Determination of Molecular Weight Distributions from Frequency-Analyzing (Dynamic) Light Scattering

Abstract

Average configuration-dependent properties (mean-square radius of gyration, mean-square end-to-end distance, helical content, helix probability profile, and average number of amino acid residues in a helical segment) have been evaluated for unperturbed partially helical polypeptides by using two weighting schemes. The weighting schemes differ with regard to whether end effects in a helical segment are assigned in like manner to amino acid residues at each end or are instead associated with only one amino acid residue. Molecules considered are block copolypeptides and specific sequence copolypeptides with amino acid sequences corresponding to those found in 44 proteins. Without exception, helix formation in the proteins is found to exhibit greater cooperativity if amino acid residues at each end of a helical segment contribute to the end effects. The helix probability profile for proteins is also found to be much smoother with this weighting scheme. Block copolypeptides show more dramatic changes in helicity, helix probability profile, and average number of amino acid residues in a helical segment. Unperturbed dimensions for both proteins and block copolypeptides are nearly independent of the weighting scheme adopted. Modification of the statistical weights used for arginyl, histidyl, and lysyl residues can produce helicities and unperturbed dimensions in reasonable agreement with helicities and dimensions deduced from circular dichroism spectra and viscosity measurements of complexes formed by reduced bovine serum albumin and sodium dodecyl sulfate.

Diffusion of polystyrene in gels

“…This is in agreement with the known behavior of polystyrene in dilute solution in a good solvent. 11 The dynamics here is consistent with the probe polymer diffusing as a Stokes-Einstein particle of hydrodynamic radius Rn ~M~°•6 in a medium of effective viscosity . It is clear that > 0, the viscosity of pure toluene and the data suggest (rffinlgei ~10t)o/?ho where Rh0 is the hydrodynamic radius of the polymer in pure toluene.…”

A study of mass transport of linear polystyrene in polyethyl methacrylate gel by dynamic light scattering

“…This is in agreement with the known behavior of PS in a dilute solution in a good solvent. The dynamics demonstrated in this case are consistent with the probe polymer diffusion as a Stokes–Einstein particle of hydrodynamic radius R H ∼ M −0.6 in a medium of effective viscosity η 7, 15, 16. For M > M c , the diffusion coefficient decreases very rapidly with increasing molecular weight and D t / D 0 ∼ M −1.3 , which implies that D ∼ M −1.9 .…”

Solid and gaseous fuels

“…NMR sequence distribution measurements were able to differentiate between styrene-ethyl acrylate copolymers prepared by different polymerization processes (E24). Carbon-13 spin-lattice relaxation times of polystyrene oxide) in CDC13 and C6De were measured at 15 MHz as a function of temperature, concentration, and molecular weight (E25). The observed segmental backbone and phenyl-group twisting motions were more rapid than those observed in polystyrene.…”