Influence of polydispersity on polymer self-diffusion measurements by pulsed field gradient nuclear magnetic resonance

Callaghan, P. T.; Pinder, D. N.

doi:10.1021/ma00145a013

Cited by 79 publications

(89 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In this way, M n and M w of each mixture are known. In the following, we introduce PGSE NMR and reproduce equations [24] for the application of the lognormal [29,30,14] and gamma [21,31] distribution models. We then explain sample preparation and outline the procedure for obtaining ν, M w /M n , and the molecular mass distribution.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Scaling exponent and dispersity of polymers in solution by diffusion NMR

Williamson

Röding

Miklavcic

et al. 2017

Journal of Colloid and Interface Science

View full text Add to dashboard Cite

Molecular mass distribution measurements by pulsed gradient spin echo nuclear magnetic resonance (PGSE NMR) spectroscopy currently require prior knowledge of scaling parameters to convert from polymer self-diffusion coefficient to molecular mass. Reversing the problem, we utilize the scaling relation as prior knowledge to uncover the scaling exponent from within the PGSE data. Thus, the scaling exponent-a measure of polymer conformation and solvent quality-and the dispersity (M w /M n ) are obtainable from one simple PGSE experiment. The method utilizes constraints and parametric distribution models in a two-step fitting routine involving first the mass-weighted signal and second the number-weighted signal. The method is developed using lognormal and gamma distribution models and tested on experimental PGSE attenuation of the terminal methylene signal and on the sum of all methylene signals of polyethylene glycol in D 2 O. Scaling exponent and dispersity estimates agree with known values in the majority of instances, leading to the potential application of the method to polymers for which characterization is not possible with alternative techniques. Keywords:Pulsed gradient spin echo, pulsed field gradient, Nuclear Magnetic Resonance spectroscopy, Molecular weight distribution, Polymers, DOSY, Polydispersity Index, Self-diffusion, Molar mass, Flory exponent, Lognormal distribution, Gamma distribution, End-group analysis, Scaling law Synthetic polymers have distributions of molecular masses determined by their synthesis [1]. Measuring the molecular mass distribution rather than its average is important because the dispersity can influence polymer properties [2]. Absolute as opposed to relative measurements are needed when using polymer physics to fully realize the potential applications of a polymer [3]. Only a handful of techniques can measure the absolute molecular mass distribution [3]. The gold standard is size exclusion chromatography (SEC) using universal calibration [4], which does not always work [5,6]. New techniques must be developed to aid in the advancement of polymer science.Pulsed gradient spin echo nuclear magnetic resonance (PGSE NMR) [7,8] is a powerful technique for obtaining the distribution of polymer self-diffusion coefficients D [9], from which the distribution of molecular masses M can be obtained by the scaling law [10] ration give PGSE NMR a competitive edge with respect to SEC. Chemical shift information [7], e.g. in a diffusion ordered spectroscopy (DOSY) plot [11], provides the ability to observe chemical heterogeneity and impurity. Sample preparation generally does not require filtration because contaminates from large particles such as dust do not impact the experiment. However, the scaling parameters of Eq. (1) specific to that polymersolvent system must be found by measuring ⟨D⟩ on fractionated samples of the polymer with known M. Therefore, currently all PGSE NMR-based methods which convert from D to M cannot independently measure the absolute molecular mass distribution [...

show abstract

mentioning

confidence: 99%

“…Many distribution models exist, and the estimation of the distribution is an inverse problem for which there is no unique solution. We are physically motivated to use the lognormal distribution [14,29,30],…”

mentioning

confidence: 99%

Scaling exponent and dispersity of polymers in solution by diffusion NMR

Williamson

Röding

Miklavcic

et al. 2017

Journal of Colloid and Interface Science

View full text Add to dashboard Cite

show abstract

“…Normalization with the g = 0 case removes the effects of relaxation from the analysis. The normalized spin-echo attenuation [i.e., E(g, )] of a polydisperse species undergoing diffusion is [31,58]:…”

Section: Frontiers In Physicsmentioning

confidence: 99%

“…Since, for many associating systems the experimentally observed attenuation is usually single exponential (i.e., "linear" when plotted on a log scale). It can be assumed that there is a process which results in ensemble averaging of the diffusion coefficients of the aggregated systems (e.g., [17,41,58]). An example of a non-linear attenuation plot on log scale for overlapped signals for two species is shown in Figure 2.…”

Section: Frontiers In Physicsmentioning

confidence: 99%

“…Ignoring the relaxation terms (i.e., assuming that any difference in relaxation properties of different sized aggregates is negligible), Equation (5) gives the combined diffusion averaging effects for the different oligomers. The averaging effect is approximated by taking the cumulant expansion of Equation (5) to second order [31,58]:…”

Section: Frontiers In Physicsmentioning

confidence: 99%

See 1 more Smart Citation

Macromolecular crowding studies of amino acids using NMR diffusion measurements and molecular dynamics simulations

et al. 2015

View full text Add to dashboard Cite

Molecular crowding occurs when the total concentration of macromolecular species in a solution is so high that a considerable proportion of the volume is physically occupied and therefore not accessible to other molecules. This results in significant changes in the solution properties of the molecules in such systems. Macromolecular crowding is ubiquitous in biological systems due to the generally high intracellular protein concentrations. The major hindrance to understanding crowding is the lack of direct comparison of experimental data with theoretical or simulated data. Self-diffusion is sensitive to changes in the molecular weight and shape of the diffusing species, and the available diffusion space (i.e., diffusive obstruction). Consequently, diffusion measurements are a direct means for probing crowded systems including the self-association of molecules. In this work, nuclear magnetic resonance (NMR) measurements of the self-diffusion of four amino acids (glycine, alanine, valine and phenylalanine) up to their solubility limit in water were compared directly with molecular dynamics simulations. The experimental data were then analyzed using various models of aggregation and obstruction. Both experimental and simulated data revealed that the diffusion of both water and the amino acids were sensitive to the amino acid concentration. The direct comparison of the simulated and experimental data afforded greater insights into the aggregation and obstruction properties of each amino acid.

show abstract

Diffusion-Based Studies of Aggregation, Binding and Conformation of Biomolecules: Theory and Practice

Price

2007

Encyclopedia of Magnetic Resonance

View full text Add to dashboard Cite

Influence of polydispersity on polymer self-diffusion measurements by pulsed field gradient nuclear magnetic resonance

Cited by 79 publications

References 5 publications

Scaling exponent and dispersity of polymers in solution by diffusion NMR

Scaling exponent and dispersity of polymers in solution by diffusion NMR

Macromolecular crowding studies of amino acids using NMR diffusion measurements and molecular dynamics simulations

Diffusion-Based Studies of Aggregation, Binding and Conformation of Biomolecules: Theory and Practice

Contact Info

Product

Resources

About