An efficient and stereoselective synthesis of the monomeric counterpart of marinomycin A

[structure: see text] The monomeric counterpart of marinomycin A, an antitumor-antibiotic marine natural product, was synthesized efficiently in 11 steps from the commercially available ethyl (R)-(-)-3-hydroxybutyrate. The strategy was highlighted by a crucial regio- and stereoselective cross-metathesis to form the C20-C21 double bond, enantioselective allyltitanations to control the configuration of the C17, C23, and C25 stereogenic centers, and a stereocontrolled construction of the tetraene moiety based on an original Horner-Wadsworth-Emmons olefination followed by a Pd-catalyzed cross-coupling.     

Disposable microfluidic ELISA for the rapid determination of folic acid content in food products

A micro-analytical system for rapid and quantitative analysis by inhibition immunoassay is presented and applied to the detection of folic acid. Eight polymer microchannels of 65-nL volume each and containing microelectrodes are embedded in a cartridge so that they can be operated simultaneously. All fluidic steps as well as the amperometric detection in the channels are operated by an instrument and software developed in-house. The fluidic steps of the immunoassay occur through hydrodynamic loading of the different solutions through the channels. The speed and duration of the flow and incubation parameters can thus be adapted to the biological and testing requirements. The effectiveness of the system was demonstrated by analysing folic acid concentrations in real infant formula samples within 5 min. In an effort to get a fully monitored assay, each fluidic step is monitored thanks to continuous amperometric detection of oxygen in the microchannel.     

High-accuracy structure of cyclobutane by femtosecond rotational Raman four-wave mixing

The femtosecond degenerate four-wave mixing (fs-DFWM) technique is applied for the measurement of accurate rotational constants of cyclobutane (C4H8). The vibrational levels of C4H8 exhibit tunneling splitting due to the ring-puckering interconversion between the symmetry-equivalent D2d minima via a planar D4h barrier. For the v = 0 ground state, the fs-DFWM method yields a rotational constant B + 0 = 10663.452(18) MHz. The ring-puckering tunneling leads to slightly different rotational constants for the 0+ and 0- levels, B + 0 - B -0 = 33 +/- 2 kHz. This difference increases by a factor of approximately 90 in the v = 1+/1- ring-puckering states to B +1 - B -1 = -3059 +/- 4 kHz. Combining the experimental rotational constants with the structure parameters and rotational constants calculated by high-level ab initio calculations allows us to determine accurate equilibrium and vibrationally averaged structure parameters for cyclobutane, for example, re(C-C) = 1.5474 A, re(C-Haxial) = 1.0830 A, re(C-Hequatorial) = 1.0810 A, and ring puckering angle theta e = 29.8 degrees .     

Recent Investigations on Thiocyanate-Free Ruthenium(II) 2,2′-Bipyridyl Complexes for Dye-Sensitized Solar Cells

Three decades ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the energy of the sun and for converting it into electricity. Since then, a lot of work has been devoted to create better global photovoltaic efficiencies and long term stability. Among photosensitizers for DSSCs, thiocyanate-free ruthenium(II) complexes have gained increasing interest due to their better stability compared to conventional thiocyanate-based complexes, such as benchmark dyes N719 and Z907. In this mini-review, two classes of thiocyanate-free Ru(II) complexes are presented: (a) bis-bipyridyl compounds bearing an ancillary cyclometalating bidentate ligand; (b) bipyridyl compounds bearing non-cyclometalating ancillary ligands. The coverage, mainly from 2014 up to now, is not exhaustive, but illustrates the most recent design strategies and photovoltaic properties of these two families of ruthenium(II) dyes.     

Evolution of the dynamic mechanical relaxations during the gel formation

Static and dynamic properties of a polyurethane system at different stages of the gelation process have been investigated. Shear modulus data were collected over a wide frequency range covering both the α-relaxation and the internal modes relaxations. The evolution of the relaxation spectra in relation with the structural transformation occurring during the growth process is analysed within the percolation model.     

Versatile synthesis of P-chiral (ephedrine) AMPP ligands via their borane complexes. Structural consequences in Rh-catalyzed hydrogenation of methyl α-acetamidocinnamate

An efficient and versatile synthesis of aminophosphine phosphinite (AMPP) ligands derived from ephedrine, with possible stereogenic P(III)-center(s) is described, using the borane complex methodology. The reaction of oxazaphospholidine borane with an organolithium reagent, leads to the formation of the ring-opened product, which is trapped by a chlorophosphine (borane), to afford the corresponding aminophosphine phosphinite boranes in good yields. Treatment of the borane complexes with dabco, gives the corresponding aminophosphine phosphinite ligands in 70–90% yield. These ligands are used for the preparation of Rh catalysts applied to the asymmetric hydrogenation of methyl α-acetamidocinnamate yielding the phenylalanine derivative with (R) 22% to (S) 99% e.e. These results show the importance of the structural modification at the P-stereogenic center(s), which could either amplify or cancel out the asymmetric induction resulting from the ephedrine backbone, for enantioselective catalysis.