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Issue 35, 2020
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Multipodal coordination and mobility of molecular cations inside the macrocycle valinomycin

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Abstract

The macrocycle valinomycin displays an outstanding ability in cation binding and carriage across hydrophobic environments (e.g., cell membranes) and constitutes a central landmark for the design of novel ionophores for the regulation of biochemical processes. Most previous investigations have focused on the capture of metal cations (primarily K+). Here, we address the versatility of valinomycin in the encapsulation of molecular ions of small and moderate size, with NH4+ and H4PO4+ as case studies. A combination of infrared action vibrational spectroscopy and quantum chemical computations of molecular structure and dynamics is employed with the two-fold aim of assessing the dominant H-bonding coordination networks in the complexes and of characterizing the positional and rotational freedom of the guest cations inside the cavity of the macrocycle. Valinomycin binds NH4+ with only moderate distortion of the C3 configuration adopted in the complexes with the metal cations. The ammonium cation occupies the center of the cavity and displays two low-energy coordination arrangements that are dynamically connected through a facile rotation of the cation. The inclusion of the bulkier phosphoric acid cation demands significant stretching of the valinomycin backbone. Interestingly, the H4PO4+ cation achieves ample positional and rotational mobility inside valinomycin. The valinomycin backbone is capable of adopting barrel-like configurations when the cation occupies a region close to the center of the cavity, and funnel-like configurations when it diffuses to positions close to the exit face. This can accommodate the cation in varying coordination arrangements, characterized by different H-bonding between the four POH arms and the ester carbonyl groups of the macrocycle.

Graphical abstract: Multipodal coordination and mobility of molecular cations inside the macrocycle valinomycin

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Article information


Submitted
03 Jun 2020
Accepted
06 Aug 2020
First published
06 Aug 2020

Phys. Chem. Chem. Phys., 2020,22, 19725-19734
Article type
Paper

Multipodal coordination and mobility of molecular cations inside the macrocycle valinomycin

J. R. Avilés-Moreno, F. Gámez, G. Berden, J. Martens, J. Oomens and B. Martínez-Haya, Phys. Chem. Chem. Phys., 2020, 22, 19725 DOI: 10.1039/D0CP02996C

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