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1.
The results of the radiolysis of aqueous solutions of thiamine (vitamin B 1) are presented. The yields for decomposition of thiamine and the product of radiolytic products were determined. The G values decrease as the dose increases. Some radiolytic products were identified. Decomposition of thiamine was slightly dependent on the presence of oxygen and on the pH of the solution. At pH 4.4 with a concentration of 2.5 × 10 −4 mol L −1 of thiamine in an oxygen free aqueous solution, the G 0 value for decomposition is 5.0. 相似文献
2.
Vitamin A,dissolved in liquid paraffin, is stable below room temperature, but suffers oxidative decomposition at 80°, giving its epoxide as the main product. The rate of decomposition of vitamin A (V A) at 80° in the presence of oxygen (partial pressure of p) and a small amount of cobaltous stearate (Co) is expressed as: d[V A]/d t = 3·15 × 10 −1:[V A][Co] p1·48 + 1·51 × 10 −5[V A] p0·33 + 0·33 × 10 −5[V A], where the last term represents the spontaneous thermal decomposition. 相似文献
3.
The acidity constants of benzidine (Bz) in aqueous solutions determined potentiometrically at 25° were Ka1 = (1.11 ± 0.08) × 10 −5, Ka2 = (1.45 ± 0.12) × 10 −4. The apparent mixed constants in 0.1 M sodium nitrate are Ka1 = (5.37 ± 0.28) × 10 −6 and Ka2 = (1.14 ± 0.09) × 10 −4. The ultraviolet spectra were recorded as a function of pH and analysed with these constants to obtain the absorption spectra of H 2Bz 2+, HBz + and Bz; the corresponding wavelengths of maximal absorption are 247, 273 and 278 nm, and molar absorptivities 1.63 × 10 4, 1.76 × 10 4 and 2.26 × 10 4 1.mole −1.cm −1. 相似文献
4.
Gamma irradiation of aerated aqueous solutions of ammonia leads to the formation of nitrite as a radiolytic product. Its yield increases with increasing concentration of NH 3 as well as O 2. OH radicals react with NH 3 to give NH 2 radicals, which in the presence of O 2 form NH 2O 2 radicals. These radicals finally lead to the formation of nitrite. G(NO 2−) decreases with increasing radiation dose due to secondary reactions. Its initial yield, however, is more than 1/2 GOH, while hydrogen peroxide yield is less than the expected value viz. G(H 2O 2) + 1/2 G(e aq−), indicating its participation in reactions with radiation produced free radicals. G(H 2) is 0.35 in aerated aqueous solutions of 10 −3 mol dm −3 NH 3 and 0.23 in the absence of oxygen. Implications of these results to the use of NH 3 in primary coolant water of pressurized water nuclear power reactors of the VVER type are discussed. 相似文献
5.
Electrical and electrokinetic phenomena (electrical resistance, streaming potential and membrane potential) in a porous polysulfone membrane was studied in the framework of the linear thermodynamics of irreversible processes and the phenomenological coefficients were determined for different concentrations of NaCl and MgCl 2 solutions (10 −3M<5×10 −2M). From experimental values, other characteristic membrane parameters such as the concentration of fixed charge in the membrane ( =−3×10−3M), the ionic transport numbers and permeabilities through the membrane (t(Na+)=0.392 and t(Mg+2)=0.363; P(Na+)=3.5×l0−8m/sec and P(Mg+2)=2.9×10−8m/sec) were also obtained. Membrane surface-electrolyte solution interface was characterized by zeta potential values. The effect of both salt concentration and pH on zeta potential results was also studied. 相似文献
6.
