Development of a fluorescent scaffold by utilizing quercetin template for selective detection of Hg2+: Experimental and theoretical studies along with live cell imaging.

Quercetin is an important antioxidant with high bioactivity and it has been used as SARS-CoV-2 inhibitor significantly. Quercetin, one of the most abundant flavonoids in nature, has been in the spot of numerous experimental and theoretical studies in the past decade due to its great biological and medicinal importance. But there have been limited instances of employing quercetin and its derivatives as a fluorescent framework for specific detection of various cations and anions in the chemosensing field. Therefore, we have developed a novel chemosensor based on quercetin coupled benzyl ethers (QBE) for selective detection of Hg2+ with "naked-eye" colorimetric and "turn-on" fluorometric response. Initially QBE itself exhibited very weak fluorescence with low quantum yield (Φ = 0.009) due to operating photoinduced electron transfer (PET) and inhibition of excited state intramolecular proton transfer (ESIPT) as well as intramolecular charge transfer (ICT) within the molecule. But in presence of Hg2+, QBE showed a sharp increase in fluorescence intensity by 18-fold at wavelength 444 nm with high quantum yield (Φ = 0.159) for the chelation-enhanced fluorescence (CHEF) with coordination of Hg2+, which hampers PET within the molecule. The strong binding affinity of QBE towards Hg2+ has been proved by lower detection limit at 8.47 µM and high binding constant value as 2 × 104 M-1. The binding mechanism has been verified by DFT study, Cyclic voltammograms and Jobs plot analysis. For the practical application, the binding selectivity of QBE with Hg2+ has been capitalized in physiological medium to detect intracellular Hg2+ levels in living plant tissue by using green gram seeds. Thus, employing QBE as a fluorescent chemosensor for the specific identification of Hg2+ will pave the way for a novel approach to simplifying the creation of various chemosensors based on quercetin backbone for the precise detection of various biologically significant analytes.

Inhibition of Human Colorectal Cancer by a Natural Product 7-Acetylhorminone and Interactions with BSA/HSA: Multispectral Analysis and In Silico and In Vitro Studies.

We have semi-synthesized a natural product 7-acetylhorminone from crude extract of Premna obtusifolia (Indian headache tree), which is active against colorectal cancer after probation through computational screening methods as it passed through the set parameters of pharmacokinetics (most important nonblood-brain barrier permeant) and drug likeliness (e.g., Lipinski's, Ghose's, Veber's rule) which most other phytoconstituents failed to pass combined with docking with EGFR protein which is highly upregulated in the colorectal carcinoma cell. The structure of 7-acetylhorminone was confirmed by single crystal X-ray diffraction studies and 1H NMR, 13C NMR, and COSY studies. To validate the theoretical studies, first, in vitro experiments were carried out against human colorectal carcinoma cell lines (HCT116) which revealed the potent cytotoxic efficacy of 7-acetylhorminone and verified preliminary investigation. Second, the drugability of 7-acetylhorminone interaction with serum albumin proteins (HSA and BSA) is evaluated both theoretically and experimentally via steady-state fluorescence spectroscopic studies, circular dichroism, isothermal titration calorimetry, and molecular docking. In summary, this study reveals the applicability of 7-acetylhorminone as a potent drug candidate or as a combinatorial drug against colorectal cancer.

Viscosity-sensitive and AIE-active bimodal fluorescent probe for the selective detection of OCl- and Cu2+: a dual sensing approach via DFT and biological studies using green gram seeds.

A novel dual-mode viscosity-sensitive and AIE-active fluorescent chemosensor based on the naphthalene coupled pyrene (NCP) moiety was designed and synthesized for the selective detection of OCl- and Cu2+. In non-viscous media, NCP exhibited weak fluorescence; however, with an increase in viscosity using various proportions of glycerol, the fluorescence intensity was enhanced to 461 nm with a 6-fold increase in fluorescence quantum yields, which could be utilized for the quantitative determination of viscosity. Interestingly, NCP exhibited novel AIE characteristics in terms of size and growth in H2O-CH3CN mixtures with high water contents and different volume percentage of water, which was investigated using fluorescence, DLS study and SEM analysis. Interestingly, this probe can also be effectively employed as a dual-mode fluorescent probe for light up fluorescent detection of OCl- and Cu2+ at different emission wavelengths of 439 nm and 457 nm via chemodosimetric and chelation pathways, respectively. The fast-sensing ability of NCP towards OCl- was shown by a low detection limit of 0.546 µM and the binding affinity of NCP with Cu2+ was proved by a low detection limit of 3.97 µM and a high binding constant of 1.66 × 103 M-1. The sensing mechanism of NCP towards OCl- and Cu2+ was verified by UV-vis spectroscopy, fluorescence analysis, 1H-NMR analysis, mass spectroscopy, DFT study and Job plot analysis. For practical applications, the binding of NCP with OCl- and Cu2+ was determined using a dipstick method and a cell imaging study in a physiological medium using green gram seeds.

