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1.
Using N •3 species as specific electron acceptor a defined ascorbate radical: AH •↔A •−+H + (λ max=360 nm, =3400 dm 3 mol −1 cm −1) is observed. The attack of DMSO •+ on vit.E results in a vit.E • radical ( k=1×10 9 dm 3 mol −1 s −1; λ max=425 nm, =2400 dm 3 mol −1 cm −1; 2 k=4.7×10 8 dm 3 mol −1 s −1). Vit.E-acetate leads to the formation of a radical cation (vit.E-ac •+). β-carotene reacts also with DMSO •+ forming a radical cation, β-car •+ ( k=1.75×10 8 dm 3 mol −1 s −1; λ max=942 nm, =14 600 dm 3 mol −1 cm −1), which probably leads to the formation of a dimer radical cation, (β-car) •+2 ( k=2.5×10 7 dm 3 mol −1 s −1). Using E.coli bacteria (AB1157) as a model system in vitro it was found that all three vitamins are rather efficient radiation protecting agents. They can also increase the activity of cytostatica, e.g., mitomycin C (MMC), by electron transfer process. The mixture of vit.E-ac and β-car acts contradictory, but adding vit.C to it a strong cooperative enhancement of the MMC activity is observed once again. A relationship between the pulse radiolysis and the radiation biological data is found and discussed. A possible explanation of the previously reported trials concerning the role of vit.E and β-car on the increased occurence of lung and other types of cancer in smokers and drinkers is presented. 相似文献
2.
The Hartree-Fock and DFT/B3LYP methods have been employed to investigate the electronic structures of 1-ethy1-3-methyl-imidazolium cation(EMIM~ ),BF_4~-,PF_6~-,EMIM~ -BF_4~-,and EMIM~ -PF_6~- using the Gaussian-94 soft-package at 6-31 G(d,p)basis set level for hydrogen,carbon,nitrogen,boron, phosphorus,and fluorine atoms.Comparison of the electronic structures of the lowest energy of EMIM~ - BF_4~- and EMIM~ -PF_6~- pairs,and single EMIM~ ,BF_4~- and PF_6~- showed that the optimized EMIM~ -BF_4~- and EMIM~ -PF_6~- pair conformers were BF_4~- and PF_6~- outside the 5-ring plane between the ethyl group and the methyl group.The cohesion of C—H…F hydrogen bond between cation and anion is reinforced by charge assistance.The interaction energy between EMIM~ and PF_6~- is 328.8 kJ/mol at the B3LYP level and 326.6 kJ/mol at the Hartree-Fock level,whereas that between EMIM~ and BF_4~- is 353.5 kJ/mol at the B3LYP level and 350.5 kJ/mol at the Hartree-Fock level.The low energy interactions caused by bulky asymmetric EMIM~ ,and charge dispersion of cation and anion give rise to the low melting point of ionic liquid EMIM~ -BF_4~- and EMIM~ -PF_6~-.The two hydrogen bonding models of single hydrogen bond formation,and the hydrogen transfer between C_2 in EMIM~ and F in BF_4~- or PF_6~- were principally depicted. 相似文献
3.
Twenty-two isomers/conformers of C 3H 6S +√ radical cations have been identified and their heats of formation (Δ Hf) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their Δ Hf data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation (4 +) with C2v symmetry. In contrast, the least energy C 3H 6O +√ isomer is the 1-propen-2-ol radical cation. The G3 Δ Hf298 of 4 + is calculated to be 859.4 kJ mol −1, ca. 38 kJ mol −1 higher than the literature value, ≤821 kJ mol −1. For allyl mercaptan radical cation (7 +), the G3 Δ Hf298 is calculated to be 927.8 kJ mol −1, also not in good agreement with the experimental estimate, 956 kJ mol −1. Upon examining the experimental data and carrying out further calculations, it is shown that the G3 Δ Hf298 values for 4 + and 7 + should be more reliable than the compiled values. For the five remaining cations with available experimental thermal data, the agreement between the experimental and G3 results ranges from fair to excellent. Cation CH3CHSCH2+√ (10+) has the least energy among the eleven distonic radical cations identified. Their ΔHf298 values range from 918 to 1151 kJ mol−1. Nevertheless, only one of them, CH2=SCH2CH2+√ (12+), has been observed. Its G3 ΔHf298 value is 980.9 kJ mol−1, in fair agreement with the experimental result, 990 kJ mol−1. A couple of reactions involving C3H6S+√ isomers CH2=SCH2CH2+√ (12+) and trimethylene sulfide radical cation (13+) have also been studied with the G3 method and the results are consistent with experimental findings. 相似文献
4.
