Exploiting Biocatalysis in the Synthesis of Supramolecular Polymers - Enzymatic Polymerisation - page 126

4 Kinetics and Thermodynamics of Enzymatic Supramolecular Polymerisations ........... 134
4.1 Enzyme-Triggered Assembly: Uncoupled ............................................ 134
4.2 Enzyme-Triggered Self-Assembly Under Thermodynamic Control ................. 136
5 Spatiotemporal Control of Nucleation and Growth in Enzymatic
Supramolecular Polymerisation............................................................... 137
6 Applications in Biomedicine and Nanotechnology .......................................... 138
7 Conclusion and Outlook ....................................................................... 140
References .......................................................................................... 140

1 Introduction

During the last two decades, chemists have become increasingly focused on how
molecules interact, i.e. on supramolecular chemistry. Dynamic intermolecular pro-
cesses provide opportunities for incorporation of control, adaptation and function
in man-made materials, as observed in living systems. In biology, these pro-
cesses 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 one-
dimensional (1D) structures, or supramolecular polymers, with unique adaptive
features.
While traditional chemistry focuses on covalent bonds, supramolecular chem-
istry examines reversible, non-covalent interactions including hydrogen bonding,
metal coordination, hydrophobic interactions, van der Waals forces, -stacking and

electrostatic interactions [ 1 , 2 ] . Supramolecular polymerisation capitalises on these
interactions and involves the controlled association of amphiphilic molecular build-
ing blocks into organised structures such as fibres. At high densities, these fibres
may become entangled, forming gel-phase structures, and building blocks are there-
fore often referred to as gelators. Supramolecular polymerisation relies on a precise
balance between hydrophobic interactions and interactions of building blocks with
solvent, and can be induced by chemical and physical triggers that cause subtle
changes in their amphiphilic balance [ 3 ]. These triggers include changes in pH [ 4 ] ,
ionic strength [ 5 , 6 ] , solvent polarity or temperature, or locally induced chemical
transformations catalysed by light [ 7 - 9 ] or (bio)catalysts [ 10 ]. Biocatalytically con-
trolled supramolecular polymerisation has a number of attractive features that will
be explored in this chapter [ 11 ].
We will first discuss some examples of biocatalytic polymerisation in biological
systems, followed by a review of recent man-made systems and the design rules that
are emerging. Unique features related to control of polymerisation (both in terms of
kinetics and thermodynamics) will be discussed, followed by a review of (potential)
applications in biomedicine and nanotechnology.

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