Autoinduction through the coupling of nucleation-dependent self-assembly of a supramolecular gelator and a reaction network.

Abstract

Autocatalytic and/or self-replicating systems are important aspects of understanding the link between living systems (origins of life) and chemical networks. As a result, many scientists around the world are attempting to better understand these phenomena by producing chemical networks and linking them to self-assembly and pathway complexity (systems chemistry). We present here a superficially autocatalytic, self-replicating system by utilising dynamic imine chemistry coupled with self-assembling supramolecular hydrogelation kinetics that is driven by a nucleation autocatalytic cycle (autoinduction). The dynamic nature of the imine bond within water allows “error checking” correction and driving of the imine equilibrium to starting materials but when coupled to the self-assembly gives rise to one reaction product from a possible thirteen intermediates and/or products (of a mixed four-step reaction). This product represents a thermodynamic minimum within the system's and reaction network's energy landscape. The self-assembly in solution of the replicator results in the formation of supramolecular polymers which would normally markedly reduce the catalytic efficiency of the system if a template mechanism of autocatalysis is in play. By overcoming the limiting effects of the self-assembly process it is possible to demonstrate exponential growth in replicator concentration once nucleation has occurred. It is only once the completed imine can undergo non-reversible tautomerisation that the product is prevented from reacting with water. We thus suggest that this sigmoidal kinetic characterisation is not inherent to autocatalysis kinetics (lowering reaction barriers and/or templating) but rather a result of the nucleation-based assembly allowing for intermediates to be prevented from reacting with water in a water-deficient environment (an autoinduction autocatalytic mechanism). Not only does this study provide a basis with which to explore aspects of self-replication connected with self-assembly, but also explores how nucleation and self-assembly growth can play a crucial role in self-replication. By controlling the kinetics of the autocatalytic chemical reaction at one end of the hierarchical assembly process we can influence the physical properties of the supramolecular gel at the other. This may have wide-ranging applications with in situ formed small molecular gelators where specific mechanical properties (rheology) are desired.