Cationic agents

Quaternary ammonium compounds (quats) are prepared - by moderate heating of the amine and the alkyl halide in a suitable solvent - as the chlorides or the bromides. Subsequently conversion to the hydroxides may be carried out. Major applications of the quat chlorides are as fabric softeners and as starch cationizing agent. Several bio-active compounds (agrochemicals, pharmaceuticals) possess the quat-structure. Important applications of quat bromides are in phase transfer catalysis and in zeolite synthesis. 

The cationic agents used for their antimicrobial activity all fall within the group known as the quaternary ammonium compounds which are variously described as QACs, quats or onium ions. These are organically substituted ammonium compounds as shown in... 

As mentioned in Table 8.1, amphoteric surfactants contain both an anionic and a cationic group. In acidic media they tend to behave as cationic agents and in alkaline media as anionic agents. Somewhere between these extremes lies what is known as the isoelectric point (not necessarily, or even commonly, at pH 7), at which the anionic and cationic properties are counterbalanced. At this point the molecule is said to be zwitterionic and its surfactant properties and solubility tend to be at their lowest. These products have acquired a degree of importance as auxiliaries in certain ways [20-25], particularly as levelling agents in the application of reactive dyes to wool. 

Anionic and cationic products generally tend to interact with each other, usually diminishing the surface-active properties of both and often resulting in precipitation of the complex formed. Amphoteric compounds can also be incompatible with anionics in acid solution but are generally compatible with cationics and nonionics. Interaction between anionic and cationic agents can sometimes be prevented by addition of a nonionic. In some cases, if an ethoxylated sulphate or phosphate is used as the anionic component a cationic compound produces no obvious precipitation, since the oxyethylene chain acts as dispersant for any complex that may be formed. 

Cationic agents generally are less useful than anionics as detergents but they have useful properties as softeners, germicides and emulsifiers. 

The complexing of chitosan and its basic derivatives with anionic substances is paralleled by compatibility with cationic and nonionic compounds. Similarly, the anionic derivatives of chitosan show complex formation with cationic agents and are compatible with anionic and nonionic compounds. The capability of these chitosan derivatives to complex with certain metal ions, notably those of the transition series, is also important, having possibilities for the removal of metal salts from effluent. The hierarchy in terms of binding capacity is Cr(III) < Cr(II) < Pb(II) < Mn(II) < Cd(II) < Ni(II) < Fe(II) < Co(II). 

The third method of obviating precipitation of an ionic agent-ionic dye complex is to choose what effectively amounts to a modified ionic agent. Ethoxylated anionic and ethoxylated cationic agents are particularly useful in this respect. The ethoxylation tends to... 

Table 10.44 Classes of polymeric cationic agents for aftertreatment of dyed cellulosic fibres [448]...

Use sulphonic acids as anionic agent and quaternary ammonium salts as cationic agent. For both agents be aware of electro-active contaminants. 

On the other hand, the negatively charged Kdo-lipid A domain constitutes a target for binding of certain antibiotics, such as polymyxin B (125) and basic peptides derived from host cells such as the bactericidal/perme-ability-increasing protein (BPI) (261). In this respect the Kdo-lipid A domain constitutes a weak site of the outer membrane, rendering bacteria vulnerable to the action of cationic agents. 

Subsequent finishing of the crude product typically involves heating the aqueous pigment suspension, frequently to temperatures of 100 to 150°C. The crude pigment slurry is thus heated under pressure. This technique may be varied to a certain extent. It is possible, for instance, to add or to exclusively use either water soluble or water immiscible organic solvents or to add surface-active nonionic, anionic, or cationic agents. 

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... 

Themis, M., Forbes, S.J., Chan, L., Cooper, R.G., Etheridge, C.J., Miller, A.D. et al. (1998) Enhanced in vitro and in vivo gene delivery using cationic agent complexed retrovirus vectors. Gene Ther., 5, 1180-1186. 

The exercise of preparing emulsions using oils-mixed additives is well described in Emulsification and Polymerization of Alkyd Resins (Gooch 1980, 2002), although without the addition of acidic or cationic agents for the purpose of inhibiting or destroying bacteria. 

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