Highly Efficient Cauliflower-like Palladium-Loaded Porous MOF as a Robust Material for the Degradation of Organic Dyes.

A series of porous MOF materials, viz., Pdx@IRMOF-9 (x = 2, 5, and 10%) were synthesized by loading varying concentrations of Pd(II) on IRMOF-9. The synthesized MOF materials were characterized by ltravioletisible (UV-Vis) spectroscopy, Fourier transform Infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), Brunauer-Emmett-Teller (BET), and scanning electron microscopy (SEM) analyses. UV, FT-IR, and PXRD data of Pd(II)@IRMOF-9 were found to be in line with those of IRMOF-9, which suggests that the structure of the IRMOF-9 remained intact upon Pd(II) loading. Surface morphology of IRMOF-9 showed sheet-like structures, and upon incorporation of Pd(II) to IRMOF-9, porous cauliflower-shaped MOFs were obtained. The SEM area mapping of Pd10%@IRMOF-9 confirmed the homogeneous dispersion of Pd(II) on IRMOF-9. BET measurements suggested an increase in the surface area as well as pore size upon incorporation of Pd(II) on IRMOF-9. Due to high porosity and high petal density, Pd10%@IRMOF-9 demonstrated degradation of seven organic dyes, namely, orange G, methylene blue, methyl orange, congo red , methyl red, rhodamine 6G, and neutral red. It showed excellent results with >90% dye degradation efficiency in case of cationic, anionic as well as neutral dyes. Degradation of organic dyes followed the pseudo-first-order kinetics. Kinetic parameters, KM and Vmax, were calculated using the double reciprocal Lineweaver-Burk plot and were found to be 13.2 µM and 26.68 × 10-8 M min-1, respectively. Recyclability studies of heterogeneous Pd10%@IRMOF-9 demonstrated the degradation of CR dye for five consecutive cycles without significant loss of its catalytic activity. Herein, a robust and efficient material for the degradation of organic dyes has been developed and demonstrated.

Dog-bone shaped gold nanoparticle-mediated chemo-photothermal therapy impairs the powerhouse to trigger apoptosis in cancer cells.

The mitochondrion has emerged as one of the uncommon targets in cancer therapeutics due to its involvement in cancer generation and progression. Consequently, nanoplatform mediated delivery of anti-cancer drugs into the mitochondria of cancer tissues demonstrated immense potential in cancer treatment. In the last couple of decades, gold nanoparticles have gained incredible attention in biomedical applications due to their easy synthesis, size-shape tenability, optical properties and outstanding photothermal ability. However, application of gold nanoparticles to target mitochondria to induce the chemo-photothermal effect in cancer has remained in its infancy. To address this, herein we have engineered dog-bone shaped gold nanoparticles (Mito-AuDB-NPs) comprising cisplatin and 10-hydroxycamptothecin as chemotherapeutic drugs along with the triphenylphosphonium (TPP) cation for mitochondria homing. Mito-AuDB-NPs exhibited a remarkable increase in temperature till 56 °C upon 18 min irradiation with 740 nm NIR LED light with a power density of 0.9 W cm-2. These Mito-AuDB-NPs successfully homed into the mitochondria of HeLa cervical cancer cells within 1 h and induced mitochondrial outer membrane permeabilization (MOMP) under the chemo-photothermal effect leading to the generation of reactive oxygen species (ROS). This Mito-AuDB-NP-mediated mitochondrial damage triggered programmed cell death (apoptosis) by decreasing the expression of anti-apoptotic Bcl-2/Bcl-xl and increasing the expression of pro-apoptotic BAX followed by caspase-3 cleavage towards extraordinary HeLa cell killing in a synergistic manner without showing toxicity towards non-cancerous RPE-1 human epithelial retinal pigment cells. We anticipate that this dog-bone shaped gold nanoparticle-mediated chemo-photothermal impairment of mitochondria in the cancer cells can open a new direction towards organelle targeted cancer therapy.

Coumarin-Calix[4]arene Conjugate-Anchored SiO2 Nanoparticles as an Ultrasensor Material for Fe3+ to Work in Water, in Serum, and in Biological Cells.

A coumarin-appended calixarene derivative ( CouC4A ) and a hybrid material generated by covalently linking this onto a silica surface ( CouC4A@SiO 2 ) were synthesized and were characterized by various analytical, spectroscopy, and microscopy methods. Both these materials are capable of sensing Fe3+ with greater sensitivity and selectivity. The sensitivity is enhanced by 30,000 fold on going from a simple solution phase to the silica surface with the limit of Fe3+ detection being 1.75 ± 0.4 pM when CouC4A@SiO 2 is used, and the sensing is partially reversible with phosphates, while it is completely reversible with adenosine 5'-triphosphate (ATP). While the calix precursor, CouC4A , has a limitation to work in water, anchoring this onto SiO2 endowed it with the benefit of its use in water as well as in buffer and thereby extends its application toward Fe3+ sensing even in the biorelevant medium such as fetal bovine serum and human serum. The hybrid material is biocompatible and shows ∼90% cell viability in the case of MDA-MB231 and 3T3 cell lines. CouC4A@SiO 2 functions as a reversible sensor for Fe3+ with the use of ATP in vitro as well as in biological cells. Thus, the inorganic-organic hybrid material, such as, CouC4A@SiO 2 , is an indispensable material for sensitive and selective detection of Fe3+ in a picomolar range in solution and in nanomolar to micromolar range in biorelevant fluids and biological cells, respectively.

Calixarene-Assisted Pd Nanoparticles in Organic Transformations: Synthesis, Characterization, and Catalytic Applications in Water for C-C Coupling and for the Reduction of Nitroaromatics and Organic Dyes.

A new type of ternary hybrid, Pd@MCM-Calixox, 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-Calixox has been established. The hybrid, Pd@MCM-Calixox, was characterized by different techniques to support the formation of well-dispersed Pd(0) NPs of 12 ± 2 nm size. The catalyst, Pd@MCM-Calixox, 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-Calixox 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.

Fluorescent Lower Rim 1,3-Dibenzooxadiazole Conjugate of Calix[4]arene in Selective Sensing of Fluoride in Solution and in Biological Cells Using Confocal Microscopy.

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 1H 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 Ca2+, 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.

Silica-Calix Hybrid Composite of Allyl Calix[4]arene Covalently Linked to MCM-41 Nanoparticles for Sustained Release of Doxorubicin into Cancer Cells.

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.

Physicochemical and Ion-Sensing Properties of Benzofurazan-Appended Calix[4]arene in Solution and on Gold Nanoparticles: Spectroscopy, Microscopy, and DFT Computations in Support of the Species of Recognition.

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 1H NMR, 13C 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, Hg2+ exhibited greater changes in these spectra, whereas Cu2+ showed only significant changes and all other ions showed no change in the spectral features. Although the Hg2+ 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 (AuNPL'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 AuNPL'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 AuNPL's exhibit greater selectivity and enhanced sensitivity for Hg2+ 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 Hg2+ to either L or AuNPL showed fluorescence quenching. The reversible recognition of Hg2+ by L was demonstrated by titrating L or AuNPL with Hg2+ followed by tetra-butyl ammonium iodide for several cycles. The structural features of Hg2+-bound species were demonstrated by density functional theory computations and were supported by the XPS data. The Hg2+ induces aggregated fibrillar morphology into supramolecular L, as demonstrated by microscopy when Hg2+ was added either to L or to AuNPL, supporting aggregation-caused quenching.