A multi-spectroscopic and molecular docking approach for DNA/protein binding study and cell viability assay of first-time reported pendent azide bearing Cu(II)-quercetin and dicyanamide bearing Zn(II)-quercetin complexes.

In the current study, one new quercetin-based Zn(II) complex [Zn(Qr)(CNNCN)(H2O)2] (Complex 1) which is developed by condensation of quercetin with ZnCl2 in the presence of NaN(CN)2 and Cu(II) complex [Cu(Qr)N3(CH3OH)(H2O)] (complex 2) which is developed by the condensation reaction of quercetin and CuCl2 in presence of NaN3, are thoroughly examined in relation to their use in biomedicine. The results of several spectroscopic studied confirm the structure of both the complexes and the Density Functional Theory (DFT) study helps to optimize the structure of complex 1 and 2. After completion of the identification process, DNA and Human Serum Albumin (HSA) binding efficacy of both the investigated complexes are performed by implementing a long range of biophysical studies and a thorough analysis of the results unveils that complex 1 has better interaction efficacy with the macromolecules than complex 2. The binding efficacy of complex 1 is comparatively higher towards both macromolecules because of its pure groove binding mode during interaction with DNA and the presence of an extra H-bond during connection with HSA. The experimental host-guest binding results is fully validated by molecular docking study. Interestingly complex 1 shows better antioxidant properties than complex 2, as well as quercetin, and it has strong anticancer property with minimal damage to normal cells, which is proved by the MTT assay study. Better DNA and HSA binding efficacy of 1 may be the reason for the better anticancer property of complex 1.

DNA/Protein Binding and Apoptotic-Induced Anticancer Property of a First Time Reported Quercetin-Iron(III) Complex Having a Secondary Anionic Residue: A Combined Experimental and Theoretical Approach.

A new quercetin-based iron(III) cationic complex [Fe(Qr)Cl(H2O)(MeO)] (complex 1) is created in the current study by condensation of quercetin with ferric chloride in the presence of Et3N. Comprehensive spectroscopic analysis and conductometric measurement are used to pinpoint complex 1. The generated complex's +3-oxidation state has been verified by electron paramagnetic resonance (EPR) research. Density functional theory analysis was used to structurally optimize the structure of complex 1. Before biomedical use, a variety of biophysical studies are implemented to evaluate the binding capacity of complex 1 with DNA and human serum albumin (HSA) protein. The findings of the electronic titration between complex 1 and DNA, as well as the stunning fall in the fluorescence intensities of the HSA and EtBr-DNA/DAPI-DNA domain after complex 1 is gradually added, give us confidence that complex 1 has a strong affinity for both macromolecules. It is interesting to note that the displacement experiment confirms partial intercalation as well as the groove binding mechanism of the title complex with DNA. The time-dependent fluorescence analysis indicates that after interaction with complex 1, HSA will exhibit static quenching. The thermodynamic parameter values in the HSA-complex 1 interaction provide evidence for the hydrophobicity-induced pathway leading to spontaneous protein-complex 1 interaction. The two macromolecules' configurations are verified to be preserved when they are associated with complex 1, and this is done via circular dichroism spectral titration. The molecular docking investigation, which is a theoretical experiment, provides complete support for the experimental findings. The potential of the investigated complex to be an anticancer drug has been examined by employing the MTT assay technique, which is carried out on HeLa cancer cell lines and HEK-293 normal cell lines. The MTT assay results validate the ability of complex 1 to display significant anticancer properties. Finally, by using the AO/PI staining approach, the apoptotic-induced cell-killing mechanism as well as the detection of cell morphological changes has been confirmed.

