Molecular aggregation of solid aromatic polymers. III. Small-angle X-ray scattering from aromatic polyamideimide film

Molecular aggregation in polytrimellitamideimide (PAI) was investigated by small-angle x-ray scattering (SAXS). PAI films annealed above the glass transition temperature show a scattering peak characteristic of two-phase structure. A one-dimensional model was used to analyze these SAXS curves. The more ordered phases are produced at higher annealing temperature. The average thickness of the ordered lamellae is comparable with the repeating length of the main chain. The relative difference of electron density between two phases is only a few percent, which shows that the two-phase structure of PAI, like that of aromatic polyimide, differs essentially from that of ordinary crystalline polymers.     

Application of environmental relaxation model to the transport behavior of glass-forming melts

The environmental relaxation model was applied successfully to explain the temperature dependence of viscosity, conductance, and the Walden product of molten Ca(NO₃)₂.3.91H₂O + NiCl₂ system in the non-Arrhenius region. This model was applied to pure melts, binary molten salt systems with ideal solutions marked by the absence of complex ions, and systems in which octahedral or tetrahedral complexes are formed. The values of the glass transition temperature obtained from the free volume and environmental relaxation models are in good agreement. The values of apparent activation energies for viscous and conductance flows derived from these two models are also comparable.     

Charge‐transfer complex formations of tetracyanoquinone (cyanil) and aromatic electron donors

Single‐electron oxidants are the primary reagents for investigations of the new oxidants and the development of electron‐accepting materials for application in optoelectronics. Quinones are the well‐known class of the neutral single‐electron oxidants. Here, we present the properties of the strongest neutral electron acceptor of this class tetracyanoquinone (cyanil) and investigate its electron‐accepting strength by analyzing the charge‐transfer complex formations with the aromatic donor molecules. Charge‐transfer complexes of tetracyanoquinone with aromatic electron donors are characterized spectroscopically in solution and isolated as the single crystals. Copyright © 2015 John Wiley & Sons, Ltd.     

Molecular structures of cation...pi(arene) interactions for alkali metals with pi- and sigma-modalities

The monovalent cations of Na(+), K(+), Rb(+), and Cs(+) derived from the highly electropositive alkali metals represent prototypical charged spheres that are mainly subject to relatively simple electrostatic and solvation (hydration) forces. We now find that the largest of these Rb(+) and Cs(+) are involved in rather strong cation...pi(arene) interactions when they are suitably disposed with the ambifunctional hexasubstituted benzene C(6)E(6). The ether tentacles (E = methoxymethyl) allow these cations to effect eta(1)-bonding to the benzene center in a manner strongly reminiscent of the classical sigma-arene complexes with positively charged electrophiles where Z(+) = CH(3)(+), Br(+), Cl(+), Et(3)Si(+), etc. The somewhat smaller potassium cation is involved in a similar M(+)...pi(arene) interaction that leads to eta(2)-bonding with the aromatic center in the pi-mode previously defined in the well-known series of silver(I)/arene complexes. We can find no evidence for significant Na(+)... pi(arene) interaction under essentially the same conditions. As such, the sigma-structure of the Rb(+) and Cs(+) complexes and pi-structure of the K(+) complex are completely integrated into the continuum of sigma-pi bondings of various types of electrophilic (cationic) acceptors with arene donors that were initially identified by Mulliken as charge-transfer.     

Structure and Chemistry of Malonylmethyl- and Succinyl-Radicals. The search for homolytic 1,2-rearrangements

Malonylmethyl radical I [· CH₂CH(COOEt)₂] and its thioester analogue II [· CH₂CH(COOEt) (COSEt)] were generated by standard photolytic and thermolytic methods from perester and bromo precursors. The structures of I and II were examined by ESR spectroscopy and found to exist in preferred conformations. However, no indication for their rearrangement by 1,2-shift of either an ethoxycarboxyl or (ethylthio)carbonyl group to the corresponding succinyl radicals III and IV , respectively, was found at temperatures below ? 40°C. At higher temperatures of up to 140°C, the search for malonylmethyl → succinyl rearrangement was examined by thorough-product analysis of the perester decomposition. There is evidence for the rearrangement of the radical I to III by photolysis and of the radical II to IV by thermolysis at 130°C in chlorobenzene to only a small extent.     

