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161.
The reaction of dimethylzinc and tri(tert‐butyl)silylphosphane in toluene yielded dimeric methylzinc tri(tert‐butyl)silylphosphanide ( 1 ) which crystallized tetrameric. Compound 1 was deprotonated with sodium in DME and the solvent‐separated dimeric ion pair [(dme)3Na]+ [(dme)Na(MeZn)2(μ‐PSitBu3)2]? ( 2 ) was isolated. The reaction of 1 in THF with two equivalents of potassium and one equivalent of tri(tert‐butyl)silylphosphane gave dimeric [{tBu3Si(H)P}{(thf)2K}2(MeZn)(PSitBu3)]2 ( 3 ). Both of these phosphanylzincates contain Zn2P2 cycles with Zn‐P bond lengths of approximately 237 pm, whereas in 1 larger Zn‐P bond lengths of 248.5 pm were found due to the larger coordination numbers of the phosphorus and zinc atoms. 相似文献
162.
Snezana S.?MiticEmail author Gordana Z.?Miletic Aleksandra N.?Pavlovic Snezana B.?Tosic 《Monatshefte für Chemie / Chemical Monthly》2004,135(8):927-936
Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H2O2. The optimum reaction conditions are PS (1.32·10–3mol·dm–3), H2O2 (0.32mol·dm–3), HClO4 (2.6·10–3mol·dm–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm–3 and a detection limit of 0.024ng·cm–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples. 相似文献
163.
Polysulfonylamines. CLXIII. Crystal Structures of Metal Di(methanesulfonyl)amides. 12. The Orthorhombic Double Salt Na2Cs2[(CH3SO2)2N]4·3H2O: A Three‐Dimensional Coordination Polymer Built up from Cesium‐Anion‐Water Layers and Intercalated Sodium Ions The packing arrangement of the three‐dimensional coordination polymer Na2Cs2[(MeSO2)2N]4·3H2O (orthorhombic, space group Pna21, Z′ = 1) is in some respects similar to that of the previously reported sodium‐potassium double salt Na2K2[(MeSO2)2N]4·4H2O (tetragonal, P43212, Z′ = 1/2). In the present structure, four multidentately coordinating independent anions, three independent aquo ligands and two types of cesium cation form monolayer substructures that are associated in pairs to form double layers via a Cs(1)—H2O—Cs(2) motif, thus conferring upon each Cs+ an irregular O8N2 environment drawn from two N, O‐chelating anions, two O, O‐chelating anions and two water molecules. Half of the sodium ions occupy pseudo‐inversion centres situated between the double layers and have an octahedral O6 coordination built up from four anions and two water molecules, whereas the remaining Na+ are intercalated within the double layers in a square‐pyramidal and pseudo‐C2 symmetric O5 environment provided by four anions and the water molecule of the Cs—H2O—Cs motif. The net effect is that each of the four independent anions forms bonds to two Cs+ and two Na+, two independent water molecules are involved in Cs—H2O—Na motifs, and the third water molecule acts as a μ3‐bridging ligand for two Cs+ and one Na+. The crystal cohesion is reinforced by a three‐dimensional network of conventional O—H···O=S and weak C—H···O=S/N hydrogen bonds. 相似文献
164.
The preconcentration and voltammetric behavior of BiIII on a sodium humate modified carbon paste electrode was studied by means of cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV). The proposed measurement involves an initial nonelectrolytic preconcentration step in which BiIII is complexed by the surface modifier in a solution of 0.05 M KNO3-0.0106 M HNO3 (pH 2.0) and a subsequent electrochemical scan step in which the preconcentrated BiIII was reduced and then oxidized promptly in supporting electrolyte of 0.5 M HNO3. The resulting DPSV anodic current was proportional to the concentration of BiIII ion over the range of 4.78 × 10−8–1.44 × 10−5 M. The detection limit was 4.78 × 10−8 M. The proposed method was used to determine bismuth in various samples. Various factors affecting the electrode behavior were also investigated at the same time. 相似文献
165.
Cs[Na(NH3)6][B10H10]·NH3 was synthesised from cesium and disodium‐decahydro‐closo‐decaborate Na2B10H10 in liquid ammonia, from which it crystallized in form of temperature sensitive colorless plates (triclinic, P1¯, a = 8.4787(7) Å, b = 13.272(1) Å, c = 17.139(2) Å, α = 88.564(1)°, β = 89.773(1)°, γ = 81.630(1)°, V = 1907.5(3) Å3, Z = 4). The compound is the first example of an alkali metal boranate with two different types of cations. The decahydro‐closo‐decaborate dianions [B10H10]2— and the cesium cations form a equation/tex2gif-stack-1.gif[Cs2(B10H10)2]2— layer parallel to the ac plane. These layers are separated by N—H···N‐hydrogen bonded hexamminesodium cations. 相似文献
166.
