Quasi-elastic light-scattering

The autocorrelation function decays to a value of P av that is the average squared scattered hght intensity. Theoretically G(Ndt) is related to a constant a, the experimental baseline B, and the decay constant r, as shown in Equation (4.10). The decay constant T is related to the translational 

Taking the natural logarithm of Equation (4.10) and substituting Equation (4.11) we find that a plot of In[(G(Ndt)/B) -1] versus time has a slope equal 

It is important to note that the translational diffusion coefficient can be determined this way for macromolecules that are less than 2 pm in their largest dimension at scattering angles less than 4°. Macromolecules larger than this or measurements made at higher scattering angles need to be corrected to get accurate values of Dt. 

Once Dt for a macromolecule is determined, it can be compared to theoretical values for prolate ellipsoids and spheres using Equations (4.12) and (4.13) for standard conditions of 20°C and the viscosity of water and a value for the axial ratio can be estimated. 

Values of Dt for various biological macromolecules are given in Table 4.3. From Dt we can get an idea of what the axial ratio of a macromolecule might be. 

The Doppler shift is very. small compared with the main frequency. To u close approximation, it is given by 

The time-avemged scattered intensity / is the basis of conventional light-scattering techniques used for aerosol measurements. 

The intensity fluctuations due to the Brownian motion lake place on a lime scale much faster than conventional photometers or the human eye can detect. The variation in the fluctuating scattered light intensity with time resembles a noise signal that can be analyzed in terms of its correlation function with respect to time. The usual practice is to measure the polarized intensity tiine correlation function that is related to the diffusion coefficient for monodisperse particles as follows 

Rearranging (5.35) gives the autocorrelation function in terms of the experimentally measured variable G( )  

Various methods arc used to determine the diffusion coefficient. For example after subtraction of the baseline constant. A, G(f) may be fitted to an exponential function to permit calculation of the decay constant q D, hence particle size from the value of D. 

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Photon Correlation Spectroscopy. Photon correlation spectroscopy (pcs), also commonly referred to as quasi-elastic light scattering (qels) or dynamic light scattering (dls), is a technique in which the size of submicrometer particles dispersed in a Hquid medium is deduced from the random movement caused by Brownian diffusion motion. This technique has been used for a wide variety of materials (60—62). 

C.Elastic and quasi-elastic light scattering measurements have revealed that their size scales as Ca13 at 1 ppm of A1 (or 3 10"... 

To determine the shape of ribosomal proteins in solution, ultracentrifugation, digital densimetry, viscosity, gel filtration, quasi-elastic light scattering, and small-angle X-ray or neutron scattering have all been used. With each technique it is possible to obtain a physical characteristic of the protein. Combining these techniques should allow the size and shape of the protein to be characterized quite well. However, the values determined in various laboratories for the same ribosomal proteins differ considerably. To help understand some of the reasons we will initially discuss each method briefly as it relates to proteins and then review the size and shape of the ribosomal proteins that have been so characterized. 

Diffusion coefficients can also be obtained from sedimentation velocity experiments, but the precision is quite low and subject to some ques-don. Quasi-elastic light scattering is a much more useful technique to obtain diffusion coefficients (see below). 

In this study, has been investigated by means of quasi-elastic light scattering and transient electric birefringence the effect of the quenching concentration on the structure of the PVC aggregates as well as the thermal stability of these aggregates. 

Selected entries from Methods in Enzymology [vol, page(s)] Anisotropy effects, 261, 427-430 determination by dynamic laser light scattering (quasi-elastic light scattering), 261, 432-433 determination for nucleic acids by NMR [accuracy, 261, 432-433 algorithms, 261, 11-13, 425, 430 carbon-13 relaxation, 261, 11-12, 422-426, 431, 434-435 cross-relaxation rates, 261,419-422, 435 error sources, 261, 430-432 phosphorus-31 relaxation, 261, 426-427, 431 proton relaxation, 261,51,418-422 relaxation matrix calculations, 261,12] deuterium solvent viscosity effects, 261,433 effect... 

Chen s laboratory used quasi-elastic light scattering to track migrating chemotactic bands of Escherichia coli in a buffer solution. The temporal development of the bacterial density profile is observed by the intensity of... 

Finsey R., Particle sizing by quasi-elastic light scattering, Adv. Colloid Interface Set, 52, 79, 1994. 

The size of molecular assembly of six synthetic dialkyl amphiphiles as determined by a quasi-elastic light scattering is varied in the presence of nonionic MEGA-n surfactants (N-D-gluco-N-methylalkanamide C = 7-9). 

Quasi-elastic light scattering was employed successfully to estimate sizes of molecular assemblies in terms of hydrodynamic radius, R . In the present paper, we concentrated on a "phase diagrammatic" study of molecular assembly size. 

Martindale, H., Marsh, J., Hallett, F.R., Albisser, A.M. (1982). Examination of insulin formulations using quasi-elastic light scattering. Diabetes, 31, 364—366. 

Heming, T., Djabourov, M., Leblond, J., and Takerkart, G. (1991). Conformation of gelatin chains in aqueous solutions 2. A quasi-elastic light scattering study. Polymer, 32, 3211-3217. 

In dynamic or quasi-elastic light scattering, a time dependent correlation function (i (0) i (t)) = G2 (t) is measured, where i (0) is the scattering intensity at the beginning of the experiment, and i (t) that at a certain time later. Under the conditions of dilute solution (independent fluctuation of different small volume elements), the intensity correlation function can be expressed in terms of the electric field correlation function gi (t)... 

A recent study has employed the new technique of quasi-elastic light scattering for estimation of diffusion constants (257). The result for the native enzyme at 24° is in close agreement with the data given in the tabulation. The value of D as a function of temperature was measured through the thermal transition. The method was also used to follow the kinetics of the urea-induced transition. 

Micellization of PS-PMA diblock and triblock copolymers in 80 20 dioxane water mixtures was investigated by Qin et al. (1994) using static and quasi-elastic light scattering, differential refractometry, viscomelry, sedimentation... 

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