Electrophoretic mobilities of neutral analytes and electroosmotic flow markers in aqueous solutions of <scp>H</scp>ofmeister salts

Křížek, Tomáš; Kubíčková, Anna; Hladílková, Jana; Coufal, Pavel; Heyda, Jan; Jungwirth, Pavel

doi:10.1002/elps.201300544

Cited by 9 publications

(9 citation statements)

References 52 publications

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“…The Raman-MCR experiments and q computations are described in Supplementary Section 3 (Supplementary Figs. [41][42][43][44][45][46][47][48][49][50][51][52][53][54].…”

Section: Discussionmentioning

confidence: 99%

Weakly hydrated anions bind to polymers but not monomers in aqueous solutions

et al. 2021

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eakly hydrated anions, such as I − , SCN − and ClO 4 − , weaken the hydrophobic effect in aqueous solutions. These large, polarizable anions denature proteins, inhibit supramolecular complexation and dissolve surfactant micelles [1][2][3] . At the molecular level, weakly hydrated anions partially shed their hydration shells and adsorb to nonpolar interfaces, thereby inhibiting hydrophobic assembly [4][5][6][7][8][9][10] . The adsorption of these anions to amide-rich polymers has been characterized by submolar to molar equilibrium dissociation constants, K D = 0.05-1.60 M (refs. 11-14 ). Even tighter adsorption has been observed at macroscopic surfaces, such as the air/water interface (K D = 0.03-0.26 M) and in the concave pockets of cavitands and proteins (K D = 0.003-0.09 M) 2,15-22 . By stark contrast, anions are repelled from small molecules, like N-methyl acetamide and tert-butyl alcohol (K D = 4-8 M) 23,24 . As a consequence, weakly hydrated anions precipitate small non-ionic solutes out of aqueous solutions, including acetone and diacetone alcohol 25 . The dramatic range of anion affinity for chemically similar aliphatic binding sites exposes a critical gap in our knowledge of the mechanisms for anion-specific effects.The surface curvature of nonpolar solutes is known to influence solubility because of the distinct local hydration of curved and flat interfaces 26,27 . The water hydrogen-bonding network can wrap around small and convex solutes to maintain its bulk-like structure. Large solutes, however, have a flatter topography that disrupts the hydrogen bonds between water molecules 27 . As such, small solutes can be incorporated into the water network, while larger ones with broken hydrogen bonds associate with each other and release water molecules into the bulk solution. The cartoon in Fig. 1 depicts a simple model for a polymer chain. The termini are highly curved due to their half-spherical geometry, while the centre of the chain is flatter because it has a cylindrical-like structure. Experimental and computational studies of nonpolar solutes with varying chain lengths have shown that this topography disorders water at the centre of the chain more than at the termini 28,29 .Here, the role of surface curvature on anion-specific effects is explored by systematically measuring the interactions of NaSCN with polyethylene oxides (PEO) of varying molecular weights, ranging from monomers to polymers. The results indicate that SCN − is repelled from monomers but attracted to oligomers of increasing chain length. These interactions are distinct because SCN − binds selectively to the centre of oligomer chains, as opposed to their termini (Fig. 1). Investigations of polyether hydration shells reveal that the water structure at the centre of the chain is more disordered than at the termini. Together, these findings imply that SCN − interacts with low-curvature interfaces to displace water at sites of hydrogen-bonding defects. The correlation of binding affinity and water structure measurements at specific locati...

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“…The Raman-MCR experiments and q computations are described in Supplementary Section 3 (Supplementary Figs. [41][42][43][44][45][46][47][48][49][50][51][52][53][54].…”

Section: Discussionmentioning

confidence: 99%

Weakly hydrated anions bind to polymers but not monomers in aqueous solutions

et al. 2021

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“…The electrophoresis procedure was identical to that described in our previous study [26], based on the mobility measurement method introduced by Williams and Vigh [27]. Every new capillary was conditioned with 1.0 M sodium hydroxide for 20 min, with deionized water for 10 min, and with BGE for 5 min.…”

