JpJ
4853
J . Am. Chem. SOC.1980,102, 4853-4854
+1.3 cm
Allosteric Effects. Remote Control of Ion Transport Selectivity
.05M
Sir:
--
Li’, Na’ and
W e recently introduced the macrocyclic polyethers 1, and
KPF6
CHC13
-
n = l Ib n = 2 I 20 n : I ; M = W(CO), 2b n = 2; M = WCCO), w la
-
N
.03M carrier
Figure 1.
I
3
demonstrated the specificity of their binding sites.’ These structures incorporate two receptors: the polyether which binds alkali metal ions and the 2,2’-bipyridyl function which binds transition metals. Though some distance separates these sites, they are mechanically coupled in that binding a t one site forces conformational restrictions which alter receptivity a t the remote
Figure 2. Binding-induced conformational changes.
Table I. Ion Transport Rates Relative to Na’ dibenzo-18-crown-6
Lit Na’
K’
3
la
Ib
2a
2b
PF,-
picrates
1-
Br-
0.012 1.0 14
0.047 1.o 3.8
0.018 1.o 16
0.037 1.o
0.05 1.0 12
