Langmuir 1992,8, 2595-2597
2595
Polymerization-Induced Shrinkage in Giant Butadienic Lipid Vesicles M. Dvolaitzky,' M. A. Guedeau-Boudeville, and L. Lbger Laboratoire de Physique de la Matikre C o n d e d e , U.A.-C.N.R.S. 792, Collkge de France, 11 Place Marcelin-Berthelot, 75231 Paris Cedex 05, France Received May 29,1992. I n Final Form: September 4, 1992
A new butadienic lipid, dimethylbis[2(tetradeca-2,4-dienoyl)oxyethyl]a"onium bromide, has been used to form giant vesicles. Under UV irradiation, a spectacularchange in the morphology of these vesicles is observed a global shrinkage, along with a thickening or crumpling of the membrane (depending upon the conditionsof irradiation). The kinetics of the shrinkageare totally different (much slower) than those of the polymerization (monitored by the disappearance of the absorption due to the conjugated double bonds of the diene at 262 nm). This is indicativeof a two-step process: the shrinkageresulting from rapid polymerization followed by slow expulsion of part of the water inside the vesicles. Introduction The polymerization of giant unilamellar vesicles is an active field of research both from a practical point of view, with the aim of stabilizing liposomes for drug deli~ery,l-~ and from a theoretical aspect, as polymer sheets are fascinating bidimensional objects which can undergo a spectacular crumpling t r a n s i t i ~ n .Diacetylenic ~~~ lipids are classicalcandidates for such investigationsbut, as they polymerize only in the ordered phase of the lipid bilayer, they do not allow the study of the polymerization of vesicle membrane in the fluid phase. The recently reported dioctadecadienoylammoniumbromide (DODIAB)appears more interesting as it polymerizes in the fluid phase of the membrane.' However, this compound requires a long swelling period above 45 "Cto form giant vesicles, which gives rise to uncontrolled thermal polymerization. Here we present an investigation of the UV-induced polymerization of fluid membrane vesicles obtained with a new butadienic lipid, the ditetradecadienoylammoniumbromide (1) (DTDIAB), a lower homologue of the DODIAB compound
[CH,(CH,),CH=CHCH=CHCO,(CH,),l,N+(CH,),, Br- (1) A progressive shrinkage always accompanies the polymerization, but both the kinetics and the appearance of the membrane are highly sensitive to the controlling parameters of the reaction. Experimental Section Materials and Vesicle Preparation. The details of the synthesis and the characterization of the lipid 1 are reported elsewhere.8 Giant vesicles were obtained by the swelling procedure of Evans! recently described in detail by Klis and Sackmann.lo (1) Ringsdorf, H.; Schlarb, B.; Venzmer, J. Angew. Chem., Znt. Ed. Engl. 1988,27,113-158. (2) Sackmann, E.; Eggl, P.; Fahn, C.; Bader, H.; Ringedorf, H.; Schollmeier,M. Ber. Bunsen-Ges. Phys. Chem. 1985,89, 1198-1208. (3) Sackmann, E. Can. J. Phys. 1990,68, 999-1012. (4) Mutz, M.; Bensimon, D.; Brienne, M. J. Phys. Rev. Lett. 1991,67, 923-926. (5) Nelson, D. R.; Peliti, L. J. Phys. (Paris) 1987, 48, 1085-1092. (6) Kantor, D. R.; Kardar, M.; Nelson, D. R. Phys. Reu. Lett. 1987,58, 2774-2777: Phvs. Rev. A 1987.35.3056-3071.
(7) Gaub, H :; Bkchl, R.; Ringsdorf, H.; Sackmann, E. Chem. Phys.
Lioids 1986. 37. 19-43. '(8) Guedeau-Boudeville,M. A. C.R.Acad. Sci., Ser. 2 1992,315,541544. (9) Needham, D.; Evans, E. Biochemistry 1988,27, 8261-8269. (10) K b , J.; Sackmann, E. Biophys. J . 1991,60, 825-844.
0743-7463/92/2408-2595$03.00/0
The lipid 1 (0.45 mg) was deposited on a Teflon disk by evaporation in vacuo of a chloroform solution (10 mg/mL). It was allowed to swell in pure water (10 mL) at room temperature in the dark, yielding a reasonable amount of large unilamellar vesicles with diameters in the range 50-100 wm after a few hours to a few days. It was not possible to measure the transition temperature T, of the lipid 1on the vesicle Suspension,probably due to lack of material; but T, of a lamellar phase could be measured by differential scanning calorimetry. These hydrated bilayers were obtained directly in the calorimeter (DSC7,PerkinElmer), by heating (5OC/min) a mixture of 1.366 mg of 1 with about 5 mg of water. A transition is first found at 32 O C ; when the mixture is cooled at the same rate down to 0 "C and left 10 min at this temperature, another heating gives a transition at 20.5 OC with a pretransition at 11 O C . This last thermogram is reobtained when further cooling-heating cycles are performed (Figure3). If observedbetween crow-polariiers,the same mixture appears birefringent at room temperature, indicatingthe presence of a liquid crystal phase. Observation and Polymerization of the Vesicles. An aliquot of the aqueous vesicle suspension was withdrawn to fill a chamber covered with a quartz window (Hellma) where the vesicles are nearly free of thermal convection (200-250 wm thickness). This chamberwas placed in a thermostated assembly resting on the stage of an inverted microscope equipped with a phase-contrast system (Nikon, diaphot TMD). The polymerization was induced by UV irradiation with a low-pressure mercury-xenon Pen Ray lamp (Oriel) positioned at 0.5-1 cm from the measuring cell. When used without a filter, 90% of the power output is concentrated at 254 nm and a small amount of energy is radiated at 185 nm. A filter was also used (short wavelength filter, Oriel) which suppressed all radiation of wavelength
