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Updated: May 21, 2026

Determination of the Gas-phase Acidities of Oligopeptides

Determination of the Gas-phase Acidities of Oligopeptides

Published on: June 24, 2013

Bulk gas-phase acidity.

Daniel Himmel¹, Sascha K Goll, Ivo Leito

¹Institut für Anorganische und Analytische Chemie, Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstrasse 19, 79104 Freiburg, Germany.

Chemistry (Weinheim an Der Bergstrasse, Germany)

|June 26, 2012

Summary

Gas-phase acidity (GA) values do not accurately describe bulk acidity. This study introduces a new theory considering pressure-dependent proton activities for accurate gas-phase acidity measurements, comparable to solution acidity.

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Area of Science:

Physical Chemistry
Chemical Thermodynamics

Background:

Gas-phase acidity (GA) is typically quantified using Gibbs energy differences.
GA values assume standard pressures for acids, bases, and protons, limiting their applicability to bulk acidity descriptions.

Purpose of the Study:

To demonstrate the limitations of standard GA values for describing bulk gas-phase acidity.
To develop a general theory for gas-phase acidity that accounts for pressure-dependent activities and can be compared to solution acidity.

Main Methods:

Investigated the pressure dependence of activities for gaseous autoprotolysis products.
Calculated the pressure-dependent absolute chemical potential of the proton in representative gaseous acids (CH4, NH3, H2O, HF, HCl).

Main Results:

Established that standard GA values are insufficient for characterizing bulk gas-phase acidity.
Developed a theoretical framework to describe bulk gas-phase acidity considering pressure effects.

Conclusions:

The new theory provides a more accurate measure of gas-phase acidity, directly comparable to solution acidity.
Accurate bulk gas-phase acidity assessment requires considering the pressure dependence of proton and species activities.