Reaction of 1,3-thiazolidine-2-thione with tellurium(IV) in hydrobromic acid medium gave the hexabromotellurate, [C 6H 9N 2S 3] 22+[Te IVBr 6] 2− (3). Reaction of 1-methylimidazoline-2-(3H)-thione (L″) with tellurium(IV), in hydrobromic acid medium, gave the mixed-ligand tellurium(II) complex [Te IIL″ 3Br] +Br − (4). The structures of [C 6H 9N 2S 3] 22+[Te IVBr 6] 2− (3) and [Te IIL″ 3Br] +Br − were determined by single crystal X-ray diffraction methods. In 3 the unit cell contains [TeBr 6] 2− anions and two [C 6H 9N 2S 3] + cations. There is no direct bonding between the metal atom and the cations. In the anion only slight angular deviations from the perfect octahedral geometry are observed. The lone pair of electrons on tellurium(IV) is found to be stereochemically inert. In the cation the two five-membered heterocyclic rings adopt different conformations. In complex 4, in the solid state, the planar [Te IIL″ 3Br] + cation and Br − anion are held together by ionic interactions. In the cation, L″ is bonded to the central tellurium atom through the sulphur atom. 相似文献
5.
Powder X-ray diffraction, 119Sn NMR spectra, and 1H NMR spin–lattice relaxation times, T1, were measured for (CH 3) nNH 4−nSnCl 3 ( n=1–4). From the Rietveld analysis, it is shown that all four compounds crystallize into deformed perovskite-type structures at room temperature. The temperature dependence of 1H T1 was analyzed in terms of the CH 3 reorientation and other motions of the whole cation. Except for the phase transition in CH 3NH 3SnCl 3, which is from monoclinic to rhombohedral at 331 K, 1H T1 was continuously changed at other phase transitions in this compound as well as in the n=2–4 compounds, suggesting that the transitions are not caused by the change of the motional state of the cation but by an instability of the [SnCl 3] nn− perovskite lattice. 相似文献
6.
The rate coefficients of the reactions: (1) CN + H 2CO → products and (2) NCO + H 2CO → products in the temperature range 294–769 K have been determined by means of the laser photolysis-laser induced fluorescence technique. Our measurements show that reaction (1) is rapid: k1(294 K) = (1.64 ± 0.25) x 10 −11 cm 3 molecule −1 s −1; the Arrhenius relation was determined as k1 = (6.7 ± 1.0) x 10 −11 exp[(−412 ± 20)/T] cm 3 molecule −1 s −1. Reaction (2) is approximately a tenth as rapid as reaction (1) and the temperature dependence of k2 does not conform to the Arrhenius form: k2 = 4.62 x 10 −17T1.71 exp(198/ T) cm 3 molecule −1 s −1. Our values are in reasonable agreement with the only reported measurement of k1; the rate coefficients for reaction (2) have not been previously reported. 相似文献
7.
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
8.
The oxidation of Cp 2MCl 2 (M= Mo, W) with perfluortriazinium tetrafluoroborate, [(FCN) 3F] +[BF 4] −, in the presence of a flouride ion acceptor (BF 3 or PF 5) in SO 2 solution yielded the cationic metallocene complexes [Cp 2MCl 2] 2+[BF 4] − or [C p2MCl 2] 2+[BF 4] −[PF 6] − (M = Mo, W), respectively. In these reactions, for the first time the perfluortriazinium cation has proved to be easy to handle and a useful oxidizer in organometallic chemistry. The oxidizer strength of three fluorotriazinium cations, [(XCN) 3F] + (X = F, Cl, H), has been computed ab initio (HF/6 − 31 + G) and calibrated on literature data which were obtained by local density functional calculations. It was anchored to its F + zero point by an experimental value for KrF +. ab]Die Oxidation von Cp 2MCl 2 mit (M = MO, W) Perfluortriaziniumtetrafluoroborat, [(FCN) 3F] +[BF 4] −, in Anwesenheit eines Fluoridionenakzeptors (BF 3 oder PF 5) führte in SO 2-Lösung zur Bildung der kationischen Metallocen-Komplexe [Cp 2MCl 2+] 2+[BF 4] 2− bzw. [Cp 2MCl 2] 2+[BF 4] − [PF 6] − (M = Mo, W). In diesen Reaktionen konnte erstmals gezeigt werden, daß Perfluortriazinium-Kationen einfach zu handhabende und nützliche Oxidationsmittel im Bereich der metallorganischen Synthese darstellen. Das (Mdationsvermögen von drei Fluorotriazinium-Kationen, [(XCN) 3F] +(X = F, Cl, H), wurde ab initio berechnet (HF/6 − 31 + G) und mit Hilfe von Literaturdaten, die mittels local density functional-Berechnungen erhalten und am experimentellen Wert von KrF + bezüglich des F + Nullpunktes verankert wurden, kalibriert. 相似文献
9.
