Aqueous Acetonitrile Medium Research Articles

Experimental and theoretical studies for instantaneous detection of l-cysteine and l-histidine using a simple Cu(II)-dppy complex

Developing simple and effective receptors for instantaneous detection of l-amino acids is vital for the recognition of life-threatening diseases in their early stage. Here, we report the synthesis and characterization of 2,6-di(pyrazin-2-yl)pyridine (dppy) based ligand L (L = 2,2′-(4-(3,4-diethoxyphenyl)pyridine-2,6-diyl)dipyrazine) and its copper (II) complex, [Cu(NO3)2L]. The in-situ prepared [Cu(H2O)2L](NO3)2 receptor in aqueous acetonitrile (4:1 v/v, 10 mM HEPES buffer, pH 7.4) medium displayed instantaneous responses towards biologically important bio-thiol l-Cysteine (Cys) and essential amino acid l-Histidine (His) over other l-amino acids through UV–Visible absorption spectral studies. Additionally, the competitive experiments confirmed that in-situ prepared [Cu(H2O)2L](NO3)2 receptor selectively detects Cys (1 equivalent) in the presence of other l-amino acids. The detection limits of Cys and His were calculated to be 8.23 × 10−7 M and 2.55 × 10−6 M, respectively. The density functional theory (DFT) calculation shows that selectivity of [Cu(H2O)2L](NO3)2 towards Cys is due to the reduction of Cu(II) to Cu(I) in the presence of Cys, while Cys is oxidized to cystine (Cys-Cys). For His, selectivity observed due to the formation of [Cu(His)2] moiety between Cu(II) ion with one His via N,O coordination mode and another His via N,N,O-coordination mode.

Carbohydrate-modified simple efficient fluorometric probe for sensing Cu2+ions in aqueous solution

Triazole-appended pyrenyl-modified carbohydrate 1 was introduced in one step for detecting Cu2+ ions over various metal ions and anions in a 90 % aqueous acetonitrile medium. Selectivity of 1 towards Cu2+ ions was established from spectroscopic (absorbance and fluorescence) variations. Probe 1 is more effective in sensing Cu2+ ions within the pH range from 6 to 11. The quenched fluorescence of 1 with Cu2+ at a second was attributed to the reverse PET process from pyrene to electron-deficient Cu2+. The Stern-Volmer plot indicated static quenching at lower concentrations of Cu2+ ions, but both static and dynamic quenching processes were involved at higher concentrations. The ligand-metal ratio (1:1) was established from the Job plot and supported by the complex's HRMS data. The detection limit of 1 (0.08 µM) indicated that probe 1 can detect Cu2+ ions in the micromolar range. The binding mode of 1 with Cu2+ and HOMO-LUMO of 1 and 1-Cu2+ were discussed from DFT calculations. Finally, the practical use of the probe was established from the recovery of Cu2+ ions from natural water samples.

A selective fluorescence chemosensor: Thiosemicarbazide Schiff base derivative for detection of Ag+ ions in living cells

Ag+ ions can be colorimetric and fluorometrically detected in the aqueous acetonitrile medium with great selectivity using TOV. Observable to the naked eye, the synthesized compound exhibited an amazing fluorometric reaction in the presence of Ag+, changing from colorless to yellow. We examine the suggested Ag+ sensor's analytical performance characteristics with a considerable detection limit of 6.138×10−9 M. The chemosensor can be used for Ag+ measurement. According to the experiment results, TOV's fluorometric response to Ag+is pH-dependent throughout a broad pH range of 1.0 to 10.0. Furthermore, EDTA can be used to repeatedly reverse the Fluorometric reaction of TOV + Ag+. Job's plot, HRMS, and 1H NMR titration experiments have all been used to study the mechanism of interaction between the TOV and Ag+ ions. These studies have validated the 1:2 binding stoichiometry between TOV and Ag+. Test paper-based detection, Measuring Ag+ in water samples, were three examples of the real-time use of Ag+detection and chemosensor was used in MCF7 cells to assess cytotoxicity.

Selective sensing of sulphide ion by a simple mercury (II) complex of an amino-substituted terpyridine in aqueous solution

A novel mercury complex HgCl2L of 4′-(4-N,N´-dimethylaminophenyl)-2,2´:6′,2´´-terpyridine ligand L has been synthesized and characterised using 1H NMR, HRMS, FT-IR spectroscopy and CHN analysis. The crystal structure of HgCl2L exhibits distorted square pyramidal geometry. Further, the complex HgCl2L is utilised for selectively detecting sulphide (S2−) anion with other competitive anions in aqueous acetonitrile (4:1 v/v) medium. UV–visible absorption spectral studies and colorimetric approach confirmed the selectivity of the complex towards S2- and the limit of detection has been determined to be 1.01 μM.