Using pulse radiolysis and steady state γ-radiolysis in combination with product analysis by HPLC the radiolytic degradation mechanism of 4-chloroanisole (4-ClAn) has been elucidated. Pulse radiolysis experiments show that OH radicals react in neutral aqueous N 2O saturated solutions with 4-ClAn by addition to all aromatic ring positions to yield hydroxycyclohexadienyl radicals (OH-adducts), k(OH + 4-ClAn) = 6.5 × 10 9dm 3mol −1s −1. Those OH-adducts formed on ipso positions of the molecule subsequently undergo HCl or CH 3OH elimination forming methoxyphenoxyl- and chlorophenoxyl radicals. Their yield corresponds to 20% of the OH-radicals, whereby the distribution is roughly 3:1 in favor of the methoxyphenoxyl radicals, which reflects the stronger ortho-, para-directing activity of the methoxy group. The OH-adducts decay second order, 2 k = 1 × 10 9dm 3mol −1s −1. The presence of oxygen leads to its addition on the hydroxycyclohexadienyl radicals, k(OH-adduct + O 2) = 3.2 × 10 8dm 3mol −1s −1. In airfree solution the reaction of H-atom with the substrate, k(H + 4-ClAn) = 1.2 × 10 9dm 3mol −1s −1, results in H-adducts which decay in bimolecular reactions, 2 k = 8.2 × 10 8dm 3mol −1s −1. The rate constant for the reaction of the solvated electrons has been determined to k(e aq− + 4-ClAn) = 2 × 10 9dm 3mol −1s −1. The absorption spectra of H- and OH-adducts were measured in the range of 280–450 nm. The products analysed by HPLC after γ-radiolysis in dependence of dose (100–600 Gy) are given for N 2O-, air-, oxygen- and argon saturated neutral aqueous solutions. In conditions favoring the OH radical oxidation 4-chlorophenol, 4-methoxyphenol, 5-chloro-2-methoxyphenol and 2-chloro-5-methoxyphenol were determined as final products. In the presence of Ar, where about equal amounts of OH and e aq− are present, additionally anisole could be detected. Under both reaction conditions the amount of identified products is about 20% of decomposed 4-ClAn. The reaction of e aq− leads to reductive dechlorination which corresponds quantitatively to the degradation of the substrate. In the presence of air or solutions saturated with pure oxygen predominantly hydroquinone, 4-chlorophenol and muconic acids are formed and the material balance is 50%. The efficient dechlorination (60% of the decomposed 4-ClAn) as well as ring fragmentation products as intermediates en route to complete mineralization in oxygenated solution indicate that high energy radiation is a promising method for degradation of halogenated aromatic compounds in water. Variation of dose rates from 79 Gy min −1 to 266 Gy min −1 did not show any influence on the product distribution. 相似文献
7.
By designing a novel flow-through electrolytic cell (FEC), bromine was produced near to the surface of the platinum electrode by electrochemical oxidation of acidic KBr. The fast and weak chemiluminescence signal produced by the chemical reaction of the electrogenerated bromine with H 2O 2 was greatly enhanced by tetracyclines Based on these observations, a new, sensitive and simple electrogenerated chemiluminescence (ECL) method for the determination of tetracyclines was developed. Under the optimum experimental conditions, the calibration graphs are linear over the range 3.0×10 −8 to 5.0×10 −5 g ml −1 for tetracycline, 2.0×10 −7 to 2.4×10 −5 g ml −1 for oxytetracycline and 1.0×10 −7 to 5.0×10 −5 g ml −1 for chlortetracycline. The limits of detection ( S/ N=3) are 1.0×10 −8 g ml −1 for tetracycline, 7.0×10 −8 g ml −1 for oxytetracycline and 1.5×10 −7 g ml −1 for chlortetracycline. For the determination 5.0×10 −7 g ml −1 tetracycline, the relative standard deviation was <5%. The proposed method was used to determine tetracyclines in pharmaceutical formulations. 相似文献
8.
A novel copper(II) thiocyanate complex [Cu(im) 2(NCS) 2] 1 (im=imidazole) has been prepared and characterized by spectroscopic analysis and crystallographic method. This supramolecular compound exhibits a three-dimensional solid state structure constituted by N–HS hydrogen bonds and π–π stacking interactions. The compound in DMF solutions has a very strong third-order non-linear optical (NLO) behavior with absorption coefficient and refractive index 2=1.18×10 −11 mw −1, n2=−9.00×10 −16 m 2w −1, respectively, and third-order NLO susceptibility χ (3) of 7.00×10 −10 esu. 相似文献
9.
To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τ p=3 × 10 −13 s, fp = 0.5 Hz, Ep = 1.1 × 10 −3J cm −2, Iav = 5.5 × 10 −4 W cm −2, Ip = 10 9 W cm −2) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm −2). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10 3 lower for pulsed radiation than for CW radiation (3.3 × 10 −1 and 7.8 × 10 2 J cm −2 respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components. 相似文献
10.
Rate constants for the reactions of OH with CH 3CN, CH 3CH 2CN and CH 2=CH-CN have been measured to be 5.86 × 10 −13 exp(−1500 ± 250 cal mole −1/ RT), 2.69 × 10 −13 exp(−1590 ± 350 cal mole −1/ RT and 4.04 × 10 −12 cm 3 molecule −1 s −1, respectively in the temperature range 298–424 K. These results are discussed in terms of the atmospheric lifetimes of nitrfles. 相似文献
11.
Trans-1,2-cyclohexanediaminetetra-acetic acid (DCTA) chelates of bismuth(III), iron(III) and copper(II) have been separated by two techniques using reversed-phase paired-ion chromatography. In one, the chelates in aqueous solution were separated within 20 min on a 6.0 × 300 mm ERC-ODS column with 10 −2M tetrabutylammonium ion (TBA +) in methanoi-water mixture (45:55 v/ v) as eluent. In the other, the metal ions in aqueous solution were separated within 10 min by direct injection into an ERC-ODS column with 10 −2M TBA +/10 −3M DCTA in methanoi-water mixture (40:60 v/ v) as eluent. 相似文献
12.
