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41.
Core-shell nanostructures from single poly(N-vinylcaprolactam) macromolecules: stabilization and visualization 总被引:1,自引:0,他引:1
Bronstein LM Kostylev M Tsvetkova I Tomaszewski J Stein B Makhaeva EE Okhapkin I Khokhlov AR 《Langmuir : the ACS journal of surfaces and colloids》2005,21(7):2652-2655
Formation of core-shell poly(N-vinylcaprolactam) (PVCL) single-molecule nanostructures due to interaction of PVCL with metal ions was studied using transmission electron microscopy, 13C NMR, and light scattering. This study demonstrates that addition of CoCl2 to PVCL in its globular conformation yields unimolecular core-shell polymer particles with the core decorated with Co(II) ions. The crucial condition for formation of well-defined unimolecular nanostructures is the presence of stable globular aggregates in aqueous solution. Moreover, the metal ions should have a sufficiently high coordination number (higher than 2) to provide a cross-linking and stabilization of the core. 相似文献
42.
The first examples of the use of racemic vinylaziridines in a Pd-catalyzed dynamic kinetic asymmetric transformation have been examined. Optimization studies of the Pd-catalyzed addition of vinylaziridines to isocyanates revealed that the chiral ligand between trans-1,2-diaminocyclohexane and 2-diphenylphosphino-1-naphthoic acid is superior to that involving 2-diphenylphosphino benzoic acid. Surprisingly, high ee's required the use of an acid whose pKa was about 4.7 +/- 0.1 as a cocatalyst. Both acetic acid and hydroxybenzotriazole meet this requirement. Less electrophilic isocyanates (e.g., benzyl, p-methoxyphenyl) gave higher ee's than more electrophilic ones (phenyl or benzoyl). Both N-benzyl and N-arylaziridines react well to give good yields and ee's, whereas N-tosylaziridines gave lower ee's. A 1,1-disubstituted aziridine led to the formation of a tertiary C-N bond with ee's comparable to the formation of the secondary C-N bond. The products were easily reduced almost quantitatively to the sensitive imidazolidines which can be readily hydrolyzed to the vicinal diamines. The reactivity pattern is consistent with a Curtin-Hammett situation wherein the enantiodiscriminating event is the cyclization of a rapidly equilibrating dynamic pi-allyl palladium intermediate. 相似文献
43.
Reaction of the beta-styryl radical with O2 in benzene results in a low yield of benzene oxide, which is shown by isotopic labeling to arise from the solvent. Ab initio and DFT calculations elucidate the mechanism of this reaction, and identify the properties of other radicals that should be more effective promoters of the reaction. The CN radical is found to be one candidate. 相似文献
44.
Dichloro-2,3,3-trimethyl-1-platinocyclobutane, , prepared by the metathetical reaction of Zeise's dimer and 1,1,2-trimethylcyclopropane, reacts with pyridine in chloroform to produce a platinum complex of 2,3-dimethyl-1-butene . Reaction of I with pyridine at low temperatures (ca. ?40° C) leads to a pyridine addition compound (III) in which the platinocyclobutane ring remains intact. The thermal isomerization of III, which may be conveniently studied using NMR, produces a mixture of II and the free olefin. 相似文献
45.
[structure: see text] We have previously described a system of 2-aminoquinoline- and 2-aminoquinazoline-based C-deoxynucleosides (TRIPsides) that are designed to be incorporated into oligomers that can specifically bind in the major groove via Hoogsteen base pairing to any sequence of native DNA. The four TRIPsides are termed antiGC, antiCG, antiTA, and antiAT with respect to the Watson-Crick base pair targets that they bind. The first three TRIPsides have been prepared, characterized, and shown to form stable and sequence-specific triplexes. In the present study, we describe the preparation of two molecules, 2-amino-4-(2'-deoxy-beta-D-ribofuranosyl)quinazoline (7) and 2-amino-6-fluoro-4-(2'-deoxy-beta-D-ribofuranosyl)quinoline (14), that can serve as the remaining antiAT TRIPside. The phosphoramidites of 7 and 14 were prepared, but only the latter was successfully incorporated into DNA oligomers. It is demonstrated using UV-visible melting experiments that 14 forms sequence-specific intramolecular triplets with A:T base pairs at physiological pH. 相似文献
46.
