Predictable and time-programmable sequences of the kind pH1(high)–pH2(low)–pH3(high) in water solution are obtained by a judicious choice of the concentration of nitroacetic acid undergoing decarboxylation.
This work reports that the composition of a dynamic library (DL) of interconverting imines can be controlled over time in a dissipative fashion by the addition of an activated carboxylic acid used as a chemical fuel. When the fuel is added to the DL, which is initially under thermodynamic equilibrium, the composition of the mixture dramatically changes and a new, dissipative (out of equilibrium) state is reached that persists until fuel exhaustion. Thus, a transient dissipative dynamic library (DDL) is generated that, eventually, reverts back to the initial DL when the fuel is consumed, closing a DL→DDL→DL cycle. The larger the amount of added fuel, the longer the time spent by the system in the DDL state. The transimination reaction is shown to be an optimal candidate for the realization of a dissipative dynamic covalent chemistry (DDCvC).
In this work,w er eport that 2-cyano-2-phenylpropanoic acid and its p-Cl, p-CH 3 and p-OCH 3 derivatives can be used as chemical fuels to control the geometry of the calix[4]arene scaffold in its cone conformation. It is shownt hat, under the action of the fuel, the cone calix[4]arenep latform assumes a" locked" shape with two opposite aromatic rings strongly convergent and the other two strongly divergent ("pinched cone" conformation). Only when the fuel is exhausted , the cone calix[4]arene scaffold returnstoi ts resting, "unlocked" shape. Remarkably,t he duration of the "locked" state can be controlled at will by varying the fuel structure or amount. Ak inetics tudy of the process shows that the consume of the fuel is catalyzed by the "unlocked"c alixarene that behaves as an autocatalyst for its own production. Am echanism is proposed fort he reaction of fuel consumption.
The host–guest
interaction of a 1,3,5-trisaminocalix[6]arene
receptor with
N
-methylisoquinolinium trifluoromethanesulfonate
(
K
ass
of 500 ± 30 M
–1
in CD
2
Cl
2
) can be dissipatively driven by
means of 2-cyano-2-(4′-chloro)phenylpropanoic acid used as
a convenient chemical fuel. When the fuel is added to a dichloromethane
solution containing the above complex, the host is induced to immediately
release the guest in the bulk solution. Consumption of the fuel allows
the guest to be re-uptaken by the host. The operation can be satisfactorily
reiterated with four subsequent additions of fuel, producing four
successive release–reuptake cycles. The percentage of the guest
temporarily released in the bulk solution by the host and the time
required for the reuptake process can be finely regulated by varying
the quantities of added fuel.
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