Heat capacity and thermal expansion coefficient of rare earth uranates RE<Subscript>6</Subscript>UO<Subscript>12</Subscript> (RE = Nd,Gd and Eu)

Rare earth uranates Nd₆UO₁₂, Gd₆UO₁₂ and Eu₆UO₁₂ were prepared by combustion synthesis and characterized by XRD. Single-phase rhombohedral structure was observed for all the above compounds. Heat capacity measurements were carried out on Nd₆UO₁₂ and Gd₆UO₁₂ with differential scanning calorimetry in the temperature range 298–800 K. Enthalpy, entropy and Gibbs energy functions were computed. Heat capacity values of Nd₆UO₁₂ and Gd₆UO₁₂ at 298 K are 436 and 400 J K⁻¹ mol⁻¹, respectively. Thermal expansion characteristics were studied using high temperature X-ray diffraction (HTXRD) in the temperature range 298–873 K. The coefficients of thermal expansion measured for Eu₆UO₁₂ are 10.5 × 10⁻⁶ and 7.3 × 10⁻⁶ K⁻¹ along a- and c-axis, respectively. Similarly, the coefficients of thermal expansion of Gd₆UO₁₂ along a-axis are 10.0 × 10⁻⁶ K⁻¹ and along c-axis is 9.7 × 10⁻⁶ K⁻¹.     

Oppolzer sultam directed aldol as a key step for the stereoselective syntheses of antitumor antibiotic belactosin C and its synthetic congeners

[reaction: see text] An efficient protocol has been developed using D-(2R)-Oppolzer sultam as a chiral auxiliary for generating anti/syn diastereomers with high enantiopurity and utilized in the efficient synthesis of natural product belactosin C and their synthetic congeners. It has been observed that a variation in the stoichiometry of the Lewis acid led to a difference in anti/syn selectivity.     

First-principles study of hydrogen storage on Li12C60

Solid state materials capable of storing hydrogen with high gravimetric (9 wt %) and volumetric density (70 g/L) are critical for the success of a new hydrogen economy. In addition, an ideal storage system should be able to operate under ambient thermodynamic conditions and exhibit fast hydrogen sorption kinetics. No materials are known that meet all these requirements. While recent theoretical efforts showed some promise for transition-metal-coated carbon fullerenes, later studies demonstrated that these metal atoms prefer to cluster on the fullerene surface, thus reducing greatly the weight percentage of stored hydrogen. Using density functional theory we show that Li-coated fullerenes do not suffer from this constraint. In particular, we find that an isolated Li(12)C(60) cluster where Li atoms are capped onto the pentagonal faces of the fullerene not only is very stable but also can store up to 120 hydrogen atoms in molecular form with a binding energy of 0.075 eV/H(2). In addition, the structural integrity of Li(12)C(60) clusters is maintained when they are allowed to interact with each other. The lowest energy structure of the dimer is one where the Li atom capped on the five-member ring of one fullerene binds to the six-member ring of the other. The binding of hydrogen to the linking Li atom and the potential of materials composed of Li(12)C(60) building blocks for hydrogen storage are discussed.     

On the solution of time-fractional dynamical model of Brusselator reaction-diffusion system arising in chemical reactions

Fractional Brusselator reaction-diffusion system (BRDS) is used for modeling of specific chemical reaction-diffusion processes. It may be noted that numerous models in nonlinear science are defined by fractional differential equations (FDEs) in which an unknown function appears under the operation of a fractional-order derivative. Even though many researchers have studied the applicability and practicality of this model, the analytical approach of this model is rarely found in the literature. In this investigation, a novel semi-analytical technique called fractional reduced differential transform method (FRDTM) has been applied to solve the present model, which is characterized by the time-fractional derivative (FD). Obtained outcomes are compared with the solution of other existing methods for a particular case. Also, the convergence analysis of this model has been studied here.     

Rigid Nanoporous Urea-Based Covalent Triazine Frameworks for C2/C1 and CO2/CH4 Gas Separation

C2/C1 hydrocarbon separation is an important industrial process that relies on energy-intensive cryogenic distillation methods. The use of porous adsorbents to selectively separate these gases is a viable alternative. Highly stable covalent triazine frameworks (urea-CTFs) have been synthesized using 1,3-bis(4-cyanophenyl)urea. Urea-CTFs exhibited gas uptakes of C₂H₂ (3.86 mmol/g) and C₂H₄ (2.92 mmol/g) at 273 K and 1 bar and is selective over CH₄. Breakthrough simulations show the potential of urea-CTFs for C2/C1 separation.     

Electronic structure of hydrogen-like impurities in nearly-free-electron metals

Recent developments in our understanding of the electronic structure of hydrogen and its isotopes in simple metals is reviewed. The role of nonlinear electron density distribution in the interpretation of the electronic properties of hydrogen-like impurities is emphasized. Calculated Knight shifts and hyperfine fields at + site and electric field gradients at cubic host nuclear sites due to interstitial + are compared with recent experimental data. The feasibility of using positive muon as a probe of defect structure is discussed. Future experiments and theoretical investigations aimed at a deeper understanding of the electronic properties of + are suggested.Work supported by the National Science Foundation and the U. S. Department of Energy.     

Synthesis of 6,6′- and 6-MeO–PEG–BINOL-Ca soluble polymer bound ligands and their application in asymmetric Michael and epoxidation reactions

Design and synthesis of a flexible spacer attached 6-MeO–PEG–BINOL ligand has been described. The enantioenriched Ca soluble polymer bound ligand (SPB-II) was generated utilizing easily available, eco-friendly CaCl₂, and applied for CC as well as CO bond forming reactions. The ligand was precipitated adding diethylether, and the same ligand was used with equal efficiency for two more cycles.