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121.
Ahmed El Abed Etienne Gaudin Jacques Darriet 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(10):i138-i140
Single crystals of Sr4Mn2.09Cu0.91O9 have been grown by flux synthesis and the structure, closely related to the hexagonal perovskite 2H, was solved from single‐crystal X‐ray data in space group P321. The structure of Sr4Mn2CuO9 is composed of chains of face‐sharing polyhedra with a sequence of two octahedra and one trigonal prism. The octahedra are filled by Mn atoms and the Cu atoms are randomly distributed at the centres of the square faces of the trigonal prism. A stacking fault is observed within one of the two chains, which can be attributed to a shifting of the chain along the c axis. 相似文献
122.
Lone Skov Henrik Hansen Henning C. Dittmar Jonathan N. W. N. Barker Jan C. Simon Ole Baadsgaard 《Photochemistry and photobiology》1998,67(6):714-719
Sensitization on skin exposed to acute low-dose UVB irradiation separates normal humans into two phenotypically distinct groups: One group, following sensitization on UVB-irradiated skin, develops contact sensitivity, designated UVB resistant (UVB-R) and the second group, following sensitization on UVB-irradiated skin, fails to develop contact sensitivity, designated UVB susceptible (UVB-S). To investigate whether UVB susceptibility in humans is related to antigen-presenting activity in the skin we studied the effect of UVB irradiation on the number and function of the epidermal antigen-presenting cells in volunteers identified as UVB-R and UVB-S. Single cell suspensions of epidermal cells from control skin and skin exposed to 3 minimal erythema doses (MED) of UVB 3 days previously were stained for Langerhans cells (CD1a+HLA-DR+) and epidermal macrophages (CD1a-HLA-DR+). The UVB exposure of the skin significantly decreased the percentage of Langerhans cells (UVB-R: n = 7, P < 0.02, UVB-S: n = 6, P < 0.03) and increased the percentage of epidermal macrophages (UVB-R: n = 7, P < 0.03, UVB-S: n = 6, P < 0.03) however to the same degree in both the UVBR and the UVB-S group. To study the effect on Langerhans cell alloreactivity, epidermal cells were harvested immediately after UVB irradiation. However, in both UVB-R and UVB-S subjects the Langerhans cell alloreactivity was blocked to the same degree immediately after UVB irradiation compared to nonirradiated epidermal cells. To determine the effect of UVB irradiation on epidermal macrophages, epidermal cells were harvested 3 days after UVB irradiation. Irradiated epidermal cells from both UVB-R and UVB-S subjects demonstrated a strong antigen-presenting capacity compared to epidermal cells from control skin leading to activation of T cells that mainly secrete interferon (1FN)-γ and not interleukin (IL)-4. In conclusion we found that UVB susceptibility was not correlated with the number of Langerhans cells or epidermal macrophages in the skin at the same time of sensitization. Neither was it correlated with the capacity of Langerhans cells nor UVB-induced epidermal macrophages to activate T cells in vitro. 相似文献
123.
Bretonnière Y Mazzanti M Pécaut J Olmstead MM 《Journal of the American Chemical Society》2002,124(31):9012-9013
The simple asymmetric tetradentate ligand 2,2':6',2' '-terpyridine-6-carboxylic acid leads to the self-assembly of the first europium nanowheel containing europium ions in two different coordination environments. Moreover the self-assembly of bis(terpyridinecarboxylate) europium species to form a hexameric wheel capable of strongly binding LnIII cations is controlled by the ligand/cation ratio. 相似文献
124.
The possibility to design new composites associating biopolymers with mineral phases relies on the understanding and control of their mutual interactions. In this work, aqueous solutions of gelatine and sodium silicate were mixed at pH 5, 37 degrees C and left to stand at 20 degrees C for 1 day. At low gelatine and high silicate contents, precipitates were obtained, containing a fixed silicon/polymer molar ratio. Scanning electron microscopy (SEM) reveals that they are formed of large aggregates of platelets, constituted of closely-packed nanoparticles. For high gelatine contents, composite gels were formed consisting of silica particles dispersed in the biopolymer matrix. Swelling studies indicate that the addition of silica decreases the stability of the gels by inducing gelatine depletion in solution. Similar experiments conducted at pH 7 show that at this pH, silicates are more effective at precipitating gelatine. A model is proposed for the formation of the composites, based on the electrostatic interactions arising between silicates and polymer chains. These results are discussed in the context of hybrid biomaterials design and biosilicification processes. 相似文献
125.
