Semi-aqueous Solution Research Articles

Colorimetric and Fluorimetric Detection of Fe(III) Using a Rhodamine-Imidazole Hydrazone Based Chemosensor: Photophysical Properties, DFT, TGA, and DSC Studies.

Rhodamine-imidazole hydrazones (RIH-1 & RIH-2) based chemosensors have been synthesized. These are characterised and evaluated by FT-IR spectroscopy, 1H-NMR, 13C-NMR, LCMS, absorption and fluorescence spectroscopy. These chemosensors exhibit enhanced sensitivity and selectivity in detecting the biologically significant Fe3+ metal ion through both colorimetric and fluorescence changes. The optical properties have been investigated using binary acetonitrile-water (7:3 v/v) semi-aqueous solution. The probe RIH-1 can be deployed as a fluorescent and colorimetric probe for the detection of Fe3+ ion. It shows an absorption band at 559nm and an intensity band at 579nm increasing up to 50-fold with the increase in the concentration of Fe3+ with the detection limit as low as 11nM. In the visible light, RIH-1 helps in the detection of Fe3+ ion through the naked eye, while the addition of Fe3+ to the probe RIH-1 results in a colour change from colourless to pink. This is primarily due to the opening of the lactone ring in RIH-1. Notably, RIH-1 probe displays a high quantum yield of 0.51, after binding with Fe3+ ions. Indeed, it has been found that sensor RIH-1 is very effective in sensing Fe3+ ions through both fluorescence based and visual detection methods. Additionally, DFT studies of these chemosensors have been evaluated, TGA and DSC analysis showed good thermal stability.

Dual function Schiff-base as a selective fluorescence “Turn-on” sensor for Zn2+ and a colorimetric sensor for Cu2+ and Fe3+ ions

A simple and adaptable salen-based Schiff base receptor (L = 6,6′-((1E,1′E)-(cyclohexane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol))was employed in the current study for colorimetric detection of Cu2+, Fe3+, and fluorescence detection of Zn2+ ions in a semi-aqueous solution. L could identify the three target ions among the many different cations and anions in the solution. The turn-on fluorescence signal of L to Zn2+ ions was boosted by the restriction of the intramolecular charge transfer process, and the resulting chelation enhances the fluorescence signal. The sensing mechanisms were validated using a Job’s plot, Electrospray Ionization Mass Spectrometry (ESI-MS) analysis, Nuclear Magnetic Resonance (NMR) titration experiment, and theoretical calculation investigations. The detection limits for Zn2+ were determined to be 0.038 μM, whereas Cu2+ and Fe3+ detection limits were 0.58 μM and 0.62 μM, respectively. Next, L was used to develop solid silica gel and test strips for instantaneous colorimetric and fluorescent detection of the three target ions in real time. The trace level of Cu2+ and Fe3+ in the tap and drinking water samples could be quantitatively measured using L. Eventually, applications for keypad locks and molecular logic gates were developed utilizing the receptor L.

Turn-off fluorescence of imidazole-based sensor probe for mercury ions

A new highly selective and sensitive fluorescent probe, 5 (2-(4-(1,3-dithian-2-yl)phenyl)-4,5-diphenyl-1H-imidazole), was developed for Hg2+ ion with colorimetric and fluorimetric behavior in organic semi-aqueous solutions.

An aggregation-induced emission-based ratiometric fluorescent chemosensor for Hg(II) and its application in Caenorhabditis elegans imaging

A chromone-based ratiometric fluorescent probe L2 was developed for the selective detection of Hg(II) in a semi-aqueous solution based on aggregation-induced emission (AIE) and chelation-enhanced fluorescence (CHEF) effect. The probe L2 fluoresced significantly at 498 nm in its aggregated state, and when chelated with Hg(II), the soluble state fluoresced 1-fold higher. In addition, Job’s plot reveals that the probe forms a 1:1 stoichiometry complex with Hg(II) with an association constant of 9.10 × 103M−1 estimated by the BH plot. The probe L2 detects Hg(II) down to 22.47 nM without interference from other interfering ions. The FTIR, ESI mass, and DFT-based computational studies investigated the binding mechanism of probe L2 with Hg(II). Taking advantage of its AIE characteristics, the probe L2 was successfully applied for bio-capability analysis in Caenorhabditis elegans (a nematode worm) imaging of Hg(II) in a living model.

