Single chemosensor for highly selective colorimetric and fluorometric dual sensing of Cu(II) as well as ‘NIRF’ to acetate ion

A dual-functional rhodamine B and azo-salicylaldehyde derivative for the simultaneous detection of copper and hypochlorite: synthesis, biological applications and theoretical insights

A multifunctional rhodamine derivative containing azo-salicylaldehyde (BBS) was designed and synthesized as a colorimetric and fluorescence turn-on probe for the selective detection of copper cations (Cu2+) and hypochlorite anions (OCl-) in aqueous media. In the presence of Cu2+, the probe BBS exhibited turn-on absorption and fluorescence change at 554 nm and 585 nm, respectively. The binding mechanism of BBS with Cu2+ induces the opening of a spirolactam ring in the rhodamine moiety by the formation of a metal-ligand complex, achieving 10-fold enhancement in fluorescence and quantum yield, along with a binding constant of 1 × 104 M-1 and a detection limit of 2.61 μM. Addition of OCl- enhanced the absorbance and fluorescence intensities at 520 nm and 575 nm, respectively. The probe BBS underwent hypochlorite-mediated oxidation, followed by hydrolysis, resulting in the formation of rhodamine B itself, which is detectable by the naked eye via the color and fluorescence enhancement by 11-fold with a high quantum yield and a detection limit of 1.96 μM. For practical applications, sensor BBS can be used to detect Cu2+ in water samples and on cotton swabs. For biological applications, the interaction of the BBS-Cu(II) complex with transport proteins such as bovine serum albumin (BSA) and ct-DNA was investigated through UV-vis and fluorescence titration experiments. Additionally, the structural optimization of BBS and the BBS-Cu(II) complex was demonstrated using DFT, and the interactions of the BBS-Cu(II) complex with BSA and ct-DNA were analysed through theoretical docking studies. Bioimaging studies were conducted by capturing fluorescence images of BBS with Cu2+ and OCl- in a physiological medium containing living plant tissue using green gram seeds.

A versatile sensor capable of ratiometric fluorescence detection of trace water and turn-on detection of Cu2+ modulating the binding interaction of a Cu(II) complex with BSA and DNA complemented by docking studies

A fluorescent molecule, pyridine-coupled bis-anthracene (PBA), has been developed for the selective fluorescence turn-on detection of Cu2+. Interestingly, the ligand PBA also exhibited a red-shifted ratiometric fluorescence response in the presence of water. Thus, a ratiometric water sensor has been utilized as a selective fluorescence turn-on sensor for Cu2+, achieving a 10-fold enhancement in the fluorescence and quantum yield at 446 nm, with a lower detection limit of 0.358 μM and a binding constant of 1.3 × 106 M-1. For practical applications, sensor PBA can be used to detect Cu2+ in various types of soils like clay soil, field soil and sand. The interaction of the PBA-Cu(II) complex with transport proteins like bovine serum albumin (BSA) and ct-DNA has been investigated through fluorescence titration experiments. Additionally, the structural optimization of PBA and the PBA-Cu(II) complex has been demonstrated by DFT, and the interaction of the PBA-Cu(II) complex with BSA and ct-DNA has been analyzed using theoretical docking studies.

A water-soluble colorimetric chemosensor for sequential probing of Cu2+ and S2- and its practical applications to test strips, reversible test, and water samples

A water-soluble colorimetric chemosensor NHOP ((E)-1-(2-(2-(2-hydroxy-5-nitrobenzylidene)hydrazineyl)-2-oxoethyl)pyridin-1-ium) chloride) was developed for the sequential probing of Cu2+ and S2-. NHOP underwent a color change from pale yellow to colorless in the presence of Cu2+ in pure water. The binding ratio between NHOP and Cu2+ was confirmed to be 1:1 by the Job plot and ESI-MS (electrospray ionization mass spectrometry). The detection limit of NHOP for Cu2+ was calculated as 0.15 μM, which was far below the EPA (Environmental Protection Agency) standard (20 μM). The NHOP-coated test strip was able to easily monitor Cu2+ in real-time. Meanwhile, the NHOP-Cu2+ complex reverted from colorless to pale yellow in the presence of S2- through the demetallation. The stoichiometric ratio between NHOP-Cu2+ and S2- was determined to be 1:1 by analyzing the Job plot and ESI-MS. The detection limit of NHOP-Cu2+ for S2- was calculated as 0.29 μM, which was very below the WHO (World Health Organization) guideline (14.7 μM). NHOP successfully achieved the quantification for Cu2+ and S2- in water samples. NHOP could work as a sequential probe for Cu2+ and S2- at the biological pH range (7.0-8.4). Moreover, NHOP could successively probe Cu2+ and S2- at least three cycles because of its reversible property. The detection mechanisms of NHOP for Cu2+ and NHOP-Cu2+ for S2- were demonstrated with Job plot, ESI-MS, and DFT (density functional theory) calculations. Therefore, NHOP could work as an efficient sequential probe for Cu2+ and S2- in environmental systems.

