Guest Commentary pubs.acs.org/JPCL
Combinatorial Science
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definition, always present and always focused on a valuable goal. Thus, while combinatorial science may appear not to be hypothesis-driven, it is an extraordinarily helpful way to develop, test, and refine hypotheses. It is a tool that every molecular scientist and engineer should be prepared to employ.
hysical chemists strive to understand the mechanistic basis of the properties and behavior of molecules and molecular systems. Information and insights are the goals, which help us to manipulate matter and energy for every conceivable purpose. It is the extent of the interplay between understanding and creation that makes chemistry unique among the physical sciences. It is obvious how understanding something allows us to make things; a carpenter needs to know the properties of wood in order to construct an effective table. This relationship also works the other way around; in building many tables, the carpenter learns about the materials from which they are made and thereby how to build better tables in the future. The more complex the creation, the more information that is both required and available. The act of constructing many candidates from different components, and selecting those that work best, is the essence of a combinatorial approach in any field. The nature of the components, and the number and manner in which they are joined, determines the label that we place on the endeavor but does not change its essential nature. Combinatorial chemistry is traditionally the purview of those seeking better small-molecule drugs, wherein the building blocks are exceedingly small, single atoms or small groups of atoms. Combinatorial materials can be made from small collections of elements or molecules, as in solid-state structures, or from assemblies of dozens to millions of molecular building blocks connected to form polymers. This issue of JPC Lett. contains a description of a combinatorial approach to the design of new photocatalytic materials, and indeed catalysis is among the most sophisticated of chemical functions, requiring careful balancing of many factors affecting thermodynamics, kinetics, and stability (Rühle, S.; Anderson, A. Y.; Barad, H.-N.; Kupfer, B.; Bouhadana, Y.; Rosh-Hodesh, E.; Zaban, A. AllOxide Photovoltaics. J. Phys. Chem. Lett. 2012, 3, 3755−3764). It is no wonder that the design of catalysts is difficult, but enzymes show us that molecular combinations can provide answers to almost any catalytic problem. Biology is inherently combinatorial in its small-molecule chemistry (such as secondary metabolites), its key polymers (proteins, nucleic acids, and polysaccharides), and even its manipulation of higher-order elements such as protein domains, genes, and pathways. What sets combinatorial efforts apart in any field is their emphasis on function. Before she starts an experiment, the combinatorial scientist never knows precisely how the desired function can be achieved; if she did, she would be able to create it directly. Instead, she can only guess what components might be most likely to produce the necessary outcome and how they can be connected. Effective testing to identify those candidates with promising function is often the most difficult step when many candidates are involved. At the end of a successful experiment, the combinatorial investigator may still not know how the function has been achieved. However, each experiment is a newly created world that can be small in scale or very complex, and the opportunity for learning something new is, by © 2012 American Chemical Society
M.G. Finn, Editor-in-Chief ACS Combinatorial Science
Published: December 20, 2012 3811
dx.doi.org/10.1021/jz302038f | J. Phys. Chem. Lett. 2012, 3, 3811−3811
