Electrochemical determination of adenine and adenosine: adsorption of adenine and adenosine at the pyrolytic graphite electrode

Adenine and adenosine are polarographically reducible from aqueous solution at pH 4.7 at the DME at the same E(1 2 ) and are also voltammetrically oxidizable at the PGE, but at different potentials, adenosine at higher potentials. Competitive adsorption of both compounds at the PGE results in a decrease in the scanning voltammetric oxidation peak of adenine in the presence of adenosine, reaching a constant value when the concentration of the latter is above 6 mM. In mixtures, the sum of the two is obtained by polarography at the DME. Solid adenosine is then added to the solution and the adenine is determined by voltamrnetry at the PGE.     

X-ray diffraction study of the structure of Al-Co melts

The structure of Al-Co melts with 0 at.%, 10 at.%, 18 at.%, 23.5 at.%, 26 at.%, 80.7 at.%, and 100 at.% Co has been studied by X-ray diffraction. Inverse Monte Carlo simulation using the experimental curves of the structural factor was employed to reconstruct the models of melts, analyzed by the Voronoi-Delaunay technique. The dependence of parameters that define short-and longer range ordering of atoms is nonmonotonous in the range 85–74 at.% Al and is extremal in the vicinity of a melt with 76.5 at.% Al. In the stated range of concentrations, the cobalt atoms basically lie at distances of ≈4.2 Å in the pentagonal rings of icosahedral type polytetrahedral clusters. Therefore one can speak about correlation in the character of atomic ordering in melts and corresponding periodic and quasiperiodic phases.     

Oxygen-independent inactivation of Haemophilus influenzae transforming DNA by monochromatic radiation: action spectrum, effect of histitine and repair.

Abstract— The action spectrum for the oxygen-independent inactivation of native transforming DNA from Haemophilus influenzae with near-UV radiation revealed a shoulder beginning at 334 and extending to 460 nm. The presence of 0.2 M histidine during irradiation produced a small increase in inactivation at 254, 290 and 313 nm, a large increase at 334 nm and a decrease in inactivation at 365, 405 and 460 nm. Photoreactivation did not reverse the DNA damage produced at pH 7.0 at 334, 365, 405 and 460 nm, but did reactivate the DNA after irradiation at 254, 290 and 313 nm. The inactivation of DNA irradiated at 254, 290 and 313 nm was considerably greater when the transforming ability was assayed in an excision-defective mutant compared with the wild type, although DNA irradiated at 334, 365, 405 and 460 nm showed smaller differences. These results suggest that the oxygen-independent inactivation of H. influenzae DNA at pH 7 by irradiation at 334, 365, 405 and 460 nm is caused by lesions other than pyrimidine dimers.     

碱性鲁米诺体系在玻碳和铂电极上的电位分辨电致化学发光研究

提出一种使用循环伏安（ＣＶ）扫描电位下的电致化学发光（ＥＣＬ）研究方法,在自制的仪器系统中同时进行ｉ－Ｅ和Ｉ－Ｅ测量,获得对应的ＣＶ和电位分辨的电致化学发光（ＰＲＥＣＬ）曲线。首先发现碱性鲁米诺体系在玻碳电极（ＧＣＥ）上呈现２个阳极发光峰（在０．３２Ｖ、０．３９Ｖｖｓ．Ａｇ）和１个阴极发光峰（在－０．６２Ｖ）,在Ｐｔ电极上呈现２个阳极发光峰（在０．４９Ｖ、０．７５Ｖ）。结合ＣＶ、一阶微分伏安、Ｃｌ     

Comparison of radiolysis of cyclopentane, 2,3-dimethylbutane,and neopentane at 4.2 K with that at 77 K as studied by analysis of dimer products

The γ-radiolysis of cyclopentane, 2,3-dimethylbutane, and neopentane at 4.2 K was compared with that at 77 K by analysis of dimer products with capillary gas chromatography. In the radiolysis of cyclopentane, the yield of bicyclopentyl dimer at 4.2 K is lower than that at 77 K. The difference of the yields at two temperatures was explained in terms of disproportionation reaction of cyclopentyl radicals at very low temperature. In the radiolysis of 2,3-dimethylbutane, the distribution of dimer products at 4.2 K is different from that at 77 K. The results is due to the effect of phase change between two temperatures. In the radiolysis of 2,3-dimethylbutane, the fraction of unsaturated dimers in all dimer products at 77 K is much larger than that at 4.2 K. The olefinic dimer-products at 77 K is related to favorable formation of olefinic cations at 77 K. In the radiolysis of solid neopentane, addition of helium gas promotes the formation of 2,2,3,3-tetramethylbutane by a non-radical process.     

