Generalizations of the Hohenberg-Kohn theorem: I. Legendre transform constructions of variational principles for density matrices and electron distribution functions

Given a general, N-particle Hamiltonian operator, analogs of the Hohenberg-Kohn theorem are derived for functions that are more general than the particle density, including density matrices and the diagonal elements thereof. The generalization of Lieb's Legendre transform ansatz to the generalized Hohenberg-Kohn functional not only solves the upsilon-representability problem for these entities, but, more importantly, also solves the N-representability problem. Restricting the range of operators explored by the Legendre transform leads to a lower bound on the true functional. If all the operators of interest are incorporated in the restricted maximization, however, the variational principle dictates that exact results are obtained for the systems of interest. This might have important implications for practical work not only for density matrices but also for density functionals. A follow-up paper will present a useful alternative approach to the upsilon- and N-representability problems based on the constrained search formalism.     

Total synthesis of gymnoconjugatins A and B

Convergent and efficient syntheses of the microbial natural products gymnoconjugatin A and B are reported and were based on a linchpin coupling strategy using a boron/tin hetero-bis-metallated butadiene system.     

Zymomonas mobilis as catalyst for the biotechnological production of sorbitol and gluconic acid

The conversion of glucose and fructose into gluconic acid (GA) and sorbitol (SOR) was conducted in a batch reactor with free (CTAB-treated or not) or immobilized cells of Zymomonas mobilis. High yields (more than 90%) of gluconic acid and sorbitol were attained at initial substrate concentration of 600 g/L (glucose plus fructose at 1:1 ratio), using cells with glucose-fructose-oxidoreductase activity of 75 U/L. The concentration of the products varied hyperbolically with time according to the equations (GA)=t(GA)(max)/(W(GA) +t), (SOR)=t (SOR)(max)/(W(Sor)+t), v(GA)=[W(GA) (GA)(max)]/(W(GA)+t)(2) and V(SOR)=[W(SOR) (SOR)(max)]/(W(SOR)+t)(2). Taking the test carried out with free CTAB-treated cells as an example, the constant parameters were (GA)(max)= 541 g/L, (SOR)(max)=552 g/L, W(GA)=4.8h, W(SOR)=4.9h, upsilon(GA)=112.7 g/L. and upsilon(SOR)=112.7 g/L.     

Crystallization of monoclinic WO3 in tungstate fluorophosphate glasses

Tungstate fluorophosphate glass compositions with high WO₃ concentration were prepared in the ternary system (80−0.8x)NaPO₃-(20−0.2x)BaF₂-xWO₃ with x = 40,50 and 60 mol%. Transparency decreases as WO₃ concentration increases but can be improved by addition of oxidizing systems such as CeO₂ or Sb₂O₃/NaNO₃. Characterizations by thermal analysis (DSC) point out that an increase in the amount of WO₃ results in a higher glass transition temperature. In addition, such compositions are very stable against devitrification since samples containing 40% and 50% of WO₃ donot even exhibit the expected crystallization event. In these samples, the stability against crystallization decreases with the WO₃ content and vitreous sample containing 60% of WO₃ exhibits an endothermic event around 620 °C due to crystallization of monoclinic WO₃ phase. In these glasses, it was shown that the nucleation stage can be induced by thermal-treatment when external nucleating agents such as Ti or Sb are used. Finally, gold-doped samples exhibit a higher crystallization tendency and monoclinic WO₃ phase can be grown in such glasses.     

Covalently functionalized hexagonal boron nitride nanosheets by nitrene addition

The covalent functionalization of exfoliated hexagonal boron nitride (h-BN) nanosheets by nitrene addition is described. Integration of functionalized h-BN nanosheets within a polycarbonate matrix is demonstrated and was found to afford significant increases in mechanical properties. This integration methodology was further extended by the covalent modification of the h-BN nanosheets with polymer chains of a polycarbonate analogue, and the integration of the polymer modified h-BN within the polymer matrix.     

Probing the Selectivity of Azomethine Imine Cycloaddition to Single‐Walled Carbon Nanotubes by Resonance Raman Spectroscopy

Selective covalent surface modification of single‐walled carbon nanotubes (SWNTs) is of great importance to various carbon nanotube‐based applications as it might offer an alternative method for enriching metallic and semiconducting nanotubes. Herein, we report on the surface modification of SWNTs through 1,3‐dipolar cycloaddition of 3‐phenyl‐phthalazinium‐1‐olate, which is a stable and reactive azomethine imine. For this reaction, microwave heating was found to be more efficient than conventional and solvent‐free heating. The sensitivity of cycloaddition to the molecular structure of SWNTs was probed using resonance Raman spectroscopy with three different laser excitations. Based on the obtained results, azomethine imine addition to the surface of nanotubes is selective for metallic and large‐diameter semiconducting SWNTs. Thermogravimetric analysis coupled with mass spectrometry showed that fragments released at high temperatures corresponded to the phenylphthalazine group, thus confirming the covalent surface functionalization. Modified SWNTs were further characterized by X‐ray photoelectron and UV/Vis‐NIR spectroscopies.     

