Synthesis and Characterization of Electroactive Ferrocene Derivatives: Ferrocenylimidazoquinazoline as a Multichannel Chemosensor Selectively for Hg2+ and Pb2+ Ions in an Aqueous Environment

Development of highly selective fluorescent ferrocenyl-iminopyridine chemosensor for biologically relevant Fe3

Design, synthesis, characterization, and ion detection studies of two ferrocene-appended Schiff bases namely N-(2-[ferrocenylamino]ethyl)-5-nitropyridin-2-amine (1) and ferrocenylamino-1H-imidazole-4-carboxamide (2) been reported. Both the chemosensors have been thoroughly characterized using Fourier transfer infrared, 1 H and 13 C nuclear magnetic resonance, high resolution mass spectrometry, and ultraviolet/visible (UV/visible) and fluorescence spectral techniques. Probes 1 and 2 were designed with the aim of appending the ferrocenyl group with pyridine ring having an amine substitution (for 1) and imidazole ring with an amide substitution (for 2). Interaction of these probes with a series of cations and anions was examined through UV/vis and fluorescence spectral techniques. Probe 2 exhibited an insignificant response towards anions and loss of selectivity for cations, whereas 1 displayed highly selective detection towards biologically important Fe3+ in 2:1 (probe:cation) stoichiometry. Notably, none of the cations and anions could interfere the selectivity of Fe3+ ensured by 1 in aqueous medium. The limit of detection for Fe3+ detection using 1 was determined to be 0.2 ppm. The results strongly suggest that 1 could find promising future application as a chemosensor for Fe3+ in biological systems for quantification and qualitative analysis.

Luminescent Pyrene-based Schiff base Receptor for Hazardous Mercury(II) Detection Demonstrated by Cell Imaging and Test Strip

Qualitative and quantitative analysis of mercury at concentration levels as low as parts per billion (ppb) is a basic and practical concern. The vast majority of research in this field has centered on the development of potent chemosensor to monitor mercuric (Hg²⁺) ions. Mercury exists in three oxidation states, + 2, + 1 and 0, all of which are highly poisonous. In this study, (N¹E,N²E)-N¹,N²-bis(pyrene-1-ylmethylene)benzene-1,2-diamine (PAPM), a novel photoluminescent sensor based on pyrene platform was synthesized. Over the tested metal ions (Cd²⁺, Co²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Ni²⁺, K⁺, Na⁺, Zn²⁺, Sr²⁺, Pb²⁺, Al³⁺, Cr³⁺ and Fe³⁺) the sensor responds only to Hg²⁺ by showing high selectivity and sensitivity. After treatment with mercuric ions at room temperature, the luminescence intensity of probe was quenched at 456 nm. The quenching of fluorescence intensity of probe upon addition of mercury is due to the effect of "turn-off" chelation enhanced quenching (CHEQ) by the formation of 1:1 complex. The ESI-MS spectrum and the Job's experimental results confirm the formation of 1:1 complex between PAPM and Hg²⁺. The detection limit and association constant of sensor for mercury is computed using fluorescence titration data and were found to be 9.0 × 10^-8 M and 1.29 × 10⁵ M^-1 respectively. The practical application of sensor towards recognition of mercury(II) ions was explored through economically viable test strips and also using cell imaging studies.

Heteroligand Metal Complexes with Extended Redox Properties Based on Redox-Active Chelating Ligands of o-Quinone Type and Ferrocene

A combination of different types of redox-active systems in one molecule makes it possible to create coordination compounds with extended redox abilities, combining molecular and electronic structures determined by the features of intra- and intermolecular interactions between such redox-active centres. This review summarizes and analyses information from the literature, published mainly from 2000 to the present, on the methods of preparation, the molecular and electronic structure of mixed-ligand coordination compounds based on redox-active ligands of the o-benzoquinone type and ferrocenes, ferrocene-containing ligands, the features of their redox properties, and some chemical behaviour.

A rhodamine based dual chemosensor for Al3+ and Hg2+: Application in the construction of advanced logic gates

A rhodamine-based compound (RBO), which has been constructed from the reaction between N-(rhodamine-6G)lactam-ethylenediamine and 2,1,3-benzoxadiazole-4-carbaldehyde, is reported here as a selective chemosensor for both Al³⁺ and Hg²⁺ ions in 10 mM HEPES buffer in water:ethanol (1:9, pH = 7.4). Absorption intensity of RBO increases considerably at 528 nm with these cations. It shows fluorescence enhancement at 550 nm by 1140- and 524-fold in the presence of Al³⁺ and Hg²⁺, respectively. LOD has been determined as 6.54 and 16.0 nM for Al³⁺ and Hg²⁺, respectively. Quantum yield and lifetime of RBO enhances with these metal ions. Fluorescence intensity of Al-probe complex or Hg-probe complex is quenched in the presence of fluoride or sulfide ion, respectively, opening a path for the construction logic gates. DFT analysis has been used to understand the spectral transitions. We have constructed a systematic development from single to five inputs complex circuit, and for the first time a time dependent five input complex logic circuit is reported herein.

