The reaction of indolizines with tetracyanoethylene

Tetracyanoethylene (TCNE) reacts with indolizines ( 1a-c ) to give mixtures of 1- and 3-sub-stituted tricyanovinylindolizines, respectively. The isomers are identified by nmr spectroscopy. The occurrence of intramolecular charge-transfer bands in the visible spectra is discussed.     

Pimaricin—VIII : Structural and configurational studies by electron impact and field desorption mass spectrometry, 13C (25.2MHz) and 1H (270 MHz)-NMR spectroscopy

Attempts to obtain a molecular ion from the polyene macrolide antibiotic pimaricin by EI and FD mass spectrometry were unsuccessful The loss of carbon dioxide and a varying number of water molecules from the molecular ion made a molecular-weight determination impossible ¹³C NMR spectroscopy of N-acetylpimaricin, its dodecahydroderivative, and of HH-2, a hydrogenation-hydrogenolysis product of N-acetylpimaricin, confirmed that the antibiotic has structure 3 containing a hemi-ketalic ring and lacking an OH group at C-8. The value of the anomeric coupling constant, J_c-1-h-1, indicates that the mycosamine moiety is β-glycosidically bound to the aglycone.The structure and configuration of the antibiotic have been studied by analysis of the 270 MHz ¹H-NMR spectra of N acetylpimaricin and HH-2. By comparison of the two spectra and by extensive decoupling experiments, all signals in the spectrum of N-acetylpimaricin have been assigned to the protons in structure 3. From chemical-shift, coupling constant, and integral values, it was deduced that the mycosamine ring is pyranoid with a chair conformation, the hemi-ketal is 6 membered and occupies a chair conformation with the substituents in equatorial positions, the epoxy protons as well as the olefinic protons are trans to each other, and the antibiotic is diastereomerically pure.     

Electronic-enthalpy functional for finite systems under pressure

We introduce the notion of electronic enthalpy for first-principles structural and dynamical calculations of finite systems under pressure. An external pressure field is allowed to act directly on the electronic structure of the system studied via the ground-state minimization of the functional E+PV(q), where V(q) is the quantum volume enclosed by a charge isosurface. The Hellmann-Feynman theorem applies, and assures that the ionic equations of motion follow an isoenthalpic dynamics. No pressurizing medium is explicitly required, while coatings of environmental ions or ligands can be introduced if chemically relevant. We apply this novel approach to the study of group-IV nanoparticles during a shock wave, highlighting the significant differences in the plastic or elastic response of the diamond cage under load, and their potential use as novel nanostructured impact-absorbing materials.     

First principles calculation of the interdiffusion coefficient in binary alloys

The atomic mechanisms of diffusion in alloys are complex due to the variations of migration energies with environment and the correlations induced by short-range order between the different components. We present a first-principles approach for calculating vacancy-mediated diffusion coefficients in crystalline binary alloys and apply it to obtain the interdiffusion coefficient of Al(1-x)Lix. The rigorous treatment of atomic migration indicates that short- and long-range order induces strongly correlated migration mechanisms that deviate from random walk behavior.     

Role of hybridization in NaxCoO2 and the effect of hydration

Density functional theory is used to understand the electronic properties of Na(1/3)CoO2 and Na(1/3)CoO2(H2O)(4/3). Comparing the charge density of CoO2 and the Na doped phases indicates that doping does not simply add electrons to the t(2g) states. In fact, the electron added in the t(2g) state is dressed by hole density in the e(g) state and electron density in the oxygen states via rehybridization. In order to fully understand this phenomenon, a simple extension of the Hubbard Hamiltonian is proposed and solved using the dynamical mean-field theory. This model confirms that the rehybridization is driven by a competition between the on-site Coulomb interaction and the hybridization, and results in an effective screening of the low-energy excitations. Finally, we show that hydration causes the electronic structure to become more two dimensional.     

Predicting crystal structures with data mining of quantum calculations

Predicting and characterizing the crystal structure of materials is a key problem in materials research and development. It is typically addressed with highly accurate quantum mechanical computations on a small set of candidate structures, or with empirical rules that have been extracted from a large amount of experimental information, but have limited predictive power. In this Letter, we transfer the concept of heuristic rule extraction to a large library of ab initio calculated information, and we demonstrate that this can be developed into a tool for crystal structure prediction.     

A necessary and sufficient condition for a Baire α function to be a product of two Darboux Baire α functions

It is proved that a real-valued Baire α function on a real interval is a product of two Darboux Baire α functions if and only if the function has a zero in each subinterval in which it changes sign.     

ChemInform Abstract: Evaluation of Tavorite‐Structured Cathode Materials for Lithium‐Ion Batteries Using High‐Throughput Computing.

Tavorite‐structured oxyphosphates, fluorophosphates, oxysulfates, and fluorosulfates are evaluated for use as cathode materials in lithium ion batteries and activation energies for lithium diffusion through LiVO(PO₄), LiV(PO₄)F, and LiFe(SO₄)F are calculated.