Azobis benzo-15-crown

IV. MOLECULAR PROBE FOR ISE MEMBRANE POTENTIALS BASED ON PHOTOSWITCHABLE AZOBIS(BENZO-15-CROWN-5) lONOPHORES [17]... 

If the photoequilibrium concentrations of the cis and trans isomers of the photoswitchable ionophore in the membrane bulk and their complexation stability constants for primary cations are known, the photoinduced change in the concentration of the complex cation in the membrane bulk can be estimated. If the same amount of change is assumed to occur for the concentration of the complex cation at the very surface of the membrane, the photoinduced change in the phase boundary potential may be correlated quantitatively to the amount of the primary cation permeated to or released from the membrane side of the interface under otherwise identical conditions. In such a manner, this type of photoswitchable ionophore may serve as a molecular probe to quantitatively correlate between the photoinduced changes in the phase boundary potential and the number of the primary cations permselectively extracted into the membrane side of the interface. Highly lipophilic derivatives of azobis(benzo-15-crown-5), 1 and 2, as well as reference compound 3 were used for this purpose (see Fig. 9 for the structures) [43]. Compared to azobenzene-modified crown ethers reported earlier [39 2], more distinct structural difference between the cis... 

When a membrane based on a derivative of azobis(benzo-15-crown-5) in contact with a solution of a primary cation is exposed to visible light, we assume that the iono-phore within the membrane phase is exclusively in the trans isomer and forms a 1 1 ionophore (I)-cation (M+) complex with a stability constant, trans. According to Eq. (10), the corresponding charge density at the membrane side of the interface, o is > can be expressed as... 

It is at present still difficult to correlate the absolute intensity of the SHG with the number of cationic complexes at the membrane surface. Therefore, a quantitative discussion, showing how the permselective uptake of primary cations forming SHG active complexes into the membrane side of the phase boundary corresponds to the increase in the membrane potential, is not possible yet. Lipophilic derivatives of photoswitchable azobis(benzo-15-crown-5) were recently shown as a molecular probe to determine photoinduced changes in the amount of the primary cation uptake into the membrane phase boundary in relation to the photoinduced EMF changes under otherwise identical conditions. 

Studies by Photoswitchable Azobis(benzo-15-crown-5) Derivatives as a Molecular Probe... 

For this puq)ose, the photoswitchable bis(crown ether)s 88 and 89 as well as the reference compound 90 have been synthesized. Compounds 88 and 89 are highly lipophilic derivatives of azobis(benzo-15-crown-5). The parent azobis crown ether was originally developed by Shinkai and its photoresponsive changes in complexation, extraction, and transport properties thoroughly examined. Compared to 87, more distinct structural difference between the cis and trans isomers can be expected for 88 and 89 because in the latter compounds the 15-crown-5 rings are directly attached to the azobenzene group. The photoequilibrium concentrations of the cis and trans forms and the photoinduced changes in the complexation constants for alkali metal ions are summarized in Table 7. 

Tohda, K. Yoshiyagawa, S. Kataoka. M. Odashima. K. Umezawa, Y. Photoswitchable azobis(benzo-15-crown-5) derivatives as a molecular probe for phase boundary potentials at ion-selective poly (vinyl chloride) liquid membranes. Anal. Chem. 1997. 69, 3360-3369. 

The condensation of 2,3-diaminobenzo-15-crown-5 2a with s-trans-chloroethanedial dioxime proceeds with the formation of the (15-crown-5)eno[g]quinoxaline-2(lfJ)-one oxime 11a, which when heated in absolute ethanol at 60 °C in the presence of C0CI2 for 4h results in 2,2 -azobis[(15-crown-5-eno[g]quinoxaline)] 12 (1986CB3870).The use of cyanogen-di-AT-oxide and (E,fr)-dichloroglyoxime instead of the s-twns-chloroethanedial dioxime in the reaction with 2,3-diamino-benzo-15-crown-5 2a and 12,13-diamino-4,7-bis(ferrocenylmethyl)-2,3,4,5,6,7,8,9-octahydrobenzo[k]-4,7-di-aza-l,10-dithiacyclo do decine (2b) makes it possible to synthesize the macrocyclic dioximes 11b,c (1986JCR(S)90, 2007JCOC2509). 

Shinkai, S., Yoshida, X, Manabe, O., and Fuchita, Y, Photoresponsive crown ethers. 20. Reversible photocontrol of association-dissociation equilibria between azobis (benzo-18-crown-6) and diammonium cation, /. Chem. Soc., Perkin Trans. 1, 1431, 1988, their earher papers and the references cited therein. 

---