Dual role of water in the oxygenation of phenylmercaptoacetic acids catalyzed by [oxo(salen)chromium(V)]+ PF6−

The sulfoxidation of eleven PMAAs by the oxo(salen)chromium(V) complex in aqueous acetonitrile medium was studied spectrophotometrically. [OCrVsalen-H2O]+ adduct was found to be the active oxidizing species. The rate of the sulfoxidation increases with increase in the polarity of the medium. The rate of the reaction is accelerated by electron donating substituents on PMAA while it is retarded by the electron withdrawing substituents. Based on the observed spectral and kinetic changes, electrophilic attack of the adduct [OCrVsalen-H2O]+ on the sulfur atom of the PMAA has been proposed.

A reversible Schiff base chemosensor for the spectroscopic and colorimetric sensing of Eu3+ ions in solution and solid-state

Herein, the metal sensing properties of a previously reported aluminium sensor (E)-N’-((2-hydroxynapthalene-1-yl)thiophene-2-Carbohydrazide) (L) have been further explored in selective sensing of lanthanide ions. Among many tested lanthanide ions sensor L showed the selective colorimetric response for only Eu3+ ions. The presence of Eu3+ ions caused electronic transitions in the visible region with a color change from colorless to yellow in aqueous acetonitrile media. A red-shift in the absorption band and enhancement in emission intensity is investigated only for the addition of Eu3+ ions to L, without any interference of other existing ions. This chemosensor binds the Eu3+ ions in 1:1 stoichiometric ratio and works upto a detection limits, 2.179 × 10-8 M (LOD for Eu3+ at 415 nm from UV–Visible), 3.443 × 10-8 M (LOD for Eu3+ at 477 nm from fluorescence) with a binding constant of 8.691 × 103 M−1 for the L-Eu3+ binding. However, the developed sensor is used as a paper, cotton-based test kit assay and solid state colorimetric sensing of Eu3+ ions. The reversibility of sensor L is checked by colorimetric observation with the addition of sodium salt ethylenediaminetetraacetic acid (EDTA) and found it reversible up to three cycles.

Donor-Acceptor Covalent Organic Frameworks as a Heterogeneous Photoredox Catalyst for Scissoring Alkenes to Carbonyl Constituents.

The conversion of alkenes to carbonyl constituents via the cleavage of the C═C bond is unique due to its biological and pharmacological significance. Though a number of oxidative C═C cleavage protocols have been demonstrated for terminal and electron-rich alkene systems, none of them were optimized for electron-deficient and conjugated alkenes. In this work, a covalent organic framework containing triphenylamine and triazine units was revealed to cleave the C═C bond of alkenes under very mild conditions involving visible light irradiation due to its photoredox property. The alkenes can be conveniently broken across the double bond to their constituent carbonyl derivatives on light irradiation in the presence of air and the covalent organic framework photocatalyst. This protocol is applicable for a wide range of alkenes in an aqueous acetonitrile medium with high functional group tolerance and regioselectivity. Though the electron-deficient alkenes required tetramethylethylene diamine as a sacrificial donor, the electron-rich alkenes do not demand any additives.

Cage-like Cu5Cs4-Phenylsilsesquioxanes: Synthesis, Supramolecular Structures, and Catalytic Activity.

A small family of nonanuclear Cu5Cs4-based phenylsilsesquioxanes 1-2 were prepared by a convenient self-assembly approach and characterized by X-ray diffraction studies. The compounds 1 and 2 show some unprecedented structural features such as the presence of a [Ph14Si14O28]14- silsesquioxane ligand and a CuII5CsI4 nuclearity in which the metal cations occupy unusual positions within the cluster. Copper ions are "wrapped" into a silsesquioxane matrix, while cesium ions are located in external positions. This resulted in cesium-involved aggregation of coordination polymer structures. Both compounds 1 and 2 realize specific metallocene (cesium-phenyl) linkage between neighboring cages. Compound 2 is evaluated as a catalyst in the Baeyer-Villiger (B-V) oxidation of cyclohexanone and tandem cyclohexane oxidation/B-V oxidation of cyclohexanone with m-chloroperoxybenzoic acid (mCPBA) as an oxidant, in an aqueous acetonitrile medium, and HNO3 as the promoter. A quantitative yield of ε-caprolactone was achieved under conventional heating at 50 °C for 4 h or MW irradiation for 30 min (for cyclohexanone as substrate); 17 and 19% yields of lactone upon MW irradiation at 80 °C for 30 min and heating at 50 °C for 4 h, respectively (for cyclohexane as a substrate), were achieved. Complex 2 was evaluated as a catalyst for the oxidation of alkanes to alkyl hydroperoxides and alcohols to ketones with peroxides at 60 °C in acetonitrile. The maximum yield of cyclohexane oxidation products was 30%. Complex 2 exhibits high activity in the oxidation of alcohols.