Growth kinetic on the optical properties of the Pb(1-x)Mn(x)Se nanocrystals embedded in a glass matrix: thermal annealing and Mn2+ concentration

Semimagnetic Pb(1-x)Mn(x)Se nanocrystals were synthesized by a fusion method in a glass matrix and characterized by optical absorption (OA), atomic/magnetic force microscopy (AFM/MFM), and photoluminescence techniques. MFM images strongly indicated the formation of Pb(1-x)Mn(x)Se magnetic phases in the glass system. Quantum dot size was manipulated by tuning annealing time. It was shown that Mn(2+) impurity affects nucleation, where Mn(2+)-doped samples present a redshift of the OA peak after a short annealing time and a blueshift after long annealing time compared to undoped PbSe NCs. This behavior was linked to the dependence of band-gap energy and the absorption selection rule on Mn(2+) concentration. Photoluminescence in the Pb(1-x)Mn(x)Se nanocrystals increases as the temperature rises up to a point and then decreases at higher temperatures. Anomalous increases in emission efficiency were analyzed by considering temperature induced carrier-transfer in semimagnetic Pb(1-x)Mn(x)Se quantum dots nanocrystals of different sizes.     

APTES-modified RE2O3:Eu3+ luminescent beads: structure and properties

Europium-doped lanthanide oxide RE(2)O(3):Eu(3+) (RE = Y or Gd) luminescent beads, with a spherical shape and a diameter of 150 ± 15 nm, have been modified by reaction with 3-aminopropyltriethoxysilane (APTES), in order to introduce reactive amine groups at their surfaces. The direct silanation has resulted in the formation of a nanometric layer at the surface of the beads, with an optimum grafting rate of 0.055 ± 0.005 mol APTES/mol RE(2)O(3). Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies confirmed the condensation of an organosilane layer, made of cross-linked -O-Si-O-Si- and of groups -O-Si-R (with R = (CH(2))(3)NH(2) or O-Et). Titration of the accessible amine groups has been performed by simultaneously measuring the luminescence of grafted fluorescein isothiocyanate and that of core particles: there are about 2.3 × 10(4) (2.8 × 10(4)) -NH(2) per Y(2)O(3):Eu(3+) (Gd(2)O(3):Eu(3+)) bead. The isoelectronic point was shifted by one pH unit after APTES modification. The surface modification by APTES at least preserved (for Gd(2)O(3):Eu(3+)) or improved (for Y(2)O(3):Eu(3+)) the red emission of the beads.     

Local quantum criticality of an iron-pnictide tetrahedron

Motivated by the close correlation between transition temperature (T(c)) and the tetrahedral bond angle of the As-Fe-As layer observed in the iron-based superconductors, we study the interplay between spin and orbital physics of an isolated iron-arsenide tetrahedron embedded in a metallic environment. Whereas the spin-Kondo effect is suppressed to low temperatures by Hund's coupling, the orbital degrees of freedom are expected to quantum mechanically quench at high temperatures, giving rise to an overscreened, non-Fermi liquid ground state. Translated into a dense environment, this critical state may play an important role in the superconductivity of these materials.     

Structural studies of AgPO3–MoO3 glasses using solid state NMR and vibrational spectroscopies

Vitreous samples (1-x) AgPO₃–x MoO₃ (0 ≤ x ≤ 0.5) were prepared by conventional melt-quenching and characterized by Differential Scanning Calorimetry (DSC). The structural evolution of the vitreous network was monitored by ³¹P solid state nuclear magnetic resonance and Raman scattering, and assignments were aided by corresponding studies on the model compound AgMoO₂PO₄. The ³¹P MAS-NMR data differentiate between species having two, one, and zero P―O―P linkages (Q⁽²⁾ Q⁽¹⁾, and Q⁽⁰⁾ species), respectively. Interatomic connectivities involving these units are revealed by two-dimensional INADEQUATE data, utilizing the formation of double quantum coherences mediated by indirect ³¹P–³¹P spin–spin interactions via P―O―P linkages. As this method discriminates against isolated P atoms, it also serves as an important spectral editing tool for constraining lineshape fits. ⁹⁵Mo NMR data and Raman spectra suggest that the Mo species are most likely six-coordinate, forming four P―O―Mo linkages and are otherwise invariant with composition, except at MoO₃ contents ≥ 40 mole %, where some Mo―O―Mo bonding and/or clustering is observed.