Charge-driven self-assembly

The issue of critical polyelectrolyte adsorption is intimately coupled to the polymer-mediated bridging attraction between oppositely charged macro-ions immersed in a polymer solution. Moreover, electrostatically driven self-assembly of single-stranded RNA molecules on the interior of positively charged capsids, as it occurs in many spherical and rod-Uke single-stranded viruses, offers another field for potential applications of our theoretical results. The WKB method developed above has recently been implemented to weak polyelectrolyte adsorption under confined conditions [49] and to adsorption onto low-dielectric interfaces [50]. The power of the WKB approach can even be extended to more complicated adsorption situations, such as patchy surfaces, specific charged patterns on concave and convex interfaces, Janus particles, etc., and other (nearly arbitrary) potentials of polyelectrolyte-surface interactions. This might open an avenue to approach more realistic situations of polyelectrolyte adsorption and to quantitatively reproduce experimental results in the future. 

More recently, a new method of assembling multilayers of PB on surfaces has been described.110 In contrast to the familiar process of self-assembly, which is spontaneous and leads to single monolayers, directed assembly is driven by the experimenter and leads to extended multilayers. In a proof-of-concept experiment, the generation of multilayers of Prussian blue (and the mixed Fein/Run analog ruthenium purple) on gold surfaces by exposing them alternately to positively charged ferric cations and [Fe(CN)6]4- or [Ru(CN)f,]4 anions has been demonstrated.110... 

The general chemistry used in this approach involves the combination of a limited amount of an amine-terminated dendrimer core reagent with an excess of carboxylic acid terminated dendrimer shell reagent [31]. These two charge differentiated species are allowed to self-assemble into the electrostatically driven supramolecular core-shell tecto(dendrimer) architecture. After equilibration, covalent bond formation at these charge neutralized dendrimer contact sites is induced with carbodiimide reagents (Scheme 1). 

D Souza E, Maligaspe E, Ohkubo K et al (2009) Photosynthetic reaction center mimicry low reorganization energy driven charge stabilization in self-assembled cofacial zinc phthalocy-anine dimer-fullerene conjugate. J Am Chem Soc 131 8787-8797... 

The technique of alternating polyelectrolyte film construction has also been adapted to incorporate semiconductors into layered films. For example, multilayer films have been constructed by alternately dipping a quartz substrate into a solution of poly(diallylmethylammonium chloride) and then a solution of a stabilized CdS or PbS colloid (41). The layer-by-layer self-assembly of alternating polymer and metal sulfide is at least partially driven by the electrostatic attraction of the cationic polymer and the negative charge of the stabilized MC colloid particles. 

There are number of common features shared by self-assemblies [4], First, self-assembly reflects information coded in individual components. The information can be shape, surface properties, charge, polarity, mass, and so on, and such characteristic information determines the interactions between components. Second, the components are mobile with respect to each other, driven by the attraction or repulsion as a result of the interactions between components. Third, the self-assembly process usually occurs in fluid phases or on smooth surface which assist the movement of components. Finally, self-assembling components should be able to reach equihbrium between aggregated and nonaggregated states, or adjust their relative position once in an aggregate. 

Electrostatic interactions are also described to be the main driving force in the self-assembly of structures between Lf (a globular protein) and a-casein, p-casein or K-casein (unstructured proteins) at neutral pH [132]. As expected for electrostatic-driven complexes, the size of the formed complexes is affected by pH and ionic strength. The size of the complex decreases with increasing salt or when the pH shifts away from the pH for charge equiUbration. For this latter case, it is assumed that the growth of the complexes is limited by the accumulation of charge on the surface of the self-assembled structures. 

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