Ultracentrifugal applications

B. Schmidt and D. Riesner, A fluorescence detection system for the analytical ultracentrifuge and its application to proteins, nucleic acids, viroids and viruses (in Ref. [77]). 

For the convenience of the reader, we have outlined the method of sequential flotation employed in our laboratory for separating chylomicrons VLDL, LDL, HDLa, HDLs, VHDL, and d> 1.25 bottom (Table 1). This method, the result of years of experience, has been highly reproducible in terms of the normal human population examined in this laboratory. Such a method may not necessarily apply to dyslipoproteinemic states, where modifications may be necessary, depending on the type of abnormality under consideration. It should also be stressed that any lipoprotein isolated is in need of purification this may be achieved by ultracentrifugation based on the assumption that contaminants are in loose association with the main complex. Whenever this purification is not achieved, other methods may be used as outlined below. For a discussion of the application of density gradient ultracentrifugation to the study of plasma lipoproteins, the reader is referred to a recent review (L3). 

A basic limitation of all these methods is the narrow range of particle sizes that can be investigated by sedimentation under gravity. Therefore, we turn next to a consideration of centrifugation, particularly the ultracentrifuge, as a means of extending the applicability of sedimentation measurements. 

Many natural polymers are monodisperse (all molecules have the same molecular weight). In this case the ullracentrifuge which separates materials according to their effective density in solutions is a most powerful tool for molecular weight determination. With poly-disperse materials, the interpretation of ultracentrifuge results becomes more complex and widespread application of this method to synthetic polymer molecular weighl determination has not yet been achieved... 

A major concern for the use of these quantum dots in liquid crystal applications is their stability. Weller et al. using NMR spectroscopy, UV-vis spectrophotometry, and analytical ultracentrifugation (AUC) showed that thiol-stabilized cadmium chalcogenide quantum dots are unstable at low particle concentrations (<10 pM in DMF), i.e., even the covalently bound thiols desorb from the quantum dot surface... 

The up to now most frequently used techniques as, for example, vapour pressure osmometry (VPO) or freezing point depression (with its limitation regarding the solvent dependent measuring temperature) are based upon the colligative properties of the system the classical absolute light-scattering and ultracentrifugation techniques are only occasionally and approximately applicable with respect to the determination of CMC values. Evaluation of critical micelle concentrations which are based on these latter methods suffer considerably from the insensitivity of these techniques if measurements below the CMC, i.e., below about 10-3 mol dm-3, are carried out. More sensitive methods will be discussed below. 

For the development, production, and application of polymer latices the determination of the size distribution and the analysis of the chemical composition and heterogeneity of the latex particles are important. The size distribution can be determined rapidly by ultracentrifugation, electron microscopy or light scattering > but for the analysis of the... 

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