Kinetics of glucose isomerization to fructose by immobilized glucose isomerase: anomeric reactivity of D-glucose in kinetic model

Step-by-Step Hybrid Conversion of Glucose to 5-acetoxymethyl-2-furfural Using Immobilized Enzymes and Cation Exchange Resin

An alternative to 5-hydroxymethyl-2-furfural (HMF), which is a promising furan derivative that can be used as a starting material for the preparation of non-petroleum-derived polymeric materials from sugars, is 5-acetoxymethyl-2-furfural (AMF). The less-hydrophilic acetyl group of AMF has advantages over the hydroxy group of HMF in terms of thermal stability and isolation. In previous studies, fructose has been used as a starting material along with lipases for the enzymatic synthesis of AMF. In this study, we designed a hybrid synthesis system that includes the isomerization and esterification of glucose into AMF. For the step-by-step conversion of glucose to 1,6-diacetylfructose (DAF), glucose-isomerase and immobilized lipase (Novozym 435) were used as enzymes. Furthermore, for the synthesis of AMF, the direct dehydration of DAF was performed using a cation exchange resin (Amberlyst 15), combined with several industrial solvents, such as dimethylsulfoxide (DMSO), acetonitrile (AN) and dimethylformamide (DMF) for the synthesis of AMF. In order to improve the final yield of AMF, we determined the best solvent conditions. While the AMF yield after the direct dehydration of DAF in a single solvent was maximum 24%, an AMF and HMF yield in the mixed solvent such as dioxane and DMS (9:1) was achieved each 65% and 15%. According to these results, we found that the addition of dioxane in aprotic polar solvents could affect the dehydration reaction and dramatically improve the formation of AMF and HMF.

Catalytic Production of Oxygenated and Hydrocarbon Chemicals From Cellulose Hydrogenolysis in Aqueous Phase

As the most abundant polysaccharide in lignocellulosic biomass, a clean and renewable carbon resource, cellulose shows huge capacity and roused much attention on the methodologies of its conversion to downstream products, mainly including platform chemicals and fuel additives. Without appropriate treatments in the processes of cellulose decompose, there are some by-products that may not be chemically valuable or even truly harmful. Therefore, higher selectivity and more economical and greener processes would be favored and serve as criteria in a correlational study. Aqueous phase, an economically accessible and immensely potential reaction system, has been widely studied in the preparation of downstream products of cellulose. Accordingly, this mini-review aims at making a related summary about several conversion pathways of cellulose to target products in aqueous phase. Mainly, there are four categories about the conversion of cellulose to downstream products in the following: (i) cellulose hydrolysis hydrogenation to saccharides and sugar alcohols, like glucose, sorbitol, mannose, etc.; (ii) selective hydrogenolysis leads to the cleavage of the corresponding glucose C-C and C-O bond, like ethylene glycol (EG), 1,2-propylene glycol (PG), etc.; (iii) dehydration of fructose and further oxidation, like 5-hydroxymethylfurfural (HMF), 2,5-furandicarboxylic acid (FDCA), etc.; and (iv) production of liquid alkanes via hydrogenolysis and hydrodeoxygenation, like pentane, hexane, etc. The representative products were enumerated, and the mechanism and pathway of mentioned reaction are also summarized in a brief description. Ultimately, the remaining challenges and possible further research objects are proposed in perspective to provide researchers with a lucid research direction.

Efficient Conversion of Glucose into Fructose via Extraction-Assisted Isomerization Catalyzed by Endogenous Polyamine Spermine in the Aqueous Phase

