Figure 3.

Enumeration with and without timescale separation. (a) Intended behaviour of two complementary strands s1 and s2. Either domains $\mathrm{a}$ and ${\mathrm{a}}^{\ast }$ (as shown) or b and ${\mathrm{b}}^{\ast }$ bind via a slow bimolecular reaction, followed by a fast unimolecular hybridization reaction of the respective other domain. (b) Pathological enumeration behaviour without a separation of timescales. Repeated bimolecular association reactions occur before the unimolecular bind reaction, generating implausibly long polymers. The kinetically and thermodynamically favoured simple duplex may never be found.