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31.
Jensen HH Lyngbye L Jensen A Bols M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(5):1218-1226
From the pK(a) values of the conjugate acids of a large series of hydroxylated piperidines and hexahydropyridazines, a consistent difference in basicity was found between stereoisomers having an axial or equatorial hydroxyl (OH) group either beta or gamma to the amine. Compounds with an equatorial OH group in the 3-position were 0.8 pH units more acidic than otherwise identical compounds with an axial OH group, whilst compounds with an equatorial OH group in the 4-position relative to the amine were 0.4 pH units more acidic than the corresponding compound with an axial OH. A similar effect was observed for the COOMe substituent. The difference in electron-withdrawing power of axial and equatorial substituents was explained by a difference in charge-dipole interactions in the two systems. Since this stereoelectronic substituent effect causes differences in basicity in different conformers, certain piperidines and hexahydropyridazines were found to change conformation upon protonation. A method for predicting the pK(a) of piperidines which takes stereochemistry into account is described. 相似文献
32.
This work illustrates the modification of polypropylene (PP) films through its grafting with glycidylmethacrelate monomer (GMA). Further chemical treatment of PP-g-GMA to convert epoxy groups into amine groups is discussed. Different factors affecting the grafting percent such as solvents, monomer concentrations, irradiation dose have been studied. Fourier transform infrared (FTIR) and thermogravimetric (TGA) analysis confirm the grafting of PP. Morphological changes of PP, PP-g-GMA and treated PP-g-GMA are confirmed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) pattern shows changes in the crystallinity on grafting. Adsorption and kinetic studies of mercury onto the prepared PP grafted and chemically treated films in sorption of Hg+ 2 metal ions from aqueous solutions have been studied. The experimental data fit favorably to the Langmuir isotherm with a high correlation coefficient. Moreover, the pseudo first and second order kinetics is also indicated. The results suggest that the pseudo-second-order kinetic model better represent the adsorption kinetics, suggesting that the adsorption process may be chemisorptions. It is more likely to predict that the adsorption behavior may involve valence forces through the sharing of electrons between Hg2 + and adsorbent. On the basis of these investigations, the applicability of the prepared membranes is discussed. Also the confirmation of metal ions adsorbed was confirmed using EDS spectrometric techniques. 相似文献
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Scherlach K Partida-Martinez LP Dahse HM Hertweck C 《Journal of the American Chemical Society》2006,128(35):11529-11536
The potent antimitotic polyketide macrolide rhizoxin, the causal agent of rice seedling blight, is not produced by the fungus Rhizopus microsporus, as has been believed for over two decades, but by endosymbiotic bacteria that reside within the fungal mycelium. Here we report the successful isolation and large-scale fermentation of the bacterial endosymbiont ("Burkholderia rhizoxina") in pure culture, which resulted in a significantly elevated (10x higher) production of antimitotics. In addition to several known rhizoxin derivatives, numerous novel natural and semisynthetic variants were isolated, and their structures were fully elucidated. Cell-based assays as well as tubulin binding experiments revealed that methylated seco-rhizoxin derivatives are 1000-10000 times more active than rhizoxin and thus rank among the most potent antiproliferative agents known to date. Furthermore, more stable didesepoxy rhizoxin analogues were obtained by efficiently inhibiting a putative P-450 monooxygenase involved in macrolide tailoring. 相似文献
37.
Alexei?VernitskiEmail author Laila?Tunsi Colette?Ponchel Alexei?Lisitsa 《Semigroup Forum》2018,97(1):75-86
It is known that a knot (link) is rational if and only if its \(\pi \)-orbifold group is dihedral. A semigroup version of this result has been formulated as a conjecture. Working towards proving the conjecture, we describe certain semigroups associated with twist links, clarify how these semigroups are related to dihedral groups and find defining relations of these semigroups. 相似文献
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Rafael Usón Antonio Laguna María U. De La Orden R.V. Parish Laila S. Moore 《Journal of organometallic chemistry》1985,282(1):145-148
Addition of a bidentate ligand (LL = 1,10-phenanthroline, o-phenylenebis(dimethylarsine)) to solutions of Au(C6F5)X2(tht) (X = Cl, Br; tht = tetrahydrothiophene) leads to potentially five-coordinate gold(III) derivatives. 197Au Mössbauer spectroscopy points, however, to four-coordinate square-planar complexes with a weak penta-coordination in the phen-containing derivatives. The complexes react with AgClO4 to give four-coordinate cationic complexes of the types [Au(C5F5)X(LL)]ClO4 or [Au(C6F5)(PPh3)(LL)](ClO4)2. 相似文献
40.
The effects of organic solvent, time and temperature on the colour-forming reaction are described. For nine solvents tested, the molar absorptivities were in the range 2.0×104?6.7×104 mol?1 cm?1; best sensitivity was obtained with a 1:1 water/2-propanol solution after a standing time of 35 min; temperature should be controlled to ±2°C. Beer's law was obeyed for 0–1.45 μg ml?1 Mn(II). The improved method was applied to determinations of manganese(II) in various herbs and chemical reagents; the values found were in the range 5.4–48.4 μg g?1 in herbs, and 0.001-0.012% (w/w) in reagents. 相似文献