9 research outputs found

    TCA Cycle Involved Enzymes SucA and Kgd, as well as MenD: Efficient Biocatalysts for Asymmetric C–C Bond Formation

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    Asymmetric mixed carboligation reactions of α-ketoglutarate with different aldehydes were explored with the thiamine diphosphate dependent enzymes SucA from <i>E. coli</i>, Kgd from <i>Mycobacterium tuberculosis</i>, and MenD from <i>E. coli</i>. All three enzymes proved to be efficient biocatalysts to selectively deliver chiral δ-hydroxy-γ-keto acids with moderate to excellent stereoselectivity. The high regioselectivity is due to the preserved role of α-ketoglutarate as acyl donor for these enzyme-catalyzed reactions

    Ferroelectricity in Simple Binary ZrO<sub>2</sub> and HfO<sub>2</sub>

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    The transition metal oxides ZrO<sub>2</sub> and HfO<sub>2</sub> as well as their solid solution are widely researched and, like most binary oxides, are expected to exhibit centrosymmetric crystal structure and therewith linear dielectric characteristics. For this reason, those oxides, even though successfully introduced into microelectronics, were never considered to be more than simple dielectrics possessing limited functionality. Here we report the discovery of a field-driven ferroelectric phase transition in pure, sub 10 nm ZrO<sub>2</sub> thin films and a composition- and temperature-dependent transition to a stable ferroelectric phase in the HfO<sub>2</sub>–ZrO<sub>2</sub> mixed oxide. These unusual findings are attributed to a size-driven tetragonal to orthorhombic phase transition that in thin films, similar to the anticipated tetragonal to monoclinic transition, is lowered to room temperature. A structural investigation revealed the orthorhombic phase to be of space group <i>Pbc</i>2<sub>1</sub>, whose noncentrosymmetric nature is deemed responsible for the spontaneous polarization in this novel, nanoscale ferroelectrics
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