Extraction and spectrophotometric determination of zinc in coal fly ash and pond sediments with 2-[2-(3,5-dibromopyridyl)azo]-5-dimethylaminobenzoic acid

An extraction-spectrophotometric method is described for the determination of traces of zinc with 2-[2-(3,5-dibromopyridyl)azo]-5-dimethylaminobenzoic acid. The reagent forms a stable, blue 1:2 zinc/reagent complex that can be extracted into chloroform. The apparent molar absorptivity of the zinc(II) complex is 1.26 × 10⁵ l mol^?1 cm^?1 at 610 nm in chloroform. The reagent is relatively selective; interferences from cobalt, copper and nickel can be masked with dimethylglyoxime and aluminium and iron with a mixture of sodium fluoride and triethanolamine. The method is applied to the determination of zinc in coal fly ash and pond sediments with good precision and accuracy.     

Structural assignment of n3-acylated uridine derivatives by means of 13c nmr spectroscopy

Diisopropylethylamine was effective as a base for acylation of 2′,3′,5′-tri-O-acetyluridine with various acid chlorides. The ¹³C NMR spectra of the products and related compounds showed clearly that the acyl groups intoduced to the uracil moiety are attached to the N³-nitrogen.     

Some triplet energy-transfer reactions initiated by photoexcitation of triplet excited state of dibenz[a,h]anthracene to the higher triplet excited states

Some triplet energy-transfer reactions initiated by photoexcitation of the triplet excited state of dibenz[a,h]anthracene to higher triplet excited states (DBA(T_n)) were observed in the presence of the triplet energy quenchers (Q) such as naphthalene, biphenyl, p-dichlorobenzene, and o-dicyanobenzene. In the case of carbon tetrachloride (CCl₄) as Q, DBA(T_n)-sensitized decomposition of CCl₄ occurred.     

Vibronic interactions and possible electron pairing in the photoinduced excited electronic States in molecular systems: a theoretical study

Electron-phonon interactions in the photoinduced excited electronic states in molecular systems such as phenanthrene-edge-type hydrocarbons are discussed and compared with those in the monoanions and cations. The complete phase patterns difference between the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) (the atomic orbitals between two neighboring carbon atoms combined in phase (out of phase) in the HOMO are combined out of phase (in phase) in the LUMO) are the main reason that the C-C stretching modes around 1500 cm(-1) afford much larger electron-phonon coupling constants in the excited electronic states than in the charged electronic states. The frequencies of the vibrational modes that play an essential role in the electron-phonon interactions for the excited electronic states are similar to those for the monoanions and cations in phenanthrene-edge-type hydrocarbons. Possible electron pairing and Bose-Einstein condensation in the photoinduced excited electronic states as well as those in the monoanions and cations in molecular systems such as phenanthrene-edge-type hydrocarbons are also discussed.     

Methane partial oxidation to formaldehyde with oxygen over SiO2-supported molybdenum oxide catalysts

The formation rate of formaldehyde increases with increasing surface area of SiO₂ support, but the selectivity does not. From the characterization of catalysts using XRD, SEM and Raman spectroscopy, highly dispersed molybdenum oxide was considered to be much more active for the formation of formaldehyde than crystallite forms of MoO₃.     

Recent progress of high-power negative ion beam development for fusion plasma heating

A negative-ion-based neutral beam injector (N-NBI) has been constructed for JT-60U. The N-NBI is designed to inject 500 keV, 10 MW neutral beams using two ion sources, each producing a 500 keV, 22 A D⁻ ion beam. In the preliminary experiment using one ion source, a D⁻ ion beam of 13.5 A has been successfully accelerated with an energy of 400 keV (5.4 MW) for 0.12 s at an operating pressure of 0.22 Pa. This is the highest D⁻ beam current and power in the world. Co-extracted electron current was effectively suppressed to the ratio of Ie/I_D⁻ < 1. The highest energy beam of 460 keV, 2.4 A, 0.44 s has also been obtained. To realize 1 MeV class NBI system for ITER (International Thermonuclear Experimental Reactor), demonstration of ampere class negative ion beam acceleration up to 1 MeV is an important mile stone. To achieve the mile stone, a prototype accelerator and a 1 MV, 1 A test facility called MeV Test Facility (MTF) were constructed. Up to now, an H⁻ ion beam was accelerated up to the energy of 805 keV with an acceleration drain current of 150 mA for 1 s in a five stage electrostatic multi-aperture accelerator.     

