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71.
C. Brescianini A. Mazzucotelli F. Valerio R. Frache G. Scarponi 《Fresenius' Journal of Analytical Chemistry》1988,332(1):34-36
Summary The interferences due to the presence of large amounts of atoms such as iron, sodium, cadmium, magnesium and potassium on the ETA-AAS determination of trace amounts of chromium(VI) in welding fumes are discussed. An ion-exchange liquid extraction separation procedure is proposed to overcome these interactions. Results obtained on international standards of welding fumes, distributed in two round robin experiments, are also presented.
Bestimmung von Chrom(VI) in Schweißereidämpfen nach Abtrennung mit Hilfe eines flüssigen IonenaustauschersUntersuchung der Störungen相似文献
72.
Weissker HC Serrano J Huotari S Bruneval F Sottile F Monaco G Krisch M Olevano V Reining L 《Physical review letters》2006,97(23):237602
We present an investigation of the dynamic structure factor and of the dielectric function epsilonM(Q,omega) of the prototypical semiconductor silicon for finite momentum transfer, combining inelastic x-ray scattering experiments and ab initio calculations. In contrast with optical spectra, for finite momentum transfer time-dependent density-functional theory in the adiabatic local-density approximation together with lifetime broadening describes the physics of valence excitations correctly. Major structures in the spectra, governed by short-range crystal and exchange-correlation local-field effects, are strongly influenced by a mixing of transitions of positive and negative energies, in striking difference to spectra for vanishing momentum transfer. This mixing gives rise to a pronounced Fano asymmetry. 相似文献
73.
Marcotullio MC Pagiotti R Campagna V Maltese F Fardella G Altinier G Tubaro A 《Natural product research》2006,20(10):917-921
In this work the mushroom Sarcodon glaucopus was studied. A new cyathane, glaucopine C (1), was isolated from the hexane extract and identified by 1H and 13C NMR spectra analysis. Glaucopine C showed anti-inflammatory acitvity. 相似文献
74.
75.
We consider the problem of deriving approximate autonomous dynamics for a number of variables of a dynamical system, which are weakly coupled to the remaining variables. In a previous paper we have used the Ruelle response theory on such a weakly coupled system to construct a surrogate dynamics, such that the expectation value of any observable agrees, up to second order in the coupling strength, to its expectation evaluated on the full dynamics. We show here that such surrogate dynamics agree up to second order to an expansion of the Mori-Zwanzig projected dynamics. This implies that the parametrizations of unresolved processes suited for prediction and for the representation of long term statistical properties are closely related, if one takes into account, in addition to the widely adopted stochastic forcing, the often neglected memory effects. 相似文献
76.
Sandro Calogero Paolo Ganis Valerio Peruzzo Giuseppe Tagliavini Giovanni Valle 《Journal of organometallic chemistry》1981,220(1):11-20
The structures of tricyclohexyltin fluoride (I), bromide (II) and iodide (III) have been determined by X-ray analysis. Compound I crystallizes in the space group P21/m with a = 10.422(6), b = 17.238(9), c = 5.769(3) Å, β = 104.6(1)° and Z = 2. Compounds II and III crystallize in the space group Pcmn with a = 10.427(6), b = 16.914(9), c = 11.366(6) Å, Z = 4; and a = 10.400(6), b = 16.900(10), c = 11.400(4) Å, Z = 4, respectively. All three structures consist of discrete tetrahedral (cyclo-C6H11)3SnX units.The temperature dependence of the Mössbauer resonance areas has been examined in order to obtain information about the relationship between chemical structure and lattice dynamics. 相似文献
77.
Alessandro Gambaro Valerio Peruzzo Gualtiero Plazzogna Guiseppe Tagliavini 《Journal of organometallic chemistry》1980,197(1):45-50
Mixed allylbutyltin halides (CH2CHCH2)SnBu3-nCln (n = 0–3) have been prepared, and characterized by carbon-13 NMR spectroscopy. Their ability to bring about allylstannylation of ketones and aldehydes, to form organostannoxy compounds, Bu3-nSnClnOC(R′)(R″)CH2CHCH2, has been shown to increase on increasing the value of n, that is on increasing the acceptor ability of the tin centre. 相似文献
78.