In the present study, natural polyamine spermine is demonstrated as a potential basic catalyst for glucose-to-fructose isomerization. For instance, spermine achieves a decent fructose yield (30% wt) and selectivity (74%) during the single-step aqueous phase isomerization under the modest operating conditions (100 °C for 15 min). In addition to the expected reaction byproduct monosugar mannose, spermine also assists in the synthesis of rare and important monosugar, that is, psicose up to 4% wt. Psicose is a zero calorie rare sugar, exhibits a low caloric value, and possesses anti-adipogenic property. A comparative study involving other polyamines concluded that the presence of 20 amines tends to exhibit the most significant impact in improving the target product yield by releasing a higher number of OH- ions, which are responsible for isomerization through the formation of an enediol anion. An attempt was made to further improve the fructose yield through the addition of neutral salts, but it promoted a meager achievement. In an alternate study, a selective extraction strategy was followed for the isolation of fructose from the reaction mixture. The employed aryl monoboronic acid remarkably improved the net fructose concentration, that is, fructose productivity up to 75% wt (cumulative) and 70% selectivity within three consecutive extractions and isomerization cycles, which is comparatively three times shorter than that reported in the literature. Notably, spermine itself provided the essential and necessary basic environment for selective fructose extraction and glucose isomerization, ruling out the use of any external reagents and thus establishing itself as a versatile material suitable for a typical isomerization reaction in an upscaled reactor.

Isomerization of glucose into fructose with homogenous amine-type base catalysts: amine structure, chain length, and kinetics

Three homogeneous organosilanes amine and aliphatic primary amine were used as amine catalysts to evaluate their catalytic activity and kinetic towards glucose isomerization. Catalysts structure (primary, secondary, tertiary amine), terminal groups and alkyl chain length were investigated and compared elaborately. Result showed organosilanes tertiary amine behaved the best and amine generated OH− and amine itself contributed the isomerization reaction. The generated acidic by-product not only decreased fructose selectivity but also affected glucose conversion kinetic. The effect of siloxane (–Si–O–CH3) substituent with methyl (–CH3) can be insignificant, but it provided guiding significance for selecting amine-type homogeneous or grafted amine catalysts for glucose isomerization reaction. Longer alkyl chain resulted in lower glucose conversion because of the alkyl chain curls that would weaken the amine catalytic effect and hydration ability. Catalyst loading and initial glucose concentration investigations further showed that amine would effectively catalyze the isomerization reaction under varied operational conditions. This work will provide more details about organic amine catalysts on glucose isomerization into fructose and promote synthesis of platform chemicals in the applications of biorenewable chemicals and fuel.

Effect of metal chlorides on glucose mutarotation and possible implications on humin formation

An in situ Raman spectroscopic kinetic study of the glucose mutarotation reaction in the presence of Lewis acids is presented herein. The effect of Lewis acids on humin formation reactions is also discussed.

Improving the thermostability and catalytic efficiency of Bacillus deramificans pullulanase by site-directed mutagenesis

Pullulanase (EC 3.2.1.41) is a well-known starch-debranching enzyme. Its instability and low catalytic efficiency are the major factors preventing its widespread application. To address these issues, Asp437 and Asp503 of the pullulanase from Bacillus deramificans were selected in this study as targets for site-directed mutagenesis based on a structure-guided consensus approach. Four mutants (carrying the mutations D503F, D437H, D503Y, and D437H/D503Y) were generated and characterized in detail. The results showed that the D503F, D437H, and D503Y mutants had an optimum temperature of 55°C and a pH optimum of 4.5, similar to that of the wild-type enzyme. However, the half-lives of the mutants at 60°C were twice as long as that of the wild-type enzyme. In addition, the D437H/D503Y double mutant displayed a larger shift in thermostability, with an optimal temperature of 60°C and a half-life at 60°C of more than 4.3-fold that of the wild-type enzyme. Kinetic studies showed that the Km values for the D503F, D437H, D503Y, and D437H/D503Y mutants decreased by 7.1%, 11.4%, 41.4%, and 45.7% and the Kcat/Km values increased by 10%, 20%, 140%, and 100%, respectively, compared to those of the wild-type enzyme. Mechanisms that could account for these enhancements were explored. Moreover, in conjunction with the enzyme glucoamylase, the D503Y and D437H/D503Y mutants exhibited an improved reaction rate and glucose yield during starch hydrolysis compared to those of the wild-type enzyme, confirming the enhanced properties of the mutants. The mutants generated in this study have potential applications in the starch industry.