Chemosensor L1 Research Articles

Substituent effect on discriminative detection of Mg2+ and Zn2+ ions by two related coumarin-based chemosensors

Two closely related coumarin-based chemosensors, L1 with a –NO2 group and L2 with an −I group, have been designed as the fluorescent sensors. Chemosensors L1 and L2 have been utilized for the selective detection of Mg2+ and Zn2+ ions, respectively. The non-fluorescent L1 and L2 exhibit ‘turn-on’ fluorescence response with Mg2+ and Zn2+ ions, respectively. The absorption spectrum of L1 in presence of Mg2+ ion exhibits a 12 nm blue-shift while L2 shows a 5 nm red-shift with Zn2+ ion. Chemosensors L1 and L2 show noteworthy detection limits of 0.10 and 0.35 μM and binding constants (Kb; ×104 M−1) of 0.45 and 1.14 for Mg2+ and Zn2+, respectively. The chemosensor-metal binding was studied by mass and proton NMR spectra while a 2:1 stoichiometry was confirmed by Job’s plot. The crystal structure of [(L2)2Zn] complex further confirms a 2:1 stoichiometry as well as binding mode of the chemosensors. Both chemosensors further worked as the colorimetric sensors for the detection of Mg2+ and Zn2+ ions. For both chemosensors, reversibility was achieved by using ATP while logic gates were also generated. Chemosensor L2 was found to be AIEE active in MeOH-H2O and EtOH-H2O solvent systems. Water promoted H-type aggregation by hindering the −CN bond rotation which enhanced the emission. The formation of aggregates was confirmed by the dynamic light scattering and florescence lifetime measurements.

Discriminative 'Turn-on' Detection of Al3+ and Ga3+ Ions as Well as Aspartic Acid by Two Fluorescent Chemosensors.

In this work, two Schiff-base-based chemosensors L1 and L2 containing electron-rich quinoline and anthracene rings were designed. L1 is AIEE active in a MeOH-H2O solvent system while formed aggregates as confirmed by the DLS measurements and fluorescence lifetime studies. The chemosensor L1 was used for the sensitive, selective, and reversible 'turn-on' detection of Al3+ and Ga3+ ions as well as Aspartic Acid (Asp). Chemosensor L2, an isomer of L1, was able to selectively detect Ga3+ ion even in the presence of Al3+ ions and thus was able to discriminate between the two ions. The binding mode of chemosensors with analytes was substantiated through a combination of 1H NMR spectra, mass spectra, and DFT studies. The 'turn-on' nature of fluorescence sensing by the two chemosensors enabled the development of colorimetric detection, filter-paper-based test strips, and polystyrene film-based detection techniques.

Methylene Spacer Mediated Detection Switch Between Copper and Zinc Ions by Two Coumarin‐Pyrene Based Chemosensors

AbstractPyrene linked‐coumarin based fluorescent chemosensors L1 and L2 are utilized for the selective detection of Cu2+ and Zn2+ ions, respectively. Both chemosensors differed by a methylene spacer that connects the coumarin and pyrene rings through an imine group. The inclusion of methylene spacer dramatically changed the detection profiles of two chemosensors. While L1 showed fluorescence “turn‐off” response towards the Cu2+ ion; L2 showed “turn‐on” emission enhancement with the Zn2+ ion. Both chemosensors illustrated nano‐molar detection limits and were selective even in the presence of other competing metal ions. The 1 : 1 stoichiometry between a chemosensor and Cu2+/Zn2+ ion was supported by the binding studies, Job's plot, NMR spectral titrations, mass spectra and density functional theory (DFT) studies. The detection ability of both chemosensors was utilized by fabricating the filter paper test‐strips as well as polystyrene films for quick and visual monitoring of these ions in different water samples. Chemosensor L2 was further utilized for the “turn‐on” detection of Zn2+ ion in HepG2 cells whereas solution generated L2‐Zn species functioned as a secondary chemosensor for the detection of cystine, an important amino acid.

