Sensing Hg(II) in Vitro and in Vivo Using a Benzimidazole Substituted BODIPY

Synthesis and Photophysical Characterizations of Benzimidazole Functionalized BODIPY Dyes

Herein, a series of new BODIPY dyes substituted by 2-phenyl benzimidazole units at the meso (C8) position including methyl/ethyl, phenyl, or p-methoxyphenyl moieties at the distal and proximal positions of the BODIPY core have been successfully synthesized and their photophysical characteristics were analyzed. Experimentally investigating absorption and fluorescence profiles in the THF media was followed by density functional theory (DFT) calculations to clarify photophysical features. Theoretical analyses have revealed that upon excitation, both electrons and holes are confined solely within the BODIPY core. The energy levels of the frontier molecular orbitals converge depending on the presence of the phenyl and p-methoxyphenyl substituents. The orbital distributions of both electron and hole were in the -3 and -5 positions, which demonstrates a continuous conjugation with the BODIPY core at these sites. However, the electron density present on the phenyl rings located at the -1, -7, and -8 (meso) positions was found to be negligible. The benzimidazole-BODIPYs exhibited photodynamic activity (Φ∆) ranging from ~ 7% to ~ 11%, determined by a comparative method. Moreover, the compounds have shown to maintain their stability thermally in a non-reactive/inert environment up to temperatures surpassing 300 °C, exhibiting primarily a two-phase decomposition process. These compounds have the potential to function as antibacterial and anti-biofilm agents when used in concentrations ranging from 0.5 to 2.0 mg/mL. The results provide a basis for evaluating heterocyclic benzimidazole units on photophysical processes containing BODIPY chromophores.

A Reversible Optical Sensor Film for Mercury Ions Discrimination Based on Isoxazolidine Derivative and Exhibiting pH Sensing

We developed a new optical sensor for tracing Hg(II) ions. The detection affinity examines within a concentration range of 0-4.0 µM Hg(II). The sensor film is based on Methyl 2-hydroxy-3-(((2S,2'R,3a'S,5R)-2-isopropyl-5,5'-dimethyl-4'-oxotetrahydro-2'H-spiro[cy-clohexane-1,6'-im-idazo[1,5-b]isoxazol]-2'-yl)methyl)-5-methylbenzoate (IXZD). The novel synthesized compound could be utilized as an optical turn-on chemosensor for pH. The emission intensity is highly enhanced for the deprotonated form concerning the protonated form. IXZD probe has a characteristic fluorescence peak at 481 nm under excitation of 351 nm with large Stocks shift of approximately 130 nm. In addition, the binding process of IXZD:Hg(II) presents a 1:1 molar ratio which is proved by the large quench of the 481 nm emission peak of IXZD and the growth of a new emission peak at 399 nm (blue shift). The binding configurations with one Hg(II) cation and its electronic characteristics were investigated by applying the Density Functional Theory (DFT) and the time-dependent DFT (TDDFT) calculations. Density functional theory (DFT) and the time-dependent DFT (TDDFT) theoretical results were provided to examine Hg(II)-IXZD structures and their electronic properties in solution. The developed chemical sensor was offered based on the intramolecular charge transfer (ICT) mechanism. The sensor film has a significantly low limit of detection (LOD) for Hg(II) of 0.025 μM in pH 7.4, with a relative standard deviation RSD_r (1%, n = 3). Lastly, the IXZD shows effective binding affinity to mercury ions, and the binding constant K_b was estimated to be 5.80 × 10⁵ M^-1. Hence, this developed optical sensor film has a significant efficiency for tracing mercury ions based on IXZD molecule-doped sensor film.

