Polycationic systems

Chitosan has been recently found to be soluble in alkaline media, viz. NH4HCO3 solutions, where it assumes the ammonium carbamate form Chit-NHC02 NH4, i.e., a transient anionic form that keeps it soluble at pH 9.6, while reversibly masking the polycationic nature of chitosan. Because ammonium carbamates and NH4HCO3 decompose thermally and liberate CO2, NH3 and water, this alkaline system is suitable for producing chitosan microspheres by spray-drying (Table 1) [206]. 

The number of known polycationic compounds of main group elements is far less than that of polyanionic compounds. Examples include the chalcogen cations S]+, S]+, Se]o and Teg that are obtained when the elements react with Lewis acids under oxidizing conditions. The ions S]1, Sc]1 and Te] have a square structure that can be assumed to have a 6n electron system. 

Formation of a complex between DNA and polycationic compounds appears to be the initial and quite possibly a critical parameter for nonviral gene delivery. Several synthetic vector systems, which are generally cationic in nature, including poly(lysines), cationic liposomes or various types of block copolymers and recently dendrimers, have been shown to self-assemble with plasmid DNA [13-15] [16]. Specific physicochemical properties manifested by these DNA complexes depend on the type of cationic agent used however, interesting patterns for such interactions are beginning to evolve [17, 18]. Under certain conditions, the interaction of DNA with polyvalent cations results in... 

The polymers are obtained directly in a conductive polycationic form in which charge-compensating counter anions from the electrolyte system are intercalated... 

The method proposed by Blumstein at is based on the conductivity measurements. It is suitable for the systems in which shift of ionization equilibrium during polymerization takes place. This method was successfully applied to follow template polymerization of p-styrene sulfonic acid in the presence of polycationic ionenes used as template. The results confirm data obtained for the same system by another methods. 

Methods were described for the incorporation of proteins in the form of noncovalent complexes with polycationic reagents, into sustained release systems where the polycation stabilizes the protein against inactivation while it resides in the delivery device, and retards release of the protein from the delivery device [469,470]. A variety of polycations have been used, including simple polyamino acids such as polylysine or polyarginine, protamine and chitosan. The end result was the release of the active agent with retention of biological activity, with a high cumulative field and over a sustained period of time. 

In DNA, the polyanionic backbone dominates the physical properties of DNA. Replacing one nucleobase with another, therefore, has only a second-order effect on the physical behavior of the molecule. That allows nucleobases to be replaced during Darwinian evolution without losing properties essential for replication. Therefore, a repeating charge may be a universal structural feature of any genetic molecule that supports Darwinian evolution in water. Polycationic backbones may be as satisfactory as polyanionic backbones, however. Thus, if NASA missions detect life in water on other planets, its genetic system is likely to be based on polyanionic or polycationic backbones even if its nucleobases differ from those found on Earth. That structural feature can be easily detected with simple analytical devices. 

This article discusses size and charge data for nanoparticles produced in both batch and continuous processes from two different polymer systems. In both systems, a polyanionic solution is atomized into a swirling bath of polycationic solution, forming nanoparticles as the solutions come together. This method of mixing solutions used to produce the nanoparticles is often referred to as titration (sequential addition of one polymer into another). Different ratios of polyanion to polycation were used to vary the composition of the nanoparticles, which were then evaluated for their size and charge. 

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