Simultaneous determination of choline and acetylcholine based on a trienzyme chemiluminometric biosensor in a single line flow injection system.

A detector for the simultaneous determination of choline (Ch) and acetylcholine (ACh) based on a sensitive trienzyme chemiluminometric biosensor in a single line flow injection (FI) system is described. Immobilized choline oxidase (ChOx), immobilized peroxidase (POx), immobilized acetylcholinesterase, and coimmobilized ChOx/POx were packed, in turn, in a transparent ETFE tube (1 mm i.d., 75 cm) and the tube was placed in front of a photomultipier tube as a flow cell. Two-peak response was obtained by one injection of the sample solution. The first and second peaks were dependent on the concentrations of Ch and ACh, respectively. The influence of some experimental parameters such as flow rate, amounts of immobilized enzymes on the behavior of the sensor was studied in order to optimize the sensitivity, sample throughput and resolution. Calibration curves were linear at 1 - 1000 nM for Ch and 3 - 3000 nM for ACh. The sample throughput was 25/h without carryover. The FI system was applied to the simultaneous determination of Ch and ACh in rabbit brain tissue homogenates.     

Preparative high-performance liquid chromatography for the purification of natural acylated anthocyanins from red radish (Raphanus sativus L.)

Preparative high-performance liquid chromatography (HPLC) is applied to the purification of anthocyanins from raw extracts of red radish (Raphanus sativus L). For each separation, the chromatographic conditions are optimized to achieve an efficient purification in the shortest time. In addition, UV-vis characterization is carried out on all purified anthocyanins. The current work shows that analytical chromatographic experiments alone are useful for the prediction of scale-up conditions of preparative HPLC separations. Ten known acylated anthocyanins (See the Appendix for compounds 1-10) are isolated from the red radish by isocratic HPLC. The structures are establishe on the basis of nuclear magnetic resonance and mass spectrometric analysis. The acylated anthocyanins are all based on pelargonidin 3-sophoroside-5-glucoside, acylated with caffeoyl, feruloyl, or p-coumaroyl moieties.     

Impact of initial lattice structures on networks generated by traces of random walks

We show that the platform stage of network evolution plays a principal role in the topology of resulting networks generated by short-cuts stimulated by the movements of a random walker, the mechanism of which tends to produce power-law degree distributions. To examine the numerical results, we have developed a statistical method which relates the power-law exponent γ to random properties of the subgraph developed in the platform stage. As a result, we find that an important exponent in the network evolution is α, which characterizes the size of the subgraph in the form V∼t^α, where V and t denote the number of vertices in the subgraph and the time variable, respectively. 2D lattices can impose specific limitations on the walker’s diffusion, which keeps the value of α within a moderate range and provides typical properties of complex networks. 1D and 3D cases correspond to different ends of the spectrum for α, with 2D cases in between. Especially for 2D square lattices, a discontinuous change of the network structure is observed, which varies according to whether γ is greater or less than 2. For 1D cases, we show that emergence of nearly complete subgraphs is guaranteed by α<1/2, although the transient power-law is permitted at low increase rates of edges. Additionally, the model exhibits a spontaneous emergence of highly clustered structures regardless of its initial structure.     

Flow-injection determination of l-tyrosine in serum with an immobilized tyrosinase reactor and fluorescence detection

Tyrosinase is immobilized on controlled-pore glass beads and packed into a stainless-steel column (5 cm × 4 mm i.d.). Serum is deproteinized with tungstate and sulphuric acid. The carrier stream is 0.3 M phosphate buffer (pH 7.2), and is mixed with 5 M potassium hydroxide after the enzyme reactor. The fluorescent dihydroxyindole formed is detected at 490 nm (excitation at 375 nm). The calibration graph is linear for 1 × 10^?7 ?1 × 10^?4 M tyrosine; the detection limit is 2 × 10^?8 M.     

Studies on the chemical transformations of rotenoids. 5 . Synthesis and cytotoxicity of 1,3-diazepino[5,6-b]benzofuran and pyridazino[4,5-b]benzofurans fused with thiazole,imidazole and pyrimidine

Novel benzofuro[2,3-d]pyridazinium chlorides fused with thiazole 5a , imidazole 5b-c and pyrimidine 5d-f were prepared starting from 4-chloropyridazino[4,5-b]benzofuran 3a . Treatment of 5b, 5d and 5e with 10% potassium carbonate solution provided the corresponding free bases 6a-c . Ring closure of methyl rotenononate 1b with amidines proceeded in the presence of sodium methoxide to give 1,3-diazepino[5,6-b]benzofuran-5-ones 7a-c . Compound 5d showed cytotoxicity against P388 and L1210 leukemia cells.     

Luminescence properties of Ge implanted SiO2:Ge and GeO2:Ge films

We have investigated cathodeluminescence (CL) of Ge implanted SiO₂:Ge and GeO₂:Ge films. The GeO₂ films were grown by oxidation of Ge substrate at 550 °C for 3 h in O₂ gas flow. The GeO₂ films on Ge substrate and SiO₂ films on Si substrate were implanted with Ge-negative ions. The implanted Ge atom concentrations in the films were ranging from 0.1 to 6.0 at%. To produce Ge nanoparticles the SiO₂:Ge films were thermally annealed at various temperatures of 600-900 °C for 1 h in N₂ gas flow. An XPS analysis has shown that the implanted Ge atoms were partly oxidized. CL was observed at wavelengths around 400 nm from the GeO₂ films before and after Ge⁻-implantation as well as from SiO₂:Ge films. After Ge⁻-implantation of about 0.5 at% the CL intensity has increased by about four times. However, the CL intensity from the GeO₂:Ge films was several orders of magnitude smaller than the intensity from the 800 °C-annealed SiO₂:Ge films with 0.5 at% of Ge atomic concentration. These results suggested that the luminescence was generated due to oxidation of Ge nanoparticles in the SiO₂:Ge films.