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61.
P. Staszewski J. Lipkowski J. Jaźwiński O. Staszewska L. Stefaniak Z. Urbańczyk-Lipkowska G.A. Webb 《Journal of chemical crystallography》1998,28(3):227-233
X-ray diffraction data are presented for the title mesoionic compound (I), its hydrochloride salt (II) and methylated derivative (III). The crystal of (I) is orthorombic, space group P212121, with cell dimensions: a = 5.857(1) Å, b = 12.494(2) Å, c = 16.328(3) Å, with four molecules per unit cell. The crystal of (II) is monoclinic, space group P21/n, with cell dimensions: a = 5.5720(10) Å, b = 21.5770(4) Å, c = 11.2330(2) Å, beta = 95.15(3)°, with four molecules per unit cell. The crystal of (III) is monoclinic, space group P21/n, with cell dimensions: a = 12.0886(5) Å, b = 7.9103(4), c = 104.29(1) Å, beta = 104.29(1)°, with four molecules per unit cell. Of particular interest is the fact that the C5–N6 bond appears to have a high double bond character in all three of the compounds studied. In addition, it is found that the exocyclic N-phenyl group changes from being in the cis conformation with respect to sulfur in compounds (I) and (III) to the trans conformation in the hydrochloric salt (II). 相似文献
62.
63.
Piotr?Ku?Email author Marta?Stefaniak 《Monatshefte für Chemie / Chemical Monthly》2004,135(5):509-511
Summary. Treatment of meso-tetra(tert-butyl)porphyrin with sulfuric acid/n-butanol affords a mixture of porphyrin and mono-tert-butylporphyrin in relatively high yield. 相似文献
64.
A. Worobiec E. A. Stefaniak S. Kiro M. Oprya A. Bekshaev Z. Spolnik S. S. Potgieter‐Vermaak A. Ennan R. Van Grieken 《X射线光谱测定》2007,36(5):328-335
A comprehensive analysis of individual welding fume particles of different size fraction has been performed by applying of an innovative combination of the energy‐dispersive x‐ray fluorescence spectroscopy (EDXRF), micro‐Raman spectroscopy (MRS) and electron probe microanalysis (EPMA). Owing to this set of analytical techniques, a systematic study of the chemical composition along with the size, morphology and structure parameters of the collected welding particles was performed. The results show distinct interdependencies between the particles' elemental composition and their sizes and structures, which are consistent with commonly assumed mechanisms of their formation and evolution. In particular, interactions between the particles of fine and coarse fractions as well as regularities in distribution of the most toxic welding fume components (Mn and its oxides) have been observed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
65.
L. Stefaniak John D. Roberts M. Witanowski G. A. Webb 《Magnetic resonance in chemistry : MRC》1984,22(4):215-220
15N NMR data are reported for 42 azoles, taken mostly at a standard concentration and in a common solvent (0.5 M dimethyl sulfoxide with a 0.01 M increment of Cr(acac)3 for each nitrogen atom present). Signal assignments were assisted by comparison with 14N line widths, the use of 2J(15N1H) couplings, and shielding calculations obtained by the INDO/S–SOS approach. The generally large differences in nitrogen-shielding changes permitted rather facile shift assignments. 相似文献
66.
67.
Lech Stefaniak 《Magnetic resonance in chemistry : MRC》1978,11(8):385-389
Nitrogen chemical shifts constitute an effective means of distinguishing between isomeric benzazole ring systems. There is a large difference in nitrogen shielding, usually more than 20 ppm, between isomeric benzenoid- and quinonoid-like structures. 13C and 1H NMR is shown to provide unambiguous structure assignment only in cases of symmetric quinonoid ring systems of azoles. 相似文献
68.
P. A. Schulte G. Roth L. L. Hodson V. Murashov M. D. Hoover R. Zumwalde E. D. Kuempel C. L. Geraci A. B. Stefaniak V. Castranova J. Howard 《Journal of nanoparticle research》2016,18(6):159
Engineered nanomaterials significantly entered commerce at the beginning of the 21st century. Concerns about serious potential health effects of nanomaterials were widespread. Now, approximately 15 years later, it is worthwhile to take stock of research and efforts to protect nanomaterial workers from potential risks of adverse health effects. This article provides and examines timelines for major functional areas (toxicology, metrology, exposure assessment, engineering controls and personal protective equipment, risk assessment, risk management, medical surveillance, and epidemiology) to identify significant contributions to worker safety and health. The occupational safety and health field has responded effectively to identify gaps in knowledge and practice, but further research is warranted and is described. There is now a greater, if imperfect, understanding of the mechanisms underlying nanoparticle toxicology, hazards to workers, and appropriate controls for nanomaterials, but unified analytical standards and exposure characterization methods are still lacking. The development of control-banding and similar strategies has compensated for incomplete data on exposure and risk, but it is unknown how widely such approaches are being adopted. Although the importance of epidemiologic studies and medical surveillance is recognized, implementation has been slowed by logistical issues. Responsible development of nanotechnology requires protection of workers at all stages of the technological life cycle. In each of the functional areas assessed, progress has been made, but more is required. 相似文献
69.
Barrett AG Hennessy AJ Le Vézouët R Procopiou PA Seale PW Stefaniak S Upton RJ White AJ Williams DJ 《The Journal of organic chemistry》2004,69(4):1028-1037
The synthesis of a range of highly functionalized peptidomimetic macrocycles has been accomplished using ring-closing metathesis and enyne tandem cross-metathesis-ring-closing metathesis reactions. This approach gives access to rigidified macrocycles modeled on the structures of cyclic peptides and designed to be biologically stable. The potential for peripheral functionalization of these templates has been demonstrated using Diels-Alder reactions, palladium(0) coupling reactions, and amide formation both in the solution phase and using polymer-supported syntheses. 相似文献
70.
Roman Luboradzki Wiktor Kozminski Lech Stefaniak 《Journal of chemical crystallography》1993,23(2):133-141
An X-ray diffraction study is reported for four molecules of mesoionic 2,3-diphenyltetrazoles. The results confirm a dipolar mesoionic structure, aromatic character of the tetrazole ring and no conjugation between the phenyl and tetrazole rings. The geometry of the exocyclic group is discussed in detail. The molecular parameters of the compounds investigated are correlated with13C and15N nmr data. The results obtained are compared with similar structures which have already been studied. 相似文献