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31.
Reaction of the isodicyclopentadienide anion and its dehydro congener with Fe(II) leads to a stereochemically homogeneous ferrocene derivative in each instance. Through chemical correlation and X-ray analysis, above-plane complexation is established for both halves within the two sandwich compounds. 相似文献
32.
[reaction: see text] A zirconocene-mediated ring contraction of 4-vinylfuranosides generated either from d-arabinose or d-glucose is followed by sequential oxidation to the ketone and alkynyl Grignard addition. The resulting cis-cyclobutanediols are subjected in turn to thermal rearrangement and intramolecular oxymercuration-demercuration. The regiochemistry of the final ring closure is controlled by the nature of R. 相似文献
33.
Carbonnelle S Loco JV Overmeire IV Windal I Wouwe NV Leeuwen SV Goeyens L 《Talanta》2004,63(5):1255-1259
Differences between chemical activated luciferase gene expression (CALUX) bioassay and chemoanalyses results are observed.This paper shows that calculations of the TEQ values using REP values instead of WHO TEF values give different results. The REP values do affect the results obtained by the CALUX technique. These differences are more marked for the dioxin like PCB compounds (CALUX TEQ values are lower than WHO TEQ values) than for the dioxin compounds (CALUX TEQ values are higher than WHO TEQ values).The CALUX results were compared with the concentrations of the congeners’ spiked into the oil. 相似文献
34.
Nineteen sulphonated 2-hydroxybenzophenones and three sulphonated 2,2′-dihydroxybenzophenones have been prepared and compared with a commercially available member of each class of uv absorber as photo-protective agents for wool. Treated fabrics were exposed to Philips ML G/74 lamps and the extent of photo-tendering was assessed by measuring breaking loads and tear strengths. In general, 2-hydroxybenzophenones with 3-alkyl substituents provide better protection against photo-tendering than absorbers lacking 3-alkyl substituents. 2,2′-Dihydroxybenzophenones are more effective than 2-hydroxybenzophenones.
On the basis of effectiveness and ease of synthesis, 2,2′-dihydroxy-4,4′-bis-w-sulphobutyloxybenzophenone (VIIb) shows most promise as a photo-protective agent. At the 5% level of application it trebles the lifetime of wool fabric during exposure to sunlight through window glass. It also retards the photo-tendering and fading of wool fabrics containing either a red or a blue milling acid dye. 相似文献
35.
The conductances of aqueous CaCl2, Ca(CH3COO)2, and Ca(CH3COO)2.nCH3COOH were measured from 348 to 523 K at pressures near 10 MPa using a flow conductometric technique. The first association constant for calcium chloride and the first and second association constants for calcium acetate in water, were derived from a least-squares fit of the measurements to a conductance model in which activity coefficients were calculated using the mean spherical approximation (MSA) and the conductance was modeled by the Turq, Blum, Bernard, and Kunz (TBBK) equation, plus a mixture model. 相似文献
36.
An activated D-residue of a protected dipeptide when coupled racemizes twice as much as an activated L-residue, which is contrary to the case for couplings of acylamino acids. 相似文献
37.
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39.
Screening of homocysteine from newborn blood spots by high-performance liquid chromatography with coulometric array detection 总被引:1,自引:0,他引:1
Accinni R Bartesaghi S De Leo G Cursano CF Achilli G Loaldi A Cellerino C Parodi O 《Journal of chromatography. A》2000,896(1-2):183-189
Homocystinuria, due to a deficiency of cystationine-beta-synthase, refers to the rare inborn error of the metabolism of homocysteine. The identification and prompt treatment of homocystinuria during the neonatal period can prevent or greatly reduce the severity of the clinical consequences. We report a new method for homocystinuria diagnosis from dried blood spots on newborn screening cards, based on high-performance liquid chromatography with electrochemical coulometric array detection. This method shows an excellent linearity (y=10.36x+0.04; r=0.999), precision (RSDs ranged from 2.7 to 5.8%), recovery (87%) and appears to be a cost-effective approach, being simple, rapid, sensitive and cheap. 相似文献
40.
Kozikowski AP Tückmantel W Böttcher G Romanczyk LJ 《The Journal of organic chemistry》2003,68(5):1641-1658
We report an improved synthesis of bis(5,7,3',4'-tetra-O-benzyl)epicatechin 4beta,8-dimer (3) from 5,7,3',4'-tetra-O-benzylepicatechin (1) and 5,7,3',4'-tetra-O-benzyl-4-(2-hydroxyethoxy)epicatechin (2) by replacing the previously employed Lewis acid, titanium tetrachloride, with the clay mineral Bentonite K-10. Under the same conditions, the benzyl-protected all-4beta,8-trimer, -tetramer, and -pentamer were obtained regioselectively from their lower homologues, albeit in rapidly decreasing yields. Reaction of 2 with an organoaluminum thiolate generated from 2-mercaptobenzothiazole and trimethylaluminum followed by acetylation produced 3-O-acetyl-4-[(2-benzothiazolyl)thio]-5,7,3',4'-tetra-O-benzylepicatechin (12). Medium-sized protected oligomers with 4beta,8-interflavan linkages are obtained in improved yields by using this compound as the electrophile and silver tetrafluoroborate as activator and are isolated by reversed-phase HPLC. Their deprotection by ester saponification followed by hydrogenolysis yielded the free procyanidins, which were characterized as their peracetates. The synthetic procyanidins are identical by normal-phase HPLC with fractions isolated from cocoa. The principle of chain extension by two members was demonstrated using a dimeric electrophile obtained by self-condensation of compound 12. Both the synthetic and natural pentamer 32 inhibit the growth of several breast cancer cell lines. Using the MDA MB 231 line, it was established that this outcome is based on the induction of cell cycle arrest in the G0/G1 phase. Subsequent cell death is more likely necrotic rather than apoptotic. Control experiments demonstrate that the polyphenol itself, rather than hydrogen peroxide potentially formed by its autoxidation, is the causative agent. 相似文献