Ion Aggregation and R3N+–C(R)–H···NR3 Hydrogen Bonding in a Fluorous Phase

Anderson, Evan L.; Gingery, Nicole M.; Boswell, Paul G.; Chen, Xin; Rábai, József; Bühlmann, Philippe

doi:10.1021/acs.jpcb.6b07299

Cited by 5 publications

(7 citation statements)

References 46 publications

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“…Previous work from our group has shown the benefits of using fluorous sensing membranes that consist of fluorous plasticized polymer matrixes doped with fluorophilic ionophores, ionic sites, and electrolytes . We found that fluorous systems exhibit substantially improved ion selectivities as compared to non‐fluorous ISE membranes, which has also resulted in remarkably low detection limits .…”

Section: Introductionmentioning

confidence: 72%

Cleaning of pH Selective Electrodes with Ionophore‐doped Fluorous Membranes in NaOH Solution at 90 °C

et al. 2017

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This work demonstrates the remarkable stability of fluorous ion‐selective electrode (ISE) membranes by exposing them to cleaning‐in‐place treatments (CIP) as they are used in many industrial processes. The sensing membranes consisted of Teflon AF2400 plasticized with a linear perfluoropolyether and doped with ionic sites and a H+ ionophore (i. e., tris[3‐(perfluorooctyl)propyl]amine, 1, or tris[3‐(perfluorooctyl)pentyl]amine, 2). To mimic a typical CIP treatment, the electrodes were repeatedly exposed for 30 min to a 3.0 % NaOH solution at 90 °C (pH 12.7). ISE membranes doped with the less strongly H+ binding ionophore 1 started to show reduced potentiometric response slopes and increased resistances after one exposure for 30 min to hot 3.0 % NaOH solution. No decomposition of the ionic sites and ionophore 1 at 90 °C was evident by 1H NMR spectroscopy, suggesting that the performance of membranes doped with 1 was compromised primarily by leaching of the negatively charged ionic sites along with H+ into the hot caustic solution. In contrast, even after ten exposures to hot 3.0 % NaOH for a cumulative 5 h at 90 °C, the fluorous sensing membranes doped with the more strongly H+ binding ionophore 2 still showed the ability to respond with a theoretical (Nernstian) slope up to pH 12. Addition of the fluorophilic electrolyte salt methyltris[3‐(perfluorooctyl)propyl]ammonium tetrakis[3, 5‐bis(perfluorohexyl)phenyl]borate reduced the membrane resistance by an order of magnitude.

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Section: Introductionmentioning

confidence: 72%

Cleaning of pH Selective Electrodes with Ionophore‐doped Fluorous Membranes in NaOH Solution at 90 °C

et al. 2017

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“…This adds uncertainty to the ion pair formation constant and, consequently, the determination of the p K a value. The formation of H + –ionophore complexes of 2:1 stoichiometry and ion aggregates larger than triple ions , may also affect the accuracy of p K a values of ionophores in ISE membranes.…”

Section: Resultsmentioning

confidence: 99%

Fluorous-Phase Ion-Selective pH Electrodes: Electrode Body and Ionophore Optimization for Measurements in the Physiological pH Range

2020

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Because of their low polarity and polarizability, fluorous sensing membranes are both hydrophobic and lipophobic and exhibit very high ion selectivities. Here, we report on a new fluorous-membrane ion-selective electrode (ISE) with a wide sensing range centered around physiologically relevant pH values. The fluorophilic tris[perfluoro(octyl)butyl]amine (N[(CH2)4Rf8]3) was synthesized and tested as a new H+ ionophore using a redesigned electrode body that provides excellent mechanical sealing and much improved measurement reliability. In a challenging 1 M KCl background, these fluorous-phase ISEs exhibit a sensing range from pH 2.2 to 11.2, which is one of the widest working ranges reported to date for ionophore-based H+ ISEs. High selectivities against common interfering ions such as K+, Na+, and Ca2+ were determined (selectivity coefficients: logK H, K pot = – 11.6; logK H, Na pot = – 12.4; logK H, Ca pot < – 10.2). The use of the N[(CH2)4Rf8]3 ionophore with its −(CH2)4– spacers separating the amino group from the strongly electron-withdrawing perfluorooctyl groups improved the potentiometric selectivity as compared to the less basic tris[perfluoro(octyl)propyl]amine ionophore. The use of N[(CH2)4Rf8]3 also made the ISE less prone to counter anion failure (i.e., Donnan failure) at low pH than the use of tris[perfluoro(octyl)pentyl]amine with its longer −(CH2)5– spacers, which more effectively shield the amino center from the perfluorooctyl groups. In addition, we exposed both conventional plasticized PVC-phase pH ISEs and fluorous-phase pH ISEs to 10% serum for 5 days. Results show that the PVC-phase ISEs lost selectivity while their fluorous-phase counterparts did not.

