SUPRAMOLECULAR ASSEMBLIES |
Particle size distribution in DMPC vesicles solutions
undergoing different sonication time
Giuseppe Maulucci 1, Marco De Spirito 1*, Giuseppe Arcovito 1, Federico Boffi 2, Agostina Congiu Castellano 2 and Giuseppe Briganti 2
1 Universitá Cattolica S. Cuore, Roma
2 Universitá di Roma
* To whom correspondence should be addressed. E-mail: m.despirito{at}rm.unicatt.it.
Submitted on August 3, 2004
Revised on September 8, 2004
Accepted on 10 January 2005
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Abstract |
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Size distributions of DMPC liposomes suspensions was investigated by dynamic light scattering as a function of the sonication time ts. Cumulant expansion (second and third order) and regularized Laplace inversion (CONTIN) of dynamic single-angle laser light scattering data were performed. With both methods the intensity weighted mean hydrodynamic radius <r>I depended on the investigated length scale. On the other hand, the number weighted mean hydrodynamic radius <r> N, obtained from CONTIN by modelling DMPC vesicle as thin-walled hollow spheres, resulted independent on the length scale. On the contrary, <r>N, obtained from Cumulant expansions still remain length scale dependent. Therefore the number weighted radius distribution function is highly asymmetric. The number weighted mean radius, the standard deviation and the number weighted radius at the peak rNpeak all decreased to a plateau when increasing sonication time. At ts longer than 1 hour, the rNpeak compares well with the radius of unilamellar vesicles in equilibrium with monomers predicted on thermodynamic basis. The reliability of our analysis is proved by the comparison of experimental Rayleight ratio with the simulated one's, using the normalized number weighted radius distribution function pN(r) determined by dynamic light scattering data. A perfect agreement was obtained at longer sonication times and the average aggregation number was determined. At lower ts values simulations did not match experimental data and this discrepancy was ascribed to the presence of large and floppy unilamellar vesicles with ellipsoidal shapes. Our investigation shows that from a single-angle DLS data the radius distribution function of the vesicles can be obtained only if pN(r) is known.
Key Words:
CONTIN, dmpc, light scattering, particle sizing, vesicle