Alexander Orahovats Barry Jackson Heinz Heimgartner Hans Schmid 《Helvetica chimica acta》1973,56(6):2007-2011
Irradiation of 2-azido-3-phenyl-propene ( 5 ) in pentane or benzene solution with a high pressure lamp (pyrex filter) yields 3-benzyl-2H-azirin ( 6 ), which on further irradiation behind quartz or vycor in the presence of trifluoroacetic acid methylester or carbon dioxide yields 4-benzyl-5-methoxy-5-trifluoromethyl-3-oxazolin ( 8 ) and 4-benzyl-3-oxazolin-5-one ( 9 ), respectively (scheme 2). A small amount of 3-phenylacetonitrile is also formed. 相似文献
47.
Abstract— Exposure of ICR 2A cells to either 265, 289, 302 or 313 nm monochromatic UV wavelengths caused the induction of chromosome aberrations with chromatid gaps and breaks being the most common type of aberration detected. Treatment of U V-irradiated cells with photoreactivating light (PRL) resulted in a lower yield of aberrations demonstrating that pyrimidine dimers are involved in the formation of chromosome aberrations induced by the UV wavelengths tested. However, the decrease in the level of aberrations resulting from PRL treatment of 313 nm-irradiated cells was significantly less than for the other wavelengths indicating that non-dimer photoproducts may have played an important additional role in the induction of chromosome aberrations by this UV wavelength. 相似文献
48.
Digrazia Philip M. Blackburn James W. Bienkowski Paul R. Hilton Barry Reed Gregory D. King J. M. Henry Sayler Gary S. 《Applied biochemistry and biotechnology》1990,(1):237-252
An experimental and mathematical method is developed for the microbial systems analysis of polyaromatic hydrocarbon (PAH)-degrading
mixed cultures in PAH-contaminated “town gas” soil systems. Frequency response is the primary experimental and data analysis
tool used to probe the structure of these complicated systems. The objective is to provide a fundamental protocol for evaluating
the performance of specific mixed microbial cultures on specific soil systems by elucidating the salient system variables
and their interactions. Two well-described reactor systems, a constant volume stirred tank reactor (CSTR) and a plug flow
differential volume reactor, are used in order to remove performance effects that are related to reactor type as opposed to
system structure. These two reactor systems are well-defined systems that can be described mathematically and represent the
two extremes of one potentially important system variable, macroscopic mass transfer. The experimental and mathematical structure
of the protocol is described, experimental data is presented, and data analysis is demonstrated for the stripping, sorption,
and biodegradation of napththalene. 相似文献
49.
An efficient synthesis of (+/-)-leporin A (1) has been developed using a tandem Knoevenagel condensation-inverse electron demand intramolecular hetero Diels-Alder reaction to construct the key tricyclic intermediate 3 from pyridone 5 and dienal 6 in one pot in 35% yield. Hydroxylation (71%) of 3 and methylation (77%) of the resulting hydroxypyridone 2 completed the first total synthesis of (+/-)-leporin A (1). 相似文献
50.
Fletcher MT Wood BJ Brereton IM Stok JE De Voss JJ Kitching W 《Journal of the American Chemical Society》2002,124(26):7666-7667
The origins of the oxygen atoms in 1,7-dioxaspiro[5.5]undecane (1) and hydroxyspiroacetal (2) from Bactrocera cacuminata, and in 2,8-dimethyl-1,7-dioxaspiro[5.5]undecane (3) and hydroxyspiroacetal (4) from B. cucumis, have been investigated by incorporation studies from both [(18)O(2)]-dioxygen and [(18)O]-water. Combined GC-MS examination and high-field NMR analysis have demonstrated that all oxygen atoms in 1 and 2 from B. cacuminata are dioxygen derived, but in contrast, the spiroacetals 3 and 4 from B. cucumis incorporate one ring oxygen from water and one ring oxygen (and the hydroxyl oxygen in 4) from [(18)O(2)]-dioxygen. These results reveal not only the generality of monoxygenase mediation of spiroacetal formation in Bactrocera sp., but also an unexpected complexity in their biosynthesis. A general paradigm accommodating these and other observations is presented. 相似文献