We report on a method for the determination of the herbicide atrazine in tap water samples using melamine-modified gold nanoparticles (Mel-AuNPs). If a solution containing atrazine is added to a solution of such NPs, a color change occurs from wine-red to blue. This is due to a transition from monodisperse to aggregated Mel-AuNPs and caused by strong hydrogen bonding between atrazine and melamine. The color change can be monitored by a UV–vis spectrophotometer or with bare eyes. The ratio of the absorbances at 640 and 523 nm is linearly related to the logarithm of the atrazine concentration in the 0.165 to 16.5 μM range, and (with different slope) in the 16.5 μM to 330 μM range. The detection limit of atrazine is as low as 16.5 nM (S/N = 3). The method was successfully applied to the determination of atrazine in spiked tap water and gave recoveries that ranged from 72.5 % to 102.3 %.
A stereodivergent synthesis of five‐membered N‐heterocycles, such as 2,3‐dihydropyrroles, and 2‐methylene and 3‐methylene pyrrolidines, has been developed through a tandem annulation of amino alkynes with diazo compounds and involves the trapping of in situ formed intermediates. Mechanistic investigations indicate that the copper‐catalyzed tandem annulations proceed by allenoate formation and subsequent intramolecular hydroamination. In contrast, the rhodium‐catalyzed protocol features a carbenoid insertion into the N H bond and subsequent Conia‐ene cyclization. 相似文献
A highly selective, controllable and synthetically useful base‐promoted intramolecular detosylative cyclization of bis‐N‐tosylhydrazones has been achieved, affording N‐containing heterocycles and cyclic olefins under transition‐metal‐free or gold‐catalyzed procedures, respectively. Moreover, an effective and practical metal‐free or gold‐catalyzed approach to synthesize polycyclic aromatic compounds is also reported. 相似文献
A novel rhodium‐catalyzed highly selective N2‐alkylation of benzotriazoles with diazo compounds/enynones is achieved, providing N2‐alkylated benzotriazoles in good to excellent yields and with excellent N2 selectivities. Importantly, different to traditional carbene insertion into X?H (X=N, O etc) bonds, DFT calculations disclose that this selective N2‐alkylation probably proceeds through a formal 1,3‐ rather than 1,2‐H shift to give the final products. 相似文献
Reported herein is the unprecedented gold‐catalyzed formal [4+1]/[4+3] cycloadditions of diazo esters with hexahydro‐1,3,4‐triazines, thus providing five‐ and seven‐membered heterocycles in moderate to high yields under mild reaction conditions. These reactions feature the use of a gold complex to accomplish the diverse annulations and the first example of the involvement of a gold metallo‐enolcarbene in a cycloaddition. It is also the first utilization of stable triazines as formal dipolar adducts in the carbene‐involved cycloadditions. Mechanistic investigations reveal that the triazines reacted directly, rather than as formaldimine precursors, in the reaction process. 相似文献
A novel rhodium‐catalyzed dearomatization of O‐substituted pyridines to access N‐substituted 2‐pyridones has been developed. A computational study suggests a mechanism involving the formation of a pyridinium ylide followed by an unprecedented 1,4‐acyl migratory rearrangement from O to C. Furthermore, the chiral dirhodium complexes serve as the catalyst for the asymmetric transformation with excellent enantioselective control. DFT calculations indicate the chirality is transferred from axial chirality to the central stereogenic centre. The stronger π–π interaction and CH–π interaction account for the high enantioselectivity. 相似文献