Design and Mechanism of Rare-Earth Singlet Oxygen Sensing: An Experimental and Quantum Chemical Approach

The sensitive detection of singlet oxygen (¹O₂) is one key issue in various photochemical analyses, reactions, and processes; it is indispensable for designing catalysts for photodynamic therapies. Corresponding fluorescence-based organic ¹O₂ monitor luminophores may be equipped with rare-earth complexes with several intrinsic advantages. The design of the necessary ligands being a tedious, time-consuming effort, often involving empirical guesswork, we decided to support our experimental work with quantum chemical calculations. Hence, next to the experimental core, this paper suggests the additional use of time-dependent density functional theory (TDDFT) on suitable, free β-diketonate ligands to devise corresponding Eu³⁺ complexes as ¹O₂ probes eventually; the free ligand calculations obviously allow profoundly reduced computational efforts. Novel β-diketonate-substituted dimethyl anthracene complexes of Eu³⁺, Tb³⁺, and Gd³⁺ and their endoperoxidized descendants were thus synthesized, compared to known related complexes and analyzed with regard to their electronic characteristics; in addition, spectroscopy of a Eu³⁺ complex with ancillary epoxiphenanthroline for subsequent attachment to biological substrates featuring -NH₂ or -SH groups was included. The spectroscopic determination of the decisive lowest triplet (T₁) states of the Gd complexes could be matched by the Tamm-Dancoff approximation (TDA)/TDDFT calculations on the free ligands satisfactorily if suitable functionals were applied. Most significantly, the results suffice to describe the luminescence "switch-on" mechanism of this complex in the presence of ¹O₂.

High brightness red emitting polymer beads for immunoassays: Comparison between trifluoroacetylacetonates of Europium

Efficiently luminescing spherical polymer particles (beads) in the nanoscale regime of up to approximately 250 nm have become very valuable tools in bioanalytical assays. Eu³⁺- complexes imbedded in polymethacrylate and polystyrene in particular proved to be extraordinarily useful in sensitive immunochemical and multi-analyte assays, and histo- and cytochemistry. Their obvious advantages derive from both, the possibility to realize very high ratios of emitter complexes to target molecules, and the intrinsically long decay times of the Eu³⁺-complexes, which allows an almost complete discrimination against bothersome autofluorescence via time-gated measuring techniques; the narrow line emission in conjunction with large apparent Stokes shifts are additional benefits with regard to spectral separation of excitation and emission with optical filters. Last but not least, a reasonable strategy to couple the beads to the analytes is mandatory. We have thus screened a variety of complexes and ancillary ligands; the four most promising candidates evaluated and compared to each other were β-diketonates (trifluoroacetylacetonates, R-CO-CH-CO-CF₃, R = - thienyl, -phenyl, -naphthyl and -phenanthryl); highest solubilities in polystyrene were obtained with trioctylphosphine co-ligands. All beads had overall quantum yields in excess of 80% as dried powders and lifetimes well beyond 600 µs. Core-shell particles were devised for the conjugation to model proteins (Avidine, Neutravidine). Their applicability was tested in biotinylated titer plates using time gated measurements and a Lateral Flow Assay as practical examples.

The microbial threat: Can rare earths help?

Despite an ever increasing demand for reliable and cheap methods in the detection and quantification of microbes, surprisingly few investigations have explored or utilized the luminescence of rare earths in the microbial context, neither in conventional, that is, plating and microscopic imaging techniques, nor in advanced methods like fluorescence flow cytometry. We have thus investigated the potential of some rare earth complexes and hybrid materials for microbiological analysis. We found fairly simple procedures for internal staining (dyes inside the bacterial cell) and external staining (dyes on the cell surface). The present paper is predominantly relying on microscopic imaging and luminescence spectroscopies (excitation, emission, decay times), but also evaluates model rare earth microspheres to estimate an eventual rare earth based stain for a fast and sensitive bacteria enumeration with luminescence flow cytometry.

Patterning of Nanoclays on Positively Charged Self-Assembled Monolayers via Micromolding in Capillaries

Nanoclays are nanomaterials with versatile adsorptive properties. This contribution describes the generation of micropatterns of a nanoclay ("laponite") on ammonium-terminated, self-assembled monolayers (SAMs) on glass and silicon. Microstructured immobilization of the laponite was performed using micromolding in capillaries (MIMIC). The immobilization was verified using contact angle goniometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and fluorescence microscopy. Furthermore, laponite was modified with Nile red to generate a fluorescence enhancement-based surface sensor for the vitamin choline.

