Vijaya Kumar Hinge

Imino-phenolic-pyridyl conjugates of calix[4]arene (L1 and L2) as primary fluorescence switch-on sensors for Zn2+ in solution and in HeLa cells and the recognition of pyrophosphate and ATP by [ZnL2].

Pyridyl-based triazole-linked calix[4]arene conjugates, viz. L(1) and L(2), were synthesized and characterized. These two conjugates were shown to be selective and sensitive for Zn(2+) among the 12 metal ions studied in HEPES buffer medium by fluorescence, absorption, and visual color change with the detection limit of ~31 and ~112 ppb, respectively, by L(1) and L(2). Moreover, the utility of the conjugates L(1) and L(2) in showing the zinc recognition in live cells has also been demonstrated using HeLa cells as monitored by fluorescence imaging. The zinc complexes of L(1) and L(2) were isolated, and the structure of [ZnL(1)] has been established by single-crystal XRD and that of [ZnL(2)] by DFT calculations. TDDFT calculations were performed in order to demonstrate the electronic properties of receptors and their zinc complexes. The isolated zinc complexes, viz. [ZnL(1)] and [ZnL(2)], have been used as molecular tools for the recognition of anions on the basis of their binding affinities toward Zn(2+). [ZnL(2)] was found to be sensitive and selective toward phosphate-bearing ions and molecules and in particular to pyrophosphate (PPi) and ATP among the other 18 anions studied; however, [ZnL(1)] was not sensitive toward any of the anions studied. The selectivity has been shown on the basis of the changes observed in the emission and absorption spectral studies through the removal of Zn(2+) from [ZnL(2)] by PPi. Thus, [ZnL(2)] has been shown to detect PPi up to 278 ± 10 ppb at pH 7.4 in aqueous methanolic (1/2 v/v) HEPES buffer.

Fluorescence and piezoresistive cantilever sensing of trinitrotoluene by an upper-rim tetrabenzimidazole conjugate of calix[4]arene and delineation of the features of the complex by molecular dynamics.

A new benzimidazole-functionalized calix[4]arene receptor (R) was synthesized and characterized. The receptor R shows better selectivity toward trinitrotoluene (TNT) compared to the other nitro explosives in solution, which also retains its effectiveness for solid-phase detection. The chemical interactions of the molecule with different nitro explosive analytes were studied by fluorescence spectroscopy and by a molecular dynamics approach. The molecular dynamics studies show a 1:3 complex between R and TNT, and hence high sensitivity was imparted by fluorescence studies. The detection of explosive vapors in ambient conditions was tested by using a sensitive coating layer of R on an SU-8/CB-based piezoresistive cantilever surface. The developed device showed large sensitivity toward TNT compared to cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) in the solid state at their respective vapor pressures at room temperature. The detection sensitivity of the device was estimated to be 35 mV for TNT at ambient conditions. Moreover, the sensor does not show a response when exposed to humidity. These results demonstrate that R can be used as one of the coating materials for a cantilever for the detection of TNT using piezoresistivity measurement. R can also detect the explosives in solution with high sensitivity and selectivity by fluorescence spectroscopy.

Quinoline Driven Fluorescence Turn On 1,3-Bis-calix[4]arene Conjugate-Based Receptor to Discriminate Fe3+ from Fe2+

The synthesis and characterization of a triazole linked quinoline appended calix[4]arene conjugate, L, and its fluorescence turn on receptor property for Fe(3+) have been demonstrated. The selective and sensitive discrimination of Fe(3+) has been shown using fluorescence and absorption titration experiments. The Fe(3+) binding to L has been further shown by ITC and ESI MS. The mode of binding of Fe(3+) by calix[4]arene conjugate has been shown by absorption, (1)H NMR and visual color change and the species were modeled based on DFT computations. The {L + Fe(3+)} has been shown to label cells with fluorescence imaging. Moreover the utility of this conjugate has been demonstrated by the combination logic gate system.

Triazole-linked-thiophene conjugate of calix[4]arene: its selective recognition of Zn2+ and as biomimetic model in supporting the events of the metal detoxification and oxidative stress involving metallothionein.