Design of a Structurally Novel Multipotent Drug Candidate by the Scaffold Architecture Technique for ACE-II, NSP15, and Mpro Protein Inhibition: Identification and Isolation of a Natural Product to Prevent the Severity of Future Variants of Covid 19 and a Colorectal Anticancer Drug.

Scaffold architecture in the sectors of biotechnology and drug discovery research include scaffold hopping and molecular modelling techniques and helps in searching for potential drug candidates containing different core structures using computer-based software, which greatly aids medicinal and pharmaceutical chemistry. Going ahead, the computational method of scaffold architecture is thought to produce new scaffolds, and the method is capable of helping search engines toward producing new scaffolds that are likely to represent potent compounds with high therapeutic applications, which is a possibility in this case as well. Here we probate a different interactive design by natural product hopping, molecular modelling, pharmacophore modelling, modification, and combination of the phytoconstituents present in different medicinal plants for developing a pharmacophore-guided good drug candidate for the variants of SARS-CoV-2 or Covid 19. In the modern era, these approaches are carried out at every level of development of scaffold queries, which are increasingly summarized from chemical structures. In this context, we report on a successfully designed drug-like candidate having a high-binding-affinity "compound SLP" by understanding the relationships between the compounds' pharmacophores, scaffold functional groups, and biological activities beyond their individual applications that abide by Lipinski's rule of five, Ghose rule, Veber rule etc. The new scaffold generated by altering the core of the known phyto-compounds holds a good predicted ADMET profile and is examined with iMODS server to check the molecular dynamics simulation with normal mode analysis (NMA). The scaffold's three-dimensional (3D) structure yields a searchable natural product koenimbine from a conformer database having good ADMET property and high availability in spice Murraya koenigii leaves. M. koenigii leaves are easily available in the market, and might ensure the immunity, good health, and well-being of people if affected with any of the variants of Covid 19. The cell viability studies of koenimbine on murine colorectal carcinoma cell line (CT-26) showed no toxicity on normal mice lymphocyte cells (MLCs). The anticancer mechanism of koenimbine was displayed by its enhanced capacity to produce intercellular reactive oxygen species (ROS) in the colorectal carcinoma cell line.

Fashionable Co-operative Sensing of Bivalent Zn2+ and Cd2+ in Attendance of OAc- by Use of Simple Sensor: Exploration of Molecular Logic Gate and Docking Studies.

The Schiff-base probe H2VL [6,6'-((1E,1'E)-hydrazine-1,2 diylidenebis(methanylylidene))bis(2-methoxyphenol)] is synthesized and structurally characterized by single crystal X-ray diffraction (SCXRD). H2VL is able to detect selectively acetate ion (OAc-) colorimetrically over other anions with 1:1 co-ordination. The detection limit is found to be 4.93 µM. On the other hand, fluorescence intensity of the receptor is drastically enhanced with Zn2+ and Cd2+ in the presence of acetate as counter anion. N, N-Dimethyl formamide (DMF) or Dimethylsulphoxide (DMSO) and acetate (OAc-) was the best solvent and counter anion for Zn2+/Cd2+ -sensing compared with other solvents and anions, respectively. Detection limit for Zn2+ and Cd2+ are calculated to be 1.94 µM and 1.99 µM, respectively. The strong selective emissive behavior could be attributed to the CHEF (chelation-enhanced fluorescence) process. According to the changes in output emission intensity in DMSO in response to the set of ions (Zn2+, Cd2+ and OAc¯) as input variables, the function of 3-input multifunctional molecular logic circuits has been demonstrated. The molecular docking studies of H2VL with DNA and BSA are also performed to confirm its possible bioactivity.

Facile and Green Fabrication of Highly Competent Surface-Modified Chlorogenic Acid Silver Nanoparticles: Characterization and Antioxidant and Cancer Chemopreventive Potential.

