Exploiting Biocatalysis in the Synthesis of Supramolecular Polymers - Enzymatic Polymerisation - page 129

supramolecular polymerisation) dictated by ATP levels when both kinase and
phosphatase are present. Dephosphorylation has also been exploited to control
supramolecular association of peptide-polymer conjugates [ 29 , 30 ] . Although most
examples that have been reported to date are based on peptides, enzyme-responsive
DNA-based hydrogels have also been described [ 38 ] and Nature's designs will
continue to inspire supramolecular polymerisation [ 39 - 41 ] .

3.2 Self-Assembly Component

Peptides and their derivatives are particularly attractive building blocks for
supramolecular polymerisations because of their rich opportunities for non-covalent
interactions (hydrogen bonding, electrostatic, -stacking, hydrophobic), ease of syn-

thesis and compatibility with biological systems. There are 20 gene-coding amino
acids commonly found in nature (identified in this text by their single-letter codes,
Fig. 2 a ) plus an infinite number of modified and non-natural monomers. The prop-
erties and self-assembly tendency of peptides generated from the combination of
these amino acids depends on the nature of their side-chain substitution. Although
an enormous number of possible sequences exist (20 5 ; 3.2 million sequences for

π

Fig. 2 The structure of ( a ) 20 natural L amino acids and ( b ) aromatic residues that gives rise to
( c ) aromatic peptide amphiphiles, which form supramolecular polymers through hydrogen bonding
and π -stacking interactions