A highly selective and sensitive rhodamine B-based chemosensor for Sn4+ in water-bearing and biomaging and biosensing in zebrafish

A novel colorimetric-fluorescent dual-mode chemosensor (JT5) based on rhodamine B has been produced for monitoring Sn4+ in the DMSO/H2O (4:1, v/v) medium. It has high sensitivity, a low detection limit, a short response time (1 s) and high stability, and can still be maintained after two weeks with the red dual fluorescence/ colorimetric response. Enhancement of red fluorescence (591 nm) and red colorimetric (567 nm) response of JT5 by Sn4+ addition. The electrostatic potential of the sensor JT5 molecule was simulated to speculate on the sensing mechanism, and the IR, mass spectrometry and 1H NMR titration were utilized to further demonstrate that JT5 was coordinated to Sn4+ with a 1:1 type, the rhodamine spironolactam ring of JT5 opens up to form a penta-membered ring with Sn4+, meanwhile, its system may have chelation enhanced fluorescence (CHEF) effect. In addition, theoretical calculations were carried out to give the energy gaps of JT5 and [JT5 + Sn4+] as well as to simulate the electronic properties of the maximal absorption peaks. Notably, the sensor JT5 was successfully applied to monitoring Sn4+ in zebrafish, and the JT5-loaded filter paper provided a solid-state platform for detecting Sn4+ by both naked eye and fluorescent methods. In summary, this work contributes to monitoring Sn4+ in organisms and solid-state materials and promotes understanding of Sn4+ functions in biological systems, environments, and solid-state materials.

A very rare fluorescent chemosensor of zinc(II) exhibiting AIEE, ESIPT and TICT: Spectroscopic, crystallographic and theoretical exploration

The basic systems in this study are HL (1; 1:2 condensation product of 2,6-diformyl-4-ethylphenol and o-anisidine) and its ZnII and CdII complexes of composition [ZnII(LH)Cl2]·CH3OH (2) and [CdII(LH)Cl2] (3), all of which are synthesized and characterized by CHN elemental analyses, single crystal X-ray crystallography, powder X-ray diffraction (PXRD) and fourier transform infrared (FT-IR) spectrum. It has been established from the following experimental and theoretical studies that 1 is a fluorescent turn on sensor of ZnII ion and it exhibits all of excited state intramolecular proton transfer (ESIPT), photoinduced electron transfer (PET), twisted intramolecular charge transfer (TICT) and aggregation induced enhanced emission (AIEE): (i) Detailed absorption and emission (steady state / time resolved) studies in various single solvents, in solvent mixtures, with pH variation, with various single metal ions, with mixtures of metal ions, on varying temperature and on varying viscosity; (ii) dynamic light scattering (DLS) and scanning electron microscopy (SEM) in solvent mixtures; (iii) density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations in ground and excites states of 1-3. It is shown that 1 can be efficaciously applied in inkless writing with the "write - erase - write" facility. The mechanisms/reasons of the observed properties have been addressed. The difference in fluorescence of ZnII and CdII complexes, unusual case of crystal structures of probe and complexes with ZnII and CdII, unusual features in the structures of 2 and 3 as well as a structure-property correlation have been discussed.

Novel pyrazoline and pyrazole "turn on" fluorescent sensors selective for Zn2+/Cd2+ at λem 480 nm and Fe3+/Fe2+ at λem 465 nm in MeCN

A small series of simple pyrazoline and pyrazole based sensors, all derived from the same chalcone precursors, were synthesised, characterised and screened for their fluorescence "turn on" properties in the presence of multiple metals. Pyrazole 8 displayed an excellent fluorescence profile with approx. 20× fold increase in λem 480 nm with Zn2+ compared to a 2.5× fold increase with Cd2+. Pyrazole 9 displayed a 30× fold increase at λem 465 nm for Fe3+ compared to Fe2+ with a Fe3+ limit of detection of 0.025 μM. The corresponding pyrazolines displayed contrasting properties with important implications for future pyrazoline and pyrazole sensor design.

A fluorescent Salamo-Salen-Salamo-Zn(II) sensor for bioimaging and biosensing H2PO4- in Zebrafish and plants

A newly designed and synthesized Salamo-Salen-Salamo-Zn(II) complex sensor (sensor ZT) was extensively explored for anion sensing studies. The selectivity and sensitivity of the sensor ZT towards H2PO4- ions were based on ICT and CHEF effects, and via displacement pathways in DMSO/H2O (9:1, v/v) medium in the presence of other anions like, PO43-, HPO42- and P2O74- in a short time, separately. The prepared ZT sensor has excellent association constant and low detection lines. The sensing mechanism and binding mode of the sensor were studied by UV-Vis spectroscopy, HR-MS, 1H NMR titration and theory calculations (DFT & TD-DFT) for analytes. The time response and stability of the sensor are also given. Meanwhile, the sensor ZT can be widely used as a simple and effective solid-state optical sensor to detect H2PO4- by intuitive fluorescence changes. In addition, besides the environment can be used as a powerful instrument for detecting H2PO4-, based on the good biocompatibility and tissue permeability of ZT, effectively monitoring H2PO4- in cellular distribution by confocal microscopy using Zebrafish and bean sprout.