The eco-friendly, cost-effective, and green fabrication of nanoparticles is considered a promising area of nanotechnology. Here, we report on the green synthesis and characterization of bovine serum albumin (BSA)-decorated chlorogenic acid silver nanoparticles (AgNPs-CGA-BSA) and the studies undertaken to verify their plausible antioxidant and antineoplastic effects. High-resolution transmission electron microscopy (HR-TEM), dynamic light scattering, X-ray diffraction, and Fourier transform infrared analyses depict an average mean particle size of ∼96 nm, spherical morphology, and nanocrystalline structure of AgNPs-CGA-BSA. DPPH scavenging and inhibition of lipid peroxidation signify the noticeable in vitro antioxidant potential of the nanoparticles. The in vitro experimental results demonstrate that AgNPs-CGA-BSA shows significant cytotoxicity to Dalton's lymphoma ascites (DLA) cells and generates an enhanced intracellular reactive oxygen species and oxidized glutathione (GSSG) and reduced glutathione (GSH) in DLA cells. Furthermore, mechanism investigation divulges the pivotal role of the downregulated expression of superoxide dismutase (SOD) and catalase (CAT), and these ultimately lead to apoptotic chromatin condensation in AgNPs-CGA-BSA-treated DLA cells. In addition, in vivo experiments reveal an excellent decrease in tumor cell count, an increase in serum GSH and CAT, SOD, and glutathione peroxidase activities, and a decrease in the malondialdehyde (MDA) level in DLA-bearing mice after AgNPs-CGA-BSA treatment. These findings suggest that the newly synthesized biogenic green silver nanoparticles have remarkable in vitro antioxidant and antineoplastic efficacy that triggers cytotoxicity, oxidative stress, and chromatin condensation in DLA cells and in vivo anticancer efficacy that enhances the host antioxidant status, and these might open a new path in T-cell lymphoma therapy.

Bioinformatics and Network Pharmacology of the First Crystal Structured Clerodin: Anticancer and Antioxidant Potential against Human Breast Carcinoma Cell.

Clerodin was isolated from the medicinal plant Clerodendrum infortunatum, and CSD search showed the first crystal structure of clerodin by a single-crystal X-ray diffraction study. We checked its binding potential with target proteins by docking and conducted network pharmacology analysis, ADMET analysis, in silico pathway analysis, normal mode analysis (NMA), and cytotoxic activity studies to evaluate clerodin as a potential anticancer agent. The cell viability studies of clerodin on the human breast carcinoma cell line (MCF-7) showed toxicity on MCF-7 cells but no toxicity toward normal human lymphocyte cells (HLCs). The anticancer mechanism of clerodin was validated by its enhanced capacity to produce intracellular reactive oxygen species (ROS) and to lower the reduced glutathione content in MCF-7 cells.

Exchange-Bias Quantum Tunneling of the Magnetization in a Dysprosium Dimer.

Single-molecule magnets (SMMs) have been shown to possess bewildering phenomena leading to their proposal in several futuristic applications ranging from data storage devices to the basic unit of quantum computers. The main characteristic for the proposal of SMMs in such schemes is their inherent and intriguing quantum mechanical properties, which in turn, could be exploited in novel devices with larger capacities, such as for data storage or enhanced properties, such as quantum computers. In the quest of SMMs displaying such intriguing quantum effects, herein, we explore the synthesis, structural, and magnetic characterization of a dimeric dysprosium-based SMM composed of a tetradentate Schiff-base ligand with formula [Dy2(HL)2(benz)2(NO3)2]. Magnetic studies show that the complex is an SMM, while sub-Kelvin µ-SQUID studies revealed the exchange-bias characteristics of the system attributed to the presence of exchange interaction between the Dy3+ pair.

A bio-compatible pyridine-pyrazole hydrazide based compartmental receptor for Al3+ sensing and its application in cell imaging.

For practical applications, the development of bio-compatible organic molecules as p-block ion chemosensors is critical. Herein, we report the single crystal (SC) of new pyridine-pyrazole derived Al3+ sensor H2PPC [(Z)-N'-(2,3-dihydroxybenzylidene)-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazide] as well as its Cu-complex SC. The probe exhibits an "off-on" fluorescence response towards Al3+ ions, and this has been modulated with different solvents. For selective detection of Al3+ ions, a special coordination pocket in the structural backbone is advantageous. The chemosensor exhibits a submicromolar detection level (LOD = 4.78 µM) for Al3+. The density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations of H2PPC and [Al(HPP)2]+ (1) reveal that a change of the structural conformation of probe H2PPC upon complexation causes the pyrazole and pyridine units to create a specific cavity to tether Al3+, and consequently H2PPC proves to be a promising molecule for Al3+ detection. Furthermore, the probe has been successfully used to evaluate Al3+ as a low-cost kit using filter paper strips, and the in situ Al3+ ion imaging in Vero cells as well as A549 cell lines shows the sensor's nuclear envelope penetrability, indicating that it has great potential for biological and environmental applications.

