Amphoteric nature

Because of its amphoteric nature, aluminum is also readily attacked by solutions of strong bases. At a pH > 8.5, the solubiUty of aluminum increases sharply because of the formation and hydration of Al(OH) 4 ions... 

The amphoteric nature of the oxide is illustrated by its abiUty to form siUcates and aluminates in the dry state at elevated temperatures... 

Isolation. Isolation procedures rely primarily on solubiHty, adsorption, and ionic characteristics of the P-lactam antibiotic to separate it from the large number of other components present in the fermentation mixture. The penicillins ate monobasic catboxyHc acids which lend themselves to solvent extraction techniques (154). Pencillin V, because of its improved acid stabiHty over other penicillins, can be precipitated dkecdy from broth filtrates by addition of dilute sulfuric acid (154,156). The separation process for cephalosporin C is more complex because the amphoteric nature of cephalosporin C precludes dkect extraction into organic solvents. This antibiotic is isolated through the use of a combination of ion-exchange and precipitation procedures (157). The use of neutral, macroporous resins such as XAD-2 or XAD-4, allows for a more rapid elimination of impurities in the initial steps of the isolation (158). The isolation procedure for cephamycin C also involves a series of ion exchange treatments (103). 

Sn02, cassiterite, is the main ore of tin and it crystallizes with a rutile-type structure (p. 961). It is insoluble in water and dilute acids or alkalis but dissolves readily in fused alkali hydroxides to form stannates M Sn(OH)6. Conversely, aqueous solutions of tin(IV) salts hydrolyse to give a white precipitate of hydrous tin(IV) oxide which is readily soluble in both acids and alkalis thereby demonstrating the amphoteric nature of tin(IV). Sn(OH)4 itself is not known, but a reproducible product of empirical formula Sn02.H20 can be obtained by drying the hydrous gel at 110°, and further dehydration... 

The amphoteric nature of AS2O3 and the trends in properties of several of the oxides and oxoacids... 

After a strain improvement and development programme similar to, but more complicated than that of penicillin, the D-a-aminoadipyl side chain containing cephalosporin C was obtained by large scale fermentation. However, cephalosporin C could not be isolated as easily as penicillin G or V. Due to its amphoteric nature it is soluble at any pH in the fermentation broth. Several costly isolation procedures involving ion-exchange chromatography have been developed, as a result of which cephalosporin C is much more expensive than penicillin G. 

Separation relies on tile amphoteric nature of amino adds. 

Corrosion of steel may take place because of its amphoteric nature (it is attacked under either strongly acidic or strongly alkaline conditions). Caustic gouging is a specific form of corrosive attack on boiler steel, effected by a very high concentration of sodium hydroxide (typically >100,000 ppm/10%), as shown here ... 

Thus we end up with an oxygen atom which is somewhat electron deficient and a carbon atom which is electron rich. The oxygen then would be expected to behave as an electrophilic reagent and the carbon (or rather the regions bounded by the w orbital) should behave as a nucleophilic reagent. The amphoteric nature of the carbonyl n- n singlet state is mirrored in its reactivity toward electron-rich and electron-deficient olefins. 

Water is amphoteric. It will act as either an acid or a base, depending upon whether the other species is a base or acid. In pure water, we find the same amphoteric nature. In pure water, a very small amount of proton transfer is taking place ... 

Before examining the equilibrium behavior of aqueous solutions of weak bases, let s look at the behavior of water itself. In the initial discussion of acid—base equilibrium above, we showed water acting both as an acid (proton donor when put with a base) and a base (proton acceptor when put with an acid). Water is amphoteric, it will act as either an acid or a base, depending on whether the other species is a base or acid. But in pure water the same amphoteric nature is noted. In pure water a very small amount of proton transfer is taking place ... 

From the realization of the amphoteric nature of proteins and the importance of [H+] in many of their functions, and as increasing numbers of enzymes were identified, it became commonplace to report their optimum pH. Corrections for non-enzymic hydrolysis of the substrates were usually made but, as was critically reviewed by Dixon and Webb (1959), from many of the results it was not possible to distinguish effects of pH on the protein in general from those on the region actually involved in interaction with the substrate. Nevertheless, many... 

