Angewandte Chemie International Edition
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For full article and contact information, see Angew. Chem. Int. Ed. 2000, 39 (11), 1955 - 1958
Man-made ion channels
soon to act as chemical sensors?
The cells in our body are all surrounded by membranes that separate the interior of the cell from its environment - these are not hermetically sealed however. Special proteins take on the important task of periodically letting ions pass through. These ion channels play a crucial role in many physiological processes and now analytical chemists have discovered them as well - as potential detectors for medical diagnosis or possibly in the environmental sphere. Artificial pores that are tailored to specific tasks are a prerequisite for this.
Stefan Matile, Bodo Baumeister and Naomi Sakai have succeeded in taking an important step in this direction: the Geneva chemists have developed the first long-lived, stable ion channel not made of biomacromolecules, but rather smaller organic molecules. Six single "rods" each consisting of eight linked benzene rings make up the framework of the pore. Each rod has short peptide strands sticking out alternately to the left and right. When the six molecules aggregate, they interlace like the fingers on two hands being brought together. This forms a barrel-shaped structure with a cavity at the center. Well-balanced repulsive and attractive interactions between the peptides maintain the rigidity of this structure. When embedded in an artificial membrane, the mini-barrel acts like a natural ion channel.
The characteristics of the pores can be influenced by variation of the peptide chains. Artificial channels could thus be developed to act as sensors for specific substances. Detection would in essence be simple: whenever a molecule passed into a pore, the electrical resistance across the membrane would change. These fluctuations can be detected with tiny electrodes; their number per unit time is proportional to the concentration of the substance being analyzed. It is even possible to differentiate between various substances by the strength and/or duration of these individual fluctuations.
"Our artificial pores demonstrate that ion channels do not necessarily have to be made up of proteins," Matile says optimistically. "Targeted channel engineering should be possible in the future."