Remarkable reactivities of the xanthone ketyl radical in the excited state compared with that in the ground state

The properties and reactivities of the xanthone (Xn) ketyl radical (XnH*) in the doublet excited state (XnH*(D1)) were examined by using two-color two-laser flash photolysis. The absorption and fluorescence of XnH*(D1) were observed for the first time. Several factors governing the deactivation processes of XnH*(D1) such as interaction and reaction with solvent molecules were discussed. The remarkable change of reactivity of XnH*(D1) compared with that in the ground state (XnH*(D0)) was indicated from the experimental results. The rapid halogen abstraction of XnH*(D1) from some halogen donors such as carbon tetrachloride (CCl4) was found to occur. The halogen abstraction occurred more efficiently in the polar solvents than in the nonpolar solvents. It is suggested that the polar solvents promote the spin distribution of XnH*(D1) of the phenyl ring favorable to the halogen abstraction.     

Highly chemoselective hydrogenation method using novel finely dispersed palladium catalyst on silk-fibroin: its preparation and activity

A palladium-fibroin complex (Pd/Fib) was prepared by soaking silk-fibroin in MeOH solution of Pd(OAc)₂ for 2 days (under Ar atmosphere)—4 days (under air). Pd(OAc)₂ was gradually absorbed by fibroin and the rapid reduction of fibroin conjugated Pd(OAc)₂ proceeded with MeOH as a reductant at room temperature to be the Pd(0) complex. Pd/Fib catalyzed chemoselective hydrogenation of acetylenes, olefins and azides in the presence of aromatic ketones and aldehydes, halides, N-Cbz protective groups and benzyl esters which are readily hydrogenated using Pd/C or Pd/C(en) as a catalyst.     

Electrocatalytic properties of Au(111)-Pd quasi-single-crystal film electrodes as probed by ATR-SEIRAS

Electrochemical and electrocatalytic properties of thin films Au(111-25 nm), which are quasi-single-crystal electrodes 25 nm thick made of gold with the (111) preferential orientation, and same electrodes modified with a monolayer (ML) of palladium are studied in 0.1 M solutions of HClO₄ and H₂SO₄ employing voltammetric techniques and surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS). Spectroscopic experiments demonstrate strong adsorption of electrolyte species (H₂O, OH_ads, anions) on the Pd surface. The weak and reversible adsorption of CO on Au(111-25 nm) does not change the interfacial-water structure. Adsorption of CO on the Pd-modified film results in an irreversibly adsorbed CO adlayer stabilized by co-adsorbed isolated water species. Various electrooxidation mechanisms are discussed. Electrochemical and spectroscopic investigations on the adsorption and electrooxidation of HCOOH on bare and 1 ML Pd-Au(111-25 nm) electrodes reveal that electrooxidation proceeds in both cases via a direct or dehydrogenation pathway. This mechanism involves the formation of formate as intermediate, which is detected by in situ ATR-SEIRAS. The reactivity on Pd-modified surfaces is higher than on bare gold. The specifically adsorbed anions (sulfate/bisulfate) and the oxide formation on the substrate surface lower the reactivity for CO and HCOOH on both surfaces. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1312–1329. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Formation and stabilization model of the 42-mer Abeta radical: implications for the long-lasting oxidative stress in Alzheimer's disease

Amyloid fibrils mainly consist of 40-mer and 42-mer peptides (Abeta40, Abeta42). Abeta42 is believed to play a crucial role in the pathogenesis of Alzheimer's disease because its aggregative ability and neurotoxicity are considerably greater than those of Abeta40. The neurotoxicity of Abeta peptides involving the generation of free radicals is closely related to the S-oxidized radical cation of Met-35. However, the cation's origin and mechanism of stabilization remain unclear. Recently, structural models of fibrillar Abeta42 and Abeta40 based on systematic proline replacement have been proposed by our group [Morimoto, A.; et al. J. Biol. Chem. 2004, 279, 52781] and Wetzel's group [Williams, A. D.; et al. J. Mol. Biol. 2004, 335, 833], respectively. A major difference between these models is that our model of Abeta42 has a C-terminal beta-sheet region. Our biophysical study on Abeta42 using electron spin resonance (ESR) suggests that the S-oxidized radical cation of Met-35 could be generated by the reduction of the tyrosyl radical at Tyr-10 through a turn structure at positions 22 and 23, and stabilized by a C-terminal carboxylate anion through an intramolecular beta-sheet at positions 35-37 and 40-42 to form a C-terminal core that would lead to aggregation. A time-course analysis of the generation of radicals using ESR suggests that stabilization of the radicals by aggregation might be a main reason for the long-lasting oxidative stress of Abeta42. In contrast, the S-oxidized radical cation of Abeta40 is too short-lived to induce potent neurotoxicity because no such stabilization of radicals occurs in Abeta40.