From DAVID ROBERTSON
John Emsley (New Scientist, Science, 14 March), describes some of the
components needed to fabricate a machine of molecular size but fails to
address the problem of how to assemble it.
Biological enzymes use hydrophilic and hydrophobic sequences of groups
to achieve the correct adhesion in a structure. Perhaps a sequence of cubes
or tetrahedra in a chain without rotational freedom could be used. The chemical
character of each face would allow a block consisting of parallel chains
to be built. One chain after another would be added. Only a chain with the
correct sequence along two sides would bond onto the block.
His rings and rods would then have a structure into which they could
be incorporated.
David Robertson Trowbridge, Wiltshire
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