One of the ultimate goals of modern systems chemistry is to construct artificial nanosystems with functionalities similar to those commonly found in the natural world, and to understand the interrelationship between molecules that generate these nanosystems. In other words, one must learn how to control the intermolecular non-covalent bonds responsible for their formation. Non-covalent bonds are responsible for a number of biologically important events, such as the base-pairing and the replication of DNA, the formation of phospholipid bilayer membranes, and the complexation of drugs, cell motility, hormones, and metabolites with their receptors – to mention just a few examples. The chemist’s drive toward synthesizing such nanoscale systems, based on the non-covalent bond, has led to a new and highly interdisciplinary field of research, namely protocellular chemistry. Protocellular chemistry deals with weak intermolecular interactions and exploit naturally-occurring phenomena like self-organization, self-assembly, self-replication, and molecular recognition. The ultimate goal of protocellular chemistry is to create functioning organized nanosystems, by analogy with the countless marvelous examples of systems already present in nature.
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Our interest is in the production of amphiphiles from precursor molecules and their subsequent self-assembly into vesicles because the dynamics of such a system may give insight into the types of chemical processes and couplings that could occur under prebiotic conditions. We have designed a chemical system in which fatty acid amphiphiles are generated from precursor ester molecules by visible light photolysis. We have shown that by the use of an external energy source and a ruthenium-based photocatalyst, we are able to convert non-structure-forming molecules, in form of a ester precursor (Figure 1, top), into amphiphiles that spontaneously assemble into vesicles (Figure 1, bottom).
The core of our system uses a ruthenium-based photocatalyst composed of an 8-oxo-guanine and a ruthenium complex. We have investigated various configurations of the photocatalytic activity both in the presence and absence of preformed vesicles (container) and found that the rate of amphiphile precursor conversion is depended on the distance between the 8-oxo-guanine and a ruthenium complex. It is of our interest to further study if the rate of this catalytic reaction could be improvement by obtaining a tightening interaction between its component and also between the components and the container. This investigation will be carried out by applying organic synthesis in the construction of novel photocatalytic systems that is subsequently investigate in the overall transformation of the ester precursor molecule into bilayer-forming molecules and vesicles assembly.
Figure 1. Catalytic conversion of non-structure-forming ester precursor molecules (top) - by the use of an external energy source - into amphiphiles that spontaneously assemble into vesicles (bottom).