Mobility of a Macromolecule

Diffusion of a macromolecule is understood as the diffusion of a co-ordinate of the centre of mass of a chain, which is, according to relation (1.18), proportional to the zeroth normal co-ordinate, that is, 

The mean square displacement of the centre of mass of a diffusing macromolecule for a time t is calculated as 

This expression reduces the calculations to the evaluation of the time-dependent velocity correlation function 

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A Macromolecule in an Entangled System Diffusive Mobility of a Macromolecule... 

The mobility of a macromolecule, constrained by other macromolecules, can be also calculated as (5.1). In the linear approximation, the zeroth normal co-ordinates of the macromolecule (equation (4.1), at z/jj = 0) define diffusive mobility of macromolecule. The one-sided Fourier transform velocity correlation function is determined by expression (4.15), so that we can write down the Fourier transform... 

Recall that the parameter D characterises the degree of deformability (mobility) of a macromolecule fragment between chemical crosslinking points. Indeed, an increase in the chain flexibility brings about an increase in C , i.e., an increase in D. It should be... 

The discussion on electrophoretic mobiliiy in previous pages did not take into account the molecular sieving action of the gels and its effect on the mobility of a macromolecule. 

Fig. 1. Mobility of a macromolecule and its particles. The mean square displacement (A ) of the centre of mass of a chain thick solid line) does not depend on parameter but the mean square displacement A] /2 of the central particle does. The values of parameter are shown at the curves for A] /2. The theoretical curves are calculated according to formulae (89) and (95) for the values of the parameters B = 100 X = 10- ...

An important application of the preceding material is to the determination of the molar mass of biological macromolecules. Electrophoresis is the motion of a charged species, such as DNA and ionic forms of amino acids, in response to an electric field. Electrophoretic mobihty is a result of a constant drift speed, so the mobility of a macromolecule in an electric field depends on its net charge, size (and hence molar mass), and shape. 

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