The interaction of carbenium ion pairs with silica is studied by means of UV-spectroscopy, electrokinetic and adsorption measurements using triphenylmethyl derivatives, (RC6H4)3CX, (X=F, Cl, Br, SCN, OH; R=Cl, I, H, CH3, C(CH3)3, OCH3, N(CH3)2) in interaction with silica particles suspended in 1,2-dichloroethane. The adsorption of triarylmethyl-halides onto silica is accompanied by the heterolytic dissociation of the tertiary carbonhalogen bond. The degree of ionization depends on the basicity of the counter anion and acidity of the cation, respectively. The influences of both concentration and structure of triarylmethyl halides on the zeta-potential are discussed with regard to steric and electronic factor. The zeta-potential values of the adsorbates decrease significantly, as compared with the free silica surface, from a certain triarylmethyl halide concentration where ionization takes place, to a constant level which is characteristic of the carbenium ion pair. These constant zeta-potential values of the adsorbates depend on the basicity of the counter ion and the
p
Hammett constants of the ring substitutents, with exclusion of sterically hindered substituents and salt derivatives, e.g., crystal violet and malachite green. 相似文献
126.
Hydrothermal synthesis and magnetic properties of novel Mn(II) and Zn(II) materials with thiolato-carboxylate donor ligand frameworks 总被引:1,自引:0,他引:1
Humphrey SM Mole RA Rawson JM Wood PT 《Dalton transactions (Cambridge, England : 2003)》2004,(11):1670-1678
The hydrothermal reaction of thiosalicylic acid, (C(6)H(4)(CO(2)H)(SH)-1,2) with manganese(III) acetate leads to formation of the coordination solid [Mn(5)((C(6)H(4)(CO(2))(S)-1,2)(2))(4)(mu3-OH)2] (1) via a redox reaction, where resulting manganese(II) centres are coordinated by oxygen donor atoms and S-S disulfide bridge formation is simultaneously observed. Reaction of the same ligand under similar conditions with zinc(II) chloride yields the layered coordination solid [Zn(C(6)H(4)(CO(2))(S)-1,2)] (2). Hydrothermal treatment of manganese(III) acetate with 2-mercaptonicotinic acid, (NC(5)H(3)(SH)(CO(2)H)-2,3) was found to produce the 1-dimensional chain structure [Mn(2)((NC(5)H(3)(S)(CO(2))-2,3)(2))(2)(OH(2))(4)].4H(2)O (3) which also exhibits disulfide bridge formation and oxygen-only metal interactions. Compound 3 has been studied by thermogravimetric analysis and indicates sequential loss of lattice and coordinated water, prior to more comprehensive ligand fragmentation at elevated temperatures. The magnetic behaviour of 1 and 3 has been investigated and both exhibit antiferromagnetic interactions. The magnetic behaviour of 1 has been modelled as two corner-sharing isosceles triangles whilst 3 has been modelled as a 1-dimensional chain. 相似文献
127.
A method for the determination of salicylate in whole blood is described. The assay uses salicylate hydroxylase to convert salicylate to catechol in the presence of NADH and molecular oxygen. The formation of catechol is monitored amperometrically by oxidation at +300 mV vs.Ag/AgCl and the size of the oxidation current is related to the concentration of salicylate in the sample. The reagents are incorporated into the working electrode of a disposable strip, allowing measurements to be made on a drop of blood within 1 min. The functional range of the assay can be extended to the equivalent of 7.2 mM plasma salicylate by incorporating benzoate as a component of the reaction system. The method has the advantages of simplicity and speed compared with standard procedures, and should prove especially useful in suspected overdose situations. 相似文献
128.
