Enantioselective, (−)-sparteine-mediated deprotonation of geranyl and neryl N,N-diisopropylcarbamate: configurational stability of the intermediate lithium compounds

(E)/(Z)-Isomeric allylic carbamate esters were deprotonated by n-butyllithium/(−)-sparteine in toluene. Trapping experiments with chlorotrimethylsilane afforded the α-substitution products, with (R)-configuration, revealing that the pro-S proton is removed predominantly to form the corresponding (S)-lithium·(−)-sparteine derivatives; k_S/k_R>15:1 and >7:1, respectively. A slow (S)→(R)-epimerization occurs at −78 °C (T_1/2>60 min). The allylic double bond is stable to (Z)-(E) isomerization under these conditions.     

A chiral porous 3D metal-organic framework with an unprecedented 4-connected network topology

A novel homochiral 3D metal-organic framework [CdL2(H2O)2][ClO4]2.2DMF.3EtOH.5/3H2O, 1, (L =(R)-6,6-dichloro-2,2-diethoxy-1,1-binaphthyl-4,4-bipyridine) exhibits an unprecedented 4-connected network topology owing to the cis- configuration of the Cd coordination and possesses permanent porosity as demonstrated by TGA, XRPD, and CO2 adsorption isotherm studies.     

Novel oxovanadium phosphate tubule incorporating 2,2-bipyridine ligands: hydrothermal synthesis and crystal structure of [(V(IV)O)(3)(mu(5)-PO(4))(2)(2,2'-bpy)(mu-OH(2))].1/3H(2)O

The novel tubular framework of [(V(IV)O)(3)(mu(4)-PO(4))(2)(2,2'-bpy)(mu-OH(2))].1/3H(2)O, which was synthesized from hydrothermal reaction, possesses some attractive structural features: (i) O=V(IV)O(4)(OH(2)) octahedra and PO(4) tetrahedra linked together by corner-sharing and face-sharing into a cylinder-shaped channel including 6 water molecules per cell unit, and (ii) (VO)(2,2'-bpy) groups regularly arranged around the tube, so that the 2,2-bpy ligands constitute an organic shell around an aqueous polar channel.     

Film-forming characteristics and thermal stability of low viscosity benzoxazines derived from melamine

A novel class of low-viscosity benzoxazines has been synthesized from melamine and formaldehyde with phenol or bisphenol A. The striking feature of the class of benzoxazines is the subtle combination of their inherently low viscosity at room temperature, good film-forming characteristics and high chemical and thermal stability mainly due to the introduction of melamine into the network of the polymers. The structure of the benzoxazines has been confirmed by proton nuclear magnetic resonance spectroscopy and fourier transform infrared spectroscopy. Thermal properties of polybenzoxazine have been studied by differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis. Transparent polybenzoxazine films were easily obtained under solvent-free conditions, exhibiting significantly improved toughness compared to the conventional polybenzoxazines. Our research may open a new path for overcoming the present drawbacks of polybenzoxazines such as high brittleness, the difficulties in preparing films and poor processibility via tailoring the structures and properties of amine in the benzoxazines.     

The First Mixed Calcium Zinc Borate with a Flexible [B8O17] Fundamental Building Block and Short UV Cutoff Edge

The first mixed calcium zinc borate with a new fundamental building block (FBB) [B₈O₁₇], Ca_1.13Zn_0.87B₈O₁₄ has been successfully synthesized. It exhibits two independent interpenetrating three-dimensional B−O anion networks constructed by [B₈O₁₇] groups, enriching the structural diversity of B−O configurations. In particular, the UV-Vis-NIR diffuse-reflectance spectrum shows that it has a short UV cutoff edge (<195 nm).     

Ultra-lightweight cellulose foam material: preparation and properties

Ultra-lightweight cellulose foams were prepared by regeneration of sodium dodecyl sulfate (SDS)/cellulose/NaOH/urea blend solution via mechanical agitation and then freeze-drying. The morphology and properties of the blend solutions and foams were investigated via optical microscope, rheometer, BET and SEM. As a result, it was found that the inclusion complex structure between cellulose macromolecules and the solvent molecules was not destroyed. Moreover, the bubbles were about 20–50 μm in the solutions and larger (>100 μm) in the foams. Not only the micropores (bubbles) but also the nanopores could be observed in the wet and dried foams. The cellulose foams possessed ultra-low density of about 30 mg/cm³ and high specific surface area. The result of X-ray diffraction and Fourier transform infrared spectroscopy indicated that the cellulose foams were transited from cellulose I to cellulose II after dissolution and gelation. Bubbles inside the wet foams weakened the mechanical properties, but inversely increased the mechanical properties in the dried foams. Typical “J”-shaped curves were observed during the mechanical test, which revealed good compressive strength of dried foams. In this work, cellulose foams with ultra-lightweight and good mechanical properties were obtained, which exhibited great potentials for further development and comprehensive utilization of cellulose.     

Voltammetric determination of theophylline in pharmaceutical formulations using aligned carbon nanotubes (ACNTs) film modified electrode

A novel rapid, convenient and sensitive electrochemical method has been described for the determination of theophylline in pharmaceutical formulations, based on the extraordinary properties of an aligned carbon nanotubes (ACNTs) thin film. The voltammetric results suggest that the ACNTs-coated glass carbon electrode can exhibit excellent electrochemical activity for direct electrochemical oxidation of theophylline. Various experimental parameters such as solution pH value, amount of ACNTs suspension, accumulation conditions and scan rate were optimized for the determination of theophylline. Furthermore, it was found that the peak current increased linearly with the concentration of theophylline in the range of 8.0 × 10^?8?1.0 × 10^?5 M and the detection limit was 1.6 × 10^?8 M using differential pulse voltammetry. This newly proposed method has been applied successfully to the determination of theophylline in drugs.     

Effect of Ag doping concentration on the electronic and optical properties of anatase TiO2: a DFT-based theoretical study

The electronic and optical properties of pure and Ag-doped anatase TiO₂ have been calculated by spin-polarized density functional theory. Ag-doped TiO₂ with different Ag doping concentrations ranging from 2.08 to 8.33 % was investigated, and the electronic and optical properties evaluated. Substitutional Ag doped at Ti sites introduced Ag 4d states just above the valence-band maximum, which may help in shifting visible-light excited electrons to the conduction band. Our results show that increasing the doping concentration will enhance visible-light absorption up to Ag doping concentration of 6.25 %; however, further increase of the doping concentration leads to a decrease in visible-light absorption. These results indicate the possibility of tailoring the band gap and optical absorption of TiO₂ doped with Ag by varying the doping concentration. The enhanced visible-light absorption for Ag-doped TiO₂ with doping concentration of 6.25 % may be due to the existence of widely distributed Ag 4d states above the valence-band maximum and the optimal doping concentration. Ag doping shifted the absorption edge of TiO₂ towards visible light, consistent with recent experimental results. Our calculation results provide a reasonable explanation for the experimental findings.