Detection of Arsenic(V) by Fluorescence Sensing Based on Chlorin e6-Copper Ion

The high toxicity of arsenic (As) can cause irreversible harm to the environment and human health. In this study, the chlorin e6 (Ce6), which emits fluorescence in the infrared region, was introduced as the luminescence center, and the addition of copper ion (Cu2+) and As(V) provoked a regular change in fluorescence at 652 nm, whereas that of As(III) was 665 nm, which was used to optionally detect Cu2+, arsenic (As(III), and As(V)). The limit of detection (LOD) values were 0.212 μM, 0.089 ppm, and 1.375 ppb for Cu2+, As(III), and As(V), respectively. The developed method can be used to determine Cu2+ and arsenic in water and soil with good sensitivity and selectivity. The 1:1 stoichiometry of Ce6 with Cu2+ was obtained from the Job plot that was developed from UV-visible spectra. The binding constants for Cu2+ and As(V) were established to be 1.248 × 105 M-1 and 2.35 × 1012 M-2, respectively, using B-H (Benesi-Hildebrand) plots. Fluorescence lifetimes, B-H plots, FT-IR, and 1H-NMR were used to postulate the mechanism of Cu2+ fluorescence quenching and As(V) fluorescence restoration and the interactions of the two ions with the Ce6 molecule.

Potential Synthetic Routes and Metal-Ion Sensing Applications of 1,3,4-Oxadiazoles: An Integrative Review

Oxadiazoles, especially 1,3,4-oxadiazole scaffolds, stand among the foremost heterocyclic fragments with a broad spectrum of applications in diverse fields, including pharmacology, polymers, material science, and organic electronics, among others. In this comprehensive review, we summarize the pivotal synthetic strategies for 1,3,4-oxadiazole derivatives including dehydrogenative cyclization of 1,2-diacylhydrazines, oxidative cyclization of acylhydrazones, condensation cyclization, C-H activation of oxadiazole ring, decarboxylative cyclization and oxidative annulation along with plausible mechanisms. The set of 1,3,4-oxadiazoles selected from the literature and discussed herein epitomize the ease of synthesis as well as the possibility of linking π-conjugated groups; thereby encouraging the use of these molecules as important starting building blocks for a wide variety of fluorescent frameworks, particularly in the development of potential chemosensors. High photoluminescent quantum yield, excellent thermal and chemical stability, and the presence of potential coordination (N and O donor atoms) sites make these molecules a prominent choice for metal-ions sensors. An overview of selective metal-ion sensing, the detection limit along with the sensing mechanisms (photo-induced electron transfer, excited-state intramolecular proton transfer, and complex formation) is also included.

Spectroscopic Recognition of Metal Ions and Non-Linear Optical (NLO) Properties of Some Fluorinated Poly(1,3,4-Oxadiazole-Ether)s

In this paper, we examined the sensing ability of some fluorinated 1,3,4-oxadiazole-containing assemblies toward various metal ions and their nonlinear optical (NLO) properties. The changes in the spectral characteristics of these compounds in the existence of Mg2+, Mn2+, Ni2+, Cd2+, Zn2+, Co2+, Cu2+, Hg2+, Sn2+, and Ag+ metal ions were performed, and they were found to be selective and more sensitive toward the addition of Ag+, Co2+, and Cu2+ ions (new bands appeared). Instead, spectral changes in the presence of Mg2+, Mn2+, Ni2+, Cd2+, Zn2+, Hg2+, and Sn2+ were not significant, so we did not evaluate the corresponding binding parameters. Therefore, all of these compounds were found to be selective and sensitive to Ag+, Co2+, and Cu2+ ions. Furthermore, the first-order polarizability (αCT), the first-order hyperpolarizability (βCT), and the second-order hyperpolarizability (γCT) were evaluated using the solvatochromic approach, and the intramolecular charge transfer (ICT) characteristics were investigated using a generalized Mulliken–Hush (GMH) analysis.

Azulene-based fluorescent chemosensor for adenosine diphosphate

AzuFluor® 435-DPA-Zn, an azulene fluorophore bearing two zinc(II)-dipicolylamine receptor motifs, exhibits fluorescence enhancement in the presence of adenosine diphosphate. Selectivity for ADP over ATP, AMP and PPi results from appropriate positioning of the receptor motifs, since an isomeric sensor cannot discriminate between ADP and ATP.