Synthesis, characterization and sensing mechanism of a novel fluorescence probe for Fe(III) in semi-aqueous solution based on a Schiff base hexadentate receptor

A new acyclic Schiff base chemosensor L was synthesized by the one pot condensation reaction of 2-[3-(formyl phenoxy)2-hydroxypropoxy]benzaldehyde and 2-aminophenol in a 1:2 molar ratio and was characterized by elemental analysis, FTIR, 1H- and 13C NMR, and fluorescence spectroscopies. These studies were complemented with a thorough conformational study at the molecular mechanics and density functional theory (DFT) levels of theory to further elucidate the structure of the compound in solution. The chemosensor L displays high sensitivity and selectivity for Fe3+ in semi-aqueous (H2O-DMF, 1:1) solution, except in the presence of a significant amount of Ni2+, with the presence of Fe3+ being signaled through the total fluorescence quenching of the fluorophore when Fe3+ binds to the recognition unit. The synthesized ligand also shows high selectivity for Fe3+ compared to the metal ions Cu2+, Zn2+, Mg2+, Mn2+, Pb2+, Hg2+, Na+, Ba2+ and Cd2+, and reasonable selectivity in the presence of Ag+, Co2+ and Cr3+. The stoichiometry and structure of the complex formed between Fe3+ and the probe L were determined from a Job’s plot and DFT calculations, respectively. The complex was characterized as a high-spin 1:1 octahedral species, in which the ligand coordinates to the metal through the two ether oxygen atoms, two nitrogen atoms and two terminal hydroxyl groups. Time dependent (TD-DFT) calculations were performed to provide information on the type of mechanism causing the quenching of the fluorescence in the presence of Fe3+.

Simultaneous visual and spectroscopic multi-analyte detection of Al3+ and AsO2− using simple salicylidene based D-π-A chromophore

The salicylidene-isoniazide Schiff base D-π-A chromophore ( L1 ) exhibits chromogenic and fluorogenic dual responsive behaviour with multiple ICT-PET-ESIPT interplaying sensing mechanism and provides diverse optical signals promising to selectively and simultaneously track multiple analytes in water rich media. • Salicylidene-isoniazide Schiff base ( L1) exhibited naked-eye detectable distinctive colour changes for Al 3+ and AsO 2 - • It displayed turn-on type distinct fluorogenic response for both Al 3+ and AsO 2 - • Multiple ICT-PET-ESIPT interplaying mechanism provided diverse optical signals to simultaneously track multiple analytes. • Applied for fluorescence imaging of Al 3+ and AsO 2 - in living cells. The present communication reports the efficacy of a salicylidene-isoniazide Schiff base based donor-π-acceptor (D-π-A) chemosensor ( L1 ) for chromogenic and fluorogenic dual mode sensing of Al 3+ and AsO 2 - in water rich semi-aqueous solution. L1 offers multiple benefits of simplicity, ease of synthesis, inexpensive, suitable binding sites for cations and anions, high sensitivity, noteworthy colourimetric response, naked-eye detection, selectivity, and good detection limits of 1.89 μM for Al 3+ and 2.2 μM for AsO 2 - . It shows selective turn-on fluorescence response for both Al 3+ and AsO 2 - , attributed to CHEF due to the combined effect of arrest of PET, inhibition of -CH=N- geometrical isomerization, prevention of ESIPT process and increase in conformational rigidity. Owing to specific interaction between Mo(VI) and arsenite, L1 -Mo(VI) ensemble system is successfully utilized for colourimetric detection of arsenite through displacement approach. The binding modes of the receptor L1 to these analytes are established through Job’s plot and 1 H-NMR spectroscopic analysis. The reversible off-on-off fluorescence switching behaviour of L1 upon binding to Al 3+ and AsO 2 - are applied to construct combinational OR, AND, and NOT molecular logic gates. Fluorescence turn-on sensing, cell permeability and low toxicity of the chemosensor allows monitoring of these analytes in living cells.

Simultaneous detection of lysosomal SO2 and viscosity using a hemicyanine-based fluorescent probe

The changes in sulfur dioxide and viscosity of lysosomes are significant indicators in physiological processes and the cell microenvironment. This study aimed to synthesize a hemicyanine-based probe for simultaneous detection of SO2 and viscosity. The probe could not only rationally detect sulfur dioxide in a semi-aqueous solution with high sensitivity (limit of detection = 0.78 μM) and fast response (within 30 s) but also monitor viscosity via fluorescence emission enhancement at 580 nm. Further, the dual-response probe was successfully used to image SO2 and viscosity in the lysosomes of living cells.

