Advances in ionic liquids as fluorescent sensors

Ionic liquids (ILs) are a class of liquid salts with characteristics such as a low melting point, an ionic nature, non-volatility, and tunable properties. Because of their adaptability, they have a significant influence in the field of fluorescence. This paper reviews the primary literature on the use of ILs in fluorescence sensing technologies. The kind of target material is utilized to classify the fluorescence sensors made with the use of ILs. They include using ILs as probes for metals, nitro explosives, small organic compounds, anions, and gases. The efficacy of an IL-based fluorescence sensor depends on the precise design to guarantee specificity, sensitivity, and a consistent reaction to the desired analyte. The precise method can differ depending on the chemical properties of the IL, the choice of fluorophore, and the interactions with the analyte. Overall, the viability of the aforementioned materials for chemical analysis is evaluated, and prospective possibilities for further development are identified.

Ionic Liquid-in-Water Emulsions Stabilized by Molecular and Polymeric Surfactants

Ionic liquids have drawn notable attention for their unique solvent properties and use in applications such as batteries and chemical separations. While many ionic liquids are water-soluble, there are numerous examples of ionic liquids that are sufficiently hydrophobic to remain phase separated from water. However, relatively little is known about the stability and properties of ionic liquid-in-water emulsions. Here, we survey a series of ionic liquid-in-water emulsions stabilized by a range of ionic and nonionic molecular surfactants and polymers. To assess droplet stability and dynamics, we characterize the ionic liquid-surfactant interfacial tension, describe qualitative coarsening rates, and quantify droplet solubilization rate. In some instances, we observe unexpected spontaneous formation of complex double and triple emulsions. Our observations highlight approaches for ionic liquid emulsion formulation and provide insight into how to address challenges surrounding stabilization of ionic liquid-in-water droplets with molecular surfactants.

Switching on the Fluorescence Emission of Polypyridine Ligands by Simultaneous Zinc(II) Binding and Protonation

The synthesis and characterization of the two new open-chain ligands 1,15-bis-[6-(2,2'-bipyridyl)]-2,5,8,11,14-pentaaza-octadecane (L1) and 1,15-bis-[2-(1,10-phenanthroline)-9-methyl]-2,5,8,11,14-pentaazaoctadecane (L2), both featuring a tetraethylenpentaamine chain linking via methylene bridges the 6 and 2 positions of two identical 2,2'-bipyridyl (bpy) and 9-methyl-1,10-phenanthroline (9-methyl-phen) moieties respectively, are reported. Their protonation and binding ability for Cu²⁺ , Zn²⁺ , Cd²⁺ and Pb²⁺ have been studied by coupling potentiometric titrations with UV-vis absorption and fluorescence emission measurements in water. L1 and L2 afford stable mono- and dinuclear complexes, in which the metal ion is bound by a single bpy or 9-methyl-phen unit and the amine groups on the aliphatic chain. However, L1 displays a greater binding ability for Cu²⁺ and Zn²⁺ with respect to L2, the stability constants of the [ML1]²⁺ complexes being 21.8 (Cu²⁺ ) and 19.4 (Zn²⁺ ) log units vs 20.34 and 16.8 log. units for the corresponding L2 species. Among all the metal ions tested, only the Zn²⁺ complex with L2 features an enhanced fluorescence emission at neutral pH, thanks to the simultaneous binding of one Zn²⁺ ion and H⁺ ion(s), that inhibits any possible photoinduced electron transfer (PET) process from the amine donors to the excited phen moiety. Binding of a second metal switches off the emission again.

