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14 pages, 2826 KiB

Open AccessArticle

Structural Analysis of Xylose Isomerase from Streptomyces avermitilis

by Ki Hyun Nam

Crystals 2024, 14(5), 446; https://doi.org/10.3390/cryst14050446 - 7 May 2024

Cited by 3 | Viewed by 1872

Xylose isomerase (XI, also known as glucose isomerase) is an oxidoreductase that interconverts aldoses and ketoses. XI catalyzes the reversible isomerization of D-glucose and D-xylose into D-fructose and D-xylulose, respectively. The molecular function of XI is widely applied in producing high-fructose corn syrup (HFCS) in the food industry and bioethanol from hemicellulose in the biofuel industry. The structural information of XI from diverse strains is important for understanding molecular properties that can provide insights into protein engineering to improve enzyme efficiency. To extend the knowledge of the structural information on XI, the crystal structure of XI from Streptomyces avermitilis (SavXI) was determined at a 2.81 Å resolution. SavXI containing TIM barrel and extended α-helix domains formed the tetrameric assembly. The two metal-binding sites and their coordinating residues showed diverse conformations, providing the structural flexibility of the active site of SavXI. The structural comparison of SavXI and XI homologs exhibited unique metal-binding sites and conformations of the C-terminal α-helix domain. These structural results extend our knowledge of the molecular flexibility and mechanism of the XI family. Full article

(This article belongs to the Section Biomolecular Crystals)

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19 pages, 3569 KiB

Open AccessArticle

Isomerization of Hemicellulose Aldoses to Ketoses Catalyzed by Basic Anion Resins: Catalyst Screening and Stability Studies

by Miriam El Tawil-Lucas, Maia Montaña, Miguel Macias-Villasevil, Jovita Moreno and Jose Iglesias

Catalysts 2023, 13(9), 1301; https://doi.org/10.3390/catal13091301 - 16 Sep 2023

Cited by 4 | Viewed by 2400

Abstract

Isomerization of aldoses to ketoses is an essential step in carbohydrate valorization routes in biorefineries to produce a wide variety of bioproducts. In this work, selective isomerization of aldoses into ketoses was investigated using different commercial Brønsted basic anion resins at low temperature conditions. Weak and strong basic resins were tested under different reaction conditions. Amberlite IRA-900 and Amberlyst A-26 (strong resins) and Amberlite IRA-67 and Amberlyst A-21 (weak resins) were tested to assess their catalytic properties. Strong basic resins provided high yields of fructose. IRA-900 was also tested in the isomerization of different sugar monosaccharides conventionally present in lignocellulosic biomass (xylose, arabinose, galactose, glucose and mannose) aiming to explore the performance of this material in hemicellulose-derived sugar mixtures. Very promising performance was observed for IRA-900, yielding fructose selectivity higher than 75% and fructose yield of 27% in the isomerization reaction. Notably, basic anionic resins were not suitable for reuse in different reaction cycles, although the use of organic cosolvents, specifically ethanol, improved the reusability of the tested resins. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for the Production of Biofuels and Biochemicals)

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19 pages, 3198 KiB

Open AccessFeature PaperReview

Sn-Beta Catalyzed Transformations of Sugars—Advances in Catalyst and Applications

by Ping Zhu, Hu Li and Anders Riisager

Catalysts 2022, 12(4), 405; https://doi.org/10.3390/catal12040405 - 6 Apr 2022

Cited by 15 | Viewed by 4822

Abstract

Beta zeolite modified with Sn in the framework (Sn-Beta) was synthesized and introduced as a heterogeneous catalyst for Baeyer–Villiger oxidations about twenty years ago. Since then, both syntheses strategies, characterization and understanding as well as applications with the material have developed significantly. Remarkably, Sn-Beta zeolite has been discovered to exhibit unprecedented high catalytic efficiency for the transformation of glucose to fructose (i.e., aldoses to ketoses) and lactic acid derivatives in both aqueous and alcoholic media, which has inspired an extensive interest to develop more facile and scalable syntheses routes and applications for sugars transformations. This review survey the progress made on both syntheses approaches of Sn-Beta and applications of the material within catalyzed transformations of sugar, including bottom-up and top-down syntheses and catalyzed isomerization, dehydration, and fragmentation of sugars. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Contributions in Biomass Catalytic Conversion for a Sustainable Future)

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15 pages, 2766 KiB

Open AccessArticle

Isomerization of Glucose to Fructose in Hydrolysates from Lignocellulosic Biomass Using Hydrotalcite

by David Steinbach, Andreas Klier, Andrea Kruse, Jörg Sauer, Stefan Wild and Marina Zanker

Processes 2020, 8(6), 644; https://doi.org/10.3390/pr8060644 - 28 May 2020

Cited by 20 | Viewed by 9997

Abstract

The isomerization of glucose-containing hydrolysates to fructose is a key step in the process from lignocellulosic biomass to the platform chemical hydroxymethylfurfural. We investigated the isomerization reaction of glucose to fructose in water catalyzed by hydrotalcite. Catalyst characterization was performed via IR, XRD, and SEM. Firstly, glucose solutions at pH-neutral conditions were converted under variation of the temperature, residence time, and catalyst loading, whereby a maximum of 25 wt.% fructose yield was obtained at a 38 wt.% glucose conversion. Secondly, isomerization was performed at pH = 2 using glucose solutions as well as glucose-containing hydrolysates from lignocellulosic biomass. Under acidic conditions, the hydrotalcite loses its activity for isomerization. Consequently, it is unavoidable to neutralize the acidic hydrolysate before the isomerization step with an inexpensive base. As a neutralizing agent NaOH is preferred over Ba(OH)₂, since higher fructose yields are achieved with NaOH. Lastly, a pH-neutral hydrolysate from lignocellulose was subjected to isomerization, yielding 16 wt.% fructose at a 32 wt.% glucose conversion. This work targets the application of catalytic systems on real biomass-derived samples. Full article

(This article belongs to the Special Issue Environmental Catalysis Processes Based on Biomass)

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