized vesicles immediately after the POH injection.Following a day of incubation no excited-state proton ejection could be observed in nonpolymerized 1 vesicles.Consequently, a k_off^* value of 6.1E9 s^-1 was observed in nonpolymerized vesicles both immediately and 1 day subsequent to the addition of POH to polymerized 1 vesicles.Similar behavior has been observed for the steady-state (P) and nanosecond time-resolved polarizations, τ_R values, of POH, as well as that for the ground state PO^- reprotonation (governed by K_on) in nonpolymerized and polymerized 1 vesicles.In nonpolymerized 1 vesicles, P values increased (from 0.12 to 0.19), τ_r was determined to be >/= 50 ns, and k_on values (4E8 M^-1 s^-1) became unobservable after a day of incubation.In polymerized 1 vesicles, P values of 0.08, values τ_R of 4 ns, and k_on values 8E8 M^-1 s^-1 remained unaffected by incubation.