Ampholytic

Physical Properties. Glycine is a colourless crystalline solid soluble in water. Owing to the almost equal opposing effects of the amino and the carboxylic groups. its aqueous solution is almost neutral (actually, slightly acidic to phenolphthalein) and glycine is therefore known as a neutral ampholyte. f It exhibits both acidic and basic properties. 

Tyrosine and cystine are colourless solids almost insoluble in water gfid in ethanol (tyrosine dissolves in hot water). They are readily soluble in dilute caustic alkali solution, in ammonia and mineral acids, but not in acetic acid. They are also classed as neutral ampholytes. ... 

Amphoteric Detergents. These surfactants, also known as ampholytics, have both cationic and anionic charged groups ki thek composition. The cationic groups are usually amino or quaternary forms while the anionic sites consist of carboxylates, sulfates, or sulfonates. Amphoterics have compatibihty with anionics, nonionics, and cationics. The pH of the surfactant solution determines the charge exhibited by the amphoteric under alkaline conditions it behaves anionically while ki an acidic condition it has a cationic behavior. Most amphoterics are derivatives of imidazoline or betaine. Sodium lauroamphoacetate [68647-44-9] has been recommended for use ki non-eye stinging shampoos (12). Combkiations of amphoterics with cationics have provided the basis for conditioning shampoos (13). 

A large part of the dissolved amino acid exists as the ampholyte (2witterion). The isoelectric point (pi) is the pH at which the net electric charge of a dissolved amino acid molecule is 2ero. p /is expressed as... 

X-Amino acids ate ampholytic compounds. The chemical reactions of amino acids can be classified according to their carboxyl, amino, and side-chain groups. Most of the reactions have been well known for a long time the details of these reactions have been reviewed (77). 

The amino group behaves as a week base, giving salts with both mineral and organic acids. The aminophenols are tme ampholytes, with no 2witterion stmcture hence they exist either as neutral molecules (4), or as ammonium cations (5), or phenolate ions (6), depending on the pH value of the solution. 

The ampholytes, which must be used in higher concentrations than many other disinfectants when employed at room temperature, are greatiy improved as the temperature is increased. At 20°C, 3250 ppm of Tego 51 killed Pseudomonas aeruginosa in 30 min, at 50°C it required only 100 ppm in the same time (184,185). 

Whereas tests (186) indicated that ampholytes were effective in skin cleansing for preoperative use, for wound cleansing, and as an antiseptic in the oral cavity (187), as well as other medical appHcations, the food and beverage industries have proved to be the principal employers of these compounds. Ampholytes are used as sanitizers and disinfectants, not as food preservatives. Low toxicity, absence of skin irritation, and noncorrosiveness, along with antimicrobial activity, has given ampholytes acceptance in dairies, meat plants, and the brewing and soft drink industries. These disinfectants have been manufactured and distributed in Europe and Japan, but not in the United States. 

Problems associated with gel-to-gel variabiUty have been rectified with the advancement of ampholyte mixtures. One commonly used mixture of ampholytes, called Immobilines, is an improved ampholyte mixture that produces no gradient drift or unequal pH gradient (26) and can be used in a gel matrix reproducibly from one day to the next. 

Because protein samples are actually ampholytes, when samples are loaded onto the gel and a current is appHed, the compounds migrate through the gel until they come to their isoelectric point where they reach a steady state. This technique measures an intrinsic physicochemical parameter of the protein, the pi, and therefore does not depend on the mode of sample appHcation. The highest sample load of any electrophoretic technique may be used, however, sample load affects the final position of a component band if the load is extremely high, ie, high enough to titrate the gradient ampholytes or distort the local electric field. 

Isoelectric focusing takes along (from ca 3 to 30 h) time to complete because sample compounds move more and more slowly as they approach the pH in the gel that corresponds to their isoelectric points. Because the gradient ampholytes and the samples stop where they have no mobiHty, the resistivity of the system increases dramatically toward the end of the experiment, and the current decreases dramatically. For this reason, isoelectric focusing is usually mn with constant voltage. Constant current appHcation can lead to overheating of the system. 

Syrexin (from bovine liver). Purified by (NH4)2S04 pptn, then by pH step elution from chromatofocusing media in the absence of ampholytes. [Scott et al. Anal Biochem 149 163 1985.]... 

Palusinski, OA Allgyer, TT Mosher, RA Bier, M Saville, DA, Mathematical Modeling and Computer Simulation of Isoelectric Focusing with Electrochemically Defined Ampholytes, Biophysical Chemistry 13, 193, 1981. 

Shimao, K, Mathematical Simulation of Steady State Isoelectric Eocusing of Proteins using Carrier Ampholytes, Electrophoresis 8, 14, 1987. 

Ampholytic surfactants based on phosphatides, betaines and alky lamino-substituted amino adds are an increasingly important group of surfactants and are generally reported to be reasonably biodegradable. 

Figure 3. Preparative isoelectric focusing. The PNL eluted from gel filtration was subjected to isoelectric focusing using a column of 110 ml capacity (LKB) with ampholytes pH 7-11. After 48 h (9.6 W constant power), fractions of 3 ml were removed and assayed for PNL activity (- - ) and pH (- -).

Figure 5. Analytical isoelectric focusing. Ultrathin layers (0.4 nun) of polyacrylamide with ampholytes pH 2-11 were used. Samples of 10 pg of protein in 10 pi of 1 % glycine were applied. A.- Silver staining. B.- Stain for activity on overlays containing pectin in tris/HCl buffer at pH 8.0 with CaClj M.- Broad pi Calibration Kit protein (Pharmacia), samples of 5 pg of protein were applied. 1.-Ammonium sulphate precipitated proteins from cultures on pectin. 2.- Fractions with PNL activity eluted from the Superdex 75HR1030 column. 3.- Purified PNL.

The ionization reactions for acids, bases and ampholytes (diprotic) may be represented by the general forms... 

The basic relationships between solubility and pH can be derived for any given equilibrium model. The model refers to a set of equilibrium equations and the associated equilibrium quotients. In a saturated solution, three additional equations need to be considered, along with the ionization Eqs. (2a)-(2d), which describe the equilibria between the dissolved acid, base or ampholyte in solutions containing a suspension of the (usually crystaUine) solid form of the compounds ... 

Figure 3.2(c) shows an example of an ampholyte, labetolol. The log S versus pH shake-flask data were taken from the Hterature [49]. Ampholyte paraboHc-shaped curves show features of both an acid and a base profile. 

Fig. 3.4 Permeability profiles for (a) warfarin (acid), (b) propranolol (base) and (c) morphine (ampholyte) based on a BBB PAMPA model (plON) composed of animal brain extract of lipids. The data (unpublished) were analyzed with the pCEL-X program (plON), with the refined parameters indicated in the three frames. In all three cases, there was evidence for the permeation of charged...

Scherrer, R. A. Biolipid pK values and the lipophilidty of ampholytes and ion pairs. In Pharmacokinetic Optimization in Drug Research Biological, Physicochemical, and Computational Strategies, Testa, B., Van de Waterbeemd, H., Folkers, G., Guy, R. (eds.), Wiley-VCH, Weinheim, 2001, pp. 351-381. 

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