A new Schiff base ligand as a fluorescence probe for Cu(II) detection in semi-aqueous solution: synthesis, characterization, fluorescence and mechanistic insight

A new Schiff base fluorescence probe for Cu2+ was designed and synthesized by reaction between 2-[(3-formylphenoxy)2-hydroxypropoxy]benzaldehyde and 4-aminophenol. The probe was characterized by elemental analysis, FTIR, 1H- and 13C NMR, and fluorescence spectroscopies. DFT calculations were carried out to further characterize the structure of the compound in solution, by carrying out an in-depth conformational study. The obtained results showed fluorescence quenching of the fluorophore when Cu2+ binds to the ligand (L) in semi-aqueous solution (DMF:H2O 1:1) and revealed that the probe has high selectivity for Cu2+ compared to the other metal ions analyzed (Ag+, Co2+, Mg2+, Ni2+, Pb2+, Zn2+, Cd2+, Cr3+, Hg2+, Na+, Ba2+, Mn2+ and Fe3+). The stoichiometry of the complex formed between Cu2+ and L has been determined from a Job’s plot as being 1:1 and a structure for the complex Cu2+/L is proposed. The mechanism for the quenching of the fluorescence in the presence of Cu2+ was evaluated on the basis of time-dependent DFT (TD-DFT) results.

Construction of a simple dual-channel fluorescence chemosensor for Cu2+ ion and GSSG detection and its mitochondria-targeting bioimaging applications

Numerous chemosensors have been developed for next-generation detection systems because of their ease of use and promising characteristics to distinguish signals between various analytes binding. However, given their typically poor emission response and arduous preparation methods, very few chemosensing probes have been commercialized to date. In this work, a simple, naphthoquinone-based mitochondria-targeting chemosensor (CIA) has been fabricated for the simultaneous detection of Cu2+ and GSSG (glutathione oxidized) through an “on-off” mode in a buffered semi-aqueous solution. Significantly, the CIA chemosensor showed a sensitive detection response towards Cu2+ and GSSG with low detection limits (0.309 μM, and 0.226 μM, respectively). In addition, the detection mechanism of CIA was thoroughly verified and confirmed using numerous analytical techniques. Furthermore, CIA was utilized as a sequential fluorescence biomarker to detect Cu2+ in human cervical cancer cell lines. These findings indicate that the chemosensor CIA can discriminate human cancer cells from normal cells. The CIA was also confirmed to possess the ability to target mitochondria. More importantly, the present CIA chemosensor detected Cu2+ in zebrafish larvae, indicating the probe has tissue penetration ability.

A naked-eye colorimetric sensor based on chalcone for the sequential recognition of copper(ii) and sulfide ions in semi-aqueous solution: spectroscopic and theoretical approaches

A chalcone-based new colorimetric sensor A01 for the sequential detection of Cu2+ and S2− ions.

Efficient FRET Approaches toward Copper(II) and Cyanide Detections via Host-Guest Interactions of Photo-Switchable [2]Pseudo-Rotaxane Polymers Containing Naphthalimide and Merocyanine Moieties.

A supramolecular [2]pseudo-rotaxane containing a naphthalimide-based pillararene host and a spiropyran-based imidazole guest was synthesized and investigated in a semiaqueous solution with 90% water fraction. Upon UV exposure, the close-form structure of nonemissive spiropyran guest could be transformed into the open-form structure of red-emissive merocyanine guest reversibly, which was utilized as a monofluorophoric sensor to detect copper(II) and cyanide ions. Moreover, the naphthalimide host as an energy donor with green photoluminescence (PL) emission at 505 nm was complexed with the merocyanine guest as an energy acceptor with red PL emission at 650 nm in 1:1 molar ratio to generate a [2]pseudo-rotaxane polymer, which was further verified by the diffusion coefficients of DOSY nuclear magnetic resonance (NMR) measurements. Due to the Förster resonance energy transfer (FRET) processes, the bifluorophoric [2]pseudo-rotaxane produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the monofluorophoric guest; therefore, the PL sensor responses of the supramolecular [2]pseudo-rotaxane toward copper(II) and cyanide ions could be further amplified via the FRET-OFF processes to turn off red PL emission of the reacted merocyanine acceptor and to recover green PL emission of the naphthalimide donor. Accordingly, the best and prominent values of the limit of detection (LOD) for the host-guest detections toward Cu2+ and CN- were 0.53 and 1.34 μM, respectively. The highest red MC emission with the optimum FRET processes of [2]pseudo-rotaxane was maintained around room temperature (20-40 °C) in wide pH conditions (pH = 3-13), which can be utilized in the cell viability tests to prove the nontoxic and remarkable biomarker of [2]pseudo-rotaxane to detect Cu2+ and CN- in living cells. The developed FRET-OFF processes with ratiometric PL behavior of the bifluorophoric supramolecular [2]pseudo-rotaxane polymer will open a new avenue to the future applications of chemo- and biosensors.

