Stéphane Petoud

Turn‐On Luminescence Sensing and Real‐Time Detection of Traces of Water in Organic Solvents by a Flexible Metal–Organic Framework

The development of efficient sensors for the determination of the water content in organic solvents is highly desirable for a number of chemical industries. Presented herein is a Mg(2+) metal-organic framework (MOF), which exhibits the remarkable capability to rapidly detect traces of water (0.05-5u2009% v/v) in various organic solvents through an unusual turn-on luminescence sensing mechanism. The extraordinary sensitivity and fast response of this MOF for water, and its reusability make it one of the most powerful water sensors known.

Highly emitting near-infrared lanthanide "encapsulated sandwich" metallacrown complexes with excitation shifted toward lower energy.

Near-infrared (NIR) luminescent lanthanide complexes hold great promise for practical applications, as their optical properties have several complementary advantages over organic fluorophores and semiconductor nanoparticles. The fundamental challenge for lanthanide luminescence is their sensitization through suitable chromophores. The use of the metallacrown (MC) motif is an innovative strategy to arrange several organic sensitizers at a well-controlled distance from a lanthanide cation. Herein we report a series of lanthanide “encapsulated sandwich” MC complexes of the form Ln3+[12-MCZn(II),quinHA-4]2[24-MCZn(II),quinHA-8] (Ln3+[Zn(II)MCquinHA]) in which the MC framework is formed by the self-assembly of Zn2+ ions and tetradentate chromophoric ligands based on quinaldichydroxamic acid (quinHA). A first-generation of luminescent MCs was presented previously but was limited due to excitation wavelengths in the UV. We report here that through the design of the chromophore of the MC assembly, we have significantly shifted the absorption wavelength toward lower energy (450 nm). In addition to this near-visible inter- and/or intraligand charge transfer absorption, Ln3+[Zn(II)MCquinHA] exhibits remarkably high quantum yields, long luminescence lifetimes (CD3OD; Yb3+, QLnL = 2.88(2)%, τobs = 150.7(2) μs; Nd3+, QLnL = 1.35(1)%, τobs = 4.11(3) μs; Er3+, QLnL = 3.60(6)·10–2%, τobs = 11.40(3) μs), and excellent photostability. Quantum yields of Nd3+ and Er3+ MCs in the solid state and in deuterated solvents, upon excitation at low energy, are the highest values among NIR-emitting lanthanide complexes containing C–H bonds. The versatility of the MC strategy allows modifications in the excitation wavelength and absorptivity through the appropriate design of the ligand sensitizer, providing a highly efficient platform with tunable properties.

Ga3+/Ln3+ Metallacrowns: A Promising Family of Highly Luminescent Lanthanide Complexes That Covers Visible and Near-Infrared Domains

Luminescent lanthanide(III)-based molecular scaffolds hold great promises for materials science and for biological applications. Their fascinating photophysical properties enable spectral discrimination of emission bands that range from the visible to the near-infrared (NIR) regions. In addition, their strong resistance to photobleaching makes them suitable for long duration or repeated biological experiments using a broad range of sources of excitation including intense and focalized systems such as lasers (e.g., confocal microscopy). A main challenge in the creation of luminescent lanthanide(III) complexes lies in the design of a ligand framework that combines two main features: (i) it must include a chromophoric moiety that possesses a large molar absorptivity and is able to sensitize several different lanthanide(III) ions emitting in the visible and/or in the near-infrared, and (ii) it must protect the Ln(3+) cation by minimizing nonradiative deactivation pathways due to the presence of -OH, -NH and -CH vibrations. Herein, a new family of luminescent Ga(3+)/Ln(3+) metallacrown (MC) complexes is reported. The MCs with the general composition [LnGa4(shi)4(C6H5CO2)4(C5H5N) (CH3OH)] (Ln-1, Ln = Sm(3+)-Yb(3+)) were synthesized in a one pot reaction using salicylhydroxamic acid (H3shi) with Ga(3+) and Ln(3+) nitrates as reagents. The molecular structure of [DyGa4(shi)4(C6H5CO2)4(C5H5N) (CH3OH)] was obtained by X-ray analysis of single crystals and shows that the complex is formed as a [12-MCGa(III)shi-4] core with four benzoate molecules bridging the central Dy(3+) ion to the Ga(3+) ring metals. The powder X-ray diffraction analysis demonstrates that all other isolated complexes are isostructural. The extended analysis of the luminescence properties of these complexes, excited by the electronic states of the chromophoric ligands, showed the presence of characteristic, sharp f-f transitions that can be generated not only in the NIR (Sm, Dy, Ho, Er, Yb) but also in the visible (Sm, Eu, Tb, Dy, Tm). All Ln-1 complexes possess very high quantum yield values with respect to other literature compounds, indicating a good sensitization efficiency of the [12-MCGa(III)shi-4] scaffold. Especially, as of today, the Yb-1 complex exhibits the highest NIR quantum yield reported for a lanthanide(III) complex containing C-H bonds with a value of 5.88(2)% in the solid state. This work is a significant step forward toward versatile, easily prepared luminescent lanthanide(III) complexes suitable for a variety of applications including highly in demand biological imaging, especially in the NIR domain.

