Turning Up the Heat: Investigation into the Driving Forces of the Hofmeister Effect in Water Vibrational Spectra
- 1Department of Chemistry, University of Texas at Austin, 105 E 24th St. A5300, Austin, TX, USA, 78712
- 2Argonne National Laboratory, 9700 S. Cass Ave., Lemont, IL, USA, 60439
- 3Department of Chemistry, University of Kansas, 1567 Irving Hill Rd. Rm. 1140, Lawrence, KS, USA, 66045
Abstract
The Hofmeister series has historically been used to rank ions according to their impact on the solubility of proteins in aqueous solutions. Strongly hydrating salts, which stabilize the native structure of proteins, leading to their “salting-out,” are referred to as kosmotropes (“structure-makers”). Weakly hydrating salts, which facilitate protein denaturing and “salting-in,” are referred to as chaotropes (“structure-breakers”). While the Hofmeister effect has been extensively studied, the underlying thermodynamic driving forces are not well understood. Recent fluctuation theory calculations have suggested that the Hofmeister effect observed in the infrared (IR) spectrum of aqueous alkali–halide solutions is predominantly entropically driven. Here, experimental support for this hypothesis is provided through temperature-dependent Fourier transform IR (FTIR) spectroscopy. The FTIR OH stretch spectrum of alkali halides dissolved in isotopically dilute HOD/D2O was collected and the temperature derivative of the lineshape was used to extract relevant thermodynamic potentials. It was observed that while the effective enthalpy is nearly ion-independent, a reduction of the entropic cost to form stronger hydrogen-bonds (H-bonds) scales with decreasing halide size, suggesting that this contribution is the driving force for this observed Hofmeister effect.
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BibTeX
@misc{cyganowski2026turning,
title = {{Turning Up the Heat: Investigation into the Driving Forces of the Hofmeister Effect in Water Vibrational Spectra}},
author = {Eric J. Cyganowski and Ashley K. Borkowski and Isaac D. Cowan and Ward H. Thompson and Carlos R. Baiz},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010378/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010378/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Turning Up the Heat: Investigation into the Driving Forces of the Hofmeister Effect in Water Vibrational Spectra
AU - Eric J. Cyganowski
AU - Ashley K. Borkowski
AU - Isaac D. Cowan
AU - Ward H. Thompson
AU - Carlos R. Baiz
PY - 2026
DA - 2026/10/13
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010378/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010378/v1
AB - The Hofmeister series has historically been used to rank ions according to their impact on the solubility of proteins in aqueous solutions. Strongly hydrating salts, which stabilize the native structure of proteins, leading to their “salting-out,” are referred to as kosmotropes (“structure-makers”). Weakly hydrating salts, which facilitate protein denaturing and “salting-in,” are referred to as chaotropes (“structure-breakers”). While the Hofmeister effect has been extensively studied, the underlying thermodynamic driving forces are not well understood. Recent fluctuation theory calculations have suggested that the Hofmeister effect observed in the infrared (IR) spectrum of aqueous alkali–halide solutions is predominantly entropically driven. Here, experimental support for this hypothesis is provided through temperature-dependent Fourier transform IR (FTIR) spectroscopy. The FTIR OH stretch spectrum of alkali halides dissolved in isotopically dilute HOD/D2O was collected and the temperature derivative of the lineshape was used to extract relevant thermodynamic potentials. It was observed that while the effective enthalpy is nearly ion-independent, a reduction of the entropic cost to form stronger hydrogen-bonds (H-bonds) scales with decreasing halide size, suggesting that this contribution is the driving force for this observed Hofmeister effect.
ER -