Preparation d'alkyl-4 γ-lactones optiquement actives

Highly pure enantiomers of 4-alkyl γ-lactones are synthesized from optically active propargylic carbinols obtained by asymmetric reduction of α-acetylenic ketones with the chiral complex [LiAlH₄,N-methylephedrine-3,5 dimethylphenol].     

Two connected inverse spectral transforms

We establish a transformation which connects the potentials of the one-dimensional Dirac and Klein-Gordon operators. This transformation links the solutions of the nonlinear evolution equations solvable by means of the two inverse spectral transforms which use the Dirac and Klein-Gordon direct and inverse spectral problems.     

Messkette zur direkten potentiometrischen Bestimmung des Enantiomerenüberschusses von 1-Phenyläthylmmonium-Ionen

Cell Assembly for the Potentiometric Determinatin of the Enantiomeric Excess of 1-Phenylethylammonium-Ions A cell assembly with two membranes containing each one enantiomer of the ionophor N,N,N′,N′,N″,N″,N?,N?-octabutyl-1,4,7,10,16-hexaoxacyclooctadecane-2,3,11,12-tetracarboxamide is used for the direct potentiomewtirc determination of the enantiomeric excess ee of 1-phenylethylammonium ions in aqueous solutions. The preference for the (R)-over the (S)-1-phenylethylammonium ion by the (2R,3R,11R,12R)-ionophor of 2.7 allows a reliable determination of ee even in the presence of known concentrations of the heavy interferent KCl.     

Molecular Recognition of Anionic Substrates. Crystal Structures of the Supramolecular Inclusion Complexes of Terephthalate and Isophthalate Dianions with a Bis-intercaland Receptor Molecule

Molecular recognition of flat substrates requires the design of receptor molecules containing complementary flat units. If two such units are incorporated into a macrocyclic framework, a face to face inclusion of a planar substrate may take place, leading to an intercalative supramolecular structure. The water-soluble macrocyclic bis-intercaland receptor 1.4H+, containing two naphthalene subunits, linked by two positively charged oxy-bis- ethylamine binding sites, is able to bind strongly flat organic anions. The crystal structures of the terephthalate 2 and isophthalate 3 inclusion complexes are reported here. Complex 2, triclinic, P-1(N°), a = 7.717(3), b = 10.625(6), c = 16.238(9) Å, = 99.00(7), = 99.70(6), = 109.46(4)°, Z = 1. Complex 3, triclinic, P1 (N°1), a = 7.513(10), b = 10.640(9), c = 16.164(10) Å, = 98.81(5), = 99.77(10), = 109.36(12)°, Z = 1. Comparison of the environment (water molecules, anions and macrocycle) in the two X-ray structures highlights the formation of a similar organized assembly with the two different substrates.     

An implicit finite volume method for the solution of 3D low Mach number viscous flows using a local preconditioning technique

This paper presents a cell-centered high order finite volume scheme for the solution of the three-dimensional (3D) Navier–Stokes equations with low Mach number. The system of non-linear equations is solved by means of a fully implicit pseudo-transient scheme. Each pseudo-time step is solved by a Newton-GMRes procedure. A local preconditioning technique is used to scale the speed of sound and to improve the system condition number for low Mach number and low cell Reynolds number. This preconditioning is applied to the AUSM+up flux vector splitting function. The method is tested on 2D and 3D low Mach number laminar flows.     

Nanosecond kinetics of hydrated electrons upon water photolysis by high intensity femtosecond UV pulses

We report a nanosecond laser study of the transient absorption of hydrated electrons generated by multiphoton ionisation of liquid water upon excitation at 266 and 400 nm by femtosecond pulses with power densities higher than 1 TW/cm². For both wavelengths, as the pump power density increases, the signal amplitude increases and the decay becomes faster proving that more electrons are produced. However, we show that in the nanosecond time range, under pump power densities higher than 1 TW/cm², the distribution of the hydrated electrons is not uniform along the optical pathway of the pump beam in the water sample.