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991.
Rider peaks are small peaks which are not well resolved from a large and asymmetrical neighbour but sit on its trailing side. The usual case is a large, tailed peak which is eluted just in front of the small peak, although the opposite situation can also occur (a small peak in front of a large peak with fronting). The common integration techniques. i.e. separating the peaks by vertical drop or by a tangent and determining area or height, give erroneous results. We propose a method for their quantification with low error. It is necessary to set up a "two-dimensional" calibration by varying both concentrations, i.e. of the large peak and of the rider. This leads to a series of linear equations which describe the rider size, as found by the integrator, as a function of the size of the large peak. The y-axis intercepts i of these equations show a linear relationship with the concentration x of the rider analyte, whereas the slopes s follow a quadratic relationship. These equations can be used to solve the equation y = s(x) x z + i(x) for x (y and z are the integrated peak size of the rider and the large peak, respectively). The procedure was tested with computer-generated peak pairs as well as with HPLC separations of 2,3-dimethylaniline (large tailing peak) and 2,3-dimethylphenol (symmetrical rider peak). 相似文献
992.
Adolf Emil Siegrist Hans Rudolf Meyer Peter Gassmann Serge Moss 《Helvetica chimica acta》1980,63(5):1311-1334
Preparation of Styryl and Distyryl Derivatives of Pyridine 2,4-, 2,5- and 2,6-Dimethylpyridines react with anils of aromatic aldehydes in the presence of dimethylformamide and potassium hydroxide to yield the corresponding distyrylpyridines (‘anil synthesis’). Under the same reaction conditions (4-methylstyryl)pyridines are converted to (stilbenylvinyl)pyridines. Similarly, the Schiff's base derived from pyridine-3-carbaldehyde and p-chloroaniline on treatment with methyl- and p-tolyl-substituted aromatic heterocycles gives the corresponding (heteroaryl-styryl)pyridines, whereas with the Schiff's bases derived from pyridine-2- and -4-carbaldehyde side reactions, such as dimerization followed by disproportionation predominate. 相似文献
993.
On CsLiCl2 CsLiCl2 crystallizes with a = 492.35(9), c = 950.0(3) pm (Guinier data), tetragonal, P4/nmm, Z = 2. The crystal structure was determined and refined from single crystal data (R = 5.2, Rw = 4.0%). It is essentially that proposed earlier for KCoO2 which is isotypic with CsLuO2. In CsLiCl2 Cs+ has C.N. = 9 (d? = 363 pm), Li+ C.N. = 5 (tetragonal pyramid) with d(Li? Cl) = 231 and 4 × 260 pm, respectively. 相似文献
994.
Helmreich M Ermilov EA Meyer M Jux N Hirsch A Röder B 《Journal of the American Chemical Society》2005,127(23):8376-8385
The synthesis and photophysical studies of a fullerene [6:0]-hexaadduct that carries 12 pyropheophorbide a units are reported. The synthesis started with the malonate 1, which was coupled under template conditions to C(60)() to give the hexaadduct 2. After removal of the protecting group with acid the dodecakis amino-substituted precursor compound 3 was generated. 3 was not isolated but directly reacted with the N-succinimid ester 4 of pyropheophorbide a (5), which delivered the desired fullerene [6:0]-hexaadduct 6 in excellent yield. The photophysical properties of 6 were studied and compared with those of the fullerene [5:1]-hexaadduct 7 with six pyropheophorbide a groups and the bispyropheophorbide a-fullerene [5:1]-hexaadduct 8. The pyropheophorbide a units in 6 undergo after light absorption very efficient energy transfer as well as partly excitonic interaction. The last process results in formation of energy traps, which could be resolved experimentally. Compared to the reference compounds 7 and 8, 6 has a higher probability of trap formation due to a higher local concentration of dye molecules and shorter distances between them. As a consequence, the excitation energy is delivered rapidly (within 23 ps) to the traps, resulting in decreases of the fluorescence, intersystem crossing, and singlet oxygen quantum yields in comparison with the values of the reference compounds. 相似文献
995.
NEt4[Re3Cl10(H2O)2] · 2 H2O ( 1 ) was obtained from hydrochloric acid solutions of ReCl3 and tetraethylammonium chloride, NEt4Cl, by isothermal evaporation as dark red crystals. 1 crystallizes in the orthorhombic crystal system, space group Pnma, Z = 4, with a = 1838,7(2), b = 1456.9(1), c = 972.08(7) pm, Vm = 391.81(6) cm3 · mol?l. The crystal structure consists of [Re3Cl10(H2O)2]? anions that are arranged in the fashion of a hexagonal closest-packing of spheres. These are held together by partially disordered NEt4+ cations and are bound into a hydrogen bonding system with the crystal water. 相似文献
996.
On the Identity of a so‐called Ammonium Carbonate Sample Commercial samples of so‐called “ammionum carbonate” are shown to contain ammonium carbamate rather than ammonium carbonate. In fact samples may contain varying quantities of α‐ and β‐(NH4)(CO2NH2), of which only the α‐phase is reported in the literature. Mixtures of both phases tend to leak the volatile α‐phase and to react with moisture to form (NH4)(HCO3). The crystal structure of the new β‐(NH4)(CO2NH2) is refined from X‐ray powder data. 相似文献
997.