Performance of 2-Hydroxy-1-Naphthaldehyde-2-Amino Thiazole as a Highly Selective Turn-on Fluorescent Chemosensor for Al(III) Ions Detection and Biological Applications

The thiazole based Schiff base 2-hydroxy-1-naphthaldehyde-2-amino thiazole (receptor1) was synthesized through a single step process and characterized by spectroscopic and analytical techniques. The cation detecting ability of the receptor1 was explored by fluorescent spectroscopic methods. The receptor1 has recognized Al3+ ions by a turn-on process over a panel of other potentially competing metal ions. The binding constant of receptor1 with Al3+ was found to be 8.27 × 103 M-1. Computational studies Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) were performed to provide detailed information on electronic states and photophysical property of receptor1 and receptor1-Al3+ ions. MTT (3-(4,5-dimethyl thiazole-2-yl)-2,5-diphenyl tetrazolium bromide) assay and bioimaging applications were made on breast carcinoma cells in humans.

Triphenyl-imidazole based reversible coloro/fluorimetric sensing and electrochemical removal of Cu2+ ions using capacitive deionization and molecular logic gates

A simple hydroxyl-substituted triphenyl-imidazole based receptor (HTPI) which selectively detects Cu²⁺ ion by colorimetric and fluorimetric methods was developed. HTPI detects the Cu²⁺ ions with the absorption enhancement and fluorescence quenching by the possible ligand to metal charge transfer (LMCT) and the chelation-enhanced quenching (CHEQ) approaches, respectively. HTPI showed high selectivity and sensitivity for Cu²⁺ ions detection over other interfering and competing metal ions. Interestingly, HTPI detects Cu²⁺ ion (LOD) at nanomolar concentrations (19 × 10^-9 M (UV-vis) & 27 × 10^-9 M (fluorescence), respectively), which is lower than the permissible level of Cu²⁺ ion reported by World Health Organization (WHO). Furthermore, HTPI was applied to the molecular logic gate function by using chemical inputs, and Cu²⁺ ion was potentially removed (95%) via Capacitive Deionization technique.

Lansoprazole-Based Colorimetric Chemosensor for Efficient Binding and Sensing of Carbonate Ion: Spectroscopy and DFT Studies

The new benzimidazole based receptor Lansoprazole has been used to detect carbonate anion by naked-eye and Uv-Vis spectroscopy. This receptor revealed visual changes withCO 3 2 - anion in ethanol. No detectable color changes were observed upon the addition of any other tested anions. The lansoprazole chemosensor selectively recognizesCO 3 2 - ion over the other interference anions in the ethanol, followed by deprotonation and reflected 1:1 complex formation between the receptor and the carbonate ion. Lansoprazole exhibits splendid selectivity toward carbonate ion via a visible color change from colorless to yellow with a detection limit of 57 μM. The binding mode ofCO 3 2 - to receptor L is supported by Density Functional Theory calculation. Moreover, this receptor shows a practical visible colorimetric test strip for the detection of carbonate ions. The transition states calculation demonstrates the occurrence of reaction from L to L-CO 3 2 - after overcoming an energy barrier of 10.1 kcal/mol, and there is considerable interaction energy between L andCO 3 2 - (94.9 kJ/mol), both of which confirmed that receptor L has high sensitivity and selectivity to the carbonate ion. The theoretical studies were performed to acquire an electronic description of the complexation mechanism byCO 3 2 - as well as to study bonding and structure in the complex. The optimized structures and binding mechanisms were supported with a high correlation and agreement by spectroscopy and DFT calculations.