Supramolecular calix[4]arene conjugate (L) has been developed as a sensitive and selective sensor for Zn(2+) in HEPES buffer among the 12 metal ion by using fluorescence, absorption and ESI MS and also by visual fluorescent color. The structural, electronic, and emission properties of the calix[4]arene conjugates L and its zinc complex, [ZnL], have been demonstrated using ab initio density functional theory (DFT) combined with time-dependent density functional theory (TDDFT) calculations. The TDDFT calculations reveal the switch on fluorescence behavior of L is mainly due to the utilization of the lone pair of electrons on imine moiety by the Zn(2+). The resultant fluorescent complex, [ZnL], has been used as a secondary sensing chemo-ensemble for the detection of -SH containing molecules by removing Zn(2+) from [ZnL] and forming {Cys/DTT·Zn} adducts as equivalent to those present in metallothioneins. The displacement followed by the release of the coordinated zinc from its Cys/DTT complex by heavy metal ion (viz. Cd(2+) and Hg(2+)), as in the metal detoxification process or by ROS (such as H(2)O(2)) as in the oxidative stress, has been well demonstrated using the conjugate L through the fluorescence intensity retrieval wherein the fluorescence intensity is the same as that observed with [ZnL], which in turn mimics the zinc sensing element (MTF) in biology.

Cd2+ Complex of a Triazole-Based Calix[4]arene Conjugate as a Selective Fluorescent Chemosensor for Cys

An N,N-Dimethylamine ethylimino-appended triazole-linked calix[4]arene conjugate, L, has been synthesized and characterized, and its Cd(2+) complex has been isolated and characterized. The structure of [CdL] was established by computational calculation using B3LYP/LANL2DZ. Time-dependent density functional theory calculations were performed to demonstrate the electronic properties of [CdL]. This highly fluorescing [CdL] has been used to recognize Cys selectively among the 20 naturally occurring amino acids. [CdL] exhibits a minimum detection limit of 58 ppb for Cys, with reusability and reversibility being imparted to the system during sensing. Thus, the sensing of Cys was well demonstrated using various techniques, viz., fluorescence, absorption, visual color change, electrospray ionization MS, (1)H NMR, and live cell imaging experiments.

Lower Rim 1,3-Di{4-antipyrine}amide Conjugate of Calix[4]arene: Synthesis, Characterization, and Selective Recognition of Hg2+and Its Sensitivity toward Pyrimidine Bases

The structurally characterized lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene (L) exhibits high selectivity toward Hg(2+) among other biologically important metal ions, viz., Na(+), K(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ag(+) as studied by fluorescence, absorption, and ESI MS. L acts as a sensor for Hg(2+) by switch-off fluorescence and exhibits a lowest detectable concentration of 1.87 ± 0.1 ppm. The complex formed between L and Hg(2+) is found to be 1:1 on the basis of absorption and fluorescence titrations and was confirmed by ESI MS. The coordination features of the mercury complex of L were derived on the basis of DFT computations and found that the Hg(2+) is bound through an N(2)O(2) extending from both the arms to result in a distorted octahedral geometry with two vacant sites. The nanostructural features such as shape and size obtained using AFM and TEM distinguishes L from its Hg(2+) complex and were different from those of the simple mercuric perchlorate. L is also suited to sense pyrimidine bases by fluorescence quenching with a minimum detection limit of 1.15 ± 0.1 ppm in the case of cytosine. The nature of interaction of pyrimidine bases with L has been further studied by DFT computational calculations and found to have interactions through a hydrogen bonding and NH-π interaction between the host and the guest.

Triazole-linked anthracenyl-appended calix[4]arene conjugate as receptor for Co(II): synthesis, spectroscopy, microscopy, and computational studies.

A new triazole-linked anthracenyl-appended calix[4]arene-1,3-diconjugate (L) has been synthesized and characterized, and its single crystal XRD structure has been established. Binding properties of L toward different biologically relevant metal ions have been studied by fluorescence and absorption spectroscopy in ethanol. L exhibits selective recognition of Co(2+) and can detect down to a concentration of 55 ppb (0.92 μM). The roles of the calix[4]arene platform as well as the preorganized binding core in Ls selective recognition have been demonstrated by studying appropriate control molecules. The mode of binding of L with Co(2+) has been modeled both by DFT and MD computational calculations. L and its Co(2+) complex could be differentiated on the basis of the nanostructural features observed in AFM and TEM.