In vitro and in vivo nanomolar Hg2+ detection in live cells and zebrafish, theoretical studies

A worldwide contaminant that has an impact on both environment and human health is mercury. Neurological disorders are eventually caused by mercury bioaccumulation in the nervous system and ultimately affecting other parts of the body. It has been an indispensable task to sensitively and selectively sense mercury in order to control the damage. In this regard, an effectual chemosensor for the trace detection of Hg2+ ions has been synthesized appertaining to imidazole-coumarin cores with extremely lower cytotoxicity (15±0.15 µM).The sensing efficiency of IMCT was assessed in aqueous acetonitrile medium. The probe IMCT demonstrated its high sensitivity towards Hg2+ ions with a limit of detection (LOD) of 23.64 nM, which is extremely lower than the World Health Organization (WHO) international norms acceptable mercury level in drinking water (6.0 µg/L). ESI-Mass spectrum and Job’s result substantiates the complex formation of IMCT with Hg2+in 1:1 ratio. In vitro and in vivo imaging was carried out in zebrafish and human cancer cells. These results illustrate the effectiveness of IMCT as a fluorescent biomarker for Hg2+ has been effectively demonstrated.

Novel [5]helicene derivative as reversible and selective Hg2+ fluorescence sensor and its application in human cells

Mercury pollution and its toxicity pose a grave threat to health. Therefore, developing new approaches for detecting mercury ions (Hg2+) in environmental and biological samples is crucial. Herein, a novel [5]helicene-based fluorescence sensor (M201NHP) was designed and synthesized for rapid, sensitive and specific detection of Hg2+. The sensor exhibits fluorescence quenching with a very large Stokes shift (192 nm) towards Hg2+ in aqueous acetonitrile media. The detection limit of the sensor is estimated to be 1.94 ppb, which is lower than the U.S. EPA specification for the maximum Hg2+ level in drinking water. Moreover, M201NHP offers five cycles of reversibility upon competitive chelation of cysteine. The sensor can also screen for Hg2+ contamination in real water samples and skincare products. Additionally, it can track Hg2+ in potential mercury-accumulated human cell lines derived from brain tumours, embryonic kidneys, skin and liver cancers with low cytotoxicity. These results indicate that M201NHP is a promising Hg2+ sensor that can prevent health risks and environmental impacts caused by mercury pollution.

A simple TICT/ICT based molecular probe exhibiting ratiometric fluorescence Turn-On response in selective detection of Cu2+

The work reported herein describes photophysical behavior of a new fluorescent probe APDA. The probe exhibited sensitivity for Cu2+ ion in 80% aqueous acetonitrile medium. Probe shows dual emission due to TICT and ICT states and upon interaction with different metal ions Cu2+ induces hydrolysis of imine bond to rejuvenate aldehyde derivative with ratiometric “turn–On” fluorescence response, through ICT state while emission due to TICT state get diminished. Similarly, the synthesized model compound ADA under similar experimental condition supported hydrolysis of imine bond in the presence of copper. Jobs plot analysis, based on emission titration data suggested a 1:1 binding stoichiometry between probe APDA and Cu2+ ion. The limit of detection (LOD) was found to be 4.4 × 10-8 M (44 nM). The probe has been applied on test paper strip to detect Cu2+ ion with naked-eye sensitive response. Also, the cell imaging studies revealed the potential applicability of probe to detect Cu2+ ion in live cells. The mechanism of sensing was confirmed by 1H, 13C NMR, FTIR and mass spectrometry data analysis.

Coordination of Distal Carboxylate Anion Alters Metal Ion Specific Binding in Imidazo[1,2-a]pyridine Congeners.

