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941.
Preparation and characterization of the first derivatives of the fused macropolyhedral anion [B22H22]2− are reported. The species [B22H21OH]2− (1) and [B22H21OEt]2− (2) are obtained from workup of the products of the reaction between HgBr2 and [NBzlEt3]2[B22H22]; a cluster involving the conjoining of a closo-B12 icosahedron with a nido-B10 cluster. Washing the products with ethanol followed by thin-layer chromatography allows the isolation of 1 and 2, reproducibly, in yields of 27 and 20%, respectively. The species were characterized by NMR spectroscopy, elemental analysis and X-ray diffraction studies. The crystal structure determinations of the two species identify novel features. Apparently the influence of the O atoms in the ions [B22H21OH]2− and [B22H21OEt]2− results in the lengthening of what was a gunwale B---B connection adjacent to the junction of the two cages such that the distances are 2.180 and 2.230 Å, respectively. These latter are longer than the corresponding distance in the parent species [B22H22]2−, which is 2.09 Å; quite long for a normal B---B distance. Thus it is assumed that these B atoms, in 1 and 2, one of which bears the substituent, are not bonded to each other.  相似文献   
942.
The title compound, [Fe2O(SO4)2(C10H8N2)4], crystallizes as two different hydrates, viz. 11H2O, (I), and 15H2O, (II). The complex is binuclear, in which the two FeIII atoms are coordinated in an octa­hedral geometry to four N atoms from the two bipyridine ligands, to one O atom from the sulfate ion and to an oxide ion on a twofold axis, which acts as a bridge between the symmetry‐related units. The Fe⋯Fe separation is 3.556 (4) Å and the Fe—O—Fe angle is 161.6 (2)° in (I); the corresponding values are 3.544 (1) Å and 165.8 (2)° in (II). In (II), one of the O atoms of the sulfate ion is disordered over two positions. In both compounds, the solvent water mol­ecules form slightly different one‐dimensional hydrogen‐bonded networks which pass along the c axis of the unit cell. In (I), three solvent water mol­ecules and, in (II), one solvent water mol­ecule, are situated on the twofold axis. In both (I) and (II), the central O atom of the metal complex lies on a twofold axis.  相似文献   
943.
Gluconacetobacter spp. synthesize a pure form of hydrophilic cellulose that has several industrial specialty applications. Literature reports have concentrated on intensive investigation of static and agitated culture in liquid media containing high nutrient concentrations optimized for maximal cellulose production rates. The behavior of these bacteria on semisolid and solid surfaces has not been specifically addressed. The species Gluconacetobacter hansenii was examined for cellulose synthesis and colony morphology on a range of solid supports, including cotton linters, and on media thickened with agar, methyl cellulose, or gellan. The concentration and chemical structure of the thickening agent were found to be directly related to the formation of contiguous cellulose pellicules. Viability of the bacteria following freezer storage was improved when the bacteria were frozen in their cellulose pellicules. This article was authored by a contractor of the US government under contract no. DEAC05-00OR22725. Accordingly, the US government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for US government purposes.  相似文献   
944.
Translational diffusion, velocity sedimentation and viscosity in acetone as well as flow birefringence (FB) and viscosity in cyclohexanone have been investigated for cyanoethyl cellulose (CEC) with degree of substitution 2.6 in the range of M = (24.5?317) × 103. The dependences of [ν], So and Do on M were obtained. The value of the hydrodynamic constant is A0 = 3.27 × 10?10erg deg?1mol?13. According to hydrodynamic data, the equilibrium rigidity of CEC molecules is characterized by the length of the Kuhn segment A = 240 ? 350 A? and the coefficient of hindrance to intramolecular motion σ = 4.5-5.4. The hydrodynamic diameter of the chain is 8–14 Å. According to the FB data, the value of A is 260 Å. This value is in agreement with hydrodynamic data. The high value of optical anisotropy of the monomer unit, a| - a = 17.8 × 10?25 cm3, is in agreement with the structure and anisotropy of the substituting groups, and the investigation of orientation angles of FB leads to the conclusion that, apart from high equilibrium rigidity, CEC in solution is characterized by considerable kinetic chain flexibility. The data for CEC are compared with the characteristics of other cellulose esters and ethers.  相似文献   
945.
[reaction: see text] The transition structures and alpha-carbon 12C/13C kinetic isotope effects for 22 S(N)2 reactions between methyl chloride and a wide variety of nucleophiles have been calculated using the B1LYP/aug-cc-pVDZ level of theory. Anionic, neutral, and radical anion nucleophiles were used to give a wide range of S(N)2 transition states so the relationship between the magnitude of the alpha-carbon kinetic isotope effect and transition-state structure could be determined. The results suggest that the alpha-carbon 12C/13C kinetic isotope effects for S(N)2 reactions will be large (near the experimental maximum) and that the curve relating the magnitude of the KIE to the percent transfer of the alpha-carbon from the nucleophile to the leaving group in the transition state has a broad maximum. This means very similar KIEs will be found for early, symmetric, and late transition states and that one cannot use the magnitude of these KIEs to estimate transition-state structure.  相似文献   
946.
Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml?1 (5 × 10?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml?1) on incubation at 37°C. The in-vitro loss is rapid (t12 ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.  相似文献   
947.
Photochemically initiated reactions of aliphatic aldehydes, namely acetaldehyde, propionaldehyde and butyraldehyde, with methyl trifluoroacrylate afforded γ-ketoesters of the type R-CO-CF2CHF-COOCH3 in the liquid phase. In the gas phase reaction further products were formed by addition of the aldehyde fragments to the olefinic bond of the methyl trifluoroacrylate.  相似文献   
948.
The known triterpene tetraoside holothurin A has been isolated from the Pacific Ocean holothurianHolothuria squamifera. By using two independent methods — enzymatic cleavage and two-stage Smith degradation — 22,25-epoxyholost-9(11)-ene-3,12,17-triol, C30H46O6, which is the native aglycone of holothurin A, was obtained. The structure of the native aglycone has been established on the basis of the results of IR, mass, and PMR spectroscopy.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 448–451, July–August, 1984.  相似文献   
949.
Methods were developed for the gas-chromatographic determination of alkyl acetates in aqueous solutions in the concentration range of 0.01–100 mg/L with the chromatomembrane gas extraction of analytes from a flow of the test liquid. The analytical potentialities of the direct-flow and counterflow techniques of chromatomembrane gas extraction were compared. It was demonstrated that the interfering effect of petroleum products on the results of analysis can be eliminated by using an additional chromatomembrane cell.  相似文献   
950.
Nonequilibrium molecular dynamics calculations are used to show that polyatomic fluids can support antisymmetric stress. In a homogeneous system where the time dependence of vorticity is a step function, it is shown that the rate at which intrinsic angular velocity approaches its steady-state value ( = 1/2 × u) is determined by the magnitude of the antisymmetric part of the pressure tensor.  相似文献   
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