Protein Chemistry. Structure, Properties, Research Methods - Shendryk A.N. 2022

Methods for experimental study of protein structure
Protein separation methods
Physical principles of protein electrophoresis

Electrical charges on protein molecules in solution arise either from the dissociation of ionogenic groups or through the adsorption of ions from the solution onto The surface of macro-molecules. This results in The formation of an electrical double layer. This layer consists of the charged surface of a colloidal or protein particle and a thin ionic film (ionic atmosphere) formed by the surrounding medium. The charges on the particle surface and in the ionic atmosphere have opposite polarities, as shown in the figure below.

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In an external electric field, the particle and its surrounding ionic atmosphere move in opposite directions because they carry opposite charges. This creates electrophoretic friction, which slows down the motion of the particle.

The mobility of a charged particle (ion) in an electric field is referred to as electrophoretic mobility. For a spherical particle in an infinitely dilute solution (an ideal case with no intermolecular Electrostatic Interactions between ions), the electrophoretic mobility (μ) is expressed by the formula:

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where Q is the net charge of the particle, r is the particle radius, μ is the viscosity of the medium in which the ion moves, and U is the potential difference (applied voltage).

It is evident from the equation that in the same medium (η=const) and at a constant voltage (U=const), the ionic mobilities are proportional to The ratio of the charge to the radius:

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This relationship forms The basis of electrophoretic Separation for mixtures of charged particles with varying mobilities.



Last update: 06/08/2026

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