Highly selective, reversible and ICT-based fluorescent chemosensor for bismuth ions: Applications in bacterial imaging, logic gate and food sample analysis

N1,N5-bis(pyridin-2-ylmethylene)naphthalene-1,5-diamine (L1) Schiff base conjugate was synthesized by the condensation reaction of 1,5-diamino naphthalene (1,5-DAN) and 2-pyridine carboxaldehyde and spectroscopically evidenced by 1H NMR, 13C NMR and Mass spectrum. The developed Schiff base conjugate was used as a fluorescent chemosensor for the selective recognition of bismuth (Bi3+) ions in the midst of various interfering heavy transition metal ions such as Ag+, Hg2+ and Cu2+ with marked fluorescence enhancement. Based on “switch-on” intramolecular charge transfer (ICT) approach, chemosensor L1 showed specific response towards bismuth ions with a low detection limit of 1.5 × 10−8 M and a high binding constant 7.11 × 105 M−1. Simultaneously, the experimental (Job’s plot, Mass spectrum, and FT-IR) and theoretical (B3LYP-D3/6–311++G(d,p)) analysis were performed for promising the 1:1 binding mode of L1 + Bi3+ complex formation. The chemosensor L1 has been successfully demonstrated in practical applications such as water and food samples, bacterial imaging and logic gate operation producing satisfactory results.

Aryl- CH and aryl-π•••hole supported selective colourimetric sensing of cyanide. Effect of ‘on- the - ring /off- the-ring’ π•••hole functionality in cyanide selectivity

ABSTRACT Electron-withdrawing natured di-nitro substituted, π···hole recognition element incorporated electron-deficient chemosensors L1, L1”, L2 and L2” have been designed and synthesised. UV-Vis and naked-eye colourimetric studies show that the nitro functionalization and numbers of nitro functionalization decide the selectivity of receptors towards cyanide anion sensing. When an electron-withdrawing natured, di-nitro substituted electron-deficient π···hole aryl moiety is present in a chemosensor, the aromatic – C-H group turns to be an additional hydrogen bonding donor, establishing selective colourimetric sensor for anion of our interest, cyanide. In addition, electron-deficient perfluoro phenyl moiety is also contributing in strengthening the sensors. The selectivity of these two chemosensors L1 and L2 towards cyanide anion is due to the overall cooperative effects of Ar-C-H···anion, traditional urea – N-H···cyanide, cyanide···π interactions present in the respective sensor molecules. To the best of our knowledge, this is the first report of colourimetric sensing of cyanide inclined by Ar-CH group.

A styrylpyridinium dye as chromogenic and fluorogenic dual mode chemosensor for selective detection of mercuric ion: Application in bacterial cell imaging and molecular logic gate

The present work demonstrates design, synthesis and chemosensing application of a styrylpyridinium based donor-π-acceptor (D-π-A) chromophore (L1) containing NS2O2 binding site. The chemosensor L1 selectively and successfully detects Hg2+ ions both visually and spectro-photometrically in perfect aqueous medium as well as in an aqueous-alcoholic mixture. Contrary to the reported literature on mercury sensing by cyanine dye which were reported to be “turn-off” Hg2+ sensor, probe L1 shows fluorescence “turn-on” response. D-π-A chromophore L1 exhibits orange colour in aqueous and aqueous-alcoholic solutions due to intramolecular charge transfer (ICT) from the N, N-disubstitutedaminostyryl donor to pyridinium acceptor moiety. It shows Hg2+-specific colour change with concomitant generation of a new absorption band and large emission enhancement (~10 fold) along with a blue shift of emission peak, owing to the formation of a selective 1: 1 L1-Hg2+ complex. 1H NMR analysis reveals the binding mode of L1 with Hg2+. Hg2+ probing process was found to be reversible in presence of sulphide anion. The reversible off-on-off fluorescence response of the sensor with Hg2+ and S2− has been used to generate an INHIBIT molecular logic gate. The probe not only provides a highly efficient, low cost, portable sensor for recognition and naked-eye detection of Hg2+ with a low detection limit in aqueous solution but its turn-on fluorescence response and cell permeability offer the possibility of using it for fluorescence imaging in living cells.

