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Transition-Metal Softener for High-Durability Hydrogen Separation Silica Membranes
Yu, Jiwon,Lim, Hyung-Kyu,Lee, Sangheon American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.42
<P>Amorphous silica typically has nano-sized pores with a narrow pore size distribution, which allows selective permeation of hydrogen from complex gas mixtures for cost-effective hydrogen purification after methane steam reforming processes. Despite many advantages, porous silica membranes exhibit poor stability in moist atmosphere, limiting their practical applications. Transition-metal doping is known to be effective in improving the hydrothermal stability of the silica membranes. By performing a series of simulations based on first-principles calculations, we elucidate the underlying mechanism of how transition-metal doping improves the hydrothermal stability of the porous silica membranes. Our calculation results highlight that transition-metal atoms added to the porous silica membrane serve as a softener to release the stress of the silica network at the severely deformed pore curvature. The diminished strain energy of the transition-metal-bound silica pore curvature in turn increases the thermodynamic energy barrier for the formation of mobile species required for pore size redistribution, ultimately leading to strengthened hydrothermal stability. This fundamental understanding can be an important theoretical basis for developing practically applicable high-durability silica-metal hybrid membrane materials.</P> [FIG OMISSION]</BR>
Yu, Jiwon,Shin, Jonghyeok,Park, Myungseo,Seydametova, Emine,Jung, Sang-Min,Seo, Jin-Ho,Kweon, Dae-Hyuk Elsevier 2018 Metabolic engineering Vol.48 No.-
<P><B>Abstract</B></P> <P>Fucosyllactoses (FLs), present in human breast milk, have been reported to benefit human health immensely. Especially, 3-fucosyllactose (3-FL) has numerous benefits associated with a healthy gut ecosystem. Metabolic engineering of microorganisms is thought to be currently the only option to provide an economically feasible route for large-scale production of 3-FL. However, engineering principles for α-1,3-fucosyltransferases (1,3-FTs) are not well-known, resulting in the lower productivity of 3-FL than that of 2′-fucosyllactose (2′-FL), although both 2′-FL and 3-FL follow a common pathway to produce GDP-<SMALL>L</SMALL>-fucose. The C-terminus of 1,3-FTs is composed of heptad repeats, responsible for dimerization of the enzymes, and a peripheral membrane anchoring region. It has long been thought that truncation of most heptad repeats, retaining just 1 or 2, helps the soluble expression of 1,3-FTs. However, whether the introduction of truncated version of 1,3-FTs enhances the production of 3-FL in a metabolically engineered strain, is yet to be tested. In this study, the effect of these structural components on the production of 3-FL in <I>Escherichia coli</I> was evaluated through systematic truncation and elongation of the C-terminal regions of three 1,3-FTs from <I>Helicobacter pylori</I>. Although these three 1,3-FTs contained heptad repeats and membrane-anchoring regions of varying lengths, they commonly exhibited an optimal performance when the number of heptad repeats was increased, and membrane-binding region was removed. The production of 3-FL could be increased 10–20-fold through this simple strategy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heptad repeats in several α-1,3-fucosyltransferases were truncated or elongated. </LI> <LI> Dimerization of 1,3-FT was essential for enzyme activity and thermostability. </LI> <LI> 3-fucosyllactose was better produced in <I>E. coli</I> with longer heptad repeats. </LI> </UL> </P>