Acenaphtoquinoxaline as a selective fluorescent sensor for Hg (II) detection: experimental and theoretical studies

A new fluorescent chemosensor based on quinoxaline was successfully synthesized through a facile and green catalytic reaction of ortho-phenylenediamine (O-PDA) and acenaphthylene-1,2-dione in the presence of SBA-Pr-SO3H. Prepared a "switch-off" quinoxaline-based receptor to recognized Hg2+ ion in high selectively and, without any interference from other metal ions, was developed. The photophysical behavior of this fluorophore was studied in acetonitrile by using fluorescence spectra. The fluorescence properties of several cations to acenaphtoquinoxaline were investigated in acetonitrile, and the competition test displayed that the probe fluorescence changes were specific for Hg2+ ion. The obtained results have shown high selectivity and sensitivity only for Hg2+. Also, the detection limit was as low as 42 ppb, and a top linear trend was observed between the concentration of Hg2+ ions and fluorescence intensity. The binding stoichiometry between chemosensor L and Hg2+ was found to be 1:1. Moreover, a computational study was performed to obtain an electronic description of the fluorescence emission and quenching mechanisms. The optimized structures and binding mechanisms were supported with a high correlation and agreement by spectroscopy and DFT calculations.

Cu(II) Ion Adsorption by Aniline Grafted Chitosan and Its Responsive Fluorescence Properties

The detection and removal of heavy metal species in aquatic environments is of continued interest to address ongoing efforts in water security. This study was focused on the preparation and characterization of aniline grafted chitosan (CS-Ac-An), and evaluation of its adsorption properties with Cu(II) under variable conditions. Materials characterization provides support for the grafting of aniline onto chitosan, where the kinetic and thermodynamic adsorption properties reveal a notably greater uptake (>20-fold) of Cu(II) relative to chitosan, where the adsorption capacity (Q_m) of CS-Ac-An was 106.6 mg/g. Adsorbent regeneration was demonstrated over multiple adsorption-desorption cycles with good uptake efficiency. CS-Ac-An has a strong fluorescence emission that undergoes prominent quenching at part per billion levels in aqueous solution. The quenching process displays a linear response over variable Cu(II) concentration (0.05–5 mM) that affords reliable detection of low level Cu(II) levels by an in situ “turn-off” process. The tweezer-like chelation properties of CS-Ac-An with Cu(II) was characterized by complementary spectroscopic methods: IR, NMR, X-ray photoelectron (XPS), and scanning electron microscopy (SEM). The role of synergistic effects are inferred among two types of active adsorption sites: electron rich arene rings and amine groups of chitosan with Cu(II) species to afford a tweezer-like binding modality.

Zinc(ii), copper(ii) and cadmium(ii) complexes as fluorescent chemosensors for cations

The fluorescence chemosensing behavior of Zn(ii), Cu(ii), and Cd(ii) based complexes toward cations has been described. Cation detection via conventional mechanisms, metal-metal exchange and chemodosimetric approaches along with the importance of metal ions and the scope, significance, and challenges with regard to the detection of cations by metal complex based probes will be discussed in detail. The fundamentals of photophysical behavior and mechanisms involved in the fluorescence detection of analytes will also be described. This article provides a detailed overview of Zn(ii), Cu(ii), and Cd(ii) based complexes as fluorescent probes for cations, together with essential discussions pertaining to detection mechanisms.

Thieno[3,2-c]pyran: an ESIPT based fluorescence “turn-on” molecular chemosensor with AIE properties for the selective recognition of Zn2+ ion

Thieno[3,2-c]pyran was synthesized as a fluorescent turn-on chemosensor for the selective recognition of Zn²⁺ ions with a low detection limit (0.67 μM), and it also exhibited AIE properties.

Development of a fused imidazo[1,2-a]pyridine based fluorescent probe for Fe3+ and Hg2+ in aqueous media and HeLa cells

A new fluorescent sensor 5 having fused imidazopyridine scaffold has been synthesized via cascade cyclization. It exhibits highly sensitive and selective detection of Fe³⁺ (‘turn-on’) and Hg²⁺ (‘turn-off’) in vitro and in HeLa cells.

