An inorganic–organic hybrid material, MCM-allylCalix, was synthesized by covalent modification of an MCM-41 surface with a tetra-allyl calixarene conjugate. The synthesized hybrid was characterized by 13C and 29Si MAS–NMR, Fourier transform infrared (FT-IR), Brunauer–Emmett–Teller surface area, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) analyses. The application of this MCM-allylCalix hybrid has been demonstrated for loading and in vitro release of doxorubicin (Dox) in phosphate-buffered saline (PBS) buffer as well as in the cancer cells, viz., MCF7, HeLa, and MDA-MB231. The Dox-loaded hybrid, MCM-allylCalix-Dox, was characterized by TEM, FT-IR, TGA, N2 sorption, diffuse refectance spectroscopy–UV, and fluorescence microscopy to confirm the presence of the drug. The release study of the drug from MCM-allylCalix-Dox was carried out in PBS buffer at pH 5 and 7.4. The results showed ∼140% increase in the release of Dox at pH 5 compared to that at pH 7.4 in 144 h, suggesting a pH-triggered release of the drug. MCM-allylCalix-Dox releases a greater amount of Dox compared to that released from unmodified MCM-Dox. Cytotoxicity studies suggested that MCM-allylCalix-Dox exhibits anticancer activity that is dependent on the nature of the cell. The Dox-loaded hybrid shows more cytotoxicity for MCF7 compared to that for the HeLa and MDA-MB231 cells. This was further supported by ∼120% more internalization of Dox into MCF7 cells compared to that in the other two cell lines. Both fluorescence microscopy and fluorescence-activated cell sorting studies suggested concentration-dependent internalization of Dox into the MCF7 and HeLa cells. The results suggested that the inorganic–organic hybrid can be useful in sustained drug delivery into cancer cells.

p- tert-Butyl-calix[4]arene was derivatized by integrating a benzooxadiazole fluorescent tag into its 1,3-arms at the lower rim to result in L and was characterized. L was titrated with 17 anions in THF and found selective for F ions with lowest detection limit of 109 ppb. L and F form a 1:1 complex. L self-assembles in THF to result in sheet like structures which converts into smaller spherical particles upon addition of F. The site of interaction of F was deduced based on H NMR spectroscopy and the coordination features by density functional theory (DFT) computations wherein six noncovalent interactions of the type X-H···F (where X = O, N, or C) were noticed. The sensing of F is reversible when titrated with Ca, and the reversibility was demonstrated for 10 cycles without losing sensitivity. The study has been extended to the biological cells using fluorescence and confocal microscopy. While L shows strong fluorescence in HeLa cells, increasing concentrations of F exhibited greater fluorescence quenching. Thus, L acts as a good sensor for F in solution as well as in biological cells, a rare and unique combination for a calixarene conjugate to exhibit such sensing behavior in dual media.

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A new type of ternary hybrid, Pd@MCM-Calix ox , based on mesoporous silica, calixarene conjugate, and Pd(0) nanoparticles (NPs) was synthesized by sacrificial oxidation of allylic calixarene conjugate eventually functionalized with mesoporous silica without using any external reducing agent. The role of the calix conjugate in the formation of Pd@MCM-Calix ox has been established. The hybrid, Pd@MCM-Calix ox , was characterized by different techniques to support the formation of well-dispersed Pd(0) NPs of 12 ± 2 nm size. The catalyst, Pd@MCM-Calix ox , has been proven to be a resourceful one in water in three different types of reactions, namely, Suzuki C–C cross coupling, reduction of both hydrophilic and hydrophobic nitroaromatic compounds, and reduction and degradation of cationic, anionic, and neutral organic dyes. The catalyst exhibited higher turnover frequencies for all these transformations even when a very low concentration of Pd-based catalyst was used. The Pd@MCM-Calix ox hybrid catalyst can be recycled several times without experiencing any significant loss in the activity. Also, the regenerated catalyst showed retention of well-spread Pd(0) species even after several catalytic cycles. The tetraallyl calixarene, allylCalix, conjugate acts as a reducing agent, also controls the size, and yields the well-dispersed Pd(0) NPs. The calix conjugate further provides a hydrophobic core in assisting the diffusion of hydrophobic substrates toward catalytic sites.

A calix[4]arene conjugate ( L ) functionalized at the lower rim with a benzofurazan fluorophore (NBD) and at the upper rim with a thioether moiety has been synthesized and characterized by 1 H NMR, 13 C NMR, and mass spectrometry techniques. Both the absorption and emission spectral data for L in different solvents exhibited progressive changes with an increase in polarity. Ion recognition studies were performed by absorption and fluorescence spectroscopy using 10 different metal ions. Among these, Hg 2+ exhibited greater changes in these spectra, whereas Cu 2+ showed only significant changes and all other ions showed no change in the spectral features. Although the Hg 2+ has dominant influence on the spectral features and provides a detection limit of 56.0 ± 0.6 ppb, the selectivity was hampered because of the presence of the derivatizations present on both the rims of L for ion interaction in solution. Therefore, L was immobilized onto gold nanoparticles (AuNP L ’s) so that the upper rim derivatizations anchor onto the gold surface through Au–S interactions, and this leaves out only the lower rim NBD derivatization for interaction with ions selectively. The AuNP L ’s were characterized by transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses. The surface characteristics were analyzed by contact angle measurements. The AuNP L ’s exhibit greater selectivity and enhanced sensitivity for Hg 2+ ions with a lowest detection limit of 48.0 ± 0.8 ppb. The immobilization of L onto AuNPs was reflected in the corresponding fluorescence lifetime values, and the addition of Hg 2+ to either L or AuNP L showed fluorescence quenching. The reversible recognition of Hg 2+ by L was demonstrated by titrating L or AuNP L with Hg 2+ followed by tetra-butyl ammonium iodide for several cycles. The structural features of Hg 2+ -bound species were demonstrated by density functional theory computations and were supported by the XPS data. The Hg 2+ induces aggregated fibrillar morphology into supramolecular L , as demonstrated by microscopy when Hg 2+ was added either to L or to AuNP L , supporting aggregation-caused quenching.