Single-Molecule Elasticity Measurements of the Onset of Excluded Volume in Poly(Ethylene Glycol)

Dittmore, Andrew; McIntosh, Dustin B.; Halliday, Sam; Saleh, Omar A.

doi:10.1103/physrevlett.107.148301

Cited by 50 publications

(101 citation statements)

References 27 publications

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“…(4)). The Marko-Siggia elastic model matches high-force stretching data on a variety of polymers in which electrostatic interactions are either missing or negligible; this includes double-stranded DNA, 30 polypeptides, 18 synthetic chains, 21 and, at certain large salt concentrations, single-stranded nucleic acids. 19,22 Indeed, I am unaware of a single-polymer experiment which has convincingly shown FJC elastic behavior.…”

Section: The Worm-like Chain (Wlc)mentioning

confidence: 99%

“…This coincidence of scales is expected for a polymer whose statistical monomers have spherically symmetric interactions-which is indeed the expected case for a chain dominated by electrostatics. 21 In contrast, the thermal blob size should become larger than the Kuhn length for rod-like monomers, 21 where the interactions along the chain differ from those orthogonal to it. Many neutral chains in a good solvent should behave as if they have rod-like monomers, since for such chains interactions along the backbone are dominated by bond rotational freedom, while excluded-volume interactions (in good solvent) are defined by sterics, two different physical mechanisms whose asymmetry leads to rod-like behavior.…”

Section: B Thermal Blobs and The Onset Of Swellingmentioning

confidence: 99%

“…This basic viewpoint was tested in single-molecule elasticity measurements of poly(ethylene glycol) (PEG), 21 a neutral polymer with a high degree of aqueous solubility that is commonly used in anti-fouling applications. Forceextension curves of long-chain PEG indeed showed a highforce Marko-Siggia behavior, an intermediate-force linear behavior, and, at the lowest accessible forces, a slight increase in extension beyond the extrapolation of the previous linear behavior (Fig.…”

Section: B Thermal Blobs and The Onset Of Swellingmentioning

confidence: 99%

“…It is only in the past few years that lower-force regimes have begun to be investigated. [19][20][21][22] Along with permitting direct measurement of chain mechanics, the introduction of single-chain stretching techniques also prompted a philosophical change: forceextension models, initially conceived as components of a broader theory of material mechanics, began to be used in conjunction with high-resolution experimental data to give new information on microscopic details of polymer structure.…”

Section: Introductionmentioning

confidence: 99%

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Perspective: Single polymer mechanics across the force regimes

Saleh

2015

The Journal of Chemical Physics

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I review theoretical and experimental results on the force-extension response of single polymers, with a focus on scaling pictures of low-force elastic regimes, and recent measurements of synthetic and biological chains that explore those regimes. The mechanical response of single polymers is an old theoretical problem whose exploration was instigated by the curious thermomechanical behavior of rubber. Up until the 1990s, the main utility of those calculations was to explain bulk material mechanics. However, in that decade, it became possible to directly test the calculations through high-precision single-chain stretching experiments (i.e., force spectroscopy). I present five major single-chain elasticity models, including scaling results based on blob-chain models, along with analytic results based on linear response theory, and those based on freely jointed chain or worm-like chain structure. Each model is discussed in terms of the regime of force for which it holds, along with the status of its rigorous assessment with experiment. Finally, I show how the experiments can provide new insight into polymer structure itself, with particular emphasis on polyelectrolytes. C 2015 AIP Publishing LLC. [http://dx

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Section: The Worm-like Chain (Wlc)mentioning

confidence: 99%

Section: B Thermal Blobs and The Onset Of Swellingmentioning

confidence: 99%

Section: B Thermal Blobs and The Onset Of Swellingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Perspective: Single polymer mechanics across the force regimes

Saleh

2015

The Journal of Chemical Physics

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“…Evidence for the random coil nature of aqueous PEG is provided by studies monitoring many different dimensionally dependent properties. These sources of evidence include gel filtration (37), light scattering (38,39), and sedimentation (40) studies of its hydrodynamic radius as a function of its molecular weight, studies of the viscosity of PEG solutions as a function of molecular weight (41), small-angle neutron scattering (SANS) (42) and simulations-based (43) studies of the polymer's radius of gyration as a function of molecular weight, and single-molecule pulling studies of PEG's extension as a function of force (44). In short, all of these physically distinct methods of monitoring the behavior of PEG produce dimensional scaling behaviors within experimental uncertainty of those expected for an expanded, excluded-volume random coil (43).…”

