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1.
Different iron hydroxide precipitation processes simulating radioactive waste, treatment have been investigated by Mössbauer spectroscopy at room temperature and at 80 K. Magnetic oxides (hematite or magnetite) partially affected by superparamagnetic relaxation have been observed. The crystallization degree and the particle size depend on the concentration and the addition order of chemicals. Much smaller particles were precipitated with Ca(OH)2 than with NaOH as neutralization reagent. 相似文献
2.
The aldol-type addition of 1,3-dibenzyl-dihydrouracil 2 to 2,3-O-isopropylidene-d-glyceraldehyde 3 was examined in different solvents and under Lewis acid catalysis in order to establish the stereochemical preferences. A stereodivergent synthesis of 5-trihydroxypropyl-dihydrouracil derivatives 4 and its C-5 epimer 5 was realized. The synthesis of ureido polyols 8 and 10 was obtained via the reductive ring opening of the templates 4 and 5. 相似文献
3.
Lattice stability in a model of an antiferromagnetic ring coupled to adiabatic phonons is investigated for different values of the spin and numbers of magnetic sites. The magnetoelastic transition is shown to be heavily affected by the spin value, displaying a qualitative difference in the nature of the instability for spin one-half. Among the different synthesized materials, Cu8 seems to be the best candidate to observe lattice dimerization in these systems. Our analysis excludes stable lattice distortions in higher spin rings. The effects of thermal fluctuations are studied in the Cu8 model, where a characteristic crossover temperature is estimated. 相似文献
4.
Viorica Spanu C. N. Turcanu G. Filoti 《Journal of Radioanalytical and Nuclear Chemistry》1992,166(4):309-320
Mössbauer effect was used for the characterization of the radioactive waste treatment products, e.g. precipitate formed during the treatment of LLAW (Low Level Active Waste) using iron compounds and their conditioned matrix obtained by cementation. 相似文献
5.
Giovanna Gasparri Fava Marisa Belicchi Ferrari Giovanni Casiraghi Gloria Rassu Pietro Spanu 《Journal of chemical crystallography》1991,21(5):629-633
The crystal structure of the title lactone, C20H30O9, a potential precursor of uncommon 11-carbon sugar derivatives, has been determined by single-crystal diffraction methods. The compound crystallizes in the orthorhombic space groupP212121 witha=15.581(3),b=14.047(2),c=9.888(2) Å, andZ=4. The structure was solved by direct methods and refined by full-matrix least-squares toR=0.054. The absolute configuration of the seven stereogenic carbon atoms was deduced as 4R, 5R, 6R, 7R, 8S, 9R, 10R, being (R)-(+)-glyceraldehyde its progenitor. An intramolecular O-HO hydrogen bond is present. Weak interaction C-HO links the molecules in sheets parallel to the (100) plane. 相似文献
6.
Ponticelli Gustavo Spanu Antonio Cocco M. Teresa Onnis Valentina 《Transition Metal Chemistry》1999,24(3):370-372
Palladium(II) and Platinum(II),(IV) complexes with 2-aminopyrimidine derivatives (L1)–(L3), prepared by reacting the corresponding metal halide with the ligand in the required stoichiometric ratio, were characterised by chemical analyses and physical measurements. The structures have been assigned on the basis of i.r. spectroscopy, electronic reflectance spectra and molar conductivities. 相似文献
7.
The nonempirical assignment of the absolute configuration of (+)-diplopyrone, the main phytotoxin of Diplodia mutila, i.e., an endophytic fungus, widespread in Sardinian oak forests, and considered one of the main causes of cork oak decline, has been approached by two different methods: (a) the exciton analysis of the circular dichroism (CD) spectrum and (b) the ab initio calculation of the optical rotatory power. Both methods indicate that (+)-diplopyrone is 6-[(1S)-1-hydroxyethyl]-2,4a(S),6(R),8a(S)-tetrahydropyrano[3,2-b]pyran-2-one, so the stereostructure of this important biomolecule is safely determined for the first time. A comparison of advantages and limitations of the two methods of analysis is also presented. 相似文献
8.
The anion influence on the hydrated oxides formed by Fe3+ and Fe2+ precipitation simulating the aqueous radioactive waste treatment has been investigated by Mössbauer spectroscopy. Fe3(SO4)2, Fe(NO3)3, FeCl3, FeSO4 and FeCl2 were used as iron sources and neutralized by NaOH. The obtained products contain several kinds of amorphous and/or poorly crystallized hydrated oxides, depending on the anion type which exists in solution and on the initial iron valence. The pH influence on the final precipitate is taken into account. 相似文献
9.
10.
An unexpected reaction of pyridine with acetyl chloride to give N-acetyl-1,2 and 1,4-dihydropyridyl acetic acid (1, 2) in high yield and regioselectivity has been reported. The key step is the formation of a zwitterionic pyridinium ketene enolate. The effect of different activating agents on the reaction yield and selectivity has been studied. Platinum(IV) mediated hydrogenation of the corresponding methyl esters (7, 8) gave piperidine derivatives (9, 10). 相似文献