The solubility of Kelex 100 has been reported to be 4.4 (pH 0.5), 1.4 (pH 1.0), and 1.6 (pH 1.5)ppm, in tests employing 0.5moldm Kelex 100 in Solvesso 150 diluent for the extraction of copper from solutions containing about 30 g dm of metals (Cu, Ni, and Co) [21]. Furthermore, over several months no change in the Kelex concentration was found in pilot plant operations with a 0.5moldm Kelex solution [21]. At higher pH values (up to 9) Kelex solubility has been determined at < 1 ppm in ammonium sulfate solutions up to 300 g dm [22]. It would be expected that the amphoteric nature of Kelex would show increasing solubility at pH values above 7, and lower than about 1, similar to the variation in solubility of... 

The amphoteric nature of hydrated thorium oxide has been established. Microgram scale preparation of Cm02, which has a face-centred cubic... 

D. Amphoteric Nature, Tendency to Form Adducts, and Reactivity... 

The structures used for the alkaloids in this chapter are numbered conventionally for the flavonoid or noreugenin moiety. The carbon atoms of the nitrogen-containing ring are numbered separately T, 2, etc. These alkaloids are of interest due to their amphoteric nature, being both bases and phenols, and also because of the reputed biological activity of some of the plants which contain them. 

Chlorine monofluoride oxide, 18 328-330 force field of, 18 329, 330 infrared spectrum of, 18 328, 329 stretching force constants for, 18 330 synthesis of, 18 328 Chlorine nitrate fluorination of, 18 332 preparation of, 5 54 Chlorine oxides, 46 109-110, 158 fluorination of, 18 348 Chlorine oxyfluorides, 18 319-389, see also specific compounds adduct formation, 18 327, 328 amphoteric nature of, 18 327, 328 bond lengths, 18 326 bond strengths, 18 323-327 geometry of, 18 320-323 ligand distribution, 18 323 reactivity of, 18 327, 328 stretching force constants, 18 324-327 Chlorine pentafluoride oxide, 18 345, 346 Chlorine trifluoride, reaction with difluoramine, 33 157... 

The metallic nature of arsenic was thoroughly established through the researches of J. F. Henckel (or Henkel), who in 1725 told how to prepare it by sublimation, and of Georg Brandt, who investigated its properties in 1733, noticed its amphoteric nature, and was surprised that "the same substance should dissolve in so many different menstrua (16, 21, 76). Bishop Johan Browall (1744), A.-M. Monnet (1774), and J. H. Pott (1720) also studied it (3,22). 

An understanding of the chemical behaviour of the element can aid in the choice of appropriate techniques and methods, the application of which would not disrupt the interaction of the element with associated constituents. For example, in the study of aluminium some relevant information may include its amphoteric nature, its ability to form predominantly ionic complexes, its tendency to form hydroxides, and the stability of aluminium complexes formed with biological ligands. It is clear that in order to maintain the ionic interactions the pH, ionic strength and, of lesser importance, the ionic composition of the medium used for sample preparation should be similar to that found in vivo. In addition, highly charged surfaces should not come into contact with the sample. 

According to our findings, all soluble metal compounds of an amphoteric nature are effective esterification catalysts. If, when concluding the theoretical considerations, the amphoteric nature of the metals is described as their ability to function as cations in salts, and also to form anionic hydroxy or alkoxy complexes, this offers the possibility of using the reaction mechanism just discussed for all effective metals in a correspondingly modified manner. 

The effect of the basicity of aldol condensation catalysts on their activity was thoroughly investigated by Malinowski et al. [372—379]. The observed linear dependence of the rate coefficients of several condensation reactions on the amount of sodium hydroxide contained in silica gel (Figs. 12 and 13) supported the view that the basic properties of this type of catalyst were actually the cause of its catalytic activity, though the alkali-free catalyst was not completely inactive. The amphoteric nature of the catalysis by silica gel, which can act also as an acid catalyst, was demonstrated [380]. By a stepwise addition of sodium acetate to a HN03-pretreated silica gel catalyst the original activity for acetaldehyde self-condensation was decreased to a minimum (when an equivalent amount of the base was added) by further addition of sodium acetate, the activity increased again because of the transition to a base... 

S02, as a ligand, exhibits amphoteric nature, behaving as either a Lewis base or a Lewis acid and correspondingly giving rise to r planar or t] 1-pyramidal (or bent) coordination... 

Table 10.5 shows the effects of adding a few drops of sodium hydroxide solution to solutions containing various metal ions, and of adding an excess. The colours of the insoluble metal hydroxides can be used to identify the metal cations present in solution. In some cases the precipitate dissolves in excess hydroxide, owing to the amphoteric nature of the metal hydroxide. This amphoteric nature can also be used to help identify metals such as aluminium and zinc. 

---