A novel phenolphthalein-based fluorescent chemosensor for pyrophosphate detection via an Al3+ displacement approach in real samples and living cells

Herein, we report a new phenolphthalein appended Schiff base (PASB) as reversible fluorescent sensor for the detection of pyrophosphate (PPi) ions through the metal displacement mechanism. PASB showed sensing exclusively toward Al³⁺ ions in DMF/H₂O (v/v = 1/4, pH 5.5) solution, which resulted in a significant fluorescence enhancement at 540 nm. The 1: 2 binding stoichiometry for the complex formation between PASB and Al³⁺ was confirmed by Job's plot and mass spectroscopic studies. Moreover, a solution of the in situ formed PASB-Al³⁺ complex displayed a high selectivity to PPi. The addition of PPi to PASB-Al³⁺ ensemble significantly quenched its fluorescence. Thus, a dual response was established based on "Off-On-Off" strategy for detection of both Al³⁺ and PPi. The detection limit is 5.86 nM and 26 nM for Al³⁺ and PPi, respectively. On this basis, we use PASB to detect Al³⁺ in food samples. Furthermore, PASB was successfully applicable to detect Al³⁺ and PPi for intracellular imaging in Human liver cancer cells.

A new diformyl phenol based chemosensor selectively detects Zn2+ and Co2+ in the nanomolar range in 100% aqueous medium and HCT live cells

A new diformyl phenol based chemosensor that can sense Zn2+ and Co2+ in the nanomolar range in 100% aqueous solution and in HCT cells was explored.

A new half-condensed Schiff base platform: structures and sensing of Zn2+ and H2PO4- ions in an aqueous medium

A newly designed and synthesized half-condensed organic moiety 2-hydroxy-5-methyl-3-[(2-phenylamino-phenylimino)-methyl]-benzaldehyde (HL') and a Zn₂L₄ complex sequentially detect Zn²⁺ and H₂PO₄^- ions as low as 1.13 nM and1.23 μM, respectively. HL' and a dinuclear Zn(ii) complex of in situ generated L^- in a solution formulated as Zn₂L₄ under investigation were characterized by physicochemical and spectroscopic studies along with detailed structural analyses by single-crystal X-ray crystallography. The selectivity and sensitivity of HL' towards Zn²⁺ ions and of the Zn₂L₄ complex towards H₂PO₄^- ions are based on CHEF and via displacement pathways, respectively. Dual sensing of Zn²⁺ ions and H₂PO₄^-ions in an aqueous medium via "Green-Blue-Green" emission with the reversible transformation of in situ formed HL' to HL was established by detailed electronic absorption and emission spectroscopic studies. This non-cytotoxic probe (HL', i.e. produced HL in solution) and Zn₂L₄ complexes are able to monitor the subcellular distribution changes of Zn²⁺ and H₂PO₄^- ions, respectively, by fluorescence microscopy using the human semen sample.

Dual recognition of Al3+ and Zn2+ ions by a novel probe based on diarylethene and its application

We synthesized a new fluorescent probe 1O by attaching a diarylethene molecule to a functional group. The probe can be used to detect Al3+ and Zn2+ at the same time with high selectivity, and its detection limit is very low. When Al3+ was added, the fluorescence intensity was increased 310 folds, and was accompanied by a fluorescent color change from black to grass-green. Similarly, after the addition of Zn2+, the fluorescence intensity was enhanced 110 folds, with a concomitant color change from black to yellow-green. Moreover, based on the properties of 1O, we designed a logic circuit, and that also can be used for water sample testing.

