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      Molecular mechanism for the ınteractions of hofmeister cations with macromolecules in aqueous solution

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      Author(s)
      Bruce, E. E.
      Okur, Halil I.
      Stegmaier, S.
      Drexler, C. I.
      Rogers, B. A.
      van der Vegt, N. F. A.
      Roke, S.
      Cremer, P. S.
      Date
      2020
      Source Title
      Journal of the American Chemical Society
      Print ISSN
      0002-7863
      Publisher
      American Chemical Society
      Volume
      142
      Issue
      45
      Pages
      19094 - 19100
      Language
      English
      Type
      Article
      Item Usage Stats
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      199
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      Abstract
      Ion identity and concentration influence the solubility of macromolecules. To date, substantial effort has been focused on obtaining a molecular level understanding of specific effects for anions. By contrast, the role of cations has received significantly less attention and the underlying mechanisms by which cations interact with macromolecules remain more elusive. To address this issue, the solubility of poly(N-isopropylacrylamide), a thermoresponsive polymer with an amide moiety on its side chain, was studied in aqueous solutions with a series of nine different cation chloride salts as a function of salt concentration. Phase transition temperature measurements were correlated to molecular dynamics simulations. The results showed that although all cations were on average depleted from the macromolecule/water interface, more strongly hydrated cations were able to locally accumulate around the amide oxygen. These weakly favorable interactions helped to partially offset the salting-out effect. Moreover, the cations approached the interface together with chloride counterions in solvent-shared ion pairs. Because ion pairing was concentration-dependent, the mitigation of the dominant salting-out effect became greater as the salt concentration was increased. Weakly hydrated cations showed less propensity for ion pairing and weaker affinity for the amide oxygen. As such, there was substantially less mitigation of the net salting-out effect for these ions, even at high salt concentrations.
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      http://hdl.handle.net/11693/55060
      Published Version (Please cite this version)
      https://dx.doi.org/10.1021/jacs.0c07214
      Collections
      • Department of Chemistry 677
      • Institute of Materials Science and Nanotechnology (UNAM) 2098
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