RESUMEN

A compact, inexpensive capillary electrophoresis instrument was developed for monitoring metal ions and evaluated for Zn(II) in remote contaminated locations in western Tasmania, Australia. The portable instrument, measuring 21 cm x 10 cm x 7 cm, was powered from the USB port of a laptop computer and built from off-the-shelf components costing ∼$1200 USD. Electrophoretic separations were conducted using a fused silica capillary (10-50 µm I.D.), applying 8.5 kV over capillaries ranging from 25 cm to 40 cm in length. The capillary inlet was connected with an electrically grounded cross-piece as flow-through injection interface. Automated fluidic management was achieved by controlling four mini peristaltic pumps and a solenoid valve. Detection was realised using a purpose-built visible LED absorption detector, optimised for the detection of Co(II), Cu(II) and Zn(II) after complexation with 4-(2-Pyridylazo) resorcinol (PAR). Limits of detection of sub-µM were obtained. The instrument was tested for continuous operation in the laboratory for up to 3 months, and relative standard deviations of <5.4% were found over 945 consecutive injections. In the field, the system was able to measure 106 samples within 11 h, the time it can be powered from the laptop computer. As Field measurement of Zn(II) in western Tasmania was demonstrated to show capability for on-site metal testing.

Asunto(s)

Electroforesis Capilar , Zinc , Australia , Electroforesis Capilar/métodos , Metales

RESUMEN

Bench- and air-stable 1-methoxy-2,2,6,6-tetramethylpiperidine (TEMPO-Me) is relatively unreactive at ambient temperature in the absence of an electrochemical stimulus. In this report, we demonstrate that the one-electron electrochemical oxidation of TEMPO-Me produces a powerful electrophilic methylating agent in situ. Our computational and experimental studies are consistent with methylation proceeding via a SN2 mechanism, with a strength comparable to the trimethyloxonium cation. A protocol is developed for the electrochemical methylation of aromatic acids using TEMPO-Me.

RESUMEN

It has been reported that pulsed irradiation can improve photosynthetic activity and phytochemical production in plants. Intrigued and inspired by these observations, we postulated that pulsed irradiation strategies may have broader implications in organic synthesis. We report here the results of a proof-of-concept study demonstrating that pulsed LED irradiation enhances the efficiency of a visible light-mediated photoredox-catalysed reaction. The design and construction of an inexpensive multiphase circuit (∼US$5) enabling power and pulse frequency modulation, which is connected to light-emitting diodes (LEDs), provides a source of pulsed visible light. This technology was then utilised to establish a novel copper-photocatalysed dual α-amino C-H/C-F functionalisation reaction. Pulsed blue LED irradiation was shown to be crucial for facilitating a much more efficient process and increasing the rate of product formation. Our results suggest that pulsed irradiation strategies have the potential to contribute to enhancing the synthetic utility and extending the scope of first row transition metal-based photoredox catalysts. We also anticipate that this approach will find wider applications in synthesis.