Croatica Chemica Acta, Vol. 91 No. 4, 2018.
Preliminary communication
https://doi.org/10.5562/cca3405
Biphasic pKa Values
Sigrid Selberg
; University of Tartu, Institute of Chemistry, 14a Ravila str, 50411 Tartu, Estonia
Sofja Tshepelevitsh
; University of Tartu, Institute of Chemistry, 14a Ravila str, 50411 Tartu, Estonia
Ivo Leito
orcid.org/0000-0002-3000-4964
; University of Tartu, Institute of Chemistry, 14a Ravila str, 50411 Tartu, Estonia
Abstract
A novel approach – termed here as biphasic pKa values – is presented for quantifying the acidity/basicity of lipophilic compounds embedded in water-immiscible media (membranes or solutions) at equilibrium with aqueous solution. In this approach the hydrogen ion activity is determined in the aqueous phase, while the concentration ratio of protonated and deprotonated forms of acid/base is measured in the lipophilic phase with any suitable technique. The approach has been demonstrated on the example of biphasic pKa values of some lipophilic indicator bases in the octanol:water system, measured using UV-Vis spectrophotometry. The measurement is straightforward if the counterion identity and concentration and overall ionic strength in the aqueous phase are included in the standard state definition.
Biphasic pKa values are envisaged to be useful for characterizing lipophilic indicators, synthetic receptors, phase transfer catalysts and other implements that are used in hydrophobic media (e.g. in sensor membranes) in contact with water.
This work is licensed under a Creative Commons Attribution 4.0 International License.
Keywords
acid strength; base strength; nonaqueous solvents; membranes; two-phase equilibria
Hrčak ID:
215675
URI
Publication date:
30.12.2018.
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