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Updated: Feb 18, 2026

Determination of the Gas-phase Acidities of Oligopeptides
Published on: June 24, 2013
A unified view to Brønsted acidity scales: do we need solvated protons?
Eno Paenurk1, Karl Kaupmees1, Daniel Himmel2
1Institute of Chemistry , University of Tartu , Ravila 14a Str , 50411 Tartu , Estonia .
Abstract:
The most comprehensive solvent acidity scale spanning 28 orders of magnitude of acidity was measured in the low-polarity solvent 1,2-dichloroethane (DCE). Its experimental core is linked to the unified acidity scale (pHabs) in an unprecedented and generalized approach only based on experimental values. This enables future measurements of acid strengths and acidity adjustments in low polarity solvents. The scale was cross-validated computationally. The purely experimental and computational data agree very well. The DCE scale includes 87 buffer systems with values between -13.0 and +15.4, i.e. similar to water at hypothetical and extreme pH values of -13.0 to +15.4. Unusually, such high acidities in DCE are not realized via solvated protons, but rather through strongly acidic molecules able to directly donate their proton, even to weak bases dissolved in the solution. Thus, in all examined cases, not a single solvated proton is present in one liter of DCE.
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