Recognition of Polycyclic Aromatic Hydrocarbons and Their Derivatives by the 1,3-Dinaphthalimide Conjugate of Calix[4]arene: Emission, Absorption, Crystal Structures, and Computational Studies

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants as well as well-known carcinogens. Therefore, it is important to develop an effective receptor for the detection and quantification of such molecules in solution. In view of this, a 1,3-dinaphthalimide derivative of calix[4]arene (L) has been synthesized and characterized, and the structure has been established by single crystal XRD. In the crystal lattice, intermolecular arm-to-arm π···π overlap dominates and thus L becomes a promising receptor for providing interactions with the aromatic species in solution, which can be monitored by following the changes that occur in its fluorescence and absorption spectra. On the basis of the solution studies carried out with about 17 derivatives of the aromatic guest molecular systems, it may be concluded that the changes that occur in the fluorescence intensity seem to be proportional to the number of aromatic rings present and thus proportional to the extent of π···π interaction present between the naphthalimide moieties and the aromatic portion of the guest molecule. Though the nonaromatic portion of the guest species affects the fluorescence quenching, the trend is still based on the number of rings present in these. Four guest aldehydes are bound to L with K(ass) of 2000-6000 M(-1) and their minimum detection limit is in the range of 8-35 μM. The crystal structure of a naphthaldehyde complex, L.2b, exhibits intermolecular arm-to-arm as well as arm-to-naphthaldehyde π···π interactions. Molecular dynamics studies of L carried out in the presence of aromatic aldehydes under vacuum as well as in acetonitrile resulted in exhibiting interactions observed in the solid state and hence the changes observed in the fluorescence and absorption spectra are attributable for such interactions. Complex formation has also been delineated through ESI MS studies. Thus L is a promising receptor that can recognize PAHs by providing spectral changes proportional to the aromatic conjugation of the guest and the extent of aromatic π···π interactions present between L and the guest.

Selective Recognition of Cysteine in Its Free and Protein-Bound States by the Zn2+ Complex of a Triazole-Based Calix[4]arene Conjugate

Zinc-ed in: A highly fluorescent zinc complex of triazole-linked calix[4]arene (see scheme), [ZnL], for the selective recognition of Cys and other protein-bound/free thiols in the blood-serum milieu by mimicking the Zn 2+ -induced redox switch has been developed.

A zinc-sensing glucose-based naphthyl imino conjugate as a detecting agent for inorganic and organic phosphates, including DNA.

Owing to the importance of zinc and phosphate in biology and human health, sensing such species is always important and continues to intrigue chemists to emerge with better receptor designs. Our recent report on sensing of Zn in blood serum milieu by a calixarene derivative prompted us to employ biologically benign receptor systems and to investigate if these receptors can also extend their sensitivity towards anions (especially phosphates). In this regard, water-soluble and biologically benign carbohydrate-based fluorescent sensors would be of great relevance to explore their in vitro and in vivo applications. Among the derivatives of phosphate, adenosine-mono/di/triphosphate (AMP, ADP, ATP), DNA, and their hydrolytic species are important. Therefore, it is essential to monitor the presence of phosphate related species in solution. If a receptor can sense both the zinc and the phosphate group, it would be doubly advantageous. Therefore, herein we investigate the primary detection of Zn by switch-on fluorescence using 1-(d-glucopyranosyl-2’-deoxy-2’-iminomethyl)-2-hydroxynaphthalene conjugate L and the successive detection of phosphates by the corresponding zinc complex through fluorescence quenching (switch-off). To demonstrate the bio-suitability of L, titrations were carried out using nucleotides and DNA. To our knowledge, this is the first carbohydrate-based receptor system shown to be sensitive towards a cation followed by an anion, including biomolecular systems. Conjugate L has been synthesized by a one-pot condensation of the neutralized C2-deoxy-C2-amino-glucose with 2hydroxy-1-naphthaldehyde and his structure has been characterized (see SI 01 in the Supporting Information). Conjugate L has been crystallized in a non-centrosymmetric triclinic system by layering methanol on to a concentrated solution in DMSO and the structure was determined by single crystal XRD (for crystal and metric data see SI 02 in the Supporting Information). Conjugate L exhibits a preformed ONO core that is suitable for metal ion binding (Scheme 1). An intramolecular hydrogen bond present between the phenolic O4 H···N1-imino orients the naphthyl moiety almost perpendicular to the mean plane of the carbohydrate moiety (see SI 02b in the Supporting Information). In the lattice, molecules form columns by interacting through two strong hydrogen bonds per each L and also by exhibiting hydrophobic p–p interactions with a centroid to centroid distance of 4.878 . The columnar structure formed in the lattice clearly exhibits hydrophobic (6 ) and hydrophilic (7 ) regions alternatively (see SI 02c in the Supporting Information). The selectivity of L has been demonstrated by titration against seven biologically and ecologically relevant metal ions, such as, Na , K , Ca , Mg , Zn , Cd , and Hg in methanol using fluorescence spectroscopy. In dry methanol, L exhibits approximately a 140-fold enhancement in the emission intensity against Zn , while none of the alkali and alkaline earth or Group XII metal ions show appreciable change under similar experimental conditions (Figure 1).