The document discusses aggregation phenomena observed when mixing liposomes and polyelectrolytes. It observes aggregation with charge inversion and reentrant condensation. Kinetically arrested states are formed due to electrostatic interactions and superficial charge heterogeneity. Detailed simulations describe the model and emergence of patch attraction and polarization effects. Experiments provide evidence of thermally activated aggregation processes.

1. Polyion-induced liposome aggregation specific interactions, kinetic arrest & structural properties. Domenico Truzzolillo Università degli Studi di Roma “La Sapienza” Dipartimento di Fisica SUPERVISORS: Prof. Federico Bordi, Prof. Cesare Cametti

3. Polyelectrolytes and Liposomes: structures and interaction Cell Modeling, drug delivery and many biotechnological applications

7. Reentrant condensation and charge inversion DLS measurements: standard correlation function analysis. R h =k b T/6  D Exponential decay Electrophoretic measurements Electrophoretic Mobility  -potential Information about the net charge on the surface of aggregates  = N - /N + Stoichiometric charge ratio

8. Reentrant condensation and charge inversion Close to the neutralization point… Position of the neutralization point dependent on the charge discretization of the system and on the chemical nature of P/L G. Gilles et al. J.Phys. Chem. B 111, 8626, 2007 J. Kleimann et al., Langmuir 2, 13 688, 2005 F. Bordi et al. PRE 71, 050401(R), 2005

11. Random charge distribution: HHF model revisited. Velegol and Thwar (2001) Random potential fluctuation Mean value of the surface potential Derjaguin approximation can be applied

12. What’s new……… The presence of charge heterogeneities introduces an attractive term of purely electrostatic nature . A potential barrier appears whose stregth depends on the electrostatic parameter of macroions (  ,  ) The larger the variance of surface potential the smaller barrier height . (  )- dependence of the range of interaction HHF result Dependence on curvature radius of interacting particles

14. Kinetically arrested states Increasing of the barrier height upon clustering Slowing down of the aggregation kinetics Stable cluster phase as a kinetically arrested aggregation process. Typical energies required to arrest the aggregation Size distributions

15. How to simply simulate the system Compactness of the aggregates Oil drop-like process R(N) The size of the uniform potential regions on the particle surface is independent on the cluster size. Brownian dynamics in the MC algorithm: the i th particle is selected with a probability proportional to R 0 /R i , where R 0 is the initial radius and Ri is the radius of the i th aggregate When two approaching particles (A and B) overcome the potential barrier (surface gap distance H < Hmax), they aggregate forming an unique particle with radius Rp=(R A 3 +R B 3 ) 1/3 and positioned in the center of mass of two aggregating spheres. Let’s start with Simulations!!! R 0

18. Experimental evidence of thermal activated process Two evident effect of the increasing temperature : Net increment of the mean cluster radius close to the isoelectric point Shifting of  -potential curves Temperature dependence of the amount of the adsorbed polyelectrolyte S.Sennato, D. Truzzolillo , F.Bordi, C.Cametti, Langmuir 24, 12181 (2008).

19. Agreement with the model and rescaling with T………  (  ) is a Bell-shaped Gaussian distribution whose width is determined by the extention of condensation region Rescaling radii with T all the points collapse on the same master curve Typical behavour of a thermal activated process

21. Deteiled MC - simulations T= 298.16 K  LJ =K B T/1.2 k F ≈ K B T Typical DOTAP liposome suface charge density  =[(2F 2 c s )/(  RT)] 1/2 Uniform charge density Debye constant for a 1:1 salt Room temperature Energy scale of excluded volume interaction Binding coupling between adjacent monomers 20 monomers for chain  = N e /S =1.67 nm -2 2R= 7nm, 10 nm

22. Deteiled MC - simulations : creation of complexes N chains + one macroion One Complex Stabilization of the adsorption process Replication of the PE-colloid complex Two complexes MC-simulation: traslational moves of single monomers and rotational moves of the whole polyelectrolyte layer around a colloid. Calculation of the mean force potential

23. Patch attraction. When does it occur? For  R<1 the interaction between complexes is well fitted by the repulsive interaction due to the presence of a residual net charge Where is the patch attraction? Non-neutral complex (  s = 0.57)