Solvent-Regulated Fluorimetric Differentiation of Al3+ and Zn2+ Using an AIE-Active Single Sensor.

The absence of d-orbital electrons or presence of full-filled d-orbital electrons in metal ions is a well-known Achilles' heel problem for the detection of these metal ions by a simple UV-visible study. For this reason, detection of metal ions such as Al3+ with no d-orbital electrons or Zn2+ with filled d-orbital electrons is a challenging task. Herein, we report a 2-naphthol-based fluorescent probe [1-((E)-((E)-(5-bromo-2-hydroxybenzylidene)hydrazono)methyl)naphthalen-2-ol] (H2L) that has been used to sense and discriminate Al3+ and Zn2+ via solvent regulation. The probe exhibits excellent selectivity and swift sensitivity toward Al3+ in MeOH-water (9:1, v/v) and toward Zn2+ in dimethyl sulfoxide (DMSO)-water (9:1, v/v) among various metal ions. The respective detection limit is found to be 9.78 and 3.65 µM. The sensing mechanism is attributed to multiple processes, viz., the inhibition of photo-induced electron transfer (PET) along with the introduction of chelation-enhanced emission (CHEF) and excited-state intramolecular proton transfer (ESIPT) inhibition, which are experimentally well verified by UV-vis absorption spectroscopy, emission spectroscopy, and NMR spectroscopy. The probe shows aggregation-induced emissive (AIE) response in ≥70% aqueous media as well as in the solid state. The experimental results are well corroborated by time-resolved photoluminescence (TRPL) and density functional theory (DFT) calculations. An advanced-level OR-AND-NOT logic gate has been constructed from a different chemical combinational input and emission output. The reversible recognition of both Al3+ in MeOH-water (9:1, v/v) and Zn2+ in DMSO-water (9:1, v/v) is also ascertained in the presence of Na2EDTA, enabling the construction of a molecular memory device. The probe H2L also detects intracellular Al3+/Zn2+ ions in Hela cells. Altogether, our fundamental findings will pave the way for designing and synthesis of unique chemosensors that could be used for cell imaging studies as well as constructing molecular logic gates.

Design and synthesis of a sulphur containing Schiff base drug: DNA binding studies and theoretical calculations.

The Schiff base compound MTA ((E)-5-methyl-N'-((5-methylthiophen-2-yl)methylene)-1H-pyrazole-3-carbohydrazide) derived from 2-thiophenecarboxaldehyde and 5-methylpyrazole-3-carbohydrazide has been designed to develop new sulphur containing DNA targeted molecule. The MTA has been characterized by elemental analyses, 1H-NMR, single crystal X-ray diffraction studies as well as by geometry optimization of using DFT/B3LYP. The interaction of MTA with Calf thymus DNA (CT-DNA) was studied by spectroscopic and calorimetric techniques. The synthesized compound was found to bind with CT-DNA through groove binding mode, and the binding constant was estimated to be (4.15 ± 0.08) × 104 M-1. The negative ΔG0 and positive ΔS0 values obtained from the calorimetric technique confirmed the spontaneity of the binding of MTA with DNA.Communicated by Ramaswamy H. Sarma.

Acetate ion augmented fluorescence sensing of Zn2+ by Salen-based probe, AIE character, and application for picric acid detection.

Counter anion-triggered metal ion detection has been rarely reported by fluorimetric method. To address this challenging issue, a fluorescent probe (H2L) has been synthesized from bromo-salicylaldehyde and hydrazine hydrate, and structurally characterized by single crystal X-ray diffraction. The probe shows very weak fluorescence itself. However, its emission intensity increases in the presence of Zn2+ over other metal ions. Surprisingly, the emission profile of this probe in presence of Zn2+ is augmented only when acetate anion (OAc¯) is present as counter anion, that allows for precise quantitative analysis by spectroscopic studies. The compositions and complexation among the probe, Zn2+ ion, and OAc¯ are supported by ESI-MS, 1H-NMR, and Job's plot. Based on these studies, it is confirmed that the binding ratio between probe: metal is 1:2 and the detection limit (LOD) for the Zn2+ is 2.18 µM. The probe is capable of recognizing Zn2+ ion in the wide range of pH∼6.5-9.5, and it could be efficiently recycled by EDTA. Furthermore, the combinatorial molecular logic gate and memory device have been constructed from the fluorescent behavior of H2L with Zn2+, OAc¯, and EDTA input as based on NOT and AND gates. Interestingly, the aggregation-induced emission (AIEE) phenomenon is also perceived with greater than 50% water content in organic water mixtures, which are then useful for the detection of picric acid often used as explosive.