Real-time monitoring of intracellular pH in live cells with fluorescent ionic liquid

Real-time monitoring of intracellular pH is of great significance due to its essential role in physiological and pathological processes. In present work, the ionic liquid (IL) N-methyl-6-hydroxyquinolinium bis(trifluoromethylsulfonyl) imide ([6MQc][NTf₂]) is proposed as a fluorescence probe for the quantitative imaging of intracellular pH in response to external stimuli. The fluorescence of the IL [6MQc][NTf₂] exhibits a sensitive response to pH variations, as the deprotonation of [6MQc][NTf₂] generates the highly fluorescent zwitterionic product [6MQz]. pH fluctuations in the range of 6.0-7.5 can be accurately sensed by monitoring the fluorescence change at 555 nm. Moreover, this IL probe exhibits favorable biocompatibility, excellent anti-photobleaching properties, and high tolerance to ionic strength. Using the IL probe, real-time sensing of hypoxia- and drug-induced intracellular pH changes in MCF-7 cells is achieved.

Playing with Structural Parameters: Synthesis and Characterization of Two New Maltol-Based Ligands with Binding and Antineoplastic Properties

Two maltol-based ligands, N,N′-bis((3-hydroxy-4-pyron-2-yl)methyl)-1,4-piperazine (L1) and N,N′,N′-tris((3-hydroxy-4-pyron-2-yl)methyl)-N-methylethylendiamine (L2), were synthesized and characterized. L1 and L2, containing, respectively, two and three maltol units spaced by a diamine fragment, were designed to evaluate how biological and binding features are affected by structural modifications of the parent compound malten. The acid-base behavior and the binding properties towards transition, alkaline-earth (AE) and rare-earth (RE) cations in aqueous solution, studied by potentiometric, UV-Vis and NMR analysis, are reported along with biological studies on DNA and leukemia cells. Both ligands form stable complexes with Cu(II), Zn(II) and Co(II) that were studied as metallo-receptors for AE and RE at neutral pH. L1 complexes are more affected than L2 ones by hard cations, the L1-Cu(II) system being deeply affected by RE. The structural modifications altered the mechanism of action: L1 partially maintains the ability to induce structural alterations of DNA, while L2 provokes single strand (nicks) and to a lesser extent double strand breaks of DNA.

Highly Charged Ruthenium(II) Polypyridyl Complexes as Effective Photosensitizer in Photodynamic Therapy

A comparative study between two novel, highly water soluble, ruthenium(II) polypyridyl complexes, [Ru(phen)₂ L'] and [Ru(phen)₂ Cu(II)L'] (L and L-Cu^II ), containing the polyaazamacrocyclic unit 4,4'-(2,5,8,11,14-pentaaza[15])-2,2'-bipyridilophane (L'), is herein reported. L and L-Cu^II interact with calf-thymus DNA and efficiently cleave DNA plasmid when light-activated. They also possess great penetration abilities and photo-induced biological activities, evaluated on an A375 human melanoma cell line, with L-Cu^II being the most effective. Our study highlights the key role of the Fenton active Cu^II center within the macrocycle framework, that would play a synergistic role with light activation in the formation of cytotoxic ROS species. Based on these results, an optimal design of Ru^II polypyridyl systems featuring specific Cu^II -chelating polyamine units could represent a suitable strategy for the development of novel and effective photosensitizers in photodynamic therapy.

Pickering Emulsion-Templated Encapsulation of Ionic Liquids for Contaminant Removal

Ionic liquids (ILs) have received attention for a diverse range of applications, but their liquid nature can make them difficult to handle and process and their high viscosities can lead to suboptimal performance. As such, encapsulated ILs are attractive for their ease of handling and high surface area and have potential for improved performance in energy storage, gas uptake, extractions, and so forth. Herein, we report a facile method to encapsulate a variety of ILs using Pickering emulsions as templates, graphene oxide (GO)-based nanosheets as particle surfactants, and interfacial polymerization for stabilization. The capsules contain up to 80% IL in the core, and the capsule shells are composed of polyurea and GO. We illustrate that capsules can be prepared from IL-in-water or IL-in-oil emulsions and explore the impact of monomer and IL identity, thereby accessing different compositions. The spherical, discrete capsules are characterized by optical microscopy, scanning electron microscopy, infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and ¹H NMR spectroscopy. We illustrate the application of these IL capsules as a column material to remove phenol from oil, demonstrating ≥98% phenol removal after passage of >170 column volumes. This simple method to prepare capsules of IL will find widespread use across diverse applications.

