Amphoteric carriers

Fig. 7.4. Diagrammatic representation of the Goldacre concept of the functioning of a contractile protein as an amphoteric carrier of ions. Above the broken line, trap set below, intake and release into the cell of ions as a consequence of contraction of the protein fibre. Energy could be fed into the system to extend the protein fibre and re-expose reactive groups external to the membrane (to set the ion trap). (From H. E. Street, as Fig. 7.3.)...

Fig. 7.5. Diagrammatic representation of the hypothesis of Bennet-CIark that a cyclic formation and breakdown of the phospholipid, lecithin, within the membrane would enable it to act as an amphoteric carrier. Energy as ATP is consumed in lecithin synthesis. (From Sutcliffe, as Fig. 7.2.)...

Aluminas. Aluminas, porous AI2O3, are available in many forms. They constitute the most important carrier material in heterogeneous catalysis. Alumina is amphoteric and, as a con.sequence, soluble in both acidic and basic media. Precipitation can be performed from an acid solution by adding a base or from a basic solution by adding an acid, as schematically represented in Fig. 3.18. If, for example, at a pH of less than about 3 a base is added to an aqueous solution of aluminium sulphate, a precipitate is formed. If this material is filtered, dried and calcined, an amorphous porous AI2O3 is obtained. At other pH values different porous aluminas can be synthesized. 

The first practical IEF experiments were carried out with the use of synthetic molecules, called carrier ampholytes, to generate the pH gradients.1,26 Carrier ampholytes are amphoteric electrolytes that carry both current and buffering capacity. Much of the early theoretical activity in electrofocusing dealt with the properties required of carrier ampholytes and is more or less irrelevant to a current discussion.1,3,9 Different varieties of... 

The polymerized ionic liquid (IL) shows great promise for diverse applications. Some polymerization methods have already been oriented toward specific applications. Polymerized ILs are useful in polar environments or where there are ion species for transport in the matrix. Amphoteric polymers that contain no carrier ions are being considered for several porposes in polymer electrolytes. Zwitterionic liquids (ZBLs) were introduced in Chapter 20 as ILs in which component ions cannot move with the potential gradient. ZILs can provide ion conductive paths upon addition of salt to the matrix. It is therefore possible to realize selective ion transport in an IL matrix. If the resulting matrix can form solid film over a wide temperature range, many useful ionic devices can be realized. This chapter focuses on the preparation and characteristics of amphoteric IL polymers. 

Only small needles, platelets, and ribbons can be grown by this technique, but both purity and perfection are high. Sublimation in a flowing inert carrier gas, however, avoids hydrogen, an amphoteric impurity that passivates both donors and acceptors. Normally, this is thought to be a dissociative process, for example ... 

The pH gradient is created with carrier ampholytes, a group of amphoteric polyaminocarboxylic acids, which have slight differences in pKa value and molecular weights of 300 to 1000. Mixtures of 50 to 100 different compounds... 

In the last few years Schneider and co-workers have performed a number of experiments on various SiC polytypes which exhibit a characteristic infrared emission in the 1.3 to 1.5 pm spectral range [98]. They have assigned this emission band to vanadium impurities substituting the various silicon sites in the lattice. In their extensive work they found three charge states of vanadium which act as an electrically amphoteric deep level in SiC. They also suggest that vanadium may have an important role in the minority-carrier lifetime in SiC-based optoelectronic devices [98,99], Recently, trace amounts of vanadium impurities have been detected in 3C-SiC grown by the modified-Lely technique [100]. 

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