Electrochemical detection of in situ DNA damage induced by enzyme-catalyzed Fenton reaction. Part I: in phosphate buffer solution

We report on a biosensor for the electrochemical detection of the damage of DNA and of antioxidant protecting DNA. The biosensor was constructed by co-immobilization of DNA and glucose oxidase (GOx) on a glassy carbon electrode. Under aerobic conditions, GOx catalyzes the oxidation of glucose, and the hydrogen peroxide produced reacts with ferrous ions in a Fenton-type reaction to generate hydroxy radical. This was validated by UV–vis spectroscopy. The hydroxy radical can cause serious oxidative damage to DNA, and this can be detected by square wave voltammetry of the electroactive indicator Co(bpy) ₃ ³⁺ . The effects of pH value, incubation time, and the concentration of glucose and ferrous ion were optimized. The effects of the antioxidants ascorbic acid and aloe emodin on DNA damage were also investigated within the concentration range from 0.05 to 200?μM. This work provides an in-vitro model system to mimic the processes in oxidative DNA damage by a simple electrochemical approach.

Generation of Multiple-Atom Entangled States with Weak Cross-Kerr Nonlinearity

We propose a scheme to generate multiple-atom entangled states in separate cavities. In our scheme, only weak cross-Kerr mediums, homodyne measurement, and some linear elements are employed. With the help of homodyne measurement, four-atom GHZ state can be obtained with high probability and fidelity, and the proposal can be easily scaled to prepare multiple-atom GHZ state. Under ideal conditions, the success probability will not be affected by atomic numbers.     

Influence of the antireflection,window, and active layers on optical properties of exponential-doping transmission-mode GaAs photocathode modules

In order to well study the influence of the thickness and doping concentration on optical properties of transmission-mode GaAs photocathode, three exponential-doping and one uniform-doping photocathode modules were prepared by molecular beam epitaxy with a structure of glass/Si₃N₄/Ga_1 ? xAl_xAs/GaAs. By use of the spectrophotometer, the optical properties were separately measured including the reflectivity and transmissivity curves. Based on thin film optical principles, the optical properties and their integral values are calculated by matrix formula for the four-layer photocathode module. The result shows that the antireflection and window layers affect the peak and valley of the optical property curves and the active layer influences the absorptivity values of the transmission-mode cathode modules. The photocathode module has high absorptivity within the response waveband when the optimal module has the Si₃N₄ antireflection layer of 0.1 μm, the Ga_1 ? xAl_xAs window layer of more than 0.4 μm, and the GaAs active layer of 1.5 μm–2 μm and low average doping concentration.     

Computer simulation of linkage of two ring chains

We performed off-lattice Monte Carlo simulations of links of two model ring chains with chain length N up to 32,768 in the theta solution or amorphous bulk state by using a random walk model (Model I), and molecular dynamics simulations of two model ring chains in solution with excluded volume interaction (Model II) to investigate topological effects on the geometry of link and ring conformation. In the case of Model I, the mean squared linking number, its distribution, and the size of two chains with fixed linking number are investigated. Our simulation results confirm the previous theoretical prediction that the mean squared linking number decays as pe(-qs(2)) with the distance of centers of chain mass s, where p and q are found to be chain length dependent and q asymptotically approaches to 0.75 as chain length increases. The linking number distribution of two chains has a universal form for long chains, but our simulation results clearly show that the distribution function deviates from the Gaussian distribution, a fact not predicted by any previous theoretical work. A scaling prediction is proposed to predict the link size, and is checked for our simulations for the Model II. The simulation results confirmed the scaling prediction of the blob picture that the link with linking number m occupies a compact volume of m blobs, and the size of the link is asymptotic to R(L) ≈ bN(ν)m(1/3-ν), where N is the chain length, and v is the Flory exponent of polymer in solutions.     

Three New Pregnane Alkaloids from Veratrum taliense

Three new alkaloids, 3‐O‐acetylveralkamine ( 1 ), veralkamine 3‐(β‐D ‐glucopyranoside) ( 2 ), and 6,7‐epoxyverdine ( 3 ), together with five known alkaloids, veramitaline, veralkamine ( 4 ), angeloylzygadenine, veratroylzygadenine, and veramiline 3‐(β‐D ‐glucopyranoside), were isolated from the whole plants of Veratrum taliense. Their structures were elucidated on the basis of spectroscopic analysis, and the NMR data of veralkamine ( 4 ) are given for the first time. In addition, the cytotoxic activities of all isolated compounds, except for veramitaline, were tested.     

Dimerization and anion binding of a fluorescent phospholipid analogue

A diarylacetylene fluorophore featuring spatially separated urea and phosphocholine (PC) groups forms a macrocyclic "head-to-tail" dimer stabilized by NH(urea)···OP(PC) hydrogen bonds. At concentrations above ～2 × 10(-5) M in CH(2)Cl(2), the emission intensity of the dimer is quenched by HCO(3)(-) and H(2)PO(4)(-) but not by Cl(-) and NO(3)(-). Under more dilute conditions, all four anions are bound unselectively with association constants on the order of 10(5) M(-1).     

Preparation and evaluation of a mixed-bed immunoaffinity column for selective purification of sixteen sulfonamides in pork muscle

This paper describes the preparation of a novel mixed-bed immunoaffinity chromatography (IAC) column by coupling four monoclonal antibodies against different sulfonamides (SAs) to Sepharose 4B. The IAC column can be used to simultaneously extract and purify 16 SAs in pork muscle. The dynamic column capacities for all SAs in mixed standard solution were between 312 and 479 ng/mL gel. After simple extraction and IAC cleanup, the sample solution can be directly injected for liquid chromatography-ultraviolet analysis. The recoveries of SAs from spiked samples at levels of 25, 50 and 100 μg/kg ranged from 83.3 to 103.1% with variation coefficient less than 8.6%. The comparison of IAC with liquid-liquid extraction and solid phase extraction indicated that IAC has better purification effect and needs less organic solution than conventional methods, thus it would be an ideal method for selective purification of SAs in pork muscle.     

7-Deazapurine and 8-aza-7-deazapurine nucleoside and oligonucleotide pyrene "click" conjugates: synthesis, nucleobase controlled fluorescence quenching, and duplex stability

7-Deazapurine and 8-aza-7-deazapurine nucleosides related to dA and dG bearing 7-octadiynyl or 7-tripropargylamine side chains as well as corresponding oligonucleotides were synthesized. "Click" conjugation with 1-azidomethyl pyrene (10) resulted in fluorescent derivatives. Octadiynyl conjugates show only monomer fluorescence, while the proximal alignment of pyrene residues in the tripropargylamine derivatives causes excimer emission. 8-Aza-7-deazapurine pyrene "click" conjugates exhibit fluorescence emission much higher than that of 7-deazapurine derivatives. They are quenched by intramolecular charge transfer between the nucleobase and the dye. Oligonucleotide single strands decorated with two "double clicked" pyrenes show weak or no excimer fluorescence. However, when duplexes carry proximal pyrenes in complementary strands, strong excimer fluorescence is observed. A single replacement of a canonical nucleoside by a pyrene conjugate stabilizes the duplex substantially, most likely by stacking interactions: 6-12 °C for duplexes with a modified "adenine" base and 2-6 °C for a modified "guanine" base. The favorable photophysical properties of 8-aza-7-deazapurine pyrene conjugates improve the utility of pyrene fluorescence reporters in oligonucleotide sensing as these nucleoside conjugates are not affected by nucleobase induced quenching.