Imidazo[1,2-a]pyridine derivatives have excellent potential for chelation with transition metal ions. Two new imidazo[1,2-a]pyridine-8-carboxylates were synthesized and characterized by 1H NMR, 13C NMR, HRMS, andsingle crystal-XRD techniques. Methyl carboxylate (probe 1) turns on fluorescence upon coordination with Zn2+, while sodium carboxylate (probe 2) turns off its fluorescence upon coordination with Co2+ or Cu2+ ions present in aqueous acetonitrile medium. 13C NMR study revealed that the change in metal ion specific binding was due to the involvement of carboxylate anion in complex formation with Co2+ or Cu2+ ions. The carboxylate anion at 8-position also enhanced the sensitivity of detection of probe 2 by an order of magnitude (detection limits: 3.804 × 10-7M, probe 1/Zn2+; 0.420 × 10-7M, probe 2/Co2+ and 0.304 × 10-7M, probe 2/Cu2+). The detection limits of probes 1 and 2 comply well with the World Health Organization (WHO) and US Environmental Protection Agency (US-EPA) guidelines for detection of heavy metal ions present in drinking water and ground water. Both the probes form a 1:1 complex with Zn2+, Co2+ or Cu2+,and the stoichiometry was verified by Job plot and ESI-mass analysis. The sensing mechanism is explained using 13C NMR experiments, ESI-mass analytical data and theoretical DFT calculations. The suitability of probes 1 and 2 for on-site detection and quantitative determination of Zn2+, Co2+ and Cu2+ ions present in biological, environmental and industrial samples is demonstrated. In addition, both 1 and 2 are used for detection of intracellular contamination of Zn2+, Co2+ or Cu2+ ions in onion epidermal cells.

Development of tissue paper-based chemosensor and demonstration for the selective detection of Cu2+ and Hg2+ ions.

Heavy metals emanate from natural and man-made sources, such as agricultural chemicals including fertilisers and pesticides, medical waste, and chemicals released from industries. Detection and monitoring toxic metal ions is one of the challenges confronting scientists in biological, environmental, and chemical systems. This study describes the design and synthesis of a new imidazole-based fluorescent and colourimetric chemosensor (DPICDT) for highly selective sensing of Hg2+ and Cu2+ ions in aqueous acetonitrile medium. The probe was synthesised by coupling benzil and substituted aldehyde using ethanolic ammonium acetate. The structure of DPICDT was confirmed via IR spectra, NMR, and HR-MS spectra. The DPICDT probe displayed a rapid naked-eye response towards Cu2+ ions from colourless to red-purple and significant fluorescence quenching response towards Hg2+ over other competitive metal ions in both solution and solid support. The binding modes of DPICDT with Cu2+ and Hg2+ ions were found to be at a 1 : 1 ratio as determined using Job plot, ESI HR-MS, and the sensing mechanism was evolved by 1H NMR titrations, HR-MS spectra, and DFT calculations. The lower detection limit was 15.1 nM for Cu2+, eventually far less than the World Health Organization guideline for drinking water (Cu2+ - 31.5 μM) and 1.17 μM for Hg2+ (permissible concentration 2 ppb). Promisingly, the tissue paper-based DPICDT test strips and silica-supported DPICDT were developed and demonstrated for on-site application without resorting to expensive instruments.

A simple copper(ii) dppy-based receptor for sensing of l-cysteine and l-histidine in aqueous acetonitrile medium

A novel copper(ii)-dppy receptor enables rapid and sensitive detection of l-cysteine and l-histidine, exhibiting exceptional selectivity and early-stage identification potential.

Novel Zn-dppy based receptor for selective sensing of pyrophosphate anion in aqueous acetonitrile medium

A new zinc(II) complex (ZnCl2L) of 4-N,N-dimethylaminophenyl substituted 2,6-dipyrazinylpyridine (dppy) ligand L was synthesized and used as a probe for selective sensing of pyrophosphate anion (P2O74-, PPi) in the presence of other anions in aqueous acetonitrile (1:1 v/v) solution (buffered with 10 mM HEPES). The sensing study was visualized through colorimetric method and measurements were done using UV–Visible spectroscopy. Further, the results were also investigated by DFT calculations in order to provide an explanation to the selectivity of the Zn-dppy hybrid receptor for PPi.

Selective cyanide sensing using a Fe(III) complex of pyridoxal-beta alanine Schiff base

Fluorogenic chemosensors using pyridoxal derivatized ligands as fluorophore is a rapidly growing field of research. Here we report a new Fe(III) complex, [Fe(HBala-pydx)(Bala-pydx)] (H2Bala-pydx is the Schiff base of pyridoxal with beta-alanine), which can serve as a sensitive and selective turn-on fluorescent sensor for the detection of cyanide(CN−) in micromolar concentrations (L.O.D. is 1.134 µM), via the ligand displacement approach, in aqueous-acetonitrile medium. The Fe(III) complex is adequately characterized by analytical and spectroscopic methods along with X-ray crystal structure determination.

