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1.
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
2.
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
3.
The heats of formation of six radical cations have been calculated using ab initio MO methods at the MP4/6-31 + G(2df, p) level with MP2/6-31G(d, p)-optimized geometries. The theoretical values for Δ H0f,298 (kJ/mol) of the radical ions considered are (experimental values in parentheses): methanol CH 3OH +√: 854 (845); methyleneoxonium CH 2OH +√2: 815 (816); methyleneimine CH 2NH +√: 1076 (1054); aminomethylene HCNH +√2: 1040 (1079); methylamine CH 3NH +√2: 863 (843) and methyleneammonium CH 2NH +√3: 855 (958). The calculated results thus confirm the discrepancy between experiment and theory on the heats of formation of nitrogen-containing radical cations. In the latter, the distonic species are calculated to be more stable than their classical isomers. The higher stability of the distonic ions has also been discussed. The recommended heat of formation of the methyleneiminium cation CH 2NH +2 is 754 kJ/mol. 相似文献
4.
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
5.
Dilatometric measurements of excess volumes VE have been made for binary liquid mixtures of methylethylketone with methylene chloride (CH 2Cl 2), 1,2-dichloroethane (CH 2ClCH 2Cl) and tetrachloroethylene (CCl 2CCl 2) at 293.15 and 303.15 K, for mixtures of methylethylketone with trichloroethylene (CHClCCl 2) at 298.15 and 308.15 K, and for mixtures of methylethylketone with cyclohexane ( c-C 6H 12) at 303.15 K. The values of VE have been found to be highly positive for methylethylketone + c-C 6H 12, slightly positive for methylethylketone + CH 2Cl 2 and methylethylketone + CCl 2CCl 2, and slightly negative for methylethylketone + CHClCCl 2 and methylethylketone + CH 2ClCH 2Cl. The results indicate the existence of specific interactions of methylethylketone with CH 2Cl 2, CH 2ClCH 2Cl, CHClCCl 2 and CCl 2CCl 2. 相似文献
7.
The fraction FΣ of excited-state oxygen formed as b 1Σ g+ was determined for a series of triplet-state photosensitizers in CCl 4 solutions. FΣ was determined by monitoring the intensities of (a) O 2(b 1Σ g+) fluorescence at 1926 nm (O 2(b 1Σ g+)→O 2(a 1Δ g) and (b) O 2(a 1 Δ g) phosphorescence at 1270 nm (O 2(a 1Δ g) → O 2(X 3Σ g−)). Oxygen excited states were formed by energy transfer from substituted benzophenones and acetophenones. The data indicate that FΣ depends on several variables including the orbital configuration of the lowest triplet state and the triplet-state energy. The available data indicate that the sensitizer-oxygen charge transfer (CT) state is not likely to influence FΣ strongly by CT-mediated mixing of various sensitizer-oxygen states. 相似文献
8.
The reactions of hydroxyl radical, hydrogen atom and hydrated electron intermediates of water radiolysis with N-isopropylacrylamide (NIPAAm) were studied by pulse radiolysis in dilute aqueous solutions. OH, H and e aq− react with NIPAAm with rate coefficient of (6.9±1.2)×10 9, (6.6±1)×10 9, and (1.0±0.2)×10 10 mol −1 dm 3 s −1. In OH and H radical addition to the double bond mainly -carboxyalkyl type radicals form, (OHCH 2CH √C(N- i-C 3H 7)O and CH 3CH √C(N- i-C 3H 7)O). In reaction of e aq− oxygen atom centered radical anion is produced (CH 2CHC √(N- i-C 3H 7)O −), the anion undergoes reversible protonation with p Ka=8.7. There is also an irreversible protonation on the β-carbon atom that produces the same radical as forms in H atom reaction (CH 3CH √C(N- i-C 3H 7)O). The -carboxyalkyl type radicals at low NIPAAm concentration (0.1–1 mmol dm −3) mainly disappear in self-termination reactions, 2 kt,m=8.4×10 8 mol −1 dm 3 s −1. At higher concentrations the decay curves reflect the competition of the self-termination and radical addition to monomer (propagation). The termination rate coefficient of oligomer radicals containing a few monomer units is 2 kt≈2×10 8 mol −1 dm 3 s 1. 相似文献
9.
