Supramol. chem-2.pptx

2. Self-assembly 2.1 Introduction 2.1.1 Self-assembly Self-Assembly: The spontaneous and reversible association of molecular species to form larger, more complex supramolecular entities according to the intrinsic information contained in the components. Examples of such self-assembly processes are repeatedly found in nature. The DNA double-helix requires two complementary strands to become entwined via hydrogen bonds and p-p stacking in a self-assembly process . Synthetic self-assembling systems rely upon the ability of the chemist to design molecules containing complementary functionalities. The syn-thetic chemist has no direct control over the assembly process– other-wise it would not be termed self-assembly. Ultimately, the chemical system itself rearranges to the most thermodynamically stable product. Among the most widely used interactions in synthetic self-assembly processes are metal–ligand interactions, primarily due to their lability and high degree of directionality as a result of predictable metal-ion coordination environments. It is possible to employ a retrosynthetic methodology towards the design of synthetic self-assembling systems. a square-planar metal ion, such as Pd2+ or Pt2+, which has two cis coordination sites blo-cked off. Makoto Fujita, J. Chem. Soc., Chem. Commun., 1996, 1535–1536. Tokyo university 2.1.2 Basic concepts of self-assembly The assembly process is kinetically rapid and both completely reversible and replicable, i.e. if taken apart (e.g. by change of conditions) the supramolecular aggregate will be reformed under a particular set of conditions so as to be indistinguishable from the original. The reversible nature of the assembly process gives rise to an important feature of self-assembling systems, namely their ability to correct ‘mistakes’ during assembly and gradually work their way towards the most thermody- namically stable product. *It is common within self-assembling systems for there to be more than one ty