Asymptotic behavior and long-range interactions in aqueous solutions of poly(ethylene oxide)

Devanand, K.; Selser, J. C.

doi:10.1021/ma00022a008

Cited by 613 publications

(662 citation statements)

References 8 publications

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“…From the bond lengths and angles, the contour length per one ethylene oxide unit is 3.5Å, while the Kuhn length for poly(ethylene oxide) is about 10Å [46]. From these values R g =5Å is obtained for the hydrophilic chains of 5 EO units, which agrees with other theoretical calculations [47] and values calculated by extrapolation of experimental data of longer chains [48,49]. The fitting model would be similar to a "crew-cut" morphology [50], with large hydrophobic cores and relative thin hydrophilic coronas.…”

Section: Small-angle Neutron Scattering (Sans) Measurementssupporting

confidence: 87%

Erratum to: Solution behavior of aqueous mixtures of low and high molecular weight hydrophobic amphiphiles

et al. 2010

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Mixtures of a hydrophobic triblock copolymer (L121, PEO 5 PPO 68 PEO 5 ) and a hydrophobic anionic surfactant (AOT, Sodium bis(2-ethylhexyl)sulfosuccinate), each alone forming turbid vesicular solutions in water, aggregate to produce a thermodynamically stable, transparent and isotropic solution. Mixed AOT/L121 aggregates could be confirmed by fluorescence, surface tension, differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC). In an isotropic region, where mixed aggregates are formed, there is a synergistic interaction between monomers of AOT and L121 in the mixture. In addition, Small Angle Neutron Scattering (SANS) experiments provided evidence that mixed aggregates have the shape of either spheres (with a certain polydispersity) or very short ellipsoids (axial ratio below 2), confirming a transition from giant multilamellar vesicles to small aggregates upon mixing the two hydrophobic amphiphiles. Upon dilution, the morphology changes to disk-like. From an examination of the results of all the methods the peculiar behavior of the mixed AOT/L121 system is explained.The online version of the original article can be found at http://dx.doi.

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Section: Small-angle Neutron Scattering (Sans) Measurementssupporting

confidence: 87%

Erratum to: Solution behavior of aqueous mixtures of low and high molecular weight hydrophobic amphiphiles

et al. 2010

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“…2B). The gradient is expected, because the radius of gyration of 20k PEO ∼ 6.9 nm is close to the inner radii of MTs (45), and at these intermediate concentrations, PEO does not readily enter the lumen because of an entropic confinement penalty.…”

Section: Resultsmentioning

confidence: 97%

Direct force measurements reveal that protein Tau confers short-range attractions and isoform-dependent steric stabilization to microtubules

Chung

Choi

Miller

et al. 2015

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

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Microtubules (MTs) are hollow cytoskeletal filaments assembled from αβ-tubulin heterodimers. Tau, an unstructured protein found in neuronal axons, binds to MTs and regulates their dynamics. Aberrant Tau behavior is associated with neurodegenerative dementias, including Alzheimer's. Here, we report on a direct force measurement between paclitaxel-stabilized MTs coated with distinct Tau isoforms by synchrotron small-angle X-ray scattering (SAXS) of MT-Tau mixtures under osmotic pressure (P). In going from bare MTs to MTs with Tau coverage near the physiological submonolayer regime (Tau/tubulin-dimer molar ratio; Φ Tau = 1/ 10), isoforms with longer N-terminal tails (NTTs) sterically stabilized MTs, preventing bundling up to P B ∼ 10,000-20,000 Pa, an order of magnitude larger than bare MTs. Tau with short NTTs showed little additional effect in suppressing the bundling pressure (P B ∼ 1,000-2,000 Pa) over the same range. Remarkably, the abrupt increase in P B observed for longer isoforms suggests a mushroom to brush transition occurring at 1/13 < Φ Tau < 1/10, which corresponds to MT-bound Tau with NTTs that are considerably more extended than SAXS data for Tau in solution indicate. Modeling of Tau-mediated MT-MT interactions supports the hypothesis that longer NTTs transition to a polyelectrolyte brush at higher coverages. Higher pressures resulted in isoform-independent irreversible bundling because the polyampholytic nature of Tau leads to short-range attractions. These findings suggest an isoform-dependent biological role for regulation by Tau, with longer isoforms conferring MT steric stabilization against aggregation either with other biomacromolecules or into tight bundles, preventing loss of function in the crowded axon environment.Tau | intrinsically disordered proteins | microtubule | SAXS | force measurement

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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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Asymptotic behavior and long-range interactions in aqueous solutions of poly(ethylene oxide)

Cited by 613 publications

References 8 publications

Erratum to: Solution behavior of aqueous mixtures of low and high molecular weight hydrophobic amphiphiles

Erratum to: Solution behavior of aqueous mixtures of low and high molecular weight hydrophobic amphiphiles

Direct force measurements reveal that protein Tau confers short-range attractions and isoform-dependent steric stabilization to microtubules

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

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