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
10.
The rate constant for the reaction between the sulphate radical (SO 4√−) and the ruthenium (II) tris-bipyridyl dication (Ru(bipy) 32+) is (3.3±0.2)×10 9 mol −1 dm 3 s −1 in 1 mol dm −3 H 2SO 4 and (4.9±0.5)×10 9 mol −1 dm 3 s −1 in 0.1 mol dm −3, pH 4.7 acetate buffer. The SO 4√−radical produced by the electron transfer quenching of Ru(bipy) 32+* by S 2O 82− reacts rapidly with both acetate buffer and chloride ions. These side reactions result in a reduction in the overall quantum yield of Ru(bipy) 33+ production and reduced reaction selectivity when Ru(bipy) 32+* is quenched by persulphate. 相似文献
11.
在水热条件下,基于配体 N, N'-双(3-吡啶基)-对苯二甲酰胺(3-bptpa)和1,3,5-苯三甲酸(1,3,5-H 3btc),合成了一例具有二维格子结构的钴(Ⅱ)MOF[Co(3-bptpa)(1,3,5-Hbtc)]·2H 2O(1),并进行了红外光谱(FT-IR)、元素分析(EDS)、差热-热重分析(DTA-TG)、X射线单晶衍射(XRD)和磁学表征。 结果表明,每个1,3,5-Hbtc 2-提供1个螯合配位羧基和1个桥连配位羧基与Co(Ⅱ)离子配位。 中心对称的二聚体[Co(3-bptpa)(1,3,5-Hbtc)] 2通过桥连配位的羧基连接成1D梯形链,相邻的梯形链通过3-bptpa与Co(Ⅱ)的配位作用连接为2D格子,从而形成CoN 2O 4变形八面体的配位构型。对配合物1在16~300 K的磁化率数据,使用八面体场下旋轨耦合的各向同性的单离子近似和分子场理论进行分析,Co(Ⅱ)离子表现强的旋轨耦合作用( λ=-100.4 cm -1),相邻的Co(Ⅱ)离子之间通过桥连配位的羧基传递弱的反铁磁相互作用( zj'=-0.618 cm -1)。 相似文献
12.
Reactions of OH radicals and some one-electron oxidants with 2-aminopyridine (2-AmPy) and 3-aminopyridine (3-AmPy) were studied in aqueous solutions using pulse radiolysis technique. The OH adduct of 2-AmPy at pH 9 has an absorption maximum at 360 nm along with a weak absorption band in the visible region and was found to be reactive with oxygen. The rate constant for its reaction with O 2 was determined to be 1.0×10 8 dm 3 mol −1 s −1. At pH 4 also, the OH adduct of 2-AmPy has an absorption band at 360 nm. However, there are differences in the absorption at other wavelengths. From the plot of ΔOD vs. pH at 340 nm, the p Ka of the OH adduct was determined to be 6.5. Among the specific oxidants, only SO 4−√ radicals were able to oxidize 2-AmPy. In the case of 3-aminopyridine (3-AmPy), the transient species formed by OH radical reaction at pH 9 has an absorption maximum at 410 nm with shoulder bands on both the sides. Its absorption spectrum at pH 4 was different indicating the existence of a p K value for the OH adduct. p Ka of 3-AmPy-OH radical adduct species was evaluated to be 5.7. This adduct species was also found to be reactive with oxygen ( k=7.6×10 6 dm 3 mol −1 s −1). Specific one-electron oxidants like N 3√, Br 2−√ C 2−√ and SO 4−√ were able to oxidize 3-AmPy indicating that it is easier to oxidize 3-AmPy as compared to 2-AmPy. 相似文献
13.
