Abstract
Incremental changes in ionic composition, solvent quality, and temperature can lead to reversible and abrupt structural changes in many synthetic and biopolymer systems. In the biological milieu, this nonlinear response is believed to play an important functional role in various biological systems, including DNA condensation, cell secretion, water flow in xylem of plants, cell resting potential, and formation of membraneless organelles. While these systems are markedly different from one another, a physicochemical framework that treats them as polyelectrolytes, provides a means to interpret experimental results and make in silico predictions. This article summarizes experimental results made on ion-induced volume phase transition in a polyelectrolyte model gel (sodium polyacrylate) and observations on the above-mentioned biological systems indicating the existence of a steep response.
Highlights
We described five unrelated biological functions whose mechanisms are based on the same underlying physical principle, namely, the nonlinear response of charged polymers to various stimuli resulting in two distinct macroscopic phases: dissolved in- and phase separated from the surrounding fluid
The conformational change of polyelectrolyte molecules is accompanied by a steep change of certain physical properties of gels, such as their swelling degree, elastic modulus, magnetic relaxation rates, electric potential difference, ion partitioning, and water and ion apparent diffusion coefficients
The nonlinear response of gels is an attractive characteristic, which is used in many industrial applications [129]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Highly idealized models may provide insight into the origins of certain phenomena, even if they do not account for all of the components and their interactions It was repeatedly demonstrated in many physical systems, especially in the vicinity of a phase transition that universal principles and macroscopic variables govern the response of the system irrespective of many of the details [3,4]. These include (1) compaction of DNA molecules [11], (2).
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