Cation-Binding of Glutamate in Aqueous Solution

Area of Science:

• Physical Chemistry
• Biophysical Chemistry
• Spectroscopy

Background:

• L-glutamate (Glu-) is a crucial neurotransmitter and biomolecule.
• Understanding cation-Glu- interactions is vital for biological and chemical processes.
• Aqueous solutions containing these ions exhibit complex dynamics.

Purpose of the Study:

• To investigate the interactions between Li+, Na+, Mg2+, and Ca2+ cations and L-glutamate (Glu-) in aqueous solution.
• To characterize the structural and dynamic changes induced by these cations using advanced spectroscopic and computational methods.
• To elucidate the formation and nature of ion pairs and potential triple ions.

Main Methods:

• Dielectric relaxation spectroscopy in the gigahertz region.
• Density functional theory (DFT) calculations.
• 3D reference interaction site model (3D-RISM) calculations.

Main Results:

• A new low-frequency relaxation mode (∼0.4 GHz) was observed upon salt addition.
• This mode was assigned to ion pairs between cations (Mg2+, Ca2+) and the Glu- side-chain carboxylate.
• For Li+, ion pairs or backbone triple ions were suggested; for Na+, the origin remained speculative.

Conclusions:

• Cations Mg2+ and Ca2+ form distinct ion pairs with L-glutamate.
• Binding affinity increases in the order Li+ < Mg2+ < Ca2+.
• The specific interactions and dynamics depend significantly on the cation identity.