Nickel-mediated cross-coupling via C–O activation assisted by organoaluminum

We report the alkylation and arylation cross-coupling of aryl ethers based on C–O bond activation using a nickel catalyst and organoaluminum reagents. Ni(cod)₂ in combination with 1,2-bis(dicyclohexylphosphino)ethane ligand in toluene solution at 130°C are the best conditions. The naphthyl ether or methoxy pyridine derivatives are suitable substrates for alkylation and arylation reaction with a wider scope of aluminum reagents in good yields. Computational analysis on the pyridine substrate is provided to help delineate the mechanistic pathway and demonstrate the important aspects of the cooperative interaction bimetallic catalysis. First, the coordination of AlMe₃ to the O atom of pyridine is essential for C–O activation. Second, the β-H transfer from methoxy to pyridine could be discouraged through the use of bidentate phosphine as a ligand. Finally, excess AlMe₃ reagent is critical for facilitating a reductive elimination process.     

Effects of thermal treatment on hydrophilicity and corrosion resistance of Ti surface

Surface treatment of titanium (Ti) surface has been extensively studied to improve its properties for biomedical applications, including hydrophilicity, corrosion resistance, and tissue integration. In this present work, we present the effects of thermal oxidation as surface modification method on metallic titanium (Ti). The Ti foils were oxidized at 300°C, 400°C, 500°C, and 600°C under air atmosphere for 3 hours, which formed oxide layer on Ti surface. The physicochemical properties including surface chemistry, roughness, and thickness of the oxide layer were evaluated in order to investigate how these factors affected surface hydrophilicity, microhardness, and corrosion resistance properties of the Ti surface. The results revealed that surfaces of all oxidized samples were modified by formation of titanium dioxide layer, of which morphology, phase, and thickness were changed according to the oxidized temperatures. Increasing oxidation temperature led to the formation of thicker oxide layer and phase transformation of anatase to rutile. The presence of the oxide layer helped the improvement of corrosion resistance and microhardness. The most improvement in surface roughness was found in the specimens treated at 400°C, which significantly improved surface hydrophilicity. But both surface roughness and hydrophilicity reduced when oxidized at 500°C and 600°C, suggesting that hydrophilicity was dominated by the surface roughness. In addition, this surface treatment did not reduce the biocompatibility of the metallic Ti substrates against murine osteoblasts (MC3T3).     

Reliable and non‐destructive Raman analysis to determine the urea concentration in a cream formulation

We present a reliable and nondestructive analytical method for the determination of urea concentration in a pharmaceutical cream formulation using Raman spectroscopy. A pharmaceutical cream is a highly viscous emulsion; therefore, its composition and physical mixing could be inhomogeneous on a microscopic scale. The local environment around the urea could vary, which could influence the molecular vibrations of the urea molecule. As expected, when Raman spectra were collected by focusing the laser onto a tiny area (∼2–3 µm), the position of the urea band at 1003 cm⁻¹ varied as a result of the microscopic inhomogeneity within the sample. Therefore, acquisition of Raman spectra representative of the entire sample rather than a localized portion of it is very important for the analysis of pharmaceutical creams. Based on the preliminary Raman mapping results of a urea cream, a sample area of at least 750 × 750 µm should be covered for reliable quantitative analysis. In this study, we used a wide‐area illumination scheme capable of covering a sample area of 28.3 mm² for Raman spectral collection in order to ensure a reliable representative sample. In addition, to simplify the measurements, Raman spectra of urea creams in plastic bottles were directly collected without further sampling, and partial least squares regression was used for quantitative analysis. The urea concentrations were accurately determined despite the spectral collection being performed through plastic bottles. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and computational exploration of the dynamic behavior of (PNP)BF2, a boron compound supported by an amido/bis(phosphine) pincer ligand

The diarylamido/bis(phosphine) PNP pincer ligand (2-(i)Pr(2)P-4-MeC(6)H(3))(2)N has been evaluated as a scaffold for supporting a BF(2) fragment. Compound (PNP)BF(2) (6) was prepared by simple metathesis of (PNP)Li (5) with Me(2)SBF(3). NMR spectra of 6 in solution are of apparent C(2) symmetry, suggestive of a symmetric environment about boron. However, a combination of X-ray structural studies, low-temperature NMR investigations, and DFT calculations consistently establish that the ground state of this molecule contains a classical four-coordinate boron with a PNBF(2) coordination environment, with one phosphine donor in PNP remaining "free". Fortuitous formation of a single crystal of (PNP)BF(2)·HBF(4) (7), in which the "free" phosphine is protonated, furnished another structure containing the same PNBF(2) environment about boron for comparison and the two PNBF(2) environments in 6 and 7 are virtually identical. DFT studies on several other diarylamido/bis(phosphine) pincer (PNP)BF(2) systems were carried out and all displayed a similar four coordinate PNBF(2) environment in the ground state structures. The symmetric appearance of the room-temperature NMR spectra is explained by the rapid interconversion between two degenerate four-coordinate, C(1)-symmetric ground-state forms. Lineshape analysis of the (1)H and (19)F NMR spectra over a temperature range of 180-243 K yielded the activation parameters ΔH(?) = 8.1(3) kcal mol(-1) and ΔS(?) = -6.0(15) eu, which are broadly consistent with the calculated values. Calculations indicate that the exchange of phosphine donors at the boron center proceeds by an intrinsically dissociative mechanism.     