Section: Resultsmentioning

confidence: 99%

Random coil negative control reproduces the discrepancy between scattering and FRET measurements of denatured protein dimensions

Watkins

Simon

Sosnick

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Small-angle scattering studies generally indicate that the dimensions of unfolded single-domain proteins are independent (to within experimental uncertainty of a few percent) of denaturant concentration. In contrast, single-molecule FRET (smFRET) studies invariably suggest that protein unfolded states contract significantly as the denaturant concentration falls from high (∼6 M) to low (∼1 M). Here, we explore this discrepancy by using PEG to perform a hitherto absent negative control. This uncharged, highly hydrophilic polymer has been shown by multiple independent techniques to behave as a random coil in water, suggesting that it is unlikely to expand further on the addition of denaturant. Consistent with this observation, small-angle neutron scattering indicates that the dimensions of PEG are not significantly altered by the presence of either guanidine hydrochloride or urea. smFRET measurements on a PEG construct modified with the most commonly used FRET dye pair, however, produce denaturant-dependent changes in transfer efficiency similar to those seen for a number of unfolded proteins. Given the vastly different chemistries of PEG and unfolded proteins and the significant evidence that dye-free PEG is well-described as a denaturant-independent random coil, this similarity raises questions regarding the interpretation of smFRET data in terms of the hydrogen bond-or hydrophobically driven contraction of the unfolded state at low denaturant.protein folding | SAXS | two state | statistical coil | Flory scaling R ecent years have seen a significant controversy arise regarding the behavior of the unfolded states of single-domain proteins in response to changing levels of chemical denaturant. That is, although small-angle X-ray scattering (SAXS) and single-molecule FRET (smFRET) results are all consistent with the argument that, at high levels of chemical denaturant (∼6 M or above), unfolded proteins adopt a swollen, self-avoiding ensemble well-approximated as an excluded volume random coil (1-3), the two approaches produce seemingly discrepant results for the dimensions of the unfolded states populated at lower (∼1 M) denaturant (4). For example, time-resolved SAXS studies of the unfolded state transiently populated when protein L is rapidly shifted from high guanidine hydrochloride (GuHCl) to low denaturant conditions produce no experimentally significant evidence for the compaction of this single-domain protein before folding (4, 5) [e.g., estimated radii of gyration of 25.1 ± 0.3 Å for the unfolded state at equilibrium in 7 M GuHCl and 24.9 ± 1.1 Å for the transient unfolded state populated at 0.67 M GuHCl; confidence intervals are SEs (4)]. In contrast, multiple smFRET studies conducted at equilibrium suggest that the unfolded state of dye-labeled protein L contracts by 20-40% over this same range of denaturant concentrations (6, 7) (Fig.

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Rheological properties and structure of step‐ and chain‐growth gels concentrated above the overlap concentration

et al. 2018

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Cross-linked polymeric gels are widely used in applications ranging from biomaterial scaffolds to additives in enhanced oil recovery. Despite this, fundamental understanding of the effect of polymer concentration and reaction mechanism on the scaffold structure is lacking. We measure scaffold properties and structure during gelation using multiple particle tracking microrheology. To determine the effect of concentration, we measure gelation as polymer interactions are increased in the backbone precursor solution: below, at and above the overlap concentration, c � . To determine structural changes due to the gelation mechanism, we measure gelation between the same polymers undergoing both step-and chain-growth reactions using self-assembling maleimide:thiol and photo-initiated acrylate:thiol chemistries, respectively. We determine the critical relaxation exponent, n, a measure of structure. n decreases with increasing concentration, indicating a change from a percolated (c < c � ) to a tightly cross-linked network (c � < c). The gelation mechanism does not have a measurable effect on the scaffold structure.Time-cure superposition (TCS) is used to analyze dynamic microrheological measurements during gelation to determine Figure 3. Non-Gaussian parameters throughout the gelation of acrylate:thiol and maleimide:thiol gels plotted as a function of normalized time. Scaffold are measured for a range of concentrations of PEG-maleimide backbone, 3 wt % (a and e), 7.5 wt % (b and f), 10 wt % (c and g), and 18 wt % (d and h). [Color figure can be viewed at wileyonlinelibrary.com] AIChE Journal

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Single-Molecule Elasticity Measurements of the Onset of Excluded Volume in Poly(Ethylene Glycol)

Cited by 50 publications

References 27 publications

Perspective: Single polymer mechanics across the force regimes

Perspective: Single polymer mechanics across the force regimes

Random coil negative control reproduces the discrepancy between scattering and FRET measurements of denatured protein dimensions

Rheological properties and structure of step‐ and chain‐growth gels concentrated above the overlap concentration

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