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41.
We report the first direct evidence for the formation of circular surface micelles (hemimicelles) on the surface of water. These highly monodisperse 30 nm hemimicelles, made from a semifluorinated alkane deposited as a Langmuir monolayer, form organized hexagonal arrays as determined by small-angle X-ray diffraction conducted directly on the water surface at grazing incidence.  相似文献   
42.
The self‐diffusion (Dc) coefficients of various lanthanum(III) diamagnetic analogues of open‐chain and macrocyclic complexes of gadolinium used as MRI contrast agents were determined in dilute aqueous solutions (3–31 mM ) by pulsed‐field‐gradient (PFG) high‐resolution 1H‐NMR spectroscopy. The self‐diffusion coefficient of H2O (Dw) was obtained for the same samples to derive the relative diffusion constant, a parameter involved in the outersphere paramagnetic‐relaxation mechanism. The results agree with an averaged relative diffusion constant of 2.5 (±0.1)×10?9 and of 3.3 (±0.1)×10?9 m2 s?1 at 25 and 37°, respectively, for 'small' contrast agents (Mr 500–750 g/mol), and with the value of bulk H2O (2.2×10?9 and 2.9×10?9 m2 s?1 at 25° and at 37°, respectively) for larger complexes. The use of the measured values of Dc for the theoretical fitting of proton NMRD curves of gadolinium complexes shows that the rotational correlation times (τR) are very close to those already reported. However, differences in the electronic relaxation time (τSO) at very low field and in the correlation time (τV) related to electronic relaxation were found.  相似文献   
43.
New families of enantiopure bis(oxazolines) with 4,5-trans (5 a-g) or 4,5-cis (6 c) stereochemistry at the individual rings have been prepared in high yield. Their eta(3)-allyl palladium complexes (8 a-g, 9 c and 10) have been used as catalytic precursors in allylic alkylation reactions with excellent enantioselectivities (up to 96 %) for the trans oxazoline derivatives, while Pd/6 c system was inactive. NMR studies on palladium eta(3)-1,3-diphenylallyl intermediates (11 a, c and e) showed the presence of syn/syn- and syn/anti-allyl isomers in solution; this resembles the first example of eta(3)-eta(1)-eta(3) isomerism in Pd allylic complexes containing bis(oxazolines) derived from malonic acid.  相似文献   
44.
Abstract

Comparative volatilization experiments were carried out using isoproturon and parathion-methyl sprayed on French beans in field experiments and on plant stands (0.5 m2) in the volatilization chamber developed by the SLFA Neustadt using both compounds 14C-labelled. The experimental conditions in the field experiments concerning wind speed, temperature and humidity fluctuations were simulated in the volatilization chamber. The laboratory experiment reflected the actual outdoor situation, showing only a negligible amount of volatile isoproturon directly measured in air samples, and providing no reduction of the A.I. residues in plants compared with the initial value in the corresponding field experiment. 77.2% of the parathion-methyl applied to the plants were volatilized and measured directly in air samples in the volatilization chamber while a reduction by 74.7% was found for the corresponding field experiment by residue analysis of the plants after 24 h. No details could be given concerning the nature of the evaporated portions in the field experiment.  相似文献   
45.
46.
A family of eight neutral, pseudotetrahedral piano-stool ruthenium complexes C, of the type [RuCl2(p-cymene)(PArPhR)] (Ar = 1-naphthyl, 9-phenanthryl and 2-biphenylyl; R = Me, i-Pr, OMe, –CH2SiMe3 and –CH2SiPh3) have been prepared and characterised, including the X-ray crystal structure for C6 (Ar = 2-biphenylyl; R = i-Pr). These complexes catalyse the asymmetric hydrogen transfer reaction of acetophenone in refluxing 2-propanol in the presence of potassium tert-butoxyde, reaching full conversions and up to 45% ee after 24 h towards the S enantiomer of 1-phenylethanol. Cationic complexes formed upon treatment of C with one equivalent of AgSbF6 or (Et3O)PF6 are active in the cyclopropanation reaction of styrene and α-methylstyrene by ethyl diazoacetate. Low to moderate conversions (up to 58%), diastereoselectivities (up to 40% de), and moderate enantioselectivities (up to 69% ee) have been found. For both reactions, bulky complexes and C6 in particular lead to the best results.  相似文献   
47.
Pyridinylazolato (N–N′) ruthenium(II) complexes of the type [(N–N′)RuCl(PMe3)3] have been obtained in high yields by treating the corresponding functionalised azolylpyridines with [RuCl2(PMe3)4] in the presence of a base. 15N NMR spectroscopy was used to elucidate the electronic influence of the substituents attached to the azolyl ring. The findings are in agreement with slight differences in the bond lengths of the ruthenium complexes. Furthermore, the electronic nature of the azolate moiety modulates the catalytic activity of the ruthenium complexes in the hydrogenation of carbon dioxide under supercritical conditions and in the transfer hydrogenation of acetophenone. DFT calculations were performed to shed light on the mechanism of the hydrogenation of carbon dioxide and to clarify the impact of the electronic nature of the pyridinylazolate ligands.  相似文献   
48.
In the present work a modular pathway towards the synthesis of a new versatile MRI contrast agent is reported and its physico-chemical properties are described. Two different functional groups were attached on two arms of the gadolinium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) in order to get a platform able to bind one probe designed to target specific biological marker and a fluorescent molecule likely to be used for optical imaging. The nuclear magnetic relaxation dispersion (NMRD) profile, the oxygen-17 relaxometric NMR study and stability assessment versus transmetalation of the Gd-complex show that this new contrast agent has a relaxivity and transmetalation stability similar to Gd–DOTA.  相似文献   
49.
Apart from energy generation, the storage and liberation of energy are among the major problems in establishing a sustainable energy supply chain. Herein we report the development of a rechargeable H2 battery which is based on the principle of the Ru‐catalyzed hydrogenation of CO2 to formic acid (charging process) and the Ru‐catalyzed decomposition of formic acid to CO2 and H2 (discharging process). Both processes are driven by the same catalyst at elevated temperature either under pressure (charging process) or pressure‐free conditions (discharging process). Up to five charging–discharging cycles were performed without decrease of storage capacity. The resulting CO2/H2 mixture is free of CO and can be employed directly in fuel‐cell technology.  相似文献   
50.
Some metal‐chelating peptides have antioxidant properties, with potential nutrition, health, and cosmetics applications. This study aimed to simulate their separation on immobilized metal ion affinity chromatography from their affinity constant for immobilized metal ion determined in surface plasmon resonance, both technics are based on peptide‐metal ion interactions. In our approach, first, the affinity constant of synthetic peptides was determined by surface plasmon resonance and used as input data to numerically simulate the chromatographic separation with a transport‐dispersive model based on Langmuir adsorption isotherm. Then, chromatographic separation was applied on the same peptides to determine their retention time and compare this experimental tR with the simulated tR obtained from simulation from surface plasmon resonance data. For the investigated peptides, the relative values of tR were comparable. Hence, our study demonstrated the pertinence of such numerical simulation correlating immobilized metal ion affinity chromatography and surface plasmon resonance.  相似文献   
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