The background to the work discussed in this paper stems from
two projects currently being pursued at the Centre for Molecular
Architecture. The first is in the area of nanotechnology
where we plan to build and test a new type of molecular switch.
Modelled very much after a bell, it has a molecular framework
with porphyrin walls which acts as the metal sides of the bell
and a mobile clapper with a group X on the end. When the X-group
actually interacts with the porphyrin, then a signal is emitted;
when it is removed away from the wall, the signal ceases. Thus,
in analogy with a bell where the signal is produced when the clapper
hits the side of the bell to emit the sound (ring), so the molecular
switch gives off a signal (e-transfer, light) when the mobile
arm (the polymethylene chain) positions the X-group close to the
porphyrin. A schematic of this system is shown in Figure 1.
The key elements in this model are the rigid molecular frame to
which the porphyrin walls are attached and the positioning of
the clapper on the inner face of the U-shaped framework system.
A similar U-shaped molecular frame is an integral part of our
second project which deals with catalyst design. Here, the molecular
framework is designed with different wall units to which guest
molecules X and Y can be specifically associated. Where the guests
are carrying groups A and B at their termini, which have the capacity
to react with one another, a termolecular species comprising the
host and the two guests (Figure 2) can be envisioned. By designing
the host, guest dimensions to allow A and B to attain the correct
transition state for reaction, then the host should catalyse the
reaction. We are presently exploring such systems to assess the
reality of this proposed catalytic, enzyme-like activity.
At the commencement of each of these projects only limited methodology
was available for the construction of rigid, U-shaped molecular
frameworks and our first task was to address this construction
deficiency. Some years down the track, we have now developed
methodology which is exceptionally versatile and efficient for
alicyclic framework construction (Figure 3). Aspects of this
work form the basis for the present plenary.