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1.
The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95–99% as Y 4− anion) precipitates with Ag + cations to form the Ag 4Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y 4− to form a complex, AgY 3−. Equilibrium studies at 25°C and ionic strength 0.50 M (NaNO 3) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) β 1 = (1.93 ± 0.07) × 10 5 M −1 and the solubility products are KS0 = [Ag +] 4[Y 4−] = (9.0 ± 0.4) × 10 −18 M 5 and KS1 = [Ag +] 3[AgY 3−] = (1.74 ± 0.08) × 10 −12 M4. The presence of Na +, rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: β 1 = (1.19 ± 0.03) × 10 6 M −1, KS0 = (1.6 ± 0.4) × 10 −19 M 5 and KS1 = (1.9 ± 0.5) × 10 −13 M 4; at ionic strength tending to zero; β 1 = (1.82 ± 0.05) × 10 7 M −1, KS0 = (2.6 ± 0.8) × 10 −22 M 5 and KS1 = (5 ± 1) × 10 −15 M 4. The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO 3. Well-defined potentiometric titration curves can be taken in the range 1–2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142°C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135–157°C), tending to pure silver at 600°C, consistent with the original Ag 4Y salt. 相似文献
2.
The collisional quenching of electronically excited germanium atoms, Ge[4p 2( 1S 0)], 2.029 eV above the 4p 2( 3P 0) ground state, has been investigated by time-resolved atomic resonance absorption spectroscopy in the ultraviolet at λ = 274.04 nm [4d( 1P 10) ← 4p 2( 1S 0)]. In contrast to previous investigations using the ‘single-shot mode’ at high energy, Ge( 1S 0) has been generated by the repetitive pulsed irradiation of Ge(CH 3) 4 in the presence of excess helium gas and added gases in a slow flow system, kinetically equivalent to a static system. This technique was originally developed for the study of Ge[4p 2( 1D 2)] which had eluded direct quantitative kinetic study until recently. Absolute second-order rate constants obtained using signal averaging techniques from data capture of total digitised atomic decay profiles are reported for the removal of Ge( 1S 0) with the following gases ( kR in cm 3 molecule −1 s −1, 300 K): Xe, 7.1 ± 0.4 × 10 −13; N 2, 4.7 ± 0.6 × 10 −12; O 2, 3.6 ± 0.9 × 10 −11; NO, 1.5 ± 0.3 × 10 −11; CO, 3.4 ± 0.5 × 10 −12; N 2O, 4.5 ± 0.5 × 10 −12; CO 2, 1.1 ± 0.3 × 10 −11; CH 4, 1.7 ± 0.2 × 10 −11; CF 4, 4.8 ± 0.3 × 10 −12; SF 6, 9.5 ± 1.0 × 10 −13; C 2H 4, 3.3 ± 0.1 × 10 −10; C 2H 2, 2.9 ± 0.2 × 10 −10; Ge(CH 3) 4, 5.4 ± 0.2 × 10 −11. The results are compared with previous data for Ge( 1S 0) derived in the single-shot mode where there is general agreement though with some exceptions which are discussed. The present data are also compared with analogous quenching rate data for the collisional removal of the lower lying Ge[4p 2( 1D 2)] state (0.883 eV), also characterized by signal averaging methods similar to that described here. 相似文献
3.
UV spectra and kinetics for the reactions of alkyl and alkylperoxy radicals from methyl tert-butyl ether (MTBE) were studied in 1 atm of SF 6 by the pulse radiolysis-UV absorption technique. UV spectra for the radical mixtures were quantified from 215 to 340 nm. At 240 nm. σ R = (2.6 ± 0.4) × 10 −18 cm 2 molecule −1 and σ RO2 = (4.1 ± 0.6) × 10 −18 cm 2 molecule −1 (base e). The rate constant for the self-reaction of the alkyl radicals is (2.5 ± 1.1) × 10 −11 cm 3 molecule −1 s −1. The rate constants for reaction of the alkyl radicals with molecular oxygen and the alkylperoxy radicals with NO and NO 2 are (9.1 ± 1.5) × 10 −13, (4.3 ± 1.6) × 10 −12 and (1.2 ± 0.3) × 10 −11 cm 3 molecule −1 s −1, respectively. The rate constants given above refer to reaction at the tert-butyl side of the molecule. 相似文献
4.
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
5.
Formation constants for recrystallized thymol blue were determined in water, using the SQUAD and SUPERQUAD programs. The best model correlating spectrophotometric, potentiometric and conductimetric data was fitted with the dissociation of HL −=L 2−+H +−log K=8.918±0.070 and H 3L 2−=2L 2−+3H +−log K=29.806±0.133 with the SUPERQUAD program at variable low ionic strength (1.5×10 −4–3.0×10 −4 M); and HL=L 2−+H +−log K=8.9±0.000, H 3L 2− =2L 2−+3H +−log K=30.730±0.032, H 4L 2=2L 2−+4H +−log K=32.106±0.033 with SQUAD at 1.1 M ionic strength. 相似文献
6.
