Kinetic Analysis of the Rebek Self-Replicating System: Is There a Controversy?

The Rebek self-replication reaction of 1 and
2, catalyzed by complexation of both reactants to the
resulting
product 3 (Tjivikua, T.; et al. J. Am. Chem. Soc.
1990, 112, 1249−1250. Nowick, J. S.; et al.
J. Am. Chem. Soc.
1991, 113, 8831−8839. Wintner, E. A.; et al.
Acc. Chem. Res. 1994, 27, 198−203.
Conn, M. M.; et al. J. Am. Chem.
Soc. 1994, 116, 8823−8824), and related
work of Menger et al. (Menger, F. M.; et al. J. Am. Chem. Soc.
1994, 116,
3613−3614. Menger, F. M.; et al. J. Org. Chem.
1995, 60, 2870−2878) have been reinvestigated.
On the basis of
our experiments with the same systems and comparing the absolute rates
of different (model) reactions, we have
identified five pathways of the reaction between 1 and
2 in the presence of template 3:  background
(k1 = 0.035
M-1
min-1 ), preassociative
(k2 = 0.0044 min-1),
termolecular (k3 = 0.030
min-1), and two bimolecular
(k4 = 0.130
M-1
min-1, k5 = 0.020
M-1 min-1). A
general kinetic model for self-replicating reactions has been used to
analyze the
Rebek−Menger controversy. We conclude that self-replication as
defined by Rebek et al. operates in this system;
other pathways obscure the simple picture of a ternary complex as the
only complex that leads to the rate enhancement
and one of those (bimolecular) pathways is that proposed by Menger et
al. Our results show that when 1 and 2
are
complexed to 3 in a termolecular complex, the rate of
reaction between 1 and 2 is 6.8 times
(k3/k2) faster than
when
3 is formed from the bimolecular complex of 1 and
2, and this rate enhancement factor represents the
efficiency of
template 3 in the self-replication process.