The configuration of β-halogenoenamines. The use of a new procedure for NOE measurements

The configurations of 16 different β-halogenoenamines have been determined using the proton NOE effect, and the same results were obtained as when the ²J(CH) coupling constants were used. A new procedure called the ‘repetitive shift frequency’ is presented for the NOE determinations which allows better reproducibility and improves the precision.     

Anion-receptor molecules: Synthesis of a chiral and functionalized binding subunit,a bicyclic guanidinium group derived from L- or D- asparagine

The optically active (4S,8S)-4, 8-bis(hydroxymethyl)-1,5,7-triazabicyclo[4.4.0]dec-5-ene ((S,S)- 1 ) has been synthesized in nine steps from L -asparagine with a total yield of 5.1%. Similarly, the enantiomer (R,R)- 1 has been prepared from D -asparagine. (S,S)- and (S,S)- 1 are representative examples of rigid and functionalized bicyclic guanidine systems and constitute useful intermediates in the construction of chiral selective anion-receptor molecules.     

Synthesis and Metal-Binding Properties of Polybipyridine Ligands Derived from Acyclic and Macrocyclic Polyamines

Synthetic procedures have been developed for the preparation of ligands bearing two to six pendent, unsubstituted or substituted 2, 2′-bipyridine groups attached to acyclic (tripode, tetrapode) and macrocyclic (triazanonade-cane, cyclam, hexacyclen, bis(bipyrido)hexaazamacrocycle) polyamines. Ligands 1-5 have been obtained in high yield by condensation of 6-(bromomethyl)-2, 2′-bipyridine ( 9b ) with the corresponding amines in the presence of NaOH, H₂O, and MeOH. Ligands 6-8 have been prepared in good yield by condensation of 9b or the di- or tetrasubstituted mono (bromomethyl) bipyridine 10b or 11b , respectively, with the corresponding amines in the presence of Na₂CO₃ and MeCN. Ligand 1 forms hemi-cage complexes with Ru^II, Fe^I, Cr^II, and Cr^III cations and trinuclear complexes with [RuCl²(bpy)²] and [ReCl(CO)⁵]. Tetrapode 2 and hexapode 4 gave tetranuclear and dinuclear complexes, respectively, by reaction with Fe11 salts. These complexes possess a variety of interesting physical and chemical properties.     

Die design: An implicit formulation for the inverse problem

Let us call a direct extrusion problem (DEP) the problem of finding the shape of the extrudate coming out of a die of prescribed shape. An implicit finite element formulation of the DEP which is geometrically general and for which a Newton-Raphson technique can be implemented has recently been proposed by Legat and Marchal. However, the problem posed to the die designer is frequently the inverse extrusion problem (IEP), i.e. finding the die shape which produces an extrudate of prescribed shape. This paper presents an extension of our original method for solving the IEP which avoids the ‘trial-and-error’ iteration on the die geometry itself. The advantage of the formulation lies in its capability to handle complex geometrics and in its low cost, because the CPU time and memory required to solve the IEP are almost identical to those of the DEP. We present benchmark results for squares and rectangles and new results obtained for geometries involving multiple corners. For an octagonal shape we also consider the case of a power-law fluid. For all results presented in this paper, surface tension has not been included.     

Supramolecular Chirality: Chiral hydrogen-bonded supermolecules from achiral molecular components

Chiral supermolecules may be obtained from suitable achiral molecular constituents associated through a dissymmetrizing interaction mode. This is the case for the supermolecules I–IV formed by hydrogen-bonding association between the achiral complementary components 1a , b and 2a , b , c . The crystal structures of the supermolecular pairs I–III and of the homochiral aggregate of two ternary supermolecules IV have been determined. The structural data are discussed.