The reaction: F + HCl→ HF ( v 3) + Cl (1), has been initiated by photolysing F 2 using the fourth-harmonic output at 266 nm from a repetitively pulsed Nd: YAG laser By analysing the time-dependence of the HF(3,0) vibrational chemiluminescence, rate constants have been determined at (296 ± 5) K for reaction (1), k1 = (7.0 ± 0.5) × 10 −12 cm 3 molecule −1 s −1, and for the relaxation of HF( v = 3) by HCl, CO 2, N 2O, CO, N 2 and O 2: kHCl = (1.18 ±0.14) × 10 −11 kCO2 = (1.04 ± 0. 13) × 10 −12, kN2O = (1.41 ± 0.13) × 10 −11 kCO = (2.9 ± 0.3) × (10 −12, kN2 = (7.1 ± 0.6) × 10 −14 and kO2 = (1.9 ± 0.6) × 10 −14 cm 3molecule −1s −1. 相似文献
13.
The solubility products of mercury(II) and lead(II) dodecylbenzenesulfonates were calculated on the basis of light scattering measurements at 20°C to be (9.33 ± 0.90) × 10 −13 and (1.03 ± 0.10) × 10 −12 respectively. The investigations of precipitation phenomena performed in diluted natural sea-water ([Cl −] = 10 −12 mol dm −3), including tenside and added heavy metal ions, showed similar behaviour for all metal dodecylbenzenesulfonates investigated in this work, i.e. the synergistic effect of tenside, of added electrolyte, and of cations and anions from sea-water. A comparison made by a statistical test of significance, chosen to measure agreement between the estimates of the solubility constants obtained in aqueous solutions and in the above mentioned sea-water solution, showed a noticeable effect, evident particularly in the case of mercury(II). The precipitation of tenside and metal nitrates in natural sea-water ([Cl −] = 5 × 10 −1 mol dm −3) covers a wide concentration region of dodecylbenzenesulfonic acid (from high concentrations to 5 × 10 −6 mol dm −3) and from high metal nitrate concentrations to very low. The microscopic textures of phases precipitated in the systems with sea-water obviously confirmed favouring formation of the liquid crystalline phase. 相似文献
14.
The polarographic reduction of lead in the presence of selenite gives rise to an additional peak corresponding to the reduction of lead (Pb) on adsorbed selenium (Se) on mercury at −0.33 V. The selenium and lead content can be determined using this peak by the addition of a known amount of one of these ions first and then the second ion. The linear domain range of lead is 5.0×10 −7–2.0×10 −5 M and for selenium 5.0×10 −7–1.0×10 −5 M. Using this method 4.90×10 −7 M Se(IV) and 1.47×10 −6 M Pb(II) in a synthetic sample could be determined with a relative error of +2.0% and 1.8%, respectively ( n=4). A recovery test after acid digestion for a synthetic sample was 97% for selenium and 96.5% for lead. The method was applied to 1 ml of digested blood, and 328±23 μg l −1 Se(IV) and 850±62 μg l −1 Pb(II) could be determined with a 90% ( n=5) confidence interval. 相似文献
15.
Pulse radiolysis of epicatechin in aqueous solution has been done to investigate the reactions of epicatechin derived phenoxy radical (EpO) at neutral pH. EpO was generated by N 3 reacting toward EpOH, the rate constant was measured to be 3 × 10 8 dm 3 mol −1 s −1. The biomolecular termination of EpO is rather slow ((2 k < × 10 6 dm 3 mol −1 s −1) and results in products exhibiting strong visible absorption around 450 nm. No reactions have been observed for EpO with O 2 and O 2 in the time scale of pulse radiolysis (0.01 s), suggesting the bimolecular rate constant are less than 10 4 and 5 × 10 6 dm 3 mol −1 s −1, respectively. 相似文献
16.
The second-order rate constants of gas-phase Lu( 2D 3/2) with O 2, N 2O and CO 2 from 348 to 573 K are reported. In all cases, the reactions are relatively fast with small barriers. The disappearance rates are independent of total pressure indicating bimolecular abstraction processes. The bimolecular rate constants (in molecule −1 cm 3 s −1) are described in Arrhenius form by k(O 2)=(2.3±0.4)×10 −10exp(−3.1±0.7 kJmol −1/ RT), k(N 2O)=(2.2±0.4)×10 −10exp(−7.1±0.8 kJmol −1/ RT), k(CO 2)=(2.0±0.6)×10 −10exp(−7.6±1.3 kJmol −1/ RT), where the uncertainties are ±2σ. 相似文献
17.
