Aluminacyclopropene: syntheses, characterization, and reactivity toward terminal alkynes

Reactions of LAl with ethyne, mono- and disubstituted alkynes, and diyne to aluminacyclopropene LAl[eta2-C2(R1)(R2)] ((L = HC[(CMe)(NAr)]2, Ar = 2,6-iPr2C6H3); R1 = R2 = H, (1); R1 = H, R2 = Ph, (2); R1 = R2 = Me, (3); R1 = SiMe3, R2 = C[triple bond]CSiMe3, (4)) are reported. Compounds 1 and 2 were obtained in equimolar quantities of the starting materials at low temperature. The amount of C2H2 was controlled by removing an excess of C2H2 in the range from -78 to -50 degrees C. Compound 4 can be alternatively prepared by the substitution reaction of LAl[eta2-C2(SiMe3)2] with Me3SiC[triple bond]CC[triple bond]CSiMe3 or by the reductive coupling reaction of LAlI2 with potassium in the presence of Me3SiC[triple bond]CC[triple bond]CSiMe3. The reaction of LAl with excess C2H2 and PhC[triple bond]CH (<1:2) afforded the respective alkenylalkynylaluminum compounds LAl(CH=CH2)(C[triple bond]CH) (5) and LAl(CH=CHPh)(C[triple bond]CPh) (6). The reaction of LAl(eta2-C2Ph2) with C2H2 and PhC[triple bond]CH yielded LAl(CPh=CHPh)(C[triple bond]CH) (7) and LAl(CPh=CHPh)(C[triple bond]CPh) (8), respectively. Rationally, the formation of 5 (or 6) may proceed through the corresponding precursor 1 (or 2). The theoretical studies based on DFT calculations show that an interaction between the Al(I) center and the C[triple bond]C unit needs almost no activation energy. Within the AlC2 ring the computational Al-C bond order of ca. 1 suggests an Al-C sigma bond and therefore less pi electron delocalization over the AlC2 ring. The computed Al-eta2-C2 bond dissociation energies (155-82.6 kJ/mol) indicate a remarkable reactivity of aluminacyclopropene species. Finally, the 1H NMR spectroscopy monitored reaction of LAl(eta2-C2Ph2) and PhC[triple bond]CH in toluene-d8 may reveal an acetylenic hydrogen migration process.     

Photoconvertible fluorescent protein EosFP: biophysical properties and cell biology applications

EosFP is a fluorescent protein from the coral Lobophyllia hemprichii that changes its fluorescence emission from green to red upon irradiation with near-UV light. Here we present the spectroscopic properties of wild-type EosFP and a variety of monomeric and dimeric mutants and provide a structural interpretation of its oligomerization and photoconversion, which is based on X-ray structure analysis of the green and red species that we reported recently. Because functional expression of the monomeric EosFP variant is limited to temperatures of 30 degrees C, we have developed a tandem dimer. This construct, in which two EosFP subunits are connected by a flexible 12 amino acid linker, expresses well after fusion with the androgen and endothelin A receptors at 37 degrees C. A variety of applications in cellular imaging, developmental biology and automated high-content screening applications are presented, which demonstrate that EosFP is a powerful tool for in vivo monitoring of cellular processes.     

Fringed sound fields and their interaction with liquid-solid interfaces

On the one hand, it is well known that Gaussian beams possess the ability to stimulate Rayleigh waves, resulting in the Schoch effect, a lateral beam displacement. This effect, often characterized by a reflected sound pattern consisting of two anti-phase beams, is due to the re-radiation of sound because of the stimulation of leaky Rayleigh waves. On the other hand, fringed sound beams are characterized by the fact that they consist of a number of neighboring anti-phase narrow beams. They are a first approximation of a sound field originating from a phased array of harmonic vibrating crystals in which each crystal vibrates in anti-phase compared to its neighbor. The individual lobes within the fringed sound pattern diverge much less than standard Gaussian beams of the same size. The current study investigates the interaction of fringed beams with a liquid-solid interface. It is found that under certain conditions, a fringed beam, incident at the Rayleigh angle, produces a reflected sound pattern that contains a wide lobe that is not fringed. It is also shown that under other conditions, contrary to the famous forward displacement of the reflected sound for incident Gaussian beams, a strong backward displacement occurs for fringed beams.     

