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A switching cascade of hydrazone-based rotary switches through coordination-coupled proton relays

Nature Chemistry volume 4, pages 757–762 (2012)Cite this article

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Abstract

Imidazole, a subunit of histidine, plays a crucial role in proton-relay processes that are important for various biological activities, such as metal efflux, viral replication and photosynthesis. We show here how an imidazolyl ring incorporated into a rotary switch based on a hydrazone enables a switching cascade that involves proton relay between two different switches. The switching process starts with a single input, zinc(II), that initiates an E/Z isomerization in the hydrazone system through a coordination-coupled proton transfer. The resulting imidazolium ring is unusually acidic and, through proton relay, activates the E/Z isomerization of a non-coordinating pyridine-containing hydrazone switch. We hypothesize that the reduction in the acid dissociation constant of the imidazolium ring results from a combination of electrostatic and conformational effects, the study of which might help elucidate the proton-coupled electron-transfer mechanism in photosynthetic bacteria.

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Figure 1: Modulating two switches using a single input.
Figure 2: Synthesis of QIH-Me.
Figure 3: Oak Ridge thermal ellipsoid plots (50% probability ellipsoids) of the X-ray crystal structures of the hydrazone-based switches.
Figure 4: Spectroscopic studies of the binding between zinc(II) and QIH-Me (1.0 × 10−5 M, CH3CN, 294 K).
Figure 5: The 1H NMR spectra (500 MHz, CD3CN, 294 K) used in confirming the CCD-initiated proton transfer that leads to the successive activation of two switches.
Figure 6: Superimposition of the optimized density functional theory (B3LYP/LACV3P**++) structures of QIH-Me(Z-H+) (blue) and Zn(QIH-Me(Z-H+)) (bronze).

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Acknowledgements

The authors dedicate this manuscript to Sir Fraser Stoddart on the occasion of his 70th birthday. This work was supported by Dartmouth College, the Burke Research Initiation Award and the American Chemical Society Petroleum Research Fund. The authors thank R. Staples for the X-ray analysis, S. Voskian for his help with the graphic for the table of contents and D.S. Glueck for his input.

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Authors and Affiliations

  1. Department of Chemistry, Dartmouth College, 6128 Burke Laboratory, Hanover, 03755, New Hampshire, USA

    Debdas Ray, Justin T. Foy, Russell P. Hughes & Ivan Aprahamian

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  1. Debdas Ray
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  2. Justin T. Foy
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  3. Russell P. Hughes
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Contributions

All experiments were conducted by D.R. and J.T.F. with input from I.A. The calculations were carried out and interpreted by R.P.H. The manuscript was co-written by I.A. and D.R. with input from R.P.H.

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Correspondence to Ivan Aprahamian.

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The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 3531 kb)

Supplementary information

Crystallographic data for compound QIH-Me (CIF 17 kb)

Supplementary information

Crystallographic data for compound QIH-Me(Z-H+) (CIF 20 kb)

Supplementary information

Crystallographic data for compound Zn(QIH-Me(Z-H+) (CIF 22 kb)

Supplementary information

Crystallographic data for compound Zn(QPH-Me(Z-H+)) (CIF 23 kb)

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Ray, D., Foy, J., Hughes, R. et al. A switching cascade of hydrazone-based rotary switches through coordination-coupled proton relays. Nature Chem 4, 757–762 (2012). https://doi.org/10.1038/nchem.1408

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