Efficient Synthesis of Novel 1,3,4-Oxadiazoles Bearing a 4-N,N-Dimethylaminoquinazoline Scaffold via Palladium-Catalyzed Suzuki Cross-Coupling Reactions

Two series of novel (symmetrical and unsymmetrical) quinazolinylphenyl-1,3,4-oxadiazole derivatives were synthesized using palladium-catalyzed Suzuki cross-coupling reactions. The presented synthetic methodology is based on the use of bromine-substituted 2-phenyl-4-N,N-dimethylaminoquinazolines and either a boronic acid pinacol ester or a diboronic acid bis(pinacol) ester of 2,5-diphenyl-1,3,4-oxadiazole. The reactions are conducted in a two-phase solvent system in the presence of catalytic amounts of [1,1′-bis(diphenylphosphino)ferrocene]-dichloropalladium(II), sodium carbonate, and tetrabutylammonium bromide, which plays the role of a phase-transfer catalyst. The luminescence properties of the obtained compounds are discussed in the context of applying these compounds in optoelectronics. Specifically, two highly-conjugated final products: N,N-dimethyl-2-phenyl-6-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)quinazolin-4-amine (8f) and 6,6′-(4,4′-(1,3,4-oxadiazole-2,5-diyl)bis(4,1-phenylene))bis(N,N-dimethylquinazolin-4-amine (9f), which contain a 1,3,4-oxadiazole moiety connected to a quinazoline ring by a 1,4-phenylene linker at the 6 position, exhibit strong fluorescence emission and high quantum yields.

Chelation of specific metal ions imparts coplanarity and fluorescence in two imidazo[1,2-a]pyridine derivatives: Potential chemosensors for detection of metal ions in aqueous and biosamples

Synthesis and chelation induced fluorescence emission from two imidazo[1,2-a]pyridine derivatives are described. The nonfluorescent molecule 1 containing N and O donor atoms, achieves coplanarity upon interactions with trivalent cations Al³⁺, Fe³⁺ and Cr³⁺, that favors fluorescence emission. Molecule 2 containing two N donor atoms attains coplanarity upon interaction with the only Zn²⁺ and becomes fluorescent. Both molecules 1 and 2 form a 1:1 complex with interacting metal ions. Other trivalent metal ions (including Bi³⁺ and In³⁺) and common divalent metal ions (including Hg²⁺ and Cd²⁺) fail to form any complex with 1 or 2, and they do not interfere in the detection of Zn²⁺, Al³⁺, Fe³⁺ or Cr³⁺ ions. Noninterference of other metal ions renders 1 and 2 suitable for the detection of fungal cells contaminated with Zn²⁺, Al³⁺, Fe³⁺ or Cr³⁺ ions.

Pyrene-phenylglycinol linked reversible ratiometric fluorescent chemosensor for the detection of aluminium in nanomolar range and its bio-imaging

Pyrene-phenylglycinol tangled ratiometric sensor (R)-1 was developed for the detection of Al³⁺ ion over other metal ions. Ratiometric behaviour of (R)-1 for Al³⁺ ion explained through monomer emission and excimer quenching leads to avoiding the π-π interactions of bis-pyrene rings. Pull-push to push-pull binding mechanism is successfully explained by DFT and sensing of Al³⁺-ions demonstrated in living cells. The LOD of (R)-1 for Al³⁺ downs to nanomolar concentrations which is lower than the allowed concentration of drinking water set by the (World Health Organization) WHO.

Metal Complexes of Oxadiazole Ligands: An Overview

Oxadizoles are heterocyclic ring systems that find application in different scientific disciplines, from medicinal chemistry to optoelectronics. Coordination with metals (especially the transition ones) proved to enhance the intrinsic characteristics of these organic ligands and many metal complexes of oxadiazoles showed attractive characteristics for different research fields. In this review, we provide a general overview on different metal complexes and polymers containing oxadiazole moieties, reporting the principal synthetic approaches adopted for their preparation and showing the variety of applications they found in the last 40 years.

Synthesis of novel profluorescent nitroxides as dual luminescent-paramagnetic active probes

Profluorescent nitroxides containing 2,5-diaryl-1,3,4-oxadiazoles as fluorophore units were synthesized and characterized as actively responsive probes to reducing agents.

Proton donor modulating ESIPT-based fluorescent probes for highly sensitive and selective detection of Cu2+

Two novel ESIPT-based fluorescent probes for Cu²⁺ detection were developed. Altering the linker in probe molecules reversed their sensing behavior. Both probes exhibited high selectivity and sensitivity to Cu²⁺, and can be used for cell imaging.

ESIPT and CHEF based highly sensitive and selective ratiometric sensor for Al3+ with imaging in human blood cells

We have synthesised a probe for the fluorescence ratiometric detection of Al³⁺. This probe can be used to image Al³⁺ in living cells.