PHOTOCYCLOADDITION REACTION OF 5,7-DIMETHOXYCOUMARIN TO THYMIDINE

Abstract— The photocycloaddition reaction of 5,7-dimethoxycoumarin to thymidine on direct irradiation (λ > 300 nm) is studied as a model for photosensitization reaction of furocoumarins. The major photoadducts were isolated by silica gel column and gel permeation chromatography. Each component of the photoadducts was further separated by reverse phase, paired-ion high performance liquid chromatography. The structure of these photoproducts isolated is consistent with 1:1 C₄-cycloadducts in accordance with characteristics of their UV, IR, NMR and mass spectra and elemental analysis data. The stereochemistry of each isomer was studied by Fourier transform NMR, UV and IR spectra. The fraction C has the anti head-to-tail configuration and the fraction D has the configuration of anti head-to-head. The fractions A and B probably have the syn configuration.     

A molecular approach to rationally constructing specific fluorogenic substrates for the detection of acetylcholinesterase activity in live cells,mice brains and tissues

Acetylcholinesterase (AChE) is an extremely critical hydrolase tightly associated with neurological diseases. Currently, developing specific substrates for imaging AChE activity still remains a great challenge due to the interference from butyrylcholinesterase (BChE) and carboxylesterase (CE). Herein, we propose an approach to designing specific substrates for AChE detection by combining dimethylcarbamate choline with a self-immolative scaffold. The representative P10 can effectively eliminate the interference from CE and BChE. The high specificity of P10 has been proved via imaging AChE activity in cells. Moreover, P10 can also be used to successfully map AChE activity in different regions of a normal mouse brain, which may provide important data for AChE evaluation in clinical studies. Such a rational and effective approach can also provide a solid basis for designing probes with different properties to study AChE in biosystems and another way to design specific substrates for other enzymes.

In this work, a new approach was developed for designing the representative P10 with high selectivity and sensitivity for imaging AChE activity in the cells and normal mouse brain.     

Effect of particle size in preparative reversed-phase high-performance liquid chromatography on the isolation of epigallocatechin gallate from Korean green tea

To isolate epigallocatechin gallate (EGCG) of catechin compounds from Korean green tea (Bosung, Chonnam), a C18 reversed-phase preparative column (250x22 mm) packed with packings of three different sizes (15, 40-63, and 150 microm) was used. The sample extracted with water was partitioned with chloroform and ethyl acetate to remove the impurities including caffeine. The mobile phases in this experiment were composed of 0.1% acetic acid in water, acetonitrile, methanol and ethyl acetate. The injection volume was fixed at 400 microl and the flow rate was increased as the particle size becomes larger. The isolation of EGCG with particle size was compared at a preparative scale and the feasibility of separation of EGCG at larger particle sizes was confirmed. The optimum mobile phase composition for separating EGCG was experimentally obtained at the particle sizes of 15 and 40-63 microm in the isocratic mode, but EGCG was not purely separated at the particle size of 150 microm.     

Synthesis of some azeto[2,1-a]isoquinolin-2-ones

Some azeto[2,1-a]isoquinolin-2-ones were synthesized from 2-(3,4-dimethoxyphenyl)ethylamine in three steps in good yield.     

Pt‐Nanoparticle Incorporated Carbon Paste Electrode for the Determination of Cu(II) Ion by Anodic Stripping Voltammetry

Pt‐nanoparticles were synthesized and introduced into a carbon paste electrode (CPE), and the resulting modified electrode was applied to the anodic stripping voltammetry of copper(II) ions. The synthesized Pt‐nanoparticles were characterized by cyclic voltammetry, scanning electron microscopy and X‐ray photoelectron spectroscopy techniques to confirm the purity and the size of the prepared Pt‐nanoparticles (ca. 20 nm). This incorporated material seems to act as catalysts with preconcentration sites for copper(II) species that enhances the sensitivity of Cu(II) ions to Cu(I) species at a deposition potential of ?0.6 V in an aqueous solution. The experimental conditions, such as, the electrode composition, pH of the solution, pre‐concentration time, were optimized for the determination of Cu(II) ion using as‐prepared electrode. The sensitivity changes on the different binder materials and the presence of surfactants in the test solution. The interference effect of the coexisted metals were also investigated. In the presence of surfactants, especially TritonX‐100, the Cu(II) detection limit was lowered to 3.9×10^?9 M. However, the Pt‐nanoparticle modified CPE begins to degrade when the period of deposition exceeds to 10 min. Linear response for copper(II) was found in the concentration range between 3.9×10^?8 M and 1.6×10^?6 M, with an estimated detection limit of 1.6×10^?8 M (1.0 ppb) and relative standard deviation was 4.2% (n=5).     

