Polycation, defined

Figure 2 (a) A schematk representation of a diamond-like network formed from tetrahedral tetracations and linear dianions. The volume of the polycation and the length of the dianion will play a crucial role in determining the size of the nanometersized voids present in the network, (b) A schematic representation of electrostatic enforcement of anion networks by polycations. For convenience, the concept is portrayed in two-dimensional space. The topology of each cation is defined by the spatial arrangement of the individual cationic centers... 

Metal oxo-alkoxides, MO (OR)x 2 > , may be considered intermediates between metal alkoxides M(OR)x and the corresponding metal oxide, and are the counterparts of the polyanions and polycations in aqueous systems. Controlled partial hydrolysis of M(OR)x (Equation (20)) does indeed sometimes result in structurally well-defined metal oxo-alkoxo oligomers (clusters) where //2—0x0 ligands connect the metal polyhedrons from which the clusters are constructed. 

Most of the results reported herein on the sorption of polycations by natural keratins have been obtained on simplified model systems. The rationale behind such an approach was to seek to determine the fate of sorbing polymer under well-defined conditions and so to obtain mechanistic insight. The results have clearly indicated that both adsorption and absorption processes can occur. They have also shown that the nature, extent, and consequences of polycation sorption can all be influenced by the presence of surfactant. In general, nonionic surfactants have a small effect on sorption, because of low interaction while cationic surfactants can have a very large effect because of competition for the sorption sites. Because of interaction and complex formation with cationic polyelectrolytes anionic surfactants can exercise an intermediate, but potentially very important, influence. 

Abstract This review concentrates on the interactions between oppositely charged polyelectrolytes and on the formation of complexes, which can be used for different applications such as paper retention or water treatment. Three different possibilities for the appearance of polyelectrolyte complexes (PECs) in flocculation applications are described. Starting with the classical dual system (step-by-step addition of polycation and polyanion to a negatively charged suspensimi of fibers or particles), the interaction between a soluble polyanion (such as anionic trash) with polycation is described as well as the formation of well-defined pre-mixed PECs and their application as flocculants. 

Some challenges remain concerning the synthesis and structure of these polymers for instance, finding new biocompatible polymers other than PEG. Moreover, in order to define clear structure-function relationships, it is necessary to use new polymerization techniques to obtain well-defined materials rather than randomized polymers [241]. Similarly, more architecturally controlled macromolecules such as dendronized polymers appear to be promising prospects in the field of polycations for gene delivery [242]. 

It has been reported [57, 58] that the formation of soluble PE-P complexes is initiated at a specific pH called the critical pH (pHc), which is a function of ionic strength, the protein isoelectric point, and the PE density charge [59]. For polycations, pHc preceded the pH of visual phase separation, named pH( ). This parameter is defined as the pH at which the half maximal value of turbidity is achieved. Since these non-soluble complexes can be considered a phase separation, the ionic strength dependences of both pHc and pH([), can be viewed as phase boundaries. The phenomenon has been ascribed to the attraction between PE charges and oppositely charged patches on the protein surface [5]. This could be applied to complexation between oppositely charged proteins and PE. 

The amorphous gel formed immediately upon neutralization of acidic solutions [55] is a metastable and poorly defined phase. It is probably due to aggregation of intermediate and inert species such as the Al polycation. During the evolution of the.gel at room temperature, the NMR peak characteristic of Al(lll) in tetrahedral... 

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