Turning Up the Heat: Investigation into the Driving Forces of the Hofmeister Effect in Water Vibrational Spectra
Year: 2026
Type: preprint
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.
Source: ChemRxiv
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221598303