Novel Nanoporous Binary Au?Ru Electrocatalysts for Glucose Oxidation

In this work, we study the fabrication, structural characterization, and electrochemical activity of titanium‐supported binary Au? Ru catalysts for glucose oxidation. The catalysts including Au₉₉Ru₁, Au₉₅Ru₅, Au₉₃Ru₇ and Au₈₈Ru₁₂ were prepared by a hydrothermal method using formaldehyde as a reduction agent. The morphologies of the prepared Au? Ru catalyst structures are characterized by porous dendritic particles with roughened surfaces with nano‐sized flakes. Electrochemical catalytic activity of the binary Au? Ru catalysts towards glucose oxidation in alkaline solutions was investigated using cyclic voltammetry and chronoamperometry. All binary Au? Ru catalysts facilitate glucose oxidation at the lower potentials and deliver higher anodic oxidation currents compared to pure Au catalyst. Among them, the binary Au₉₅Ru₅ catalyst presents the most negative onset potential of ?0.872 V (vs. Ag/AgCl, 3 M KCl) for glucose oxidation in 0.1 M NaOH solution. For the Au₉₅Ru₅ catalyst, chronoamperometric data at the potential step of ?0.65 V (vs. Ag/AgCl,3 M KCl) exhibit a well linear dependence of the anodic oxidation current density on glucose concentration in the range of 0 to 15 mM glucose.     

Synthesis of Phospholipid?Ribavirin Conjugates

New conjugates of antiviral nucleoside Ribavirin (=1‐(β‐D ‐ribofuranosyl)‐1H‐1,2,4‐triazole‐3‐carboxamide; 1 ) with 1,2‐ and 1,3‐diacyl glycerophosphates have been synthesized by the phosphoramidite method. A combination of 2′,3′‐phenylboronate protecting group for the sugar moiety of the ribonucleoside 1 and 2‐cyanoethyl protection for the phosphate fragment ensured the preparation of the desired compounds with reasonable yields via a small number of synthetic steps.     

Oxindole Synthesis by Direct Coupling of C?H and C?H Centers

An sp ² /sp ³ get‐together : A novel and efficient method can be used to synthesize 3,3‐disubstitued oxindoles by the direct intramolecular oxidative coupling of an aryl C? H and a C? H center (see scheme; DMF=N,N‐dimethylformamide).

     

Synthesis and properties of new Si?H-containing polymers

Poly[(methylsilylene)ethynylene] ( 1 ) and poly[2,5-thiophenediyl(methylsilylene)] ( 2 ) are prepared in good yields. Thermogravimetric analysis and differential scanning calorimetry indicate the Si H group to increase the pyrolysis residue yields. Gelation was achieved from polymer 1 to get improved preceramic materials. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2275–2282, 1998     

Studies on the Synthesis and Characterization of Pd?TiO2?SiO2 Nanocomposite for Electroanalytical Applications

A nanocomposite of Pd? TiO₂? SiO₂ is developed through a sol‐gel process from the reaction products of titanium isopropoxide followed by mixing the same with palladium linked 3‐glycidoxypropyltrimethoxysilane. The reaction product is sonicated and calcinated to obtain the nanocomposite of Pd? TiO₂? SiO₂. The calcination at 600 °C yielded an amorphous structure whereas at 900 °C it resulted into a nanocrystalline structure. The nanocomposite of palladium was further characterized by TEM, XRD, IR and EDS. The material acts as an efficient electrocatalyst. Electrocatalysis of ascorbic acid is observed at 0.1 V vs. Ag/AgCl, shows linearity between 1 µM and 1 mM in 0.1 M phosphate buffer (pH 7.0).     

Palladium Nanoparticles on Graphite Oxide as Catalyst for Suzuki?Miyaura,Mizoroki?Heck,and Sonogashira Reactions

Pd²⁺‐Exchanged graphite oxide (GO) serves as a precatalyst for the formation of Pd‐nanoparticles which are then deposited on the highly functionalized carbonaceous support. This versatile, air‐stable, and ligand‐free system was applied successfully to Suzuki? Miyaura couplings of some aryl chlorides and to the Mizoroki? Heck as well as the Sonogashira reaction showing relatively high activities and good selectivities. Like with other ligand‐free supported systems, the reaction proceeded dominantly by a homogeneous mechanism, but attack of an aryl iodide to Pd‐nanoparticles can be excluded as substantial contribution to the entire catalytic process. Beside its straightforward preparation and its stability in air, the system combines the advantages of both homogeneous and heterogeneous catalysis.     

