A single probe for solvent dependent optical recognition of iron(II/III) and arsenite: discrimination between iron redox states with single crystal X-ray structure evidence.

The detection and discrimination of Fe2+ and Fe3+ ions have been investigated using a simple probe (L), produced by the condensation of ethylenediamine and 3-ethoxysalicyaldehyde. Single crystal X-ray structures demonstrate that L interacts with Fe2+ and Fe3+. In aqueous-DMSO media, the L recognises AsO2- by fluorescence and colorimetry techniques. The AsO2- aided PET inhibition and H-bond assisted chelation enhanced fluorescence (CHEF) boost fluorescence by 91-fold. The L can detect 0.354 ppb Fe2+, 0.22 ppb Fe3+ and 0.235 ppt AsO2-.

A polynuclear Cu(ii) complex for real time monitoring of mitochondrial cytochrome C release during cellular apoptosis.

A new amide-imine conjugate, 2-hydroxybenzoic acid-(2-hydroxybenzylidene)-hydrazide (L1), is employed to prepare a single crystal X-ray structurally characterized poly-nuclear Cu(ii) complex (M1). M1 selectively and spatially interacts with cytochrome C (Cyt C) to allow fluorescence imaging of intracellular translocation events in living cells. Thus, direct visualization of a Cyt C translocation event during an apoptotic process is achieved for the first time. The binding constant and LOD are 7.52 × 104 M-1 and 34.0 nM, respectively.

Sequential Fluorescence Recognition of Molybdenum(VI), Arsenite, and Phosphate Ions in a Ratiometric Manner: A Facile Approach for Discrimination of AsO2 - and H2PO4.

An amide-based smart probe (L) is explored for nanomolar detection of Mo(VI) ion in a ratiometric manner, involving hydrogen-bond-assisted chelation-enhanced fluorescence process through inhibition of photoinduced electron transfer process. The recognition of Mo(VI) is associated with a 17-fold fluorescence enhancement and confirmed by single-crystal X-ray diffraction of the resulting Mo(VI) complex (M1). Further, M1 selectively recognizes arsenite through green emission of their adduct (C1) with an 81-fold fluorescence enhancement. Interestingly, dihydrogen phosphate causes dissociation of C1 back to free L having weak fluorescence. The methods are fast, highly selective, and allow their bare eye visualization at physiological pH. All of the interactions have been substantiated by time-dependent density functional theory calculations to rationalize their spectroscopic properties. The corresponding lowest detection limits are 1.5 × 10-8 M for Mo(VI), 1.2 × 10-10 M for AsO2 -, and 3.2 × 10-6 M for H2PO4 -, whereas the respective association constants are 4.21 × 105 M-1 for Mo(VI), 6.49 × 104 M-1 for AsO2 -, and 2.11 × 105 M-1 for H2PO4 -. The L is useful for efficient enrichment of Mo(VI) from aqueous solution, while M1 efficiently removes AsO2 - from environmental samples by solid-phase extraction.

Oxovanadium(V) and Dioxomolybdenum(VI) Complexes of Amide-Imine Conjugates: Structures, Catalytic and Antitumor Activities.

Three new amide-imine conjugates, namely [(E)-2-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide] (SALNP), [(E)-N'-(4-(diethylamino)-2-hydroxybenzylidene)-2-hydroxybenzohydrazide] (SALSD), and [(E)-N'-(3-ethoxy-4-hydroxybenzylidene)-2-hydroxybenzohydrazide] (SALVN), derived by reacting 2-hydroxybenzohydrazide (SAL) with three different aldehyde, 2-hydroxynapthaldehyde, 4-(diethylamino)-2-hydroxybenzaldehyde, and 3-ethoxy-4-hydroxybenzaldehyde, respectively. Three mononuclear oxovanadium(V) and two µoxo-bridged dinuclear molybdenum(VI) complexes have been synthesized using SALNP and SALSD. Besides, SALVN is used to prepare oxovanadium(V) and dioxomolybdenum(VI) complexes. All five metal complexes along with three amide-imine conjugates are characterized by single crystal XRD analysis. Some of them have been explored as catalyst for oxidation of alkyl benzene and styrene. Antitumor activities of the metal complexes along with ligands have been studied on Dalton lymphoma (DL) and 2PK3 murine lymphoma cells.

Azouracil and Its Cu(II)-Catalyzed Cyclization to an Anticancer Active Triazole Derivative: Symmetrical and Asymmetrical Reductive Cleavage, DNA Interaction, and Molecular Docking Studies.

