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Published on: August 1, 2016
Unraveling the Reverse Hofmeister Effect of 3,3',5,5'-Tetramethylbenzidine for Anion-Responsive Color-Changing
Yuan Xu1, Hong Yang1, Kangchun Fu1
1Jiangsu Engineering Laboratory of Smart Carbon-Rich Materials and Device, Jiangsu Province Hi-Tech Key Laboratory for Bio-Medical Research, School of Chemistry and Chemical Engineering, Medical School, Southeast University, Nanjing 211189, China.
Chemical & Biomedical Imaging
|June 1, 2026
Summary
Small molecules, like tetramethylbenzidine oxidation product (TMB ox1), can exhibit Hofmeister effects, influencing aggregation and color changes in response to ions. This reveals ion-specific behaviors in simple systems, impacting sensing technologies.
Area of Science:
- Physical Chemistry
- Biophysical Chemistry
- Materials Science
Background:
- The Hofmeister series describes ion-specific effects on biomacromolecules, but their influence on small molecules is less understood.
- Proteins and other biomacromolecules exhibit ion-dependent stability and function, classically explained by the Hofmeister series.
Purpose of the Study:
- To investigate if small molecules can display Hofmeister effects.
- To explore the ion-specific behavior of the tetramethylbenzidine oxidation product (TMB ox1) in aqueous solutions and hydrogels.
Main Methods:
- Experimental studies combined with density functional theory (DFT) and molecular dynamics (MD) simulations.
- Analysis of TMB ox1 aggregation, anion interactions, and hydrogel discoloration using MD-based thermodynamic analyses.
Main Results:
- TMB ox1 exhibits a reverse Hofmeister effect, with anion-dependent aggregation driven by terminal amino groups and π-π stacking.
- Chaotropic anions promote denser, entropy-favored states by disrupting hydration and shortening π-π separations.
- Confining TMB ox1 in agarose hydrogels leads to anion-responsive discoloration instead of aggregation.
Conclusions:
- Small molecules can recapitulate complex Hofmeister behaviors traditionally seen in biomacromolecules.
- Ion-specific effects in TMB ox1 are determined by terminal amino groups and π-π stacking interactions.
- Findings have implications for developing colorimetric sensors and hydrogel-based applications.
