Novel Approach of Evaluating Polymer Nanocomposite Structure by Measurements of the Freezing‐Point Depression

Summary: A novel experimental approach based on the freezing‐point depression of a solvent in a swollen gel has been developed to characterize the structure of nanocomposites. A higher depression in the freezing point has been related with an exfoliated nanocomposite. This increased depression not only depends on the formation of a tighter network but also on the decrease of the size of the solvent cages where the nucleation takes place.

The nucleation process of unfilled and organoclay‐filled natural rubber with the same crosslinking density.     

Solid-phase approaches to regiospecific double disulfide formation. Application to a fragment of bovine pituitary peptide

A 21-residue, two disulfide-containing peptide has been synthesized on solid phase. Three alternative protection schemes, based on Boc/benzyl chemistry and combinations of the 4-methylbénzyl with either acetamidomethyl, 9-fluorenylmethyl or 3-nitro-2-pyridylsulfenyl groups for pairs of cysteine residues have been examined. The most successful route involved formation of the first disulfide on the resin via 9-fluorenylmethylcysteine deprotection-oxidation.     

Synthesis and self-association of syn-5,10,15-trialkylated truxenes

syn-Trialkylated truxenes have been synthesized by alkylation of the truxene trianion followed by base-catalyzed isomerization of the anti isomers. 1H NMR studies, including a determination of diffusion coefficients, as well as molecular mechanics calculations, demonstrate that these derivatives self-associate in solution through arene-arene interactions. The benzyl derivatives show the strongest associations, which are a result of both benzyl-benzyl and truxene-truxene interactions.     

New fluorescence PET systems based on N2S2 pyridine-anthracene-containing macrocyclic ligands. spectrophotometric, spectrofluorimetric, and metal ion binding studies

Three new fluorescent devices for protons and metal ions have been synthesized and characterized, and their photophysical properties have been explored; these are the macrocycles 7-(9-anthracenylmethyl)-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) and 7-(10-methyl-9-anthracenylmethyl)-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L2) and the bis macrocycle 7,7'-[9,10-anthracenediylbis(methylene)]bis-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L3). All these systems have a pyridil-thioether-containing macrocycles as a binding site and an anthracene moiety as a signaling agent. The coordination properties of these ligands toward Cu(II), Co(II), Ni(II), Zn(II), and Pd(II) have been studied in solution and in the solid state. The addition of these metal ions to dichloromethane solutions of L1, L2, and L3 produce strong changes in the absorption and emission spectra of these ligands. The stoichiometry of the species, formed at 298 K, have been determined from absorption and fluorescence titrations. The Co(II) and Cu(II) complexes of L1 have been studied by EPR spectroscopy. This last complex and its free ligand have also been characterized by X-ray crystallography.     

Metrology of polymorph identification tests

Identification of polymorphs – compounds containing the same chemical entities, but differing by their solid state properties – is a challenge for analytical chemists, since the solid state characteristics of polymorphs sometimes have subtle differences in their infrared (IR) spectra. A method based on the evaluation of FTIR spectra by Principal Component Analysis and a Software Independent Modelling Class Analogy package is proposed for estimation of reliability of polymorph identification. It is demonstrated that by proper choice of the spectral region, the same approach can be used for identification of polymorphs in low dosage formulations.Presented at the Second International Conference on Metrology – Trends and Applications in Calibration and Testing Laboratories, November 4–6, 2003, Eilat, Israel.     

Fluorobenzene-argon ground-state intermolecular potential energy surface

The ground-state intermolecular potential energy surface for the fluorobenzene-argon van der Waals complex is evaluated using the coupled-cluster singles and doubles including connected triple excitations model, with the augmented correlation consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. In the surface minima the Ar atom is located above and below the fluorobenzene plane at a distance of 3.562 A from the fluorobenzene center of mass and at an angle of 6.33 degrees with respect to the axis perpendicular to the fluorobenzene plane. The corresponding binding energy is 391.1 cm(-1). Both these results and the eigenvalues obtained from the potential compare well with the experimental data available.     

Synthesis of new indoyl-1,3,4-oxadiazole and oxadiazine derivatives. Potential monoamine oxidase inhibitor activity

New indolyl-1,3,4-oxadiazole and oxadiazine derivatives were prepared as reversible monoamine oxidase inhibitors. The compound 5-(3-methylindolyl)-1,3,4-oxadiazol-2(3H)one was shown to be a good monoamine oxidase B inhibitor.     

Accurate intermolecular ground-state potential-energy surfaces of the HCCH-He, Ne, and Ar van der Waals complexes

Accurate ground-state intermolecular potential-energy surfaces are obtained for the HCCH-He, Ne, and Ar van der Waals complexes. The interaction energies are calculated at the coupled cluster singles and doubles including connected triple excitations level and fitted to analytic functions. For the three complexes we start with systematic basis set studies carried out at several intermolecular geometries, and using augmented correlation consistent polarized valence basis sets x-aug-cc-pVXZ (x=-,d; X=D,T,Q,5), also extended with a set of 3s3p2d1f1g midbond functions. The aug-cc-pVQZ-33211 surfaces of HCCH-He, Ne, and Ar complexes are characterized by absolute minima of -24.22, -50.20, and -122.17 cm(-1) at distances R between the rare-gas atom and the HCCH centers of mass of 4.35, 3.95, and 3.99 A, respectively; and at angles between the vector R and the HCCH main symmetry axis of 0 degrees , 43.3 degrees , and 60.6 degrees . The results are compared and considerably improve those previously available.     

The chlorobenzene-argon ground state intermolecular potential energy surface

Using the coupled cluster singles and doubles including connected triple excitations model with the augmented correlation consistent polarized valence double zeta basis set extended with a set of 3s3p2d1f1g midbond functions, we evaluate the ground state intermolecular potential energy surface of the chlorobenzene-argon van der Waals complex. The minima of 420 cm(-1) are characterized by Ar atom position vectors of the length 3.583 A, forming an angle of 9.87 degrees with respect to the axis perpendicular to the chlorobenzene plane. These results are compared to those obtained for similar complexes and to the experimental data available. From the potential the three-dimensional vibrational eigenfunctions and eigenvalues are calculated and the results allow to correct and complete the experimental assignment.     

The furan approach to oxacycles. Part 6: From THF to fused polyoxepanes

We describe a stereoselective synthesis of cis or trans fused bisoxepane ring system with the iterative use of the furan approach, enlarging the scope of our methodology.