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Analysis of the spectroscopic signatures of the R2-W48F/D84E biferric peroxo intermediate identifies a cis mu-1,2 peroxo coordination geometry. DFT geometry optimizations on both R2-W48F/D84E and R2-wild-type peroxo intermediate models including constraints imposed by the protein also identify the cis mu-1,2 peroxo geometry as the most stable peroxo intermediate structure. This study provides significant insight into the electronic structure and reactivity of the R2-W48F/D84E peroxo intermediate, structurally related cis mu-1,2 peroxo model complexes, and other enzymatic biferric peroxo intermediates.

The detection and identification of subatomic particles is an important scientific problem with implications for medical devices, radiography, biochemical analysis, particle physics, and astrophysics. In addition, the development of efficient detectors of neutrons generated by fissile material is a pressing need for nuclear nonproliferation efforts. A critical objective in the field of radiation detection is to obtain the physical insight necessary for rational design of scintillation materials. Many factors affect the quantum efficiency and timing of scintillator light output, including chemical composition, electronic structure, interchromophore interactions, crystal symmetry, and atomic density. None of the material types currently used in radiation detection, which include crystalline inorganic compounds such as LaBr 3 :Ce, organic compounds, and plastics, have the inherent synthetic versatility to exert systematic control over these factors. Therefore, it is likely that major advances in radiation detection will require the development of new materials outside the scope of traditional scintillators. Here, we propose that metal-organic frameworks (MOFs) could potentially offer the desired level of structural control, leading to an entirely new class of radiation detection materials.MOFs are crystalline materials consisting of metal clusters linked by coordinating organic groups. Yaghi, O'Keefe, and coworkers have shown that structures resulting from the selfassembly of specific metal ions and linkers can be predicted through an understanding of the geometric nets accessible to particular metal-linker combinations (''reticular chemistry''), [1][2][3]

This paper presents a novel device for the dielectrophoretic manipulation of particles and cells. A two-level isotropic etch of a glass substrate was used to create three-dimensional ridge-like structures in micrometer-sized channels. Due to the insulating properties of glass, locally patterned regions of nonuniform electric field form near the ridges when a dc field is applied along the channel. The ridges are designed using the method of faceted prisms, such that substantially uniform fields are produced on each side of the faceted interfaces that form each ridge. The dielectrophoretic force that results from the electric field gradient near the ridges is used to affect particle motion parallel to the ridges in the absence of a bulk pressure-driven flow. Trapping and deflection of particles and continuous concentration and separation of Bacillus subtilis from a two-component sample mixture are demonstrated. The flow of B. subtilis is restricted to a selected channel of a planar, multichannel device as a result of negative dielectrophoresis arising from the presence of the insulating ridges when the applied electric field exceeds a threshold of 30 V/mm. Dielectrophoresis has a negligible impact on 200-nm-diameter polystyrene particles under the same conditions.