Synthesis of (trans-A2)BC-Type Porphyrins with Acceptor Diethoxyphosphoryl and Various Donor Groups and their Assembling in the Solid State and at Interfaces

International audienceA versatile synthetic approach to accessing unsymmetrically substituted (trans-A2)BC-type porphyrins bearing two heteroatoms at the macrocycle periphery is developed. For this purpose, experimental conditions for the substitution of the bromine atom in zinc 5-bromo-15-(diethoxyphosphoryl)-10,20-diphenylporphyin (2) by S-, O-and N-nucleophiles were explored. SNAr reactions afford AlkO-, ArO-and AlkS-substituted porphyrins in good to high yields. In contrast, SNAr reactions of 2 with N-nucleophiles lead to meso-amino-substituted porphyrins in preparative yields only with cyclic secondary amines. Primary amines, anilines and azacrowns may also react with bromide 2 but the palladium catalyst is needed to obtain the products in acceptable yields. The interest of the compounds under investigation for biomimetic assembly of tetrapyrroles was demonstrated by the studies of self-assembly of ditopic morpholinyl-substituted porphyrin 5a in the solid state. Moreover, we have prepared emissive porphyrin monolayers at the air/water interface and revealed that the porphyrin films were suitable for detection of zinc(II) ions in aqueous solutions

Aminoquinoxaline-Based Dual Colorimetric and Fluorescent Sensors for pH Measurement in Aqueous Media

International audienceThis research is focused on the development of pH indicators based on the quinoxaline signaling group for acidic aqueous solutions (pH 1–5). A push–pull quinoxaline QC1 in which two electron-donating (3-aminopropyl)amino substituents are attached to positions 6 and 7 of the electron- deficient quinoxaline moiety was prepared using the palladium-catalyzed C–N cross-coupling re- action. The 3-aminopropyl residues are mostly protonated in aqueous solutions below pH 8, thus serving as hydrophilizing substituents that render quinoxaline derivative QC1 water-soluble in this range of acidities and useful for measurements in the pH range of 1–5. This chromophore is a dual optical chemosensor that exhibits shifts of both absorption and emission bands in response to external stimuli. The presence of naturally relevant metal cations (13 ions) does not interfere with spectrophotometric and fluorescence measurements of the optical response of aminoquinoxaline in the visible region. Moreover, these spectral changes are easily observed by the naked eye, allowing for rapid semi-quantitative analyses under “in-field” conditions

Dual-Responsive and Reusable Optical Sensors Based on 2,3-Diaminoquinoxalines for Acidity Measurements in Low-pH Aqueous Solutions

This work is focused on the age-old challenge of developing optical sensors for acidity measurements in low-pH aqueous solutions (pH < 5). We prepared halochromic (3-aminopropyl)amino-substituted quinoxalines QC1 and QC8 possessing different hydrophilic–lipophilic balance (HLB) and investigated them as molecular components of pH sensors. Embedding the hydrophilic quinoxaline QC1 into the agarose matrix by sol-gel process allows for fabrication of pH responsive polymers and paper test strips. The emissive films thus obtained can be used for a semi-quantitative dual-color visualization of pH in aqueous solution. Being exposed to acidic solutions with pH in the range of 1–5, they rapidly give different color changes when the analysis is performed in daylight or under irradiation at 365 nm. Compared with classical non-emissive pH indicators, these dual-responsive pH sensors allow for an increase in the accuracy of pH measurements, particularly in complex environmental samples. pH indicators for quantitative analysis can be prepared by the immobilization of amphiphilic quinoxaline QC8 using Langmuir–Blodgett (LB) and Langmuir–Schäfer (LS) techniques. Compound QC8 possessing two long alkyl chains (n-C8H17) forms stable Langmuir monolayers at the air–water interface, and these monolayers can be successfully transferred onto hydrophilic quartz and hydrophobic polyvinylchlorid (PVC) substrates using LB and LS techniques, respectively. The 30-layer films thus obtained are emissive, reveal excellent stability, and can be used as dual-responsive pH indicators for quantitative measurements in real-world samples with pH in the range of 1–3. The films can be regenerated by immersing them in basic aqueous solution (pH = 11) and can be reused at least five times

Ultra-thin film sensors based on porphyrin-5-ylphosphonate diesters for selective and sensitive dual-channel optical detection of mercury(II) ions