A novel ratiometric and turn-on fluorescent coumarin-based probe for Fe(iii)

6-Methoxy-3-(pyridin-2-yl)-2H-chromen-2-one exhibited fluorescence enhancement in the presence of Fe(iii). This molecule was a selective fluorescent chemosensor for Fe(iii).

Ionic Liquid-Containing Pickering Emulsions Stabilized by Graphene Oxide-Based Surfactants

Emulsions stabilized by particles (i.e., Pickering emulsions) are complementary to those stabilized by small molecules or polymers and most commonly consist of oil droplets dispersed in a continuous water phase, with particles assembled at the fluid-fluid interface. New particle surfactants and different fluid-fluid interfaces are critical for developing next-generation systems for a number of advanced applications. Herein we report the preparation of IL-containing emulsions stabilized by graphene oxide (GO)-based nanoparticles using the IL [Bmim][PF₆]: GO nanosheets stabilize IL-in-water emulsions, and alkylated GO nanosheets (C₁₈-GO) stabilize IL-in-oil emulsions. The impact of particle concentration, fluid-fluid ratio, and addition of acid or base on emulsion formation and stability is studied, with distinct effects for the water and oil systems observed. We then illustrate the broad applicability of GO-based particle surfactants by preparing emulsions with different ILs and preparing inverted emulsions (water-in-IL and oil-in-IL emulsions). The latter systems were accessed by tuning the polarity of GO nanosheets by functionalization with a perfluorinated alkyl chain such that they were dispersible in IL. This work provides insight into the preparation of different IL-containing emulsions and lays a foundation for the architecture of dissimilar materials into composite systems.

Methylene blue-containing liposomes as new photodynamic anti-bacterial agents

Novel cationic liposomes containing the photo-activatable drug methylene blue (MB) strongly enhance the antibacterial activity of MB towards Gram-negative bacteria and improve biofilm penetration.

On the role of a coumarin derivative for sensing applications: Nucleotide identification using a micellar system

The recognition of nucleotides is of crucial importance because they are the basic constituents of nucleic acids. The present study is focused on the selective interaction between a novel amphiphilic fluorophore containing coumarin and imidazole, CI (1-methyl-3-(12-((2-oxo-2H-chromen-7-yl)oxy)dodecyl)-1H-imidazol-3-ium bromide), and different nucleotide-monophosphates (NMPs). It was supposed that the solubilization of the low water soluble CI in a micelle system of hexadecyltrimethylammonium chloride (CTAC) would make the coumarin moiety of CI available to the interaction with the water-soluble NMPs. Changes in CTAC critical micelle concentration suggested that CI strongly interacted with the host cationic surfactant, thus forming a positively charged interface enriched with coumarin able to interact with the anionic NMPs. Steady-state fluorescence quenching revealed that CI/CTAC system was capable of distinguish between purine- and pyrimidine-based nucleotides. A modified Stern-Volmer equation permitted the use of a quenching model that accounted for the possible interactions between the micelles and the nucleotides. The data analysis allowed calculating selective parameters that differentiated according to the type of nucleotide either at 25 or 50°C. Our results established the utility of the novel coumarin derivative fluorophore, supported by the simple and suitable micellar systems, as a tool for DNA sensing applications.

Optimization of ionic liquid based dispersive liquid–liquid microextraction combined with dispersive micro-solid phase extraction for the spectrofluorimetric determination of sulfasalazine in aqueous samples by response surface methodology

A new method based on fluorescent IL-DLLME and μ-SPE was applied for the pretreatment of sulfasalazine (SSZ) prior to determination by fluorimetry.

Fluorescent lactose-derived catanionic aggregates: synthesis, characterisation and potential use as antibacterial agents

The antibacterial properties of catanionic surfactants based on fluorescent lactose-derivative organic salts using low-cost starting materials were investigated towards multi-drug-resistant Gram-positive bacteria.