Self-assembly in natural and unnatural systems

Although there are no fundamental factors hindering the development of nanoscale structures, there is a growing realization that "engineering down" approaches, in other words a reduction in the size of structures generated by lithographic techniques below the present lower limit of roughly 1 lam, may become impractical. It has, therefore, become increasingly clear that only by the development of a fundamental understanding of the self-assembly of large-scale biological structures, which exist and function at and beyond the nano-scale, downwards, and the extension of our knowledge regarding the chemical syntheses of small-scale structures upwards, can the gap between the promise and the reality ofnanosystems be closed. This kind of construction of nanoscale structures and nanosystems represents the so-called "bottom up" or "engineer-. ing up" approach to device fabrication. Significant progress can be made in the development of nanoscience by transferring concepts found in the biological world into the chemical arena. Central to this mission is the development of simple chemical systems capable of instructing their own organization into large aggregates of molecules through their mutual recognition properties. The precise programming of these recognition events, and hence the correct assembly of the growing superstructure, relies on a fundamental understanding and the practical exploitation of non-covalent bonding interactions between and within molecules. The science of supramolecular chemistry-chemistry beyond the molecule in its very broadest sense-has started to bridge the yawning gap between molecular and macro-molecular structures. By utilizing interactions as diverse as aromatic ~-Tz stacking and metal-ligand coordination for the information source for assembly processes, chemists have, in the last decade, begun to use biological concepts such as self-assembly to construct nanoscale structures and superstructures with a variety of forms and functions. Here, we provide a flavor of how self-as-sembly operates in natural systems and can be harnessed in unnatural ones.