Copolymer-supported heterogeneous organocatalyst for asymmetric aldol addition in aqueous medium.

In the current study, a convenient and simple way is presented to synthesize a novel type of supported heterogeneous organocatalyst in 21-81% yield by the copolymerization of 9-amino-9-deoxy-epi-cinchonine organocatalyst with acrylonitrile using AIBN as radical initiator. The chemical compositions (x/y) and weight-average molecular weights of copolymers 1a-d were determined by (1)H NMR and GPC analysis respectively. Their porous and layered structure, and surface morphology were characterized by nitrogen adsorption-desorption, XRD and TEM. In the asymmetric aldol addition of p-nitrobenzaldehyde to cyclohexanone and 1-hydroxy-2-propanone in water, all the supported organocatalysts 1a-d afforded excellent isolated yields (90.2-94.7%) and stereoselectivities (96.8-97.8%ee anti, anti/syn = 91/9). The highest catalytic property (96% yield, anti/syn = 90/10 and 99%ee anti) in water as the sole solvent was achieved under the optimized conditions. Compared with cyclohexanone, cyclopentanone and acetone showed the less desired enantioselectivities in the same aldol reactions. At the end of the aldol reaction, the copolymer-supported organocatalyst 1a was readily recovered in 95-98% yield from reaction mixture by simple filtration using an organic membrane. Even in the fifth run, there was no significant loss in catalytic activity and stereocontrol (94.3% yield, 97.2%ee anti, anti/syn = 90/10). After continuous reuse five times, there was some drop in catalytic activity and stereoselectivity.

A reliable and durable approach for real-time determination of cellular superoxide anion based on biomimetic superoxide dismutase stabilized by a zeolite.

This paper demonstrates a reliable and durable method for in situ real-time determination of O(2)˙(-) based on direct electron transfer of Mn(3)(PO(4))(2), which acts as a superoxide dismutase (SOD). Mn(2+) is ion-exchanged into zeolite-ZSM-5 microstructures, and further coated with poly(diallyldimethylammonium chloride) (PDDA). Direct electron transfer of Mn(2+) is greatly facilitated by zeolite microstructures with the formal potential of 561 ± 6 mV vs. Ag|AgCl, which is just located between thermodynamic potentials of O(2)˙(-)/O(2) and O(2)˙(-)/H(2)O(2). The biomimetic catalytic activity of Mn(3)(PO(4))(2), together with the enhanced electron transfer of Mn(2+) obtained at the zeolite electrode has provided a platform for determination of O(2)˙(-) with high selectivity, wide linear range, low detection limit, and quick response. On the other hand, the present Mn(2+)-ZSM/PDDA electrode shows relatively long-term stability, good reproducibility, and biocompatibility, which opens up a way to adhering cells directly onto the film surface for in situ monitoring of cellular species. As a sequence, the remarkable analytical performance of the present O(2)˙(-) biosensor, combined with the characteristics of the Mn(2+)-ZSM/PDDA electrode surface has established a novel approach for real-time determination of O(2)˙(-) released from living cells.