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.

Fluoride ion Coordination-Induced Turn-On Fluorescence of Tailored N-Methyl N-Confused Tripyrromonomethene Analogues

Inorder to achieve striking compromise between flexibility and rigidity, two unprecedented highly air-stable N-methyl N-Confused tripyrromonomethene analogues in near quantitative yields have been synthesized by chloranil oxidation under aerobic condition....

A series of benzothiazole-based Schiff bases for the colorimetric sensing of fluoride and acetate ions: acetate-induced turn-on fluorescence for selectivity

Benzothiazole-based Schiff bases show colorimetric sensing of fluoride and acetate ions. It also exhibits selective acetate-induced turn-on fluorescence.

Discovery of boron-containing compounds as Aβ aggregation inhibitors and antioxidants for the treatment of Alzheimer's disease

A novel series of boron-containing compounds were designed, synthesized and evaluated as multi-target-directed ligands against Alzheimer's disease. The biological activity results demonstrated that these compounds possessed a significant ability to inhibit self-induced Aβ aggregation (20.5-82.8%, 20 μM) and to act as potential antioxidants (oxygen radical absorbance capacity assay using fluorescein (ORAC-FL) values of 2.70-5.87). In particular, compound 17h is a potential lead compound for AD therapy (IC₅₀ = 3.41 μM for self-induced Aβ aggregation; ORAC-FL value = 4.55). Compound 17h also functions as a metal chelator. These results indicated that boron-containing compounds could be new structural scaffolds for the treatment of AD.

Remarkable colorimetric sensing behavior of pyrazole-based chemosensor towards Cu(ii) ion detection: synthesis, characterization and theoretical investigations

We report the synthesis of a new imine based ligand, 3-((3-methoxybenzylidene)amino)-1H-pyrazol-5-ol (HL) and its Cu(ii) complexes in 2 : 1 (HL : metal) and 1 : 1 : 1 (HL : metal : HQ) stoichiometric ratio using 8-hydroxyquinoline (HQ) as an additional bidentate ligand. The synthesized ligand (HL) and its Cu(ii) complexes (1 and 2) are structurally characterized using FT-IR, electronic absorption and emission, NMR and MS techniques. Furthermore, the complexation of Cu2+ with HL leads to the immediate formation of brown colour solution which indicates that HL can act as simple colorimetric sensor for Cu2+ ions. We further investigated that the sensor could selectively bind to the Cu2+ ions even in the presence of competitive ions such as Mn2+, Fe2+, Co2+, Ni2+, Zn2+, Ag+ and Na+ ions in aqueous solutions which was studied by electronic absorption spectroscopy. The HL ligand has been investigated for its reactive properties by density functional theory (DFT) calculations. Quantum molecular descriptors describing local reactive properties have been calculated in order to identify the most reactive molecule sites of title compounds. DFT calculations encompassed molecular electrostatic potential (MEP), local average ionization energies (ALIE), Fukui functions and bond dissociation energies for hydrogen abstraction (H-BDE).

