Page 117 - Visions of the Future Chemistry and Life Science

106 A. R. HEMSLEY AND P. C. GRIFFITHS

oil-in-water or water-in-oil (micro) emulsion droplets form. Ultimately, at
high surfactant compositions, liquid crystalline (lamellar) structures form.
In the natural system the sites of spore wall formation, i.e. the sporan-
gial loculus, act as mini-reactor vessels in which the above interactions can
occur. If a polymerisation occurs within one such structure, the resulting
(polymer) architectures will probably closely resemble the self-assembled
ones formed in our artificial sporangia.

6.3 Synthetic self-assembled architecture and evolutionary
implications

6.3.1 An experimental example
Following identification of the colloidal crystal layer within our spore
walls, an attempt was made to utilise a simple colloid consisting of poly-
styrene particles in water (a latex) to mimic the natural structure. To cause
flocculation of the particles, carboxymethylcellulose (CMC) was intro-
duced with the intention of initiating a depletion interaction as described
above. Although different from sporopollenin, polystyrene shares some
properties and is at least reasonably well understood with regard to its col-
loidal behaviour. CMC was chosen as a relatively ‘natural’ polysaccharide.
These initial experiments proved successful and resulted in the formation
of colloidal crystals like those within the spore walls, but more signifi-
cantly, they were built by processes and components which we believe
behave in a similar manner to those in the natural system. Similar particle
flocculations, but of an amorphous nature and formed from particles of
inconsistent size could be produced by either depletion or bridging floccu-
lation. Subsequent experiments have utilised hydrocarbons and lipids
(known from the natural system of wall production) to synthesise mimics
resembling other types of spore wall with some success.
It is disconcerting how ‘life-like’ some structures built from synthetic
colloidal particles can be (Figures 6.2(b) and 6.5(a–d). Hollow spheres of
Figure 6.5. Experiments involving mimics of sporopollenin (the principal
component of spore walls) demonstrate that patterns very similar, if not identical
to those of natural spores and pollen, can be produced from mixtures containing
colloidal particles. All scales refer to bar in (a). (a) Spore-like structures of
polystyrene particles and particle aggregates formed around a droplet of
hydrocarbon. Scale 10 m. (b) A broken structure like that shown in (a). Scale
5 m. (c) Detail of the composition of the wall of the mimic spore shown in