A theoretical investigation of Zn?Zn and Be?Be one electron bond

Attachment of one electron to 1,2-diBeX-benzene and 1,2-diZnX-benzene derivatives leads to the formation of stronger Be Be and Zn Zn interaction compared to the neutral one. This is reflected in the dramatic shortening of the Be Be and Zn Zn distance. The formation of these 2-center-1-electron bonds have also been confirmed by topological survey of electron density using quantum theory of atoms in molecules and electron localization function. The formation of these bonds is expected to render stability to these radical anions. These radical anions are stable toward electron detachment and computed bond dissociation energy values are also significant.     

Highly Modular P?OP Ligands for Asymmetric Hydrogenation: Synthesis,Catalytic Activity,and Mechanism

A library of enantiomerically pure P? OP ligands (phosphine–phosphite), straightforwardly available in two synthetic steps from enantiopure Sharpless epoxy ethers is reported. Both the alkyloxy and phosphite groups can be optimized for maximum enantioselectivity and catalytic activity. Their excellent performance in the Rh‐catalyzed asymmetric hydrogenation of a wide variety of functionalized alkenes (26 examples) and modular design makes them attractive for future applications. The lead catalyst incorporates an (S)‐BINOL‐derived (BINOL=1,1′‐bi‐2‐naphthol) phosphite group with computational studies revealing that this moiety has a dual effect on the behavior of our P? OP ligands. On one hand, the electronic properties of phosphite hinder the binding and reaction of the substrate in two out of the four possible manifolds. On the other hand, the steric effects of the BINOL allow for discrimination between the two remaining manifolds, thereby elucidating the high efficiency of these catalysts.     

Solid‐State Luminescence of Au?Cu?Alkynyl Complexes Induced by Metallophilicity‐Driven Aggregation

A new series of homoleptic alkynyl complexes, [{Au₂Cu₂(C₂R)₄}_n] (R=C₃H₇O ( 1 ), C₆H₁₁O ( 2 ), C₉H₁₉O ( 3 ), C₁₃H₁₁O ( 4 )), were obtained from Au(SC₄H₈)Cl, Cu(NCMe)₄PF₆, and the corresponding alkyne in the presence of a base (NEt₃). Complexes 1 – 4 aggregate upon crystallization into polymeric chains through extensive metallophilic interactions. The cluster that contains fluorenolyl functionalities, C₁₃H₉O ( 5 ), crystallizes in its molecular form as a disolvate, [Au₂Cu₂(C₂C₁₃H₉O)₄] ? 2 THF. The substitution of weakly bound THF molecules with pyridine molecules leads to the complex [Au₂Cu₂(C₂C₁₃H₉O)₄] ? 2 py ( 6 ), thus giving two polymorphs in the solid state. Such structural diversity is established through metal‐chain and hydrogen‐bond formation, which depends on the stereochemical characteristics of the organic ligands. More interestingly, this solid‐state structural arrangement affords good emission properties, such as intensity and spectroscopic profile, which are otherwise very weakly emissive in solution. Metallophilic aggregation of the {Au₂Cu₂} cluster units, as observed in the crystals, results in dramatic enhancement of the room‐temperature phosphorescence, thereby reaching a maximum quantum efficiency of 95 % ( 4 ). A theoretical approach further indicates a synergistic effect of the array of the metal chain upon aggregation, which greatly enhances the spin‐orbit coupling and, hence, the phosphorescence, thereby opening up a new direction in the field of aggregate‐enhanced emission.     

A General and High‐Yield Galvanic Displacement Approach to Au?M (M=Au,Pd, and Pt) Core–Shell Nanostructures with Porous Shells and Enhanced Electrocatalytic Performances

In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au? M (M=Au, Pd, and Pt) core–shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au? Au, Au? Pd, and Au? Pt core–shell nanostructures with typical porous shells. Moreover, the Au? Au isomeric core–shell nanostructure is reported for the first time. The lower oxidation states of Au^I, Pd^II, and Pt^II are supposed to contribute to the formation of porous core–shell nanostructures instead of yolk‐shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au? Pd core–shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core–shell nanostructures. As expected, the Au? Pd core–shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44 mV and 32 mV), a much improved CO tolerance (I_f/I_b is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au? M (M=Au, Pd, and Pt) core–shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface‐enhanced Raman scattering, and so forth.     