The [Fe(II)(Cys)(4)](2-) site of rubredoxin from Clostridium pasteurianum (Rd(red)) has been studied by M?ssbauer spectroscopy in both purified protein and whole cells of Escherichia coli overproducing it. Excellent fits were obtained to an S = 2 spin Hamiltonian for D = 5.7(3) cm(-1), E/D = 0.25(2), delta = 0.70(3) mm/s, DeltaE(Q) = -3.25(2) mm/s, eta = 0.75(5), A(x) = -20.1(7) MHz, A(y) = -11.3(2) MHz, and A(z) = -33.4(14) MHz. These parameters were analyzed with crystal-field theory for the (5)D manifold of iron(II), revealing a d(z(2)) orbital ground state that is admixed by approximately 0.21 d(x(2) - y(2)). The spin-Hamiltonian parameters are consistent within the (5)D theory, apart from the zero-field splitting parameter, D. This problem was solved by extending the crystal-field treatment with spin-orbit coupling to spin-triplet d-d excited states of the iron. Theoretical estimates are given for the spin-triplet (D(T)) and spin-quintet contributions (D(Q)) to D based on excitation energies derived from time-dependent density functional theory, TD-DFT. The computational results were interpreted in terms of crystal-field theory, yielding the Racah parameters B = 682 cm(-1) and C = 2583 cm(-1). The theoretical analysis gives the relative magnitudes D(Q):D(T):D(ss) = 51%: 42%:7% (D(ss) originates from spin-spin interaction). The DFT analysis corroborates the pivotal role of the torsion angles (omega(i)) of the C-S(i) bonds in shaping the electronic structure of the iron(II) site. Rd(red) in overexpressing whole cells accounts for 60% of the M?ssbauer absorption. The Rd(red) spectra from whole cells are virtually identical to those of the purified protein. By using the theoretical omega dependence of the spin Hamiltonian parameters, the torsions for Rd(red) in whole cells and purified protein samples are estimated to be the same within 2 degrees. These findings establish M?ssbauer spectroscopy as a structural tool for investigating iron sites in whole cells. 相似文献
998.
The phase behavior of the system water, n-heptane and the nonionic surfactant Igepal® CA520 has been studied by visual inspection, high-performance liquid chromatography, polarizing microscopy and freeze-fracture electron microscopy. The phase diagram at 25?°C contains two large homogeneous microemulsion phases, an extended region of a lamellar liquid crystalline structure and some two- and three-phase regions. The oil-rich part of the phase diagram has been investigated by static and dynamic light scattering in order to examine the behavior of the collective diffusion coefficient and the scattering intensity in the presence of increasing concentrations of water, starting from the binary system of n-heptane and Igepal® CA520. The results suggested that at a very low water content the aggregates of the microemulsion are small. With the exception of this region the structure is bicontinuous. 相似文献
999.
Synthesis, Structure and Thermolysis of NH4[Re3Br10] NH4[Re3Br10] crystallizes as dark brown single crystals upon slow cooling of a hot, saturated hydrobromic-acid solution of [Re3Br9(H2O)2] after the addition of NH4Br. The crystal structure (monoclinic, C2/m (Nr. 12); Z = 4; a = 1461.6(7), b = 1 085.6(4), c = 1030.3(7) pm, β = 92.63(4)°, Vm = 245.9(4)cm3/mol; R = 0.097, Rw = 0.043) contains [Re3Br12]? units that share two common edges. These chains run along [010] and are held together by NH4+ ions. Each NH4+ is surrounded by eight Br? from four different chains. The first step of the thermal decomposition at 290°C is the disproportionation to ReBr3 (ReCl3 type), rhenium metal and (NH4)2[ReBr6]. Secondly, the internal reduction of (NH4)2[ReBr6] at 390°C to rhenium metal takes place. 相似文献
1000.
Giffin D. Jones W. C. Meyer N. B. Tefertiller D. C. MacWilliams 《Journal of polymer science. Part A, Polymer chemistry》1970,8(8):2123-2138
2-Chloromethylbutadiene has been converted to quaternary ammonium and sulfonium monomers which have been polymerized at room temperature. They show a very great tendency to dimerize on heating in water solution. The aqueous quaternary monomer dimerized 25 times as fast as the aqueous sulfonium monomer and nearly 105 times as fast as neat isoprene at 50°C. The quaternary monomer dimerized with itself in a water solution to which 2-hydroxymethylbutadiene has been added as an example of a nonionic diene. The latter monomer did not dimerize rapidly in water, nor did 2-aminomethylbutadiene. The hydrochlorides of 2-aminomethylbutadiene and 2-dimethylaminomethylbutadiene dimerized at rates comparable to that of the sulfonium monomer. Poly 2-chloromethylbutadiene contains reactive chlorine except for the structure resulting from the minor extent of 1,2 addition. Water-soluble derivatives have been made from it with nucleophilic tertiary amines and sulfides. Cationic polymers are substantive to paper pulp, and the sulfonium polymers can be cured in paper to give improved wet strength. 相似文献