EPR lineshape simulation studies have been performed on a specimen of 80MoO 3–20B 2O 3 glass in the temperature range of 300–77 K. The values of the obtained spin Hamiltonian parameters are: g=1.940, g=1.974, A=150.0×10 −4 cm −1, A=35.6×10 −4 cm −1 and g=1.935, g =1.975, A=141.9×10 −4 cm −1, A=34.5×10 −4 cm −1 at 300 and 77 K, respectively. The paramagnetic site in the specimen is molybdenyl, MoO 3+, ion in which the Mo is in a distorted octahedral environment of six oxygen atoms with C 4v symmetry. The 11-parallel and 11-perpendicular line feature of the EPR lineshape shows that two Mo nuclei are magnetically equivalent in the glassy matrix, in the temperature range 300–77 K. 相似文献
10.
The triplet state ( 32T) and the radical cation (2T +√) of 2,2′-bithiophene (2T) are characterized by pulse radiolysis in CCl 4. Two main absorption bands at 360 and 420 nm are respectively attributed to 32T* and to 2T +√. The triplet, induced in an excited state through a Förster mechanism, undergoes a conformational rearrangement ( k6=(6.8±0.9)×10 6 s −1). The radical cation is produced both through a resonance charge transfer and a second diffusional process; the two oxidizing species are respectively CCl 4+√ and (CCl +3Cl −) solv through the mediation of a singlet excited state, 12T*. 相似文献
11.
Pulse radiolysis technique has been employed to study the reactions of oxidizing ( √OH, N 3√) and reducing radicals (e −aq, CO 2√−, acetone ketyl radical) with 2-hydroxy-3-methoxybenzaldehyde ( o-vanillin) at different pH. Hydroxyl radicals react mostly by addition reaction forming radical adducts (λ max=420 nm) and the oxidation is only a minor process even in the alkaline region. The reaction with azide radicals produced phenoxyl radicals (λ max=340 nm), which are formed on fast deprotonation of solute radical cation. Using PMZ √+/PMZ and ABTS √−/ABTS 2− as the reference couple, different methods are employed to determine the one-electron reduction potential of o-vanillin and the average value is estimated to be 1.076±0.004 V vs. NHE at pH 6. The phenoxyl radicals of o-vanillin were able to oxidize ABTS 2− quantitatively. The e aq− is observed to react with o-vanillin with rate constant value of 2×10 10 dm 3 mol −1 s −1. CO 2√− and acetone ketyl radical are also observed to react with o-vanillin by electron transfer mechanism and showed the formation of transient absorption bands with λ max at 350 and 390 nm at pH 4.5 and 9.7, respectively. The p Ka of the one-electron reduced species was determined to be 8.1. The results indicate that the aldehydic group is the most preferred site for electron addition. 相似文献
12.
Solution NMR studies of silyl cations [ArSiMe 2] +X − (X = I, CF 3SO 3) incorporating the terdentate aryl diamine ligand Ar - C 6H 3− 2,6-(CH 2NMe 2) 2 have been carried out in a protic solvent (methanol- d4) and in an aprotic solvent (CD 2Cl 2). This study has shown that the structure of these silyl cations is highly dependent on the solvent. In CD 2Cl 2, the silyl cation is five-coordinated owing to the coordination of one NMe 2 group and of the anion to the silicon centre which gives rise to a dissymmetric structure. On the other hand, in CD 3OD there is no coordination of the anion, but the silyl cation is also probably five-coordinated due to the coordination of the solvent to the silicon atom which is supported by the X-ray analysis of the compound 9. With the weakly nucleophilic anion BPh 4− in CD 2Cl 2, in addition to the silyl cation previously described, another five-coordinated silyl cation resulting from the coordination of both NMe 2 groups to the Si centre was postulated. 相似文献
13.
