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1.
Haim Gvirtzman Mordeckai Magaritz Eugenia Klein Arie Nadler 《Transport in Porous Media》1987,2(1):83-93
Cold stage Scanning Electron Microscopy (SEM) with a rapid cooling technique makes it possible to investigate the water phase within unsaturated porous media. It is thought that this technique preserves the main features of the micromorphology of the water menisci as it exists in the liquid phase in soils. Saddle-shaped elements, as well as pendular rings of water, were observed with concave and convex curvatures of the water-air interface. The hydraulic conductivity of an unsaturated soil may be inferred from SEM photographs. Observations of isolated water menisci indicate the existence of an immobile water domain. The surface geometry of the water menisci was analyzed quantitatively and surface tension and capillary pressure were determined. 相似文献
2.
3.
Michal Shahar Haim Meshulam Shlomo Margel 《Journal of polymer science. Part A, Polymer chemistry》1986,24(2):203-213
Two sytrene derivatives formylstyrene and styrene sulfonylcholoride, were synthesized. Polymeric microspheres in diameters ranging from 0.1 to 2 μm were synthesized by polymerization of chlormoethylstyrene, formylstyrene, and styrene sulfonylcholoride in organic solvents, in the presence of appropriate surfactants. The kinetics of microsphere formation were studied. The molecular weight distribution of the products was determined by gel permeation chromatography. Conditions for binding various amino ligands to the microspheres were also established. 相似文献
4.
The synthesis of a new ligand system for mono- and bimetallic complexes based on a calixarene is described. Ligand BBPC (3, bis(bipyridine)-calix[4]arene) is obtained in three steps in 40% overall yield by first brominating one of the methyl groups of the 4,4'-dimethyl-2,2'-bipyridine in two steps and subsequently reacting it with p-tert-butylcalix[4]arene under basic conditions. Reaction of BBPC (3) with 2 equiv of [Rh(NBD)(2)]BF(4) or [Rh(NBD)(CH(3)CN)(2)]BF(4) (NBD = norbornadiene) produces the bimetallic compound BBPC[Rh(NBD)BF(4)](2) (4). Treatment of the ligand with PdCl(2)(CH(3)CN)(2) leads to the isolation of the bimetallic complex BBPC[PdCl(2)](2) (5). When the nickel precursor NiBr(2)(DME) (DME = dimethoxyethane) is reacted with BBPC, the bimetallic complex BBPC[NiBr(2)](2) (6) is isolated which, upon crystallization from methanol, gives the mononuclear bis(bipyridine) complex BBPC[NiBr(OMe)] (7). Full characterization includes X-ray structural studies of complexes 4, 5, and 7. The bimetallic compounds 4 and 5 show metal to metal distances of 4.334 A (for 4) and 3.224 A (for 5). For all three complexes, unique molecular packing arrangements were found, based on hydrophobic/hydrophilic interactions. 相似文献
5.
Poverenov E Gandelman M Shimon LJ Rozenberg H Ben-David Y Milstein D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(19):4673-4684
Novel anionic dialkyl, diaryl, and dihydride platinum(II) complexes based on the new "long-arm" hemilabile PCN-type ligand C6H4[CH2P(tBu)2](CH2)2N(CH3)2 with the general formula Li+[Pt(PCN)(R)2]- (R=Me (4), Ph (6) and H (9)) were prepared by reaction of [Pt(PCN)(R)] complexes (obtained from the corresponding chlorides) with an equivalent of RLi, as a result of the opening of the chelate ring. Alkylating agents based on other metals produce less stable products. These anionic d8 complexes are thermally stable although they bear no stabilizing pi acceptors. They were characterized by 1H, 31P[1H], 13C, and 7Li NMR spectroscopy; complex 9 was also characterized by single crystal X-ray crystallography, showing that the Li+ ion is coordinated to the nitrogen atom of the open amine arm and to the hydride ligand (trans to the P atom) of a neighboring molecule (H--Li=2.15 A), resulting in a dimeric structure. Complexes 4 and 9 exhibit high nucleophilic reactivity, upon which the pincer complex is regenerated. Reaction of 4 with water, methyl iodide, and iodobenzene resulted in the neutral complex [Pt(PCN)(CH3)] (3) and methane, ethane, or toluene, respectively. Labeling studies indicate that the reaction proceeds by direct electrophilic attack on the metal center, rather than attack on the alkyl ligand. The anionic dihydride complex 9 reacted with water and methyl iodide to yield [Pt(PCN)(H)] (8) and H2 or methane, respectively. 相似文献
6.
