Selective alkali metal binding of valinomycin by electrospray ionization mass spectometry

Abstract

Selective binding of alkali metal ions by the ionophore antibiotic valinomycin in alcoholic media was detected by electrospray ionization mass spectrometry (ESI-MS). The relative cation affinity for valinomycin is in the order Rb+ > Cs+ > K+ ? Na+ in both methanol and ethanol. With a 1:1:1 mixture of valinomycin and synthetic mimics 18-crown-6 and [2,2,2]-cryptate (methanol, excess KOAc) valinomycin showed much higher affinity than the other ionophores. This study has shown that the potential of ESI-MS as a very useful tool for research involving metal binding is great. Problems with sodium ion interference and quantitation are discussed.