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“…We previously showed that ISEs with fluorous membranes doped with 2 exhibit selectivities 9–11 orders of magnitude over K + , Na + , and Cu 2+ . ,, For this work, we focused on the selectivities for Ag + over the tetraethylammonium ion, Et 4 N + , because we wanted to avoid complications from multiple stoichiometries for both the primary and the interfering ion. While tetraalkylammonium ions have been shown to bind in fluorous solvents to trialkylamine derivatives by formation of hydrogen bonds of the type R 3 N + –C(R)–H···NR 3 and should not be considered inert under all circumstances, binding of Et 4 N + to thioethers is not a concern. Thioethers have a p K a in water of approximately −5.4 (value estimated for (CH 3 ) 2 SH + ), a basicity that is approximately 15 orders of magnitude lower than that for trialkylamines.…”

Section: Resultsmentioning

confidence: 99%

Potentiometric Selectivities of Ionophore-Doped Ion-Selective Membranes: Concurrent Presence of Primary Ion or Interfering Ion Complexes of Multiple Stoichiometries

Yılmaz

Chen

et al. 2019

Anal. Chem.

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The selectivities of ionophore-doped ion-selective electrode (ISE) membranes are controlled by the stability and stoichiometry of the complexes between the ionophore, L, and the target and interfering ions (I zi and J zj, respectively). Well-accepted models predict how these selectivities can be optimized by selection of ideal ionophore-to-ionic site ratios, considering complex stoichiometries and ion charges. These models were developed for systems in which the target and interfering ions each form complexes of only one stoichiometry. However, for a few ISEs, the concurrent presence of two primary ion complexes of different stoichiometries, such as IL zi and IL2 zi, was reported. Indeed, similar systems were probably often overlooked and are, in fact, more common than the exclusive formation of complexes of higher stoichiometry unless the ionophore is used in excess. Importantly, misinterpreted stoichiometries misguide the design of new ionophores and are likely to result in the formulation of ISE membranes with inferior selectivities. We show here that the presence of two or more complexes of different stoichiometries for a given ion may be inferred experimentally from careful interpretation of the potentiometric selectivities as a function of the ionophore-to-ionic site ratio or from calculations of complex concentrations using experimentally determined complex stabilities. Concurrent formation of JL zj and JL2 zj complexes of an interfering ion is shown here to shift the ionophore-to-ionic site ratio that provides the highest selectivities. Formation of IL n–1 zi and IL n zi complexes of a primary ion is less of a concern because an optimized membrane typically contains an excess of ionophore, but lower than expected selectivities may be observed if the stepwise complex formation constant, K ILn, is not sufficiently large and the ionophore-to-ionic site ratio does not markedly exceed n.

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Ion Aggregation and R₃N⁺–C(R)–H···NR₃ Hydrogen Bonding in a Fluorous Phase

Cited by 5 publications

References 46 publications

Cleaning of pH Selective Electrodes with Ionophore‐doped Fluorous Membranes in NaOH Solution at 90 °C

Cleaning of pH Selective Electrodes with Ionophore‐doped Fluorous Membranes in NaOH Solution at 90 °C

Fluorous-Phase Ion-Selective pH Electrodes: Electrode Body and Ionophore Optimization for Measurements in the Physiological pH Range

Potentiometric Selectivities of Ionophore-Doped Ion-Selective Membranes: Concurrent Presence of Primary Ion or Interfering Ion Complexes of Multiple Stoichiometries

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