Valinomycin-proton interaction in low-polarity media

Area of Science:

• Biochemistry
• Physical Chemistry
• Molecular Biophysics

Background:

• Valinomycin is a known ionophore, typically studied for its potassium ion transport capabilities.
• Understanding its interaction with protons is crucial for elucidating its full biological function.
• Proton transport is fundamental to many biological processes, including cellular energy production.

Purpose of the Study:

• To investigate the complex formation between valinomycin and protonated species (H3O+).
• To quantify the stability and binding affinity of the valinomycin-H3O+ complex.
• To explore the structural and dynamic aspects of this interaction and its implications for biological membranes.

Main Methods:

• 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy.
• Fourier Transform (FT) Infrared spectroscopy.
• Ab initio-density functional theory (DFT) quantum mechanical calculations.
• Determination of equilibrium constants (K) from NMR chemical shifts.

Main Results:

• Valinomycin forms a stable complex with hydronium (H3O+) ions in solution.
• The equilibrium constant for complex formation (K) was determined to be 5.9, with a proton affinity constant of 10(5.3).
• Structural analysis revealed an asymmetric binding of H3O+ to valinomycin's carbonyl groups, which is averaged by rapid ion exchange.

Conclusions:

• Valinomycin exhibits significant affinity for H3O+ ions, relevant under physiological conditions.
• The observed complexation and rapid H3O+ exchange suggest valinomycin can function as a proton carrier.
• These findings expand the known transport capabilities of valinomycin beyond alkali metal cations.