The 6-amino-1,3-dimethyl uracil-based azo derivative (p-carboxy phenylazouracil, L11) undergoes Cu(II)-catalyzed cyclization to a triazole derivative, namely, 1,3-dimethyl-8-(p-carboxy phenyl) azapurine (L11P). Interestingly, the azo functionality of L11 undergoes both symmetrical and asymmetrical reductive cleavage at two different reaction conditions. The chloride salts of Mn(II), Ni(II), and Pd(II) catalyze reductive cleavage of an azo moiety in an asymmetric manner, producing a new uracil hydrazine derivative (A3). On the other hand, hydrazine catalyzes symmetrical reductive cleavage of the azo moiety of L11, resulting in 5,6-diamino-1,3-dimethyl uracil (A2) along with the starting p-aminobenzoic acid (A1). Time-dependent density functional theoretical (TD-DFT) studies provide optimized geometries of L11, L11P, and A3 along with their orbital energies. The L11 and L11P bind firmly to genomic DNA of E. coli with a site size n ∼ 9 and n ∼ 8. The L11P shows anticancer activity on selected murine lymphoma cancer cell lines (DL, YAC1, and 2PK3). In addition, its antiproliferative activity is measured with several cancer cell lines and found hemocompatible toward blood cells. Corresponding molecular docking studies of L11P with caspase-3 (cysteine-aspartic proteases) unlock their mode of interaction.

Exploring Anticancer and (Bio)catalytic Activities of New Oxovanadium(V), Dioxomolybdenum(VI), and Copper(II) Complexes of Amide-Imine Conjugates.

An amide-imine conjugate, (E)-N'-((2-hydroxynaphthalen-1-yl) methylene)-4-methylbenzohydrazide (PTANAP), derived from 4-methyl-benzoic acid hydrazide (PTA) and 2-hydroxynapthaldehyde, is explored to prepare dinuclear oxovanadium(V), mononuclear dioxomolydenum(VI), and Cu(II) complexes. Single crystal X-ray structurally characterized complexes have been exploited as catalyst for oxidation of ethylbenzene, catechol, and o-aminophenol. The anticancer properties of the oxo-vanadium complex have been explored against human leukemia cell (K-562) and mouse lymphoma cells (2PK3).

Subtle structural variation in azine/imine derivatives controls Zn2+ sensitivity: ESIPT-CHEF combination for nano-molar detection of Zn2+ with DFT support.

Excited-state intra-molecular proton transfer (ESIPT)-active imine and azine derivatives, structurally characterised by XRD, and denoted L1, L2, L3 and L4, possess weak fluorescence. The interaction of these probes with Zn2+ turns ON the fluorescence to allow its nano-molar detection. Among the four ESIPT-active molecules, L2, L3 and L4 are bis-imine derivatives while L1 is a mono-imine derivative. Among the three bis-imine derivatives, one is symmetric (L3) while L2 and L4 are unsymmetrical. The lowest detection limits (DL) of L1, L2, L3 and L4 for Zn2+ are 32.66 nM, 36.16 nM, 15.20 nM and 33.50 nM respectively. All the probes bind Zn2+ (105 M-1 order) strongly. Computational studies explore the orbital level interactions responsible for the associated photo-physical processes.

A unique benzimidazole-naphthalene hybrid molecule for independent detection of Zn2+ and N3- ions: Experimental and theoretical investigations.

Single crystal X-ray structurally characterized benzimidazole-naphthalene hybrid (NABI) functions as a unique dual analyte sensor that can detect Zn2+ cation and N3- anion independently. The NABI forms chelate with Zn2+ to inhibit internal charge transfer (ICT) and CHN isomerisation resulting chelation enhanced fluorescence (CHEF). On the other hand, the sensing of N3- is based on formation of supramolecular H-bonded rigid assembly. The association constant of NABI for Zn2+ and N3- ions are 19 × 104 M-1 and 11 × 102 M-1, respectively. Corresponding limit of detections (LOD) are 6.85 × 10-8 and 1.82 × 10-7 M, respectively. NABI efficiently detects intracellular Zn2+ and N3- ions with no cytotoxicity on J774A.1cells under fluorescence microscope. DFT studies unlock underlying spectroscopic properties of free NABI and Zn2+/N3- bound forms.

Exploring aggregation-induced emission through tuning of ligand structure for picomolar detection of pyrene.

Tuning of ligand structures through controlled variation of ring number in fused-ring aromatic moiety appended to antipyrine allows detection of 7.8 × 10-12  M pyrene via aggregation-induced emission (AIE) associated with 101-fold fluorescence enhancement. In one case, antipyrine unit is replaced by pyridine to derive bis-methylanthracenyl picolyl amine. The structures of four molecules have been confirmed by single crystal X-ray diffraction analysis. Among them, pyrene-antipyrine conjugate (L) undergoes pyrene triggered inhibition of photo-induced electron transfer (PET) leading to water-assisted AIE.

Azine based smart probe for optical recognition and enrichment of Mo(vi ).

Single crystal X-ray structure-characterized azine derivative (L) was explored for the selective detection of molybdenum (Mo(vi)) cations through green fluorescence emission. The Mo(vi) cation assisted inhibition of photo-induced electron transfer (PET) resulted in a 37-fold fluorescence enhancement via chelation enhanced fluorescence (CHEF) that allows detection of Mo(vi) with concentration as low as 2 × 10-9 M. The chelation of Mo(vi) cations by L has been confirmed by the single crystal X-ray structure of the resulting complex. The binding constant of L for Mo(vi) is fairly high (1.33 × 106 M-1). Moreover, L is very efficient for enrichment of Mo(vi) from aqueous solution. Density functional theoretical (DFT) studies substantiate the experimental results.

