Amphoteric electrolytes

NH2RCO2H + H3O+ = +NH3RCO2H + H2O, whereas a strong base was believed to react with the — CO2H group, viz., NH2RCO2H + OH- = NHiRCOj + H2O. 

The products are, of course, the same as in the alternative representation, since there is no doubt that in acid solution the amino-acid forms +NH3CH2CO2H ions while in alkaline solution the anions NHaCHaCOjT are formed. It should be noted, however, that the groups exhibiting the acidic and basic functions are the reverse of those accepted in the original treatment of amino-acids the basic property of the ampholyte is due to the — CO2 group whereas the acidic property is that of the — NH group. 

The addition of formaldehyde to an aqueous solution of an amino-acid results in no change in the curve showing the variation of pH in the course of the neutralization by acid, but that for the neutralization by alkali is shifted in the direction of increased acid strength, as shown in Fig. 107. It is known that the formaldehyde reacts with the amino- 

Titration of amino-arid with and without formaldehyde 

Important evidence for the dual-ion structure of aliphatic amino-acids has been provided by a study of their Raman spectra in these spectra each group, or, more exactly, each type of linkage, exhibits a 

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It is interesting to note that the amino acid side chains may be either neutral as in valine, acidic as in glutamic acid or basic as in lysine. The presence of both acidic and basic side chains leads to proteins such as casein acting as amphoteric electrolytes and their physical behaviour will depend on the pH of the environment in which the molecules exist. This is indicated by Figure 30.2, showing a simplified protein molecule with just one acidic and one basic side group. 

Figure 9.5 Generation of a pH gradient by ampholytes within a capillary flanked by an acid as anodic solution and base as cathodic solution. Ampholyte solutions are composed of high numbers of low-molecular weight amphoteric electrolytes (from which the name is derived) with slightly different pi values. Because ampholytes possess buffering capacity, they maintain a pH value in the specific area occupied by the different molecular species. The sample, which is also amphoteric, focuses in between ampholytes with higher and lower pi. To achieve resolution, there must be at least one ampholyte with a pi intermediate to the two sample components of interest.

Thus any amphoteric electrolyte may cause similar variations in precipitative power on each side of its isoelectric point. Tii the following table are given the isoelectric points of a few typical amphoteric electrolytes ... 

The isoelectric poiat of an amphoteric electrolyte is likewise displaced by the addition of neutral salts as is instanced by the following values for chromated gelatine in the presence of various neutral salts. 

Gelatine is an amphoteric electrolyte (Procter, J.G.S. cv. 313, 1914 Loeb, Jour. Gen. Physiol, i. 483, 551, 1918-1919 I. 39, 237, 363) having an isoelectric point at Ph = 4 7-6 0. On the alkaline side salts or gelatinates, e.g. calcium gelatinate, are formed, whilst on the acid side we obtain soluble gelatine salts, e.g. gelatine chloride, whilst isoelectric gelatine is apparently almost insoluble in water. ... 

Substances having this dual nature are amphoteric and are often called ampholytes (from amphoteric electrolytes ). A simple monoamino monocarboxylic a-amino acid, such as alanine, is a diprotic acid when fully protonated—it has two groups, the —COOH group and the —NHj group, that can yield protons ... 

Svensson, H., A discussion on the meaning of equivalent weights and transport (transference) numbers for amphoteric electrolytes, especially protolytes. Sci. Tools, 3, 30 (1956). 

Ethanol belongs to the class of polar solvents. Dielectric constant of ethanol is sufficiently high (e 24.3). Ethanol is an amphoteric electrolyte, i.e. it can be both proton acceptor and proton donor. Ethanol mixes readily with toluene, does not... 

This view was supported later by Walden [17]. Considering the high electrical conductivity of nitric acid he believed that HN03 should be regarded as an amphoteric electrolyte, an idea expressed by the equilibrium equation ... 

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... 

Some substance (like HS04, H2P04 , HP04-, NH3, H20 etc.) can function both as acids and bases, depending on the circumstances. These substances are called amphoteric electrolytes or ampholytes. 

Theoretically, the precipitation of a protein, which is built up of amino-acids and functions as a typical amphoteric electrolyte, should best be accomplished at the isoelectric point, that is, at the hydrogen ion concentration at which the acidic and basic functions of the protein are equal and at a minimum. According to Soerensen, the iso-electric point of egg albumin is at pH 4.8,10 and while precipitation would undoubtedly be most complete at this point, it is not necessarily the most favorable for crystallization, as the egg albumin crystals are not isoelectric protein, but a compound of this with the sulfate ion, and perhaps the ammonium ion as well.11... 

Ampholyte An amphoteric electrolyte. In proteomics, this term is used to describe small multicharged organic buffers used to establish pH gradients in isoelectric... 

Ampholytes (amphoteric electrolytes) can function as either weak acids or weak bases in aqueous solution and have plC values corresponding to the ionisation of each group. They may be conveniently divided into two categories - ordinary ampholytes and zwitterionic ampholytes - depending on the relative acidity of the two ionisable groups. 

Electrophoresis is more often used to separate proteins than amino acids. The degree of separation obtained for amphoteric electrolytes depends on the pH of the buffer and on the isoelectric point of the substances. This experiment illustrates the use of a horizontal low voltage paper method, which separates acidic, basic and neutral amino acids, but is not satisfactory for separating the members of one group from each other. 

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