NIEDERKOORDINIERTE PHOSPHORVERBINDUNGEN, 631. IMINO(BISMETHYLEN)PHOSPHATE

Abstract

Two imino(bismethylene)phosphat-ions can be synthesized via reaction of phenylamino- and α-naphthylaminobismethylenephosphorane with n-butyllithium in tetrahydrofuran. Anions containing [sgrave]³λ⁶-bounded phosphorus are stabilized in the crystal with THF-solvated lithium-kations.

Zwei Imino(bismethylen)phosphat-ionen werden durch Umsetzung des Phenylamino- und des α-Naphthylaminobismethylenphosphorans mit n-Butyllithium in Tetrahydrofuran erhalten. Die Anionen mit [sgrave]³λ⁶-gebundenem Phosphor werden im Kristall durch THF-solvatisierte Lithium-Kationen stabilisiert.     

Robotic heavy metal anodic stripping voltammetry: ease and efficacy for trace lead and cadmium electroanalysis

A novel strategy for the automation of trace lead (Pb²⁺) and cadmium (Cd²⁺) anodic stripping voltammetry (ASV) is described. This was achieved using an electrode assembly comprising a small standard reference electrode, a Pt wire counter electrode, and an in situ bismuth-plated pencil lead working electrode for ASV in a robotic device adapted for measurements in a 24-well microtiter plate format. The movement of the electrode assembly through individual wells was by computer-controlled micropositioning, and each microtiter plate run included a sequence of electrode pretreatment, water rinsing, and simultaneous Pb²⁺ and Cd²⁺ ASV measurements. Analyte concentrations down to 2 μg/L (Pb²⁺) and 20 μg/L (Cd²⁺) could be measured in drinking and tap water, a wastewater reference material and a soil sample, with an accuracy and standard deviation typical of stripping analysis. This robotic electrochemical strategy offers automated trace metal analysis with simple instrumentation and is suggested as an option for routine use in analytical laboratories such as those providing environmental heavy metal testing services.     

Microengineered PEG Hydrogels: 3D Scaffolds for Guided Cell Growth

Designing three‐dimensional (3D) scaffolds for selective manipulation of cell growth is of high relevance for applications in regenerative medicine. Especially, scaffolds with oriented morphologies bear high potential to guide the restoration of specific tissues. The fabrication of hydrogel scaffolds that support long‐term survival, proliferation, and unidirectional growth of embedded cells is presented here. Parallel channel structures are introduced into the bulk hydrogels by uniaxial freezing, providing stable, and uniform porosity suitable for cell invasion (pore diameters of 5–15 µm). In vitro assessment of the scaffolds with murine fibroblasts (NIH L929) shows a remarkable unidirectional movement along the channels, with the cells traveling several millimeters through the hydrogel.

     

Recoil-proton polarization in high-energy deuteron photodisintegration with circularly polarized photons

We measured the angular dependence of the three recoil-proton polarization components in two-body photodisintegration of the deuteron at a photon energy of 2 GeV. These new data provide a benchmark for calculations based on quantum chromodynamics. Two of the five existing models have made predictions of polarization observables. Both explain the longitudinal polarization transfer satisfactorily. Transverse polarizations are not well described, but suggest isovector dominance.     

Design of broadband RF pulses with polynomial-phase response

The achievable bandwidth of common linear-phase RF pulses is limited by the maximum feasible B1 amplitude of the MR system. It has been shown previously, that this limitation can be circumvented by overlaying a quadratic phase in the frequency domain, which spreads the power across the pulse duration. Quadratic-phase RF pulses are near optimal in terms of achieving minimal B1max. In this work, it is demonstrated that further B1max reduction can be achieved by combining quadratic with higher-order polynomial-phase functions. RF pulses with a phase response up to tenth order were designed using the Shinnar-Le Roux transformation, yielding considerable increases in bandwidth and selectivity as compared to pure quadratic-phase pulses. These benefits are studied for a range of pulse specifications and demonstrated experimentally. For B1max = 20 microT and a pulse duration of 2.1 ms, it was possible to increase the bandwidth from 3.1 kHz for linear and 3.8 kHz for a quadratic to 9.9 kHz for a polynomial-phase pulse.     

