Stefano Levi Mortera

Hydrogen bonded supramolecular assemblies from uranyl ion complexes of tetrahomodioxacalix[4]arenes with various counterions

Abstract Reaction of the expanded calixarenes p-R-tetrahomodioxacalix[4]arenes (R=methyl, phenyl) with uranyl ions in the presence of amines (butylamine, pyrrolidine, triethylamine) gives complexes in which the metal ion is in a distorted square-planar, tetra-phenoxide, equatorial environment. Changes in para-substituents and/or in the amine lead to different supramolecular assemblies, resulting in sheets or columns held by hydrogen bonds and cation–π interactions. The importance of primary or secondary amines, able to give divergent hydrogen bonds, to promote such structures, is evidenced.

Dynamic HPLC of stereolabile iron(II) complexes on chiral stationary phases.

A series of chiral tris-(1,10)-phenanthroline iron(II) complexes have been resolved by HPLC on chiral stationary phases based on either cellulose tris-(3,5-dimethylphenylcarbamate) or teicoplanin. At sub ambient temperatures, baseline separation of the enantiomers was observed for five different iron(II) complexes featuring substituted phenanthroline ligands. Dynamic HPLC profiles were observed near or above room temperature, indicating on-column Delta/Lambda enantiomerization. Rate constants for the Delta/Lambda interconversion in free solution and during chromatography were obtained by thermal racemization experiments and by computer simulation of the HPLC dynamic plots, respectively.

The dynamic chromatographic behavior of tri-o-thymotide on HPLC chiral stationary phases.

The interconverting stereoisomers of tri-o-thymotide have been separated by HPLC on chiral stationary phases and the temperature dependence of the dynamic chromatographic patterns has been interpreted in terms of exchange between enantiomeric propeller and helical conformations. Computed low energy structures and CD spectra were used in absolute configuration assignment.

Towards enzyme-like enantioselectivity in the gas phase: conformational control of selectivity in chiral macrocyclic dimers

Conformational factors in self-assembled chiral tetraamide macrocycles control their gas-phase enantioselectivity towards the ethyl ester of naphthylalanine to levels typical of enzymes.

Enantiodiscrimination of bilirubin-IXα enantiomers in biomembrane models: Has chirality a role in bilirubin toxicity?

Simple biomembrane models, namely micellar aggregates formed by enantiopure sodium N-acylprolinates, are able to convert the racemic mixture of bilirubin-IXalpha into an enantiomerically enriched mixture, thus suggesting a possible role of chirality in bilirubin toxicity due to the perturbation of neuron membrane dynamics. The length of alkyl chain does not influence the extent of equilibrium displacement, however, it affects the conformation of bilirubin, thus confirming the role of lipid structure in the membrane/bilirubin interaction, and suggesting a non-superficial main site of association.

Inclusion of diprotonated [2.2.2]cryptand in the cavity of uranyl-complexed p-phenyl­tetra­homodioxacalix[4]arene

In the title compound, 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane dioxo[7,13,21,27-tetraphenyl-3,17-dioxapentacyclo[23.3.1.1(5,9).1(11,15).1(19,23)]ditriaconta-1(29),5,7,9(30),11(31),12,14,19(32),20,22,25,27-dodecaene-29,30,31,32-tetraolato]uranium dimethyl sulfoxide trisolvate, (C(18)H(38)N(2)O(6))[U(C(54)H(40)O(6))O(2)].3C(2)H(6)OS, the uranyl ion is bound to the four phenoxide groups of the deprotonated p-phenyltetrahomodioxacalix[4]arene ligand in a cone conformation, resulting in a dianionic complex. The diprotonated [2.2.2]cryptand counter-ion is located in the cavity defined by the eight aromatic rings of the homooxacalixarene, where it is held by cation-anion, cation-pi and possibly C-H...pi interactions. Dimerization in the packing leads to the formation of sandwich assemblages in which two diprotonated [2.2.2]cryptands are encompassed by two uranyl complexes.