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101.
Abstract— The quantum yields for the photohydration of dimethyluracil were determined for concentrations in the range 5 × 10--1--1 × 10--3M by use of 240–280 nm irradiation. The average quantum yield (0.0139 f 0.0005) was independent of both concentration and irradiation wavelength. 相似文献
102.
Thermolysis of perfluoroazidobenzene, perfluoro-4- azidotoluene, perfluoro-4-azidopyridine, 4-azido-3- chlorotrifluoropyridine, and 4-azido-3, 5-dichlorodifluoropyridine (ArFN3) in the presence of a large excess (. 10 molar) of 1,3,5-trimethyl- or 1,3,5-trimethoxy-benzene (ArH) gave the diarylamines expected from nitrene ‘insertions’ at nuclear CH bonds (ArFN3 + ArH→ArFNHAr + N2); product yields in the cases of the perfluorinated azides are the highest ever recorded for this type of reaction. By contrast, no recognisable products were obtained when either perfluoro-(2-azido-4-isopropylpyridine) or 2-azido- 4-chlorotrifluoropyridine were decomposed thermally in 1,3,5-trimethylbenzene. 相似文献
103.
Labeling conditions of synkavit (2-methyl-1,4-naphthoquinol disodium phosphate) with iodine-125 have been studied. In this study, labeling temperature, reaction time, successive using of iodogen coated tubes, iodogen amount and synkavit concentrations have been determined to get optimum conditions for maximum labeling. Final results showed that when the labeling temperature, reaction time, synkavit concentration, and iodogen amount were, at room temperature, 15 min (in the case of successive using of three iodogen coated tubes), 2 mg ml–1 and 5 mg, respectively; labeling yield was 90% and specific activities of the order of 555 GBq mmol–1 (15 Ci mmol–1) have been obtained. 相似文献
104.
The reactions of perfluoroalkyl- and perfluoroacyl-iminosulfur difluorides with chlorine monofluoride result in the preparation of perfluoroalkyldichloroamines and a new class of compounds N,N-dichloroperfluoroamides, RfC(O)NCl2, via the elimination of SF4. The amides, FC(O)NCl2 and CF3C(O)NCl2, in addition to 1,2-bis-(dichloroamino)tetrafluoroethane, Cl2NCF2CF2NCl2, are reported and characterized. The reactions of CIF with other sulfur(IV) imines proceed in an analogous manner to form perfluoroalkyl-dichloroamines via the elimination of the corresponding sulfur(IV) fluoride. 相似文献
105.
Fluoride ions and, in about 0.005M concentration, tungstate ions form gelatinous precipitates, poorly soluble in water, with calcium ions. The radiometric determinations
of the above ions are based on these reactions. Accurate radiometric determination can be carried out only if the gelatinous
precipitate formed during titration can be properly separated from the solution. It has been found that in the case of fluoride
ions the application of crystalline, easily filtrable Ca(COO)2·H2O or CaCO3, and in the case of tungstate ions the application of CaWO4 precipitate improves the filtration properties of45CaF2 and45CaWO4, respectively, formed during titration, whereby the radiometric determinations of the above ions become possible. Titrations
were carried out with 0.05M and 0.005M CaCl2 solutions, labelled with45Ca. 相似文献
106.
Alginate beads containing entrapped DNA were produced using both external and internal calcium sources, and coated with chitosan
or poly-l-lysine membranes. The beads were assayed with DNase nuclease to determine formulation conditions offering the highest level
of DNA protection fromnucleic acid hydrolysis, simulating gastrointestinal exposure. A method was developed to extract and
assay intracapsular DNA through a modified agarose electrophoresis system. Both external and internally gelled beads were
permeable to DNase (Mw=31 kDa), indicated by the absence of DNA after nuclease exposure. At low levels of DNase exposure, coated high guluronic
content alginate beads offered a higher level of DNA protection compared with coated beads with low guluronic alginate. No
apparent correlation was found with chitosan membrane molecular weight and degree of deacetylation; however, increasing poly-l-lysine molecular weight appeared to increase DNase exclusion from beads. At elevated levels of DNase exposure, DNA hydrolysis
was evident within all coated beads with the exception of those coated with the highest molecular weight poly-l-lysine (Mw=197.1 kDa), which provided almost total nuclease protection. Optimal combination then for DNA protection from nucleases is
a high guluronic alginate core, coated with high molecular weight poly-l-lysine. 相似文献
107.
Perfluorotoluene, pentafluoropyridine, 3-chlorotetrafluoropyridine, and 3,5-dichlorotrifluoropyridine react with pyridinium t-butoxycarbonylmethylide (I) in acetonitrile at 0 – 20 °C to yield, nucleophilic displacement of a 4-F substituent in each case, the new pyridinium methylides (II)–(V), respectively. Treatment of perfluoropropene with (I) gives 1-(t-butoxycarbonyl)-2-fluoro-3-(trifluoromethyl)- pyrrolo[1,2-]pyridine (VI) and 1,3-bis(t-butoxycarbonyl)-2- (1,2,2,2-tetrafluoroethyl)pyrrolo[1,2-]pyridine (VII), formation of the latter (minor) product providing evidence that the former arises a stepwise dipolar cycloaddition. 相似文献
108.
The stereochemistry and regiochemistry of cycloadditions of α-amino acid ester imines is dependent both on imine structure and on the reactivity of the dipolarophile. Phenylglycine imines undergo competing dipole stereomutation and cycloaddition with some dipolarophiles. 相似文献
109.
Air samples collected at the second Bosporus bridge of Istanbul which carries a heavy traffic load between Asia and Europe,
were analyzed for 22 elements by the INAA method. Pb, Cd and Fe concentrations in the samples were determined by AAS. Iron
concentrations were used as a cross check between the two methods. In order to define the enrichment factors for the elements
in the bridge area, a sample collected from our university campus which can be considered as a rural site, was also analyzed.
Differences were observed especially for Br, Al, Mg, Ti, Cu and Na between the two sites. Based on the results of the samples
from the bridge, we got a value of 0.58(16) for the Br/Pb-ratio. 相似文献
110.
Jerald S. Bradshaw Krzysztof E. Krakowiak Reed M. Izatt Ronald L. Bruening Bryon J. Tarbet 《Journal of heterocyclic chemistry》1990,27(2):347-349
Two new dithia-crowns containing a hydroxy group and 1,4,7,10-tetrathia-18-crown-6 containing an allyl-oxymethyl substituent were prepared in good yields. Two of these crowns were covalently attached to silica gel. The silica gel-bound thia-crowns were used to separate gold( III ), palladium( II ), silver( I ) and mercury( II ) ions from an aqueous 0.1 M nitric acid solution which also contained 1.0 M ferric chloride. 相似文献