Polycationic nature

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]. 

Stoddart and co-workers have made use of Frechet-type dendrons as dendritic stoppers for self-assembled [n]rotaxanes [65]. The solubility enhancement that results from incorporating dendritic wedges at the termini facilitated the purification of these materials by column chromatography despite the polycationic nature of their bipyridinium backbone. Again, the dendritic wedges did not alter the electrochemical characteristics of the viologen subunits. Flowever, the enhanced solubility resulting from the presence of the dendritic components en-... 

In cell membranes both poly-APS (77) and halitoxin (74) induce transient pores [30,53,55]. These pores are large enough to allow the introduction of macromolecules such as DNA into cells. It has been shown that poly-APS are particularly effective in this regard [54]. Their polycationic nature enables them to bind and condense DNA and subsequently allow passage of large pieces of supercoiled DNA or a particular cDNA plasmid into the cell. 

Chitosan, due to its polycationic nature, is gaining enormous attention for its unique properties such as biodegradability, biocompatibility with animal and plant tissues, non-toxic nature, anti-bacterial, anti-fungal, anti-viral, anti-acid, anti-ulcer, non-toxic, non-allergenic, etc., as well as film formation, fiber formation, bead formation, hydrogel formation, etc. By virtue of these properties, chitosan has prospective applications in many fields such as medical, water treatment, cosmetics, dentifrices, food, and textile industries. In textiles, it can be used in the primary production of fibers, textile auxiliary chemicals and finishing agents [1,4-6]. 

Attributing to the polycationic nature and several inherent properties, chitosan is currently receiving a great deal of interest as regards its applications in several diversified areas such as medical, food, textiles, water processing, cosmetics, agriculture, and paper [2],... 

A major drawback of nanopartides formulated using cationic polymers that has limited thdr progress toward use in dinical trials is toxidty. Although the molecular basis of toxidty is undear, the polycationic nature of the polymers appears to be the main origin of toxidty. Thus, recent efforts to devdop polymers with reduced toxidty have focused on low-MW polymers, biodegradable polymers, and polymers with reduced cationic charge density. 

As mentioned previously, because of the polycationic nature of chitosan in acidic media, the biopolymer may be intercalated in sodium montmorillonite through cation exchange and hydrogen-bonding processes, the resulting nanocomposites showing interesting structural and functional properties. 

PAIs have been explored for a range of biomedical applications based around their polycationic nature, which allow electrostatic interactions with anions. In most applications the anion is a phosphate group, as present in nucleic acids. However, a few applications with other anions have been reported as well. This section will introduce the most important biomedical applications of PEI, again limited by the sparse literature on the use of other PAI analogues. 

Cuanidino groups are also present in streptomycin, which was the first aminoglycoside antibiotic used in treating tuberculosis. Streptomycin and related antibiotics interfere in the translation of RNA into protein and this is probably due to their polycationic nature and ability to mimic both Mg and polyamines that are involved in phosphate group stabilisation. 

Polyamines (PAs) are biologically ubiquitous aliphatic nitrogen-containing compounds of low molecular weight and polycationic nature. The diamine putrescine and the triamine spermidine are probably synthesized by all orga-... 

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