Abstract
Highly charged polyelectrolytes can self-assemble in presence of condensing agents such as multivalent cations, amphiphilic molecules or proteins of opposite charge. Aside precipitation, the formation of soluble micro- and nano-particles has been reported in multiple systems. However a precise control of experimental conditions needed to achieve the desired structures has been so far hampered by the extreme sensitivity of the samples to formulation pathways. Herein we combine experiments and molecular modelling to investigate the detailed microscopic dynamics and the structure of self-assembled hexagonal bundles made of short dsDNA fragments complexed with small basic proteins. We suggest that inhomogeneous mixing conditions are required to form and stabilize charged self-assembled nano-aggregates in large excess of DNA. Our results should help re-interpreting puzzling behaviors reported for a large class of strongly charged polyelectrolyte systems.
Highlights
Diverse suspended aggregates can be formed in solution by interaction of oppositely charged components
Previous light scattering studies[26,27] showed that DNA and protamine molecules diluted in an aqueous solution of low ionic strength may form soluble complexes of dozens of nanometer size. This soluble state contrasts with the macroscopic phase separation observed at the isoneutrality point for which the charge ratio R+/− was found equal to 0.85, a value slightly lower than the nominal isoneutrality R+/− = 1
We are interested here in studying the soluble DNA-protamine complexes formed in the two regions of solubility, namely in excess of DNA (R+/− < 0.85) and in excess of protamines (R+/− > 0.85) when a small drop of a concentrated protamine solution is directly added to the DNA solution
Summary
Diverse suspended aggregates can be formed in solution by interaction of oppositely charged components. Let us mention for example hexagonal polymer-cationic surfactant complexes[1,2], hollow icosahedron made of catanionic surfactants[3], DNA-dendrimers or DNA-lipopolyamines complexes[4,5,6]. Such nano-aggregates have been often obtained with biological components and their structure has been explored (see for example[7,8,9,10]). We focus here on the mechanisms involved in their formation and stability by using a combination of multiple experimental and simulation approaches
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