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81.

The electrochemical behaviour of the herbicide Asulam was studied by cyclic and square wave voltammetry. Asulam may be irreversibly oxidised at a glassy carbon electrode. Maximum currents were obtained at pH = 1.9 in aqueous electrolyte solution. Based on the electrochemical behaviour of Asulam, two analytical methodologies were developed for its determination in water samples, using square wave voltammetry (SWV) and flow injection analysis (FIA) coupled with an amperometric detector. Limits of detection of 7.1 2 10 m 6 mol L m 1 and 1.2 2 10 m 8 mol L m 1 for SWV and FIA respectively, were achieved. Repeatability was calculated by assessing the relative standard deviation (%) for 10 consecutive determinations of one sample. The found values were 2.1% for SWV and 5.0% for FIA. Validation of the results provided by SWV and FIA methodologies was performed by comparison with results from an HPLC-DAD technique. Good relative deviations were found (< 5%). Recovery trials were performed to assess the accuracy of the results and the obtained values were between 84% and 107% for both methods.  相似文献   
82.
83.
A new three‐component reductive arylation of amides with stable reactants (iPrOH and arylboronate esters), making use of a 2‐pyridinyl (Py) directing group, is described. The N‐Py‐amide substrates are readily prepared from carboxylic acids and PyNH2, and the resulting N‐Py‐1‐arylalkanamine reaction products are easily transformed into the corresponding chlorides by substitution of the HN‐Py group with HCl. The 1‐aryl‐1‐chloroalkane products allow substitution and cross‐coupling reactions. Therefore, a general protocol for the transformation of carboxylic acids into a variety of functionalities is obtained. The Py‐NH2 by‐product can be recycled.  相似文献   
84.
For an increased lifetime of polymer:fullerene bulk heterojunction (BHJ) solar cells, an understanding of the chemical and morphological degradation phenomena taking place under operational conditions is crucial. Phase separation between polymer and fullerene induced by thermal stress has been pointed out as a major issue to overcome. While often the effect of thermal stress on the morphology of polymer:fullerene BHJ is investigated in the darkness, here we observe that light exposure slows down fullerene crystallization and phase separation induced at elevated temperatures. The observed photo‐stabilizing effect on active layer morphology is quite independent on the polymer and is attributed to light‐induced dimerization of the fullerene. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1209–1214  相似文献   
85.
Abstract

Seven tetracyclic spiro-alkaloids, i.e. glucoerysodine (1), erysodine (2), epi-erythratidine (3), erysovine (4), erythratidine (5), erysotrine (6) and erythraline (7) were isolated from the seeds of Erythrina latissima by means of conventional separation methods and HPLC-DAD-SPE-NMR. Their structures were elucidated by spectroscopic means. This is the first report on the isolation of compounds 3, 5 and 6 from this plant. Antiplasmodial activity against the chloroquine-resistant strain Plasmodium falciparum K1 and cytotoxicity against MRC-5 cells (human fetal lung fibroblast cells) was assessed in vitro. Erysodine (2) and erysovine (4) showed moderate activity (IC50 6.53?µM and 4.05?µM, respectively), compared with the standard chloroquine (IC50 = 0.14?µM). No cytotoxicity was observed in a concentration up to 64.0?µM.  相似文献   
86.
Rapid Buchwald-Hartwig amination of electron neutral and rich aryl chlorides and bromides have been achieved using temperature-controlled microwave heating. Primary and secondary aliphatic amines can be coupled with these substrates in good yields within a reaction time of only 10 min.  相似文献   
87.
The preparation of the chloro complex trans-[FeCl2{(R,R)-diph}2] (1) and the alkynyl complexes trans-[M(4-CCC6H4R)Cl{(R,R)-diph}2] [M=Fe, R=NO2 (2); M=Ru, R=H (4), NO2 (5), (E)-CH=CH-4-C6H4NO2 (6); M=Os, R=NO2 (7)], incorporating the optically active diphosphine 1,2-bis(methylphenylphosphino)benzene (diph), are described. Oxidation potentials, as determined by cyclic voltammetry, increase as 2<7<5. Molecular quadratic nonlinearities by hyper-Rayleigh scattering at 1064 nm increase upon introduction of an acceptor group (4<5), chain-lengthening of bridging group (5<6), and proceeding from 3d to 4d and 5d metal (257). Two-level-corrected nonlinearities reproduce the first two trends, but metal variation follows the sequence 2<7<5. The experimental and two-level-corrected nonlinearities for 6 (2795×10−30 and 406×10−30 esu, respectively), are amongst the largest observed thus far for organometallic complexes. Crystals of complexes 2 and 7 exhibit second-harmonic generation (assessed using the Kurtz powder technique), with an efficiency for the former of twice that of urea.  相似文献   
88.
89.
The synthesis of five naturally occurring polyoxygenated coumarins is described. It concerns two 5,6,7-trioxygenated coumarins, i.e., 6-hydroxy-5,7-dimethoxycoumarin (fraxinol) 1 and 5,6,7-trimethoxycoumarin 2, and three 5,7,8-trioxygenated coumarins, i.e., 8-hydroxy-5,7-dimethoxycoumarin (leptodactylone) 3, 5,7,8-trimethoxycoumarin 4 and 8-(3-methyl-2-butenyloxy)-5,7-dimethoxycoumarin (artanin) 5. Key feature of the synthetic pathway is the synthesis of suitable tetraoxygenated benzaldehydes, which are then converted to the corresponding coumarins via a Wittig reaction.  相似文献   
90.
The secret of a successful affinity biosensor partially hides in the chemical interface layer between the transducer system and the biological receptor molecules. Over the past decade, several methodologies for the construction of such interface layers have been developed on the basis of the deposition of self-assembled monolayers (SAMs) of alkanethiols on gold. Moreover, mixed SAMs of polyethylene oxide (PEO) containing thiols have been applied for the immobilization of biological receptors. Despite the intense research in the field of thiol SAMs, relatively little is known about their biosensing properties in correlation with their long-term stability. Especially the impact of the storage conditions on their biosensing characteristics has not been reported before to our knowledge. To address these issues, we prepared mixed PEO SAMs and tested their stability and biosensing performance in several storage conditions, i.e., air, N2, ethanol, phosphate buffer, and H2O. The quality of the SAMs was monitored as a function of time using various characterization techniques such as cyclic voltammetry, contact angle, grazing angle Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In addition, the impact of the different storage conditions on the biosensor properties was investigated using surface plasmon resonance. Via the latter technique, the receptor immobilization, the analyte recognition, and the nonspecific binding were extensively studied using the prostate specific antigen as a model system. Our experiments showed that very small structural differences in the SAM can have a great impact in their final biosensing properties. In addition it was shown that the mixed SAMs stored in air or N2 are very stable and retain their biosensor properties for at least 30 days, while ethanol appeared to be the worst storage medium due to partial oxidation of the thiol headgroup. In conclusion, care must be taken to avoid SAM degradation during storage to retain typical SAM characteristics, which is very important for their general use in many proposed applications.  相似文献   
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