Energetics and Mechanism of Conformational Transitions of Protein‐Like NIPAM‐Sodium Styrene Sulfonate Copolymers in Aqueous Solutions

Grinberg, V. Ya.; Burova, Tatiana V.; Grinberg, Natalia V.; Dubovik, Alexander S.; Plaschina, Irina G.; Laptinskaya, T. V.; Yao, Ping; Khokhlov, Alexei R.

doi:10.1002/macp.201500253

Cited by 7 publications

(3 citation statements)

References 42 publications

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“…It is of importance to note that the transition heat capacity increment of PNIPAM in the water–methanol mixed solvents is negative. This is typical for many thermoresponsive polymer systems, aqueous solutions, and hydrogels. ,,− The negative heat capacity increment implies that the transition under investigation is associated with a significant decrease in the solvent-accessible surface area of macromolecules or gel subchains because of the melting of their hydration structure and subsequent aggregation. It seems that this concept could be applied to the PNIPAM solutions in the water–methanol mixed solvents at the relatively low methanol content ( x MeOH < 0.25).…”

Section: Resultsmentioning

confidence: 96%

Energetics and Mechanisms of poly(N-isopropylacrylamide) Phase Transitions in Water–Methanol Solutions

et al. 2020

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The phase transitions of poly(N-isopropylacrylamide) (PNIPAM) in water−methanol mixed solutions were studied in detail by high-sensitivity differential scanning calorimetry. From this study, the dependences of the transition temperature, enthalpy, heat capacity increment, and width on the methanol molar fraction (x MeOH ) were obtained. The transition temperature passed through a minimum at the methanol molar fraction x MeOH * ∼ 0.35. At x MeOH < x MeOH *, the transition enthalpy decreased quickly with the methanol content and became so small that it could not be measured, even with an increase in the polymer concentration by a hundred times (up to 150 mg mL −1 ). Furthermore, over this x MeOH range, the transition heat capacity increment being negative remained practically constant, but the transition width sharply increased. The transition thermograms were quantitatively described by the Okada−Tanaka theory, which takes into account the role of the polymer−solvent interaction cooperativity in the polymer thermoresponsivity. In terms of this approach, it is assumed that over the defined range of methanol content, PNIPAM possesses the cooperative hydro-solvation structure in the form of water−methanol complexes. The energetics of this structure smoothly decreases with the increase in the methanol content up to a complete disappearance of the structure at x MeOH > x MeOH *. In this range of the methanol content, the phase behavior of PNIPAM seems to be dictated by regularities typical of polymer solutions in organic solvents, that is, how the Flory−Huggins parameter depends on temperature.

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Section: Resultsmentioning

confidence: 96%

Energetics and Mechanisms of poly(N-isopropylacrylamide) Phase Transitions in Water–Methanol Solutions

et al. 2020

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“…Additionally, note that the transition heat capacity increment is negative for all gels; that is, the transition was accompanied by a decrease in the partial heat capacity of the polymer. This feature is typical of aqueous solutions and gels of thermoresponsive polymers. ,,− It reveals that hydrophobic hydration of these polymers diminishes significantly upon heating in the course of the conformational or phase transitions.…”

Section: Resultsmentioning

confidence: 88%

Salt-Induced Thermoresponsivity of Cross-Linked Polymethoxyethylaminophosphazene Hydrogels: Energetics of the Volume Phase Transition

et al. 2018

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Biodegradable hydrogels of cross-linked polymethoxyethylaminophosphazenes (PMOEAPs) of various cross-linking density and apparent subchain hydrophobicity were investigated by high-sensitivity differential scanning calorimetry and equilibrium swelling measurements. The volume phase transition of the hydrogels was found to be induced by salts of weak polybasic acids. The transition parameters were determined depending on the pH, phosphate concentration, cross-linking density, and apparent hydrophobicity of the gels. The transition enthalpy increased three times and reached 60 J g at the phosphate concentrations 5-100 mM. The transition temperature decreased by 60 °C when the pH changed from 6 to 8. A decrease in the transition temperature (by ∼20 °C) was achieved due to incorporation of 9.4 mol % of some alkyl groups into the gel subchains. The classic theory of the collapse of polymer gels coupled with the data of protein science on hydration energetics for various molecular surfaces reproduces correctly thermodynamics of the collapse of PMOEAP hydrogels.

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“…The broadening of the phase transition implies a decrease in the cooperativity of the system. 58 This effect is opposite to the change in the transition width caused by citrate anions (Figures 4 and 5) which enhances the cooperativity of the PEAP transition.…”

Section: ■ Results and Discussionmentioning

confidence: 90%

Salt-Induced Thermoresponsivity of a Cationic Phosphazene Polymer in Aqueous Solutions

Burova

Grinberg

et al. 2018

Macromolecules

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Poly(ethylaminophosphazene) (PEAP) in salt-free aqueous solution does not reveal thermoresponsive properties but acquires thermoresponsivity upon addition of various poly(protic acid)s. Energetics of the salt-induced phase separation transition of the PEAP solutions upon heating was investigated by high-sensitivity differential scanning calorimetry at pH 3.5. At low concentrations of poly(carboxylic acid)s (10–100 mM), the transition temperature and enthalpy vary from 90 to 25 °C and from 1.5 to 35 J g–1, respectively, depending on the pK a1 and the apparent hydrophobicity of the acids. Dependences of the transition parameters (T t, Δt h, and Δt c p ) on the citrate buffer concentration were obtained. The binding curve of citrate anions to PEAP was derived. High concentrations of sulfate anions (0.1–0.8 M) induced a marginal phase transition at high temperatures. A mechanism of the PEAP thermoresponsivity is proposed. The Okado–Tanaka model for cooperative hydration of macromolecules is used to quantitatively describe the energetics of the thermoresponsive behavior of PEAP.

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Energetics and Mechanism of Conformational Transitions of Protein‐Like NIPAM‐Sodium Styrene Sulfonate Copolymers in Aqueous Solutions

Cited by 7 publications

References 42 publications

Energetics and Mechanisms of poly(N-isopropylacrylamide) Phase Transitions in Water–Methanol Solutions

Energetics and Mechanisms of poly(N-isopropylacrylamide) Phase Transitions in Water–Methanol Solutions

Salt-Induced Thermoresponsivity of Cross-Linked Polymethoxyethylaminophosphazene Hydrogels: Energetics of the Volume Phase Transition

Salt-Induced Thermoresponsivity of a Cationic Phosphazene Polymer in Aqueous Solutions

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