A sinapic acid–calix[4]arene hybrid selectively binds Pb over Hg and Cd

The binding affinity for Pb²⁺, Cd²⁺ and Hg²⁺ of the sinapic acid–calix[4]arene hybrid 2, having four sinapyl pendants at the upper rim, has been investigated via an UV–Vis study. Compound 2 has better complexing ability than the monomeric p-phenetidine derivative 1. This highlights that the clustering of sinapyl units in a basket-like structure, dictated by the calixarene scaffold, greatly enhances the complexing properties. Ligand 2 forms complexes even with Hg²⁺, which is not complexed by 1 at all; the complexes formed by 2 with Pb²⁺ and Cd²⁺ are much stronger than the analogous complexes formed by 1. The UV–Vis investigation shows that the hybrid 2 markedly favors Pb²⁺ over Cd²⁺ and Hg²⁺. Information on the structural properties of the complex species was obtained by ¹H NMR spectroscopy. NMR data show that all three metal ions are placed into the cavity consisting of the calixarene scaffold and the sinapyl pendants, though their binding affects the coordinating regions to a different extent.     

A microcalorimetric enzymatic method for trehalose determination in food

As trehalose is a glucose font and also an additive in food, a new reliable method for trehalose determination is proposed. The analytical method uses an isothermal microcalorimeter, directly relates the analyte concentration with the heat variation of the enzymatic decomposition of trehalose into two glucose molecules. The enzymatic reaction is performed inside the calorimeter in the presence of trehalase enzyme immobilized on amino activated glass beads. Through the calibration curve, the trehalose quantity in some food samples (mushrooms and honey) has been determined. The calorimetric procedure was compared to a previously identified methodology based on an amperometric biosensor.     

DNA interaction of platinum(II) complexes with 1,10-phenanthroline and extended phenanthrolines

The interaction with DNA of the platinum(II) square planar complexes [Pt(N-N)(py)(2)](2+) (N-N = 1,10-phenanthroline (phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), dipyrido[3,2-a:2',3'-c]phenazine (dppz), benzodipyrido[b:3,2-h:2'3'-f]phenazine (bdppz)) has been investigated by means of absorption, circular and linear dichroism spectroscopy, DNA melting, and viscosity. In the presence of excess [DNA] all the complexes intercalate to the double helix. For those with the most extended phenanthrolines the binding mode depends on the [DNA]/[complex] ratio (q); at low q values the substances bind externally to DNA probably self-aggregating along the double helix. When the DNA concentration is large enough, the aggregate breaks up and the complex intercalates within the nucleobases. The complexes self-aggregate, without added DNA, in the presence of a large salt concentration.     

On the Influence of the Kinetic Energy¶on the Stability of Equilibria¶of Natural Lagrangian Systems

Natural Lagrangian systems (T,Π) on R ² described by the equation are considered, where is a positive definite quadratic form in and Π(q) has a critical point at 0. It is constructively proved that there exist a C ^∞ potential energy Π and two C ^∞ kinetic energies T and such that the equilibrium q(t)≡ 0 is stable for the system (T,Π) and unstable for the system . Equivalently, it is established that for C ^∞ natural systems the kinetic energy can influence the stability. In the analytic category this is not true. Accepted: October 20, 1999     

Lyotropic mesomorphism of alkyl esters of acyl-L-carnitines

The lyotropic polymorphism of a series of alkyl esters of acyl-L-carnitine has been studied by optical polarizing microscopy and X-ray diffraction. The different structures observed as a function of concentration and temperature have been characterized and their topology determined. As a result, two different phase sequence patterns have been detected: esters of normal alcohols bearing an alkyl chain of 6 or more carbon atoms in the acyl substituent display only a lamellar phase, while compounds which bear a relatively short alkyl chain (4 or less carbon atoms) show in addition non-lamellar type I hexagonal and cubic Q²³⁰ phases. From the analysis of the areas-per-molecule at the polar/apolar interface, the ability of the compounds investigated to form not only non-lamellar phases, but also direct micelles in isotropic solution has been related to the structural characteristics of the molecules. Curved, convex interfaces (in micelles and in non-lamellar phases) are possible only for the most polar acylcarnitines which have a relatively short alkyl chain, so that they behave like single chain surfactants; the most paraffinic derivatives, which have a relatively long alkyl chain, are effective double chain surfactants and then generate only quasi-planar interfaces.     

Multiplicity of subharmonic solutions of forced Hamiltonian systems near an equilibrium

We prove existence and multiplicity of long time periodic solutions for a class of nonlinear nonautonomous Hamiltonian systems locally near an equilibrium solution. The result relies on a variational principle and on the spectral analysis of an associated linear operator.Work performed under the auspices of the Ministero della Pubblica Istruzione (40%).     

Asymmetric aminolysis of aromatic epoxides: a facile catalytic enantioselective synthesis of anti-beta-amino alcohols

[reaction: see text] The first asymmetric aminolysis of trans-aromatic epoxides with anilines is described. The process affords enantioenriched anti-beta-amino alcohols in up to 99% ee. The complete regio- and diastereoselectivity observed uses commercially available [Cr(Salen)Cl] as a Lewis acid catalyst and in combination with a very simple experimental procedure renders the present reaction a facile and practical tool for the synthesis of chiral nonracemic anti-beta-amino alcohols.