Construction and Photoluminescent Properties of Schiff-Base Macrocyclic Mono-/Di-/Trinuclear ZnII Complexes with the Common 2-Ethylthiophene Pendant Arm

A new flexible 2-ethylthiophene pendant-armed dialdehyde (H₂tdd) was reacted with 1,3-propanediamine, [( S, S),( R, R),(±)]-1,2-diaminocyclohexane, and 1,2-bis(2-aminoethoxy)ethane, giving birth to 36-membered [2 + 2] Schiff-base macrocyclic trinuclear Zn^II complex 1, 18-membered [1 + 1] mononuclear Zn^II macrocycles 2-4, chiral/racemic 34-membered [2 + 2] dinuclear Zn^II complexes 5-9, and 46-membered [2 + 2] dinuclear Zn^II macrocycles 10-12 via Zn^II ion template-assisted Schiff-base condensation. It is worth mentioning that the secondary template effects for nitrate and halide counterions have been observed in the 1,3-propanediamine involved imine condensation. In all [2 + 2] Zn^II macrocycles, dinuclear complexes 5-9 display a full-folded molecular conformation, while trinuclear complex 1 and dinuclear complexes 10-12 exhibit distinct half-folded structures in the presence or absence of intramolecular π-π stacking interactions between two phenolic rings of the dialdehyde component. Interestingly, a solvent-induced single-crystal-to-single-crystal transformation was first achieved for two types of solvated mononuclear macrocycles 3a and 3b (H₂O vs CH₃CN) with folded and unfolded ligand conformations. In addition, the photoluminescent properties were studied for this family of Schiff-base macrocyclic Zn^II complexes as well as the dialdehyde precursor H₂tdd.

A cationic tetrahedral Zn(ii) cluster based on a new salicylamide imine multidentate ligand: synthesis, structure and fluorescence sensing study

We present here a monocationic Zn^II tetrahedral cluster which is extremely stable and exhibits highly sensitive and selective recognition of phosphates against other common anions in water containing media.

Highly Sensitive Ratiometric Chemosensor and Biomarker for Cyanide Ions in the Aqueous Medium

A newly designed cyanide-selective chemosensor based on chromone containing benzothiazole groups [3-(2,3-dihydro-benzothiazol-2-yl)-chromen-4-one (DBTC)] was synthesized and structurally characterized by physico-chemical, spectroscopic, and single-crystal X-ray diffraction analyses. The compound DBTC can detect cyanide anions based on nucleophilic addition as low as 5.76 nM in dimethyl sulfoxide-N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid buffer (20 mM, pH 7.4) (v/v = 1:3). The binding mode between receptor DBTC and cyanide nucleophile has also been demonstrated by experimental studies using various spectroscopic tools and theoretical studies, and the experimental work has also been verified by characterizing one supporting compound of similar probable structure of the final product formed between DBTC and cyanide ion (DBTC-CN compound) by single-crystal X-ray analysis for detailed structural analyses. In theoretical study, density functional theory procedures have been used to calculate the molecular structure and the calculation of the Fukui function for evaluation of the electrophilic properties of each individual acceptor atom. Furthermore, the efficacy of the probe (DBTC) to detect the distribution of CN^- ions in living cells has been checked by acquiring the fluorescence image using a confocal microscope. Notably, the paper strips with DBTC were prepared, and these could serve as efficient and suitable CN^- test kits successfully.

Fluorescent ZnII Chemosensor Mediated by a 1,8-Naphthyridine Derivative and It's Photophysical Properties

One of the greatest challenges in using fluorescent chemosensors for highly selective and sensitive transition-metal ions is finding an efficient and simple method for its synthesis. In this study, a highly efficient fluorescence chemosensor for ZnII was developed from N-Boc-L-proline modified 1,8-naphthyridine. The fluorescence intensity of the chemosensor was increased significantly only in the presence of ZnII ion which provided a perceived color change for rapid visual sensing, while other metal ions showed fluorescence quenching or little changes. It was worth noting that the chemosensor L distinguished ZnII from CdII commonly having similar properties. The solvent effect and possible bonding mode for fluorescence enhancement have been also discussed. Results of this study indicated that the Boc-group in l-proline significantly improved the sensitivity and selectivity for ZnII detection performance, as confirmed by comparison experiments and time dependent-density functional theory (TD-DFT) calculations.

A hexa-quinoline basedC3-symmetric chemosensor for dual sensing of zinc(ii) and PPi in an aqueous mediumviachelation induced “OFF–ON–OFF” emission

“OFF–ON–OFF” luminescence switching behavior of a hexa-quinoline based sensor towards Zn²⁺and PPi in an aqueous buffer medium is demonstrated.

Combined experimental and theoretical studies on selective sensing of zinc and pyrophosphate ions by rational design of compartmental chemosensor probe: Dual sensing behaviour via secondary recognition approach and cell imaging studies

A compartmental chemosensor probe HL was designed and synthesized for dual sensing of zinc ions and PPi via secondary recognition approach.

Terpyridine derivatives as “turn-on” fluorescence chemosensors for the selective and sensitive detection of Zn2+ ions in solution and in live cells

A terpyridine based compound L1 was designed and synthesized as an “off–on” chemosensor for the detection of Zn²⁺.