Isomorphous inclusions of silicon, aluminum, and titanium in the germanate zeolite IPC-3

The zeolite IPC-3, isomorphous with germanate zeolite ASU-16, and its silicon, aluminum, and titanium analogs, were obtained in the presence of 1,6-diaminohexane as a template. It is possible to incorporate selectively the elements in different crystallographic positions, determined by the nature of the element, particularly its valency and its coordination number with respect to oxygen. Silicon takes tetrahedral positions in the IPC-3 lattice, Al either tetrahedral or octahedral positions, and Ti octahedral positions. Small amounts of the lithium cations facilitate tetrahedral coordination and increase the Al content in IPC-3. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 4, pp. 246–251, July–August, 2006.     

High-Throughput Analysis of Sofalcone in Human Plasma by Use of Automated 96-Well Protein Precipitation and LC-MS-MS

A sensitive and selective method for the determination of sofalcone in human plasma was established by use of protein precipitation and liquid chromatography-tandem mass spectrometry. Plasma samples were transferred into 96-well plate using an automated sample handling system and spiked with 10 L of 2 g mL^–1 internal standard solution (d₃-sofalcone). 0.5 mL of acetonitrile was added to the 96-well plate and the plasma samples were then vortexed for 30 sec. After centrifugation, the supernatant was transferred into another 96-well plate and completely evaporated at 40 °C under a stream of nitrogen. The dry residue was reconstituted with mobile phase. All sample transfer and protein precipitation was automated through the application of both the PerkinElmer MultiPROBE II HT and TOMTEC Quadra 96 workstation. The limit of quantitation of sofalcone was 2 ng mL^–1 using a sample volume of 0.2 mL for the analysis. The reproducibility of the method was evaluated by analyzing five samples at nine quality control (QC) levels over the nominal concentration range from 2 ng mL^–1 to 1000 ng mL^–1. Validation of the method showed that the assay has good precision and accuracy. Sofalcone and internal standard produced a protonated precursor ion ([M+H]⁺) at m/z 451 and 454, and both gave a corresponding product ion at m/z 315. The high sample throughput of the method has been successfully applied to a pharmacokinetic study of sofalcone in human plasma.     

New tetradentate Schiff-base polymers: preparation of poly[2,5-(didodecyloxy)phenylene-1,4-diyl-alt-N,N-(o-phenylene)-bis(salicylideneiminato-4,4-diyl)] and poly[2,5-(didodecyloxy)phenylene-1,4-diyl-alt-N,N-(alkylidene)-bis(salicylideneiminato-4,4-diyl)]s

New tetradentate Schiff-base polymers, in which phenylene units alternate with salicylideneiminato units, have been prepared by condensation of 2,5-(didodecyloxy)-1,4-bis(3-formyl-4-hydroxyphenyl)benzene (DFHB) with appropriate diamines in a mixed solution of CHCl₃/toluene/acetic acid with 31-79% yields. DFHB as the key building block was prepared by the Suzuki reaction of 2,5-(didodecyloxy)benzene-1,4-diboronic acid with 5-bromosalicylaldehyde in a two-phase solution of tetrahydrofuran/water in the presence of NaHCO₃/Pd(PPh₃)₄ in 45% yield. The molecular structures of the prepared compounds were identified by spectroscopy. Their absorption spectroscopic profiles have been analyzed.     

Synthesis, characterization, and dioxygen reactivity of tetracarboxylate-bridged Diiron(II) complexes with coordinated substrates

The synthesis and characterization of [Fe(2)(micro-O(2)CAr(Tol))(4)L(2)] complexes, where L is benzylamine or 4-methoxybenzylamine (BA(p)()(-)(OMe)), are described. The reaction of the latter diiron(II) complex with dioxygen at -78 degrees C affords a metastable mixed-valent Fe(II)Fe(III) green intermediate. When O(2) is introduced at ambient temperature, N-dealkyation occurs to yield anisaldehyde, eliminating N-oxidation as a viable pathway for the reaction. Use of [Fe(2)(micro-O(2)CAr(T)(omicron)(l))(4)(alpha-d(1)-BA(p)()(-)(OMe))(2)] allowed a deuterium kinetic isotope of approximately 3 to be determined.     

Electronic structure and field emission of multiwalled carbon nanotubes depending on growth temperature

The electronic structure of multiwalled carbon nanotubes (CNTs) has been investigated, depending on the growth temperature, using synchrotron X-ray photoelectron spectroscopy (XPS) and field emission measurements. The vertically aligned CNTs are grown via pyrolysis of ferrocene and acetylene in a broad temperature range 600-1000 degrees C. The CNTs have a cylindrical structure with a uniform diameter of 20 nm. As growth temperature increases, due to an improved crystallinity of the graphitic sheets, the width of the XPS C 1s peak becomes narrower and the intensity of the valence band increases. Field emission from the as-grown CNTs exhibits a large enhancement of current density with growth temperature, strongly correlated with the electronic structure revealed by XPS.