The anodization of mercury microelectrodes was investigated in synthetic samples containing several strong and weak electrolytes at different concentrations. In particular, the effects on mercury anodization due to the presence of NaOH, HClO 4, NaCl, NaI, NaF, Na 2SO 4, NaHCO 3, Na 2CO 3, tartaric and citric acids, were studied in solutions containing either each species or mixtures of them, and without addition of supporting electrolyte. Some of the electrode processes studied led to linear calibration plots e.g. 1 × 10 −5 − 1 × 10 −4M Cl−, 1 × 10 −6 − 1 × 10 −5M I−, 5 × 10 −4 − 3 × 10 −3M SO42−, 5 × 10 −4 − 2 × 10 −2M HCO3−, with typical correlation coefficients of 0.998–0.999. The anodization of mercury microelectrodes was also investigated directly in wine, rain, tap and mineral water, without pretreatment and without addition of supporting electrolyte. In the real samples only the ions Cl − and HCO 3− could be quantified, and the values found were in agreement, within 3–5%, with the reference values obtained by using Italian standard methods for food. 相似文献
18.
A new spectrophotometric flow-injection (FI) method is proposed for the determination of glucose based on the redox reaction of hydroquinone with iron(III). When a glucose solution containing quinone is passed through the immobilized glucose oxidase column introduced in FI system, quinone is reduced to hydroquinone by glucose. In the presence of 1,10-phenanthroline (phen), iron(III) is then quantitatively reduced by hydroquinone to iron(II) followed by the formation of iron(II)-phen complex ( λmax=510 nm). An FI peak observed at 510 nm corresponds to the concentration of glucose. The wide dynamic range for glucose was obtained in the range of 1×10 −6–1×10 −3 mol l −1 at a sampling rate of 24 h −1 and the detection limit (S/N=3) was 5×10 −7 mol l −1. Relative standard deviations were 0.78, 0.44 and 0.23% ( n=5) for 5×10 −6, 5×10 −5 and 5×10 −4 mol l −1 of glucose, respectively. The proposed method was successfully applied to the determination of glucose in control blood sera, human blood plasma and wine. 相似文献
19.
At 25°C, I = 1.0 M (CF 3SO 3−Li ++CF 3SO 3H), [H +] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H 2O), 63+ by bromine was found to be: −d/[Br 2] T/d t= kK/[Br 2][Ti III]/[H +]+ K+ kK/[Br 3−][Ti III]/[H ++ K, where k = 9.2 × 10 −3 M −1 s −1 and K = 4.5 × 10 −3 M. At [H +] = 1.0 M, [Br −] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br −] increases. The pH-dependence of the oxidation of TiIII-edta by bromine is interpreted in terms of the change in identity of the TiIII-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k0edta)2 weighting into an equation of the form: k0edta =k1+k2K1[H+]−1+k3K1K2[H+]−2/1+K1[H+[H+−1+K1K2[H+]−2, with K1 and K2 fixed as earlier determined at 9.55 × 10−3 and 2.29 × 10−9 M, respectively, for the oxidation of bromine. k1=k2=(3.1±0.32)×103M−1s−1 k3=(2.3±0.45)×106N−1s−1. It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br2.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for TiIII-edta+TiIV-edta is estimated at 32 M−1 s−1. 相似文献
20.
Two novel uranyl PVC matrix membrane sensors responsive to uranyl ion are described. The first sensor incorporates tris(2-ethylhexyl)phosphate (TEHP) as both electroactive material and plasticizer and sodium tetraphenylborate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response for UO 22+ ions over the concentration range 1×10 −1–2×10 −5 mol l −1 UO 22+ with a cationic slope of 25.0±0.2 mV decade −1. The working pH range is 2.8–3.6 and the life span is 4 weeks. The second sensor contains O-(1,2-dihydro-2-oxo-1-pyridyl)- N, N, N′, N′-bis(tetra-methylene)uronium hexafluorophosphate (TPTU) as a sensing material, sodium tetraphenylborate as an ion discriminator and dioctyl phenylphosphonate (DOPP) as a plasticizer. Linear and stable response for 1×10 −1–5×10 −5 mol l −1 UO 22+ with near-Nernstian slope of 27.5±0.2 mV decade −1 are obtained. The working pH range is 2.5–3.5 and the life span of the sensor is 6 weeks. Interference from many inorganic cations is negligible for both sensors. However, interference caused by some ions (e.g. Th 4+, Cu 2+, Fe 3+) is eliminated by a prior ion exchange or solvent extraction step. Direct potentiometric determination of as little as 5 μg ml −1 uranium in aqueous solutions shows an average recovery of 97.2±1.3%. Application for the determination of uranium at levels of 0.01–1 wt.% in naturally occurring and certified ores gives results with good correlation with data obtained by X-ray fluorescence. 相似文献
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