Biological systems, supramolecular chemistry

The emphasis on molecular information in supramolecular chemistry finds its response in the operation of biological systems. 

During the last two decades, chemists have become increasingly focused on how molecules interact, i.e. on supramolecular chemistry. Dynamic intermolecular processes provide opportunities for incorporation of control, adaptation and function in man-made materials, as observed in living systems. In biology, these processes are tightly controlled by the catalytic action of enzymes. In this chapter, we focus on enzymatically controlled supramolecular polymerisation, whereby self-recognising molecular building blocks assemble to form extended onedimensional (ID) structures, or supramolecular polymers, with unique adaptive features. 

Despite the prominence of anion recognition chemistry in biological systems, the design of supramolecular anion receptors was slow to develop with respect to the analogous chemistry of cations, and this discrepancy may readily be traced to a number of inherent difficulties in anion binding ... 

These problems have been addressed in a wide variety of imaginative and novel ways and progress in anion complexation has been rapid in recent years " to the extent that it has now been described by Lehn as a full member of the field of supramolecular chemistry. It is important to note that the search for anion-selective receptors has not been limited to the mimicry of Mother Nature s approach. Indeed, a great number of the hosts developed are far from being biocompatible as the tools of the chemist are not limited to the building blocks of natural systems. This aspect of anion recognition chemistry lies at the heart of supramolecular chemistry, the interface between chemistry and biology. ... 

One of the points made in Schwenz and Moore was that the physical chemistry laboratory should better reflect the range of activities found in current physical chemistry research. This is reflected in part by the inclusion of modem instrumentation and computational methods, as noted extensively above, but also by the choice of topics. A number of experiments developed since Schwenz and Moore reflect these current topics. Some are devoted to modem materials, an extremely active research area, that I have broadly construed to include semiconductors, nanoparticles, self-assembled monolayers and other supramolecular systems, liquid crystals, and polymers. Others are devoted to physical chemistry of biological systems. I should point out here, that with rare exceptions, I have not included experiments for the biophysical chemistry laboratory in this latter category, primarily because the topics of many of these experiments fall out of the range of a typical physical chemistry laboratory or lecture syllabus. Systems of environmental interest were well represented as well. 

Biological systems have provided much of the inspiration for the development of supramolecular chemistry (see Chapters 1 and 6). One ofthe main challenges in this area is to mimic the enzymatic systems and to understand the assembly processes involved. These natural systems have an extremely high selectivity and catalytic efficiency. Although there are many successful results in this area [26], a complete understanding of these systems is still lacking. 

In the preceding chapters, reference has often been made to biological molecules and processes, for both biomimetic and abiotic purposes. The emphasis on molecular information in supramolecular chemistry finds its response in the operation of biological systems. There is a molecular logic of living organisms [10.24]. 

Biological systems have provided much of the inspiration for the development of supramolecular chemistry. Many synthetic supramolecular systems have been designed to mimic the structure or function of more complex biological processes. Such artifical, abiotic (non-biological) molecules or reaction mimics are termed models. By this we mean that, on a smaller scale, the artificial systems resemble, and help chemists to understand some or all of the properties of the real, biological chemistry. The concept of a biological model has been summarised beautifully by Donald Cram in his Nobel Prize lecture ... 

---