Ampholytic properties

The prerequisite for peptide synthesis is the temporary disappearance of the ampholytic properties of amino acids. The different methods and steps in the synthesis of peptides (1) are concerned with the following ... 

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. 

Stoyanov, A.V. and Righetti, P.G., Ampholyte dissociation theory and properties of ampholyte aqueous solutions, Electrophoresis, 18, 1944, 1997. 

Chemically modified cellulose supports are also used in TLC, either as fibres or a crystalline powder. The most widely known of these is DEAE-cellulose, a basic phase containing diethylaminoethyl groups. The hydrophilic character of other polar phases with ion exchange properties can be used for the separation of ampholytes. 

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,... 

Ampholyte — A substance that can react both as an acid and as abase is called an ampholyte, or amphoteric compound. Usually this property refers to the - Bronsted acid-base theory. An example is HCOj which can act as a proton acceptor and as a proton donator. An ampholyte can be a zwitterion, as in case of amino acids in the range between pH = pJCai and pH = pfCa2, they exist as [+(H3N)HRC-COO-]. 

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... 

Corpart JM, Candau F (1993) Aqueous solution properties of ampholytic copolymers prepared in microemulsions. Macromolecules 26(6) 1333-1343... 

ZIL monomers, having both cation and anion in the same monomer unit, were prepared in order to give different types of ampholyte polymers. Figure 30.4 shows the structure of the monomers used here [6]. Four different monomers were synthesized to study the relation between structure and such properties as ionic conductivity and Tg. 

Hydrated oxides with clearly exhibited basic and acidic properties are well soluble in water. They are prepared by the interaction of the corresponding oxides or metals with water. Weak bases, ampholytes and weak acids are practically insoluble or poorly soluble. Exchange reactions between the solutions of the corresponding salts and strong bases are used to synthesize them. 

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. 

Similarly, when the excess of added alkali is sufficiently great to make the concentration of the cations CA 3 very much less than CA"3i then the basic properties of the ampholyte may be disregarded and it may be thought of simply as a weak acid. 

PAMPA-pKa fiux optimized design (pOD)-permeabiiity Iso-pH mapping unstirred PAMPA was used to measure the effective permeability, Pe, as a function of pH from 3 to 10, of five weak monoprotic acids (ibuprofen, naproxen, ketoprofen, salicylic acid, benzoic acid), an ampholyte (piroxicam), five monoprotic weak bases (imipramine, verapamil, propranolol, phenazopyridine, metoprolol), and a diprotic weak base (quinine). The intrinsic permeability, Po, the UWL permeability, Pu, and the apparent pKa (pKa.fiux) were determined from the pH dependence of log Pg. The underlying permeability-pH equations were derived for multiprotic weak acids, weak bases, and ampholytes. The average thickness of the UWL on each side of the membrane was estimated to be nearly 2000 p, somewhat larger than that found in Caco-2 permeability assays (unstirred). As the UWL thickness in the human intestine is believed to be about forty times smaller, it is critical to correct the in vitro permeability data for the effect of the UWL. Without such correction, the in vitro permeability coefficient of lipophilic molecules would be indicative only of the property of water. In single-pH PAMPA (e.g., pH 7.4), the uncertainty of the UWL contribution can be minimized if a specially selected pH (possibly different from 7.4) were used in the assay. From the analysis of the shapes of the log Pe-pH plots, a method to improve the selection of the assay pH, called pOD-PAMPA, was described and tested. From an optimally selected assay pH, it is possible to estimate Pg, as well as the entire membrane permeability-pH profile. 

R from RCOOH of commercially available fatty acids. When R is H, they are ampholytic and show cationic properties at low pHs, anionic properties at high pHs. When R = CH2Z, pH sensitivity is more closely related to that of V-alkylbetaines (below). Compatible with anionics, cationics, and nonionics, soluble in water in the presence of high concentrations of electrolytes, acids, and alkalies. When R contains a second carboxylic acid group, products show very little skin and eye irritation. 

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