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Modification of the Spectral Absorbance Difference Method for Determining the Dissociation Constants of Polyprotic
Huy Do1, Galina Z Goloverda1, Vladimir L Kolesnichenko1
1Chemistry Department, Xavier University of Louisiana, 1 Drexel Dr., New Orleans, Louisiana 70125, United States.
ACS Omega
|October 20, 2025
Summary
Triprotic organic acids like tenacic acid are key for novel materials. This study determined their dissociation constants, enhancing methods for pH-dependent spectral analysis of related compounds.
Area of Science:
- Materials Science
- Organic Chemistry
- Physical Chemistry
Background:
- Polyprotic organic acids are crucial for developing novel nano- and macroscale materials.
- These acids can bridge organic-inorganic interfaces, facilitating material junctions.
- Tenacic acid and its derivatives show potential for these applications.
Purpose of the Study:
- To investigate the potential of triprotic 2-hydroxyisophthalic (tenacic) acid and its derivatives in material development.
- To determine the dissociation constants (Ka) of tenacic acid and 4-nitrotenacic acid.
- To modify existing methods for improved accuracy in determining acid dissociation constants.
Main Methods:
- Utilized the spectral absorbance difference method to determine dissociation constants.
- Applied the method without modification for the first dissociation constants.
- Modified the method to accurately determine the second and third dissociation constants for the acids and their conjugate bases.
Main Results:
- Observed strong pH-dependent absorbance spectra for tenacic and 4-nitrotenacic acids.
- Attributed spectral changes to varying electron delocalization in the conjugate bases' π-systems.
- Successfully determined the first, second, and third dissociation constants for the studied acids.
Conclusions:
- The modified spectral absorbance difference method accurately determines dissociation constants for polyprotic acids.
- This approach is valuable for understanding pH-dependent spectral variations in compounds with π-electron systems.
- Findings support the use of tenacic acid derivatives in advanced material design.
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