Transport ultracentrifuge

Lenhoff, A. M., Pjura, P. E., Ddmore, J. G. and Godlewski, T. S. Jr. (1997). Ultracentrifugal crystallization of proteins transport-kinetic modelhng, and experimental behavior of catalase. J. Crust. Growth 180, 113-126. 

Rasa M, Meier MAR, Schubert US (2007) Transport of guest molecules by unimolecular micelles evidenced in analytical ultracentrifugation experiments. Macromol Rapid Commun... 

Transport Analysis Using the Ultracentrifuge Schlieren Optics... 

The use of absorption optics with the ultracentrifuge has allowed us to monitor the rapid transport of PVP in the standard PVP/dextran system as a function of g. It was demonstrated that while the rate of the PVP transport increases with increasing g acting on the system, the rate is rather insensitive to the magnitude of the gravitational force. We found 51) that the linear time rate of the transport varies as g°19. Note, however, that although rapid PVP transport has been found at various values of g, we cannot be sure whether structured flows exist. 

We have now identified the presence of structured flows in a wide variety of ternary systems of polymer/polymer/solvent 52-53>. in all cases associated with structured flow formation there was concomitant rapid transport of the polymer as compared to its behaviour in water. Indeed, even in the presence of dextran concentration gradients structures are formed which move relatively slowly but are nevertheless highly regular. The only conditions where structures have not been observed is at dextran concentrations below C values where, incidentally, polymer transport is not rapid. (See also the low rate of transport of PVP 360 in a dextran T10 medium with a concentration of 40 kg m 3 as measured in the ultracentrifuge Fig. 9.) These studies confirm the striking correlation between this parameter and the onset of rapid polymer transport and structured flow formation. 

We will consider an instructive prototype transport process. This process is the gravity (or ultracentrifuge) induced sedimentation of a collection of identical noninteracting macroscopic particles each of mass M. Assume that the particles are suspended in a long tube filled with a viscous fluid and that the tube is aligned parallel to the Z-axis. The particles thus descend in the negative Z-direction. Further assume that the fluid exerts only a simple frictional force - z t) on each particle. Then the equation of motion for a typical particle is... 

The expressions that describe the equilibrium concentrations of solutes in the ultracentrifuge cell have been derived from both classic thermodynamics, in which there are few uncertainties, and from material transport theory, in which approximations exist. Svedberg (47,48) derived expressions from the two approaches and showed that identical results can be deduced from both methods for ideal solutions. 

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