Ether based flexible bis Schiff base fluorescent colorimetric chemosensors for selective and sensitive detection of HF2− ion

Two simple and low cost bis Schiff base fluorescent colorimetric chemosensors L1 and L2 have been designed and synthesized. These sensors could detect important anion HF2− by change in both absorption and fluorescence intensity in methanol tris HCl buffer (1:1 v/v) solution at physiological pH. The mechanism of selectivity and sensitivity of these receptors to HF2− has proposed to be on the basis of photo-induced electron transfer (PET), chelation enhanced fluoresence (CHEF) and hydrogen bonding mechanism, confirmed by FT-IR, 1H-NMR and ESI-mass spectra. Interestingly, chelation of HF2− to the receptors takes place in 1:2 ratio, which has been confirmed by job plots analysis, ESI-mass spectra, DFT and TD-DFT studies. The detection limits of the probes L1 and L2 for HF2− were determined to be 6.1 μM for L1 and 3.94 μM for L2 respectively, on the basis of 3σ/K. Importantly, the low detection limits of L1 and L2 for HF2−suggest that L1 and L2 are sensitive sensors for detection of these ions in drinking water. The receptors L1 and L2 can successfully applied for detection and quantification of HF2− in real samples. To the best of our knowledge this is the third report of fluorescent colorimetric chemosensors for HF2− ions.

Simple salicylaldimine-functionalized dipodal bis Schiff base chromogenic and fluorogenic chemosensors for selective and sensitive detection of Al3+ and Cr3+

Two salicylaldimine-functionalized dipodal bis Schiff base low cost fluorescent colorimetric chemosensors L1 (bis([4-(2-hydroxy-3-methoxybenzyl-ideneamino)phenyl]ether) and L2 (di[(4-phenylimino)4-diethylsalicyl-aldehyde]ether) have been designed and synthesized. These sensors could simultaneously detect two biologically important metal ions (Al3+ and Cr3+) by change in both absorption and fluorescence intensity in CH3CN-H2O (1/1, v/v) solvent mixture at physiological pH. The jobs plot analyses indicate the 2:2 binding stereochemistry for Al3+ and Cr3+ ions with both the probes L1 and L2, which were further been confirmed by 1H NMR and ESI-MS studies. The binding constant values for L1 were found to be 2.35 × 105 M−1 for Al3+ and 1.26 × 105 M−1 for Cr3+ and in case of L2 these values are 1.46 × 105 M−1 for Al3+ and 3.0 × 105 M−1 for Cr3+. The detections limits of the sensor L1, for Al3+ (1.73 × 10−7 M) and Cr3+ (1.12 × 10−7 M) and of the sensor L2, for Al3+ (4.34 × 10−7 M) and Cr3+ (7.73 × 10−7 M) are far below than the limit set by the World Health Organization (WHO) for drinking water. Moreover, visible colorimetric test kits and real samples for rapid detection of Al3+ and Cr3+ could be successively applied for all practical purposes, indicating their potential use in environmental samples.

Coumarin-based multifunctional chemosensor for arginine/lysine and Cu2+/Al3+ ions and its Cu2+ complex as colorimetric and fluorescent sensor for biothiols

A new chemosensor L1 based on coumarin was synthesized straightforward. It serves as a colorimetric and fluorescent probe for selective and sensitive detection of Arg and Lys over other common amino acids Cys, Hcy, GSH, Phe, His, Met, Gly, Val, Tyr, Glu and Leu. Among various metal ions L1 is able to detect Cu2+ ion by the naked eye with high selectivity and sensitivity. The probe L1 can be utilized for fluorescent sensing of Cu2+ and Al3+ ion with the detection limit of 8 μM and 2 μM, respectively. The ‘in situ’ formed L1–Cu2+ ensemble may be used for colorimetric and fluorescent recognition of Cys, Hcy and GSH over other common amino acids including Phe, His, Met, Gly, Val, Tyr, Glu, Arg, Lys and Leu. The detection limit of the ensemble L1–Cu2+ toward Cys, Hcy and GSH reached 10 μM, 10 μM and 16 μM, respectively. Possible sensing mechanism of L1 toward Arg/Lys and Cu2+/Al3+ ions and the ensemble L1–Cu2+ toward the biothiols is proposed.

