Chemistry Reference
In-Depth Information
OH
(b)
(a)
O
O
N
O
H
OMe
d
n
1
r
3
n
g
|
5
16
O
OH
Subtilisin
O
O
N
O
H
OH
17
O
(c)
(d)
3
.
Figure 4.5
(a) Chemical structure of Fmoc-YL-OMe and their subtilisin-catalysed
hydrolysis to Fmoc-YL-OH gelator. (b) Schematic of nucleation and
growth mechanism of self-assembly controlled by subtilisin. (c) AFM
analysis of initial stages of the self-assembly process. (d) Melting tem-
perature (T
gel
) of gels formed catalytically (black) and by a heating-
cooling cycle (red) at different enzyme concentrations.
Modified from ref. 43.
initiation of fibre growth starts from the cluster of enzymes (Figure 4.5c). The
rate of catalytic self-assembly and hence the properties of the self-assembled
structures could be tuned simply by changing the amount of enzyme present in
the system. The resulting materials were structurally different, as was imme-
diately evident from a comparison of the melting behaviour of these gels, which
showed that higher enzyme concentrations gave rise to increasingly stable gels
with increasing melting temperatures (Figure 4.5d). The supramolecular or-
ganisation was systematically different and AFM images also demonstrated
clearly that the self-assembled network was directly controlled by the amount
of enzyme with higher enzyme concentrations giving rise to longer and more
bundled fibres. Thus, the enzymatic conversion in these reactions was dictated
by its concentration leading to higher-ordered structure formed more quickly at
high enzyme concentration. It was proposed that the increasing enzyme con-
centration controls the size of the biocatalytic cluster and activity at the ag-
gregation nuclei, thus allowing locking of the structure under kinetic control,