A microcalorimetry and binding study on interaction of dodecyl trimethylammonium bromide with wigeon hemoglobin

The thermodynamic parameters for the binding of dodecyl trimethylammonium bromide (DTAB) with wigeon hemoglobin (Hb) in aqueous solution at various pH and 27 °C have been measured by equilibrium dialysis and titration microcalorimetry techniques. The Scatchard plots represent unusual features at neutral and alkaline pH and specific binding at acidic pH. This leads us to analyze the binding data by fitting the data to the Hill equation for multiclasses of binding sites. The best fit was obtained with the equation for one class at acidic pH and two classes at neutral and alkaline pH. The thermodynamic analysis of the binding process shows that the strength of binding at neutral pH is more than these at other pH values. This can be related to the more accessible hydrophobic surface area of wigeon hemoglobin at this pH. The endothermic enthalpy data which was measured by microcalorimetry confirms the binding data analysis and represents the more regular and stable structure of wigeon hemoglobin at neutral pH.     

Photoluminescence Properties of Silica Aerogel During Sintering Process

We report photoluminescence spectra measured for two series of silica aerogel sintered at 1000°C in different time intervals. In the photoluminescence spectra of nonsintered sample, bands at 1.8, 2.0 and 2.2 eV are identified. During sintering process, the bands at 1.8 and 2.0 eV decrease and vanish, while the band at 2.2 eV shows more complicated behavior. According to infrared spectra of the same samples we find that the photoluminescence band at 1.8 eV originates from nonbridged oxygen hole center defect, and that at 2.0 eV originates from silane in the gel network. Nonstoichiometric SiOx causes photoluminescence band at 2.2 eV.     

The teaching of Analytical Chemistry in Norway

Summary Training in Analytical-Chemistry at the University of Oslo, at the Oslo Technical College and at the School for Medical Technologists at Oslo University Hospital is briefly outlined.Presented at Euroanalysis III conference, Dublin, August 20–25, 1978     

Cathodic stripping voltammetric determination at a hanging mercury drop electrode of the environmental heavy metal precipitant trimercapto-s-triazine (TMT)

Trimercapto-s-triazine (TMT) is available commercially for precipitating heavy metals in effluents prior to discharge and for recovering silver and copper. The TMT content of an effluent for discharge is normally monitored down to about 2 ppm by means of its UV absorption at 285 nm. Indirect cathodic-stripping voltammetric methods of determining TMT at sub-ppb levels in standard solutions are reported here. These methods might prove suitable for the determination of TMT in effluent at levels lower than is currently possible. TMT can be accumulated and determined indirectly at pH 9.0 as its mercury salt down to sub-ppb levels. Accumulation is made at 0 V and the mercury TMT reduction peak is at -0.47 V. Alternatively, by adding nickel(II), TMT can be determined optimally at pH 7.8, using the catalytic nickel peak at -0.73 V and accumulating between -0.10 and -0.60 V: at this pH the HgTMT peak at -0.47 V is small. At slightly higher pH (pH 8.6) the nickel TMT complex can be accumulated directly at -0.40 V, but at this pH, however, a slightly increased sensitivity can be achieved by accumulating TMT as its mercury salt, at -0.1 V in the presence of nickel(II), the nickel TMT complex being formed during the potential sweep on the release of the TMT when the mercury salt is reduced. Unlike many other thiols TMT is not accumulated as its copper(I) salt on addition of copper(II) to the solution.     