A simple Cu(II) complex of phenolic oxime: synthesis, crystal structure, supramolecular interactions, DFT calculation and catecholase activity study.

A copper (II) complex [Cu(4-MeO-salox)2](1) based on saloxime ligand was synthesized and characterized using single crystal X-ray diffraction studies. The geometry was further emphasized by DFT optimization. The complex was found to be pseudo-macrocyclic mononuclear having square planer geometry. The complex 1 shows two types of supramolecular hydrogen bonding interactions and forms the multi-dimensional framework with the help of CH∙∙∙O, OH∙∙∙O and π∙∙∙π(chelate) interactions. The complex 1 performs as efficient catalyst in catecholase activiy having good turnover number (TON), k cat = 22.97 h-1 where TON is the number of catechol molecules converted into quinone by catalyst molecule i.e 1 in a unit time.

Adaptable DNA-Interactive Probe Proficient at Selective Turn-On Sensing for Al3+: Insight from the Crystal Structure, Photophysical Studies, and Molecular Logic Gate.

The synthesized Schiff base ligand 3-hydroxy-N'-(2-hydroxy-3-methoxybenzylidene)-2-naphthohydrazide (H2NPV) is structurally characterized by single-crystal X-ray diffraction (XRD) and exhibits weak fluorescence in the excited state owing to the effect of excited-state-induced proton transfer (ESIPT). However, in the presence of Al3+, the ESIPT is blocked and chelation-enhanced fluorescence (CHEF) is induced because of complexation with the cations, resulting in turn-on emission for Al3+. The probe H2NPV selectively detects Al3+ among the various metal ions, and the detection limit is found to be 1.70 µM. The composition and modes of complex coordination were determined by spectroscopic, theoretical studies and molecular logic gate applications. Finally, DNA binding studies were performed by spectroscopic and calorimetric methods to elucidate possible bioactivity of H2NPV.

Biophysical and Thermodynamic Investigations on the Differentiation of Fluorescence Response towards Interaction of DNA: A Pyrene-Based Receptor versus Its Fe(III) Complex.

The Fe(III) complex [Fe(L)(NO3)(H2O)]+ (1) was prepared using a structurally characterized Schiff base ligand, 1-((pyren-1-ylimino) methyl) naphthalen-2-ol (HL), to develop an optical probe for fluorimetric recognition of DNA. An electrospray ionization-mass spectrometry (ESI-MS) study was carried out to ascertain the composition of 1 and the geometry of 1 was optimized by density functional theory (DFT) calculations. Compared to the strong intrinsic fluorescence of the ligand (HL), 1 was only weakly fluorescent. The interaction of 1 with DNA was investigated through different biophysical techniques. The fluorescence emission of 1 appeared to increase progressively in the presence of calf thymus (CT) DNA and this was utilized for the fluorimetric recognition of DNA. In comparison with 1, in the presence of DNA, the ligand HL showed quenching in its emission. The selectivity of 1 towards DNA was also confirmed in the presence of a large number of environmentally pertinent anions (NO3-, SO42-, Cl-, Br-, I-, OAC-, PO43-, ClO4-, HCO3-, H2PO4-, HPO42-, CO32-). Comprehensive DNA-binding experiments also showed that complex (1) and HL interacted with CT-DNA with different efficacies; the affinity of 1 was about six times higher than that of HL. Calorimetric studies showed that the 1-DNA association progressed with large positive entropy changes. In contrast, the association of HL with DNA was an enthalpy-driven process. Molecular docking results confirmed that the binding of 1 with CT-DNA progressed by intercalation and other noncovalent interactions.

Rhodamine-azobenzene based single molecular probe for multiple ions sensing: Cu2+, Al3+, Cr3+ and its imaging in human lymphocyte cells.

