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H(aq)+ structures in proton wires inside nanotubes.

ABSTRACT: The hydrated carborane acid H(CHB(11)I(11)).8H(2)O crystallizes in nanometer-diameter tubes of H(aq)(+) enclosed by walls of carborane anions. Three different types of H(aq)(+) clusters are found in these tubes: a symmetrical H(13)O(6)(+) ion with an unusually elongated Zundel-type H(5)O(2)(+) core, two hydrated H(7)O(3)(+) ions, and an unprecedented H(17)O(8)(+) ion having a nearly square core. All of the H(aq)(+) cations show unexpectedly longer O...O separations than in discrete H(aq)(+) ions, indicating greater delocalization of positive charge. The centrosymmetric H(aq)(+) ions are linked via short H bonds, forming a true one-dimensional proton wire.

SUBMITTER: Stoyanov ES

PROVIDER: S-EPMC2787796 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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H(aq)+ structures in proton wires inside nanotubes.

Stoyanov Evgenii S ES Stoyanova Irina V IV Tham Fook S FS Reed Christopher A CA

Journal of the American Chemical Society 20091201 48

The hydrated carborane acid H(CHB(11)I(11)).8H(2)O crystallizes in nanometer-diameter tubes of H(aq)(+) enclosed by walls of carborane anions. Three different types of H(aq)(+) clusters are found in these tubes: a symmetrical H(13)O(6)(+) ion with an unusually elongated Zundel-type H(5)O(2)(+) core, two hydrated H(7)O(3)(+) ions, and an unprecedented H(17)O(8)(+) ion having a nearly square core. All of the H(aq)(+) cations show unexpectedly longer O...O separations than in discrete H(aq)(+) ions ...[more]

PMID: 19911820

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Project description:Designing molecular platforms for controlling proton and electron movement in artificial photosynthetic systems is crucial to efficient catalysis and solar energy conversion. The transfer of both protons and electrons during a reaction is known as proton-coupled electron transfer (PCET) and is used by nature in myriad ways to provide low overpotential pathways for redox reactions and redox leveling, as well as to generate bioenergetic proton currents. Herein, we describe theoretical and electrochemical studies of a series of bioinspired benzimidazole-phenol (BIP) derivatives and a series of dibenzimidazole-phenol (BI2P) analogs with each series bearing the same set of terminal proton-accepting (TPA) groups. The set of TPAs spans more than 6 pK a units. These compounds have been designed to explore the role of the bridging benzimidazole(s) in a one-electron oxidation process coupled to intramolecular proton translocation across either two (the BIP series) or three (the BI2P series) acid/base sites. These molecular constructs feature an electrochemically active phenol connected to the TPA group through a benzimidazole-based bridge, which together with the phenol and TPA group form a covalent framework supporting a Grotthuss-type hydrogen-bonded network. Infrared spectroelectrochemistry demonstrates that upon oxidation of the phenol, protons translocate across this well-defined hydrogen-bonded network to a TPA group. The experimental data show the benzimidazole bridges are non-innocent participants in the PCET process in that the addition of each benzimidazole unit lowers the redox potential of the phenoxyl radical/phenol couple by 60 mV, regardless of the nature of the TPA group. Using a series of hypothetical thermodynamic steps, density functional theory calculations correctly predicted the dependence of the redox potential of the phenoxyl radical/phenol couple on the nature of the final protonated species and provided insight into the thermodynamic role of dibenzimidazole units in the PCET process. This information is crucial for developing molecular "dry proton wires" with these moieties, which can transfer protons via a Grotthuss-type mechanism over long distances without the intervention of water molecules.

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H(aq)+ structures in proton wires inside nanotubes.

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H(aq)+ structures in proton wires inside nanotubes.

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