Biological Oxidations and Nitrations Promoted by the Hemin–Aβ16 Complex

: Both β-amyloid (Aβ) peptides and oxidative stress conditions play key roles in Alzheimer's disease. Hemin contributes to the development of the disease as it possesses redox properties and its level increases in pathological conditions or traumatic brain injuries. The aim of this work was to deepen the investigation of the reactivity of the hemin-Aβ16 complex, considering its ability to catalyze oxidation and nitration reactions. We performed kinetic studies in the presence of hydrogen peroxide and nitrite with phenolic and catechol substrates, as well as mass spectrometry studies to investigate the modifications occurring on the peptide itself. The kinetic constants were similar for oxidation and nitration reactions, and their values suggest that the hemin-Aβ16 complex binds negatively charged substrates with higher affinity. Mass spectrometry studies showed that tyrosine residue is the endogenous target of nitration. Hemin degradation analysis showed that hemin bleaching is only partly prevented by the coordinated peptide. In conclusion, hemin has rich reactivity, both in oxidation and nitration reactions on aromatic substrates, that could contribute to redox equilibrium in neurons. This reactivity is modulated by the coordination of the Aβ16 peptide and is only partly quenched when oxidative and nitrative conditions lead to hemin degradation

Carbon nanotubes in high internal phase emulsion polymer composite for packed-cartridge micro-solid-phase extraction of fluoroquinolones in urine

Aim of this study stands in the evaluation of a carbon nanotubes-based polymerized high internal phase emulsion composite (CNT/polyHIPE) as sorptive phase in biological sample preparation. A micro-solid-phase extraction procedure (µSPE) was developed for trace fluoroquinolone (FQ) antimicrobials, namely Ciprofloxacin, Levofloxacin, Lomefloxacin, Moxifloxacin, Norfloxacin and Sparfloxacin, in human urine samples. PolyHIPEs modified by incorporation of different concentrations of nanotubes (0.2–0.8 wt %) were one-pot synthesized and applied in the packed-cartridge setting. The sorption affinity for the drugs was investigated in tap water and buffered aqueous solutions, demonstrating the key role of the nanotubes embedded in the polymer. The 0.5 wt % CNT composite was selected to develop a straightforward µSPE procedure directly in raw urine (1 mL sample), followed by HPLC-MS/MS. Targets were retained on the sorbent at near neutral pH and, after an aqueous washing (0.1 % v/v formic acid), eluted in a single-step with 4 % v/v ammonia aqueous solution (15 % v/v acetonitrile), thus combining extraction and clean-up. The method allowed accurate quantification of FQs, as evidenced by the recoveries (74–116 %, n = 3) obtained on blank pooled urine samples spiked with 40, 75, 150 µg L−1, accompanied by good inter-day precision (RSD < 14 %, n = 3). To confirm the applicability of the analytical method, some real-life blind samples were processed as a proof of concept

Introduction of a triphenylamine substituent on pyridyl rings as a springboard for a new appealing brightly luminescent 1,3-di-(2-pyridyl)benzene platinum(ii) complex family

International audienceThe preparation and characterization of three new complexes, namely [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-4,6-difluoro-benzene)Cl] ([(PtLCl)-Cl-1]), [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-5-triphenylamine-benzene)Cl] ([(PtLCl)-Cl-2]), and [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-5-mesityl-benzene)Cl] ([(PtLCl)-Cl-3]), is reported. All of them are highly luminescent in dilute deaerated dichloromethane solution (phi(lum) = 0.88-0.90, in the yellow-green region; the lambda(max,em) in nm for the monomers are: 562, 561 and 549 for [(PtLCl)-Cl-1], [(PtLCl)-Cl-2] and [(PtLCl)-Cl-3], respectively).[(PtLCl)-Cl-1] is the most appealing, being characterized by a very long lifetime (103.9 mu s) and displaying intense NIR emission in concentrated deaerated solution (phi(lum) = 0.66) with essentially no &quot;contamination&quot; by visible light &lt; 600 nm. This complex allows the fabrication of both yellow-green and deep red/NIR OLEDs; OLED emissions are in the yellow-green (CIE = 0.38, 0.56) and deep red/NIR (CIE = 0.65, 0,34) regions, for [(PtLCl)-Cl-1] 8 wt% (with 11% ph/e EQE) and pure [(PtLCl)-Cl-1] (with 4.3% ph/e EQE), respectively

An attractive family of cyclometalated Ir(III) dyes functionalized with tryptophan for potential neuroimaging applications

International audienceThree novel luminescent iridium(III) dyes functionalized with a tryptophan amino acid and bearing two cyclometalated 2-phenylpyridines, 2-(2,4-difluorophenyl)pyridines or 2-phenylquinolines have been prepared and well characterized. They emit at 522-561 nm with a luminescence quantum yield in the range 0.33-0.98. All the dyes are able to stain neuronal cells in rat cerebellum tissue, as evidenced by fluorescence microscopy, showing affinity for granule neurons. The complexes bearing cyclometalated 2-(2,4-difluorophenyl)pyridines or 2-phenylquinolines also have a good affinity for brain white matter. The dye with two cyclometalated 2-phenylquinolines is characterized by the best luminescence quantum yield (0.98). Besides, giving the greatest image contrast, the dye with two cyclometalated 2-phenylquinolines shows the strongest affinity for a distinct subtype of neurons found in cerebellum tissue, the purkinje neurons (as evidenced with fluorescence microscopy)

Introduction of a mesityl substituent on pyridyl rings as a facile strategy for improving the performance of luminescent 1,3-bis-(2-pyridyl)benzene platinum(ii) complexes: a springboard for blue OLEDs

International audienceWhile the development of red and green phosphorescent organic light-emitting diodes (OLEDs) has seen rapid progress, that of efficient blue phosphorescent OLEDs remains a challenge. In the present report, the introduction of a bulky substituent on the pyridyl rings of a cycloplatinated 1,3-bis(pyridine-2-yl)-4,6-difluoro-benzene appears as a facile strategy to hinder strong Pt and ctdot;Pt interactions, allowing the fabrication of efficient blue OLEDs. Thus, the preparation and characterization of a chlorido platinum(ii) complex bearing a well-designed new N&lt;^&gt;C&lt;^&gt;N-cyclometalating ligand, namely 1,3-bis(4-mesityl-pyridin-2-yl)-4,6-difluoro-benzene, are reported. Its structure, along with that of the related pro-ligand, is determined by X-ray diffraction studies on a single crystal. The shortest Pt and ctdot;Pt distance is much longer (8.59 and Aring;) than that observed for other N&lt;^&gt;C&lt;^&gt;N-platinum(ii) chlorido complexes including one with the bulky mesityl group on the cyclometalated benzene ring (4.4 and Aring;). This new complex exhibits intense blue phosphorescence (470-471 nm) in dichloromethane solution (Phi lum = 0.97) and in the PMMA film (1 wt% complex, Phi lum = 0.95) whereas red phosphorescence (672 nm) is observed in a neat film (Phi lum = 0.72). Even in the solid state, the novel complex is highly luminescent suggesting that the introduction of mesityl groups on the pyridine rings is a way to inhibit self-quenching both in the PMMA matrix and in neat films. It represents a useful tool for the fabrication of efficient blue OLEDs (8% wt complex) with CIE coordinates (0.13, 0.29) approaching true blue. The molecular geometry, ground state, electronic structure, and excited electronic states of the complex, both as a monomer and dimer aggregate in solution, are calculated using density functional theory (DFT) and time-dependent (TD) DFT approaches, giving insight into the electronic origin of the absorption spectra