International audienceReusable dual-channel optical sensors for Hg2+ ions were prepared by Langmuir-Schaefer (LS) method from amphiphilic (trans-A2)BC-type porphyrins functionalized at meso-positions of the tetrapyrrolic macrocycle by sterically demanding diethoxyphosphoryl and mesityl groups as well as electron donating RO, RS or RNH substituents (R = n-C8H17). These three novel amphiphilic porphyrin derivatives were synthesized in good yields and their floating films at the air⎯water interface were investigated. In these monolayers, porphyrin molecules display a slipped stack-of-card orientation, but their strong π stacking is prohibited by bulky diethoxyphosphoryl and mesityl groups. The heteroatom substituent plays a key role in the molecular organization of the monolayers because it can participate in intermolecular hydrogen bonding, which influences the monolayer structure. Sensing properties of the porphyrins organized in Langmuir monolayers differ from those in the solution environment. Selective spectrophotometric detection of Hg2+ ions by these floating films is observed because interfering Cu2+, Zn2+, Cd2+, and Pb2+ ions are coordinated to donor centers located at the periphery of the macrocycle. Transfer of these floating films onto a polyvinyl chloride surface by LS technique affords perforated multilayer films with a tight molecular coverage of the solid support. The effect of the heteroatoms on the organization of these films was demonstrated by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Both absorption and emission studies provide a strong evidence that chromophore-chromophore interactions are rather weak in these LS films. Binding of mercury(II) ions by the films and the regeneration of the sensors were explored visually and using reflection absorbance and fluorescence spectroscopies and then confirmed by X-ray fluorescence analysis. Detection limit of these selective and reusable dual-channel (absorbance and fluorescence) thin-film sensors is about 10-8 M (2 ppb), that corresponds to the action level for Hg2+ ions in drinking water recommended by the U.S. Environmental Protection Agency (EPA)

Colorimetric Hg 2+ Sensing in Water: From Molecules toward Low-Cost Solid Devices

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Testing the Role of Glutamate NMDA Receptors in Peripheral Trigeminal Nociception Implicated in Migraine Pain

The pro-nociceptive role of glutamate in the CNS in migraine pathophysiology is well established. Glutamate, released from trigeminal afferents, activates second order nociceptive neurons in the brainstem. However, the function of peripheral glutamate receptors in the trigeminovascular system suggested as the origin site for migraine pain, is less known. In the current project, we used calcium imaging and patch clamp recordings from trigeminal ganglion (TG) neurons, immunolabelling, CGRP assay and direct electrophysiological recordings from rat meningeal afferents to investigate the role of glutamate in trigeminal nociception. Glutamate, aspartate, and, to a lesser extent, NMDA under free-magnesium conditions, evoked calcium transients in a fraction of isolated TG neurons, indicating functional expression of NMDA receptors. The fraction of NMDA sensitive neurons was increased by the migraine mediator CGRP. NMDA also activated slowly desensitizing currents in 37% of TG neurons. However, neither glutamate nor NMDA changed the level of extracellular CGRP. TG neurons expressed both GluN2A and GluN2B subunits of NMDA receptors. In addition, after removal of magnesium, NMDA activated persistent spiking activity in a fraction of trigeminal nerve fibers in meninges. Thus, glutamate activates NMDA receptors in somas of TG neurons and their meningeal nerve terminals in magnesium-dependent manner. These findings suggest that peripherally released glutamate can promote excitation of meningeal afferents implicated in generation of migraine pain in conditions of inherited or acquired reduced magnesium blockage of NMDA channels and support the usage of magnesium supplements in migraine

Emerging specific selectivity towards mercury(II) cations in water through supramolecular assembly at interfaces

International audienceThis work deals with the development of ultra-thin film nanosensors for selective and sensitive detection of toxic Hg2+ cations in aqueous media. 1,8-Bis[(2-aminoethyl)amino]anthraquinone D0 was functionalized by alkoxy groups of different length to prepare ligands D3 and D12 with linear arrangement of two polyamine receptors and two lipophilic alkyl chains. Chemosensor D0 only binds copper(II) and mercury(II) cations in water/methanol (1:1 v/v) solutions with no interference by other metal cations. The introduction of alkoxy groups to the anthraquinone scaffold, which are required to form Langmuir monolayers and ultra-thin films on solid supports, does not change the sensing properties of the anthraquinone D0. In contrast to systems without specific molecular order (i.e. solutions and drop-cast films), Langmuir monolayers and ultra-thin Langmuir-Blodgett films of alkoxy-substituted ligands selectively bind only mercury(II) cations, even in the presence of copper(II) ions and 10 other interfering cations. Selective binding of mercury(II) cations was confirmed by the UV–vis absorption and X-ray fluorescence spectroscopies. Thus, ultra-thin films, in which chemosensor molecules are assembled in highly ordered supramolecular systems, display a higher selectivity as compared to that of disordered molecular systems. Ultra-thin sensory film allows for the selective detection of Hg2+ ions in water when their concentration is exceeded 0.01 μM, which corresponds to the action level for Hg2+ ions in drinking water recommended by the U.S. Environmental Protection Agency. Chemosensor D12 is also suitable for the fabrication of electrochemical sensors for mercury(II) cations that show similar sensitivity