Shasta?Lee?Moser Valerio?Bertolasi Keith?VaughanEmail author 《Journal of chemical crystallography》2005,35(4):307-312
Methyl 4-((E)-2-{3-[(3-{(E)-2-[4-(methoxycarbonyl)phenyl]-1-diazenyl}-5, 5-dimethyl hexahydro-1-pyrimidinyl)methyl]-5, 5- dimethylhexahydro-1- pyrimidinyl}-1- diazenyl) benzoate (1) has been synthesized by reaction of a mixture of formaldehyde and 2,2-dimethyl-1,3-propanediamine with p-methoxycarbonylbenzenediazonium chloride. The crystal structure of 1 has been determined by single crystal X-ray diffraction analysis. The crystals of 1 displayed problems of disorder; the asymmetric unit is built up by two independent molecules, which display disorder within a methoxycarbonyl group. The two independent molecules in the asymmetric unit are very similar, differing only slightly about the mutual orientation of the aryltriazenyl groups. With respect to the N–C–N bridge between the hexahydropyrimidinyl rings, the two equivalent fragments containing the triazene moieties are in a cis orientation. The N–N single bonds, in the range 1.319(4)–1.348(4) Å, and the N=N double bonds, in the range 1.255(5)–1.275(4) Å, indicate significant conjugations within the triazene moieties. All the hexahydropyrimidine six-membered rings adopt a chair conformation as shown by their puckering parameters. The crystal packing is determined only by simple van der Waals interactions. The crystal structure of 1 is compared with the previously reported structure of the unbranched hexahydropyrimidine analogue 2. Crystal data: 1 C29H40N8O4, triclinic, space group P-1, a = 13.9652(2), b = 14.2908(3), c = 16.6129(4) Å, = 97.279(1), = 90.872(1), = 107.385(1), V = 3133.6(1) Å3, for Z = 4. 相似文献
79.
The pentasaccharide sequence of the most active components of the antitumor drug PI-88, currently in phase II clinical trial, has been rapidly assembled in high overall yield and in only three steps starting from three monosaccharide building blocks. The procedure takes advantage of the first reported strategy of sequential one-pot glycosidations conducted exclusively under catalytic activation. In addition, the procedure relies only on shelf-stable and mild promoters such as Yb(OTf)(3) and Bi(OTf)(3). 相似文献
80.
Alessandro Dondoni Alessandro Massi Erik Minghini Valerio Bertolasi 《Helvetica chimica acta》2002,85(10):3331-3348
The use of glycosylated reagents in Hantzsch‐type cyclocondensation reactions leading to C‐glycosylated dihydropyridines (DHPs) has been investigated. A three‐component approach with an anomeric sugar aldehyde (galacto, manno, and ribo derivatives), a β‐keto ester, and an aminocrotonate afforded C(4)‐glycosylated DHPs in high yield (70–90%). A two‐component cyclocondensation approach based on different glycosylated β‐amino acrylates (sugar enamines) and an enone derived from the Knoevenagel condensation between benzaldehyde and ethyl acetoacetate was followed for the preparation of C(6)‐glycosylated 4‐phenyl‐substituted DHPs in fair yields (60–70%). The latter compounds were obtained as mixtures of diastereoisomers owing to the asymmetric induction of the sugar moiety in the formation of the C(4)‐stereogenic center of the DHP ring. The diastereomer excess of the major products varied from 30 to 60%. The structure of selected compounds was determined by X‐ray crystallography and by chiroptical measurements. The two‐component cyclocondensation method was also employed for the preparation of a C(6)‐ribofuranosyl‐containing analogue of the well‐known hypotensive agent nifedipine. 相似文献