Polycations reactions

Table 5 summarizes the type of complex produced for each polyanion-polycation pair investigated. There are relatively few systems which yielded soluble complexes (13.6%) with the majority of polyanion-polycation reactions yielding either precipitates (43.7%) or weak membranes (30.7%). Indeed, as one scans across rows of polycations or down columns of polyanions, many of the naturally occurring or synthetic species predominantly form precipitates. This is, perhaps, due to the high content of ionic groups (one per repeat unit) charac-... 

The increase in entropy associated with release of counterions in a polyanion-polycation reaction has been reported for some polycation—polyanion pairs. Interestingly, data reported for binding of positively charged hgands to double stranded DNA generally confirm that the extent of counterion release is near... 

Preparation of Pillared Clay Catalysts. PAG products are used for the preparation of zeolite-like catalysts by intercalation, the insertion of Al polycations molecules between the alurninosiHcate sheets of clay (3,33). Aqueous clay suspensions are slowly added to vigorously stirred PAG solutions, and the reaction mixture is aged for several hours. The clay is separated from the PAG solution and washed free of chloride ion. The treated clay is first dried at low temperature and then calcined in air at 450—500°G, producing a high surface area material having a regular-sized pore opening of about 0.6 to... 

Meisel etal. [18-20] were the first to investigate how the addition of a polyelectrolyte affects photoinduced ET reactions. They found that charge separation was enhanced as a result of the retardation of the back ET when poly(vinyl sulfate) was added to an aqueous reaction system consisting of tris(2,2 -bipyridine)ruthenium(II) chloride (cationic photoactive chromophore) and neutral electron acceptors [21]. More recently, Sassoon and Rabani [22] observed that the addition of polybrene (a polycation) had a significant effect on separating the photoinduced ET products in an aqueous solution containing cir-dicyano-bis(2,2 -bipyridine)ruthenium(II) (photoactive donor) and potassium hexacyano-ferrate(III) (acceptor). These findings are ascribable to the electrostatic potential of the added polyelectrolytes. 

As a polycation, chitosan spontaneously forms macromolecular complexes upon reaction with anionic polyelectrolytes. These complexes are generally water-insoluble and form hydrogels [90,91]. A variety of polyelectrolytes can be obtained by changing the chemical structure of component polymers, such as molecular weight, flexibility, fimctional group structure, charge density, hydrophilicity and hydrophobicity, stereoregularity, and compatibility, as... 

The interaction of polycations with free chalcogens leads, in some cases, to new cluster compounds.185 Reaction of the aromatic tetraatomic selenium dication with diphenyldiselenide affords Ph2Se62+ - compound 159 with a six-membered selenium ring (Scheme 66).186... 

Sensors based on the above reaction scheme have been developed for Al3+, Zn2+, Cu2+, Ca2+, Pb2+, Hg2"1", K+, Li+, etc. A polycation, protamine sensor has also been developed using 2/7/-dichlorofluorescein octadecyl ester (DCFOE) doped in polymer membranes. However, most of these sensors are pH dependent due to the pH dependence of the cation complexation reactions. The cation ion indicators can be immobilized on any solid support, such as silica, cellulose, ion-exchange resin, porous glass, sol-gel, or entrapped in polymer membranes. 

Aluminum polycations are obtained by the controlled hydrolysis of AI(III) solutions the extent of the hydrolysis reaction can be monitored with pH measurements. The products of the hydrolysis reactions, I.e. the successive generation of polycations of Increasing degree of polymerization with Increasing extent of hydrolysis, must be Inferred from non-equilibrium measurements. Thus, equilibria between many polycatlonic species, I.e. [Al2lOH)2] , [A124(0H)5q]" 12, etc., were proposed. More recently, " A1 NMR has... 

The effect of dilution on the polycations present In the Chlorhyd-rol solution can be understood by considering two types of reactions - hydrolysis and olatlon. A typical hydrolysis reaction Is Illustrated by Equation 1. 

Polycations result from the concurrent process of polymerization or olatlon. An example of an olatlon reaction Is given by Equation 2 where the basic complexes react with each other via hydroxyl bridges to form polycations. 

These polycations can be further hydrolyzed or react with each other to give a large number of possible polycations. The olatlon reaction occurs without a change In solution acidity but does change the concentration of hydrolyzed species In solution. Dilution causes the reversal of reaction 2 (I.e., depolymerization) and the Introduction of new hydrolyzed species Into solution. The new species formed can then re-equilibrate through the hydrolysis reaction. The kinetics of aging depend on the relative rates of the olatlon and hydrolysis reactions. 

The eight-atom systems provide a compelling illustration of the structural diversity of tellurium polycations. There are examples of (a) structural isomers of the monomeric dication Tcg, (b) a polymeric (Teg ) cation and (c) a tetracation Teg" . Unlike cyclo-Sg and -Seg , the Teg dication cannot be made by oxidising tellurium with MF5 (M = As or Sb) in liquid SO2. However, the reactions of (a) the tellurium subhalide Te3Cl2 with ReC at 200 °C and (b) tellurium with WCl6 at 180°C produce the salts Teg[MCl6] (w=l, M = Re ... 

The activation parameters are presented in Table 819 For the reactions be between the Co(III) complex2+ and Fe-edta2-, (a) to (c) in Table 8, the activation enthalpy is smaller and the activation entropy larger than for the reduction by Fe2+, (d) to (f), which is a reaction of two cations. A comparison of the parameters for the polymer complex, (b) or (c), with those for the pyridine complex, (a) shows that the acceleration for the PVP or QPVP complex is based on a decrease in activation enthalpy and an increase in activation entropy. This is the opposite of the polyelectrolyte-catalyzed reaction, in which the acceleration is due to an increase in activation entropy (compare(e) with (d)). In the polyelectrolyte-catalyzed system the acceleration and increase in activation entropy are attributed to the increase in the local concentration of the two reactants, the Co(HI)-Py complex2 and Fe2+ 84, whereas in the reaction of the polymer complex the large activation entropy and small activation enthalpy are held to be due to the increase in the local concentration of the reactant Fe(II)-edta2 and the electrostatic attraction between the reactant and the Co(III) complex, which is fixed to the polycation chain. 

The electrostatic effect of the poly(4-vinylpyridine)-Cu(II) catalyst was also reported by Dadze et al. 115). Oxidation of ascorbic acid, salicylic acid, and tri-t-butylphenol was accelerated and that of p-phenylenediamine retarded by the poly(4-vinylpyridine) ligand at lower pH. As described in Section IIIA, a polymer-metal complex behaves as a polycation in aqueous solution, and the reaction is sensitive to the charge of low-molecular-weight species. The electrostatic effect due to the polycationic domain of a polymermetal catalyst is also predominant in the oxidation of charged substrates. 

There are mercury compounds with mercury oxidation numbers lower than +1, e.g. +0.5,16,21 +0.6713,15,27 or +0.35.18,20 Yellow crystals of Hg3(AsF6)2 have been formed by the reaction of metallic mercury with AsFs in liquid S02.13 X-Ray structure determination showed a linear polycation Hg+—Hg—Hg+ with Hg—Hg distances of 255 pm.15 Metallic mercury and SbF5 react in liquid S02 to form Hg3(Sb2Fu)2.15,23 The Hg—Hg distances in the complex Hg3(AlCU)2 are 256 pm 14 the Hg—Cl distances are 251 and 256 pm the Hg—Hg—Hg angle is 174°. Dark red crystals of Hg4(AsF6)2 were obtained in liquid S02. This coordination compound contains centrosymmetric Hg4+ ions, which are connected to chains (see l).21... 

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