Modulation of hydrophobic effect by cosolutes

Area of Science:

• Physical Chemistry
• Biophysical Chemistry
• Solution Chemistry

Background:

• Understanding how solutes affect water structure is crucial for biological processes.
• Hydrophobic interactions play a key role in protein folding and self-assembly.
• Osmolytes like TMAO and GB are vital for cellular function under stress.

Purpose of the Study:

• To compare the hydration and self-association of tert-butyl alcohol (TBA), trimethylamine-n-oxide (TMAO), and glycine betaine (GB) in aqueous solutions.
• To investigate the impact of these solutes on water's hydrogen-bonded network.
• To correlate solute-induced changes in water structure with their effects on micellization and biomolecular stability.

Main Methods:

• Raman spectroscopy was used to analyze water's OH-stretching region (3,800–2,800 cm⁻¹).
• Alkyl CH stretching bands (3,100–2,900 cm⁻¹) were studied to probe solute self-aggregation.
• The critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS) was measured with varying solute concentrations.

Main Results:

• TBA induced nonadditive perturbations in water's hydrogen-bonded network, unlike TMAO and GB.
• TBA began to self-aggregate at a molar fraction of approximately 0.025.
• TMAO and GB showed no significant self-aggregation up to the highest concentrations studied.
• No direct correlation was found between a solute's effect on water structure and its impact on micelle or protein stability.

Conclusions:

• TMAO and GB exhibit a neutral effect on hydrophobic interactions, making them compatible osmolytes.
• The absence of nonlinear effects in TMAO and GB solutions explains their ability to accumulate without disrupting cellular processes.
• TBA's disruptive effect on water structure suggests it is less compatible in biological systems compared to TMAO and GB.