A new Schiff-base chemosensor for selective detection of Cu2+ and Co2+ and its copper complex for colorimetric sensing of S2- in aqueous solution

A new Schiff-base colorimetric chemosensor 1 was developed for the detection of Cu²⁺, Co²⁺ and S^2-. Sensor 1 could simply monitor Cu²⁺ and Co²⁺ by a color change from colorless to yellow. The binding modes of 1 to Cu²⁺ and Co²⁺ were determined to be a 2 : 1 complexation stoichiometry through Job's plot and ESI-mass spectrometry analysis. The detection limits (0.02 μM and 0.63 μM) for Cu²⁺ and Co²⁺ were lower than the recommended values (31.5 μM and 1.7 μM) by the World Health Organization (WHO) for Cu²⁺ and the Environmental Protection Agency (EPA) for Co²⁺, respectively. Importantly, 1 could detect and quantify Cu²⁺ in real water samples. In addition, the Cu²⁺-2·1 complex could be used as a highly selective colorimetric sensor for S^2- in the presence of other anions without any interference. Moreover, the sensing mechanisms of Cu²⁺ and Co²⁺ by 1 were explained by theoretical calculations.

A concise treatment of pterins: some recent synthetic and methodology aspects and their applications in molecular sensors

A concise account of pterins in chemistry and biology and their applications in molecular sensors including their optical spectroscopic properties are described. Different natural, synthetic, biological and photophysical aspects are also discussed. Synthetic access to direct functionalised pterins and a recently reported new thiophene annulation technique are described for the synthesis of Form B of molybdenum cofactor. The receptor properties of fluorescent pterin molecules including selenopyrimidines which are rarely reported for their binding of anions and neutral molecules are also of major importance in this review. For such an old and still so young, unexplored pterin system on its power to be sensitive for physical studies especially the interaction with cations, anions and neutral molecules are fascinating and research in this area is relatively new and expected to increase fast. Pterin based receptors are for the first time put into a useful review for the advantage of those who want to explore pterin and modified pterin as chromogenic and fluorogenic sensors.

A carbon dots/rutin system for colorimetric and fluorimetric dual mode detection of Al3+ in aqueous solution

Colorimetric and fluorimetric dual mode detection of Al³⁺ in aqueous solution was achieved using a carbon dots/rutin (CDs/rutin) coexisting system.

Harnessing a pyrimidine based molecular switch to construct reversible test strips for F-/AcO- with respect to Al3+: A colorimetric approach

We report novel compound 4-nitro-2-((pyrimidin-2-ylamino) methyl) phenol (1) synthesized by the condensation of 5-nitro salicylaldehyde with 2-amino pyridine. Compound 1 serves as a dual signalling chromogenic receptor for F^-/AcO^- and Al³⁺ ions. The chromogenic response of 1 towards the aforementioned analytes is reversible with respect to either Al³⁺/X (=F/AcO)^- or X(F/AcO)^-/Al³⁺. The limit of detection of 1 for F^- and AcO^- are 1.0025×10^-7M and 0.79×10^-7M, respectively. The optical switching has been rationalized on the basis of UV-Vis titrations and ¹H NMR titrations respectively. The optical switching has been successfully use by constructing reversible paper strips for detecting Al³⁺ as well as F^-/AcO^-.

Design, synthesis, characterization and cation sensing behavior of amino-naphthoquinone receptor: Selective colorimetric sensing of Cu(II) ion in nearly aqueous solution with mimicking logic gate operation

An amino-naphthoquione receptor (R1) has been rationally designed, synthesized and characterized using ¹H and ¹³C NMR, LCMS and single crystal X-ray diffraction studies. The receptor exhibits an instantaneous colour change from yellow to blue selectively with Cu(II) ions in water-DMF (98:2% v/v) medium. The results of UV-Vis and fluorescence spectral studies indicates that the mechanism of sensing involves formation of a 1:1 complex between R1 and Cu(II) ion. The proposed mechanism has been confirmed through product analysis using FT-IR, UV-Vis, EPR and HRMS studies in addition to magnetic moment and elemental analysis measurements. The formed [Cu(R1)Cl₂] possess a square planar geometry. The binding constant for the interaction of Cu(II) ion with the present unsubstituted quinone is found to be relatively higher than that with quinones containing electron withdrawing chlorine atom and electron releasing methyl group reported in literature. The detection limit of Cu(II) ion in aqueous solution by R1 is observed to be 8.7nM. The detection of Cu(II) ion by R1 in aqueous solution produces remarkable changes in the electronic and fluorescence spectra, which is applied to construct logic gate at molecular level.

