Diketones from ozonolysis of fused 3-phospholene oxides: Cyclizations to 3-phosphorinone and to 1,4-dihydro-1,4-azaphosphinine derivatives

1-R-3-Methyl-2,4,5,6,7,7a-hexahydro-1(H)-phosphindole 1-oxide and 1-R-3-methyl-6-methoxy-2,8,9,9a-tetrahydro-1(H)-benzo[e]phosphindole 1-oxide (R = Me or Ph) were prepared and ozonized at −78°C to give diketones in good yield. The intramolecular aldol condensation was performed on certain of these ketones to give multicyclic 3-phosphorinone derivatives. In some cases, double-bond rearrangement into the ring-fusion position was encountered. The 1-phenyl derivative in the benzophosphindole series could not be cyclized due to ready displacement of the P fragment from the tetralone system. The diketones reacted with ammonium acetate to give multicyclic derivatives of the 1,4-dihydro-1,4-azaphosphinine ring system. 1,2,3,4,5,6,7,8-Octahydro-3-oxo-1-phenylphosphinoline 1-oxide was used to demonstrate the value of the bicyclic 3-phosphorinones as precursors of 1-phosphadecalone derivatives. The carbonyl group was protected as the ethylene ketal and the double bond (as well as the benzene ring) was hydrogenated with ease. Hydrolysis gave the 1-phospha-3-decalone derivative. Reduction of the same 3-phosphorinone with NaBH₄ gave a mixture of diastereomeric alcohols.     

Synthesis of new 1,3-oxaphosphorinanium salts. Stereochemistry of hydroxide-induced displacement of methoxide ion

[reaction: see text] The synthesis of pure cis- and trans-3-methoxy-2,2,6-trimethyl-3-phenyl-1,3-oxaphosphorinanium tetrafluoroborate salts 3a and 3b, respectively, molecules designed to evaluate the effect of oxygen on the steric course of base-induced nucleophilic displacement of the methoxy group at phosphorus, was accomplished. It was found that these isomeric salts react with aqueous sodium hydroxide to produce the corresponding phosphine oxides 7a and 7b with complete retention of configuration at phosphorus.     

Biomineralization of superhydrophilic vertically aligned carbon nanotubes

Vertically aligned carbon nanotubes (VACNT) promise a great role for the study of tissue regeneration. In this paper, we introduce a new biomimetic mineralization routine employing superhydrophilic VACNT films as highly stable template materials. The biomineralization was obtained after VACNT soaking in simulated body fluid solution. Detailed structural analysis reveals that the polycrystalline biological apatites formed due to the -COOH terminations attached to VACNT tips after oxygen plasma etching. Our approach not only provides a novel route for nanostructured materials, but also suggests that COOH termination sites can play a significant role in biomimetic mineralization. These new nanocomposites are very promising as nanobiomaterials due to the excellent human osteoblast adhesion.     

Time resolved ultrafast ARPES for the study of topological insulators: The case of Bi2Te3

We discuss the application of time-resolved ultrafast angle resolved photoelectron spectroscopy to the study of photoexcited topological insulators. Measurements performed on the prototype material Bi₂Te₃ clearly show that all the main processes involved in the ultrafast surface carrier dynamics of topological insulators can be clearly observed and quantitatively analyzed. The comparison with other experimental results shows that the relative position of surface and bulk conduction bands with respect to the system Fermi level play an essential role in the recombination processes following ultrafast optical excitation.     

Potentiometric-spectroscopic evaluation of metal-ion complexes by humic fractions extracted from corn tissue

Humic fraction (HF) functional group-type and content are expected to depend on molecular size, which in turn, is expected to influence formation of heavy-metal complexes. In this study, corn (Zea mays L.) stalks and leaves were decomposed for an 8-month period to produce water-soluble humic substances. These substances were separated into three water-soluble fractions, HF1, HF2 and HF3, from highest to lowest relative molecular size. Functional group determination showed that carboxylic, and phenolic OH acidity increased as relative molecular size of humic fractions decreased. We also observed decreasing C/O ratios from larger to smaller corn tissue-derived humic fractions, whereas N/C and H/C ratios remained relatively unaffected. Furthermore, using potentiometric titration and FTIR spectroscopy we studied formation of Ca2+-, Cd2+-, and Cu2+-humic fraction complexes and how they were affected by pH and molecular size. We determined that metal-humic complexes exhibited at least two types of functional group-sites with respect to Ca2+, Cd2+, and Cu2+ complexation. Strength of metal-ion humic complexes followed the order Cu2+ > Cd2+ > Ca2+ and was affected by pH, especially for low affinity sites. Carboxylic groups were most likely the dominant group-sites involved in complex formation. Magnitude of the metal-humic formation constants in the logarithmic form at the lowest equilibrium metal-ion concentration, under the various pH values tested, varied from 5.39 to 5.90 for Ca2+, 5.36 to 6.01 for Cd2+, and 6.93 to 7.71 for Cu2+. Furthermore, the formation constants appeared to be positively influenced by decreasing molecular size of water-soluble humic fraction, and increasing pH. However, our molecular spectra showed that the pKa of corn humic fractions increased with decreasing relative molecular size and that Cu2+ was more covalently bonded by humic fractions than were Ca2+ and Cd2+, and the nature of the covalent bond character was independent of pH.     

How does the strength of exchange interactions in iron oxides influence the EPR line intensity and the catalytic activity?

Fe(III) ions may form ordered domains wherein the EPR resonance extends to the whole particle volume, leading to a major increase of spectral line intensities. This phenomenon of “strong exchange“ is known as ferromagnetic resonance (fmr). The authors observed another type of exchange, a weak one, characterized by drastically reduced resonances. Interestingly, both exchanges run parallel (up- or downwards) with the catalytic activity of iron oxide nano-particles as catalysts in the N₂O-mediated selective oxidation of benzene.