Cationic properties

The higher aUphatic amine oxides are commercially important because of their surfactant properties and are used extensively in detergents. Amine oxides that have surface-acting properties can be further categorized as nonionic surfactants however, because under acidic conditions they become protonated and show cationic properties, they have also been called cationic surfactants. Typical commercial amine oxides include the types shown in Table 1. 

Positively charged ion in aqueous solution such as hydrogen (H+) or calcium (Ca2+) ions. Certain chemicals may therefore be cationic and exhibit cationic properties. 

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. 

Reaction 2.10 describes the loss of a radical, whereas reaction 2.11 corresponds to the loss of a molecule, thereby conserving the radical cation property of the molecular ion in the fragment ion. Bond breaking is a endothermal process and thus the potential energy of the fragment ion is usually located at a higher energy level (Fig. 2.4). 

As previously mentioned, amphoteric surfactants presently represent a minor fraction of the total surfactants production with only specialty uses. They are compounds with both anionic and cationic properties in aqueous solutions, depending on the pH of the system in which they work. The main types of these compounds are essentially analogs of linear alkane sulfonates, which provide numerous points for the initiation of biodegradation, and pyridinium compounds that... 

At its isoelectric point, histidine is said to be zwitterionic, as it has both anionic and cationic properties. Most other amino acids are also zwitterionic at neutral pH. Peptides and proteins also have isoelectric points, which can vary widely depending on the composition of the amino acids. 

Chlorhexidtne is a symmetrical cationic molecule that is most stable as a salt the highly water-soluble digluconate is the most commonly used preparation. Because of its cationic properties, it binds strongly to hydroxyapatite (the mineral component of tooth enamel), the organic pellicle on the tooth surface, salivary proteins, and bacteria. Much of the chlorhexidine binding in the mouth occurs on the mucous membranes, such as the alveolar and gingival mucosa, from which sites it is slowly released in active form. 

The stability constants are defined here in terms of concentrations and hence have dimensions. True thermodynamic stability constants K° and (3° would be expressed in terms of activities (Section 2.2), and these constants can be obtained experimentally by extrapolation of the (real) measurements to (hypothetical) infinite dilution. Such data are of limited value, however, as we cannot restrict our work to extremely dilute solutions. At practical concentrations, the activities and concentrations of ions in solution differ significantly, that is, the activity coefficients are not close to unity worse still, there is no thermodynamically rigorous means of separating anion and cation properties for solutions of electrolytes. Thus, single-ion activity coefficients are not experimentally accessible, and hence, strictly speaking, one cannot convert equations such as 13.6 or 13.8 to thermodynamically exact versions. 

Arsenobetaine is zwitterionic in solution, displaying cationic properties at pH <3.5 (39). The first reported isolation of arsenobetaine was greatly facilitated by its retention on a cation-exchange resin and subsequent elution with dilute aqueous ammonia (48). Arsenocholine, however, remains cationic at high pH and requires forceful conditions (e.g., 6 M HC1) to displace it from cation-exchange resins—a property it shares with TeMA. 

Although there are similarities between the chemistry of the chalcogenide elements, the properties of selenium and tellurium clearly lie between those of non-metallic sulfur and metallic polonium. The enhancement in metallic character as the group is descended is illustrated in the emergence of cationic properties by polonium, and marginally by tellurium, which are reflected in the ionic lattices of polonium(IV) oxide and tellurium(IV) oxide and the formation of salts with strong acids. 

III. Influence of Cation Properties on Metal(I) Coordination Number... 

That there is a relationship between the coordination number of the metal in crystalline halogenocuprates(I) and halogenoargentates(I) and the properties of the cation with which it is coprecipitated would now seem to be well established. The tuning of anionic configurations to cation properties reflects the versatility in coordination requirements not only of the metal but also of the ligands. Cation size would appear to be of prime importance for the determination of a particular metal(I) coordination number, the tendency to attainment of a higher coordina-... 

Box 3.1 Selective binding of Alkali Metal Cations Properties of alkali metal cations ... 

Amine oxides are the reaction products of tertiary amines and hydrogen peroxide. In aqueous solutions fatty amine oxides exhibit non-ionic or cationic properties depending on pH, and under neutral or alkaline conditions they exist as non-ionised hydrates. 

Similar surface active but polymeric substances, partly possessing additional cationic properties [e.g. 4], have been synthesized by Ferrutti et al. (29). 

Some drugs have both anionic and cationic properties (amphoteric) examples include amino acids [e.g., levocamitine CH3 - N+(CH3)2CH2CH(OH)CH2COO ]. The ampholytes act as acids or bases depending on the pH of the solution. At high pH,... 

Surfactants are usually classified into three main groups—i.e., anionic, cationic, and nonionic, depending on their ionic nature in solution. A fourth group is sometimes included, and these are called amphoteric surfactants, which show both anionic and cationic properties depending on pH. 

Iwayama et al. (7) showed that paraxylene selectivity of alkaline Y zeolites exhibits a maximum with K (Table 10.2). This demonstrates that there is an optimum value in the cation properties (size, electronegativity and position). As was demonstrated by Seko et al. (8), the Si/Al ratio is also important paraxylene selectivity increases with increasing Si/Al in the range of 1.2 to 3. 

Pistoia investigated the electroinitiated polymerisation of styrene in propylene carbonate-lithium perchlorate solutions at 25°C. Mechanistic evidence was obtained for the formation of perchloric acid at the anode and the cationic nature of the process thus proved. The kinetic analysis yielded a kp value of 0.5 M sec . Although no comparisons can be made between this result and previous ones in other solvents, the presence of lithium perchlorate was here a source of homocorgugation for the acid produced and thus the cause of considerable deactivation of its initiating power. As in previous cases, this was not recognised by the author. A simflar study by Pistoia and Scro-sati in dimethylsulphate gave an insoluble polymer at the anode and the nature or the initiator was not elucidated, but it did not seem to be perchloric acid. The cationic properties of this process was however proved... 

From these results (Table 1, Figs. 2 and 3), we assumed that the adsorbing activity of aminated-cellulose adsorbents for biopolymers was induced by the simultaneous effects of their cationic properties and hydrophobic or other properties. The charge of LPS is anionic at pH... 

The present results suggest that PL-cellulose spherical particles can reduce the concentrations of natural LPS to 1 EU/mL or lower in drugs and fluids used for intravenous injection, at a neutral pH and ionic strengths of fi=0.05-0.4. These processes did not affect the recovery, even of acidic proteins such as BSA. The high LPS-adsorbing activity of the PL cellulose is possibly due to the cationic properties of the ligand and its suitable hydrophobic properties. The high LPS selectivity of the particles with small pore size is due to the size-exclusion effects on protein molecules. By contrast, that of the particles with... 

Neostigmine has a mechanism of action quite similar to that of physostigmine. It effectively inhibits cholinesterase a about 10 M concentration. Its activity docs not vary with pH. and at all ranges it exhibits similar cationic properties (Fig. 17-IS). Skeletal muscle is also slimulatcd by nco-itigmine. a property that physostigtnine docs not have. 

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