4853 Allosteric Effects. Remote Control of Ion ... - ACS Publications

SOC. 1980, 102, 4853-4854. 4853. Allosteric Effects. Remote Control of Ion Transport. Selectivity. Sir: We recently introduced the macrocyclic polyeth...
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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