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Oxygen vacancy is conducive to molecular oxygen adsorption and activation, and it is necessary to estimate its contribution on catalysts, especially the doped system for volatile organic compound (VOC) oxidation. Herein, a series of doped Mn x Zr1–x O2 catalysts with oxygen vacancy were prepared by partially substituting Zr4+ in a zirconia with low-valent manganese (Mn2+). Compared with the corresponding mechanically mixed samples (MB-x) without oxygen vacancy, Mn x Zr1–x O2 catalysts exhibited better toluene conversion and specific reaction rate, where the differential values were calculated to estimate the contribution of oxygen vacancy on catalytic performance. The increase in oxygen vacancy concentrations in Mn x Zr1–x O2 catalysts can boost the differential values, implying the enhancement of oxygen vacancy contribution. Density functional theory (DFT) calculations further confirmed the contribution of oxygen vacancy, and molecular oxygen is strongly absorbed and activated on a defective Mn-doped c-ZrO2 (111) surface with oxygen vacancy rather than a perfect m-ZrO2 (−111) surface or a perfect Mn-doped c-ZrO2 (111) surface, thus resulting in the significant improvement in catalytic activity for toluene oxidation. In situ DRIFTS spectra revealed that the oxygen vacancy can alter the toluene degradation pathway and accelerate the intermediates to convert into CO2 and H2O, thus leading to a low activation energy and high specific reaction rate.

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Two crystal structures of human ornithine transcarbamylase (OTCase) complexed with the substrate carbamoyl phosphate (CP) have been solved. One structure, whose crystals were prepared by substituting N-phosphonacetyl-L-ornithine (PALO) liganded crystals with CP, has been refined at 2.4 A (1 A=0.1 nm) resolution to a crystallographic R factor of 18.4%. The second structure, whose crystals were prepared by co-crystallization with CP, has been refined at 2.6 A resolution to a crystallographic R factor of 20.2%. These structures provide important new insights into substrate recognition and ligand-induced conformational changes. Comparison of these structures with the structures of OTCase complexed with the bisubstrate analogue PALO or CP and L-norvaline reveals that binding of the first substrate, CP, induces a global conformational change involving relative domain movement, whereas the binding of the second substrate brings the flexible SMG loop, which is equivalent to the 240s loop in aspartate transcarbamylase, into the active site. The model reveals structural features that define the substrate specificity of the enzyme and that regulate the order of binding and release of products.

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