Sonication technique, small unilamellar

Some techniques to produce small, mainly unilamellar vesicles from MLV (sonication, French pressure cell) are discussed below in separate paragraphs. 

Chaimovich and coworkers have prepared large unilamellar vesicles of DODACl by a vaporization technique which gives vesicles of ca 0.5 pm diameter. These vesicles are much larger than those prepared by sonication, where the mean diameter is 30 nm, and their effects on chemical reactivity are very interesting. The reaction of p-nitrophenyl octanoate by thiolate ions is accelerated by a factor of almost 10 by DODACl vesicles (Table 2), but this unusually large effect is due almost completely to increased concentration of the very hydrophobic reactants in the small region of the vesicular surface and an increased extent of deprotonation of the thiol. There is uncertainty as to the volume element of reaction in these vesicles, but it seems that second-order rate constants at the vesicular surface are similar to those in cationic micelles or in water (Cuccovia et al., 1982b Chaimovich et al., 1984). 

---