Self-assembled 3D heterometallic Cu(II)/Fe(II) coordination polymers with octahedral net skeletons: structural features, molecular magnetism, thermal and oxidation catalytic properties

The new three-dimensional (3D) heterometallic Cu(II)/Fe(II) coordination polymers [Cu(6)(H(2)tea)(6)Fe(CN)(6)](n)(NO(3))(2n)·6nH(2)O (1) and [Cu(6)(Hmdea)(6)Fe(CN)(6)](n)(NO(3))(2n)·7nH(2)O (2) have been easily generated by aqueous-medium self-assembly reactions of copper(II) nitrate with triethanolamine or N-methyldiethanolamine (H(3)tea or H(2)mdea, respectively), in the presence of potassium ferricyanide and sodium hydroxide. They have been isolated as air-stable crystalline solids and fully characterized including by single-crystal X-ray diffraction analyses. The latter reveal the formation of 3D metal-organic frameworks that are constructed from the [Cu(2)(μ-H(2)tea)(2)](2+) or [Cu(2)(μ-Hmdea)(2)](2+) nodes and the octahedral [Fe(CN)(6)](4-) linkers, featuring regular (1) or distorted (2) octahedral net skeletons. Upon dehydration, both compounds show reversible escape and binding processes toward water or methanol molecules. Magnetic susceptibility measurements of 1 and 2 reveal strong antiferromagnetic [J = -199(1) cm(-1)] or strong ferromagnetic [J = +153(1) cm(-1)] couplings between the copper(II) ions through the μ-O-alkoxo atoms in 1 or 2, respectively. The differences in magnetic behavior are explained in terms of the dependence of the magnetic coupling constant on the Cu-O-Cu bridging angle. Compounds 1 and 2 also act as efficient catalyst precursors for the mild oxidation of cyclohexane by aqueous hydrogen peroxide to cyclohexanol and cyclohexanone (homogeneous catalytic system), leading to maximum total yields (based on cyclohexane) and turnover numbers (TONs) up to about 22% and 470, respectively.     

On-line sample concentration of organic anions in capillary zone electrophoresis by micelle to solvent stacking

Micelle to solvent stacking (MSS) is a new on-line sample concentration technique for charged analytes in capillary zone electrophoresis (CZE). Sample concentration in MSS mainly relies on the reversal in the effective electrophoretic mobility of the analyte at the boundary zone between the sample solution (S) and CZE background solution (BGS) inside the capillary. The basic condition for MSS is that the S is prepared in a matrix that contains an additive (i.e., micelles) which interacts with and has an opposite charge compared to the analytes. In addition, the BGS must contain a sufficient percentage of organic solvent. MSS was first reported for organic cations using anionic dodecyl sulfate micelles as additive in the S and methanol or acetonitrile as organic solvent in the BGS. Here, theoretical and experimental studies on MSS are described for organic anions using cationic cetyltrimethyl ammonium micelles as additive in the S and methanol as organic solvent in the BGS. Up to an order of magnitude improvement in concentration sensitivity was obtained for the test hypolipidaemic drugs using MSS in CZE with UV detection. The optimized method was also evaluated to the analysis of a spiked wastewater sample that was subjected to a simple extraction step.     

Alkane oxidation by the H2O2-NaVO3-H2SO4 system in acetonitrile and water

A simple system is described, which oxidizes saturated hydrocarbons either in acetonitrile or (less efficiently) in water. The system consists of 50% aqueous hydrogen peroxide as an oxidant, sodium metavanadate, NaVO₃, as a catalyst and sulfuric (or oxalic) acid as a co-catalyst. The reactions were carried out at 20-50 °C. In the oxidation of cyclohexane in acetonitrile, the highest yield (37% based on cyclohexane) and turnover number (TON=1700) were attained after 3 h at 50 °C. The corresponding parameters were 16% and 1090 for n-heptane oxidation under the same conditions. The oxidation of higher alkanes, RH, in acetonitrile gives almost exclusively the corresponding alkyl hydroperoxides, ROOH. Light alkanes (n-butane, propane, ethane, and methane) have been also oxygenated by the system under consideration. The highest TON (200) was attained for ethane and the highest yield (19%) was obtained in the case of n-butane. The selectivity parameters measured for the oxidation of linear and branched alkanes are low, the reaction with cis- and trans-1,2-dimethylcyclohexanes is not stereoselective. These facts lead us to conclude that the oxidation occurs with the formation of hydroxyl radicals in the crucial step.     

Metal‐Mediated [2+3] Cycloaddition of Nitrones to Palladium‐Bound Isonitriles

[2+3] Cycloadditions! The metal‐mediated [2+3] cycloaddition of acyclic [^?O⁺N(R²)?(H)R³] and nonaromatic cyclic nitrones [^?O⁺N^a?CHCH₂CH₂C^bMe₂(N^a? C^b)] to palladium‐bound isonitriles cis‐[PdCl₂(C?NR)₂] proceeds under mild conditions to furnish novel heterocyclic carbene complexes, which then undergo N? O bond rupture to give imino complexes and free isocyanates (see scheme).

     

Vibrational analysis and thermodynamic properties of C120 nanotorus: a DFT study

Density functional theory (DFT) computational methods are applied to a C₁₂₀ carbon nanotorus studied as an isolated molecular species, using the functional GGA PW91. This toroidal form of carbon contains five fold, six fold, and sevenfold rings. The calculated cohesive energy of the nanotorus, indicates that the ground state of this structure is energetically more stable than that of fullerene C₆₀. Geometry and stability, Raman and IR vibrational analysis and thermodynamic properties have been reported and compared to the values obtained by other authors.     

Investigating the Properties of Multi-Loop Implicit Regularization Surface Terms through Renormalizability of Massless Scalar Theories

Renormalizability of scalar quantum field theories can be proved using the Callan-Symanzik equation. We investigate the implications of the induction proof on the so-called surface terms when the correlation functions multi-loop massless scalar theories are renormalized within the implicit regularization scheme.     

Computer-Assisted 3D Structure Elucidation (CASE-3D): The Structural Value of 2JCH in Addition to 3JCH Coupling Constants

We present a method to use long-range CH coupling constants to derive the correct diastereoisomer from the molecular constitution of small molecules. A set of 79 ²J_CH and ³J_CH values collected from a single HSQMBC experiment on a sample of strychnine were used in the CASE-3D (computer-assisted 3D structure elucidation) protocol. In addition to the most commonly used ³J_CH coupling constants, the subset of 32 ²J_CH values alone showed an excellent degree of configuration selection. The study is mainly based on comparison of DFT-calculated ^2,3J_CH values with experimental ones, critical for the case of ²J_CH. But the configuration selection also works well using ³J_CH values predicted from a semi-empirical Karplus-based equation limited to H−C−C−C fragments. The robustness, shown using strychnine as a proof of concept, makes the J-based CASE-3D analysis a viable option for the application in fields such as peptide and carbohydrate research, organic synthesis, natural-product identification and analysis, as well as medicinal chemistry.     

Anti-inflammatory and antiproliferative activities of Ixora brevifolia Benth. (Rubiaceae)

The crude extract and fractions from the branches of Ixora brevifolia, a tree found in the Brazilian Cerrado, were tested for anti-inflammatory and in vitro antiproliferative effects. The crude extract and n-hexane fraction exhibited significant inhibition of ear oedema in mice, while n-hexane-precipitated and chloroform fractions strongly inhibited the myeloperoxidase activity in ear tissue. The n-hexane and n-hexane-precipitated fractions showed strong growth inhibition for glioma cell line and the hydromethanolic fraction inhibited the growth of leukaemia cell line.