The postsynthetic modification strategy is adopted to demonstrate for the first time the syntheses of catalytically active chiral MOPMs from a preassambled achiral framework, MIL-101, by attaching L-proline-derived chiral catalytic units to the open metal coordination sites of the host framework. Various characterization techniques (including PXRD, TGA, IR, and N(2) absorption measurements) indicated that the chiral units are successfully incorporated into MIL-101, keeping the parent framework intact. The new chiral MOPMs show remarkable catalytic activities in asymmetric aldol reactions (yield up to 90% and ee up to 80%). It is interesting to note that these heterogeneous catalysts show much higher enantioselectivity than the corresponding chiral catalytic units as homogeneous catalysts. This study demonstrates a simple and efficient route for the generation of catalytically active chiral MOPMs. A variety of chiral catalytic units can be, in principle, incorporated into chemically robust achiral MOPMs with large pores by postmodification and the resulting chiral MOPMs may find useful applications in catalytic asymmetric transformations.

The authors herein report optimized conditions for ultrasensitive phosphatase-based immunosensors (using redox cycling by a reducing agent) that can be simply prepared and readily applied to microfabricated electrodes. The optimized conditions were applied to the ultrasensitive detection of cardiac troponin I in human serum. The preparation of an immunosensing layer was based on passive adsorption of avidin (in carbonate buffer (pH 9.6)) onto indium-tin oxide (ITO) electrodes. The immunosensing layer allows very low levels of nonspecific binding of proteins. The optimum conditions for the enzymatic reaction were investigated in terms of the type of buffer solution, temperature, and concentration of MgCl(2), and the optimum conditions for antigen-antibody binding were determined in terms of incubation time, temperature, and concentration of phosphatase-conjugated IgG. Very importantly, the antigen-antibody binding at 4 °C is extremely important in obtaining reproducible results. Among the four phosphatase substrates (L-ascorbic acid 2-phosphate (AAP), 4-aminophenyl phosphate, 1-naphthyl phosphate, 4-amino-1-naphthyl phosphate) and four phosphatase products (L-ascorbic acid (AA), 4-aminophenol, 1-naphthol, 4-amino-1-naphthol), AAP and AA meet the requirements most for obtaining easy dissolution and high signal-to-background ratios. More importantly, fast AA electrooxidation at the ITO electrodes does not require modification with any electrocatalyst or electron mediator. Furthermore, tris(2-carboxyethyl)phosphine (TCEP) as a reducing agent allows fast redox cycling, along with very low anodic currents at the ITO electrodes. Under these optimized conditions, the detection limit of an immunosensor for troponin I obtained without redox cycling of AA by TCEP is ca. 100 fg/mL, and with redox cycling it is ca. 10 fg/mL. A detection limit of 10 fg/mL was also obtained even when an immunosensing layer was simply formed on a micropatterned ITO electrode. From a practical point of view, it is of great importance that ultralow detection limits can be obtained with simply prepared enzyme-based immunosensors.

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