A novel indolium salt as a rapid colorimetric probe for cyanide detection in aqueous solution

In this study, a new chemosensor IDTTH for rapid detection of cyanide (CN─) based on 6,6,12,12-Tetrakis(4-hexylphenyl)-6,12-dihydrodithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]di- thiophene-2,8-dicarboxaldehyde-hemicyanine conjugate has been developed. The 6,6,12,12-tetrakis(4-hexylphenyl)-6,12-dihydrodithi-eno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene was served as a signal unit and hemicyanine as a recognition unit. This probe shows high selectivity towards CN─ ions among tested anions. Addition of CN─ ions to probe IDTTH in semi-aqueous solution (acetonitrile/H2O = 1/1, V/V) could lead to a 195 nm blue shift of absorption band, together with colour changes from blue to yellow. The sensing mechanism is attributed to the nucleophilic addition between CN─ and the C=N bond of indolium group, which could be clearly clarified through the 1H NMR titration and MS spectral. Moreover, probe IDTTH could be used as the test strips with low cost to detect CN─ ions conveniently by naked eyes.

Selective receptor for Fe(III) ion with a fluorescence-ON pyrene motif in semi-aqueous solution

A novel fluorescent sensor for the selective and sensitive detection of Fe3+ based on fluorescent enhancement has been developed in the present study. The sensor 3-(4-bromo-2-hydroxyphenyl)-1-(pyren-1-yl)prop-2-en-1-one (ABS) was synthesized by Claisen-Schmidt reaction between acetyl pyrene and 5-bromosalicylaldehyde. It was characterized by FT-IR, HR-MS,1H and 13C NMR. The sensor exhibited weak fluorescence due to C = C isomerization and intramolecular charge transfer (ICT) process but upon binding with Fe3+ it exhibited increase in fluorescence due to blockage of ICT and C = C isomerization. While adding above 50 μM Fe3+, the probe exhibited decrease in fluorescence, as against the saturation curve. The decrease was ascribed to ligand to metal charge transfer (LMCT). This phenomenon of electron transfer from the fluorophore to the bound metal ion resulted in decrease of the fluorescence via non-radiative energy transfer. The binding constant was found to be 2 × 103 M−1. The binding mechanism was established based on theoretical calculations whereas the fluorescence enhancement and decrease were confirmed by quantum yield and life-time studies. The binding mode of ABS-Fe3+ complex was ascertained by using 1H NMR and DFT studies. When increasing Fe3+ concentration from 50 nM to 1 μM, the emission intensity was linearly increased against the concentration of Fe3+ with a correlation coefficient of 0.999 and LOD was found to be 11.2 nM (3σ/S). Finally, the probe was successfully employed to determine Fe3+ in real samples and cell imaging studies.

Controllable and reversible proton transfer for inorganic cyanide visual sensing based on the deprotonation of azo-phenolic hydroxyl group

ABSTRACTMethods for optical detection of inorganic cyanide based on the single molecule sensor with high selectivity and sensitivity have attracted increasing interest recently due to the high toxicity of cyanide ions. In this work, a visual sensor (S1) containing both imidazole NH and azo-phenolic OH was synthesised and characterised. The spectral experimental data indicated that protic aqueous solution facilitated enhancing the selectivity of cyanide ions with the nanomolar-level detection limit in semi-aqueous solution. The visual sensing mechanism arising from the deprotonation of azo-phenolic OH and the enhancement of intramolecular charge transfer could be clearly demonstrated by titration experiments of 1H NMR, HR MS and energy changes between the HOMO−LUMO band gaps. Furthermore, the reversibility and reusability of S1 upon alternating addition of CN− and H+ were studied.

