Self-aggregating calix[4]arenes carrying four DOTA ligands on the upper rim for stable complexation of paramagnetic GdIII-ions have already been proposed as MRI probes. In this work, we investigate the luminescence properties of TbIII-DOTA-calix[4]arene-4OPr containing four propyl-groups and compare them with those of the analog substituted with a phthalimide chromophore (TbIII-DOTA-calix[4]arene-3OPr-OPhth). We show that, given its four aromatic rings, the calix[4]arene core acts as an effective sensitizer of Tb-centered luminescence. Substituents on the lower rim can modulate the aggregation behavior, which in turn determines the luminescence properties of the compounds. In solid state, the quantum yield of the phthalimide derivative is almost three times as high as that of the propyl-functionalized analog demonstrating a beneficial role of the chromophore on Tb-luminescence. In solution, however, the effect of the phthalimide group vanishes, which we attribute to the large distance between the chromophore and the lanthanide, situated on the opposite rims of the calix[4]arene. Both quantum yields and luminescence lifetimes show clear concentration dependence in solution, related to the strong impact of aggregation on the luminescence behavior. We also evidence the variability in the values of the critical micelle concentration depending on the experimental technique. Such luminescent calix[4]arene platforms accommodating stable lanthanide complexes can be considered valuable building blocks for the design of dual MR/optical imaging probes.

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Luminescence Properties of Self-Aggregating TbIII-DOTA-Functionalized Calix[4]arenes.

Controllable synthesis of an intercalated ZIF-67/EG structure for the detection of ultratrace Cd2+, Cu2+, Hg2+ and Pb2+ ions

The hydrothermal reaction of Ln(NO3)3·6H2O with 2,3′-oxybis(benzoic acid) (2,3′-H2oba) and 1,10-phenanthroline (phen) afforded the metal–organic frameworks (Ln-MOFs), [Ln2(2,3′-oba)3(phen)2]n (Ln = La 1, Eu 2, Gd 3, and Tb 4). 1 possesses a 3D network with [La1O7N2] and [La2O7N2] polyhedra, and 2–4 exhibit similar 3D networks containing [Ln1O7N2] and [Ln2O6N2] polyhedra. These complexes are thermally stable in air and have high stability in water in a wide pH range (acidic pH = 3 and alkaline pH = 13 solutions). Notably, MOFs 2 and 4 display bright red and green emission with the high fluorescence quantum yields of 75.57% and 41.86%, respectively. The highly luminescent chemically stable Eu-MOF shows multi-responsive luminescence sensing functions to detect Fe3+, Cr6+, and metronidazole (MDZ) in aqueous medium even in acidic conditions (pH = 3) via a fluorescence quenching mechanism. Excess Fe3+, Cr6+, and antibiotics can cause environmental pollution and serious diseases; thus, their detection is very important. In addition, one of the important advantages of Eu-MOF is that this complex can be excited at a long excitation wavelength (352 nm), which is in the near-visible radiation region of 350 nm < λex < 420 nm, and is an important requirement for its applications.

Construction of metal–organic frameworks (MOFs) and highly luminescent Eu(III)-MOF for the detection of inorganic ions and antibiotics in aqueous medium

This review (with 99 refs.) summarizes the progress that has been made in colorimetric (i.e. spectrophotometric) determination of organophosphate pesticides (OPPs) using gold and silver nanoparticles (NPs). Following an introduction into the field, a first large section covers the types and functions of organophosphate pesticides. Methods for colorimetric (spectrophotometric) measurements including RGB techniques are discussed next. A further section covers the characteristic features of gold and silver-based NPs. Syntheses and modifications of metal NPs are covered in section 5. This is followed by overviews on enzyme inhibition-based assays, aptamer-based assays and chemical (non-enzymatic) assays, and a discussion of specific features of colorimetric assays. Several Tables are presented that give an overview on the wealth of methods and materials. A concluding section addresses current challenges and discusses potential future trends and opportunities.

A review on colorimetric methods for determination of organophosphate pesticides using gold and silver nanoparticles

A novel unsymmetrical bis(salamo)-based sensor H5L has been firstly synthesized, and characterized by means of elemental analyses, fourier transform infrared spectroscopy and ESI-mass spectrometry, 1HNMR and Gaussian-09 software program. The RGB analysis is made by Color Assist software. The sensor has good selectivity and sensitivity for Cu2+ ions, which is due to the paramagnetism of Cu2+ ions. When Cu2+ ions were added to the sensor H5L solution, the color was changed from light yellow to dark brown. The experimental results of solvent effect, pH range and aqueous system show that the sensor has high efficiency in different organic solvents and wide pH ranges. In addition, L–Cu2+ complex can be used as a new sensor to test Cys and GSH.

A novel unsymmetric bis(salamo)-based chemosensor for detecting Cu2+ and continuous recognition of amino acids

Calixarenes are considered as third generation supramolecules with hollow cavity-like architecture whereas nanoparticles are small entities with dimensions in the nanoscale. Many exciting achievements are seen when the calix system merges with nanoparticles which produces many fascinating facets in all fields of contemporary chemistry. The properties of nanoparticles which are tuned by calixarenes find applications in sensing, catalysis, molecular recognition, etc. Here, we have reviewed the chemistry of calix-based nanoparticles, and emphasis is laid on the modified, reducing, templated and stabilizing roles of calixarenes. This review covers the research being carried out in the domain of calix protected metal nanoparticles during last 18 years under the canopy of important 109 references. This article contains 58 figures which include 81 easy to understand structures. Calix-protected nanoparticles have enthralled researchers in the field of nanoscience with a tremendous growth in its applications, which heralds much promise to become in future a separate area of research.