Faceting and stability of smectic A droplets on a solid substrate

It is shown that a smectic A droplet deposited on a solid substrate treated for strong homeotropic anchoring is faceted at the top in spite of the fact that there are no steps at the free surface, but instead edge dislocations in the bulk. The radius of the facet and the full profile of the curved part of the droplet are determined as a function of the temperature in the vicinity of a nematic-smectic A phase transition. It is shown that the observed profiles do not correspond to the actual equilibrium shape, but to metastable configurations close to their point of marginal stability. In addition, we predict that the profiles must be different for a given temperature depending on whether the droplet has been heated or cooled down to reach this temperature. Finally, we discuss the problem of the formation of giant dislocations in big droplets (Grandjean terraces).     

Prediction of Gear Dynamics Using Fast Fourier Transform of Static Transmission Error*

ABSTRACT

An analytical computer simulation procedure for dynamic modeling of low-contact-ratio spur gear systems is presented. The procedure computes the gear static transmission error and uses a Fast Fourier Transform (FFT) to generate its frequency spectrum at various tooth profile modifications. The dynamic loading response of an unmodified (perfect involut) gear pair is compared with that of gears with profile modifications. Correlations are found between several profile modifications and the resulting dynamic loads. An effective error, obtained from frequency domain anal     

Disordered carbon nanofibers/LiCoPO<Subscript>4</Subscript> composites as cathode materials for lithium ion batteries

LiCoPO₄-coated disordered carbon nanofibers (CNFs/LiCoPO₄) were obtained by a sol–gel method, using triethyl phosphite or triethyl phosphate as the phosphorous source. The crystal structure of the products was analyzed by X-ray powder diffraction, while morphology was studied using scanning electron microscopy, transmission electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. Optimal synthesis conditions for the CNFs/LiCoPO₄ in light of the best electrochemical performance are discussed. The best discharge capacity 105 mAh/g (or ca. 63% of the theoretical capacity) shows the material with 40% CNFs/LiCoPO₄ and addition coating by carbon black. This composition has a best purity of active materials and point coverage of CNFs. The X-ray photoelectron C1s spectra of the CNFs surface without and with sputter erosion show enhancement of C–O bonds at the fiber surface, which does not influence significantly electrochemical behavior of the composite materials.     

Complexes of type C6H7(+)·L (L = N2 and CO2) studied by explicitly correlated coupled cluster theory

Complexes of the benzenium ion (C(6)H(7)(+)) with N(2) or CO(2) have been studied by explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level [T. B. Adler et al., J. Chem. Phys. 127, 221106 (2007)] and the double-hybrid density functional B2PLYP-D [T. Schwabe and S. Grimme, Phys. Chem. Chem. Phys. 9, 3397 (2007)]. Improved harmonic vibrational wavenumbers for C(6)H(7)(+) have been obtained by CCSD(T?)-F12a calculations with the VTZ-F12 basis set. Combining them with previous B2PLYP-D anharmonic contributions we arrive at anharmonic wavenumbers which are in excellent agreement with recent experimental data from p-H(2) matrix isolation IR spectroscopy [M. Bahou et al., J. Chem. Phys. 136, 154304 (2012)]. The energetically most favourable conformer of C(6)H(7)(+)·N(2) shows a π-bonded structure similar to C(6)H(7)(+)·Rg (Rg = Ne, Ar) [P. Botschwina and R. Oswald, J. Phys. Chem. A 115, 13664 (2011)] with D(e) ≈ 870 cm(-1). For C(6)H(7)(+)·CO(2), a slightly lower energy is calculated for a conformer with the CO(2) ligand lying in the ring-plane of the C(6)H(7)(+) moiety (D(e) ≈ 1508 cm(-1)). It may be discriminated from other conformers through a strong band predicted at 1218 cm(-1), red-shifted by 21 cm(-1) from the corresponding band of free C(6)H(7)(+).     

Remarks on Multilevel Bases for Divergence-Free Finite Elements

The connection between the multilevel factorization method recently proposed by Sarin and Sameh for solving mixed discretizations of the Stokes equation using a divergence-free finite element formulation, and hierarchical basis preconditioners for the Poisson problem is established. For the 2D triangular Taylor–Hood element, a preconditioner is proposed that could be useful in fractional step methods.     

3β‐Acetoxy‐5α,6β‐di­hydroxybisnorcholanic acid 2216 lactone

In the title compound, C₂₄H₃₆O₆, the ester linkage in ring A is equatorial. The six‐membered rings A, B and C have chair conformations. The five‐membered ring D adopts a 13β,14α‐half‐chair conformation and the E ring adopts an envelope conformation. The A/B, B/C and C/D ring junctions are trans, whereas the D/E junction is cis.