Dynamics of excited and ionic states of N,N,N′,N′-tetramethyl-p-phenylenediamine in poly(methyl methacrylate) under ablation condition

The nanosecond transient dynamics of N,N,N′,N′-tetramethyl-p-phenylenediamine in poly(methyl methacrylate) has been investigated under ablation condition. Time-resolved spectroscopic data can be interpreted in terms of the dynamics of the lowest excited singlet and triplet states and the cation of TMPD. The decay processes of all the detected transients became rapid with an increase in the laser fluence. It is shown directly that TMPD absorbs about eight 248 nm photons during a nanosecond laser pulse at the ablation threshold of 220 mJ/cm². These results are well explained by cyclic multiphotonic absorption mechanism where dopant transients work as repetitive absorbers of laser photons.     

Supramolecular modulation of action of polyamine on enzyme/DNA interactions

Thread-in-hole complexation of cucurbit[6]uril (CB[6]) with spermidine and spermine either enhances or reduces the activity of the polyamine on the enzymatic reactions of DNA.     

Phase transformations in Li2WO4 at high pressure

The phase diagram of Li₂WO₄ has been determined at high pressure up to 160 kbars and a temperature of 800°C. Three new high-pressure phases have been found in the present study. Crystallographic data are given for Li₂WO₄ III and Li₂WO₄ IV by means of single crystal and powder X-ray analyses. Li₂WO₄ III is orthorhombic with the large unit cell containing 16 molecules and having the edges: a₀ = 10.12(4) Å, b₀ = 10.07(1) Å, c₀ = 11.68(6) Å. Li₂WO₄ IV has an orthorhombic unit cell with the parameters: a₀ = 4.96(7) Å, b₀ = 9.72(8) Å, c₀ = 5.93(8)Å and Z = 4. The total volume decrease is estimated to be 24.8% through the high pressure transformations in Li₂WO₄. No spinel-like structure could be found in the present study.     

Vinyliodonium salts : their stereospecific synthesis and reactions as the activated vinyl halides

Vinyliodonium salts $\text{2}$ were synthesized from vinylsilanes $\text{1}$ by the reaction with iodosylbenzene and triethyloxonium tetrafluoroborate. The reaction occurs stereospecifically with retention of configuration. Vinyliodonium salts $\text{2}$ are highly effective as the activated species of vinyl iodides. Thus, a variety of substituted olefins including α-cyano and α-nitro olefins, vinyl sulfides, vinyl halides, and α,β-unsaturated esters, were prepared from $\text{2}$ under mild reaction conditions.     

An amperometric sensor for carbon dioxide based on immobilized bacteria utilizing carbon dioxide

A biosensor consisting of a CO₂-utilizing autotrophic bacterium (strain S-17, Pseudomonas type) and an oxygen-sensing electrode was constructed for the amperometric determination of CO₂. The correlation between current decrease and CO₂ concentration was linear in the range 5–200 mg l^?1 CO₂. The optimum temperature and pH for operation of the biosensor were 30°C and 5.5, respectively. The sensor did not respond to other volatile compounds except for acetic acid. The sensor could be operated continuously for about a month.     

Deoxydative thiation of 3-substituted pyridine N-oxides with 4-methoxytoluene-α-thiol: A divergent route to pyridinethiols

Synthesis of 3-substituted 2-pyridinethiols was achieved by thiation of pyridine N-oxides with 4-methoxytoluene-α-thiol in the presence of diethylcarbamoyl chloride followed by cleavage of the resulting sulfides. The ease of substitution was shown to be affected by nucleophilicity of the N-oxide oxygen. Addition of zinc bromide to the reaction, a need for triethylamine, decreased most of the yield for thiation products but the formation of 3-methoxy-2-methoxybenzylthiopyridine was only improved. A plausible mechanism of the substitution, particularly β-thiation to the N-oxide function, is discussed compared with the regiochemistry observed in the reaction with diethoxyphosphoryl chloride instead of diethylcarbamoyl chloride. The debenzylation to pyridinethiol was also found to be dependent on the electron-density in the pyridine ring.     

Regioselective synthesis of substituted 1-indanols, 2,3-dihydrobenzofurans and 2,3-dihydroindoles by electrochemical radical cyclization using an arene mediator

Electrochemical reduction of haloarenes carrying 2-(1-hydroxybut-3-enyl), 2-allyloxy or N-allyl-N-methylamino group in the presence of phenanthrene as a mediator generated the corresponding aryl radicals and gave the corresponding 5-exo cyclization products in good yields. Higher regio- and stereoselectivities than those of usual radical cyclization using AIBN-Bu₃SnH were achieved.     

Radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. VI. Temperature dependence and effects of additives on methyl methacrylate–silica gel system

To elucidate the reaction mechanism of radiation-induced polymerization of methyl methacrylate adsorbed on silica gel, the temperature dependence and effects of acetone and pyridine were investigated. It was found that even at ?78°C the polymerization rate was quite fast. The amounts of high molecular weight GPC peaks of both graft polymers and homopolymers increased with increasing irradiation temperature. The activation energy of the adsorbed state polymerization was low compared with that of bulk polymerization. The low molecular weight peaks of homopolymers decreased with acetone addition but were almost unaffected by pyridine. The low molecular weight peaks of homopolymers were thus polymerized by an anionic mechanism. In the methyl methacrylate–silica gel system both radical and anionic polymerization take place at the same time in formation of graft polymers and homopolymers. A reaction mechanism for the methyl methacrylate–silica gel system was proposed based on the results obtained to date.     

Reaction of 3-chloroallyltrimethylsilane with acid chloride and exploitation of a new regioselective synthesis of αβ-unsaturated epoxide

α-Chloro-βγ-unsaturated ketone (2) was synthesized from the reaction of 3-chloroallyltrimethylsilane (1) with acid chloride. The ketone was converted into αβ-unsaturated epoxide (3) regioselectively in good yield via reduction with NaBH₄ or LiAlH₄ followed by treatment with NaOH. Treatment with methyl lithium instead of reduction gave homologous epoxide (5).     

Preparation of mordenite composite membranes with seeding

Mordenite composite membranes were prepared by means of coating a porous α-alumina support with nanosized mordenite seeds followed by hydrothermal crystallization. A systematic investigation was performed on the influence of several factors such as ageing of the reaction mixture, alkalinity, salt addition and temperature on the formation of a mordenite membrane on the seeded support. The ageing of the reaction mixture reduces the growth rate of mordenite crystal along a-axis and b-axis but hardly influences the growth rate along c-axis. As a result, the boundaries between the surface crystals become a little larger with prolonging the period of ageing time. The growth rate of the mordenite crystal along individual axes increases first and then decreases with increasing concentration of sodium hydroxide. A higher alkalinity is unfavorable for the formation of a continuous mordenite membrane. The addition of salt in the reaction mixture has different effect on the growth rate of the mordenite crystal along each axis. With increasing the amount of salt, there was hardly influence on the growth rate along c-axis, whereas an obvious decline was observed in the growth rate along either a-axis or b-axis, which enlarges the boundaries between the surface crystals. The growth rate of the mordenite crystal increases more along c-axis than that along a-axis or b-axis with increasing temperature for hydrothermal crystallization. The use of a temperature as high as 473 K produces a membrane composed of bar-like crystals with larger boundaries. __________ Translated from Journal of Zhejiang University (Science Edition), 2005, 32(4) (in Chinese)