Folding and Formation of Mesoglobules in Dilute Copolymer Solutions

Zhang, Guangzhao

doi:10.1007/12_050

Cited by 128 publications

(58 citation statements)

References 132 publications

(201 reference statements)

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“…The overall result is therefore a reduction of the R h . Further aggregation of the particles is probably suppressed at the highest crosslinker concentration, since the compactness of the particles and the already very high aggregation number will increase the time the particles need to be in contact with each other before they stick together [39][40][41]. At high polymer concentrations, the R h increased with TPP:chitosan ratios up to 15:85, but the compactness was the same as for low polymer concentrations (Fig.…”

Section: Discussionmentioning

confidence: 62%

“…This was supported by the insensitivity of the zeta potential to TPP in the presence of 0.15 M NaCl, suggesting that few TPP-ions were binding to the nanoparticle surface. The aggregation of polymer nanoparticles into larger aggregates has also been shown to be governed by the local polymer concentration inside the nanoparticles [39][40][41][42]. Previously, it has been argued that the formation of aggregates is dependent on the contact time between the particles when they collide (t c ) and the time needed to obtain a permanent chain entanglement between the particles (t e ) [42].…”

Section: Discussionmentioning

confidence: 97%

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Effects of ionic strength on the size and compactness of chitosan nanoparticles

2012

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In this work, chitosan nanoparticles were prepared by ionotropic gelation of chitosan with tripolyphosphate (TPP). The effects of the ionic strength of the solvent employed in the particle preparation on the average size and compactness of the particles were investigated. In addition, the effects of the chitosan concentration and the crosslinker to polymer ratio on the particle characteristics were studied. The chitosan-TPP nanoparticles were characterized by dynamic light scattering, zeta potential, and turbidity measurements. The compactness of the nanoparticles was estimated with a method based on the size of the nanoparticles and the turbidity of the nanoparticle suspension. All the investigated preparation parameters, i.e., the ionic strength of the solvent, the chitosan concentration, and the TPP to chitosan ratio, affected the particle characteristics. For instance, smaller and more compact particles were formed in saline solvents, compared to particles formed in pure water. Further, the addition of monovalent salt rendered it possible to prepare particles in the nanometer size range at a higher polymer concentration. Solvent salinity is thus an important parameter to address in the preparation of chitosan nanoparticles crosslinked with TPP.

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Section: Discussionmentioning

confidence: 62%

Section: Discussionmentioning

confidence: 97%

Effects of ionic strength on the size and compactness of chitosan nanoparticles

2012

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“…For finite-sized heteropolymeric sequences, we show that large changes in R E are compatible with negligible changes in R G (22,25). We discuss that such differences are minimized in long homopolymers and long block copolymers that are characterized by the chemical similarity of the interacting units (25). Accordingly, the estimates of R G and R E lead to mutually consistent inferences regarding conformational preferences and the physics of coil-to-globule transitions for long homopolymers (26).…”

Section: Significancementioning

confidence: 66%

“…Instead, estimates of R G and R E yield different inferences because these quantities interrogate distinct length scales and are influenced by very different types of averaging. For finite-sized heteropolymeric sequences, we show that large changes in R E are compatible with negligible changes in R G (22,25). We discuss that such differences are minimized in long homopolymers and long block copolymers that are characterized by the chemical similarity of the interacting units (25).…”

Section: Significancementioning

confidence: 79%

Decoupling of size and shape fluctuations in heteropolymeric sequences reconciles discrepancies in SAXS vs. FRET measurements