Exploring the Scope of Photo-Induced Electron Transfer-Chelation-Enhanced Fluorescence-Fluorescence Resonance Energy Transfer Processes for Recognition and Discrimination of Zn2+, Cd2+, Hg2+, and Al3+ in a Ratiometric Manner: Application to Sea Fish Analysis.

A rhodamine-based smart probe (RHES) has been developed for trace-level detection and discrimination of multiple cations, viz. Al3+, Zn2+, Cd2+, and Hg2+ in a ratiometric manner involving photo-induced electron transfer-chelation-enhanced fluorescence-fluorescence resonance energy transfer processes. The method being very fast and highly selective allows their bare eye visualization at a physiological pH. The optimized geometry and spectral properties of RHES and its cation adducts have been analyzed by time-dependent density functional theory calculations. RHES detects as low as 1.5 × 10-9 M Al3+, 1.2 × 10-9 M Zn2+, 6.7 × 10-9 M Cd2+, and 1.7 × 10-10 M Hg2+, whereas the respective association constants are 1.33 × 105 M-1, 2.11 × 104 M-1, 1.35 × 105 M-1, and 4.09 × 105 M-1. The other common ions do not interfere. The probe is useful for intracellular imaging of Zn2+, Cd2+, and Hg2+ in squamous epithelial cells. RHES is useful for the determination of the ions in sea fish and real samples.

Metal-Ion Displacement Approach for Optical Recognition of Thorium: Application of a Molybdenum(VI) Complex for Nanomolar Determination and Enrichment of Th(IV).

An azine-based molybdenum (Mo(VI)) complex (M1) is exploited for selective detection of thorium (Th(IV)) ions through a metal-ion displacement protocol. Th(IV) displaces Mo(VI) from M1 instantly leading to the formation of the Th(IV) complex, having orange-red emission. Consequently, a red shift of the emission wavelength along with 41-fold fluorescence enhancement is observed. This unique method allows detection of Th(IV) as low as 1.5 × 10-9 M. The displacement of Mo(VI) from M1 by Th(IV) is established by spectroscopic studies and kinetically followed by the stopped-flow technique. The displacement binding constant for Th(IV) is notably strong, 4.59 × 106 M-1. Extraction of Th(IV) from aqueous solution to the ethyl acetate medium using M1 has been achieved. The silica-immobilized M1 efficiently enriches Th(IV) from its reservoir through solid-phase extraction. Computational studies (density functional theory) support experimental findings.

Pyridine-antipyrine appended indole derivative for selective recognition of Fe3+: Concentration dependent coloration.

Combination of pyridine, antipyrine and indole in a single molecule (L2) allows selective recognition of Fe3+ colorimetrically in CH3CN. The structure of L2 is confirmed from single crystal X-ray diffraction analysis. The probe displays two different visible bands at 541nm and 715nm in the presence of Fe3+, associated with two different colors, viz. green and pink-violet allowing determination of unknown Fe3+ concentration. Interestingly, removal of 2-picolyl group from indole N-center of L2 generates L3 that behaves similarly at low Fe3+ concentration (>0 to 1.1mM) but differently at higher Fe3+ concentration (>1.1mM), indicating involvement of pyridyl-N donor towards Fe3+, and hence different coordination environment around Fe3+ at higher concentration.

Structurally Characterized Zn2+ Selective Ratiometric Fluorescence Probe in 100 % Water for HeLa Cell Imaging: Experimental and Computational Studies.

Fluorescence recognition of Zn2+ in 100% aqueous medium using 2-((1, 3 dihydroxy-2-(hydroxymethyl)propan-2 ylimino) methyl) phenol (SALTM) as ratiometric probe is reported. Moreover, SALTM can discriminate Zn2+ from Cd2+very effectively. The binding constant and detection limit of the probe for Zn2+ is 2.2×10(4) M(-1/2) and 2.79×10(-8) M respectively.Interestingly, corresponding naphthalene derivative(HNTM) having less water solubility fails to be a ratiometric sensor. SALTM can detect intracellular Zn2+ in HeLa cervical cancer cells under fluorescence microscope. Moreover, DFT and TD-DFT studies support experimental findings.

Dual mode ratiometric recognition of zinc acetate: nanomolar detection with in vitro tracking of endophytic bacteria in rice root tissue.

Several naphthalene-based aldazine derivatives were developed as efficient colorimetric and fluorescence probes for selective ratiometric recognition of traces of zinc acetate. The derivative structures were characterized by single-crystal X-ray diffraction. The probes were used for in vitro tracking of zinc acetate in endophytic bacteria within rice root tissue and to image zinc acetate in human breast cancer cells (MCF7) by normal and fluorescence microscopy. Density functional theoretical studies were in close agreement with the experimental findings.