A nitrobenzoxadiazole (NBD)-appended calix[4]arene conjugate (L) possessing a cyclic core formed by connecting the 1,3-positions at the lower rim has been designed. The L has been developed as a receptor for the selective recognition of biologically and ecologically relevant trivalent metal ions, viz., Cr 3+ , Fe 3+ , and Al 3+ . The interaction and region of binding of these metal ions by the receptor L have been explored by isothermal titration calorimetry, spectroscopy, microscopy, and density functional theory (DFT) computational studies. The probe L itself exhibits weak fluorescence emission intensity, and the quantum yield is enhanced by ∼4-fold upon addition of the M 3+ ion due to the chelate enhanced fluorescence effect. Fluorescence enhancement also takes place in L when it interacts with M 3+ even in the solid state and in the MCF7 cancer cells. The binding constant (K b ) for M 3+ by L is ∼10 4 M −1 , supporting that these ions bind to L with moderate strength. The detection limit for all the three metal ions is as low as 4−5 μM. The 1 H NMR data reflects the region of binding of the M 3+ ion to L. The binding is further supported by DFT studies where the space filling structures evidently shows the binding core in L, and the M 3+ ion is buried in this core. As a result of this, the microscopy features are almost the same for L and {L + M 3+ }. The reversible utility of the sensor has been achieved by the addition of H 2 PO 4 − . Based on the input−output information, a molecular logic circuit (INHIBIT logic gate) has been built, which will provide an electronic basis for designing a memory device by the concerned experts.

Seed powder of vegetable drum stick (Moringa oleifera) is a household known material for the coagulation of impurities from water. We find from our lab experiments that this material indeed removes toxic inorganic heavy metal ions and organic dyes; however, the latter can be degraded in the presence of H 2 O 2 under Cu 2+ as catalyst. To understand the details of the treatment of water that is taking place by this seed powder, a simple inorganic−protein nanoflower system was developed using copper phosphate (CuP), and a low molecular weight, cationic, and coagulant protein of Moringa oleifera (MOCP), to result in the nanoflowers (NFs), CuPNF_MOCP. The CuPNF_MOCPs were synthesized at different ratios of inorganic versus protein components and characterized by spectroscopy and microscopy techniques. Both the time-and the protein concentration-dependent flower growth showed complete flower morphology within 24 h with tightly packed petals having smooth surface upon increasing the protein concentration as noticed from SEM. The anionic dyes were adsorbed more preferentially over the cationic ones by these NFs, due to the cationic charge present on MOCP, as understood by studying six different dyes of which three are anionic and three are cationic in nature. The dyes are oxidatively degraded by a Fenton-type mechanism that takes place between Cu 2+ present in the NFs and added H 2 O 2 with the generation of • OH radicals. These NFs also adsorb heavy metal ions, such as Pb 2+ , Cd 2+ , and Hg 2+ , with high selectivity of >99% for Pb 2+ . Upon adsorption of Pb 2+ , the surface of the NFs revealed needle-shaped structures at petal edges in their micrographs, where the needles were confirmed by elemental mapping, powder XRD, and energy dispersive X-ray spectroscopy. Thus, the water purification routinely carried out by the households using the drum stick seed powder is essentially due to the coagulant protein present in it. This has been demonstrated in the form of CuPNF_MOCP for scavenging toxic heavy metal ions and organic dyes from water sources. Hence, this study provides a lead for the purification of water in a sustainable manner.

A triazole-derivatized, spiro-indoline-linked, 1,3-di-derivative of calix[4]arene ( L ) has been synthesized to take advantage of its ion-binding capability in the ring-open form. Indeed, the spiro-indoline moiety is well known for its photochromic, acidochromic, and metallochromic properties. Therefore, the L has been explored for Cu 2+ binding, cell imaging, and anticancer activity of the corresponding complex since Cu 2+ complexes are known for such activity. The conversion from the closed to open form of L is expedited by light or proton, while the metal ion can open as well as stabilize it. The open form of L showed binding of Cu 2+ ratiometrically as demonstrated by absorption and fluorescence spectroscopy. This leads to the formation of 1:1 complex with a binding constant of (6.9 ± 2.3) × 10 5 M –1 , with the lowest detection limit being 1.9 nM. In the complex, the Cu 2+ is bound by two triazole-N and two phenolic-O groups resulting in a distorted tetrahedral coordination core of CuN 2 O 2 as demonstrated based on density functional theory studies. To form such coordination core, the arms underwent considerable changes in some of the dihedral angles. The binding of Cu 2+ to L induces self-assembly of L by varying from simple particles to rodlike structures when bound to Cu 2+ . The on–off fluorescence intensity of L and its Cu 2+ -bound species are responsible for imaging cancer cells. The L shows red fluorescence in MDA-MB-231 cancer cells by targeting mitochondria as proved based on the colocalization study carried out using MitoTracker Green. While the L alone is nontoxic to cancer cells, the presence of Cu 2+ brings cell death to an extent of 90% with an IC 50 value of 165 nM by bringing a substantial quench in the fluorescence of L . A shift of population from G 0 /G 1 and G 2 M phases to the Sub-G 1 phase was observed as the concentration of the complex was increased, indicating cell death as studied by fluorescence-activated cell sorting. Thus, the present work clearly proved that a calix[4]arene functionalized at the lower rim with spiro-indoline moieities when complexed with Cu 2+ acts as an efficient anticancer agent and is capable of imaging cancer cells.

A lower rim dansyl appended calix[4]­arene, DanC4A has been synthesized and characterized. DanC4A is a promising sensor for selective detection of toxic metal ions, Hg2+, among the twelve separate metal ions studied. The fluorescence titration of DanC4A with Hg2+ shows approximately 80% quenching. Competitive metal ion studies suggest the selective binding of Hg2+ to DanC4A. The biocompatibility of DanC4A has been confirmed by an MTT assay performed using HeLa cells. Confocal microscopy and fluorescence microscopy studies suggest that DanC4A exhibits strong green fluorescence in HeLa cells, and the same is quenched as the concentration of Hg2+ increases in the cells. Apart from sensing, the main concern is the removal of Hg2+ from water and this is not possible with the direct use of DanC4A due to its solubility. Therefore, DanC4A has been embedded into a zeolitic imidazolate framework (ZIF8) to result in an inorganic–organic hybrid nanomaterial, DanC4A_ZIF8_MOFs, by an in situ reaction. Approximately 95% of the Hg2+ ions were removed from water by using the hybrid material, viz., DanC4A_ZIF8_MOFs. Thus, DanC4A is not only a superior sensor for Hg2+ in solution and in mammalian cells but can be converted into an organic–inorganic hybrid material, DanC4A_ZIF8_MOFs, for efficient removal of Hg2+ from water.

Protein – inorganic hybrids with tunable morphology offer excellent applications in several fields due to their versatile characteristics. Here in, we report a new hybrid material prepared using commercially available...