The rate coefficients for the reactions of C 2H and C 2D with O 2 have been measured in the temperature range 295 K T 700 K. Both reactions show a slightly negative temperature dependence in this temperature range, with kC2H+O2 = (3.15 ± 0.04) × 10 −11 ( T/295 K) −(0.16 ± 0.02) cm 3 molecule −1 s −1. The kinetic isotope effect is kC2H/ kC2D = 1.04 ± 0.03 and is constant with temperature to within experimental error. The temperature dependence and the C 2H + O 2 kinetic isotope effect are consistent with a capture-limited metathesis reaction, and suggest that formation of the initial HCCOO adduct is rate-limiting. 相似文献
14.
A thin, gas-tight palladium (Pd) membrane was prepared by the counter-diffusion chemical vapor deposition (CVD) process employing palladium chloride (PdCl 2) vapor and H 2 as Pd precursors. A disk-shaped, two-layer porous ceramic membrane consisting of a fine-pore γ-Al 2O 3 top layer and a coarse-pore -Al 2O 3 substrate was used as Pd membrane support. A 0.5–1 μm thick metallic membrane was deposited in the γ-Al 2O 3 top layer very close to its surface, as verified by XRD and SEM with a backscattered electron detector. The most important parameters that affected the CVD process were reaction temperature, reactants concentrations and top layer quality. Deposition of Pd in the γ-Al 2O 3 top layer resulted in a 100- to 1000-fold reduction in He permeance of the porous substrate. The H 2 permeation flux of these membranes was in the range 0.5–1.0 × 10 −6 mol m −2 s −1 Pa −1 at 350–450°C. The H 2 permeation data suggest that surface reaction steps are rate-limiting for H 2 transport through such thin membranes in the temperature range studied. 相似文献
15.
This Letter reports the first kinetic study of 2-butoxy radicals to employ direct monitoring of the radical. The reactions of 2-butoxy with O 2 and NO are investigated using laser-induced fluorescence (LIF). The Arrhenius expressions for the reactions of 2-butoxy with NO ( k1) and O 2 ( k2) in the temperature range 223–311 K have been determined to be k1=(7.50±1.69)×10 −12×exp((2.98±0.47) kJmol −1/RT) cm 3 molecule −1 s −1 and k2=(1.33±0.43)×10 −15×exp((5.48±0.69) kJmol −1/RT) cm 3 molecule −1 s −1. No pressure dependence was found for the rate constants of the reaction of 2-butoxy with NO at 223 K between 50 and 175 Torr. 相似文献
16.
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
17.
The generality of a two-electron reduction process involving an
mechanism has been established for M 3(CO) 12 and M 3(CO) 12− n(PPh 3) n (M = Ru, Os) clusters in all solvents. Detailed coulometric and spectral studies in CH 2Cl 2 provide strong evidence for the formation of an ‘opened’ M 3(CO) 122− species the triangulo radical anions M 3(CO) 12−· having a half-life of < 10 −6 s in CH 2Cl 2. However, the electrochemical response is sensitive to the presence of water and is concentration dependent. An electrochemical response for “opened” M 3(CO) 122− is only detected at low concentrations < 5 × 10 −4 mol dm −3 and under drybox conditions. The electroactive species ground at higher concentrations and in the presence of water M 3(CO) 112− and M 6(CO) 182− were confirmed by a study of the electrochemistry of these anions in CH 2Cl 2; HM 3(CO) 11− is not a product. The couple [M 6(CO) 18] −/2− is chemically reversible under certain conditions but oxidation of HM 3(CO) 11− is chemically irreversible. Different electrochemical behaviour for Ru 3(CO) 12 is found when [PPN][X] (X = OAc −, Cl −) salts are supporting electrolytes. In these solutions formation of the ultimate electroactive species [μ-C(O)XRu 3(CO) 10] − at the electrode is stopped under CO or at low temperatures but Ru 3(CO) 12−· is still trapped by reversible attack by X presumably as [η 1-C(O)XRu 3(CO) 11] −. It is shown that electrode-initiated electron catalysed substitution of M 3(CO) 12 only takes place on the electrochemical timescale when M = Ru, but it is slow, inefficient and non-selective, whereas BPK-initiated nucleophilic substitution of Ru 3(CO) 12 is only specific and fast in ether solvents particulary THF. Metal---metal bond cleavage is the most important influence on the rate and specificity of catalytic substitution by electron or [PPN]-initiation. The redox chemistry of M 3(CO) 12 clusters (M = Fe, Ru, Os) is a consequence of the relative rates of metal---metal bond dissociation, metal-metal bond strength and ligand dissociation and in many aspects resembles their photochemistry. 相似文献
18.
