A new iron-based metal-organic framework with enhancing catalysis activity for benzene hydroxylation.

A new Fe-based metal-organic framework (MOF), termed Fe-TBAPy Fe2(OH)2(TBAPy)·4.4H2O, was solvothermally synthesized. Structural analysis revealed that Fe-TBAPy is built from [Fe(OH)(CO2)2]∞ rod-shaped SBUs (SBUs = secondary building units) and 1,3,6,8-tetrakis(p-benzoate)pyrene (TBAPy4-) linker to form the frz topological structure highlighted by 7 Å channels and 3.4 Å narrow pores sandwiching between the pyrene cores of TBAPy4-. Consequently, Fe-TBAPy was used as a recyclable heterogeneous catalyst for benzene hydroxylation. Remarkably, the catalysis reaction resulted in high phenol yield and selectivity of 64.5% and 92.9%, respectively, which are higher than that of the other Fe-based MOFs and comparable with those of the best-performing heterogeneous catalysts for benzene hydroxylation. This finding demonstrated the potential for the design of MOFs with enhancing catalysis activity for benzene hydroxylation.

FRET detection of calmodulin binding to the cardiac RyR2 calcium release channel.

Calmodulin (CaM) binding to the type 2 ryanodine receptor (RyR2) regulates Ca release from the cardiac sarcoplasmic reticulum (SR). However, the structural basis of CaM regulation of the RyR2 is poorly defined, and the presence of other potential CaM binding partners in cardiac myocytes complicates resolution of CaM's regulatory interactions with RyR2. Here, we show that a fluorescence-resonance-energy-transfer (FRET)-based approach can effectively resolve RyR2 CaM binding, both in isolated SR membrane vesicles and in permeabilized ventricular myocytes. A small FRET donor was targeted to the RyR2 cytoplasmic assembly via fluorescent labeling of the FKBP12.6 subunit. Acceptor fluorophore was attached at discrete positions within either the N- or the C-lobe of CaM. FRET between FKBP12.6 and CaM bound to SR vesicles indicated CaM binding at a single high-affinity site within 60 Å of FKBP12.6. Micromolar Ca increased the apparent affinity of CaM binding and slowed CaM dissociation, but did not significantly affect maximal FRET efficiency at saturating CaM. FRET was strongest when the acceptor was attached at either of two positions within CaM's N-lobe versus sites in CaM's C-lobe, providing CaM orientation information. In permeabilized ventricular myocytes, FKBP12.6 and CaM colocalized to Z-lines, and the efficiency of energy transfer to both the N- and C-lobes of CaM was comparable to that observed in SR vesicle experiments. Results also indicate that both the location and orientation of CaM binding on the RyR2 are very similar to the skeletal muscle RyR1 isoform. Specific binding of CaM to functional RyR2 channels in the cardiac myocyte environment can be monitored using FKBP biosensors and FRET.