Joachim G. Heck

Luminescence tuning of MOFs via ligand to metal and metal to metal energy transfer by co-doping of 2∞[Gd2Cl6(bipy)3]*2bipy with europium and terbium

The series of anhydrous lanthanide chlorides LnCl3, Ln = Pr–Tb, and 4,4′-bipyridine (bipy) constitute isotypic MOFs of the formula 2∞[Ln2Cl6(bipy)3]·2bipy. The europium and terbium containing compounds both exhibit luminescence of the referring trivalent lanthanide ions, giving a red luminescence for Eu3+ and a green luminescence for Tb3+ triggered by an efficient antenna effect of the 4,4′-bipyridine linkers. Mixing of different lanthanides in one MOF structure was undertaken to investigate the potential of this MOF system for colour tuning of the luminescence. Based on the gadolinium containing compound, co-doping with different amounts of europium and terbium proves successful and yields solid solutions of the formula 2∞[Gd2−x−yEuxTbyCl6(bipy)3]·2bipy (1–8), 0 ≤ x, y ≤ 0.5. The series of MOFs exhibits the opportunity of tuning the emission colour in-between green and red. Depending on the atomic ratio Gd:Eu:Tb, the yellow region was covered for the first time for an oxygen/carboxylate-free MOF system. In addition to a ligand to metal energy transfer (LMET) from the lowest ligand-centered triplet state of 4,4′-bipyridine, a metal to metal energy transfer (MMET) between 4f-levels from Tb3+ to Eu3+ is as well vital for the emission colour. However, no involvement of Gd3+ in energy transfers is observed rendering it a suitable host lattice ion and connectivity centre for diluting the other two rare earth ions in the solid state. The materials retain their luminescence during activation of the MOFs for microporosity.

Luminescent cell-penetrating pentadecanuclear lanthanide clusters.

A novel pentadecanuclear lanthanide hydroxy cluster [{Ln15(μ3-OH)20(PepCO2)10(DBM)10Cl}Cl4] (Ln = Eu (1), Tb (2)) featuring the first example with peptoids as supporting ligands was prepared and fully characterized. The solid-state structures of 1 and 2 were established via single-crystal X-ray crystallography. ESI-MS experiments revealed the retention of the cluster core in solution. Although OH groups are present, 1 showed intense red fluorescence with 11(1)% absolute quantum yield, whereas the emission intensity and the quantum yield of 2 were significantly weaker. In vitro investigations on 1 and 2 with HeLa tumor cells revealed an accumulation of the clusters in the endosomal-lyosomal system, as confirmed by confocal microscopy in the TRLLM mode. The cytotoxicity of 1 and 2 toward the HeLa cells is moderate.

[Ln(BH4)2(THF)2] (Ln = Eu, Yb)—A Highly Luminescent Material. Synthesis, Properties, Reactivity, and NMR Studies

The divalent lanthanide borohydrides [Ln(BH(4))(2)(THF)(2)] (Ln = Eu, Yb) have been prepared in a straightforward approach. The europium compound shows blue luminescence in the solid state, having a quantum yield of 75%. Nonradiative deactivation of C-H and B-H oscillator groups could be excluded in the perdeuterated complex [Eu(BD(4))(2)(d(8)-THF)(2)], which showed a quantum yield of 93%. The monocationic species [Ln(BH(4))(THF)(5)][BPh(4)] and the bis(phosphinimino)methanides [{(Me(3)SiNPPh(2))(2)CH}Ln(BH(4))(THF)(2)] have been prepared from [Ln(BH(4))(2)(THF)(2)]. They show significantly lower or no luminescence. Using the diamagnetic compound [{(Me(3)SiNPPh(2))(2)CH}Yb(BH(4))(THF)(2)], we performed a 2D (31)P/(171)Yb HMQC experiment.

Metal-organic framework luminescence in the yellow gap by codoping of the homoleptic imidazolate ∞(3)[Ba(Im)2] with divalent europium.

The rare case of a metal-triggered broad-band yellow emitter among inorganic-organic hybrid materials was achieved by in situ codoping of the novel imidazolate metal-organic framework ∞(3)[Ba(Im)2] with divalent europium. The emission maximum of this dense framework is in the center of the yellow gap of primary light-emitting diode phosphors. Up to 20% Eu2+ can be added to replace Ba2+ as connectivity centers without causing observable phase segregation. High-resolution energy-dispersive X-ray spectroscopy showed that incorporation of even 30% Eu2+ is possible on an atomic level, with 2-10% Eu2+ giving the peak quantum efficiency (QE = 0.32). The yellow emission can be triggered by two processes: direct excitation of Eu2+ and an antenna effect of the imidazolate linkers. The emission is fully europium-centered, involving 5d → 4f transitions, and depends on the imidazolate surroundings of the metal ions. The framework can be obtained by a solvent-free in situ approach starting from barium metal, europium metal, and a melt of imidazole in a redox reaction. Better homogeneity for the distribution of the luminescence centers was achieved by utilizing the hydrides BaH2 and EuH2 instead of the metals.

