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

Putative two-dimensional coding systems can be constructed from aqueous sol utions of purine and pyrimidine nucleic acid bases evaporated at moderate t emperatures on the surfaces of inorganic solids. The resultant structures a re monolayers which are formed spontaneously by molecular self-assembly and they have been observed with molecular resolution by scanning tunnelling m icroscopy (STM). When formed from solutions of a single base, the monolayer s of adenine and uracil have crystalline characteristics and the STM images can be interpreted in terms of the geometrical placement of planar arrange d molecules that interact laterally by intermolecular hydrogen bonding. Whe n formed from solutions containing a mixture of adenine and uracil, the mon olayers have aperiodic structures. Small crystalline domains within these m onolayers can be interpreted in terms of the single phase configurations of the molecules and the remaining aperiodic structures can presumably be int erpreted, 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 pyri midine bases could provide the necessary complexity to act as a primitive g enetic mechanism and may have relevance to the origin of life.