A highly selective sensor for Cu2+ and Fe3+ ions in aqueous medium: Spectroscopic, computational and cell imaging studies

A rationally designed chemosensor L1 (2-(2-amino-4,5-dihydrothiazol-4-yl)-5,5-dimethylcyclohexane-1,3-dione) is capable for the detection of biologically important Cu2+ and Fe3+ ions. The observable change in absorbance and emission in HEPES buffer solution and binding parameters display notable sensing ability of Cu2+ and Fe3+ ions. From Job’s plot and ESI-MS spectra, 1:1 stoichiometric complexation with Cu2+ and Fe3+ ions have been established. The chemosensor was also utilized to develop logic gate by reversibility cycles for Fe3+ ion by EDTA. In addition, complex formation between the receptor and Cu2+/Fe3+ ion was investigated by spectroscopically and computational studies. The cell imaging study indicated that L1 is highly efficient for the detection of Fe3+ ion in live cells. The simple synthetic route, multi-stimuli response, regenerative action and solution visualization of the proposed chemosensor potentially make it as excellent sensor for real samples.

Pyrene based chalcone as a reversible fluorescent chemosensor for Al3+ ion and its biological applications

A pyrene scaffold bearing a phenol molecule has been designed and synthesized as a chemosensor L1 by an aldol type of condensation reaction. The sensor showed high sensitivity and selectivity for Al3+ ions by the enhancement of fluorescene intensity and distinguishes from the other potentially competing metal ions. The effect of pH, time and the reversibility of the sensor are studied. The fluorescence experiments suggested that the proposed binding of L1 and Al3+ ion is in a 1:1 stoichiometry. The chemosensor’s direct application in the electrosorptive removal of Al3+ ion and several other biological applications including the bio-imaging of bacterial cells were examined.

Fluorescent detection of multiple ions by two related chemosensors: structural elucidations and logic gate applications

Two related chemosensors L1 and L2 display selective detection of multiple ions (Cu2+, Al3+, Cd2+ and S2−) as a result of minor variation of functional groups at a remote arene ring.

Fluorescent turn-on sensors based on pyrene-containing Schiff base derivatives for Cu2+ recognition: spectroscopic and DFT computational studies

A new fluorescent chemosensor L1, a pyrene containing a long chain Schiff base derivative at the 1-position has been synthesized. Similarly, the receptors L2 and L3 are also designed in order to compare the binding ability for detection of Cu2+. The receptors exhibit very weak fluorescence (Φ=0.01) due to the photoinduced electron transfer (PET). Upon addition of 10 equiv of Cu2+, the emission intensity of ligands L1 and L2 are increased 65-fold (Φ=0.31) and 25-fold (Φ=0.08) in CH3CN/CH2Cl2 solvents system, respectively. NMR titration experiments, spectroscopic and DFT computational studies confirmed the binding phenomena and sensitivity of Cu2+.

RETRACTED: A new quinoline-based chemosensor for Zn2+ ions and their application in living cell imaging

Abstract The synthesis and evaluation of new quinoline based fluorescent chemosensor L1 for the detection of Zn 2+ in THF/H 2 O. The absorption and fluorescent spectra change was observed upon addition of Zn 2+ indicate that L1 is highly selective for Zn 2+ over other metal ions. The probe displayed an apparent color change while addition of Zn 2+ , which could be observed by the naked eye under a UV lamp. The experimental results have been verified with DFT and TDDFT calculation. In vitro sensitivity to Zn 2+ was demonstrated in Hela cells with the use of fluorescence confocal microscopy.

Reversible fluorescent and colorimetric rhodamine based-chemosensor of Cu2+ contact ion-pairs using a ditopic receptors

Rhodamine chemosensors based on excimer-fluorescent resonance energy transfer (Em-FRET), combined with energy donor from excimer emission (naphthalene excimer) and energy acceptor from dye absorption (rhodamine dye) (L1) and fluorescent chemosensor (L2) were designed and synthesized. Complexation studies using UV–vis absorption and fluorescence spectroscopy showed that L1 and L2 were chemosensors selective for AcO−. Allowing the chemosensors L1 and L2 to complex with Cu2+ resulted in a hyperchromic shift of UV–vis absorption and a quenching of fluorescence in the presence of anions such as AcO−, F−, BzO− and H2PO4−. The incremental stability constants of anion complexation upon addition of Cu2+ were illustrated due to the allosteric effect and inductive effect from Cu2+ complexation. The adduct L1·Cu2+ could still be used to detect AcO−, whilst the adduct L2·Cu2+ turned out to bind BzO−.

