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41.
M. Pealat D. Debarre J.-M. Marie J.-P.E. Taran A. Tramer C.B. Moore 《Chemical physics letters》1983,98(4):299-304
Coherent anti-Stokes Raman scattering (CARS) has been used to observe H2 from H2CO + hv H2 + CO. Photolysis of K = 1 (ortho) lines of the 2141 S1 ← S0 transition produced no para-H2 (<4% statistical); and demonstrated nuclear spin conservation. H2 states v = 1, 2 and 3 were comparably populated. 相似文献
42.
M.?Prasad S.?P.?MoulikEmail author A. Al.?Wardian S.?Moore A.?van?Bommel R.?PalepuEmail author 《Colloid and polymer science》2005,283(8):887-897
The clouding points (CP) of the nonionic surfactants p-tert-octyl phenyl polyoxyethylene ether (Triton X 100), Brij-56 and Brij-97, and the water soluble polymer polyvinylmethylether (PVME) have been measured in the presence of the ionic surfactants alkyl (C10, C12, C14 and C16) triphenyl phosphonium bromides (ATPBs). The threshold additive concentrations required for efficient CP enhancement of the systems that were studied have been determined. Considering CP as the threshold state of phase separation, the energetics of the process at different additive concentrations has been evaluated. The spontaneity of free energy of the clouding process (G
c
0
) at the transition concentrations followed the order PVME > TX 100 Bj 56 > Bj 97. The clouding process has been found to be energetically endothermic with fairly large enthalpy and entropy changes that nicely compensate each other. The compensation temperature has been evaluated and compared with different types of the clouding agents.This revised version was published online in January 2005 with corrections to the names of the authors. 相似文献
43.
13C NMR data for a series of arylthallium trifluoroacetates (ArTlX2, X = OCOCF3) are reported and assigned. The range of carbon—thallium couplings to be expected, the dependence on the disposition of coupled nuclei, and chemical shift effects are discussed. The Tl(OCOCF3)2 group is shown to be a powerful electron withdrawing group, from both the 13C data and 19F substituent chemical shifts of the p-fluorophenyl derivative. 相似文献
44.
Blum AS Ren T Parish DA Trammell SA Moore MH Kushmerick JG Xu GL Deschamps JR Pollack SK Shashidhar R 《Journal of the American Chemical Society》2005,127(28):10010-10011
Reported in this contribution are the synthesis, characterization, and charge transport properties of wire-like Ru2(ap)4(OPEn), where ap is 2-anilinopyridinate and OPE is -(CCC6H4)nSCH2CH2SiMe3 with n = 1 (1) and 2 (2). Scanning tunneling microscopy (STM) measurements of compound 2 inserted into a SAM of C11 thiol reveal that molecule 2 exhibits (i) the stochastic switching characteristic of wire molecules embedded in insulating SAMs and (ii) higher conductivity than the C11 thiol SAM. More importantly, analysis of the molecular electronic decay constant (beta) exhibits a decrease of at least 15% as compared to purely organic molecular analogues. Hence, the transport characteristics of molecules can be significantly improved for nanoscale electronics through the incorporation of a Ru2 fragment into conjugated backbone. 相似文献
45.
Krasnovsky AA Cheng P Blankenship RE Moore TA Gust D 《Photochemistry and photobiology》1993,57(2):324-330
Measurements of pigment triplet-triplet absorption, pigment phosphorescence and photosensitized singlet oxygen luminescence were carried out on solutions containing monomeric bacteriochlorophylls (Bchl) c and d, isolated from green photosynthetic bacteria, and their magnesium-free and farnesyl-free analogs. The energies of the pigment triplet states fell in the range 1.29-1.34 eV. The triplet lifetimes in aerobic solutions were 200-250 ns; they increased to 280 +/- 70 microseconds after nitrogen purging in liquid solutions and to 0.7-2.1 ms in a solid matrix at ambient or liquid nitrogen temperatures. Rate constants for quenching of the pigment triplet state by oxygen were (2.0-2.5) x 10(9) M-1 s-1, which is close to 1/9 of the rate constant for diffusion-controlled reactions. This quenching was accompanied by singlet oxygen formation. The quantum yields for the triplet state formation and singlet oxygen production were 55-75% in air-saturated solutions. Singlet oxygen quenching by ground-state pigment molecules was observed. Quenching was the most efficient for magnesium-containing pigments, kq = (0.31-1.2) x 10(9) M-1 s-1. It is caused mainly by a physical process of singlet oxygen (1O2) deactivation. Thus, Bchl c and d and their derivatives, as well as chlorophyll and Bchl a, combine a high efficiency of singlet oxygen production with the ability to protect photochemical and photobiological systems against damage by singlet oxygen. 相似文献
46.
