Determination of chain stiffness and polydispersity from static light‐scattering

Abstract

SYNOPSISChain stiffness is often difficult to distinguish from molecular polydisperity. Both effects cause a downturn of the angular dependence at large q 2 ( q = (4?r/X)sin 612) in a Zimm plot. A quick estimation of polydisperity becomes possible from a bending rod ( B R ) plot in which lim(c + O)qRe/Kc is plotted against q ( (.?)>.) "* = u. Flexible and semiflexible chains show a maximum whose position is shifted from u,,, = 1.41 for monodisperse chains toward larger values as polydispersity is increased, while simultaneously, the maximum height is lowered. Stiff chains display a constant plateau at large q , its value is ?rML where ML is the linear mass density. Using Koyama's theory, the number of Kuhn segments can be determined from the ratio of the maximum height to the plateau height, if the polydispersity index z = (M,/M, -1 I-' is known. Thus, if the weight-average molecular weight M,, is known, the contour length L,, the number of Kuhn segments (Nk),, the Kuhn segment length and the polydispersity of the stiff chains can be determined. The influence of excluded volume is shown to have no effect on this set of data. The reliability of this set can be cross-checked with the mean-square radius of gyration ( s ' ) , which can be calculated from the Benoit-Doty equation for polydisperse chains. Rigid and slightly bending rods exhibit no maximum in the BR plot, and the effect of polydispersity can no longer be distinguished from a slight flexibility if only static scattering techniques are applied.

Size and shape of the repetitive domain of high molecular weight wheat gluten proteins. I. Small‐angle neutron scattering

“…l p , and only depends on the radius of gyration, q max R G Ϸ 1.4. 26,27 This is in very nice agreement with the radii of gyration determined from the Guinier fit.…”

“…The second protein, dB4, with a molecular mass of 63.8 kDa, is composed of four dB1 segments resulting in a molecular mass comparable to the full central domain ( Figure 1A). The amino acid sequences of dB1 and dB4 are very similar to the central domains of HMW Dx5 and other x-type HMW subunits: The sequences are almost completely covered with three different consensus repeats, whose occurrences are 42% (PGQGQQ), 29% (PGQGQQGQQ), and 17% (GYYPTSPQQ) in dB1 and dB4, while the relative proportions in the central domain in HMW Dx5 are 45,27, and 23%, respectively. 6,15,16,19 -21 We thus consider dB1 and dB4 appropriate models for the wild-type domain of the HMW Dx5 protein.…”

“…23 This transition is predicted to be located at q p Ϸ 1.9. 26,27 However, the transition region is often fairly broad. A particularly sensitive way to represent scattering data for semiflexible polymers is the so-called "Holtzer plot" (or "bending rod plot" shown in Figure 6, in which ql(q) is plotted versus q.…”

Physicochemical studies on xylinan (acetan). I. Characterization by G permeation chromatography on sepharose Cl‐2B coupled with static light scattering and viscometry

“…Effects of chain stiffness and polydispersity on theoretical scattering curves have also been discussed in Ref. 25 for different types of distribution. Excluded volume effects are said to be negligible if the number of chain segments per molecule is sufficiently small.…”

Small-angle X-ray-scattering studies of the C hordeins of barley (Hordeum vulgare)

“…2) gives a number related to the number of Kuhn statistical segment lengths (nk). Using the value of R = 2.4, and a plot of R versus nk for a monodisperse polymer [14,16] [8]), as 0.21+0.04 nm per residue. These values are calculated from the Rg value at a finite concentration.…”