German chemists have demonstrated how porous molybdenum compounds can be used as models for cellular transport proteins. The team, led by Achim Müller of Bielefeld University, utilised Raman spectroscopy and ⁹⁵Mo and ⁷Li NMR to study their synthetic structures and to demonstrate stability and activity.

Müller and colleagues Erhard Haupt, Claudia Wontorra, and Dieter Rehder of the University of Hamburg, suggest that new insights into how cellular channels transport cations could improve our understanding of cellular processes and what happens when they fail. As such, they might lead to new targets for drug discovery. Modelling the cell's molecular channels might also lead to new technological applications such as sensors, chemical separation technology, and drug-delivery agents.

The question Müller and his colleagues asked is whether or not inorganic supramolecular chemistry might accurately emulate the protein-based channels found in nature. They have found that ⁷Li NMR can be used to follow the uptake and release processes of lithium cations in such an inorganic model - the unique porous nanocapsule {{(Mo^VI)Mo^VI₅O₂₁ (H₂O)₆}₁₂ {Mo^V₂O₄^-(SO₄)}₃₀}₇₂₂. This species, the researchers explain, behaves as a semi-permeable inorganic membrane that is open to the passage of water molecules and small cations, such as Li⁺, and as such can channel traffic in a similar manner to certain membrane channels.

The team has also found that their inorganic channel has a strong dependence on ??environmental?? effects such as solvent properties, the amount of water present, and competing complexing chemical groups, or ligands. Ultimately, its behaviour resembles the complex chemical equilibrium observed in biological leak channels. The study provides model information for biological cation transport processes in the direction of the electrochemical gradient (down hill), explains Müller. This an especially important process and occurs in open K⁺ leak-type channels, which are ubiquitous in eukaryotic cells and maintain the cell membrane at constant electrical potential.

The research may also have implications for understanding Li⁺/Na⁺ counter transport. This, Müller adds, plays a key role in the treatment of dipolar disorder (manic depression) and is of interest in hypertension research. He told Spectral Lines that the team has now studied this using ²³Na NMR but is yet to publish details.

• Bielefeld University - Faculty of Chemistry
• Erhard Haupt's homepage
• Chem Commun 2005, 3912-3914

Article by David Bradley