Small Molecules Containing Amphoteric Imidazole Motifs as Sensitizers for Dye-Sensitized Solar Cells: An Overview

Organic dyes, porphyrins and inorganic complexes containing imidazole (IM) motifs have been demonstrated as a new class of sensitizers in dye-sensitized solar cells (DSSCs). Particularly, the amphoteric nature of IM-based motifs allows them to be used as donors (D), auxiliary donors (D_A), linker/branch (π), or acceptors (A) in D-π-A-based organic dyes and porphyrins and also employed as cyclometalated heteroleptic and ancillary ligands in the Ru(II) and Ir(III) complexes for DSSCs. It is noteworthy that the introduction of IM chromophores in the dyes of D-π-A configuration can improve the light-harvesting properties and prohibit the charge recombination reactions due to the extension of the π-conjugated structures and hydrophobic nature. Similarly, in the case of inorganic complexes, the presence of IM motifs as ligands can improve the light-harvesting ability, give facilely tuned HOMO and LUMO energy levels, increase the charge recombination resistance and photostability. This results in enhanced photocurrent (J_SC) and photovoltage (V_OC) and consequently solar-to-power conversion efficiency (η) of DSSC devices based on Ru(II) and Ir(III) complexes. Considering the interesting DSSC applications of IM-derived molecules, in this review, we therefore comprehensively discuss their photophysical, electrochemical and photovoltaic properties reported so far and establish their structure-activity relationship to further advance the η of DSSCs. To the best of our knowledge, there is no such a review interpreting the importance of molecules possessing IM-motifs for DSSC applications to date.

An AIE active BODIPY based fluorescent probe for selective sensing of Hg2+ via dual mechanism PET and CHEF

A pyrazole appended BODIPY ligand (L) is synthesized and thoroughly characterized by various spectroscopic studies (1H, [Formula: see text]C, [Formula: see text]B, [Formula: see text]F, ESI–MS, UV-vis and fluorescence). The ligand (L) displays aggregation induced emission (AIE) in solution (a mixture of CH3OH and water) and solid state. The vital role of the restriction of intramolecular rotation (RIR) in AIE is supported by viscosity experiments and fluorescence lifetime studies. Photophysical behaviour and aggregate morphology is investigated by UV-vis, emission and scanning electron microscopy (SEM). Multiple strong intermolecular hydrogen bonds (C–H[Formula: see text]N and C–H[Formula: see text]F) play a significant role in the AIE response. In addition, L shows strong sensitivity toward Hg[Formula: see text]ion via chelation induced enhanced fluorescence (CHEF) mechanism. Job’s plot analysis suggested a 1:1 binding stoichiometry between L and Hg[Formula: see text], which has been further supported by electrospray ionization mass spectrometry and density functional theory.

BODIPY-Hg2+ Complex: A Fluorescence "Turn-ON" Sensor for Cysteine Detection

A BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) based pioneering sensing material (HLPy) having 2-amino pyridine as receptor was synthesized and used for the selective detection of Hg2+ ions. The synthesized HLPy features a high affinity towards Hg2+ (ka = 2.04 × 105 M-1), accompanied by effective quenching of fluorescence in DMF:H2O (1:9 v/v, 10 mM HEPES buffer, pH 7.4) with 54 nM limit of detection (LOD). The emission titration experiments (Job's plot) in the presence of varying mole-fraction of Hg2+ ions reveals the formation of non-fluorescent 2:1 coordination complex [Hg(LPy)2]. The resulting non-fluorescent [Hg(LPy)2] was thoroughly characterized using various spectroscopic techniques and analyses. Interestingly, the non-fluorescent complex [Hg(LPy)2] is able to specifically respond towards Cys over other biothiols and amino acids through a reversible de-complexation mechanism. As a result, the remarkable recovery of the fluorescence can be observed. The limit of detection (LOD) for Cys detection is estimated to be 29 nM in DMF:H2O (1:9 v/v, 10 mM HEPES buffer, pH 8.0). The reversibility and reusability of [Hg(LPy)2] were achieved by the sequential addition of Cys and Hg2+ ions up to five cycles. Moreover, the removal of Hg2+ ions up to 89% from aqueous samples using HLPy was successfully demonstrated.