Synthesis and properties of fluorinated benzotriazole-based donor-acceptor-type conjugated polymers via Pd-catalyzed direct C?H/C?H coupling polymerization

Fluorine substituted benzotriazole (BTz) units have shown great potential in improving various conjugated polymers (CPs)-based optoelectronic devices' performance. Thus, it is highly expected for the establishment of simple, efficient, and inexpensive accesses to such polymers. In this paper, Pd-catalyzed direct C H/C H coupling polymerization is first employed for the synthesis of 5,6-difluorobenzotriazole containing π-CPs, which fully avoids prefunctionalization of monomers. Under the optimized conditions, a series of donor-acceptor-type π-CPs with excellent regio-regularity are facilely obtained via the direct C H/C H coupling reaction of 5,6-difluoro-2-(2-hexyldecyl)-2H-BTz with different thiophene analogs. The chemical structure of the as-synthesized polymers are confirmed by NMR technique including ¹H NMR, ¹⁹F NMR, and the edited heteronuclear singular quantum correlation and heteronuclear multiple bond correlation spectra as well as comparative study on the same polymers obtained via Stille coupling and direct (hetero)arylation polymerization. Further, their optical properties, electrochemical properties, and thermal stabilities are also carefully explored by UV–Vis absorption spectra, cyclic voltammograms as well as thermogravimetric analysis, respectively. On the basis of density functional theory (DFT) simulation, the effect of alkyl substituents attached to thiophene units on the reactivity and optical performance of the resultant polymers is explained. Our protocol exhibits remarkable advantages in synthetic simplicity, atom-economy, high efficiency, and excellent regioselectivity of cross-coupling, providing an alternative synthetic strategy for high-performance optoelectronic materials.     

Accurate Prediction of Au?P Bond Strengths by Density Functional Theory Methods

The recent development of Au‐catalyzed reactions has greatly enriched the methods of organic synthesis. The phosphine or phosphate‐coordinated Au complexes have shown high efficiency in catalyzing various C? C and C? H activations. In many of these reactions, the Au? P bond strength was found to play an important role in determining the catalytic efficiency. In the present study, the accuracy of different theoretical methods for prediction of Au? P strengths has been examined on basis of the experimental enthalpy changes between different ClAu(PR₃) and ClAu(THT) (THT=tetrahydrothiophene). By comparing the different DFT functionals (e.g. B3LYP, TPSS, M06), different basis sets (including the different effective core potentials on Au and the total electron basis sets on all other atoms), and different solution phase single point calculations, we found that the TPSS/(CPE‐121G+f:6‐311+G(d,p)(SMD)//TPSS/(CPE‐121G:6‐31G(d) ( M1 ) method gives the best correlations with the available experimental results. Meanwhile, the calculations with B3LYP//TPSS and M05//TPSS also give comparable calculation results. Finally, the specified method ( M1 ) is used to calculate the Au? P bond dissociation enthalpies and energies of different ClAu(PR₃)/ClAu(P(OR)₃) complexes. By accurately reproducing the available experimental results, we believe that the method ( M1 ) is reliable for the theoretical analysis of Au‐P systems.     

Simultaneous measurement of N?H and Cα?Hα coupling constants in proteins

We present a pulse sequence for the simultaneous measurement of N? H and Cα? Hα couplings in double‐labeled proteins from 2D spectra. The proposed sequence, a modification of the HN(CO)CA experiment, combines the J‐modulation method and the IPAP scheme. The couplings can be readily retrieved from a series of 2D ¹⁵N? ¹H correlation spectra, differing in the time point at which a ¹H 180° pulse is applied. This induces an intensity modulation of the ¹⁵N? ¹H correlation peaks with the Cα? Hα coupling. The Cα? Hα coupling is then obtained by fitting the observed intensities to the modulation equation. The N? H coupling is measured in each member of the set from peak‐to‐peak separations in the IPAP subspectra. The pulse sequence is experimentally verified with a sample of ¹⁵N/¹³C‐enriched ubiquitin. Copyright © 2009 John Wiley & Sons, Ltd.     

On the reactivity of metal and organometallic halides toward R3Sn?O?SnR3 systems

Interaction of metallic salts (M = Hg, Sb, and Te) with bis(triorganotin)oxide, (R₃Sn)₂O, where (R = C₆H₅, p‐CH₃C₆H₄, and cyclo‐C₆H₁₁) at room temperature proceeded with the simultaneous cleavage of the Sn C and Sn O bonds, invariably yielding R₂SnO along with other products. Thus the treatment of HgX₂ (X = Cl, CN, SCN) with (R₃Sn)₂O resulted in the formation of polymeric diorganotin oxide R₂SnO along with R₃SnX and RHgX derivatives. The reaction of SbCl₃ with (R₃Sn)₂O was found to give R₂SnO, R₃SnCl, and RSbCl₂, whereas interaction with SbCl₅ provided R₂SnO, R₂SnCl₂, and R₂SbCl₃. Treatment of TeCl₄ with (R₃Sn)₂O provided R₂SnO, R₃SnCl, and RTeCl₃ at room temperature. At reflux temperature, reaction of PhTeCl₃ with (R₃Sn)₂O yielded R₂SnO, R₃SnCl, and mixed diorganotellurium dichloride, RPhTeCl₂. The course of reaction indicated the instability of Sn O Sn system proceeding via a four‐centered mechanism, providing organometallic compounds in profitable yield. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:278–283, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20547