Hyaluronic acid (hyaluronan, HA) is a negatively charged polysaccharide forming highly swollen random coils in aqueous solutions. Their size decreases along with growing salt concentration, but the mechanism of this phenomenon remains unclear. We carry out molecular-dynamics simulations of a 48-monosaccharide HA oligomer in varying salt concentration and temperature. They identify the interaction points of Na + ions with the HA chain and reveal their influence on the HA solvation-shell structure. The salt-dependent variation of the molecular size does not consist in the distribution of the dihedral angles of the glycosidic connections but is driven by the random flips of individual dihedral angles, which cause the formation of temporary hairpin-like structures effectively shortening the chain. They are induced by the frequency of cation-chain interactions that grow with the salt concentration, but is reduced by the simultaneous decrease of ions' activities. This leads to an anomalous random-coil shrinkage at 0.6 M salt concentration.
The paper is closely related to the challenge of the most important greenhouse gas - carbon dioxide. Both, the effective capture and secure storage of CO2, is an urgent environmental problem. Approximately ¾ of all anthropogenic emissions of CO2are related to the use of fossil fuels. Great attention is given to the absorption processes for the capture of the gas. Carbon Capture and Storage (CCS) is a promising solution for achieving a significant reduction in CO2- emissions. Capture of combustion gases using standard volatile organic solvents are the source of numerous problems like environmental pollution, instability and corrosivity of such solvents. An effective solution seems to be the use of ionic liquids. Ionic liquids are a relatively new class of compounds, which are chemically and thermally stable and are able to dissolve a wide range of substances. The negligible volatility of ionic liquids is their most important property. Research and development of the CO2- capture technology has not yet reached the stage of commercial exploitation under economically acceptable conditions. The aim of this article is to show the possibilities of use of ionic liquids in the absorption separation processes for CO2-capture.
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