Complexes ampholytic

Isoelectric Points.—An ampholyte is at its isoelectric point when the concentration of positive ions is equal to that of the negative ions, i.e., when CrhJ is equal to crh . Since these ions have almost the same equivalent conductances, because of their size, equal amounts of positive and negative ions of the ampholyte will migrate in opposite directions. At the isoelectric point, therefore, an amino-acid, or more complex ampholyte, will appear to remain stationary in an electrical field, although the solution may have an appreciable conductance. According to equation (1),... 

When particles or large molecules make contact with water or an aqueous solution, the polarity of the solvent promotes the formation of an electrically charged interface. The accumulation of charge can result from at least three mechanisms (a) ionization of acid and/or base groups on the particle s surface (b) the adsorption of anions, cations, ampholytes, and/or protons and (c) dissolution of ion-pairs that are discrete subunits of the crystalline particle, such as calcium-oxalate and calcium-phosphate complexes that are building blocks of kidney stone and bone crystal, respectively. The electric charging of the surface also influences how other solutes, ions, and water molecules are attracted to that surface. These interactions and the random thermal motion of ionic and polar solvent molecules establishes a diffuse part of what is termed the electric double layer, with the surface being the other part of this double layer. 

Shang TQ, Ginter JM, Johnston MV, Larsen BS, McEwen CN. Carrier ampholyte-free solution isoelectric focusing as a prefractionation method for the proteomic analysis of complex protein mixtures. Electrophoresis 2003 24 2359-2368. 

The metal complexation of ampholytes may cause unwanted results when iron-containing tools are used for handling the sample (e.g., syringes with metal needles, metal tubing, etc.). This was demonstrated with transferrin, a metalbinding protein, when iron-complexed forms of transferrin appeared in the mobilization pattern of an iron-free sample upon mixing the ampholytes and the protein solution with a Hamilton syringe equipped with metal needle [36]. 

From these equations, it is possible to predid the effective lipophilicity (log D) of an acidic or basic compound at any p H value. The data required to use the relationship in this way are the intrinsic lipophilicity (log P), the dissociation constant (piCa), and the pH of the aqueous phase. The overall outcome of these relationships is the effective lipophilicity of a compound, at physiological pH, which is approximately the logP value minus one unit of lipophilicity for every unit of pH, the pit, value is below (for acids) and above (for bases) pH 7.4. Obviously, for compounds with multifunctional ionizable groups, the relationship between log P and log D, as well as log D as a function ofpH, becomes more complex [62, 65, 67]. For diprotic molecules, there are already 12 different possible shapes of log D-pH plots. Ion pairs (salts), zwitterions, and ampholytes are special cases and both measurement of log P/D and their interpretation need special attention [44, 49]. 

Unfortunately, substantial problems remain with the CIEF-MS approach. Most importantly, the ampholyte used in CIEF co-elutes with the analyte and perturbs the electrospray ionization (ESI) process in a manner that suppresses analyte signal intensity and degrades mass resolution. In addition, the resolution of CIEF alone is not sufficient to separate proteins completely in complex samples. When proteins co-elute from an ESI source, some... 

Abbreviations HSV = herpes simplex virus HeLa = human carcinoma of the cervix PyBHK = polyoma-virus transformed B(aby) H(amster) K(idney) cells SV = simian virus 3T3 = mouse fibroblasts and + = ampholyte forms complexes. 

Heparin, then, consists of a series of highly sulfated compounds, identical in carbohydrate composition but separated by complexing with LKB ampholyte (with progressive adjustment of pH), into a large number of separate chains. These chains are flexible molecules, probably in a Gaussian coil, and are characterized by a shell of negative charges... 

Figure 2. Electrophoretic migration patterns of commercial heparins. The cathode and the point of application are considerably to the left of each pattern, the anode is to the right. Separation in agarose on the basis of charge density, in polyacrylamide on the basis of molecular size, and in LKB ampholyte on the basis of pH and chain length, producing a specific insoluble complex with ampholyte. (2)...

This chapter also considers the more complex situations involved in polybasic acid equilibria and ampholytes. 

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