Cooperative Binding of Metal Cations to a Spiropyran‐Conjugated Calix[4]arene

Abstract

Cooperative binding occurs frequently in biological systems, but is less exploited in synthetic receptor molecules. We synthesized a bis(spiropyran)‐conjugated calix[4]arene (bSPTC) through a 1,2,3‐triazole linker and found cooperativity in bindings of a series of divalent metal cations (Ca2+, Mg2+, Cd2+, Co2+, Fe2+, Hg2+, Ni2+, and Zn2+). UV‐vis absorption spectroscopy and principle component analysis were used to differentiate the recognized metal cations. The binding stoichiometry was determined by various continuation methods, which indicated that bSPTC has two binding ratios, 1:1 for Zn2+ and 1:2 for all other metal cations. Importantly, positive cooperativity was suggested for the 1:2 stoichiometry of bSPTC to Mg2+ ions from the sigmoidal saturation curve and Hill equation analysis. Density functional theory (DFT) calculations imply that the first binding of Mg2+ to one spiropyran destabilizes the second spiropyran, which facilitates binding of a second Mg2+.

Ratiometric Cu2+ Binding, Cell Imaging, Mitochondrial Targeting, and Anticancer Activity with Nanomolar IC50 by Spiro-Indoline-Conjugated Calix[4]arene

“…Each arm of the lower rim of L contributes one phenolic-O and one triazole-N for coordination. Such coordination features were also noted for Mg 2+ complex of triazole-linked nitro-functionalized spiro-pyran-derivatized calix[4]­arene in the literature . The complexation energy for the formation of the complex of Cu 2+ of L is −518 kcal/mol.…”

“…Although there are a number of spiro-indoline derivatives being reported in the literature for sensing Zn 2+ and Cu 2+ by both fluorescence enhancement and quenching, none of these is based on the calixarene platform. − All of these non-calixarene-based ones showed micro- to submicromolar level of detection, and few of these were used for cell imaging. However, to our knowledge, there are only two spiro-indoline-linked 1,3-derivatized calix[4]­arenes known in the literature, one of which is involved in sensing Mg 2+ and the other is involved in selective sensing of Eu 3+ . ,, The sensing features of all such molecular systems are listed in Table S4 in the Supporting Information.…”

“…Although there are a number of spiro-indoline derivatives being reported in the literature for sensing Zn 2+ and Cu 2+ by both fluorescence enhancement and quenching, none of these is based on the calixarene platform. − All of these non-calixarene-based ones showed micro- to submicromolar level of detection, and few of these were used for cell imaging. However, to our knowledge, there are only two spiro-indoline-linked 1,3-derivatized calix[4]­arenes known in the literature, one of which is involved in sensing Mg 2+ and the other is involved in selective sensing of Eu 3+ . ,, The sensing features of all such molecular systems are listed in Table S4 in the Supporting Information. The importance of the current probe is due to (i) the derivatization being on the calix[4]­arene platform, which is scarce in the literature, (ii) its nanomolar sensing for Cu 2+ , (iii) its mitochondrial targeting ability, and (iv) its nanomolar IC 50 value (165 nM) for MDA-MB231 cancer cells.…”

Hydrogen‐Bonded Dimeric Capsules with Appended Spiropyran Units: Towards Controlled Cargo Release

“…Specifically, SP units were incorporated in macrocyclic receptors such as crown ethers, [27,28] cyclodextrins [29] and calix [4] arenes. [30,31,32] To the best of our knowledge, SP units have not been incorporated into the molecular components of self-assembled containers. We envisaged that the SP!MC (or SP!MCH + ) isomerization process of the switching units might be coupled to the assembly/disassembly of the container and the uptake and release of its cargo.…”

“…Specifically, SP units were incorporated in macrocyclic receptors such as crown ethers,[ 27 , 28 ] cyclodextrins [29] and calix[4]arenes. [ 30 , 31 , 32 ]…”