Crystallinity and transitions in ethylene hexene copolymers

Copolymers of ethylene with hexene-1 have been prepared by catalytic polymerization. Three types of specimens were studied: (a) as the polymerized material; (b) the same after extraction with heptane; (c) the low molecular weight extract. These specimens were subjected to one or more of the following characterization techniques: $\text{M}$_n by several methods, X-ray diffraction, GPC, DSC, Rheovibron at 110 Hz, and T_g by an ESR spin probe technique. The hexene content of the extracted polymer did not exceed 4 mol%; that in the extract was as high as 89.5%. The characterization data and dynamic mechanical loss results in this paper have been examined in the context of an exhaustive study of ethylene-ethylene-α-olefin copolymers by Shirayama et al. with some additional details by Wilson et al. All T_g data are summarized in the form of a plot of temperature vs log (wt% hexene-1). It is emphasized that increasing hexene content decreases crystallinity, crystallite size and molecular weight, so that caution is required in interpreting results. For high mol wt low hexene-1 whole and extracted polymers, the spin probe method gives T_g for the amorphous phase whereas Rheovibron data reflect T_β( >T_g) for the composite amorphous-crystallite specimens. The ESR data indicate that T_g for amorphous PE, called T_g(L), is very close to 200 K which is above and distinct from T_γ at c, 150 K. It would still be desirable to investigate a series of ethylene-hexene-1 copolymers over the entire composition range at essentially constant, high molecular weight.     

Activation of ammonia and hydrazine by electron rich Fe(ii) complexes supported by a dianionic pentadentate ligand platform through a common terminal Fe(iii) amido intermediate

We report the use of electron rich iron complexes supported by a dianionic diborate pentadentate ligand system, B₂Pz₄Py, for the coordination and activation of ammonia (NH₃) and hydrazine (NH₂NH₂). For ammonia, coordination to neutral (B₂Pz₄Py)Fe(ii) or cationic [(B₂Pz₄Py)Fe(iii)]⁺ platforms leads to well characterized ammine complexes from which hydrogen atoms or protons can be removed to generate, fleetingly, a proposed (B₂Pz₄Py)Fe(iii)–NH₂ complex (3_Ar-NH₂). DFT computations suggest a high degree of spin density on the amido ligand, giving it significant aminyl radical character. It rapidly traps the H atom abstracting agent 2,4,6-tri-tert-butylphenoxy radical (ArO˙) to form a C–N bond in a fully characterized product (2_Ar), or scavenges hydrogen atoms to return to the ammonia complex (B₂Pz₄Py)Fe(ii)–NH₃ (1_Ar-NH₃). Interestingly, when (B₂Pz₄Py)Fe(ii) is reacted with NH₂NH₂, a hydrazine bridged dimer, (B₂Pz₄Py)Fe(ii)–NH₂NH₂–Fe(ii)(B₂Pz₄Py) ((1_Ar)₂-NH₂NH₂), is observed at −78 °C and converts to a fully characterized bridging diazene complex, 4_Ar, along with ammonia adduct 1_Ar-NH₃ as it is allowed to warm to room temperature. Experimental and computational evidence is presented to suggest that (B₂Pz₄Py)Fe(ii) induces reductive cleavage of the N–N bond in hydrazine to produce the Fe(iii)–NH₂ complex 3_Ar-NH₂, which abstracts H˙ atoms from (1_Ar)₂-NH₂NH₂ to generate the observed products. All of these transformations are relevant to proposed steps in the ammonia oxidation reaction, an important process for the use of nitrogen-based fuels enabled by abundant first row transition metals.

Synopsis: a highly reactive Fe(iii)–NH₂ complex is generated via activation of ammonia or hydrazine in reactions of relevance to fundamental steps in ammonia oxidation processes mediated by an abundant, first row transition metal.     

Embedding lp, {infty} into Lp, {infty}[0, 1] Complementably

We show that l^p, embeds into L^p, [0, 1] as a complemented sublattice.     