A method based on Ge(Li) γ-ray spectrométry is applied to the determination of 224Ra (t= 3.64 days) in natural waters. The 224Ra is first removed from several hundred liters of water by preconcentration onto manganese dioxide-impregnated acrylic fibers. The fibers are leached, radium is coprecipitated with barium sulfate, and the γ-ray activity is counted so that activity ratios among 224Ra, 225Ra and 226Ra can be calculated. Concentrations are determined by using the 226Ra concentration determined on a small separate sample. Results from samples collected from ground water, estuarine, and continental shelf environments are presented. 相似文献
47.
A. W. P. Jarvie C. G. Moore D. Skelton 《Journal of polymer science. Part A, Polymer chemistry》1971,9(11):3105-3114
The reactions of the allylic peroxides ascaridole, cyclohexadiene endoperoxide, and α-phellandrene peroxide with triphenylphosphine follow an SN i'-type mechanism. In contrast, the acyclic allylic compounds, allyl tert-butyl peroxide, α-cumyl cyclohexenyl peroxide, and tert-butyl cyclohexenyl peroxide apparently react with triphenylphosphine by a free-radical mechanism. The saturated cyclic peroxide dihydroascaridole, in which there is no possibility of an allylic rearrangement, gives with triphenylphosphine a mixture of olefinic alcohols. Di-n-butyl peroxide is readily cleaved by sodium dialkyl phosphites, but sterically hindered peroxides do not react under similar conditions. Reaction can, however, take place at the oxygen adjacent to a large group if a smaller substituent is present on the other oxygen atom. 相似文献
48.
The heat capacities of MnBr2 · 4D2O and MnCl2 · 4D2O have been experimentally determined from 1.4 to 300 K. The smoothed heat capacity and thermodynamic functions (H°TH°0) and S°T are reported for the two compounds over the temperature range 10 to 300 K. The error in the thermodynamic functions at 10 K is estimated to be 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. A λ-shaped heat capacity anomaly was observed for MnCl2 · 4D2O at 48 K. The entropy associated with the anomaly is 1.2 ± 0.2 J/mole K. 相似文献
49.
Stereoselective syntheses of novel 5,6-difunctionalized-2-azabicyclo[2.1.1]hexanes containing 5-anti-fluoro or hydroxyl in one methano bridge and a variety of syn- or anti-chloro, fluoro, hydroxy, methyl, or phenyl substituents in the other methano bridge have been effected. Rearrangements of iodides to alcohols were initiated using Selectfluor. Rearrangement of alcohols to fluorides was initiated using Deoxo-Fluor. Ring opening of 2-azabicyclo[2.2.0]hex-5-ene exo-epoxide with organocopper reagents is regioselective at C(5). 相似文献
50.
We report the synthesis, structural and spectroscopic characterization, and magnetic and electrochemical studies of a series of iron(II) complexes of the pyridyl-appended diazacyclooctane ligand L(8)py(2), including several that model the square-pyramidal [Fe(II)(N(his))(4)(S(cys))] structure of the reduced active site of the non-heme iron enzyme superoxide reductase. Combination of L(8)py(2) with FeCl(2) provides [L(8)py(2)FeCl(2)] (1), which contains a trigonal-prismatic hexacoordinate iron(II) center, whereas a parallel reaction using [Fe(H(2)O)(6)](BF(4))(2) provides [L(8)py(2)Fe(FBF(3))]BF(4) (2), a novel BF(4)(-)-ligated square-pyramidal iron(II) complex. Substitution of the BF(4)(-) ligand in 2 with formate or acetate ions affords distorted pentacoordinate [L(8)py(2)Fe(O(2)CH)]BF(4) (3) and [L(8)py(2)Fe(O(2)CCH(3))]BF(4) (4), respectively. Models of the superoxide reductase active site are prepared upon reaction of 2 with sodium salts of aromatic and aliphatic thiolates. These model complexes include [L(8)py(2)Fe(SC(6)H(4)-p-CH(3))]BF(4) (5), [L(8)py(2)Fe(SC(6)H(4)-m-CH(3))]BF(4) (6), and [L(8)py(2)Fe(SC(6)H(11))]BF(4) (7). X-ray crystallographic studies confirm that the iron(II)-thiolate complexes model the square-pyramidal geometry and N(4)S donor set of the reduced active site of superoxide reductase. The iron(II)-thiolate complexes are high spin (S = 2), and their solutions are yellow in color because of multiple charge-transfer transitions that occur between 300 and 425 nm. The ambient temperature cyclic voltammograms of the iron(II)-thiolate complexes contain irreversible oxidation waves with anodic peak potentials that correlate with the relative electron donating abilities of the thiolate ligands. This electrochemical irreversibility is attributed to the bimolecular generation of disulfides from the electrochemically generated iron(III)-thiolate species. 相似文献