Biomedical Engineering Reference
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Fig. 6 Small molecule regulated target amplification using an allosteric enzyme mimic ( right )
with a reaction cascade analogous to PCR ( left ). Reprinted with permission from [ 30 ]. Copyright
2008 American Chemical Society
with a fluorescent pH indicator. By replacing the target effector Cl anion with
acetate to generate a trans acetate and CO ligand at each Rh(I) site, the reaction was
run under basic conditions to produce additional acetate from the same acyl transfer
reaction. In the early stages of the reaction, only a minor amount of the catalyst is
activated (in the form of 5), but as the reaction proceeds, more acetate is generated,
which leads to the formation of more 5 and progressively faster catalysis. The pH-
sensitive fluorescent dye allows one to follow the amount of acetate generated
during the catalytic cycles. This type of cascade reaction results in an exponential
increase in the amount of initial target. As with PCR, slow induction followed by
rapid exponential amplification, linear growth, and then eventual saturation was
observed regardless of initial acetate concentrations. The time at which the expo-
nential step turns on correlated well with the initial acetate target concentration. In
principle, this approach can be operational in completely aqueous environments by
incorporating water-soluble ligands [ 33 ] and extended to other analytes as long as
one can envision catalytic reactions that generate an analyte of interest.
The above examples demonstrate that, through exquisite control over the
synthesis of macrocyclic coordination complexes containing well-defined cavities,
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