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
7.
A UV spectrometric method was developed to determine the molar absorptivity ( C) and formation constant ( Kc) of the association complex of unsubstituted chalcone in cyclohexane, in the concentration range from 4.00·10 −4 to 2.00·10 −2 mol dm −3. The thermodynamic and spectroscopic magnitudes such as Kc and C contribute to the understanding of the physicochemical behavior of several , β-unsaturated carbonylic compounds, of low solubility in water, as it is the case of numerous flavonoids of chemical and biological importance. The studied association complex, formed by two chalcone molecules, is characterized by the constants C (300.8 nm)=4.98·10 4 dm 3 mol −1 cm −1 and Kc=5.58·10 3. The method proposed is convenient for the study of solute–solute molecular associations particularly those due to dipole–dipole interactions. 相似文献
8.
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
9.
The far-UV (193 nm) laser flash photolysis of nitrogen-saturated isooctane solutions of 1,1-dimethylsiletane allows the direct detection of 1,1-dimethylsilene as a transient species, which (at low laser intensities) decays with pseudo-first-order kinetics (τ 10 μs) and exhibits a UV absorption spectrum with λ max 255 nm. Characteristic rapid quenching is observed for the silene with methanol ( kMcOH = (4.9 ± 0.2) × 10 9 M −1 s −1), tert-butanol ( kBuOH = (1.8 ± 0.1) × 10 9 M −1 s −1) and oxygen ( kO2 = (2.0 ± 0.5) × 10 8 M −1 s −1). The Arrhenius activation parameters for the reaction with methanol have been determined to be Ea = −2.6 ± 0.6 kcal mol −1 and log A = 7.7 ± 0.3. 相似文献
10.
The singlet exciton quenchings due to SS and ST interactions in crystalline anthracene have been separated by considering the kinetics of the two interactions. The corresponding rate constants are γSS = (1 ± 0.5) × 10 −8 and γST = (f ± 3) × 10 −9 cm 3 sec −1. 相似文献
11.
Derivative photometric methods for trace analysis of Th(IV) and UO 2(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO 2(II) complexes at their λ max, 614.5 nm and 637.0 nm are, 1.19 × 10 4 1/mol/cm and 1.12 × 10 4 1/mol/cm and 1.95 × 10 −2 μg/cm 2 and 2.13 × 10 −2 μg/cm 2 μg/cm 2, respectively. Calibration graph is linear over the range 9.28 × 10 −2−18.56 μg/ml of Th(IV) and 9.52 × 10 −2−19.04 μg/ml of UO 2(II). Though presence of Th(IV) and UO 2(II) causes interference in each others determination, 9.28 × 10 −1−9.28 μg/ml Th(IV) and 9.52 × 10 −1−9.52 μg/ml UO 2(II) when present together, can be simultaneously determined using derivative spectra. 相似文献
12.
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
13.
The 183.038 nm resonance absorption transition of I( 2P 3/2) has been studied using a flash photolysis set-up for gas-phase chemistry and a radio frequency powered electrodeless discharge lamp filled with iodine. The dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume was measured. The optimum iodine partial pressure, with self-absorption minimized and acceptable intensity, is determined to be approximately 2.5×10 −3 mbar. A method is described to estimate the temperature of the emitting atoms using direct measurements of relative absorption at different absorber concentrations. This yields an emission temperature of 923±50 K. Using this temperature, the oscillator strength for the I( 2P 3/2) transition at 183.038 nm is determined to be f=(3.87±0.57)×10 −3, corresponding to an absorption cross-section at the center of the line of σ=(5.42±0.8)×10 −14 cm 2 atom −1. This shows a difference from one of two earlier measurements, but is close to the other. The remaining difference from the latter measurement is probably due to tendencies of opposite biases inherent to the experiments. 相似文献
14.
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
15.
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
16.
Nest-shaped cluster [MoOICu 3S 3(2,2′-bipy) 2] (1) was synthesized by the treatment of (NH 4) 2MoS 4, CuI, ( n-Bu) 4NI, and 2,2′-bipyridine (2,2′-bipy) through a solid-state reaction. It crystallizes in monoclinic space group P2 1/ n, a=9.591(2) Å, b=14.820(3) Å, c=17.951(4) Å, β=91.98(2)°, V=2549.9(10) Å 3, and Z=4. The nest-shaped cluster was obtained for the first time with a neutral skeleton containing 2,2′-bipy ligand. The non-linear optical (NLO) property of [MoOICu 3S 3(2,2′-bipy) 2] in DMF solution was measured by using a Z-scan technique with 15 ns and 532 nm laser pulses. The cluster has large third-order NLO absorption and the third-order NLO refraction, its 2 and n2 values were calculated as 6.2×10 −10 and −3.8×10 −17 m 2 W −1 in a 3.7×10 −4 M DMF solution. 相似文献
17.
