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    Anion Specificity in Dimethyl Sulfoxide-Water Mixtures Exemplified by a Thermosensitive Polymer

    Year: 2018

    Journal: J. Phys. Chem. B, Volume 122, AUG 30, page 8293–8300

    Authors: Zhu, Renwei; Baraniak, Monika K.; Jakle, Frieder; Liu, Guangming

    Organizations: National Natural Science Foundation of China [21574121, 21622405, 21374110]; Youth Innovation Promotion Association of CAS [2013290]; Fundamental Research Funds for the Central Universities [WK2340000066]; US National Science Foundation [1609043]

    In the present work, we have investigated the anion-specific upper critical solution temperature (UCST) behavior of polymer-supported borinic acid (PBA) in dimethyl sulfoxide-water (DMSO-H2O) mixtures. An inverted V-shaped series CH3COO- < Cl- < salt-free > NO3- > ClO4- > SCN- is observed in terms of the anion-specific UCST of PBA in the DMSO-H2O mixtures. Both direct anion-polymer interactions and indirect solvent-mediated anion-polymer interactions are involved in the specific anion effect on the UCST behavior of PBA. The direct binding of anions to the PBA surface generates a salting-in effect on PBA, causing the UCST for the different types of anions to increase from chaotropic to kosmotropic anions due to the stronger binding of the more chaotropic anions. On the other hand, the indirect anionic polarization of hydrogen bonding between PBA and DMSO molecules also produces a salting-in effect on PBA, leading the UCST for the different types of anions to increase from kosmotropic to chaotropic anions because of the stronger capability of the more kosmotropic anions to polarize the hydrogen bonding. Thus, the dominating anion-PBA interactions change from the direct anion binding to the indirect anionic polarization of hydrogen bonding as the anions change from chaotropes to kosmotropes. The observed inverted V-shaped series suggests that the specific anion effect on the UCST behavior of PBA in the DMSO-H2O mixtures is determined by the combined effects of the binding of anions to the PBA surface and the anionic polarization of hydrogen bonding between PBA and DMSO molecules.
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