Circular Dichroism is Sensitive to Monovalent Cation Binding in Monensin Complexes

Area of Science:

• Coordination Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Monensin is a natural antibiotic with known affinity for metal ions.
• Understanding its coordination chemistry can reveal new applications.
• Circular dichroism (CD) is a sensitive technique for studying chiral molecules.

Purpose of the Study:

• To explore the coordination chemistry of monensin with monovalent cations.
• To investigate the structural and electronic properties of monensin-cation complexes in solution.
• To assess the utility of CD spectroscopy for discriminating between different monovalent cations bound to monensin.

Main Methods:

• Circular dichroism (CD) spectroscopy of monensic acid A (MonH) and its derivatives with Li+, Na+, K+, Rb+, Ag+, and Et4N+ in methanol.
• Synchrotron radiation circular dichroism (SRCD) for extended wavelength range (178-192 nm).
• Computational modeling using Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT).

Main Results:

• CD spectra showed significant variations in signs and intensities depending on the bound monovalent cation.
• SRCD extended the spectral range, revealing additional electronic transitions.
• DFT and TDDFT simulations indicated that the solution structure conserves the solid-state conformation and suggested cation-induced conformational changes and electronic involvement.
• Experimental and computational data confirmed the sensitivity of monensin CD spectra to the captured ion.

Conclusions:

• Monensin's CD spectra are highly sensitive to the type of monovalent cation bound.
• CD spectroscopy, particularly SRCD, is a viable method for discriminating between different monovalent cations complexed with monensin.
• Computational modeling supports experimental findings and provides insights into the electronic origins of spectral changes.