Giovanni Dario Andreetti

p-t-Butylcalix[4]arene tetra-acetamide: a new strong receptor for alkali cations [1]

From the reaction ofp-t-butylcalix[4]arene with α-chloro-N,N-diethyl acetamide a new lipophilic ether-amide ligand (2) has been obtained in high yield. Solution studies show (2) to be a very strong cation receptor for alkali cations, especially sodium and potassium. The X-ray crystal structure determination of the free ligand (2) and two potassium complexes (KI and KSCN) shows the calix[4]arene in a fixed ‘cone’ structure and the cation completely encapsulated in a polar cavity of eight oxygen atoms.

Symbolic representation of the molecular conformation of calixarenes

In calixarene chemistry there is a continuous search for new shaping units or substructures useful for molecular recognition or for the binding of ions. The problem of assigning their molecular conformations cannot be dealt with by the use of the dihedral angles as done until now, because this method contains intrinsic ambiguities. The new approach, proposed here, is based on the use of the set ofn pairs of torsion angles (conformational parameters) which involve the flexible part of the calixarene and it is free of ambiguities. Moreover, knowledge of the set of conformational parameters allows one to build straightforwardly three-dimensional molecular models. A symbolic representation of the molecular conformation of any calix[n]arene may be obtained by combining the Schöenflies symbol of the molecular symmetry together with the signs of the conformational parameters.

Synthesis, 1H NMR, 13C NMR spectra and conformational preference of open chain ligands on lipophilic macrocycles☆

Abstract Several open chain ligands (polypodands) 3 and 4 have been synthesized introducing short oligoethylene glycol units (-CH 2 CH 2 O) m CH 3 , (m = 1,2,) on lipophilic matrices represented by cyclic tetra- 1 and octa- 2 oligomers obtained from the base catalyzed reaction of p-butylphenol or p-octylphenol and formaldeyde. 1 H NMR and 13 C NMR spectral data have been used to establish the conformational freedon of the ligands, which is important for cation binding studies.

Solid State Studies on p.t-Butyl-Calix[6]Arene Derivatives

Calix[n]arenes1 (1) are a class of phenol-formaldehyde macrocyclic oligomers which exhibit different sizes and shapes depending on the number of phenolic units in the cyclic array and on the nature of substituents on the aromatic nucleus (R1) and on the phenolic oxygen (R2).

Molecular inclusion in functionalized macrocycles. Part 9. The crystal and molecular structure of p-t-butylcalix[4]arena–anisole (2 : 1) complex: a new type of cage inclusion compound

p-t-Butylcalix[4]arene (1a), the cyclic tetramer obtained by the condensation of p-t-butylphenol and formaldehyde, crystallizes from anisole forming a new type of cage inclusion compound with the solvent. Crystals having a 2 : 1 host–guest stoicheiometry are tetragonal, space group P4/n, a=b= 12.823(6); c= 25.618(8)A, Z= 2, final R values 0.073. Two molecules of the macrocycle, in the cone conformation, face the methyl groups of the para-substituents creating a closed cavity which encapsulates one molecule of anisole. The guest is disordered in the cavity in at least eight equivalent orientations.

The modulated structure of Bi2Sr3−xCaxCu2O8: A commensurate model from single crystal X-ray diffraction data

Abstract The modulated structure of Bi 2 Sr 3− x Ca x Cu 2 O 8 is analyzed in the conventional three-dimensional space group Pnm utilizing single crystal X-ray diffraction data collected from a crystal showing a commensurate modulation period p =5 a . The correlations of the parameters of related ions were large but a reliable model ( R =0.0.082, R w =0.071) is obtained. On the basis of the obtained results the structural modulation seems to be produced mainly by the mismatch between the perovskite block and the sterochemical requirements of Bi in the BiO layers. Differently from what was suggested in recent works, no clear evidence of extra oxygen in the BiO layer was found; a charge modulation on the Bi atoms seems indeed to play a role in determining the superconducting properties of this place.

Crystal and molecular structure of a crown-bridgedp-t-butyl-calix[4]arene (1:1) pyridine complex. Host-guest interaction model based on molecular mechanics analysis [1]

The crystal and molecular structure of a crownedp-t-butyl-calix[4]arene (1:1) pyridine complex is reported. Colourless transparent prismatic crystals (obtained from pyridine) C54H74O8·C5H5N,a=13.486(4),b=15.193(4),c=16.432(5) Å, β=116.44(4)°, space groupP21,Z=2,Dcalc=1.02g cm−3, CuKα radiation λ=1.5418 Å μ(CuKα)=4.99 cm−1. Refinement was carried out using 1702 reflections withI>3σ(I) toR 0.12. The macrocycle shows a distorted cone conformation which defines an intramolecular apolar cavity whose elliptical aperture is 11.5×8.6 Å calculated as distances between the two opposite central C atoms of the But groups. A molecule of pyridine is included in this cavity, whereas the intermolecular cavities of the host lattice remain empty. The influence of the guest molecule on the conformation of the calixarene-crown is discussed. Potential energy calculations are performed in order to understand the nature of the host-guest interactions responsible for the stabilisation of the complex. Evidence for stabilizing CH3-π interactions are obtained from the calculations.

Crystal and molecular structure of cyclo{quater[(5-t-butyl-2-hydroxy-1,3-phenylene)methylene]} toluene (1 : 1) clathrate

Single-crystal X-ray analysis has shown the tetrameric structure of the low melting point product obtained from the base catalysed condensation of formaldehyde and para-t-butylphenol and its ability to form a stable cage-type clathrate with toluene.

Hydrogen bonding in thiosemicarbazide

In a recent paper (Domiano, Fava Gasparri, Nardelli & Sgarabotto, 1969, DGNS) the crystal-structure analysis of thiosemicarbazide, carried out by photographic methods, was reported (final R=9 .9%) . The positions of the hydrogen atoms were postulated from consideration of the hybridization of the nitrogen atoms and the packing interactions, no direct determination of position being possible from the final difference synthesis. In order to obtain a more accurate structure analysis, suitable for the location of the hydrogen atoms, new data have been collected at room temperature with an automated Picker diffractometer.

Stereochemistry of cercosporin

Abstract The absolute configuration of the asymmetric carbons and the axial chirality of the natural mold metabolite cercosporin (from Cercospora sp .) have been established on the basis of X-ray analysis and chemical reactions. The results confirm the inherent dissymmetry of the perylenequinone ring, the twisting of which gives rise to the diastereoisomer isocercosporin. The energy barrier for the conversion of cercosporin into isocercosporin has been evaluated.