A photoinduced electron transfer (PET) and chelation-enhanced fluorescence (CHEF) regulated rhodamine-azobenzene chemosensor (L) was synthesized for chemoselective detection of Al3+, Cr3+, and Cu2+ by UV-Visible absorption study whereas Al3+ and Cr3+ by fluorimetric study in EtOH-H2O solvent. L showed a clear fluorescence emission enhancement of 21 and 16 fold upon addition of Al3+ and Cr3+ due to the 1:1 host-guest complexation, respectively. This is first report on rhodamine-azobenzene based Cr3+ chemosensor. The complex formation, restricted imine isomerization, inhibition of PET (photo-induced electron transfer) process with the concomitant opening of the spirolactam ring induced a turn-on fluorescence response. The higher binding constants 6.7 × 103 M-1 and 3.8 × 103 M-1 for Al3+ and Cr3+, respectively and lower detection limits 1 × 10-6 M and 2 × 10-6 M for Al3+ and Cr3+, respectively in a buffered solution with high reversible nature describes the potential of L as an effective tool for detecting Al3+ and Cr3+ in a biological system with higher intracellular resolution. Finally, L was used to map the intracellular concentration of Al3+ and Cr3+ in human lymphocyte cells (HLCs) at physiological pH very effectively. Altogether, our findings will pave the way for designing new chemosensors for multiple analytes and those chemosensors will be effective for cell imaging study.

Mono- and dinuclear oxidovanadium(v) complexes of an amine-bis(phenolate) ligand with bromo-peroxidase activities: synthesis, characterization, catalytic, kinetic and computational studies.

The mono- and dinuclear oxidovanadium(v) complexes [VVO(L1)(Cl)] (1) and [L1VVO(µ2-O)VO(L1)] (2) of ONNO donor amine-bis(phenolate) ligand (H2L1) were readily synthesized by the reaction between H2L1 and VCl3.(THF)3 or VO(acac)2 in MeOH or MeCN, respectively, and then characterized through mass spectroscopy, 1H-NMR and FTIR techniques. Both the complexes possess distorted octahedral geometry around each V centre. Upon the addition of 1 equivalent or more acid to a MeCN solution of complex 1, it immediately turned into the protonated form, which might be in equilibrium as: [L1ClVV[double bond, length as m-dash]OH]+ ↔ [L1ClVV-OH]+ (in the case of [L1ClVV[double bond, length as m-dash]OH]+ oxo-O is just protonated, whereas in [L1ClVV-OH]+ it is a hydroxo species), with the shift in λmax from 610 nm to 765 nm. Similar was the case for complex 2. The complexes 1 and 2 could efficiently catalyze the oxidative bromination of salicylaldehyde in the presence of H2O2 to produce 5-bromo salicylaldehyde as the major product with TONs of 405 and 450, respectively, in the mixed solvent system (H2O : MeOH : THF = 4 : 3 : 2, v/v). The kinetic analysis of the bromide oxidation reaction indicated a first-order mechanism in the protonated peroxidovanadium complex and a bromide ion and limiting first-order mechanism on [H+]. The evaluated kBr and kH values were 5.78 ± 0.20 and 11.01 ± 0.50 M-1 s-1 for complex 1 and 6.21 ± 0.13 and 20.14 ± 0.72 M-1 s-1 for complex 2, respectively. The kinetic and thermodynamic acidities of the protonated oxido species of complexes 1 and 2 were pKa = 2.55 (2.35) and 2.16 (2.19), respectively, which were far more acidic than those reported by Pecoraro et al. for peroxido-protonation instead of oxido protonation. On the basis of the chemistry observed for these model compounds, a mechanism of halide oxidation and a detailed catalytic cycle are proposed for the vanadium haloperoxidase enzyme and these were substantiated by detailed DFT calculations.

Oxime Based Selective Fluorescent Sensor for Arsenate Ion in a Greener Way with Bio-Imaging Application.

A newly designed oxime based probe, 2,4-dihydroxyacetophenone-oxime (DHAO), was found to recognize H2AsO4- selectively with ∼3 fold "turn-on" fluorescence enhancement and LOD of 29 µM, K = (2.10 ± 0.54) × 104 M-1 in purely aqueous medium. The structures of the DHAO and its adduct with H2AsO4- were optimized by DFT calculations. Intracellular imaging of As(V) in HepG2 cells demonstrate the possibilities of in vitro/in vivo applications for selective monitoring of such species.