X-Ray crystallographic studies on [NEt 4] 2[Cr 2[(O 2CC 2H 5) 4(NCS) 2] show that the Cr–Cr separation (2.467Å) in the dinuclear anion is one of the longest known. The thiocyanato groups are N-bonded, and the results emphasize the known sensitivity of the quadruple Cr–Cr bond to the nature of the axial ligands. The compound crystallises in the tetragonal space group P4/ mnc with two molecules per unit cell, the dimensions of which are a = b = 9.785(1), c = 21.186(2) Å. Magnetic investigations from room to liquid nitrogen temperature on the tetra-μ-propionato complex and on [NMe 4] 2 [Cr 2(O 2CCH 3) 4(NCS) 2] show that both complexes have been obtained free from paramagnetic chromium(III) impurities. Their weak paramagnetic susceptibilities ( Xcr is approx. 200 x 10 −6 cm 3 mol −1 at 295 K and 50 x 10 −6cm 3mol −1 at 90 K) are inherent, and are ascribed to temperature independent paramagnetism at low temperature plus para-magnetism arising from slight population of the triplet state (2 J 700 cm −1, g = 2, N = 50 x 10 −6cm 3mol −1) at higher temperatures. 相似文献
19.
This survey begins with the photochemistry at 254 nm and 298 K in the system H 2O 2COO 2RH, the primary objective of which is to determine the rate constants for the reaction OH + RH → H 2O + R relative to the well-known rate constant for the reaction OH + CO → CO 2 + H. Inherent in the scheme is that the reaction HO 2+CO→OH+CO 2 is negligible compared with the OH reaction, and a literature consensus gives kHO2 < 10 −19 cm 3 molecule −1 s −1, or some 10 6 less than kOH at 298 K. Theoretical calculations establish that the first stage in the HO 2 reaction is the formation of a free radical intermediate HO 2 + CO → HOOCO (perhydroxooxomethyl) which decomposes to yield the products, and that the rate of formation of the intermediate is equal to the rate of formation of the products. The structure of the intermediate and a reaction profile are shown. High temperature rate data reported subsequent to the data in the consensus and theoretical calculations lead here to a recommendation that, in the range 250–800 K, kHO2 = 3.45 × 10−12T1/2 exp(1.15 × 104/T) cm3 molecule−1 s−1, the hard-sphere-collision Arrhenius modification. This yields kHO2(298) = 1.0 × 10−27 cm3 molecule−1 s−1 or some 1014 slower than kOH(298). 相似文献
20.
The bis(μ 3-ethylidyne) tricobalt cluster [(CpCo) 3(μ 3-CCH 3) 2] (1b) is protonated by trifluoroacetic acid to give the dicobalt edge-protonated cation [H(CpCo) 3(μ 3-CCH 3) 2] + [lb + H] +. Protonation of the μ 3-ethylidyne tetracobalt cluster hydride [H(CpCo) 4(μ 3-CCH 3)] (3) takes place in two consecutive steps. At low temperature [H 2(CpCo) 4(μ 3-CCH 3)] + [3 + H] + is formed first, and is then slowly converted into [H 3(CpCo) 4(μ 3-CCH 3)] 2+ [3 + 2H] 2+ by an excess of acid. As judged by the 1H NMR data and the crystal structure of [3 + X] +[(CF 3COO) 2X] − (X = H or D) the endo hydrogens in [3 + H] + and [3 + 2H] 2+ occupy μ 3-(Co 3) face capping hydridic positions. The cations [1b + H] + and [3 + H] + show hydride fluxionality in solution, which in the case of [3 + H] + can be frozen out on the NMR timescale at low temperature (ΔG ≠ (203 K) = 40.8 kJ/mol). The structure of [3 + X] + [(CF 3COO) 2X] − (X = H or D) was determined by X-ray crystallography. One of the hydrides/deuterides is located on the crystallographic mirror plane, capping a tricobalt face of the cluster cation. The other endo hydrogen atom is believed to be disordered between the other two μ 3-(Co 3) sites, which are related by space group symmetry. Deuteronation of 3 shows a strong normal kinetic deuterium isotope effect. From the temperature independence of the 1H NMR spectrum of [3 + 2D] 2+ a non-fluxional solution structure can be inferred. In all the systems studied, hydridic (μ 2- or μ 3-) sites are thermodynamically preferred to possible isomeric agostic CoHC or Co 2HC sites for the endo hydrogens. Agostic interactions cannot, however, be ruled out in transient intermediates during the course of the protonations. 相似文献
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