N-Heterocyclic Tridentate Aromatic Ligands Bound to [Ln(hexafluoroacetylacetonate)3] Units: Thermodynamic, Structural, and Luminescent Properties

Herein, we discuss how, why, and when cascade complexation reactions produce stable, mononuclear, luminescent ternary complexes, by considering the binding of hexafluoroacetylacetonate anions (hfac(-)) and neutral, semi-rigid, tridentate 2,6-bis(benzimidazol-2-yl)pyridine ligands (Lk) to trivalent lanthanide atoms (Ln(III)). The solid-state structures of [Ln(Lk)(hfac)(3)] (Ln=La, Eu, Lu) showed that [Ln(hfac)(3)] behaved as a neutral six-coordinate lanthanide carrier with remarkable properties: 1) the strong cohesion between the trivalent cation and the didentate hfac anions prevented salt dissociation; 2) the electron-withdrawing trifluoromethyl substituents limited charge-neutralization and favored cascade complexation with Lk; 3) nine-coordination was preserved for [Ln(Lk)(hfac)(3)] for the complete lanthanide series, whilst a counterintuitive trend showed that the complexes formed with the smaller lanthanide elements were destabilized. Thermodynamic and NMR spectroscopic studies in solution confirmed that these characteristics were retained for solvated molecules, but the operation of concerted anion/ligand transfers with the larger cations induced subtle structural variations. Combined with the strong red photoluminescence of [Eu(Lk)(hfac)(3)], the ternary system Ln(III)/hfac(-)/Lk is a promising candidate for the planned metal-loading of preformed multi-tridentate polymers.

Hypoxia-Regulated Overexpression of Soluble VEGFR2 Controls Angiogenesis and Inhibits Tumor Growth

VEGFs are found at high levels in hypoxic tumors. As major components directing pathologic neovascularization, they regulate stromal reactions. Consequently, novel strategies targeting and inhibiting VEGF overproduction upon hypoxia offer considerable potential for modern anticancer therapies controlling rather than destroying tumor angiogenesis. Here, we report the design of a vector expressing the soluble form of VEGF receptor-2 (sVEGFR2) driven by a hypoxia-responsive element (HRE)-regulated promoter. To enable in vivo imaging by infrared visualization, mCherry and IFP1.4 coding sequences were built into the vector. Plasmid construction was validated through transfection into embryonic human kidney HEK293 and murine B16F10 melanoma cells. sVEGFR2 was expressed in hypoxic conditions only, confirming that the gene was regulated by the HRE promoter. sVEGFR2 was found to bind efficiently and specifically to murine and human VEGF-A, reducing the growth of tumor and endothelial cells as well as impacting angiogenesis in vitro. The hypoxia-conditioned sVEGFR2 expression was shown to be functional in vivo: Tumor angiogenesis was inhibited and, on stable transfection of B16F10 melanoma cells, tumor growth was reduced. Enhanced expression of sVEGFR2 was accompanied by a modulation in levels of VEGF-A. The resulting balance reflected the effect on tumor growth and on control of angiogenesis. A concomitant increase of intratumor oxygen tension also suggested an influence on vessel normalization. The possibility to express an angiogenesis regulator as sVEGFR2, in a hypoxia-conditioned manner, significantly opens new strategies for tumor vessel–controlled normalization and the design of adjuvants for combined cancer therapies. Mol Cancer Ther; 13(1); 165–78. ©2013 AACR.

A Bis(pyridine N-oxide) Analogue of DOTA: Relaxometric Properties of the GdIII Complex and Efficient Sensitization of Visible and NIR-Emitting Lanthanide(III) Cations Including PrIII and HoIII†

We report the synthesis of a cyclen-based ligand (4,10-bis[(1-oxidopyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid=L1) containing two acetate and two 2-methylpyridine N-oxide arms anchored on the nitrogen atoms of the cyclen platform, which has been designed for stable complexation of lanthanide(III) ions in aqueous solution. Relaxometric studies suggest that the thermodynamic stability and kinetic inertness of the Gd(III) complex may be sufficient for biological applications. A detailed structural study of the complexes by (1) Hu2005NMR spectroscopy and DFT calculations indicates that they adopt an anti-Δ(λλλλ) conformation in aqueous solution, that is, an anti-square antiprismatic (anti-SAP) isomeric form, as demonstrated by analysis of the (1) Hu2005NMR paramagnetic shifts induced by Yb(III) . The water-exchange rate of the Gd(III) complex is

Lanthanide-to-Lanthanide Energy-Transfer Processes Operating in Discrete Polynuclear Complexes: Can Trivalent Europium Be Used as a Local Structural Probe?

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Lanthanide hexafluoroacetylacetonates vs. nitrates for the controlled loading of luminescent polynuclear single-stranded oligomers

=6.7×10(6) u2005s(-1) , about a quarter of that for the mono-oxidopyridine analogue, but still about 50u2009% higher than the

Perfluorinated Aromatic Spacers for Sensitizing Europium(III) Centers in Dinuclear Oligomers: Better than the Best by Chemical Design?

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Mechanistic Studies of Gd3+‐Based MRI Contrast Agents for Zn2+ Detection: Towards Rational Design

of GdDOTA (DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). The 2-methylpyridine N-oxide chromophores can be used to sensitize a wide range of Ln(III) ions emitting in both the visible (Eu(III) and Tb(III) ) and NIR (Pr(III) , Nd(III) , Ho(III) , Yb(III) ) spectral regions. The emission quantum yield determined for the Yb(III) complex (