Supramolecular array, definition

Because of limited space, this chapter covers porphyrins and expanded porphyrins as receptors through mostly non-covalent or supramolecular interactions. As a general rule, examples wherein the porphyrin acts as a receptor via metal coordination are excluded. For a further reading on this latter topic, the reader is referred to a recent Chemistry Review article entitled Supramolecular Chemistry of Metallopor-phyrins. On the other hand, inspired by a recent review by Anslyn entitled Supramolecular Analytical Chemistry, we expand our definition of receptor-substrate interactions to include certain boronic acid binding motifs and several representative examples of metalated porphyrins that are applied to sensing applications, wherein the proposed mode involves metal complexation. Thus, included in this chapter is a brief summary of the seminal work carried out by Suslick and his group, where porphyrins are used to create the so-called artificial nose, that is, an array-based sensing device for various vapors. Also included are... 

The biological self-assemblies inspired the chemists to design molecular recognition-directed supermolecules [3-6]. Multiple hydrogen-bonds between complementary molecular components and metal coordination interactions have been used to design small receptor-guest complexes [3], bulk supramolecular systems such as liquid crystals [7-10], and molecular cocrystals [11-18]. Supramolecular polymers are broadly defined as polymeric arrays of repeating molecular units which are assembled by reversible and directional noncovalent interactions [19,20]. This definition refers to their primary structures, and control on their secondary and ternary structures has not been a critical issue. 

With regard to its electronic properties, no studies are available that clearly demonstrate that electron transfer through such a supramolecular assembly is possible. Solid-state electrochemical studies on the crystalline material are not available at the present time. The closest to supramolecular electrochemistry are studies of ordered two-dimensional peptide arrays on gold. For some Fc-peptide cystamines, self-assembled monolayers of Fc-peptide cystamines were prepared that allow the quantification of the electron transfer kinetics by electrochemical techniques. Similar to the supramolecular assemblies, H-bonding plays an important role. At the present time (2003), only a few systems were studied and offer a rather complex picture of the ET properties. Additional experimental work is required to obtain definite results on the influence of the peptide primary and secondary structure on ET kinetics. In addition, tile issue of lateral interactions needs to be addressed by detailed dilution studies with alkylthiols. 

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