Chemistry Reference
In-Depth Information
4
Kinetics and Thermodynamics of Enzymatic
Supramolecular Polymerisations
In terms of thermodynamics, two situations may arise in biocatalytic self-assembly:
(1) the enzyme reaction and self-assembly process are both favoured in isolation,
or (2) the enzyme reaction itself is thermodynamically unfavoured but involves a
small change in free energy that can be overcome by the overall free energy change
from the stabilisation of the self-assembled structure. The latter gives rise to a fully
4.1
Enzyme-Triggered Assembly: Uncoupled
Uncoupled systems operate under kinetic control and allow access to kinetically
trapped supramolecular structures (i.e. structures that do not represent the global
free energy minimum), which can be achieved by simply altering the amount of
catalyst present, allowing for enzymatic control of emergent properties. Such differ-
ential control of supramolecular polymerisation rate directly affects the viscoelastic
properties of the resulting gel network. Rheology studies have shown that rapid
formation of the self-assembled structure induces more mechanical strength to the
hydrogel matrix than does a structure that is formed more slowly, with variations of
orders of magnitude reported (Table 2).
The ability to control mechanical properties enzymatically has been demon-
strated in two recent examples based on phosphatase-triggered self-assembly of
ADP
Precursors
ATP
Building Blocks
Building Blocks
Precursors
Supramolecular
polymer
Supramolecular
polymer
Fig. 4
Free energy diagram for the two possible situations in enzyme-triggered formation of
supramolecular assembly.
Left
: The enzyme-catalysed reaction and self-assembly process are both
favoured independently and therefore uncoupled.
Right
: Enzyme-triggered self-assembly under
thermodynamic control; formation of the building blocks is thermodynamically unfavoured in
isolation and occurs in reversible fashion when coupled to a sufficiently stable self-assembled
structure formation