原位拉曼技术研究Mo催化剂的还原和硫化

运用原位激光拉曼技术研究了Mo/Al_2O_3和Mo/TiO_2-Al_2O_3催化剂的氢还原和硫化行为．结果清楚显示，两种载体上不同配位形态的Mo物种的氢还原能力有明显差异，其硫化性能也不相同．TiO_2对Al_2O_3表面的复盖可显著促进Mo物种的还原和硫化。     

Raman spectroscopy of likasite at 298 and 77 K

Raman spectroscopy at 298 and 77K has been used to study the structure of likasite, a naturally occurring basic copper(II) nitrate of formula Cu3NO3(OH)5.2H2O. An intense sharp band is observed at 3522 cm(-1) at 298 K which splits into two bands at 3522 and 3505 cm(-1) at 77 K and is assigned to the OH stretching mode. The two OH stretching bands at 3522 and 3505 provide estimates of the hydrogen bond distances of these units as 2.9315 and 2.9028 angstroms. The significance of this result is that equivalent OH units in the 298 K spectrum become two non-equivalent OH units at 77 K suggesting a structural change by cooling to liquid nitrogen temperature. A number of broad bands are observed in the 298 K spectrum at 3452, 3338, 3281 and 3040 cm(-1) assigned to H2O stretching vibrations with estimates of the hydrogen bond distances of 2.8231, 2.7639, 2.7358 and 2.6436 angstroms. Three sharp bands are observed at 77 K at 1052, 1050 and 1048 cm(-1) attributed to the nu1 symmetric stretching mode of the NO3 units. Only a single band at 1050 cm(-1) is observed at 298 K, suggesting the non-equivalence of the NO3 units at 77 K, confirming structural changes in likasite by cooling to 77 K.     

VUV/SOFT-X-RAY SPECTROSCOPIC FACILITIES AT THE SYNCHROTRON RADIATION LABORATORIES IN JAPAN

The present status is described of the vacuum ultraviolet/soft-X-ray spectroscopic facilities at the synchrotron radiation laboratories in Japan. An overview is presented of the spectroscopic instruments available and under development at the SOR-RING at the Institute for Solid State Physics, University of Tokyo, the Photon Factory-ring at the National Laboratory for High Energy Physics, the UVSOR at the Institute for Molecular Science, and the TERAS at the Electrotcchnical Laboratory. Emphasis is placed upon the unique features of the instruments developed in Japan.     

Notable shift of ultraviolet intensity on Sn-doped ZnO nanostructure fabricated by sol–gel method

Sn-doped ZnO (SZO) thin films are deposited by sol–gel dip-coating method with Sn content at 0 at.% and 1–15 at.% with an increment of 2 at.%. The structure and luminescence of the films are investigated. X-ray diffraction results indicate that all the SZO samples show preferential orientation along the (002) direction, and the scanning electron microscope exhibits that the surface morphology of the films change from nanoparticles to nanorods with increasing Sn concentration. X-ray photoelectron spectroscopy reveals that Sn exists as valence of +4 in the matrix. The photoluminescence peaks at 381 and 398 nm are observed in all the samples. The ratio of intensity of peak at 381 nm to that of peak at 398 nm differed markedly. The intensity of peak at 398 nm might be due to the response for the Sn atoms, while the intensity of peak at 381 nm is probably related to the quantum size effect.     

Adsorption behaviour of lactoferrin in oil-in-water emulsions as influenced by interactions with beta-lactoglobulin

Oil-in-water emulsions (pH 7.0 or pH 3.0) containing 30 wt% soya oil and various concentrations of lactoferrin were made in a two-stage valve homogenizer. The average droplet size (d32), the surface protein coverage (mg/m2) and composition, and the zeta-potential of the emulsions were determined. The value of d32 decreased with increasing lactoferrin concentration up to 1%, and then was almost independent of lactoferrin concentration beyond 1% at both pH 7.0 and pH 3.0. The surface protein coverage of the emulsions made at pH 7.0 increased almost linearly with increasing lactoferrin concentration from 0.3 to 3%, but increased only slightly in emulsions made at pH 3.0 at lactoferrin concentrations >1%. The surface protein coverage of the emulsions made at pH 3.0 was lower than that of the emulsions made at pH 7.0 at a given protein concentration. The emulsion droplets had a strong positive charge at both pH 7.0 and pH 3.0, indicating that stable cationic emulsion droplets could be formed by lactoferrin alone. When emulsions were formed with a mixture of lactoferrin and beta-lactoglobulin (beta-lg) (1:1 by weight), the charge of the emulsion droplets was neutralized at pH 7.0 suggesting the formation of electrostatic complexes between the two proteins. The composition of the droplet surface layer showed that both proteins were adsorbed, presumably as complexes, from the aqueous phase at pH 7.0 in equal proportions, whereas competitive adsorption occurred between lactoferrin and beta-lg at pH 3.0. At this pH, beta-lg was adsorbed in preference to lactoferrin at low protein concentrations (1%), whereas lactoferrin appeared to be adsorbed in preference to beta-lg at high protein concentrations.     

