Schmid, Philipp and Hohenschutz, Max and Grass, Xaver and Witzmann, Michael and Touraud, Didier and Diat, Olivier and Pfitzner, Arno and Bauduin, Pierre (2022) Counterion effect on a-Keggin polyoxometalates in water: The peculiar role of H+ on their salting-in effect and co-assembly with organics. JOURNAL OF MOLECULAR LIQUIDS, 359: 119214. ISSN 0167-7322, 1873-3166
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Hofmeister effects of ions in aqueous solution strongly affect chemical and biological systems. High and low charge density anions, such as SO42-and SCN- respectively, decrease (salting-out) or increase (salting in) the solubility of organic solutes in water. Due to their very low charge-density, nanometric anions, e.g. polyoxometalates (POMs), increase the solubility of organic solutes tremendously (highly salting-in) as they bind to neutral hydrated solutes strongly - a property that is attributed to the (super-)chaotropic effect. Here, we show that salting-out anions can be turned into salting-in anions in the presence of a superchaotropic POM, alpha-PW12O403-. The effect of salts composed of salting-out anions, e.g. SO42-, was investigated on the cloud point (CP) of an ethoxylated surfactant (C8E4) and a propoxylated co-solvent (C3P2) in the presence of SiW(12)O(40)(4-)and PW(12)O(40)(3-)with different counter-cations (H+, Li+, Na+, K+). SiW12O40 4-and PW(12)O(40)(3-)lead to a monotonic strong CP-increase regardless of the counterion, except for PW12O403- combined with H+. Indeed, H3PW12O40 shows a CP decrease at high POM concentrations. This peculiar behavior is attributed to the formation of large H3PW12O40-C3P2 (and H3PW12O40-C8E4) co-assemblies, as shown by SAXS. The formation of these co-assemblies results from the "bridging " effect of H+ and the lower charge density of PW12O403-compared to SiW12O404-. The addition of (basic) salting-out anions leads to (i) the consumption of H+, then to (ii) the disruption of the large H3PW12O40-C3P2 (and H3PW12O40- C8E4) co-assemblies and subsequently to (iii) a CP-increase. In the peculiar case, this shows how commonly used salting-out anions can become apparently salting-in. (C) 2022 Elsevier B.V. All rights reserved.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | HOFMEISTER SERIES; AGGREGATION; SPECIATION; REVERSAL; BINDING; ANIONS; PNIPAM; PH; Chaotropic effect; Hofmeister effects; Polyoxometalates; Ion effects; Self-assembly; Counterion effects |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Anorganische Chemie > Chair Prof. Dr. Arno Pfitzner Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 26 Jan 2024 08:26 |
| Last Modified: | 26 Jan 2024 08:26 |
| URI: | https://pred.uni-regensburg.de/id/eprint/57299 |
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