Soft Report - Dipartimento di Fisica - Sapienza

Biopolymer-Vescicle InteractionsLarge interest is devoted to clarify the behavior ofcolloid systems composed by proteins (or DNA) andsurfactant-based vesicles. [1] Catanionic ones (anacronym derived from the term [cationic + anionic])are studied in more detail. [2] Such vesicles, VES, areeasily prepared and are a valid alternative toliposomes as carriers in gene therapy. They arethermodynamically and kinetically stable. Their layeris similar to biological membranes and allowsencapsulating hydrophilic and hydrophobicmolecules. Many properties of catanionic vesicles,such as their surface charge density, double layerfluidity, etc., can be properly tuned. Suchpossibilities ensure their use in bio-chemicallyrelevant methods.It is important to define which driving forcesinfluences the interaction process between VES andDNA, or proteins. Object of this research line is tounderstand the mechanisms responsible for theformation of vesicle-protein complexes, termed lipoplexes.Studies reported so far are based on TEM[3](Cryo-TEM) or fluorescence microscopy. Noinformation on the parameters controlling theinteraction processes, i.e. the charge density and theiso-electric point of the complexes, can be obtainedfrom the above techniques. The driving forcecontrolling biopolymer-vesicle interactions iselectrostatic, and the thickness of the electricaldouble layer around biopolymers, vesicles and theircomplexes is significantly affected from theinteractions. The surface charge density and somerelated quantities may be significantly modified. Todetect polarization effects and modifications in theelectrical double layer around such charged particles,CONTIN distribution function of the vesicles size,expressed as normalized intensity (in arbitraryunits) vs. the particle diameter, R H (nm) in 6.0mmol l -1 , mole ratio [1.7/1.0], SDS-CTAB catanionicmixtures, up, in the same system with 0.14 mmoll -1 added LYS, medium, and with 1.4 mmol l -1 LYS,down, at 20.0 °C.Dielectric relaxation spectra, reported as ε vs.applied frequency in the SDS-CTAB vesiculardispersion [6.0 mmol l -1 and 1.7/1.0 mole ratio], ○,for 0.42, ◊, 0.82, □, and 1.40, ∆, mmol l -1 LYS in thevesicular pseudo-solvent, at 20.0 °C.Dielectric Relaxation Spectroscopy (DS),Electrophoretic mobility and ζ-potential (ζ-P) areused.They allow to characterize in detail the interactionprocesses and give information on the chargedistribution around vesicles, proteins, DNA and theirlipo-plexes. Dynamic Light Scattering (DLS), andCircular Dichroism (CD) are also used. The firstmethod estimates the average size of the vesiclesand lipo-plexes formed upon interaction withbiopolymers, the second gives information on theconformation of the biomacromolecules bound ontovesicles.Vesicles formed by SDS and CTAB are used. They arenegatively charged, i.e. the SDS content is in excesswith respect to CTAB. Hence, interactions withproteins having high iso-electric point, such aslysozyme, LYS, may be experienced. The behavior ofmixtures containing SDS-CTAB based negativelychargedvesicles in the presence of increasingamounts of LYS is under study. The interactionprocess continues up to complete saturation of theavailable binding sites onto the vesicles and theprotein release from vesicles is demonstrated.References1- Zuber, G., Dauty, E., Nothisen, M., Belguise, P.,Behr, J.P. Adv. Drug Delivery Rev., 52, 245, (2001).2- Marques, E.F., Regev, O., Khan, A., Lindman, B.Adv. Colloid Interface Sci.,100-102, 83 (2003).3- Mel’nikova, Y.S., Lindman, B. Langmuir, 16, 5871(2000).AuthorsAdalberto Bonincontro 1 and Camillo La Mesa 21Dipartimento di Fisica; 2 Dipartimento di ChimicaUniversità di Roma “La Sapienza”85SOFT Scientific Report 2004-06