24. Patch attraction. When does it occur? Increasing the ionic strength short range attraction appears Dominance of the attractive interaction between opposite heterogeneous surfaces. Confinement of interactions: Interacting surfaces rather than interacting particles Overlap of opposing PE-layer generates Repulsive steric contribution at very short distance

25. The effect of charge ratio on the potential shape . . .  R = 5 ≈ (  R) pd-liposomes Existence of a potential barrier as predicted by double layer theory. Competition between monopole-monopole repulsions and energetic bridging. The presence of flat PE-layer induces Energetic bridging between complexes (attractive interaction)  s =2  Superficial charge ratio

26. on the the total pair interaction potential . . . The presence of PE-layer adds a “soft” repulsive contribution at very short distances Reentrant behavior of the global minimum depth The depth of the global minimum is strongly influenced by the PE-layer structure. In presence of tails the overlap of chains increases the repulsion.

27. Polarization effects: antiparallel dipolar doublets The dipole moments are always directed in opposite directions. Inversion at the isoelectric point. Anti-parallel doublets.

28. The standard deviation of the surface potential Low PE content : flat layers   A with negative concavity and global maximum (stripes model). High PE content : protruding tails  monotonic increase of  A.

32. Perspectives and future developments Further investigations on the second virial coefficient close to the isoelectric point. SLS tecnique  Zimm plot + lipoplexes static form factor. AFM measurements: Structural properties of adsorbing polyelectrolytes. Possible biomedical applications: developing a new class of vectors for multi-drug delivery . Anti-HIV therapy. Simulations: Study of the effect of the size of spherical macroions, temperature and valence of chains (charge mismatch); Extension to Polyampholytes.

33. Thank you for your attention! Acknowledgments: Dr. S. Sennato, Prof. F. Bordi, Prof C. Cametti, Prof. F. Sciortino, Dr. E. Zaccarelli. Grazie, Roma! … and now let’s go to Crete!

34. 1 . D.Truzzolillo, F.Bordi, C.Cametti, S.Sennato. Phenomenological sur face characterization of cationic-lipid monolayers in the presence of oppositely charged polyions. Coll. Surf. A, 319, 51. (2008) 2 . F.Bordi, C.Cametti, S.Sennato, D.Truzzolillo. Strong repulsive in teractions in polyelectrolyte-liposome clusters close to the isoelectric point: a print for an arrested state. Phys. Rev. E, 76, 061403, (2007) 3 . D.Truzzolillo, F.Bordi, F.Sciortino, C.Cametti. Kinetic arrest in inhomogeneously-charged particle aggregation. Eur. Phys. J. E 29 2 (2009) 229-237. 4 . S. Sennato, D.Truzzolillo, F. Bordi, C. Cametti. Effect of Tempera ture on the Reentrant Condensation in Polyelectrolyte-Liposome com plexation . Langmuir, 24 (21), 12181-12188, (2008). 5 . D. Truzzolillo, F. Bordi, C. Cametti, S. Sennato. The counterion condensation of differently flexible polyelectrolyte aqueous solutions in the dilute and semidilute regime. Phys. Rev. E, 79 011804, (2009). 6 . D.Truzzolillo, C.Cametti, S.Sennato. Dielectric properties of differ ently flexible polyions: a scaling approach. Phys. Chem. Chem. Phys., 11, 1780, (2009). 7 . S.Sennato, D.Truzzolillo, F.Bordi, F.Sciortino, C.Cametti. Colloidal particle aggregates induced by particle surface charge heterogeneity. Coll. Surf. A, 343, 34. (2009) 8 . F. Bordi, S. Sennato, D. Truzzolillo. Polyelectrolyte induced aggrega- tion of liposomes: a new cluster phase with interesting applications. REVIEW - J. Phys: Condensed Matter, 21, 203102, (2009) 9 . C. Cametti, S. Sennato, D. Truzzolillo. Deviations from a simple Debye relaxation in aqueous solutions of differently flexible polyions induced by polymer concentration. J. Chem. Phys. 131, 034901 (2009) Publications In Preparation: 10 - D. Truzzolillo, F. Bordi, F. Sciortino, S. Sennato. Interaction between polyelectrolyte-colloid complexes: a Monte Carlo simulation study in the Debye-Huckel approximation.

35. Nota linguistica nanòmetro o nanomètro [comp. di nano- e metro; 1981] s. m. * (fis.) Unità di misura di lunghezza pari a 10 -9 m. SIMB. nm. fonte: Zingarelli