Removal of phosphate in presence of interfering sulphate and arsenate by a tripodal thiourea receptor by precipitation through crystallization in semi-aqueous medium

A cyanuric acid platform based tripodal thiourea receptor, L shows encapsulation of phosphate, sulphate and arsenate anions in semi-aqueous medium. Solution phase 1H NMR showed selective recognition of phosphate anion in presence of various anions (e.g. Cl−, Br−, I−, NO3−, HSO4−, CH3CO2− and H2PO4− as TBA salts) in DMSO-d6 at 298 K. L showed partial removal and separation of phosphates from semi-aqueous solution in the presence of interfering arsenate and sulphate via precipitation through crystallization. In the absence of phosphate, L is found to remove/separate arsenate from semi-aqueous medium in presence of sulphate which is the first report of partial removal of arsenate from semi-aqueous medium by a neutral anion receptor. In absence of phosphate and arsenate anions, L could partially remove sulphate anions from mixture of other anions from semi-aqueous solution. All the extracted complexes were characterized by NMR, PXRD, TEM-EDX and Single crystal X-Ray diffraction analysis.

Ratiometric fluorescent probe based on pyrrole-modified rhodamine 6G hydrazone for the imaging of Cu2+ in lysosomes.

A novel rhodamine-based Schiff base derivative was obtained via the simple condensation of substituted formyl-1H-pyrrole and rhodamine 6G hydrazone. Fluorescence resonance energy transfer enabled the subsequent use of the derivative as a naked-eye colorimetric and ratiometric fluorescent sensor for Cu2+ in semi-aqueous solution, and the existence of the morpholine group enabled the further application of the sensor in imaging Cu2+ in the lysosomes of HeLa cells.

A functionalized fluorochrome based on quinoline-benzimidazole conjugate: From facile design to highly sensitive and selective sensing for picric acid

Two important fluorophores (quinoline and benzimidazole) have been successfully combined to achieve a novel fluorochrome with desirable fluorescent performance in solution and solid state. This original fluorochrome exhibits not only visual fluorescence quenching toward picric acid (PA) over other nitroaromatics and common interferents, but also ppb-level (4.86 ppb) of detection limit in semi-aqueous solution. In addition, the other sensing properties such as rapid response (second-level), good environmental compatibility (pH tolerability) and sensitivity are also evidentially revealed. The dominant quenching mechanism involves a synergistic effect of inner filter effect and photoinduced electron transfer (PET), which is fully supported by spectral analysis, 1H NMR assay, morphological studies, lifetime experiments and theoretical calculation. Noteworthily, the fluorochrome can be readily used in real water samples for quantitative determination of PA and processed as fluorescent paper or thin layer chromatography (TLC) plate for naked-eye detection, which enable itself to be functionalized as applicable PA sensor.

Urolithin B as a Simple, Selective, Fluorescent Probe for Sensing Iron(III) in Semi-Aqueous Solution.

The development of simple, environmental friendly, and cheap reagents with metal binding properties are quite important not only for the treatment of environmental pollution but also for their application in medicine. Within this study, for the first time, we displayed a natural chromen analogue, Urolithin B, as a simple, selective, fluorescent iron (III) sensing probe. Following the synthesis and structure identification studies, the selective metal binding property of the compound was displayed employing fluorescence techniques. Accordingly, urolithin B has the capacity to coordinate selectively to iron (III) with a 3:2 stoichiometry.

AEE active Schiff base-bearing pyrene unit and further Cu2+–induced self-assembly process

Abstract A novel pyrene-based Schiff base derivative, 1, was synthesized by one-pot reaction. This compound was then used for aggregation emission enhancement and as fluorescence turn-on sensor toward Cu2+ in semi-aqueous solution based on metal-induced self-assembly. Detection limit of Cu2+ ion was 35 nM. The fluorescent sensor was further applied in monitoring intracellular Cu2+ in HeLa cells.

Fluorescent triazolium for sensing fluoride anions in semi-aqueous solution

A new triazolium-based receptor for fluorescent sensing of inorganic fluoride anions in semi-aqueous solution and the solid state was reported.