Fluorinated Azobenzenes Switchable with Red Light

Molecular photoswitches triggered with red or NIR light are optimal for photomodulation of complex biological systems, including efficient penetration of the human body for therapeutic purposes (“therapeutic window”). Yet, they are rarely reported, and even more rarely functional under aqueous conditions. In this work, fluorinated azobenzenes are shown to exhibit efficient E→Z photoisomerization with red light (PSS_660nm >75 % Z) upon conjugation with unsaturated substituents. Initially demonstrated for aldehyde groups, this effect was also observed in a more complex structure by incorporating the chromophore into a cyclic dipeptide with propensity for self-assembly. Under physiological conditions, the latter molecule formed a supramolecular material that reversibly changed its viscosity upon irradiation with red light. Our observation can lead to design of new photopharmacology agents or phototriggered materials for in vivo use.     

Electrochemiluminescence Bioassays with a Water‐Soluble Luminol Derivative Can Outperform Fluorescence Assays

The most efficient and commonly used electrochemiluminescence (ECL) emitters are luminol, [Ru(bpy)₃]²⁺, and derivatives thereof. Luminol stands out due to its low excitation potential, but applications are limited by its insolubility under physiological conditions. The water‐soluble m‐carboxy luminol was synthesized in 15 % yield and exhibited high solubility under physiological conditions and afforded a four‐fold ECL signal increase (vs. luminol). Entrapment in DNA‐tagged liposomes enabled a DNA assay with a detection limit of 3.2 pmol L^?1, which is 150 times lower than the corresponding fluorescence approach. This remarkable sensitivity gain and the low excitation potential establish m‐carboxy luminol as a superior ECL probe with direct relevance to chemiluminescence and enzymatic bioanalytical approaches.     

Correlation between thermal conductivity and bond length alternation in carbon nanotubes: A combined reverse nonequilibrium molecular dynamics—Crystal orbital analysis

The thermal conductivity (λ) of carbon nanotubes (CNTs) with chirality indices (5,0), (10,0), (5,5), and (10,10) has been studied by reverse nonequilibrium molecular dynamics (RNEMD) simulations as a function of different bond length alternation patterns (Δr_i). The Δr_i dependence of the bond force constant (k_rx) in the molecular dynamics force field has been modeled with the help of an electronic band structure approach. These calculations show that the Δr_i dependence of k_rx in tubes with not too small a diameter can be mapped by a simple linear bond length–bond order correlation. A bond length alternation with an overall reduction in the length of the nanotube causes an enhancement of λ, whereas an alternation scheme leading to an elongation of the tube is coupled to a decrease of the thermal conductivity. This effect is more pronounced in carbon nanotubes with larger diameters. The formation of a polyene‐like structure in the direction of the longitudinal axis has a negligible influence on λ. A comparative analysis of the RNEMD and crystal orbital results indicates that Δr_i‐dependent modifications of λ and the electrical conductivity are uncorrelated. This behavior is in‐line with a heat transfer that is not carried by electrons. Modifications of λ as a function of the bond alternation in the (10,10) nanotube are explained with the help of power spectra, which provide access to the density of vibrational states. We have suggested longitudinal low‐energy modes in the spectra that might be responsible for the Δr_i dependence of λ. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Regiochemistry of S-alkyl-substituted alkynes in Pauson-Khand reactions. Is a correlation with X-ray data and charge distribution calculations of the Co(2)(CO)(6)-alkyne complexes possible?

[reaction: see text] Pauson-Khand reactions (PKR) of RSCtbd1;CR' (6-10) yielded in all cases as the main product the regioisomer with the alkyl-S group disposed alpha to the CO group (16a-22a). Correlation of these results with X-ray data and charge distribution calculations of the corresponding dicobalthexacarbonyl complexes proves that a recently postulated "trans effect" in these complexes is not suitable for predicting the regiochemical outcome of the PKR unambiguously.