Chalcogen Bond Mediated Enhancement of Cooperative Ion-Pair Recognition

A series of heteroditopic receptors containing halogen bond (XB) and unprecedented chalcogen bond (ChB) donors integrated into a 3,5-bis-triazole pyridine structure covalently linked to benzo-15-crown-5 ether motifs exhibit remarkable cooperative recognition of halide anions. Multi-nuclear ¹H, ¹³C, ¹²⁵Te and ¹⁹F NMR, ion pair binding investigations reveal sodium cation–benzo-crown ether binding dramatically enhances the recognition of bromide and iodide halide anions, with the chalcogen bonding heteroditopic receptor notably displaying the largest enhancement of halide binding strength of over two hundred-fold, in comparison to the halogen bonding and hydrogen bonding heteroditopic receptor analogues. DFT calculations suggest crown ether sodium cation complexation induces a polarisation of the sigma hole of ChB and XB heteroditopic receptor donors as a significant contribution to the origin of the unique cooperativity exhibited by these systems.     

Scaling factors for vibrational frequencies and zero-point vibrational energies of some recently developed exchange-correlation functionals

The scaling factors for the vibrational frequencies and zero-point vibrational energies evaluated at various combinations of recently developed exchange-correlation functionals and various basis sets are reported. The exchange-correlation functionals considered are B972, B98, HCTH, OLYP, O3LYP, G96LYP, PBE0 and VSXC functionals; the basis sets employed are 3-21G, 6-31G*, 6-31G**, 6-31+G, 6-311G*, 6-311G**, 6-311G(df,p), 6-311+G(df,p), cc-pVDZ and aug-cc-pVDZ. The experimental harmonic frequencies of 122 small molecules and the zero-point vibrational energies of 39 small molecules are used to determine the scaling factors through the least-square fitting procedure. It was found that the scaling factors do not depend significantly on the basis sets considered. The vibrational frequency scaling factors evaluated by using the B98 and PBE0 functionals are recommended on the basis of smallest root mean square error. The zero-point vibrational energy scaling factors evaluated from the B972 functional with Pople's double-zeta basis set and the HCTH functional with Pople's triple-zeta basis set are recommended on the basis of smallest root mean square error.     

The Mechanism of Sugar C−H Bond Oxidation by a Flavoprotein Oxidase Occurs by a Hydride Transfer Before Proton Abstraction

Understanding the reaction mechanism underlying the functionalization of C−H bonds by an enzymatic process is one of the most challenging issues in catalysis. Here, combined approaches using density functional theory (DFT) analysis and transient kinetics were employed to investigate the reaction mechanism of C−H bond oxidation in d -glucose, catalyzed by the enzyme pyranose 2-oxidase (P2O). Unlike the mechanisms that have been conventionally proposed, our findings show that the first step of the C−H bond oxidation reaction is a hydride transfer from the C2 position of d -glucose to N5 of the flavin to generate a protonated ketone sugar intermediate. The proton is then transferred from the protonated ketone intermediate to a conserved residue, His548. The results show for the first time how specific interactions around the sugar binding site promote the hydride transfer and formation of the protonated ketone intermediate. The DFT results are also consistent with experimental results including the enthalpy of activation obtained from Eyring plots, as well as the results of kinetic isotope effect and site-directed mutagenesis studies. The mechanistic model obtained from this work may also be relevant to other reactions of various flavoenzyme oxidases that are generally used as biocatalysts in biotechnology applications.     

Chalcogen Bond Mediated Enhancement of Cooperative Ion‐Pair Recognition

A series of heteroditopic receptors containing halogen bond (XB) and unprecedented chalcogen bond (ChB) donors integrated into a 3,5‐bis‐triazole pyridine structure covalently linked to benzo‐15‐crown‐5 ether motifs exhibit remarkable cooperative recognition of halide anions. Multi‐nuclear ¹H, ¹³C, ¹²⁵Te and ¹⁹F NMR, ion pair binding investigations reveal sodium cation–benzo‐crown ether binding dramatically enhances the recognition of bromide and iodide halide anions, with the chalcogen bonding heteroditopic receptor notably displaying the largest enhancement of halide binding strength of over two hundred‐fold, in comparison to the halogen bonding and hydrogen bonding heteroditopic receptor analogues. DFT calculations suggest crown ether sodium cation complexation induces a polarisation of the sigma hole of ChB and XB heteroditopic receptor donors as a significant contribution to the origin of the unique cooperativity exhibited by these systems.     

Phenylglycol Metabolites from Cultures of the Basidiomycete Mycena pruinosoviscida BCC 22723

Mycenadiols A–D ( 1 – 4 , resp.), phenylglycols possessing an ethynyl or vinyl (ethenyl) group were isolated from cultures of the basidiomycete Mycena pruinosoviscida BCC 22723. The structures were elucidated on the basis of NMR‐spectroscopic and mass spectrometric data. The absolute configurations of 1 and 2 were determined by synthesis. Compounds 1 – 4 are synthetically known, but, they have not been previously isolated from natural sources.