Crystal and molecular structure of 17-β-methyl-α-isolupanine perchlorate

The formula of the title compound is C₁₆H₂₇ClN₂O₅,P2₁/a = 8.348(1),b = 10.127(1),c = 11.264(2) Å, = 116.42(1) °,Z = 2,D _x = 1.41 g cm^–3,V _c = 852.8(2) ų,MW = 362.9, (CuK) = 2.25 mm^–1. The structure was solved by direct methods and refined by full-matrix least squares to anR value of 0.055 for 1197 reflections. The cation consists of twotrans quinolizidine systems. RingA is a distorted half-chair, and the remaining rings are chairs. The CH₃ group attached to C(17) is in the axial position. There is a weak hydrogen bond between N(16) and O(2) of the ClO ₄ ^– group with N(16) ... O(2) distance 2.968(7) Å.     

Distillation preconcentration and clean-up of aqueous samples for direct aqueous injection-gas chromatographic determination of volatile polar organic pollutants

The applicability of distillation to concentrate and clean up heavily loaded aqueous samples for the analysis of volatile polar organic compounds by means of direct aqueous injection-gas chromatography was studied. Recoveries for acetone, acetonitrile, acrolein, acrylonitrile, butanone, 1,4-dioxane, ethyl acetate, and 3-pentanone were in the range of 60.6 to 73.4% with relative standard deviations of 3.6 to 5.5%. The corresponding enrichment factors were in the order of 200. The recovery did not depend on the concentration in the studied range of 0.70 to 89 μg/kg. The detection limits with the mass selective detector operating in the selected ion monitoring mode were in the order of 0.1 μg/kg. The method was successfully applied to treated waste water from a pharmaceutical factory. The content of the above analytes in the real sample ranged from below 0.1 to ca. 83 μg/kg. Received: 16 December 1996 / Revised: 9 April 1997 / Accepted: 16 April 1997     

Substituent Reactivity and Tautomerism of Isoguanosine and Related Nucleosides

The substituent reactivity and tautomerism of isoguanine nucleosides is studied. Benzoylation or tosylation of isoguanine nucleosides (pyridine, room temperature) yields the 2-benzoyl derivatives 7c, 11 , and 12 or the 2-tosyl compounds 13 and 14 . The isobutyrylation of the 6-amino group which did not occur under these conditions was induced in the presence of Me₃SiCl. In the absence of Me₃SiCl, the reactivity of isoguanine substituents decreases in the order from 2-oxo → 5′-OH → 3′-OH → 6-NH₂. From isoguanine nucleosides, the N¹-( 2b ), N³-( 17 ), N⁶-( 15a,b ), and 2-O-alkylated ( 3b ) derivatives were prepared. Their pK_a values were determined and the UV and ¹³C-NMR spectra compared with regard to the alkylation position. Also the tautomeric forms of isoguanine nucleosides were determined UV-spectrophotometrically in aqueous and nonaqueous solution. Isoguanosine ( 1a ), its 2′-deoxy analogue 1b as well as the N⁶-methyl- and 8-substituted derivatives form lactam tautomers in aqueous solution, whereas the lactim form is present in dioxane.     

On the Auslander-Reiten Periodicity of Self-Injective Algebras

This paper investigates how to relate the syzygy periodicityof a self-injective algebra A to its Auslander–Reitenperiodicity. Moreover, a characterization is provided of theAuslander–Reiten bounded A–A-bimodules that areperiodic. 2000 Mathematics Subject Classification 16G70, 16E40(primary), 16G20 (secondary).     

Crystal structure, magnetism and spectroscopy of bis(tetraphenylphosphonium)tetrakis(dicyanamido)cobaltate(II) with bridging and pendant dicyanamide ligands

The synthesis, structure and magnetic properties of the cobalt(II) complex, (Ph₄P)₂[Co(NCNCN)₄] (1) is reported. The compound crystallises in the monoclinic system, space group C2/c, with cell constants: β=105.65(2)°, Z=4 and The structure of 1 consists of octahedral CoN₆ chromophores with uni- and bidentate N(CN)₂ ligands. Cobalt atoms are doubly bridged by bidentate NCNCN groups forming infinite ribbons along the crystallographic b-axis. As first representative of an anionic dicyanamide complex 1 behaves as a weak ferromagnet at low temperatures.     

2′-Deoxyisoguanosine and Base-Modified Analogues: Chemical and Photochemical Synthesis

The synthesis of 2′-deoxyisoguanosine ( 2 ), and the pyrrolo[2,3-d]pyrimidine and pyrazolo[3,4-d]pyrimidine 2′-deoxyribonucleosides 3 and 4 is described. Condensation of the imidazole precursor 5 with benzoyl isocyanate followed by reaction with ammonia gave 2 . Its N(7) regioisomer was obtained from 6 . Compound 2 was also prepared by the photochemically induced conversion of 2-Chloro- and 2-bromopurine 2′-deoxyribofuranosides 9a and 10 , respectively, in aqueous solution, The photo reaction was further used for the synthesis of the compounds 3 and 4 starting with the amino-chloro-2′-deoxynucleosides 9b and 9c , respectively.     

Determination of benzene alkyl derivatives in heavily loaded environmental aqueous samples by means of combination of distillation and purge and trap-gas chromatography-mass spectrometry

Simple distillation was used to prepare aqueous environmental samples (especially those with high content of accompanying dissolved and suspended organic and inorganic matter) for determination of benzene, toluene, ethylbenzene, and xylenes (BTEX) by means of purge and trap (PT) coupled to gas chromatography-mass spectrometry (GC-MS). The PT step was carried out with a laboratory-built device in which alalytes desorbed from a Primary trap (macrotrap) are focused in a microtrap (also with sorbent) and moisture is removed from purge gases by a Nafion tube (walls selectively permeable to water vapor). Recoveries, if only the first 10 ml distillate was collected, were of the order of 40% at optimum distillation parameters. At a probability level of 95% recoveries were independent of concentration in a studied concentration range of 0.50–30 ppb. Enrichment factors for distillation were of the order off 20. Real samples, i.e., raw and treated waste water were analyzedc for BTEX content by the developed medthod.     

Laser-assisted synthesis of superparamagnetic Fe@Au core-shell nanoparticles

A novel method combining wet chemistry for synthesis of an Fe core, 532 nm laser irradiation of Fe nanoparticles and Au powder in liquid medium for deposition of an Au shell, and sequential magnetic extraction/acid washing for purification has been developed to fabricate oxidation-resistant Fe@Au magnetic core-shell nanoparticles. The nanoparticles have been extensively characterized at various stages during and up to several months after completion of the synthesis by a suite of electron microscopy techniques (HRTEM, HAADF STEM, EDX), X-ray diffraction (XRD), UV-vis spectroscopy, inductively coupled plasma atomic emission spectroscopy, and magnetometry. The surface plasmon resonance of the Fe@Au nanoparticles is red shifted and much broadened as compared with that of pure colloidal nano-gold, which is explained to be predominantly a shell-thickness effect. The Au shell consists of partially fused approximately 3-nm-diameter fcc Au nanoparticles (lattice interplanar distance, d = 2.36 A). The 18-nm-diameter magnetic core is bcc Fe single domain (d = 2.03 A). The nanoparticles are superparamagnetic at room temperature (300 K) with a blocking temperature, T(b), of approximately 170 K. After 4 months of shelf storage in normal laboratory conditions, their mass magnetization per Fe content was measured to be 210 emu/g, approximately 96% of the Fe bulk value.