Cation-responsive cavity expansion of valinomycin revealed by cryogenic ion trap infrared spectroscopy

Abstract

Valinomycin (VM) is a natural K+-selective ionophore that transports K+ through the cell membrane. VM captures K+ in its central cavity with a C3-symmetric β-turn-like backbone. Although the binding affinity...

Ion Recognition beyond Size Matching: Cooperative Hydration Effect on the K+ Selectivity of Valinomycin over Na+ Revealed by Cryogenic Double Ion Trap Infrared Spectroscopy

“…The IRPD spectrum of bare Na + VM was reported in a previous paper (reprinted in Figure a) . The IRPD spectrum shows an intense single band at 3260 cm –1 assigned to amide NH stretches.…”

“…The IRPD spectrum of bare Na + VM was reported in a previous paper (reprinted in Figure 2a). 15 The IRPD spectrum shows an intense single band at 3260 cm −1 assigned to amide NH stretches. The molecular structure of Na + VM was determined to have the C 3 -symmetric bracelet structure based on the comparison between the experimental and calculated IR spectra.…”

“…This approximation does not characterize the molecular nature of solvation of VM and its metal ion complexes, though it has been widely applied to various ionophores. , From the experimental side, the NMR or IR spectrum may be contaminated by uncomplexed VM, which is inevitably present in polar solvents due to the low affinity of VM to Na + . A further complexity to the size-matching model for VM arises from a recent study that demonstrates the flexibility of VM to effectively bind all alkali metal ions by adjusting its cavity size . To some extent, this negates the concept of size-matching for a flexible ionophore.…”

“…Copyright 2021 American Chemical Society. The IRPD spectrum of Na + VM is adapted from ref (Hirata K. et al, Phys . Chem .…”

“…12 A further complexity to the sizematching model for VM arises from a recent study that demonstrates the flexibility of VM to effectively bind all alkali metal ions by adjusting its cavity size. 15 To some extent, this negates the concept of size-matching for a flexible ionophore. In any case, clear structural information is needed to reconsider the traditional size-matching model for K + selectivity by VM and develop an alternative.…”