RECOGNITION OF DIGITAL INFORMATION IN SYNTHETIC MACROMOLECULES

Just as the information contained in a book is embodied in a linear sequence of letters, so the information needed for all living systems to function and reproduce is embodied in a sequence of chemical units ( monomers ) which make up linear polymer chains known as nucleic acids (DNA and RNA). Such information is read and acted upon through the recognition of specific monomer sequences by other molecules.This nucleic-acid-based system, on which all life depends, represents an ultra-miniaturised information technology operating at the molecular level. However, there is no fundamental reason why polymer-based information-processing should be restricted to biologcal systems. Any polymer molecule containing two chemically distinct monomers is the logical equivalent of a string of binary numbers, on which all current technological information-processing is based. The present research proposal sets out the first definite programme to develop a prototype for a synthetic molecular-scale information processing system. The long-term potential of such a system is reflected in the fact that the binary information-bearing capacity of only one gram of a typical 2-monomer copolymer is some one hundred billion gigabytes.This project will not make use of the relatively fragile copolymers found in biological systems, but will focus on a family of extremely robust yet highly versatile synthetic polymers (the polyimides) which were developed originally for high-temperature, aerospace applications. The concept on which the proposal is based involves a molecular tweezer , some one billionth of a metre long, which is able to probe the monomer sequences in co-polyimides. The two arms of the tweezer feel all the different sequences available on the polyimide chain, but bind strongly only at the sequence where the chain-structure and tweezer-structure are most closely complementary. The potential of this system for reading sequence information has been demonstrated in our recently-published preliminary studies, but far more research is needed to explore and understand the way in much such systems function at the molecular level. In this proposal we also develop schemes for writing information to polyimide chains, at least to the extent that nature writes information to DNA through mutation (i.e. single-site insertion or replacement of monomers in a single polymer chain) and recombination (i.e. the exchange of extended sequences between two different polymer chains). The tweezer molecule should, in principle, be able read the sequence-changes produced by these processes.Potential applications of this work in the long term include high-density information processing and storage (several million times higher than current electronic systems, when three-dimensional storage is considered). The fundamental principles of sequence-recognition emerging from this work could also lead to a better understanding of the way in which molecular information- processing (i.e. biology) may have first originated on earth some three billion years ago.