Fluorescent sensor for Cu2+ with a tunable emission wavelength

A concept of fluorescent metal ion sensing with an easily tunable emission wavelength is presented and its principle demonstrated by detection of Cu(2+). A fluorescein dye was chemically modified with a metal chelating group and then attached to the terminus of ss-DNA. This was combined with a complementary ss-DNA modified with another fluorescent dye (ATTO 590), emitting at a longer wavelength. In the assembled duplex, fluorescence resonance energy transfer (FRET) between the fluorescein donor (excited at 470 nm) and the ATTO 590 acceptor (emitting at 624 nm) is observed. Proper positioning within the rigid DNA double helix prevents intramolecular contact quenching of the two dyes. Coordination of paramagnetic Cu(2+) ions by the chelating unit of the sensor results in direct fluorescence quenching of the fluorescein dye and indirect (by loss of FRET) quenching of the ATTO 590 emission at 624 nm. As a result, emission of the acceptor dye can be used for monitoring of the concentration of Cu(2+), with a 20 nM detection limit. The emission wavelength is readily tuned by replacement of ATTO-DNA by other commercially available DNA-acceptor dye conjugates. Fluorescent metal ion sensors emitting at >600 nm are very rare. The possibility of tuning the emission wavelength is important with respect to the optimization of this sensor type for application to biological samples, which usually show broad autofluorescence at <550 nm.     

Über Chalkogenolate. 163. Umsetzungen von Hydrazin mit Kohlenstoffdisulfid. 2. Kristallstruktur von Dikalium-1,2-hydrazin-bis(dithioformiat)

On Chalcogenolates. 163. Reactions of Hydrazine with Carbon Disulfide. 2. Crystal Structure of Dipotassium 1,2-Hydrazine-bis (dithioformate) The title compound K₂[S₂C? NH? NH? CS₂] ( 1 ) crystallizes with Z = 4 in the orthorhombic space group Pbna with cell dimensions a = 6.635(1), b = 10.825(2), c = 12.866(2) Å. The crystal structure has been determined from single crystal X-ray data measured at ?85 °C and refined to a conventional R of 0.034 for 969 independent reflections (R_w = 0.042). The [S₂C? NH? NH? CS₂]^2? ions are linked together by hydrogen bridges N? H…?S. The K⁺ ions are surrounded by seven sulfur atoms in irregular coordination.     

Reaktion von Formamid mit Kohlenstoffdisulfid 2. Kristallstruktur von Kalium-N-formyldithiocarbamat [1]

On Chalcogenolates. 148. Reaction of Formamide with Carbon Disulfide. 2. Crystal Structure of Potassium N-Formyl Dithiocarbamate K[S₂C? NH? CO? H] crystallizes with Z = 16 in the monoclinic space group Cc with cell dimensions a = 13.187(13) Å, b = 12.928(3) Å, c = 13.962(6) Å, and β = 101.75 (3)°. The crystal structure has been determined from single crystal X-ray data measured at 20°C and refined to a conventional R of 0.034 for 1857 independent reflections (R_w = 0.038). The compound crystallizes by building a super-structure, which is based on an H-bridged 16-membered ring-system, formed by four[S₂C? NH? CO? H]^? anions. Two different binuclear K⁺ coordination polyhedra are formed with two oxygen and two sulfur atoms in common.     

Observation of Unusual Molecular Diffusion Behaviour below the Lower Critical Solution Temperature of Water/2‐Butoxyethanol Mixtures by using Fluorescence Correlation Spectroscopy

The effect of solute affinity on solute diffusion in binary liquids well below the lower critical solution temperature (LCST) was studied by using fluorescence correlation spectroscopy. We measured the hydrodynamic radii of a hydrophobic and an amphiphilic fluorescent dye under systematic variation of the relative molar fractions of water/2‐butoxyethanol and, for comparison, of water/methanol mixtures, which do not show phase separation. We found that the apparent hydrodynamic radius of the hydrophobic dye almost doubled in water/2‐butoxyethanol, whereas it remained largely unchanged for the amphiphilic dye and in water/methanol mixtures. Our results indicate that the translational diffusion of solutes is influenced by transient local solution structures, even at temperatures well below the LCST. We conclude that, even far below LCST, different solutes can experience different environments in binary liquid mixtures depending on both the solute and solvent properties, all of which impact their reactivity.     

First Measurement of the Gerasimov-Drell-Hearn Sum Rule for 1H from 0.7 to 1.8 GeV at ELSA

To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68-1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4pi detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9+/-2.4(stat)+/-2.2(syst)] microb.     

Accurate time delay determination for femtosecond X-ray diffraction experiments

Intensity correlations and noise reduction are observed and characterized in the broadband supercontinuum generated by spatio-temporal solitons propagating in air, i.e., in filamentation of ultrashort laser pulses. Large correlations and reduction of the laser noise are observed already at the first steps of the filamentation process, while further propagation results in cascaded χ⁽³⁾ broadening processes and yield complex correlation maps. The spectral range yielding an optimal laser noise reduction of 3.6 dB is found to cover 10 nm around the fundamental wavelength. PACS 42.65.Jx; 42.65.Tg; 42.65.Ky; 42.50.Lc     

Preparation of porous manganese oxide nanomaterials by one-pot synthetic sol–gel method

For the first time, the simple epoxide addition, sol–gel method has been employed to successfully prepare porous, high surface area manganese (II) aerogel nanomaterials. These uniform materials can then undergo calcination at relatively low temperature to selectively yield the mixed-valent Mn₃O₄ complex illustrating both an ease of preparation and synthesis versatility.