Surface chemical states of gold nanoparticles prepared using the solution-plasma method in a CsCl aqueous solution

In this study, gold nanoparticles (AuNPs) prepared in a 5 mM CsCl aqueous solution using the solution-plasma method are characterized via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy with synchrotron radiation (SR-XPS). The particle diameter is measured over the process time via TEM. During the solution-plasma process, small particles of 2.1 to 2.2-nm diameter are generated in the CsCl aqueous solution; these particles then enlarge via Ostwald ripening over time until they reach an equilibrium size of ~13 nm after 36 days. In addition, the surface chemical states of the AuNPs are characterized at different depths via SR-XPS. The SR-XPS measurements obtained using incident X-ray energy (hν) of 945.0 eV revealed that Cs─Au, Cl─Au, and Cs─Cl─Au bonds are present 1.2 nm below the surface. The measurements obtained at an incident X-ray energy of 2515.0 eV showed that Cs─Cl─Au bonding is also present 2.5 nm below the surface, indicating that Cs and Cl strongly interact with Au. The TEM and SR-XPS measurements revealed that 2 processes occur cyclically during the growth process via Ostwald ripening: (i) the Cs and Cl in the aqueous solution adsorb on the AuNP surface and (ii) Au atoms subsequently bond to the AuNPs surface.     

Palladium-catalyzed oxidative homocoupling reaction of terminal acetylenes using trans-bidentatable 1-(2-pyridylethynyl)-2-(2-thienylethynyl)benzene

Palladium-catalyzed oxidative homocoupling of terminal acetylenes, in air, occurred in the presence of 1-(2-pyridylethynyl)-2-(2-thienylethynyl)benzene as ligand, affording the corresponding conjugated diynes.     

Synthesis of unsymmetrically disubstituted ethynes by the palladium/copper(I)-cocatalyzed sila-Sonogashira–Hagihara coupling reactions of alkynylsilanes with aryl iodides,bromides, and chlorides through a direct activation of a carbon–silicon bond

In this paper, we explore the copper/palladium-cocatalyzed cross-coupling reactions of 1-aryl-2-trimethylsilylethynes with aryl iodides, bromides, and chlorides as coupling partners, to furnish unsymmetrically disubstituted ethynes in moderate to excellent yields. Various aryl iodides were subjected to reaction under the optimized conditions with 5 mol % of Pd(PPh₃)₂ and 50 mol % of CuCl. The steric properties of the aryl iodide proved more influential to the outcome of the cross-coupling reaction than electronic factors. In addition, we succeeded in synthesizing unsymmetrical diarylethynes using two different aryl iodides in one-pot. Furthermore, under the same reaction conditions with 10 mol % of PdCl₂, 40 mol % of P(4-FC₆H₄)₃, and 50 mol % of CuCl as catalyst, we succeeded in synthesizing unsymmetrical diarylethynes from various aryl bromides. Finally, we explored reactions with aryl chlorides and duly discovered that unsymmetrical diarylethynes were obtainable in moderate to good yields when 10 mol % of Pd(OAc)₂, 10 mol % of (?)-DIOP, and 10 mol % of CuCl were used. These reactions proceed through a direct activation of a carbon–silicon bond in alkynylsilanes by CuCl to generate the corresponding alkynylcopper species via transmetalation from silicon to copper. Mechanistic investigations on the reaction of alkynylsilanes with aryl bromides confirmed that the trimethylsilyl bromide generated in situ retarded both transmetalation steps between CuCl and alkynylsilane, and between palladium(II) species formed by oxidative addition and alkynylcopper species.     

Metal array fabrication through self-assembly of Pt-complex-bound amino acids

A new type of Pt-complex-bound amino acid was synthesized by condensation of a cyclometalated Pt complex with the side-chain residue of N- and C-alkylated glutamic acid. Self-assembly of the Pt-bound lipophilic amino acid afforded a supramolecular gel in organic solvents, which comprised fibrous lamellar aggregates that supported a highly oriented Pt array.     

Generation of radical species from dihydropyrazines having DNA strand-breakage activity and other characteristics

The various biological activity of dihydropyrazines(DHPs)due to the radical generation potency has been described in previous papers. Detailed data about radical species generating be mentioned here. The electron spin resonance (ESR) spin-trapping technique revealed that DHPs generate free radical species such as ·OH, ·OOH, ·CHR(2) and ·CR(3). Oxygen radicals and two carbon-centered radicals were detected as adducts of the spin traps DMPO and DBNBS, respectively. All the 5,5-dimethyl-1-pyrroline-N-oxide (DMPO)- and 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS)-adducts of compounds DHP-1-8 exhibited approximately the same signal patterns, with various levels of intensity depending on the substituent of the dihydropyrazine ring. The ESR signal intensity of DHPs also increased remarkably upon addition of Cu(2+), resulting that the effects of DHPs were enhanced.     

