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71.
A. Da Settimo C. Primofiore G. Biagi V. Santerini 《Journal of heterocyclic chemistry》1976,13(1):97-100
Some derivatives of 11H-indolo[3,2-c] [1,8]naphthyridine, a new heterocyclic system, have been prepared using the Fischer indole synthesis on the appropriately phenylhydrazones. The preparation of some substituted 5,6-dihydro-11H-indolo[3,2-c][1,8]naphthyridines is also described. 相似文献
72.
Zhi L Gorelik T Wu J Kolb U Müllen K 《Journal of the American Chemical Society》2005,127(37):12792-12793
Novel naphthalocyanine (Nc) nanotubes with special wall structures were fabricated by a template method using Nc molecules as building blocks. Thermal stabilization of the ordered columnar structures of the tetrakis(tert-butyl)naphthalocyanine (Ni-BNc) molecules, induced from the pi-pi interactions in the nanoscale channels of an alumina template, resulted in Nc nanotubes with walls consisting of well-ordered Nc molecular disks. Further thermal treatment of Ni-BNc at 600 degrees C produced carbonized Nc nanotubes containing ordered columnar, graphitic wall structures with the graphene disks arranged perpendicular to the tube axis. These nanotubes may be useful for extending the application of Nc molecules for nanodevice fabrication. 相似文献
73.
Analysis of free metal clusters studied with photoionization mass spectrometry or photoelectron spectroscopy requires theoretical predictions of the photoionization cross sections to gain a deeper physical understanding. Calculated energy-dependent photoionization cross sections of Na2–8 and K2–8 clusters are presented in this study. The ground state electronic structure of the clusters are calculated using the Local Spin Density method (LSD) which is also the starting point for the cross section calculation with the continuum multiple scattering method. A basic analysis of the photoionization process is given within the independent electron picture. Strong resonances are predicted in the UV cross sections (5–10 eV) of K3–8 but not for Na3–8, interpreted as shape resonances, i.e. quasibound states in which electrons are trapped by a potential barrier. Unfortunately experimental data are only known close to the ionization threshold and a comparison between our values and experimental data in a broad energy range is not possible. 相似文献
74.
75.
Eleven Lycopodium alkaloids with a lycopodine‐type skeleton were isolated from the basic material of the whole plant of Huperzia serrata (Thunb .) Trev. (Huperziaceae). Among them, 12‐epilycodoline N‐oxide (=(12α,15R)‐12‐hydroxy‐15‐methyllycopodan‐5‐one N‐oxide; 1 ), 7‐hydroxylycopodine (=(15S)‐7‐hydroxy‐15‐methyllycopodan‐5‐one; 2 ), and 4,6α‐dihydroxylycopodine (=(6α,15R)‐4,6‐dihydroxy‐15‐methyllycopodan‐5‐one; 3 ) are new compounds. Their structures were identified spectroscopically, especially by means of 1D‐ and 2D‐NMR. 相似文献
76.
Porous ceria-zirconia composite with narrow particle size distribution and large specific surface area was synthesized by a sol-gel process. Chromatographic properties of the native supports was investigated in normal phase mode for the separation of test mixtures of basic, neutral and acidic compounds. The new packing material exhibited polar and basic properties, which are suitable for the separation of basic compounds. Lypophilic packing has been obtained by the modification of the ceria-zirconia with stearic acid, which exhibited strong hydrophobicity relative to the native packing. Therefore, the modified ceria-zirconia behaves as a reversed-phase packing material. Different selectivity towards basic compounds was observed on the new packing compared to the native ceria-zirconia and conventional ODS stationary phase. 相似文献
77.
Sullens TA Jensen RA Shvareva TY Albrecht-Schmitt TE 《Journal of the American Chemical Society》2004,126(9):2676-2677
Novel open-framework alkali metal uranyl periodates, having the formula A[(UO2)3(HIO6)(OH)(O)(H2O)].1.5H2O (A = Li, Na, K, Rb, Cs), have been prepared through mild hydrothermal synthesis. These isostructural compounds contain distorted UO7 pentagonal bipyramids that are linked through a uranyl (UO22+) to uranyl cation-cation interaction. This interaction arises from a single axial uranyl oxygen coordinating at an equatorial site of an adjacent uranyl unit. These uranium oxide polyhedra are further bound by IO6 distorted octahedra creating an open-framework structure whose channels contain the alkali metal cations. 相似文献
78.
A new steroidal saponin was isolated from the leaves of Agave attenuata. Its structure was established as (3beta,beta,25S)-spirostan-3-yl O-beta-D-glucopyranosyl-(1 --> 2)-beta-D-glucopyranosyl-(1 --> 2)-O-[beta-D-glucopyranosyl-(1 --> 3)]-beta-D-glucopyranosyl-(1 --> 4)-beta-D-galactopyranoside. The structural identification was performed using detailed analyses of 1H- and 13C-NMR spectra including 2D NMR spectroscopic techniques (COSY, HETCOR, and COLOC) and chemical conversions. The hemolytic activity of the steroidal saponin was evaluated using an in vitro assay. 相似文献
79.
Torres-Lapasió JR García-Alvarez-Coque MC Bosch E Rosés M 《Journal of chromatography. A》2005,1089(1-2):170-186
The problems associated to the modelling and optimisation of the chromatographic resolution of mixtures involving ionisable solutes at varying pH and acetonitrile content are discussed. Several retention models that separate the contributions of solute, column and stationary phase, were used. The retention was predicted with low errors in large pH domains (2-12), which was an essential requirement to face the optimisation of resolution. The selected mixture was particularly problematic under the viewpoint of resolution, owing to the excessively diverse acid-base behaviour of solutes. This variety led to sudden drops in retention at different pH for each solute, yielding numerous peak crossing, which made finding shared regions of high resolution especially difficult. Conventional resolution diagrams for these situations are scarcely informative, since both the overall and the worst elementary resolutions drop to zero if at least two compounds remain overlapped, even when all the others are baseline resolved. A new chromatographic objective function is proposed to address this drawback. This function, called "limiting peak count", is based on the limiting peak purity concept, and measures the success in the resolution focusing on the resolved solutes, in contrast to conventional resolution assessments that attend mainly to the least resolved solutes. Limiting peak count yields the same result as conventional assessments when full resolution is possible, but it is also able to discriminate the maximal resolving power in low-resolution situations. It offers a different perspective to that given by the complementary mobile phases approach, and the computation is far simpler. 相似文献
80.
Summary A global LSER model that relates HPLC retention to mobile phase composition and pH is tested for a varied group of solutes,
both neutral and ionizable, in a polymeric column and methanol-water mobile phases. It is compared to the local LSER model
developed only for a given mobile phase, i.e., a fixed organic modifier content, and to the global LSER model set only for
neutral solutes. The global LSER model for neutral and ionizable solutes requires a few supplementary parameters over the
other models tested, but it accounts for retention under any experimental conditions for a given column and methanol-water
mobile phases, describing properly the interactions established in the HPLC system (hydrophobicity, hydrogen-bond acidity
and basicity, dipolarity/polarizability…).
This paper is number 13 of a series with the same general title: “Retention of Ionizable Compounds on HPLC” published in various
journals. 相似文献