Halide anions driven self-assembly of haloperfluoroarenes: Formation of one-dimensional non-covalent copolymers

The supramolecular organization in six solid assemblies involving iodo- and bromoperfluoroarene derivatives is described. Single crystal X-ray analyses show that the formation of the supramolecular architectures is controlled by I⁻?Br–Ar_F, I⁻?I–Ar_F, Br⁻?I–Ar_F, and Cl⁻?I–Ar_F halogen bondings thus proving the X⁻?X′–Ar_F supramolecular synthon, where X can be the same as or different from X′, is particularly robust. In five of the described architectures halide anions form two halogen bondings and form infinite chains wherein dihaloperfluoroarenes, which function as bidentate electron acceptors, and halide anions, which function as bidentate electron donors, alternate. This behaviour shows halide anions have a fair tendency to work as bidentate halogen bonding acceptors.     

Positive integer solutions of the diophantine equation x 2 − L n xy + (−1) n y 2 = ±5 r

In this paper, we consider the equation x ²?L _n x y+(?1) ⁿ y ² = ±5 ^r and determine the values of n for which the equation has positive integer solutions x and y. Moreover, we give all positive integer solutions of the equation x ²?L _n x y+(?1) ⁿ y ² = ±5 ^r when the equation has positive integer solutions.     

Sequence distribution of beta-hydroxyalkanoate units in bacterial copolyesters determined by desorption chemical ionization mass spectrometry.

The sequence distributions of poly(beta-hydroxyalkanoate) copolymers were determined by analyzing oligomers obtained by the pyrolysis direct-chemical-ionization (DCI) mass spectrometry technique. Oligomers up to nonamers were identified and the comparison between the experimental and calculated peak intensities makes it possible to calculate repeating unit compositions and sequence distributions. Comparisons with other earlier methods are given.     

Thermal behaviour of solid complexes of phenoxyalkanoic acids and divalent metals

Solid cadmium and mercury(II) phenoxyacetates were prepared and investigated by DSC and TG techniques. The cadmium salt decomposed in two steps with the loss of 1.5 water molecules at first and the successive formation of CdCO₃ as final product. _deh H ^* associated with the loss of one water molecule was compared with the corresponding values obtained for other phenoxyacetates previously studied and the obtained results were discussed. Anhydrous mercury(II) phenoxyacetate gave, on heating, HgCO₃ which successively decomposed with the formation of gaseous products and a little amount of solid residue.Authors thank the Italian M.U.R.S.T. for financial support.     

Enzymatic Approach to and Odor Description of the Twelve Enantiomerically Pure Isomers of Pelargene®

Pelargene^® is a commercial fragrance sold as a mixture of three regioisomeric pyran derivatives ( 1 – 3 ). The enantiomers of each of the two possible diastereoisomers of 1 – 3 were prepared by means of a biocatalyzed approach, and the odor properties of the twelve isolated stereoisomers were evaluated.     

Protonation and complex formation constants of 3-amino-1,2,4-triazole in NaCl and CaCl(2) media at different temperatures and ionic strengths

The protonation of 3-amino-1,2,4-triazole was studied potentiometrically (glass electrode) in sodium chloride and calcium chloride solutions, 0.13 I 0.92M, at 10, 25, 37 and 45 degrees . The effect of the background electrolyte on the protonation constants is explained by a complex formation model. The species CaL(+), CaHL(2+) and H(2)LCl (HL = 3-amino-1,2,4-triazole) are proposed. Stability constants, together with their dependence on temperature (DeltaH degrees ) and on ionic strength, are reported for the protonated and complex species.