6-Polyamino-substituted quinolines: synthesis and multiple metal (CuII, HgII and ZnII) monitoring in aqueous media

Chemoselective palladium-catalyzed arylation of polyamines with 6-bromoquinoline has been explored to prepare chelators for the detection of metal cations in aqueous media. The introduction of a single aromatic moiety into non-protected polyamine molecules was achieved using the commercially available Pd(dba)2/BINAP precatalyst to afford nitrogen chelators, in which the aromatic signalling unit is directly attached to the polyamine residue. Water-soluble receptors were then synthesized using N-alkylation of these polyamines by hydrophilic coordinating residues. By combining rich photophysical properties of the 6-aminoquinoline unit with a high coordination affinity of chelating polyamines and a hydrophilic character of carboxamido-substituted phosphonic acid diesters in a single molecular device, we synthesized chemosensor 5 for selective double-channel (UV-vis and fluorescence spectroscopies) detection of CuII ions in aqueous media at physiological levels. This receptor is suitable for the analysis of drinking water and fabrication of paper test strips for the naked-eye detection of CuII ions under UV-light. By increasing the number of donor sites we also obtained chemosensor 6 which is efficient for the detection of HgII ions. Moreover, chemosensor 6 is also suitable for multiple detection of metal ions because it chelates not only HgII but also CuII and ZnII ions displaying different responses of emission in the presence of these three cations.

Selective red-emission detection for mercuric ions in aqueous solution and cells using a fluorescent probe based on an unnatural peptide receptor

The selective ratiometric red-emission detection of Hg²⁺ions in aqueous buffered solutions and live cells is still a significant challenge.

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.

Detection of Zn2+, Cd2+, Hg2+, and Pb2+ ions through label-free poly-L-glutamic acid

Detection of heavy metal ions in water is important for environmental sustainability and food safety. Current fluorescent sensors interact with metal ions directly through chelation or chemical reactions. Those sensors are expensive to produce and often can detect only one ion at a time. Here we report a fluorescent turn-on sensor that can detect three group IIB metal ions and Pb²⁺ ions through label-free polypeptides in water. In our sensor-polypeptide mixture, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ ions induce helix formation and inter-chain aggregation in poly-L-α-glutamic acid (PGA). The acridinium-based sensor molecules incorporate into the polypeptides and emit strongly with characteristic color for each group IIB ion under UV lamp. By adjusting the size of polypeptides or the length of the side chain carboxyl groups, we can selectively turn off or turn on the sensor emission for Hg²⁺ ions.

A simple quinolone Schiff-base containing CHEF based fluorescence 'turn-on' chemosensor for distinguishing Zn2+ and Hg2+ with high sensitivity, selectivity and reversibility

A new simple 'dual' chemosensor MQA ((E)-2-methoxy-N-((quinolin-2-yl)methylene)aniline) for distinguishing Zn²⁺ and Hg²⁺ has been designed, synthesized and characterized. The sensor showed excellent selectivity and sensitivity with a fluorescence enhancement to Zn²⁺/Hg²⁺ over other commonly coexisting cations (such as Na⁺, Mg²⁺, Al³⁺, K⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ga³⁺, Cd²⁺, In³⁺ and Pb²⁺) in DMSO-H₂O solution (1/99 v/v), which was reversible with the addition of ethylenediaminetetraacetic acid (EDTA). The detection limit for Zn²⁺/Hg²⁺ by MQA both reached the 10^-8 M level. The 1 : 1 ligand-to-metal coordination patterns of the MQA-Zn2+ and MQA-Hg2+ were calculated through a Job's plot and ESI-MS spectra, and were further confirmed by X-ray crystal structures of complexes MQA-Zn2+ and MQA-Hg2+. This chemosensor can recognize similar metal ions by coherently utilizing intramolecular charge transfer (ICT) and different electronic affinities of various metal ions. DFT calculations have revealed that the energy gap between the HOMO and LUMO of MQA has decreased upon coordination with Zn(ii)/Hg(ii).

Synthesis of novel AIEE active pyridopyrazines and their applications as chromogenic and fluorogenic probes for Hg2+ detection in aqueous media

A series of AIEE active novel pyridopyrazine derivatives showing selective and sensitive detection of Hg²⁺ in aqueous media is reported.

Design and synthesis of BODIPY-clickate based Hg2+ sensors: the effect of triazole binding mode with Hg2+ on signal transduction

Highly selective BODIPY-clickates for mercury sensing are reported. These BODIPY clickates exhibits emission in red region with unprecedented large Stokes shifts (116 and 154 nm) upon mercury ion binding due to the intramolecular charge transfer processes.

