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Scientific Report 2007-2009
Condensed matter physics and biophysics
C25. Biopolymer Vesicle Interactions
The interactions between biopolymers (proteins or nucleic
acids) and self-assembled surfactants have raised increasing
interest within the scientific community. Studies
along these lines constitute an interdisciplinary approach
of chemical/physical nature at the biomolecular
level. In addition to so much intrinsic interest, the
investigations contribute to important applications in
biomedicine as gene therapy. Synthetic vectors, such
as liposomes, represent an interesting alternative to viral
delivery systems. However, they are rather difficult
to prepare and generally have limited stability and shelf
life duration. A new class of self-assembled amphiphilic
aggregates, called cat-anionic vesicles, has been developed
in recent years, and their chemical-physical properties
have been exhaustively characterized. The acronym
cat-anionic defines surfactant aggregates formed by nonstoichiometric
amounts of anionic and cationic surfactants
coexisting with tiny amounts of simple electrolytes.
Cat-anionic vesicles are easily prepared and very stable.
[1]. The formation of lipoplexes among proteins and
SDS-CTAB vesicles was characterized [2]. Other work
concerns studies of DNA interacting with several catanionic
vesicles [3, 4]. In particular, an investigation on
DNA, interacting with SDS-DDAB cat-anionic vesicles,
was performed, mainly used dielectric relaxation (Fig.
1) and Zeta-potential (Fig.2) techniques.
Figure 2: Zeta-potential as function of DNA in the vesicular
pseudosolvent, expressed in terms of molar ratio R. The gray
area indicates the region where complexes tend to flocculate.
The shift to near zero values of the dielectric increment
and Zeta-potential, caused by the addition of
DNA to the vesicular suspension and the occurence of
a subsequent contribute of the nucleic acid, at higher
concentrations, clearly demonstrates the electrostatic
nature of the interactions (Fig. 1, 2). The conditions
of saturation of the molecular bond were established.
Important indications about the structural arrangement
of DNA on the vesicle surface were achieved.
Finally, the possibility of a controlled release of the
bio-macromolecule was verified.
Figure 1: Dielectric dispersion of DDAB-SDS vesicle suspension
with increasing DNA content. R is the molar ratio.
Panel A: bare vesicles, R=0, (◦); R=0.2, (▽); R=0.4, (□);
R=0.6, (♢). Panel B: R=0.6, (•); R=1.2, (); R=1.5, ().
The insets show the dielectric relaxation loss.
References
1. A. Ciurleo et al., Biomacromolecules 8, 399, (2007).
2. C. Letizia et al., J. Phys. Chem. B 111, 898 (2007).
3. A. Bonincontro et al., Biomacromolecules 8, 1824, (2007).
4. A. Bonincontro et al., Langmuir 24, 1973, (2008).
Authors
A. Bonincontro, C. La Mesa 2 , G. Risuleo 2
The biophysical characterization of vesicle - biopolymer
interactions may contribute to a better use of these
surfactant aggregates in biotechnology. A biophysical
approach, mainly based on the combination of biochemical
assays, electrochemical and spectroscopic techniques,
is used in our laboratory. Different surfactant systems
interacting with proteins and DNA were investigated. A
fully fluorinated surfactant, lithium perfluorononanoate,
induces a molten globule conformation for lysozyme
Sapienza Università di Roma 78 Dipartimento di Fisica