Targeted delivery of glucocorticoids to macrophages in a mouse model of multiple sclerosis using inorganic-organic hybrid nanoparticles

&NA; Glucocorticoids (GC) are widely used to treat acute relapses in multiple sclerosis (MS) patients, but their application is accompanied by side effects due to their broad spectrum of action. Here, we report on the therapeutic option to apply GC via inorganic‐organic hybrid nanoparticles (IOH‐NP) with the composition [ZrO]2+[(BMP)0.9(FMN)0.1]2− (designated BMP‐NP with BMP: betamethasone phosphate; FMN: flavinmononucleotide). We found that these BMP‐NP have an increased cell type‐specificity compared to free GC while retaining full therapeutic efficacy in a mouse model of MS. BMP‐NP were preferentially taken up by phagocytic cells and modulated macrophages in vivo more efficiently than T cells. When GC were applied in the form of BMP‐NP, treatment of neuroinflammatory disease in mice exclusively depended on the control of macrophage function whereas effects on T cells and brain endothelial cells were dispensable for therapeutic efficacy. Importantly, BMP‐NP were not only active in mice but also showed strong activity towards monocytes isolated from healthy human volunteers. We conclude that application of GC via IOH‐NP has the potential to improve MS therapy in the future. Graphical abstract Figure. No caption available.

Zirconyl Clindamycinphosphate Antibiotic Nanocarriers for Targeting Intracellular Persisting Staphylococcus aureus

[ZrO]2+[CLP]2– (CLP: clindamycinphosphate) inorganic–organic hybrid nanoparticles (IOH-NPs) represent a novel strategy to treat persisting, recurrent infections with multiresistant Staphylococcus aureus. [ZrO]2+[CLP]2– is prepared in water and contains the approved antibiotic with unprecedented high load (82 wt % CLP per nanoparticle). The IOH-NPs result in 70–150-times higher antibiotic concentrations at difficult-to-reach infection sites, offering new options for improved drug delivery for chronic and difficult-to-treat infections.

White light emission and temperature dependent chromaticity shifts by modification of luminescent ZrO(FMN) nanoparticles with rare earth halides

The photoluminescence of the dispersions of zirconyl flavinmononucleotide nanoparticles (ZrO[FMN]: FMN = flavinmononucleotide) in pyridine was deliberately influenced by the addition of rare earth halides LnCl3, resulting in a modification to core/shell structures with the nanoparticle as the core. The particle dispersions original intense green luminescence of the flavin chromophore can therefore be shifted in chromaticity from green via white to blue. The shift depends on the reaction conditions as well as on the rare earth halide. Heating of the systems during the modification initiates these chromaticity shifts and they remain even after cooling to room temperature. For Ln = Y, La and Ho, all three halides can be used to create a broad band white light emission with a high general colour rendering index (CRI) of 84–88. The colour shift starts at 180 °C for Y and La, whereas HoCl3 addition already approaches the white point at 200 °C, whereas unmodified dispersions of ZrO(FMN) do not show a chromaticity shift at this temperature. The La-modified dispersion requires 250 °C to emit white light. The luminescence of the modified nanoparticles is also temperature dependent upon cooling to low temperatures, which shifts the colour point to intense blue for Y and La at −196 °C. Determination of the photoluminescence lifetimes indicates the modification of the chromophore and no solvent participation.

Zirconyl acetaminophen phosphate: A nanoscaled analgetic with very high drug load

Drug release belongs to the most challenging aspects of nanoparticles addressing molecular biology and medicine. Besides targeted delivery, obvious challenges are related to high drug load and continuous slow drug release. Based on our recently developed concept of inorganic-organic hybrid nanoparticles (IOH-NP), we here present [ZrO](2+)[AAP](2-) IOH-NPs containing the analgetic phosphate prodrug acetaminophen phosphate for drug release. [ZrO](2+)[AAP](2-) combines an uncomplex synthesis in water with a high prodrug load of 68wt.%. [ZrO](2+)[AAP](2-) nanoparticles exhibit a diameter of 37(11)nm and can be readily obtained as colloidally highly stable suspension in water. The chemical composition is studied in detail based on infrared spectroscopy, energy-dispersive X-ray analysis, thermogravimetry and elemental analysis. Moreover, the release of acetaminophen from [ZrO](2+)[AAP](2-) is studied by means of model experiments indicating the carbon content of the nanoparticles and, in alternative, the fluorescence of labeled nanoparticles. Both data show a continuous release of 80wt.% of the analgetic acetaminophen on a time scale up to 48h.