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991.
992.
Prélot B Poinsignon C Thomas F Schouller E Villiéras F 《Journal of colloid and interface science》2003,257(1):77-84
Relationships between lattice parameters of manganese dioxides and their surface properties at the solid-aqueous solution interface were investigated. The studied series ranged from ramsdellite to pyrolusite and encompassed disordered MD samples. The structural model used takes into account structural defects: Pr (rate of pyrolusite intergrowth) and Tw (rate of microtwinning). Water adsorption isotherms showed that the cross sectional area of water molecules adsorbed in the first monolayer is positively correlated to Pr. Titration of the surface charge of the MD series evidenced a positive linear relationship between the PZC and Pr (Pr=0, Tw=0, PZC=1 for ramsdellite; Pr=1, Tw=0, PZC=7.3 for pyrolusite; gamma-MD with intermediate values of Pr (0.2 to 0.45) have increasing PZC values). The rate of microtwinning appeared as a secondary factor for the increase of the PZC. The above correlations are explained by the chemical defects at the origin of the structural disorder, respectively Mn(3+)/Mn4+ substitution for Pr and Mn vacancies for Tw, which result in proton affinity and thus in increased PZC. The experimental results are compared with data collected in the literature for manganese dioxides as well as for dioxides of transition elements with tetragonal structure. 相似文献
993.
N. Batbayar D. Batsurén B. Tashkhodzhaev I. M. Yusupova M. N. Sultankhodzhaev 《Chemistry of Natural Compounds》1993,29(1):38-43
Aconitine, mesaconitine, and a new alkaloid, which has been called altaconitine, have been isolated from the total alkaloids of the epigeal part ofAconitum altaicum. Altaconitine has the structure of 8-acetoxy-14-benzoyloxy-2,3,13,-15-tetrahydroxy-1,6, 16-trimethoxy-4-methoxymethy-N-ethylaconitan, which was established on the basis of a study of IR, PMR,13C NMR, and mass spectra and by the x-ray structural method.Institute of Chemistry, Mongolian Peoples' Republic Academy of Sciences, Ulan-Bator. Institute of the Chemistry of Plant Substances of the Uzbekistan Republic of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 47–53, January–February, 1993. 相似文献
994.
It was demonstrated that adsorbed CO is obtained from the reduction of NaHCO3 solution when Pt(100), Pt(110), disordered Pt(111) and polycrystalline electrodes are employed. Reduction of CO2 coming from the dissociation of the hydrogencarbonate anion is proposed as the reaction that produces CO. By using Fourier transform infrared spectroscopy, linear and multi-bonded CO were detected on polycrystalline platinum electrodes. The shape of the band associated with linearly adsorbed CO is monopolar as a consequence of the partial overlapping, at lower wavenumbers, of the absolute bands at both potentials (0.05 and 0.35 V). 相似文献
995.
Raymundo Cea-Olivares Jesús Wingartz Jorge Cárdenas Jesus Valdés-Martínez Thelma Alvarado 《Transition Metal Chemistry》1991,16(1):62-64
Summary The interaction of non-anhydrous solutions of the ligand 1,3-bis-(2-hydroxyphenyl)-1,3-propanedione (bhppH3) with hydrated rare earth chlorides resulted in the formation of anhydrous, non-solvated, complexes M(bhppH2)3 (M=Y, La, Nd, Pr, Sm or Yb). The complexes have been characterized by elemental analysis, t.g., i.r. and1H n.m.r. spectroscopy. The evidence suggests that the coordination is through the -diketone site. 相似文献
996.
Abstract— We determined the polarized and isotropic visible/UV absorption spectra of chlorophyll a (Chi a ) and pheophytin a (Pheo a ) oriented in the lamellar phase of glycerylmonooctanoate/H2 O. Resolution into mutually perpendicular X- and Y-polarized absorption spectra of the pigments was achieved assuming that the transition moments of Chi a and Pheo a are located in the plane of the chromophores. The polarized spectra were deconvoluted into harmonic progressions and the resultant assignment of band positions in the long-wavelength region was found to correlate well with independent spectral measurements, such as the polarisation of fluorescence. However, the correlation of the experimentally determined transitions with the results of theoretical calculations is not straightforward. The overall conclusions are of fundamental interest in the determination of orientations of the tetrapyrrole macrocycle in lipid lamellae and pigment-protein structures of photosynthetic membranes. 相似文献
997.
Yolanda Prieto Marcelo Muoz Vernica Arancibia Mauricio Valderrama Fernando J. Lahoz M. Luisa Martín 《Polyhedron》2007,26(18):5527-5532
The reaction of the dimer complex [{Ru(CO)3Cl2}2] with the ligands 4,6-dichloroquinoline-5,8-dione and 6-methoxybenzo[g]quinoline-5,10-dione in ethanol solution led to the neutral mononuclear complexes of general formula [Ru(CO)2Cl2(κ2-quinolinedione-N,O)]. The complexes were characterized by elemental analysis, IR and RMN spectroscopy, and the molecular structure of [Ru(CO)2Cl2(6-methoxybenzo[g]quinoline-5,10-dione)] was determined by single-crystal X-ray diffraction. The redox chemistry of ligands and complexes was investigated by cyclic voltammetry, and their potential antitumor activity was also evaluated. 相似文献
998.
999.
Determination of aflatoxins in peanuts by matrix solid-phase dispersion and liquid chromatography 总被引:7,自引:0,他引:7
A new method based on matrix solid-phase dispersion (MSPD) extraction was studied to determine aflatoxin B1, B2, G1 and G2 from peanuts. Optimization of different parameters, such as type of solid supports for matrix dispersion and elution solvents were carried out. The method used 2 g of peanut sample, 2 g of C18 bonded silica as MSPD sorbent and acetonitrile as eluting solvent. Recoveries of each aflatoxin spiked to peanut samples at 2.5 ng/g (5 ng/g for aflatoxin G2) level were between 78 and 86% with relative standard deviations ranging from 4 to 7%. The limits of quantification ranged from 0.125 to 2.5 ng/g for the four studied aflatoxins using liquid chromatography (LC) with fluorescence detection. In addition, LC coupled to mass spectrometry with an electrospray interface was used for confirmation of aflatoxins present in real samples. Eleven peanut samples from different countries were analyzed by the proposed method and by using an enzyme-linked immunosorbent assay (ELISA). ELISA test is a good screening method for investigation of these mycotoxins in peanut samples. 相似文献
1000.
Jorge Bravo Jesús Castro Soledad García‐Fontn Elvira M. Lamas Pilar Rodríguez‐Seoane 《无机化学与普通化学杂志》2003,629(2):297-302
The manganese carbonyl complex [MnBr(CO)3 L ] ( 1 ), where L = Ph2POCH2CH2OPPh2, was prepared by reacting [MnBr(CO)5] with the bidentate ligand 1, 2‐Bis(diphenylphosphinite)ethane. From this compound and the appropriate phosphite, phosphinite or phosphonite ligands were synthesized the complexes [MnBr(CO)2 LL ′], where L ′ = P(OMe)3 ( 2 ) or P(OEt)3 ( 3 ) and [MnBr(CO)3 L ′2], where L ′ =PPh(OEt)2 ( 4 ) or PPh2(OEt) ( 5 ). The obtained compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR (1H, 13C and 31P) spectroscopies and X‐ray diffractometry for the complexes 1 , 4 and 5 . 相似文献