A novel sensing capabilities and structural modification from thiourea to urea derivative by Hg(ClO4)2: Selective dual chemodosimeter for Hg2+ and F− ions

A new rhodamine-6G phenylthiourea derivative (L1) condensed product was developed as a fluorescent and colorimetric dual chemosensor in acetonitrile with more selective towards Hg2+ and F− ions. Hg2+-promoted spirolactam ring opening of the rhodamine moiety induced urea formation through the diphenylcarbodiimide intermediate from the thiourea moiety. It demonstrates high selectivity for sensing Hg2+ with about 700-fold enhancement in fluorescence emission intensity and micromolar sensitivity (limit of detection 4.52×10−7M) in comparison with other various metal ions. Hg2+ ions coordinated reversibly to L1, forming a 1:2 metal–ligand complex. The thiourea moiety provided an anion binding site, and the rhodamine system was responsible for fluorescence. In turn, the chemosensor L1 acted as a selective chemosensor toward F− among various anions. Thus, L1 associated with F− with 1:1 stoichiometry. A recognition mechanism based on the binding modes of Hg2+ and F− ions were proved by the analytical techniques like UV–vis, changes in fluorescence, 1H NMR, FT-IR, ESI-mass and HRMS. In addition, this chemosensor exhibited highly selective and sensitive recognition of azide (N3−) anions upon the addition of Hg2+ with a color change back to colorless in the same solution.

Highly reversible “on–off–on” fluorescence switch and logic gate accurately controlled by pH based on nitrophenylfuran–acylhydrazone

A series of colorimetric and fluorescent pH chemosensors L1∼L3, bearing acylhydrazone moiety as pH sensing site and nitrophenylfuran moiety as signal group, were designed and synthesized. Among these sensors, L1 showed excellent reversible pH response for a specific pH change in very narrow pH range (at pH ranged from 12.0 to 12.5, within 0.5 pH unit) through sharp optical spectra and obvious fluorescent color changes. Common anions (such as F−, Cl−, Br−, I−, AcO−, H2PO4−, HSO4−, ClO4−, CN−, OH−) and cations (such as Fe3+, Hg2+, Ag+, Ca2+, Cu2+, Zn2+, Pb2+, Cd2+, Ni2+, Co2+, Cr3+, Mg2+) did not interfere with the pH response process. These properties make L1 act as an accurate pH controlled “on–off–on” fluorescence switch and implication (IMP) function logic gate.

A benzothiazole containing CHEF based fluorescence turn-ON sensor for Zn2+ and Cd2+ and subsequent sensing of H2PO4− and P4O74− in physiological pH

A benzothiazole functionalized chemosensor L1, exhibited colorimetric as well as fluorometric response to Zn2+ ion at physiological pH based on CHEF process. Selective naked eye detection of Zn2+ ion over most of the biologically important cations was also demonstrated. Sensing of biologically hazardous cadmium ion was also possible with L1. Further, both the zinc and cadmium ensembles of L1 were found to respond P4O74− and H2PO4− anion among other important biological anions and nucleotides via fluorescence quenching. Chemosensor L1, was also found to be reversible and recyclable toward Zn2+ and pyrophosphate ions over more than six cycles and responds to a INHIBIT logic gate. NMR titration and theoretical calculations were also conducted to understand the sensing behavior of L1.

Preparation of fluorescein-based chemosensors and their sensing behaviors toward silver ions

Two fluorescein-based fluorescent chemosensors L1 and L2 have been synthesized successfully by simultaneously introducing two functional groups as metal ion bonding sites on the 4,5-positions of fluorescein via a one-pot Mannich-type reaction. The chemosensors exhibit high selectivity and sensitivity for Ag+ ions due to the high thiophility and selenophility of silver ions. The detection mechanism is based on the Ag+-induced ring opening process of the spironolactone of the fluorescein fluorophore. The stoichiometry of the complex between the sensor and Ag+ is indicative of a 1 : 2 ratio which was determined by a Job's plot yielded from fluorescence titrations.

An “off–on–off” fluorescent probe for the sequential detection of Zn2+ and hydrogen sulfide in aqueous solution

The fluorescent chemosensor L1 has been synthesized for the sequential detection of Zn2+ and hydrogen sulfide.