A new genosensor for meningococcal meningitis diagnosis using biological samples

In this work, a new electrochemical biosensor for DNA detection of bacterial meningitis is proposed. The system is based on specific DNA fragments from the Neisseria meningitidis genome as a probe incorporated on graphite electrodes modified with poly(4-aminophenol). Detection of a complementary oligonucleotide sequence, a specific 710-base pair amplicon, and the genomic DNA of bacteria was carried out by differential pulse voltammetry, using ethidium bromide as an electroactive indicator of hybridization. The complementary oligonucleotide and the genomic DNA of Neisseria meningitidis were quantified by the genosensor, showing detection limits of 0.6 ng μL^?1 and about 6 ng μL^?1, respectively. Morphological differences were observed between hybridized and unhybridized surfaces by atomic force microscopy. The biosensor showed high selectivity, discriminating non-specific targets, and high stability retaining over 98% of its original activity after 120 days of storage. The bioelectrode was effective in discriminating the genomic DNA in samples with human serum without significant interference, proving to be an interesting platform for meningococcal meningitis diagnosis.     

Asymmetric synthesis of syn- and anti-1,3-amino alcohols

The first application of metalloenamines derived from N-sulfinyl imines is reported for the highly diastereoselective addition to aldehydes. Reduction of the beta-hydroxy-N-sulfinyl imine products with catecholborane and LiBHEt3 provides syn- and anti-1,3-amino alcohol derivatives, respectively, with very high diastereomeric ratios.     

Electrochemical activation of acyl ligands in organometals. ESR studies of acetyl- and benzoyliron(III) complexes

The anodic oxidation of two series of acyliron(II) complexes, the neutral CpFe(CO)₂COR(I) and the anionic CpFe(CO)(CN)COR^? (II) where R = CH₃ and C₆H₅, are examined in acetonitrile solutions. The cyclic voltammograms of II are reversible, whereas those of I are irreversible even at sweep rates as high as 10 V s^?1. The neutral CpFe^III (CO)(CN)COCH₃ radical is sufficiently stable at 20°C to examine its ESR spectrum, as well as the kinetics and mechanism of thermal decomposition to afford acetone in high yields. However the cation-radical CpFe^III(CO)₂COCH⁺₃ from I is too reactive to observe directly, and it undergoes rapid solvolytic substitution in the presence of ethanol to afford ethyl acetate. The distinction between neutral and cationic acyliron(III) radicals is discussed in the context of acyl activation of organometals by electrochemical methods.     

Regiocontrolled copolymerization of methyl acrylate with carbon monoxide

An alternating copolymer of methyl acrylate with carbon monoxide has been synthesized for the first time via coordination polymerization using palladium complexes of phosphine-sulfonic acid as catalysts. The highly controlled head-to-tail structure of the copolymer was confirmed by NMR spectra. Subsequent insertion of carbon monoxide and methyl acrylate to methylpalladium species provided gamma-ketoalkylpalladium 2. The present system apparently conquered the difficulty in coordination-insertion of CO to 2.     

The spectral elucidation versus the X-ray structure of the critical precursor complex in bimolecular electron transfers: application of experimental/theoretical solvent probes to ion-radical (redox) dyads

The mechanistic conundrum is commonly posed by the intrinsic structural disconnect between a bimolecular (reactive) intermediate that is fleetingly detected spectroscopically in solution versus that rigorously defined by isolation and X-ray crystallography. We resolve this ambiguity by the combined experimental and theoretical application of the solvent media probe to the transient (1:1) precursor complex in the simplest chemical reaction involving direct adiabatic electron transfer (ET) among various donor/acceptor pairs. Of particular help in our resolution of such an important ET problem is the characterization of the bimolecular precursor complex as Robin-Day class II (localized) or class III (delocalized) from either the solvent-dependent or the solvent-independent response of the diagnostic intervalence absorption bands for the quantitative evaluation of the electronic coupling elements. The magnitudes of these intracomplex bindings are confirmed by theoretical (ab initio and DFT) computations that derive from X-ray structures and Marcus-Hush theories. Most importantly, the experimental solvent-induced ET barriers evaluated from the intervalence absorption bands are also quantitatively verified by the calculated outer-shell reorganization energies to establish unambiguously the intimate interconnection between the loosely bound bimolecular intermediate identified concurrently in solution and in the solid state.