Shaakov S Galili T Stavitski E Levanon H Lukas A Wasielewski MR 《Journal of the American Chemical Society》2003,125(21):6563-6572
We have synthesized a series of structurally related, covalently linked electron donor-acceptor triads having highly restricted conformations to study the effects of radical ion pair (RP) structure, energetics, and solvation on charge recombination. The chromophoric electron acceptor in these triads is a 4-aminonaphthalene-1,8-dicarboximide (6ANI), in which the 4-amine nitrogen atom is part of a piperazine ring. The second nitrogen atom of the piperazine ring is part of a para-substituted aniline donor, where the para substituents are X = H, OMe, and NMe(2). The imide group of 6ANI is linked to a naphthalene-1,8:4,5-bis(dicarboximide) (NI) electron acceptor across a phenyl spacer in a meta relationship. The triads undergo two-step photoinduced electron transfer to yield their respective XAn(*)(+)-6ANI-Ph-NI(*)(-) RP states, which undergo radical pair intersystem crossing followed by charge recombination to yield (3)NI. Time-resolved electron paramagnetic resonance experiments on the spin-polarized RPs and triplet states carried out in toluene and in E-7, a mixture of nematic liquid crystals (LCs), show that for all three triads, the XAn(*)(+)-6ANI-Ph-NI(*)(-) RPs are correlated radical pairs and directly yield values of the spin-spin exchange interaction, J, and the dipolar interaction, D. The values of J are all about -1 mT and show that the LC environment most likely enforces the chair conformation at the piperazine ring, for which the RP distance is larger than that for the corresponding boat conformation. The values of D yield effective RP distances that agree well with those calculated earlier from the spin distributions of the radical ions. Within the LC, changing the temperature shows that the CR mechanism can be changed significantly as the energy levels of the RPs change relative to that of the recombination triplet. 相似文献
7.
The photoexcited triplet state of phenazine in toluene glasses at 35 K is investigated by light modulation-EPR spectroscopy. From the transient EPR spectra and the kinetics in the three canonical orientations (p = x, y, z) the rate parameters are determined. Thus, the depopulation rate constants kp, the anisotropic spin lattice relaxation rate constants Wp, and the ratios between the population constants Ap are calculated: kx = (2.2 ± 0.3) × 102 s?1, ky = (0.21 ± 0.04) × 102 s?1, kz = (0.06 ± 0.03) × 102 s?1, Wx = (8.6 ± 0.9) × 103 s?1, Wy = (11.0 ± 1.0) × 103 s?1, Wz = (14.0 ± 1.4) × 103 s?1, and Ax: Ay:Az ≈ 1:0.04:0.02. It is concluded therefore that the in-plane spin state |τx > is the active one. 相似文献
8.
Transgressive dune fields, which are active sand areas surrounded by vegetation, exist on many coasts. In some regions like in Fraser Island in Australia, small dunes shrink while large ones grow, although both experience the same climatic conditions. We propose a general mathematical model for the spatiotemporal dynamics of vegetation cover on sand dunes and focus on the dynamics of transgressive dunes. Among other possibilities, the model predicts growth parallel to the wind with shrinkage perpendicular to the wind, where, depending on geometry and size, a transgressive dune can initially grow although eventually shrink. The larger is the initial area the slower its stabilization process. The model’s predictions are supported by field observations from Fraser Island in Australia. 相似文献
9.
AbstractThe reactions of methyl radicals with MII-(ntp)(H2O)2 complexes were studied. The formation of an unstable intermediate (ntp)(H2O)MIII-CH3 is observed. This reaction is an equilibrium process, i.e. the MIII-C bond decomposes via homolysis. The (ntp)(H2O)MIII-CH3 complexes isomerize to a more stable form. The results compared to those obtained in analogous reactions of the MII-(nta)(H2O)2 complexes were shown to be similar with one exception – for the nta complexes no isomerization process is observed. 相似文献
10.
Israel Zilbermann Avraham Meshulam Haim Cohen Dan Meyerstein 《Supramolecular chemistry》2013,25(2):325-332
Abstract The mechanisms and kinetics of oxidation of ascorbate, AH?, by Ni(III)Li aq and by LiNi(III) (HPO4)2 ? complexes (L1 = meso-(5,12)-7,7,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane; L2 = 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane) in neutral aqueous solutions have been investigated. The oxidation of ascorbate by the LiNi(III) (HPO4)2 ? and Ni(III)L1 aq proceeds via two consecutive reactions well separated in time. The products of the first reaction are the A.? radical anion and the corresponding Ni(II) complex. The oxidations by the LiNi(III)(HPO4)2 ? complexes proceed via the outer sphere mechanism, whereas the detailed mechanism of reaction of Ni(III)L1 aq cannot be determined. The rate of reaction decreases with the increase in the concentration of phosphate, thus indicating that LiNi(III)(HPO4)(H2O)+ and LiNi(III)OH2+ are stronger oxidizing agents than LiNi(III)(HPO4)? 2. The oxidation of ascorbate by Ni(III)L2 aq proceeds via three consecutive reactions which are well separated in time. Thus the results clearly point out that this process occurs via the inner sphere mechanism. The first transient observed is tentatively identified as L2(H2O)Ni(II)(A.?)2+, i.e., an unexpected complex of the ascorbate anion radical. Also in this process the last transient observed is the A.? anion radical. The stabilization of the ascorbyl radical in a transient complex might be of biological significance. 相似文献