Light‐Modulated Self‐Blockage of a Urea Binding Site in a Stiff‐Stilbene Based Anion Receptor

Abstract

Anion binding to a receptor based on stiff‐stilbene, which is equipped with a urea hydrogen bond donating group and a phosphate or phosphinate hydrogen bond accepting group, can be controlled by light. In one photoaddressable state (E isomer) the urea binding site is available for binding, while in the other (Z isomer) it is blocked because of an intramolecular interaction with its hydrogen bond accepting motif. This intramolecular interaction is supported by DFT calculations and 1H NMR titrations reveal a significantly lower anion binding strength for the state in which anion binding is blocked. Furthermore, the molecular switching process has been studied in detail by UV/Vis and NMR spectroscopy. The presented approach opens up new opportunities toward the development of photoresponsive anion receptors.

Stiff‐Stilbene Photoswitches: From Fundamental Studies to Emergent Applications

“…In an attempt to fully block the binding site of a stiff‐stilbene based receptor in one of its photoaddressable states, we attached a urea hydrogen bond donating group and either a phosphate or phosphinate hydrogen bond accepting group (receptor 21 and 22 in Scheme c) . Irradiation of E ‐ 21 and E ‐ 22 with 340 nm light in [D 6 ]DMSO led to PSS mixtures containing the E and Z isomer in a 47:53 and a 42:58 ratio, respectively.…”

“…However, full synthetic details and characterization have not been reported for these mixed McMurry reactions. Our group recently described the mixed McMurry coupling of 6‐bromoindanone with TBS‐protected 6‐hydroxyindanone . When the reaction was carried out in a 1:1 stoichiometry, the homocoupled product of 6‐bromoindanone, homocoupled TBS‐protected 6‐hydroxyindanone, and the desired heterocoupled product were obtained in a 10:34:27 ratio.…”

“…However,full synthetic details and characterization have not been reported for these mixed McMurry reactions.Our group recently described the mixed McMurry coupling of 6-bromoindanone with TBS-protected 6-hydroxyindanone. [29] When the reaction was carried out in a1 :1 stoichiometry,t he homocoupled product of 6-bromoindanone,h omocoupled TBS-protected 6-hydroxyindanone,a nd the desired heterocoupled product were obtained in a1 0:34:27 ratio.O ther successful mixed McMurry couplings were recently reported by the groups of Boulatov [30] and Wu. [31] In an attempt to synthesize dibromo-functionalized tetramethyl-stiff-stilbene 12,t he group of Shinmyozu used McMurry conditions,b ut the reaction failed.…”

“…In an attempt to fully block the binding site of as tiffstilbene based receptor in one of its photoaddressable states, we attached aurea hydrogen bond donating group and either ap hosphate or phosphinate hydrogen bond accepting group (receptor 21 and 22 in Scheme 3c). [29] Irradiation of E-21 and E-22 with 340 nm light in [D 6 ]DMSO led to PSS mixtures containing the E and Z isomer in a4 7:53 and a4 2:58 ratio, respectively.T he reverse process was achieved by using 385 nm light, resulting in aPSS ratio (E/Z)of94:6f or 21 and 93:7 for 22.Itwas envisioned that upon E!Z isomerization, the binding affinity would decrease significantly,a si nt he Z isomer the urea binding site would be blocked by intramolecular hydrogen bonding.B inding studies were performed with dihydrogen phosphate,a cetate and chloride in [D 6 ]DMSO/0.5 %H 2 O. In general, binding to the E isomer was found to be stronger,however, the differences in binding affinity between the E and Z isomers were not as large as expected.…”

Controlled Diffusion of Photoswitchable Receptors by Binding Anti-electrostatic Hydrogen-Bonded Phosphate Oligomers

“…Recently, some of us developed the first photoswitchable receptors exhibiting strong dihydrogen phosphate binding. 12 These receptors were based on molecular motor and stiff-stilbene scaffolds 13 containing urea anion-binding motifs. These hosts could be converted from a weakly guest-binding E to a strongly binding Z form using near-UV light ( Figure 1 a).…”