Antibodies of a polyclonal antiserum against benzo[ a]pyrene were characterized by determining thermodynamic and kinetic constants of the antigen–antibody reaction. Label-free binding assays with optical detection based on reflectometric interference spectroscopy were performed to determine these constants. Different evaluation methods for kinetic measurements were compared. Also, cross-reactivity against two other polycyclic aromatic hydrocarbons, chrysene and pyrene, was checked. The affinity constant between the antibodies and benzo[ a]pyrene in homogeneous phase was determined to be K=(5.3±0.3)×10 7 M −1 which was in the middle of the usual range of antibody affinities. The association rate constant for the reaction at the surface was determined to be (3.8±0.9)×10 5 M −1 s −1, the dissociation rate constant as (9.7±0.5)×10 −3 s −1. Different evaluation methods applied to the kinetic measurements led to the same results. This antiserum would be suitable for the selective determination of benzo[ a]pyrene in concentrated samples. 相似文献
18.
The reactive Kr +F 2− potential energy surface is probed by two-photon, laser-induced chemical bond formation during a Kr+F 2 collision. This is compared with the pulsed laser excitation (two-photon) of Kr(2p 9) followed by collision with F 2 leading to the formation of KrF(B, C). In addition to reporting the excitation spectrum for the two-phonon-induced collision process, these techniques were used to determine quenching rate constants of Kr 2F *. Quenching by Xe gives XeF(B, C) with rate constant (1.5±0.2)×10 −10 cm 3 s −1; the quenching rate constant for F 2 is (1.5±0.2)×10 −10 cm 3 s −1, and the radiative lifetime of Kr 2F * is 240±35 ns. The quenching rate constant for the coupled Kr(2p 8) and Kr(2p 9) levels by F 2 is (13±2)×10 −10 cm 3 s −1. 相似文献
19.
The kinetics of the association reaction of CF 3 with NO was studied as a function of temperature near the low-pressure limit, using pulsed laser photolysis and time-resolved mass spectrometry. CF 3 radicals were generated by photolysis of CF 3I at 248 nm and the kinetics was determined by monitoring the time-resolved formation of CF 3NO. The bimolecular rate constants were measured from 0.5 to 12 Torr, using nitrogen as the buffer gas. The results are in very good agreement with recent data published by Vakhtin and Petrov, obtained at room temperature in a higher pressure range and, therefore, the two studies are quite complementary. A RRKM model was developed for fitting all the data, including those of Vakhtin and Petrov and for extrapolating the experimental results to the low- and high-pressure limits. The rate expressions obtained are the following: k1(0) = (3.2 ± 0.8) × 10 −29 ( T/298) −(3.4±0.6) cm 6 molecule −2 s −1 for nitrogen used as the bath gas and k1(∞) = (2.0 ± 0.4) × 10 −11 ( T/298) (0±1) cm 3 molecule −1 s −1. RRKM calculations also help to understand the differences in reactivity between CF 3 and other radicals, for the same association reaction with NO. 相似文献
20.
Kinetic studies on the interactions between self-assembled monolayers of mannosylerythritol lipids (MELs), which are glycolipid biosurfactants abundantly produced by microorganisms, and various classes of immunoglobulins including human IgG, IgA, and IgM were performed using surface plasmon resonance (SPR). The effect of the MEL structure on the binding behavior of HIgG was examined. Assembled monolayers of MEL-A having two acetyl groups on the headgroup gave a high affinity ( Kd = 1.7 × 10 −6 M) toward HIgG, while those of MEL-B or MEL-C having only one acetyl group at C-6′ or C-4′ position gave little affinity. Our kinetic analysis revealed that the binding manner of HIgG, HIgA ( Kd = 2.4 × 10 −7 M), and HIgM ( Kd = 2.2 × 10 −7 M) to the assembled monolayers of MEL-A is not the monovalent mode but the bivalent mode, and both the first and second rate association constants ( ka1, ka2) increase with an increase in the number of antibody binding sites, while those for dissociation ( kd1, kd2) changed little. Moreover, we succeeded in directly observing great amounts of HIgG, HIgA, and HIgM bound to MEL-A monolayers using atomic force microscopy (AFM). Finally, we found that MEL-A assembled monolayer binds toward various IgG derived from mouse, pig, rabbit, horse, goat, rat, and bovine as well as human IgG (HIgG), and the only exception was sheep IgG. These results clearly demonstrate that MEL-A assembled monolayers would be useful as noble affinity ligand system for various immunoglobulins. 相似文献
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