Selective Inactivation of Resistant Gram-Positive Pathogens with a Light-Driven Hybrid Nanomaterial

Herein, we present a straightforward strategy to disperse highly insoluble photosensitizers in aqueous environments, without major synthetic efforts and keeping their photosensitizing abilities unaffected. A layered nanoclay was employed to adsorb and to solubilize a highly efficient yet hydrophobic Si(IV) phthalocyaninate in water. The aggregation of the photoactive dye was correlated with its photophysical properties, particularly with the ability to produce highly cytotoxic singlet oxygen. Moreover, the resulting hybrid nanomaterial is able to selectively photoinactivate Gram-positive pathogens, due to local interactions between the bacterial membranes and the negatively charged nanodiscs. Nanotoxicity assays confirmed its innocuousness toward eukaryotic cells, showing that it constitutes a new class of "phototriggered magic bullet" for the inactivation of pathogens in phototherapy, as well as in the development of coatings for self-disinfecting surfaces.

Cyclo-thiazenokomplexe von Molybdän und Wolfram. Die Kristallstruktur von AsPh4[WCl4(N3S2)] / Cyclo-thiazeno Complexes of Molybdenum and Tungsten. The Crystal Structure of AsPh4[WCl4(N3S2)]

The dark brown cyclo-thiazeno com plexes [MoCl3(N3S2)]2 and [WCl3(N3S2)]2 are obtained by quantitative reactions of MoNCl3 with (NSCl)3 and of WOCl4 or WSCl4 with excess (NSCl)3, respectively. They are diamagnetic, thermally stable up to 200 °C, and only slightly sensitive towards moist air, but react explosively with aqueous bases. According to the IR spectra [MoCl3(N3S2)]2 is dimerized via chloro bridges whereas the tungsten com pound is associated via the γ-nitrogen atoms of the cyclo-thiazeno ligand. By reaction with [AsPh4]Cl or [PPh4]Cl in CH2Cl2, the compounds EPh4[MCl4(N3S2)] are obtained (E = P, As; M = Mo, W). The crystal structure of AsPh4[WCl4(N3S2)] was determined from X-ray diffraction data (1845 observed reflexions, R = 0.045). It crystallizes in the monoclinic space group P21/c with four formula units per unit cell. The lattice constants are a = 1352.4, b = 968.4, c = 2393.8 pm and β = 115.1°. The com pound is built up from AsPh4 ⊕ cations and [WCl4(N3S2)]⊖ anions in which the W atoms are coordinated in a distorted octahedral fashion by four Cl and two N atoms of the N3S2 ligand. The WN bond lengths (182 and 188 pm) correspond to douple bonds. The WN3S2 ring is planar and has SN bond lengths between 154 and 161 pm.

Phosphaniminatokomplexe von Molybdän / Phosphaneiminato Complexes of Molybdenum

We report the syntheses and IR spectra of phosphanciminato complexes of molybdenum:

(MoVCl4(NPPh3)(PPh3)] (I)

PPh4[MoIVCl4(NPPh3)(PPh3)] · 2CCl4 (II)

PPh4[MoVCl5(NPCl3)] (III)

I is obtained from [MoNCl4]2 and triphenylphosphane, or from [MoCl4(NSCl)]2 and triphenylphosphane: II was prepared by reacting MoNCl4 with triphenylphosphane followed by treatment with tetraphenylphosphonium chloride; III can be generated from PPh4[MoNCl4] with PCl3/PCl5. Complex I is paramagnetic (μeff, = 1.83 B.M., d1-configuration): II is diamagnetic (d2-system).

Efficient Red Emission from Europium Chelate-Silicone Host-Guest Hybrids

Due to their ease of fabrication, chemical stability and optical transparency polydimethylsiloxanederived silicones ([O-Si(CH3)2]∞) are excellent matrices to enable optical functions. We here report on the luminescence of silicone hybrids with red-emitting europium diketonate complexes, which have not been described previously in this matrix. The problem of too low solubility of the pure complexes has been resolved by co-coordination with trioctylphosphine oxide (TOPO), which permits complex concentrations of up to 5×10−3 mol L−1, at the same time maintaining complete transparency. Quantum efficiencies in excess of 60% could thus be obtained for benzoyltrifluoroacetonates, and near 50% for thenoyltrifluoroacetonates. These high efficiencies have been confirmed by room-temperature life time measurements, which displayed straight single-exponential decay behavior for both complexes independent of their concentration in the silicone.

The synthesis and characterisation of europium terpyridine-N-oxide complexes

Europium complexes of a series of terpyridine-N-oxide ligands have been prepared and structurally characterised by crystallographic studies. While the addition of three equivalents of terpyridine-1-oxide or terpyridine-1,1'-bisoxide results in complexes with nine co-ordinate tricapped trigonal prismatic or monocapped square antiprismatic geometries, respectively, three equivalents of the terpyridine-1,1',1'-trisoxide yields an unexpected 8 co-ordinate geometry. Luminescence studies of the three complexes in acetonitrile show a typical europium emission spectra, dominated by the (5)D(0)-(7)F(2) transition. While no simple trend in the relative quantum yields could be ascertained, the terpyridine-1-oxide complex was observed to have the most intense luminescence for this set of complexes.