A TEMPO-conjugated fluorescent probe for monitoring mitochondrial redox reactions

We report a mitochondrial targeted redox probe (MitoRP) that comprises a nitroxide radical (TEMPO) moiety and coumarin 343. Using isolated mitochondria in the presence/absence of substrates and inhibitors of oxidative phosphorylation, we demonstrated that MitoRP is a useful probe to monitor the electron flow associated with complex I.     

Synthesis of periodic copolymers via ring‐opening copolymerizations of cyclic anhydrides with tetrahydrofuran using nonafluorobutanesulfonimide as an organic catalyst and subsequent transformation to aliphatic polyesters

To synthesize polyesters and periodic copolymers catalyzed by nonafluorobutanesulfonimide (Nf₂NH), we performed ring‐opening copolymerizations of cyclic anhydrides with tetrahydrofuran (THF) at 50–120 °C. At high temperature (100–120 °C), the cyclic anhydrides, such as succinic anhydride (SAn), glutaric anhydride (GAn), phthalic anhydride (PAn), maleic anhydride (MAn), and citraconic anhydride (CAn), copolymerized with THF via ring‐opening to produce polyesters (M_n = 0.8–6.8 × 10³, M_n/M_w = 2.03–3.51). Ether units were temporarily formed during this copolymerization and subsequently, the ether units were transformed into esters by chain transfer reaction, thus giving the corresponding polyester. On the other hand, at low temperature (25–50 °C), ring‐opening copolymerizations of the cyclic anhydrides with THF produced poly(ester‐ether) (M_n = 3.4–12.1 × 10³, M_w/M_n = 1.44–2.10). NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra revealed that when toluene (4 M) was used as a solvent, GAn reacted with THF (unit ratio: 1:2) to produce periodic copolymers (M_n = 5.9 × 10³, M_w/M_n = 2.10). We have also performed model reactions to delineate the mechanism by which periodic copolymers containing both ester and ether units were transformed into polyesters by raising the reaction temperature to 120 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation of organic/inorganic hybrid and hollow particles by catalytic deposition of silica onto core/shell heterocoagulates modified with poly[2-(N,N-dimethylamino)ethyl methacrylate

The organic/inorganic hybrid particles PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2) were prepared by catalytic hydrolysis and subsequent polycondensation of tetraethoxysilane in the poly[2-(N,N-dimethylamino)ethyl methacrylate] (PDMAEMA) layers grafted on the PSt/P(St-CPEM)(θ) core/shell heterocoagulates. The micron-sized PSt core and the submicron-sized P(St-CPEM) shell particles bearing ATRP initiating groups were synthesized by dispersion polymerization of styrene (St) and emulsifier-free emulsion polymerization of St with 2-chloropropionyloxyethyl methacrylate (CPEM), respectively. The raspberry-shaped PSt/P(St-CPEM)(θ) heterocoagulates with a controlled surface coverage (θ=0.51, 0.81) were prepared by hydrophobic coagulation between the core and the shell particles in an aqueous NaCl solution near the T(g) of P(St-CPEM). Surface modification of heterocoagulates was carried out by ATRP of DMAEMA from the shell particles adsorbed on the core particles. Silica deposition was performed by simply adding tetraethoxysilane to a water/methanol dispersion of PSt/P(St-CPEM)(θ)-g-PDMAEMA. The SEM and TGA revealed that the resulting PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2) composites maintain a raspberry-like morphology after deposition of silica onto the PDMAEMA layer grafted on heterocoagulates. The micron-sized, raspberry-shaped or the submicron-sized, hole-structured silica hollow particles were obtained selectively by thermal decomposition of the PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2). The oriented particle array was fabricated by dropping anisotropically perforated silica particles onto a glass substrate settled at the bottom of a bottle filled with chloroform.     

Valence states of 57Fe decayed from 57Mn implanted into KMnO4

In-beam Mössbauer spectra of ⁵⁷Fe, decayed from short-lived ⁵⁷Mn (T_1/2 = 1.45 min) implanted into potassium permanganate, KMnO₄, were measured at temperatures between 11 K and 130 K. This is the first application of a secondary RI beam to the study of valence states after nuclear transformation. The in-beam Mössbauer spectra obtained below 90 K could be analyzed with two components, a doublet and a singlet. From the calculations of the molecular orbital wave functions, the singlet is suggested to be substitutional ⁵⁷Fe atoms for Mn-sites in tetrahedral [MnO₄]^– with an unusually high valence state of Fe⁸⁺.