Calix-Based Nanoparticles: A Review

In the present study, the interaction of the calix[4]resorcinarene polyhydrazide (CPH) capped nanoparticles (CPH-AuNps) and (CPH-AgNps) with different amino acids like arginine, aspartic acid, glutamic acid, glycine, leucine, methionine, histidine, tryptophan and cysteine has been studied by using UV–vis and fluorescence spectroscopy. CPH-AuNps and CPH-AgNps were found to be the selective and sensitive fluorescent probe for l -DOPA and histidine, respectively. The minimum detectable limit for both l -DOPA and histidine was found at 10 nM by a facile way of fluorescence quenching i.e. by a turn off mechanism. CPH-AuNps and CPH-AgNps have also been studied for their antioxidant activity and interaction with DNA by UV–vis spectrophotometry. Furthermore, electrophoresis technique confirmed the interaction of ethidium bromide (EtBr) intercalated CT-DNA and S-DNA with CPH-AuNps and CPH-AgNps, respectively. The simplicity, sensitivity and specificity for the detection of amino acids by the CPH-AuNps and CPH-AgNps, indicates that the synthesized nanoparticles can be used as nano biosensor, with a potential prospect in the biomedical analysis.

A comparative study: Metal nanoparticles as fluorescent sensors for biomolecules and their biomedical application

Herein, a fluorescent oxacalix[4]arene-based receptor, DAQTNOC(5,17-di(N-(9,10-dioxo-9,10-dihydroanthracen-1-yl)acetamide) tetranitrooxacalix[4]arene), was described for the specific recognition of N-methyl-p-nitroaniline (MNA). Among the array of explosives, DAQTNOC shows selective behaviour for MNA in the absorption and as well as emission spectra. The binding constants, stoichiometry, quantum yields, and fluorescence quenching were determined to elucidate the inclusion behaviour. Furthermore, computational insights were rendered for studying the stability and spectroscopic analysis of the inclusion complex using docking, molecular dynamics simulations, and density functional theory (DFT) along with time-dependent density functional theory (TD-DFT). The calculations considerably complement the findings and elucidate the structural geometry and mode of interactions in supramolecular complexation. Herein, we observed that DAQTNOC was selectively stabilized by van der Waals forces and hydrophobic contacts with MNA to generate a low-energy complex. These findings are of wide interest, especially because MNA is a well-known insensitive munition and has been detected for the first time via an oxacalixarenes platform.

A turn-off fluorescence sensor for insensitive munition using anthraquinone-appended oxacalix[4]arene and its computational studies

Quinoline appended oxacalixarene as turn-off fluorescent probe for the selective and sensitive determination of Cu 2+ ions: A combined experimental and DFT study

Newly synthesized Au nanoparticles (AuNPs) capped by calix[4]pyrrole tetrahydrazide (CPTH) has been explored for the colorimetric and fluorimetric detection of Pb(II) ions. The molecular modeling studies reveal the surface mediated properties of CPTH around AuNPs. It is observed that reduction of Au(III) to Au(0) occurs due to the presence of hydrazide groups of CPTH and charge transfer preferably through N atoms and carbonyl group. These interactions further govern the stability of the CPTH-AuNPs. The optical sensing of Pb(II) was carried out in water and the linear range of detection falls between 10 nM and 1 μM concentration range. Moreover, a concomitant pink-to-violet color change is observed providing a useful optical method of detecting Pb(II) in water. The mechanistic insights for the sensing of Pb(II) is based on the overarching hypothesis that Pb(II)ions disturbs the non-covalent interactions of the capping CPTH ligand around the Au° particles causing aggregation of CPTH-AuNPs. The aggregation of CPTH-AuNPs has been elucidated by TEM and DLS experiments. Also, the plausible binding behavior of CPTH-AuNPs with Pb(II) due to hydrogen bonding interactions through –NH groups is discussed. CPTH-AuNPs have also shown their utility for analysis of Pb(II) in industrial waste water and human serum samples. The ability of CPTH-AuNPs for its in vitro anti-oxidant activity and radical scavenging efficiencies has been studied. Thus, the present study suggests notable potential of supramolecular functionalized nanoparticles as a promising chemosensor for toxic ions and a beneficial tool for biomedical applications.

Anita Kongor

Papers

Calix-Based Nanoparticles: A Review

A comparative study: Metal nanoparticles as fluorescent sensors for biomolecules and their biomedical application

A turn-off fluorescence sensor for insensitive munition using anthraquinone-appended oxacalix[4]arene and its computational studies

Quinoline appended oxacalixarene as turn-off fluorescent probe for the selective and sensitive determination of Cu 2+ ions: A combined experimental and DFT study

Synthesis and modeling of calix[4]pyrrole wrapped Au nanoprobe for specific detection of Pb(II): Antioxidant and radical scavenging efficiencies