Jerry L. Atwood Hosny Elgamal Gregory H. Robinson Simon G. Bott James A. Weeks William E. Hunter 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(1-2):367-376
In contrast to aluminum alkyls, alkyl aluminum halides such as EtAlCl2 react with crown ethers to form cation-anion pairs which exhibit the liquid clathrate effect. Specifically, [12-C-4·AlCl2][AlCl3Et] and [18-C-6·AlCl2][AlCl3Et] have been isolated and characterized by X-ray diffraction techniques. The cations show aluminum in an octahedral environment made up of four of the oxygen atoms from the crown and two chlorine atoms. The 12-C-4 derivative crystallizes in the monoclinic space group P21/c with cell constants of a=7.497(4), b=22.121(8), c=12.339(5) Å, =94.99(3)o, and Z=4 for =1.43 g cm–3. Least-squares refinement based on 1413 observed reflections led to a final conventional R value of 0.093. The 18-C-6 complex belongs to the triclinic space group P1 with a=8.414(4), b=12.193(6), c=12.394(6) Å, =73.14(4), =86.07(4), =81.52(4)o, and Z=2 for =1.45 g cm–3. Refinement based on 2605 observed reflections led to R=0.063. The complex aluminum-containing species are related to a class of compounds called aluminoxanes. 相似文献
129.
130.
Simon Doherty Julian G. Knight Tom H. Scanlan Mark R. J. Elsegood William Clegg 《Journal of organometallic chemistry》2002,650(1-2):231-248
The aprotic and protic bi- and multidentate iminophosphines 2-Ph2PC6H4N=CR1R2 (R1=H, R2=Ph=2a; R1=Me R2=Ph=2b; R1=H, R2=2-thienyl=2c; R1=H, R2=C6H4-2-PPh2=2d; R1=H, R2=C6H4-2-OH=2e, R1=H, R2=C6H4-2-OH-3-But=2f; R1=H, R2=CH2C(O)Me=2g) have been prepared by the acid catalyzed condensation of 2-(diphenylphosphino)aniline with the corresponding aldehyde–ketone. Iminophosphine 2d can be reduced with sodium cyanoborohydride to give the corresponding amino-diphosphine 2-Ph2PC6H4N(H)CH2C6H4-2-PPh2 (2h). In the presence of a stoichiometric quantity of acid, 2-(diphenylphosphino)aniline reacts in an unexpected manner with benzaldehyde, salicylaldehyde, or acetophenone to give the corresponding 2,3-dihydro-1H-benzo[1,3]azaphosphol-3-ium salts and with pyridine-2-carboxaldehyde to give N-(pyridin-2-ylmethyl)-2-diphenylphosphinoylaniline, the latter of which has been characterized by single-crystal X-ray crystallography, as its palladium dichloride derivative. The attempted condensation of 2-(diphenylphosphino)aniline with pyridine-2-carboxaldehyde to give the corresponding pyridine-functionalized iminophosphine resulted in an unusual transformation involving the diastereoselective addition of two equivalents of aldehyde to give 1,2-dipyridin-2-yl-2-(o-diphenylphosphinoyl)phenylamino-ethanol, which has been characterized by a single-crystal X-ray structure determination. The bidentate iminophosphine 2-Ph2PC6H4N=C(H)Ph reacts with [(cycloocta-1,5-diene)PdClX] X=Cl, Me) to give [Pd{2-Ph2PC6H4N=C(H)Ph}ClX] and the imino-diphosphine 2-Ph2PC6H4N=C(H)C6H4-PPh2 reacts with [(cycloocta-1,5-diene)PdClMe] to give [Pd{2-Ph2PC6H4N=C(H)C6H4---PPh2}ClMe] and each has been characterized by single-crystal X-ray crystallography. The monobasic iminophosphine 2-Ph2PC6H4N=C(Me)CH2C(O)Me reacts with [Ni(PPh3)2Cl2] in the presence of NaH to give the phosphino–ketoiminate complex [Ni{2-Ph2PC6H4N=C(Me)CHC(O)Me}Cl], which has been structurally characterized. Mixtures of iminophosphines 2a–h and a palladium source catalyze the Suzuki cross coupling of 4-bromoacetophenone with phenyl boronic acid. The efficiency of these catalysts show a marked dependence on the palladium source, catalysts formed from [Pd2(OAc)6] giving consistently higher conversions than those formed from [Pd2(dba)3] and [PdCl2(MeCN)2]. Catalysts formed from neutral bi- and terdentate iminophosphines 2a–d gave significantly higher conversions than those formed from their monobasic counterparts 2e–f. Notably, under our conditions the conversions obtained with 2a–c compare favorably with those of the standards; catalysts formed from tris(2-tolyl)phosphine and tris(2,4-di-tert-butylphenyl)phosphite and a source of palladium. In addition, mixtures of [Ir(COD)Cl]2 and 2a–h are active for the hydrosilylation of acetophenone; in this case catalysts formed from monobasic iminophosphines 2e–f giving the highest conversions. 相似文献