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O ne of the great hopes of nanotechnology is that molecules can be connected together to make predesigned structures with useful functions. By combining carefully chosen molecules it should, in principle, be possible to build nanoscale electronic devices such as wires, or more complex examples such as transistors, capacitors and memories. The integration of these components into a so-called ‘molecular computer ’ is one of the ultimate goals of such endeavours, but there are enormous scientific challenges that must first be overcome. On the Nature Nanotechnology website today, Leonhard Grill and co-workers1 fro