Synthesis, structure, photophysical, electrochemical properties and antibacterial activity of brominated BODIPYs

The unusual di-bromo product, 5b, confirmed by spectral analysis, showed the most potency with the lowest IC₅₀ and MIC values, with excellent activity comparable to the standard antibacterial drug, tetracycline.

An efficient non-reaction based colorimetric and fluorescent probe for the highly selective discrimination of Pd0 and Pd2+ in aqueous media

A novel anthraquinone-imidazole based colorimetric and fluorogenic probe 1 discriminates the oxidation states of Pd⁰ and Pd²⁺ by naked eye with high selectivity in aqueous media due to the difference in coordination in the pocket of probe molecule.

Synthesis, Luminescent Properties of aza-Boron-Diquinomethene Difluoride Complexes and Their Application for Fluorescent Security Inks

Two aza-boron-diquinomethene (aza-BODIQU) complexes bearing phenyl and carbazyl substituents were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. Both complexes exhibit strong (1)π-π* transition absorptions (λ(abs) = 400-540 nm) and intense fluorescent emissions (λ(em) = 440-600 nm, Φ(PL) = 0.93 and 0.78) in CH2Cl2 solution and in solid state at room temperature. Compared to the complex with phenyl groups, the complex bearing carbazyl groups shows significant bathochromic shift in both absorption and emission. This could be attributed to the larger π-electron conjugation of the carbazole unit and intramolecular charge transfer feature from carbazole to aza-BODIQU component. In addition, the complexes exhibit intense photoluminescence and good stability on antacid, anti-alkali and stability in printing ink samples, which makes them potential dopants for the application of fluorescent security inks.

Far-red and near infrared BODIPY dyes: synthesis and applications for fluorescent pH probes and bio-imaging

Far-red and near infrared (NIR) emissive dyes have advantages in the development of fluorescent probes and labelling for bio-imaging in living systems since fluorescence in the long-wavelength region would generate minimum photo-toxicity to biological components, deep tissue penetration and minimal background from auto-fluorescence by bio-molecules. BODIPY dyes are attractive due to their excellent photo-physical properties and potential for fluorescence-based sensing and bio-imaging applications. Thus, numerous research papers have emerged to develop BODIPY-based dyes with absorption and emission in the long-wavelength spectral region (650-900 nm). This review summarizes the general strategies to obtain far-red and NIR BODIPYs. Moreover, their applications for fluorescent pH probes and imaging or labelling in living systems are highlighted.

A fluorescent chemosensor for Hg(2+) and Cd(2+) ions in aqueous medium under physiological pH and its applications in imaging living cells

A new BODIPY derivative with 2,2'-(ethane-1,2-diylbis(oxy))bis(N,N-bis(pyridine-2-ylmethyl)aniline unit as the metal receptor has been designed and synthesized. The dye selectively detects either Cd(2+) or Hg(2+) ions in the presence of hosts of other biologically important and environmentally relevant metal ions in aqueous medium at physiological pH. Binding of metal ions causes a change in the emission behavior of the dye from weakly fluorescent to highly fluorescent. Confocal microscopic experiments validate that the dye can be used to identify changes in either Hg(2+) or Cd(2+) levels in living cells.

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⁺.

Fluorescence ‘on–off–on’ chemosensor for the sequential recognition of Hg2+and cysteine in water

Fluorescent chemosensor showed the sequential detection of Hg²⁺and cysteine, and could be applied for quantification of Hg²⁺in water samples.

A pyrene based Schiff base probe for selective fluorescence turn-on detection of Hg2+ ions with live cell application

A novel pyrene based free thiol containing a Schiff base derivative PT1 was synthesized and reported as a fluorescence turn-on sensor for Hg²⁺ ions, via CHEF and excimer (PT1-PT1*) formation with live cell imaging.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

Effect of alkyl substituents in BODIPYs: a comparative DFT computational investigation

A detailed computational investigation encompassing the effects of alkyl groups on the structural and electronic properties of BODIPY dyes is presented.