Section: Methodsmentioning

confidence: 99%

“…In our previous research, we have found that small neutral marker molecules can be mobilized, even by small inorganic ions [26]. This mobilization has not been accounted for in the aforementioned studies.…”

Section: Introductionmentioning

confidence: 96%

“…These interactions can mobilize markers, which results in inaccuracies in physicochemical measurements. The interactions underlying the mobilization of EOF markers are similar to those that cause the salting‐in and salting‐out effects of proteins, and thus, readers should refer to the Hofmeister series when discussing the mobilization of EOF markers [26]. Although EOF markers are expected to be mobilized in BGEs containing surfactants or charged polymers, significant inaccuracies in EOF velocity determination due to marker mobilization in simple BGEs consisting of small ions, such as the sodium cation and the acetate anion, are consistently overlooked.…”

Section: Introductionmentioning

confidence: 99%

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Mobilization of electroosmotic flow markers in capillary zone electrophoresis

et al. 2021

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UV‐absorbing neutral substances are commonly used as markers of mean electroosmotic flow in capillary electrophoresis for their zero electrophoretic mobility in an electric field. However, some of these markers can interact with background electrolyte components and migrate at a different velocity than the electroosmotic flow. Thus, we tested 11 markers primarily varying in their degree of methylation and type of central atom in combination with five background electrolyte cations differing in their ionic radii and surface charge density, measuring the relative electrophoretic mobility using thiourea as a reference marker. Our results from this set of experiments showed some general trends in the mobilization of the markers based on the effects of marker structure and type of background electrolyte cation on the relative electrophoretic mobility. As an example, the effects of an inadequate choice of marker on analyte identification were illustrated in the electrophoretic separation of glucosinolates. Therefore, our findings may help electrophoretists appropriately select electroosmotic flow markers for various electrophoretic systems.

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“…Third, in contrast to other electrophoretic detection methods, it requires no background electrolyte and/or pH buffer that may lend charge to small neutral entities. 27 − 29 Finally, the technique works well at low salt (and polymer) concentrations where direct ion–solute interactions dominate and screening effects are less significant. Ion binding at PNIPAM-covered model surfaces has often been studied, 30 − 33 but there is a lack of observations in dilute (here, at 10 mM monomer equivalent, therefore with no interactions between the extended chains) bulk solutions.…”

Section: Introductionmentioning

confidence: 99%

Weak Anion Binding to Poly(N-isopropylacrylamide) Detected by Electrophoretic NMR

Fang

Furó

2021

J. Phys. Chem. B

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Ion specific effects are ubiquitous in solutions and govern a large number of colloidal phenomena. To date, a substantial and sustained effort has been directed at understanding the underlying molecular interactions. As a new approach, we address this issue by sensitive 1 H NMR methods that measure the electrophoretic mobility and the self-diffusion coefficient of poly( N -isopropylacrylamide) (PNIPAM) chains in bulk aqueous solution in the presence of salts with the anion component varied from kosmotropes to chaotropes along the Hofmeister series. The accuracy of the applied electrophoretic NMR experiments is exceptionally high, on the order of 10 –10 m 2 /(V s), corresponding to roughly 10 –4 elementary charges per monomer effectively associated with the neutral polymer. We find that chaotropic anions associate to PNIPAM with an apparent Langmuir-type saturation behavior. The polymer chains remain extended upon ion association, and momentum transfer from anion to polymer is only partial which indicates weak attractive short-range forces between anion and polymer and, thereby and in contrast to some other ion–polymer systems, the lack of well-defined binding sites.

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Electrophoretic mobilities of neutral analytes and electroosmotic flow markers in aqueous solutions of Hofmeister salts

Cited by 9 publications

References 52 publications

Weakly hydrated anions bind to polymers but not monomers in aqueous solutions

Weakly hydrated anions bind to polymers but not monomers in aqueous solutions

Mobilization of electroosmotic flow markers in capillary zone electrophoresis

Weak Anion Binding to Poly(N-isopropylacrylamide) Detected by Electrophoretic NMR

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