9-CIS, 11-CIS-RETINAL* FROM DIRECT IRRADIATION OF ALL-TRANS-RETINAL. NEW GEOMETRIC ISOMERS OF VITAMIN A AND CAROTENOIDS 9

Abstract The irradiation mixture of all-trans-retinal in acetonitrile was shown to contain four cis,cis isomers as well as the four cis isomers reported earlier. The relatively new 9-cis, 11-cis-retinal was isolated and characterized.     

Intermediates in the reduction of the antituberculosis drug PA-824, (6S)-2-nitro-6-{[4-(trifluoromethoxy)benzyl]oxy}-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine, in aqueous solution

The reduction chemistry of the new anti-tuberculosis drug PA-824, together with a more water-soluble analogue, have been investigated using pulse and steady-state radiolysis in aqueous solution. Stepwise reduction of these nitroimidazo-dihydrooxazine compounds through electron transfer from the CO(2) (-) species revealed that, unlike related nitroimidazoles, 2-electron addition resulted in the reduction of the imidazole ring in preference to the nitro group. In mildly acidic solution a nitrodihydroimidazo intermediate was formed, which was reduced further to the amine product. In both alkaline and neutral solution, an intermediate produced on 2-electron reduction was resistant to further reduction and reverted to parent compound on extraction or mass spectrometric analysis of the solution. The unusual reduction chemistry of these nitroimidazole compounds, exhibiting ring over nitro group reduction, is associated with alkoxy substitution in the 2-position of a 4-nitroimidazole. The unique properties of the intermediates formed on the reduction of PA-824 need to be considered as playing a possible role in its bactericidal action.     

Unexpected rearrangement products from animations of 5-bromo-2-nitrothiazole

While reaction of 2-bromo-5-nitrothiazole ( 2 ) with weakly basic secondary aliphatic amines gives the expected 2-amino products from nucleophilic displacement of the bromine, reaction of the isomeric 5-bromo-2-nitrothiazole ( 3 ) with such amines gives mixtures of the expected 5-amino products together with 2-aminated 5-nitrothiazole rearrangement products. The identity of the latter were detemined by alternative synthesis, and by X-ray crystallographic determination of a derivative. The mechanism proposed is a slow thermal isomerization of 5-bromo-2-nitrothiazole ( 3 ) to the much more reactive 2-bromo-5-nitro isomer 2 which competes, in the case of relatively weak amine nucleophiles, with the direct (but slow) nucleophilic displacement of the 5-bromo group to form the normal displacement products.     

Simplified Liquid-Phase Preparation of Four Decadeoxyribonucleotides and their Preliminary Spectroscopic Characterization

Four self-complementary decadeoxyribonucleotides, dApTpApTpApTpApTpApT, dApTpApTpCpGpApTpApT, dApTpApTpGpCpApTpApT and dApApApApApTpTpTpTpT, were chemically synthesized by the phosphotriester procedure. Efforts were concentrated on keeping the procedure as simple as possible, concomitant with obtaining high-purity products at each step of the process. The decamers were elaborated from the 3'-end, starting with a 3'?O-benzoylated monomer according to the scheme: monomer + monomer → dimer + dimer → tetramer + dimmer → hexamer + tetramer → decamer. Purity of intermediates and of the fully blocked decamers were monitored by chromatography and by 300-MHz ¹H? N M R. spectroscopy. The deblocked decadeoxyribonucleotides were characterized by their UV., CD., and ¹H? NMR. spectra.     

Non‐smooth atomic decomposition for generalized Orlicz‐Morrey spaces

In the present paper, we consider the non‐smooth atomic decomposition of generalized Orlicz‐Morrey spaces. The result will be sharper than the existing results. As an application, we consider the boundedness of the bilinear operator, which is called the Olsen inequality nowadays. To obtain a sharp norm estimate, we first investigate their predual space, which is even new, and we make full advantage of the vector‐valued inequality for the Hardy‐Littlewood maximal operator.