Electrophoretic mobility complex formation

The movement of an electrically charged particle of mass m and charge Q under the influence of a uniform electric field of strength E is called electrophoresis. These particles may be biological cells, colloids, macromolecules, or low-molar-mass substances. Even electrically neutral particles can be made electrophoretically mobile through formation of suitable complexes. An example is the formation of borate complexes by polysaccharides ... 

Another example is the separation of several sulfonamides in acetonitrile by adding silver ions. Compounds such as N-containing heterocyclics were found to build selective charge transfer complexes with Ag+, which improves the selectivity of the separation. Phenols, carboxylic acids, and alcohols interact with anions such as CIO, BE, NO, Cl t,SO , and Cl in acetonitrile as solvent. The resulting electrophoretic mobility of the weak Bronsted acids (HA) in the presence of such anions is the result of the formation of complexes of the type [X. .. HA] due to the formation of hydrogen bonds (13). 

CAE employing antibodies or antibody-related substances is currently referred to as immunoaf-hnity capillary electrophoresis (lACE), and is emerging as a powerful tool for the identification and characterization of biomolecules found in low abundance in complex matrices that can be used as biomarkers, which are essential for pharmaceutical and clinical research [166]. Besides the heterogeneous mode utilizing immobilized antibodies as described above, lACE can be performed in homogeneous format where both the analyte and the antibody are in a liquid phase. Two different approaches are available competitive and noncompetitive immunoassay. The noncompetitive immunoassay is performed by incubating the sample with a known excess of a labeled antibody prior to the separation by CE. The labeled antibodies that are bound to the analyte (the immuno-complex) are then separated from the nonbound labeled antibody on the basis of their different electrophoretic mobility. The quantification of the analyte is then performed on the basis of the peak area of the nonbonded antibody. 

Incubation of a cell-free extract of L. minor in the presence of NAD+ and UDP-D-[U-14C]glucuronic acid generated two compounds, each containing a different radioactive C5 sugar.96 The presence of apiose after hydrolysis was diagnosed by (a) paper chromatography, (b) specific complex-formation with benzeneboronic acid, (c) electrophoretic mobility, and (d) formation of its isopropylidene acetal. Treatment with ammonia at 0° showed that the compound was formed by a nonenzymic cyclization.96 Treatment with phosphoric diesterase plus phosphatase further supported an earlier report of the existence of a D-apiosyl cyclic phosphate.95... 

Since Ag-Ab complex formation is a reversible reaction, a certain degree of complex dissociation will take place inside of the capillary. Once the complex dissociates, the Ag and Ab will rapidly move apart due to the differences in their electrophoretic mobilities. The level of the complex detected may actually be lower than that formed in the original mixture. The amount of decrease depends on the dissociation kinetics and the time required for separation. To obtain maximal complex signal, a short separation time is normally recommended (61,66). 

Bourne and coworkers studied the electrophoretic behavior of many polyols in copper acetate and basic copper acetate solutions as electrolytes. Although the sugars were found to be rather unresponsive, all alditols tested showed considerable mobility, which was interpreted as being due to complex-formation with Cu " ions. Actually, the preponderant ionic species in those solutions are [Cu2(OH)2] " and CuOAc" " the behavior of copper acetate with carbohydrates will be discussed in Section III,2. 

The electrophoretic mobihties of a large number of carbohydrates have been determined in buffered calcium acetate solution. The method is very sensitive for the detection of complex-formation the smallest detectable mobility Mi 0.01, compared to that of c/r-inositol) represents less than 1 % of complex-formation. All carbohydrates that have two vicinal hydroxyl groups on a six-membered ring or on an acyclic chain, or cis on a five-membered ring, show some mobihty only derivatives lacking vicinal hy-... 

Although paper electrophoresis has been recommended for pre-testing separations before performing them on a preparative column, t.l.c. is more suitable for this purpose. Electrophoretic mobility is not strictly proportional to the extent of complex-formation it depends also on the bulk and shape of the molecule, which influence ionic mobility. In particular, bulky substituents retard the passage of the complex ion through the electrolyte. These effects have been discussed in detail.T.l.c. is also affected by the bulk of substituents but to a much lesser extent hence, it is more likely to predict the separations obtainable on a column. ... 

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