Triazole-linked pyrene appended xylofuranose derivatives for selective detection of Au3+ ions in aqueous medium and DFT calculations

The sugar-modified simple fluorometric sensors 1 and 2 for detection of Au3+ in the aqueous acetonitrile have been reported. The sensors are double-responsive (absorbance and fluorescence) selective Au3+ sensors in CH3CN-H2O (1:1, v/v). Both the sensors exhibited remarkable selectivity and excellent sensitivity (limit of detection values are 0.53 µM for 1 and 0.83 µM for 2). The stoichiometry of each complex was established by Job's plot and supported by the ESI-mass spectrum of the complex. Finally, the coordination mode of each sensor with Au3+ ions was supported by DFT calculations in CH3CN-H2O (1:1, v/v) medium. The energy-optimized structures of 1-Au3+ and 2-Au3+ suggested that sensors 1 and 2 followed different binding modes with Au3+ ions in the aqueous acetonitrile medium, which account for the ESI-MS spectra of the complexes. Interestingly, we observed that fluorometric sugar derivatives 1 and 2 did not show any specific selectivity towards metal ions in CH3CN.

Light responsive, electrochemically dimerizable, capture and release device based on photochromic oxazine for nanomolar level detection of Hg2+ ions

Photochromic oxazine was synthesized and screened for the colorimetric detection of heavy metal ions in an aqueous solution. The “OX” (closed) form of the oxazine converted rapidly to the “IN” (open) form in presence of mercuric ions. The mercuric ion-induced structural alteration led to the appearance of an intense band in the visible region of the absorption spectrum in an aqueous acetonitrile medium. Naked eye, UV–Visible, cyclic voltammetry (CV), and smartphone-based techniques were successfully employed to study the detection process. The probe provided a 40 nM limit of detection value for Hg2+ ions using CV. The 1H NMR spectroscopy confirmed the interaction of the mercury ion with the oxazine unit and the ring-opening process. The cyclic voltammetric studies indicated the formation of CC bonds producing dimeric oxazine. The process of formation of a CC bond was investigated in the presence of Hg2+ ions, which was used as a detection method. The development of color in the complex was exploited to develop the solution and paper-based detection techniques aided by digital images of easily available smartphones and software. The probe-Hg2+ complex released mercuric ion upon exposure to visible light (450 nm) in water.

Micellar effects on the kinetics and mechanism of ceric ammonium nitrate oxidation of bicyclic monoterpenes under acid free conditions

Abstract Ceric ammonium nitrate (CAN) oxidation of bicyclic monoterpenes (BMT) such as borneol (BORN), isoborneol (IBORN) and camphor (CAMP) in aqueous acetonitrile medium did not proceed even under reflux conditions and mineral acid-free conditions. But addition of micelle forming surfactants (M) like sodium dodecylsulfate (SDS), cetyltrimethylammonium bromide (CTAB), and Triton X-100 accelerated the rate of oxidation. Kinetics of oxidation of the reactions revealed first order dependence on both [CAN] and [BMT]. Mechanism of oxidation has been explained through the participation of micelle-bound oxidant (M-CAN) and bicyclic monoterpene in the slow step.

Brønsted Acid Catalysis in the Oxidation of Purine Based Alkaloids by Mn(VII) in Aqueous Acetonitrile and Sodium Fluoride Medium: A Kinetic Approach

Brønsted acid (HClO4, H2SO4) catalyzed Mn(VII) oxidation of purine alkaloids such as caffeine, theophylline and theobromine in aqueous acetonitrile and sodium fluoride medium revealed first order kinetics in both [(Mn(VII)] and [Alkaloid] at constant acidity and temperature. Sodium fluoride was added to the reaction mixture in order to avoid/suppress auto catalytic reaction due to the generation of Mn(III) and Mn(IV) species during the course of Mn(VII) oxidations in acidic solutions. An increase in the Brønsted acids (HClO4, H2SO4) concentration accelerated the rate of oxidation. Rate enhancements observed here in are analyzed by Zucker-Hammett, Bunnett and Bunnett-Olsen criteria of acidity functions. On the basis of observed Bunnett-Olsen criteria of acidity functions, the most plausible mechanism has been proposed with the involvement of water molecule in the slow step (as proton transferring agent).