Imine ligands based on ferrocene: synthesis, structural and Mössbauer characterization and evaluation as chromogenic and electrochemical sensors for Hg2+

Synthesis of imine ligands based on ferrocene and their evaluation as chromogenic and electrochemical sensors for Hg²⁺.

The first colorimetric receptor for the B4O72− anion based on nitro substituted phenanthroimidazole ferrocene derivatives

Four phenanthroimidazole ferrocene derivatives (2a–2d) were synthesized. Recognition of 12 anions by 2a–2d was investigated by UV-Vis absorption analysis, showing that 2b and 2d sensed B₄O₇²⁻ selectively with an obvious color change observed.

A reusable multichannel anthraimidazoledione-based receptor for Hg2+and Cu2+ions: ultrasensitive, economical and facile detection of Hg2+in real water sources through fluorescence readout

A multichannel, ultrasensitive and selective receptor (1) has been developed for practical detection of Hg²⁺in various drinking waters.

An Ionic 1,4-Bis(styryl)benzene-Based Fluorescent Probe for Mercury(II) Detection in Water via Deprotection of the Thioacetal Group

Highly sensitive and selective mercury detection in aqueous media is urgently needed because mercury poisoning usually results from exposure to water-soluble forms of mercury by inhalation and/or ingesting. An ionic conjugated oligoelectrolye (M1Q) based on 1,4-bis(styryl)benzene was synthesized as a fluorescent mercury(II) probe. The thioacetal moiety and quaternized ammonium group were incorporated for Hg²⁺ recognition and water solubility. A neutral Hg²⁺ probe (M1) was also prepared based on the same molecular backbone, and their sensor characteristics were investigated in a mixture of acetonitrile/water and in water. In the presence of Hg²⁺, the thioacetal group was converted to aldehyde functionality, and the resulting photoluminescence intensity decreased. In water, M1Q successfully demonstrated highly sensitive detection, showing a binding toward Hg²⁺ that was ~15 times stronger and a signal on/off ratio twice as high, compared to M1 in acetonitrile/water. The thioacetal deprotection by Hg²⁺ ions was substantially facilitated in water without an organic cosolvent. The limit of detection was measured to be 7 nM with a detection range of 10–180 nM in 100% aqueous medium.

Synthesis, DNA binding, cellular DNA lesion and cytotoxicity of a series of new benzimidazole-based Schiff base copper(II) complexes

A series of new benzimidazole containing compounds 2-((1-R-1-H-benzimidazol-2-yl)phenyl-imino)naphthol HL(1-3) (R = methyl, ethyl or propyl, respectively) have been synthesized by Schiff base condensation of 2-(1-R-1-H-benzo[d]imidazol-2-yl)aniline and 2-hydroxy-1-naphthaldehyde. The reactions of HL(1-3) with Cu(NO3)2·2.5H2O led to the corresponding copper(II) complexes [Cu(L)(NO3)] 1-3. All the compounds were characterized by conventional analytical techniques and, for 1 and 3, also by single-crystal X-ray analysis. The interactions of complexes 1-3 with calf thymus DNA were studied by absorption and fluorescence spectroscopic techniques and the calculated binding constants (K(b)) are in the range of 3.5 × 10(5) M(-1)-3.2 × 10(5) M(-1). Complexes 1-3 effectively bind DNA through an intercalative mode, as proved by molecular docking studies. The binding affinity of the complexes decreases with the size increase of the N-alkyl substituent, in the order of 1 > 2 > 3, which is also in accord with the calculated LUMO(complex) energies. They show substantial in vitro cytotoxic effect against human lung (A-549), breast (MDA-MB-231) and cervical (HeLa) cancer cell lines. Complex 1 exhibits a significant inhibitory effect on the proliferation of the A-549 cancer cells. The antiproliferative efficacy of 1 has also been analysed by a DNA fragmentation assay, fluorescence activated cell sorting (FACS) and nuclear morphology using a fluorescence microscope. The possible mode for the apoptosis pathway of 1 has also been evaluated by a reactive oxygen species (ROS) generation study.

Nanostructured Thin Films Obtained from Fischer Aminocarbene Complexes

The synthesis of four amphiphilic organometallic complexes with the general formula RC = M(CO)₅NH(CH₂)₁₅CH₃, where R is a ferrocenyl 2(a-b) or a phenyl 4(a-b) group as a donor moiety and a Fischer carbene of chromium (0) or tungsten (0) as an acceptor group, are reported. These four push-pull systems formed Langmuir (L) monolayers at the air-water interface, which were characterized by isotherms of surface pressure versus molecular area and compression/expansion cycles (hysteresis curves); Brewster angle microscopic images were also obtained. By using the Langmuir-Blodgett (LB) method, molecular monolayers were transferred onto glass substrates forming Z-type multilayers. LB films were characterized through ultraviolet-visible spectroscopy, atomic force microscopy and X-ray diffraction techniques. Results indicated that films obtained from 2b complex [(Ferrocenyl)(hexadecylamine)methylidene] pentacarbonyl tungsten (0) are the most stable and homogeneous; due to their properties, these materials may be incorporated into organic electronic devices.