A single fluorescent chemosensor for multiple targets of Cu2+, Fe2+/3+ and Al3+ in living cells and a near-perfect aqueous solution

A naphthol-based chemosensor 1 was developed for detection of Cu²⁺ and Fe^2+/3+ by fluorescence quenching and Al³⁺ by fluorescence emission change.

A new Schiff-based chemosensor for chromogenic sensing of Cu2+, Co2+and S2−in aqueous solution: experimental and theoretical studies

A new Schiff-based multifunctional colorimetric chemosensor1was developed for the detection of various analytes (Cu²⁺, Co²⁺and S²⁻).

A novel and simple solvent-dependent fluorescent probe based on a click generated 8-aminoquinoline–steroid conjugate for multi-detection of Cu(ii), oxalate and pyrophosphate

A novel and simple deoxycholic acid-based fluorescent probe was facilely constructed for solvent-dependent multi-detection of Cu²⁺, C₂O₄²⁻and P₂O₇⁴⁻.

Functionalized calix[4]arene as a colorimetric dual sensor for Cu(ii) and cysteine in aqueous media: experimental and computational study

The sensors developed detect Cu²⁺and the metal complex recognizes cysteine, detectable by the naked eye, and DFT calculations corroborate the experimental results.

Synthesis and properties of new N,N′-phenyltetrazole podand

The synthesis of a new chromogenic N,N′-phenyltetrazole receptor is reported here. The cationbinding properties of this receptor in solution were investigated by naked-eye colour change, electrochemical methods and UV-Vis spectroscopy in various solvents (CH

Highly sensitive and selective “naked eye” sensing of Cu(ii) by a novel amido–imine based receptor: a spectrophotometric and DFT study with practical application

Synthesis of (E)-bis-N'-((1H-pyrrol-2-yl)-methylene)-pyridine-2,6-carbohydrazide and its sensing ability towards copper(ii) ion in aqueous medium by color change, the sensing limit being 4.0 × 10⁻⁹ M.

A reaction-based fluorescent turn-on probe for Cu2+ in complete aqueous solution

FP can detect Cu²⁺ in complete aqueous solution with a rapid response time, high sensitivity, and high selectivity.

New duel fluorescent "on-off" and colorimetric sensor for Copper(II): Copper(II) binds through N coordination and pi cation interaction to sensor

Schiff base derived from naphthylamine and benzil (L) binds to two Cu(2+) ions, one by coordination through N of the Schiff base and another by pi cation interaction through benzil rings. This bonding pattern determined by DFT calculation has been proved by matching electronic spectrum obtained from TDDFT calculation to the experimental one. L acts as "on-off" fluorescent and bare eye detectable colorimetric (purple color) sensor for Cu(2+) ion over the metal ions - Na(+), K(+), Ca(2+) Mn(2+), Co(2+) Ni(2+), Zn(2+), Pb(2+), Cd(2+), Hg(2+), Ag(+), Hg(2+) and Al(3+) in 1:1 v/v CH3CN:H2O. These metal ions do not interfere the fluorescent/colorimetric sensing. As fluorescent sensor the linear range of detection is 5×10(-5) to 3×10(-4)M and detection limit 10(-5)M.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

Rapid detection of hydrazine in a naphthol-fused chromenyl loop and its effectiveness in human lung cancer cells: tuning remarkable selectivity via the reaction altered pathway supported by theoretical studies

A new chemosensor (NAC) is reported for fast and selective detection of N₂H₄ in a novel way.

A single probe for sensing both acetate and aluminum(iii): visible region detection, red fluorescence and human breast cancer cell imaging

A single probe (L) can recognise both AcO⁻ and Al³⁺ as prepared by coupling 2-hydroxy-1-naphthaldehyde with hydrazine. The probe allows both colorimetric and fluorescence detection of both the ions.

A single chemosensor for multiple analytes: fluorogenic detection of Zn2+ and OAc− ions in aqueous solution, and an application to bioimaging

A single fluorescent chemosensor 1 for multiple analytes (Zn²⁺ and OAc⁻) has been developed and it can monitor Zn²⁺ ions in living cells.