Fuertes

Banterle

Ruff

et al. 2017

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

215

313

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Unfolded states of proteins and native states of intrinsically disordered proteins (IDPs) populate heterogeneous conformational ensembles in solution. The average sizes of these heterogeneous systems, quantified by the radius of gyration (R G ), can be measured by small-angle X-ray scattering (SAXS). Another parameter, the mean dye-to-dye distance (R E ) for proteins with fluorescently labeled termini, can be estimated using single-molecule Förster resonance energy transfer (smFRET). A number of studies have reported inconsistencies in inferences drawn from the two sets of measurements for the dimensions of unfolded proteins and IDPs in the absence of chemical denaturants. These differences are typically attributed to the influence of fluorescent labels used in smFRET and to the impact of high concentrations and averaging features of SAXS. By measuring the dimensions of a collection of labeled and unlabeled polypeptides using smFRET and SAXS, we directly assessed the contributions of dyes to the experimental values R G and R E . For chemically denatured proteins we obtain mutual consistency in our inferences based on R G and R E , whereas for IDPs under native conditions, we find substantial deviations. Using computations, we show that discrepant inferences are neither due to methodological shortcomings of specific measurements nor due to artifacts of dyes. Instead, our analysis suggests that chemical heterogeneity in heteropolymeric systems leads to a decoupling between R E and R G that is amplified in the absence of denaturants. Therefore, joint assessments of R G and R E combined with measurements of polymer shapes should provide a consistent and complete picture of the underlying ensembles.single-molecule FRET | intrinsically disordered proteins | denatured-state ensemble | protein folding | polymer theory Q uantitative characterizations of the sizes, shapes, and amplitudes of conformational fluctuations of unfolded proteins under denaturing and native conditions are directly relevant to advancing our understanding of the collapse transition during protein folding. These types of studies are also relevant to furthering our understanding of the functions and interactions of intrinsically disordered proteins (IDPs) in physiologically relevant conditions (1). Polymer physics theories provide the conceptual foundations for analyzing conformationally heterogeneous systems such as IDPs and unfolded ensembles of autonomously foldable proteins (2-4). Specifically, order parameters in theories of coil-toglobule transitions and analytical descriptions of conformational ensembles (5, 6) are based on ensemble-averaged values of radii of gyration (R G ) and amplitudes of fluctuations measured by end-toend distances (R E ).Estimates of R G are accessible through small-angle X-ray scattering (SAXS) measurements because scattering intensities are directly related to the global protein size (Fig. 1) (7, 8). At finite concentrations, assuming the absence of intermolecular interactions, R G is proportional to the square root o...

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“…PNIPAM can undergo a coil-to-globule transition with varying temperature [1,2] and is known for co-nonsolvation when dissolved in water/ethanol mixtures [3]. Co-nonsolvation means that the polymer demixes in solvent mixtures while it mixes well in the individual solvents.…”

Section: Introductionmentioning

confidence: 99%

Single-Chain Conformation for Interacting Poly(N-isopropylacrylamide) in Aqueous Solution

Hammouda

Di²,

Cheng

2015

The Open Access Journal of Science and Technology

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Abstract. The demixing phase behavior of Poly(N-isopropylacrylamide) (PNIPAM) aqueous solution is investigated using smallangle neutron scattering. This polymer phase separates upon heating and demixes around 32 ∘ C. The pre-transition temperature range is characterized by two scattering modes; a low-Q (large-scale) signal and a high-Q dissolved chains signal. In order to get insight into this pre-transition region, especially the origin of the low-Q (large-scale) structure, the zero average contrast method is used in order to isolate single-chain conformations even in the demixing polymers transition region. This method consists of measuring deuterated and non-deuterated polymers dissolved in mixtures of deuterated and non-deuterated water for which the polymer scattering length density matches the solvent scattering length density. A fixed 4% polymer mass fraction is used in a contrast variation series where the d-water/h-water fraction is varied in order to determine the match point. The zero average contrast (match point) sample displays pure single-chain scattering with no interchain contributions. Our measurements prove that the large scale structure in this polymer solution is due to a transient polymer network formed through hydrophobic segmentsegment interactions. Scattering intensity increases when the temperature gets close to the phase boundary. While the apparent radius of gyration increases substantially at the Lower Critical Solution Temperature (LCST) transition due to strong interchain correlation, the single-chain true radius of gyration has been found to decrease slightly with temperature when approaching the transition.

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Folding and Formation of Mesoglobules in Dilute Copolymer Solutions

Cited by 128 publications

References 132 publications

Effects of ionic strength on the size and compactness of chitosan nanoparticles

Effects of ionic strength on the size and compactness of chitosan nanoparticles

Decoupling of size and shape fluctuations in heteropolymeric sequences reconciles discrepancies in SAXS vs. FRET measurements

Single-Chain Conformation for Interacting Poly(N-isopropylacrylamide) in Aqueous Solution

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