Solvatochromic Determination of Second-order Polarizabilities of Chromophore-functionalized Dextran and Amylose Derivatives

Linear dextran and helix amylose were covalently bonded with nonlinear optical (NLO) chromophores. The influence of the conformation of the polymer matrix on the NLO behavior of the supramolecular structure has been studied. The second order hyperpolarizability depends not only on the secondary structure of the biopolymer, but also on the position of the chromophore towards the polymeric backbone. Functionalization of NLO-phores with biopolymers led to increased thermo- and photostability.     

Regioselective alkylation of the lower rim of p-tert-butylthiacalix[4]arene with N-(p-nitrophenyl)-α-bromoacetamide

The preparation of partially substituted thiacalix[4]arenes 2–6 has been accomplished by conducting the reaction of the thiacalixarene 1 with N-(p-nitrophenyl)-α-bromoacetamide in acetone or acetonitrile in the presence of M₂CO₃ (M = Na, K and Cs). The influence of the reaction conditions (temperature, time, solvent, ratio of the reagents and the nature of the alkali metal carbonate) on regio- and stereoselectivity of this reaction is described.     

Theoretic study of the electronic spectra of neutral and cationic PaO and PaO2

The electronic spectra of neutral PaO and PaO₂ and their mono- (PaO⁺, PaO₂ ⁺) and dications (PaO²⁺, PaO₂ ²⁺) were studied by performing multiconfigurational quantum chemical calculations at the CASSCF/CASPT2 level of theory taking into account spin–orbit coupling. Including the protactinium 7s, 6d, and 5f orbitals as well as selected orbitals of oxygen in the active space, the vertical excitation energies at the ground-state geometries have been computed up to ca. 36,000 cm^?1. The gas-phase electronic spectra at 298 and 3,000 K were evaluated on the basis of the computed oscillator strengths.     

Structural characterization of electrochemically and in vitro biologically generated oxidation products of atorvastatin using UHPLC/MS/MS

Ultrahigh-performance liquid chromatography coupled with high-mass-accuracy tandem mass spectrometry (UHPLC–MS–MS) has been used for elucidation of the structures of oxidation products of atorvastatin (AT), one of the most popular commercially available drugs. The purpose of the study was identification of AT metabolites in rat hepatocytes and comparison with electrochemically generated oxidation products. AT was incubated with rat hepatocytes for 24 h. Electrochemical oxidation of AT was performed by use of a three-electrode off-line system with a glassy carbon working electrode. Three supporting electrolytes (0.1 mol L^?1 H₂SO₄, 0.1 mol L^?1 HCl, and 0.1 mol L^?1 NaCl) were tested, and dependence on pH was also investigated. AT undergoes oxidation by a single irreversible process at approximately +1.0 V vs. Ag/AgCl electrode. The results obtained revealed a simple and relatively fast way of determining the type of oxidation and its position, on the basis of characteristic neutral losses (NLs) and fragment ions. Unfortunately, different products were obtained by electrochemical oxidation and biotransformation of AT. High-mass-accuracy measurement combined with different UHPLC–MS–MS scans, for example reconstructed ion-current chromatograms, constant neutral loss chromatograms, or exact mass filtering, enable rapid identification of drug-related compounds. β-Oxidation, aromatic hydroxylation of the phenylaminocarbonyl group, sulfation, AT lactone and glycol formation were observed in rat biotransformation samples. In contrast, a variety of oxidation reactions on the conjugated skeleton of isopropyl substituent of AT were identified as products of electrolysis.

Avoiding problems with hydrogen misplacement in reporting crystal structures

Intermolecular hydrogen bonding is an integral part of many crystal structures. Hydrogen bonding sometimes results in one‐, two‐ or three‐dimensional supramolecular assemblies, a common feature of which is positional disorder of H atoms related to space‐group symmetry. Yet some reported structures fail to include all possible donor–acceptor close contacts, or to seek H‐atom electron densities associated with apparent D—H...A trios, while some H‐atom positions violate principles of chemistry or crystal physics. Modern diffraction equipment and sophisticated computing systems provide high‐quality data; thus, failure to characterize and report fully an accurate, complete and physically correct hydrogen‐bonding model should not be acceptable. We illustrate the relevant issues with three published examples in the hope of slowing the proliferation of these problems, with the scientifically desirable goal of improving the accuracy of crystallographic models while also providing improved search keys for information retrieval.     

The relationship between nanosilica dispersion degree and the tensile properties of polyurethane nanocomposites

The tensile properties and structure of silica-based polyurethane (PU) nanocomposites were parametrically studied as a function of silica type and weight concentration, polyol OH number, and mixing methods. The variation of the silica functionalization groups (from silanols to silazanes) had a relevant effect on dispersion. An elevated interparticle distance of the silica agglomerates improved substantially the tensile strength (from 44.3 to 82.8 MPa) and strain to failure (from 3.0 to 7.95) while maintaining elastic modulus (from 2.08 to 2.31 GPa) with respect to the neat PU matrix. Polyol’s with different OH numbers have shown to dramatically modify the silica dispersion degree by the modification of the stability of the colloidal dispersion. An increase of its value deteriorated dispersion and the tensile properties of the nanocomposites. The effect of three dispersion methods (ultrasonic dispersion, high shear mixing, and tip sonication) has shown to have a relative effect on the reduction of agglomerate size and the interparticle distance. High power sonication methods were more effective in reducing agglomerate size in contrast to shear methods. Classical theories of colloidal dispersion (Derjaguin, Landau, Verwey, and Overbeek) have been able to explain the correlation between the silica aggregation state and the final tensile properties of the nanocomposite.     

Synthesis of the Aliphatic Subunit of the Macrolide LL‐Z 1640‐2 via Vasella Ring Opening of a 6‐Iodo‐4‐deoxy‐D‐mannose

The synthesis of the aliphatic subunit 9 of the macrolide LL‐Z1640‐2 (I), starting from a 4‐deoxy‐D‐mannose derivative 2a, is described. The procedure includes the first successful application of a Vasella ring opening reaction for a 4‐deoxypyranoside. Nucleophilic addition of an alkynyllithium reagent to the aldehyde 4 led to the propargylic alcohol 7, which was converted to the advanced building block 9 in two further steps.     

One-pot synthesis of 2-(dicyanomethylene)-1,2-dihydropyridine derivatives

The synthesis of 2-(dicyanomethylene)-1,2-dihydropyridine derivatives from the reactions of arylmethylidene derivatives of malononitrile dimers with 1,3-dicarbonyl compounds is described.     

Free-radical selective functionalization of 1,4-naphthoquinones by perfluorodiacyl peroxides

Perfluoroalkyl radicals, generated by thermal decomposition of perfluorodiacyl peroxides, react selectively with quinone rings of 1,4-naphthoquinones. In the presence of a non-conjugated alkene such as 1-hexene, perfluoroalkyl radicals add to the double bonds of the olefin forming a radical adduct, which selectively adds to the naphthoquinone ring. Several perfluorodiacyl peroxides have been synthesized and used for the direct and alkene-mediated functionalization of naphthoquinones. Geometrical parameters and electron density topology of all perfluorodiacyl peroxides have been calculated by the density functional formalism and quantum theory of atoms in molecules to attempt a rationalization of the experimental reactivity.