The enthalpies of formation of the complexes between the silver(I) ion and some sulphur-containing aminopyridines of general formula
N(CH 2) n−1-S-(CH 2) m-NH 2 where n = 1, and m = 1,2; 1,3; 2,2; 2,3 have been determined by direct calorimetric titration at 25°C in 0.5 M (K)NO 3 solution. The corresponding entropy terms, Δ S, have been calculated using the obtained enthalpy values and the previously reported Δ G values. In acid medium (pH < 3) coordination occurs through the thioether group and the protonated species AgLH3+2 and AgL2H5+4 are enthalpy-stabilized and entropy-destabilized. At higher pH values (pH &>; 3) additional chelation through the pyridine nitrogen is obvious by a marked increase in the enthalpy of formation of the complexes AgL2H4+3, AgL2H3+2 and AgLH2+. The last complex dimerizes into a cyclic dimer Ag2L, H4+2. At still higher pH values (pH &>; 6) the participation of the amino group in the dimeric chelates Ag2L2H3+ and Ag2L2+2 is revealed again by a marked increase in the heat of complexation. 相似文献
14.
Free radical reactions of dehydrozingerone (DZ), a methoxy phenol, were studied at dfferent pHs with a variety of oxidants using nanosecond pulse radiolysis technique. Hydroxyl radical (OH) reaction with the phenolic form at pH 6 led mainly to the formation of an OH-adduct absorbing at 460 nm in addition to a minor oxidation product. On the other hand, at pH 10 with the deprotonated phenoxide ion, the only reaction observable was oxidation generating a phenoxyl radical absorbing at 360 nm. HPLC analysis indicated formation of two different products at pH 6 from addition and oxidation reactions, whereas at pH 10, only the oxidation product was detectable. Reactions of more specific secondary oxidizing radicals, N3√, Br√, Br −2√ and Tl(II) with DZ gave rise to the phenoxyl radical over the entire pH range. DZ in the phenoxide ion form reacted with nitrogen dioxide and trichloromethyl peroxyl radicals with rate constants 6×10 8 and 8.8×10 8 dm 3 mol −1 s −1 respectively leading to the phenoxyl radicals. The DZ phenoxyl radical reacted with trolox C (an analogue of -tocopherol) with a rate constant of 8.3×10 7 dm 3 mol −1 s −1. One electron reduction potential of the DZ phenoxyl radical at pH 6 was determined to be +1.1 V vs NHE using N3√/N −3 as the standard couple. 相似文献
15.
Hydrogen bonding to the photoaccumulated secondary acceptor radical anion A 1√− in photosystem (PS) I has been studied using pulsed Q-band ENDOR spectroscopy. With deuterated quinone in protonated PS I particles it is demonstrated that the observed radical anion has only one hydrogen-bond hyperfine coupling (hfc) tensor with tensor components above the 2 MHz range. Below 2 MHz the protein matrix protons dominate and a second weak H-bond could not be detected. The spectral resolution of pulsed Q-band ENDOR is critically required to separate the signals of the H-bond proton from those of the primary chlorophyll acceptor, A 0√−, which cannot be avoided to be formed to some extent in the photoaccumulation procedure. The determined H-bond hfc tensor of A 1√− is found to be close to axial symmetry with a small isotropic component, as expected from a predominantly dipolar electron–proton spin interaction in a hydrogen-bond. The principal tensor components are A=(+)7.7, MHz A=(−)4.9 MHz, Aiso=(−)0.7 MHz. The magnitude of the dipolar tensor corresponds to an unusually short H-bond which can be estimated from the point-dipole approximation (1.5±0.1 Å). Based on previous studies with A- and B-branch specific site-directed mutants of the A 1 site of PS I and the chosen photoaccumulation protocol, the observed A 1√− radical anion can be assigned to the Q K–A site of the A-branch. The observed H-bond hfc tensor is compared to those determined for related quinone radical anions observed in frozen protic solution as well as in the Q A site of type II bacterial reaction centers. 相似文献
16.