Chromogenic and fluorogenic multianalyte detection with a tuned receptor: refining selectivity for toxic anions and nerve agents

In the present study, a chemical probe was finely tuned for the highly selective and sensitive chromogenic and fluorogenic detection of toxic anions and a nerve agent.

A single chemosensor for bimetal Cu(ii) and Zn(ii) in aqueous medium

A new quinazoline-based bimetal chemosensor for Cu(ii) and Zn(ii) in aqueous medium was synthesized. It can act as a “turn-off” sensor for Cu(ii) with the excitation wavelength of 356 nm, and a “turn-on” sensor for Zn(ii) when excited at 416 nm.

A dual functional probe for "turn-on" fluorescence response of Pb(2+) and colorimetric detection of Cu(2+) based on a rhodamine derivative in aqueous media

A dual functional probe L based on rhodamine was devised and synthesized. Probe L can sense Pb(2+) and Cu(2+) in aqueous solution through two approaches: a significant fluorescence enhancement caused by Pb(2+) and a visible color change from colorless to orchid induced by Cu(2+). Competitive experiments showed that probe L had high fluorescence sensitivity for Pb(2+) and excellent colorimetric selectivity for Cu(2+) over many environmentally relevant ions. The mechanisms of L for sensing Pb(2+) and Cu(2+) have been well demonstrated by ESI-MS, (1)H NMR titration, IR, the crystal structure of L-Pb(2+) and density functional theory calculation of L-Cu(2+). In addition, fluorescence image detection of Pb(2+) in living cells displayed an enhanced fluorescence effect.

Development of fluorescent lead II sensor based on an anthracene derived chalcone

A simple anthracene based chalcone as a fluorescent chemosensor 1, capable of detecting Pb(2+) in aqueous media, has been synthesized by the reaction between pyridine 2-carboxaldehyde and 9-acetyl anthracene. The Pb(2+) recognition processes follows a photo induced electron transfer (PET) mechanism and are scarcely influenced by other coexisting metal ions. In addition, determination of lead in a variety of samples was also determined.

Cu(ii) complex-based fluorescence chemosensor for cyanide in aqueous media

A Cu²⁺ complex-based fluorescence “off–on” chemosensor for the direct detection of CN⁻ in the environment and in living cells was designed and prepared.

NBD-based fluorescent chemosensor for the selective quantification of copper and sulfide in an aqueous solution and living cells

A fluorescent chemosensor (NL) has been developed for the selective quantification of copper and sulfide in aqueous solutions and living cells.

The effect of central and planar chirality on the electrochemical and chiral sensing properties of ferrocenyl urea H-bonding receptors

Ferrocenyl urea receptors containing planar and central chirality electrochemically sense carboxylate anions via formation of H-bonded complexes.

A dual-responsive “turn-on” bifunctional receptor: a chemosensor for Fe3+ and chemodosimeter for Hg2+

Synthesis and characterization of L1–L3 along with their selective detection toward Fe³⁺ and Hg²⁺ at ppb level, exhibiting bifunctional behaviour have been presented.

Metal ion-assisted ring-opening of a quinazoline-based chemosensor: detection of copper(ii) in aqueous media

A fluorescence chemosensor for Cu(ii) in aqueous media was synthesized. The experiments and theoretical calculations confirmed that the Cu(ii) ion assisted the ring-opening of the quinazoline derivative, forming a Cu(ii) Schiff base during the detection.

A highly sensitive C3-symmetric Schiff-base fluorescent probe for Cd2+

A new C3-symmetric Schiff-base fluorescent probe (L) based on 8-hydroxy-2-methylquinoline has been developed. As expected, the probe L can display high fluorescent selectivity for Cd(2+) over Zn(2+) and most other common ions in neutral ethanol aqueous medium. Moreover, the mechanism of the L-Cd(2+) complex has been confirmed by X-ray crystallography and density functional theory calculation results. More importantly, L could be used to image Cd(2+) within living cells.

Structural and mechanistic insights into an Fe³⁺-triggered quinazoline based molecular rotor

Highly fluorescent, multifunctional and thermoreversible conformational switching (1) has been designed and developed by embedding two imidazo[1,2-c]quinazoline (IQ) units in the pyridyl scaffold. The origin of the conformational and optical switching of 1 to 1' has been established by various studies and by developing a model compound.