Self-programmable, self-assembling two-dimensional genetic matter.

Putative two-dimensional coding systems can be constructed from aqueous solutions of purine and pyrimidine nucleic acid bases evaporated at moderate temperatures on the surfaces of inorganic solids. The resultant structures are monolayers which are formed spontaneously by molecular self-assembly and they have been observed with molecular resolution by scanning tunnelling microscopy (STM). When formed from solutions of a single base, the monolayers of adenine and uracil have crystalline characteristics and the STM images can be interpreted in terms of the geometrical placement of planar arranged molecules that interact laterally by intermolecular hydrogen bonding. When formed from solutions containing a mixture of adenine and uracil, the monolayers have aperiodic structures. Small crystalline domains within these monolayers can be interpreted in terms of the single phase configurations of the molecules and the remaining aperiodic structures can presumably be interpreted, geometrically, in terms of the 21 theoretically possible adenine-adenine, uracil-uracil and adenine-uracil hydrogen bonding interactions. We propose that combinatorial arrangements of planar arranged purine and pyrimidine bases could provide the necessary complexity to act as a primitive genetic mechanism and may have relevance to the origin of life.