Rotational-state distributions of the CO + (A–X, B–X) and N 2+(B–X) emissions produced by the collisions of He(2 3S) with CO and N 2 were studied in the collision energy ( ER range 100–200 meV. The rotational populations of the emitting states can be fitte by single Boltzmann temperatures ( TR. The TR (320 ± 30 K) for the ν′ = 3 and 4 levels of the CO + (A 2Π) state are nearly independent of, or slightly increase with, ER, while TR for the CO +(B 2Σ +, ν′ = 0) state increases rapidly with ER.The TR (430 ± 20 K) for the N 2+(B 2Σ +, ν′ = 0) state is nearly independent or slightly decreases with increasing ER. Interactions providing these trends are discussed. 相似文献
17.
The self-termination rates of the benzyl radical (C 6H 5---CH 2√) and para-substituted benzyl radicals (X---C 6H 4---CH 2√) were studied in aqueous solutions. The Arrhenius parameters and activation energies were determined in the temperature range 275.5–328 K. The kinetic activation energies of these radicals were close to the dynamic activation energy of the solvent, indicating that the termination rate is controlled by diffusion. The values for the rate constants (2 kt (10 9 dm 3 mol −1 s −1)) and the activation energies ( E (kJ mol −1)) were 5.94±0.52 and 14.69±0.61 for CH 3O---C 6H 4---CH 2√, 4.52±0.2 and 17.65±1.16 for CH 37z.sbnd;C 6H 4---CH 2√, 3.07±0.45 and 17.58±0.97 for H---C 6H 4---CH 2√, 4.13±0.81 and 19.10±1.20 for Cl---C 6H 4---CH 2√ and 4.17±0.44 and 14.62±0.52 for NO 2---C 6H 4---CH 2√. 相似文献
18.
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
19.
The crystal and magnetic structure of Sr 2ErRuO 6 has been studied by means of neutron powder diffraction as well as magnetization and susceptibility measurements. Neutron diffraction profile measured at 50 K shows that the Ru 5+ and Er 3+ are ordered in the B-sites of the perovskite-type structure, while the Sr atoms occupy the A-site. This compound crystallizes with a monoclinic unit cell, space group P2 1/ n and lattice parameters are approximately √2 ap × √2 ap × 2 ap. Magnetic susceptibility measurements reveal the existence of antiferromagnetic interactions in which Ru 5+ and Er 3+ sublattices are involved. The field dependence of the magnetization indicates the presence of a weak ferromagnetic component at the transition temperature, arising from the spin canting of the antiferromagnetically ordered Ru 5+ and Er 3+ moments. Thermal evolution of the neutron diffraction patterns indicate that the Nèel temperature is 36 K and the magnetic reflections can be indexed on the basis of a propagation vector k = [0, 0, 0]. The spin arrangement is described by the A xA z magnetic modes where the Ru 5+ and Er 3+ moments are mainly aligned along the c-axis of the structure, forming an angle of 6° with the c-axis in the case of the Er 3+ sublattice and 15° for the Ru 5+ moment. 相似文献
20.
Rate constants for the tunneling reaction (HD + D → h + D 2) in solid HD increase steeply with increasing temperature above 5 K, while they are almost constant below 4.2 K. The apparent activation energy for the tunneling reaction above 5 K is 95 K, which is consistent with the energy (91–112 K) for vacancy formation in solid hydrogen. The results above 5 K were explained by the model that the tunneling reaction was accelerated by a local motion of hydrogen molecules and hydrogen atoms. The model of the tunneling reaction assisted by the local motion of the reactans and products was applied to the temperature dependence of the proton-transfer tunneling reaction (C 6H 6− + C 2H 5OH → C 6H 7 + C 2H 5O −) in solid ethanol, the tunneling elimination of H 2 molecule of H 2 molecule ((CH 3) 2 CHCH(CH 3) 2+ → (CH 3) 2 C = C(CH 3) 2+ + H 2) in solid 2,3-dimethylbutane, and the selective tunneling reaction of H atoms in solid neo-C 5H 12-alkane mixtures. 相似文献
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