现场热引发聚丙烯酸酯类电解质的性能及应用

应用热引发现场聚合方法制备聚丙烯酸酯类电解质,并考察其电化学性能.实验表明:该聚合物电解质具有 4. 5V的电化学稳定窗口,较高的室温电导率及良好的低温性能.当前驱体电解液中液态电解质含量为 85%时,其室温电导率为 3. 2×10-3S·cm-1, -30℃下的电导率达到 5. 6×10-4 S·cm-1.采用现场聚合技术制备的聚合物电池,其电化学性能与液态锂离子电池基本一致,首次充放电效率为 92. 1%, 1. 0C率放电容量为 0. 2C率的 95%, -20℃下的放电容量为室温容量的 72%,以 0. 5C率循环 300周后,仍保持初始容量的 85%以上.     

Theoretical study of the stability of lithium atoms in alpha-rhombohedral boron

The stability of lithium atoms in alpha-rhombohedral boron was investigated by first-principles calculations of total energies and molecular dynamics (MD) simulations. In the case of a low concentration (1.03 at. %), Li at the center of the icosahedral B12 site (the I-site) had a negative binding energy, which suggests Li at the I-site is unstable. However, MD simulations at temperatures below 750 K indicated that Li is still confined in the B12 cage under these conditions, which means Li at the I-site is metastable. Over 800 K, Li began to move away from the B12 site and settled at the tetrahedral site (the T-site) or at the octahedral site (the O-site). Li at the T-site also had a negative binding energy, but MD simulations indicated it was metastable up to 1400 K and did not move to other sites. Li at the O-site was energetically the most favorable, having a positive binding energy. In the case of a high concentration (7.69 at. %), the I-site changed to an unstable saddle point. At this concentration, the T-site was metastable and the O-site became the most stable. In MD simulations at 1400 K, Li atoms at the O-site never jumped to other sites regardless of concentration. Considering these facts, the diffusion coefficient of Li in alpha-rhombohedral boron would have to be very small below 1400 K.     

电滴定分析的新方法

利用示波极谱图上切口的出现或消失来指示滴定终点的示波极谱滴定法具有终点直观、操作简便和抗干扰能力强等优点。但该法要求试剂(滴定剂、被滴物或指示剂)能在示波极谱图上产生敏锐切口才能应用。     

Fluorescence studies of selected 2-alkylaminopyrimidines

The reactions of 2-chloropyrimidine with methylamine, ethylamine and piperidine gave the corresponding 2-N-methylamino-, 2-N-ethylamino- and 2N- piperidinopyrimidines, respectively. The fluorescence properties of these alkylamino derivatives in chloroform, ethyl acetate, carbon tetrachloride, acetone, ether, ethanol and methanol were studied. All the alkylamino derivatives showed the highest fluorescence intensity in polar protic solvents; thus 2-N-methylaminopyrimidine (highest fluorescence intensity at 377 nm when excited at 282 nm) and 2-N-ethylaminopyrimidine (highest fluorescence intensity at 375 nm, when excited at 286 nm) showed the highest fluorescence in methanol. In ethanol, 2-N-piperidinopyrimidine showed a fluorescence peak at 403 nm when excited at 360 nm and in chloroform it fluoresced at 392 nm when excited at 356 nm.     

Melt–gas phase equilibria and state diagrams of the selenium–tellurium system

The partial pressures of saturated vapor of the components in the Se–Te system are determined and presented in the form of temperature–concentration dependences from which the boundaries of the melt–gas phase transition are calculated at atmospheric pressure and vacuums of 2000 and 100 Pa. The existence of azeotropic mixtures is revealed. It is found that the points of inseparably boiling melts correspond to 7.5 at % of Se and 995°C at 101325 Pa, 10.9 at % at 673°C and 19.5 at % at 522°C in vacuums of 2000 and 100 Pa, respectively. A complete state diagram is constructed, including the fields of gas-liquid equilibria at atmospheric and low pressures, the boundaries of which allow us to assess the behavior of selenium and tellurium upon distillation fractionation.