Shuhua?HanEmail author Wanguo?Hou Jun?Xu Zhengmin?Li 《Colloid and polymer science》2004,282(11):1286-1291
Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N2 gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N2 adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased 相似文献
167.
Manfred Schlosser 《Angewandte Chemie (International ed. in English)》1974,13(11):701-706
Merits and drawbacks of known carbon-carbon linking procedures are outlined. Two novel methods are discussed in some detail: the copper-catalyzed alkylation of Grignard reagents and reactions with allylpotassium compounds. Both methods provide a very efficient access to saturated, unsaturated, as well as functionally substituted hydrocarbons and moreover permit an astonishing degree of regio- and stereoselective control of olefin synthesis. 相似文献
168.
Separation of sodium dodecyl sulfate (SDS)-protein complexes is difficult on plastic microchips due to protein adsorption onto the wall. In this paper, we elucidated the reasons for the difficulties in separating SDS-protein complexes on plastic microchips, and we then demonstrated an effective method for separating proteins using polymethyl methacrylate (PMMA) microchips. Separation difficulties were found to be dependent on adsorption of SDS onto the hydrophobic surface of the channel, by which cathodic electroosmotic flow (EOF; reversed flow) was generated. Our developed method effectively utilized the reversed flow from this cathodic EOF as a driving force for sample proteins using permanently uncoated but dynamic SDS-coated PMMA microchips. High-speed (6 s) separation of proteins and peptides up to 116 kDa was successfully achieved using this system. 相似文献
169.
Martina Gudelj Paola urina Lucija Jurko Ante Prki Perica Bokovi 《Molecules (Basel, Switzerland)》2021,26(12)
Micellar systems are colloids with significant properties for pharmaceutical and food applications. They can be used to formulate thermodynamically stable mixtures to solubilize hydrophobic food-related substances. Furthermore, micellar formation is a complex process in which a variety of intermolecular interactions determine the course of formation and most important are the hydrophobic and hydrophilic interactions between surfactant–solvent and solvent–solvent. Glycols are organic compounds that belong to the group of alcohols. Among them, propane-1,2-diol (PG) is a substance commonly used as a food additive or ingredient in many cosmetic and hygiene products. The nature of the additive influences the micellar structure and properties of sodium dodecyl sulfate (SDS). When increasing the mass fraction of propane-1,2-diol in binary mixtures, the c.m.c. values decrease because propane-1,2-diol is a polar solvent, which gives it the ability to form hydrogen bonds, decreasing the cohesivity of water and reducing the dielectric constant of the aqueous phase. The values of are negative in all mixed solvents according to the reduction in solvophobic interactions and increase in electrostatic interaction. With the rising concentration of cosolvent, the equilibrium between cosolvent in bulk solution and in the formed micelles is on the side of micelles, leading to the formation of micelles at a lower concentration with a small change in micellar size. According to the 1H NMR, with the addition of propylene glycol, there is a slight shift of SDS peaks towards lower ppm regions in comparison to the D2O peak. The shift is more evident with the increase in the amount of added propane-1,2-diol in comparison to the NMR spectra of pure SDS. Addition of propane-1,2-diol causes the upfield shift of the protons associated with hydrophilic groups, causing the shielding effect. This signifies that the alcohol is linked with the polar head groups of SDS due to its proximity to the SDS molecules. 相似文献
170.
Tsujimi Y. Kobayashi M. Furuta H. Yagi T. 《Journal of Thermal Analysis and Calorimetry》1999,57(3):859-865
The ultra-slow modes with a relaxation time much longer than 1 ns are discovered by a time-resolved spectroscopy in uniaxial ferroelectric (NH2CH2COOH)3H2SO4 (TGS) and in glass-former HOCH2(CHOH)4CH2OH (D-sorbitol). A mode discovered in TGS is a thermal relaxational mode and is proved to be the physical origin of the central peak found by Brillouin scattering. Two modes are discovered in D-sorbitol. One is a thermal relaxational mode. The other is a mode characterized by the Kohlraush-Williams-Watts function with a relaxation time R. A remarkable result is that R indicates a critical behavior not at the liquid-glass transition temperature Tg =–7°C but at the ergodic to nonergodic transition temperature Tc=33°C.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献