Mixtures Of D-xylose Research Articles

Giving Pure Shift NMR Spectroscopy a REST─Ultrahigh-Resolution Mixture Analysis.

Most interesting problems in chemistry, biology, and pharmacy involve mixtures. However, analysis of such mixtures by NMR remains a challenge, often requiring the mixture components to be physically separated before analysis. A variety of methods have been proposed that exploit species-specific properties such as diffusion and relaxation to distinguish between the signals of different components in a mixture without the need for laborious separation. However, these methods can struggle to distinguish between components when signals overlap. Here, we exploit the relaxation properties of selected nuclei to distinguish between different components of a mixture while using pure shift methods to increase spectral resolution by up to an order of magnitude, greatly reducing signal overlap. The advantages of the new method are demonstrated in a mixture of d-xylose and l-arabinose, distinguishing unambiguously between the five major species present.

Influence of glucose on xylose metabolization by Spathaspora passalidarum

The yeast Spathaspora passalidarum is able to produce ethanol from D-xylose and D-glucose. However, it is not clear how xylose metabolism is affected by D-glucose when both sugars are available in the culture medium. The aims of this work were to evaluate the influence of D-glucose on D-xylose consumption, ethanol production, gene expression, and the activity of key xylose-metabolism enzymes under both aerobic and oxygen-limited conditions. Ethanol yields and productivities were increased in culture media containing D-xylose as the sole carbon source or a mixture of D-xylose and D-glucose. S. passalidarum preferentially consumed D-glucose in the co-fermentations, which is consistent with the reduction in expression of genes encoding the key xylose-metabolism enzymes. In the presence of D-glucose, the specific activities of xylose reductase (XR), xylitol dehydrogenase (XDH), and xylulokinase (XK) were lower. Interestingly, in accordance with other studies, the presence of 2-deoxyglucose (2DG) did not inhibit the growth of S. passalidarum in culture medium containing D-xylose as the sole carbon source. This indicates that a non-canonical repression pathway is acting in S. passalidarum. In conclusion, the results suggest that D-glucose inhibits D-xylose consumption and prevents the D-xylose-mediated induction of the genes encoding XR, XDH, and XK.

Stereoselective acetylation of hemicellulosic C5-sugars

The stereoselective peracetylation of α-d-xylose (1) and α-l-arabinose (4) using a combination of triethylamine and acetic anhydride in the presence or absence of a catalytic amount of dimethylaminopyridine (DMAP) is described. The peracetylated d-xylose and l-arabinose alpha pyranose anomers 2α and 5α are obtained in 97% and 56% yields respectively. The peracetylated d-xylose beta pyranose anomer 2β is obtained in 71% yield through simple modification of the reaction conditions. Details regarding synthesis and isolation optimization studies under different conditions are presented below. The stereoselective peracetylation reactions disclosed here have been used to separate mixtures of d-xylose and l-arabinose as their peracetylated derivatives 2β and 5α in 47% and 42% yields and can provide pure pentoses after deacetylation.

Fermentative Production of Xylitol: A First Trial on Xylose Bifurcation

Background/Objectives: Xylitol production through chemical processes pathway involves high energy usage and production cost. Alternative method via microbial biotransformation and biocatalyst offer more sustainable and environmental friendly feedstock to be used for xylitol production. Methods: Production of xylitol by Aspergillus niger PY11 using different conditions on 2 carbon source, glucose and xylose, were done for the development of this research. Batch fermentation of A. niger PY11 was conducted for 4 days or 96 hours in temperature set at 30oC and agitation speed of 200 rpm. Samples were taken at 12 hours interval, filtered and analyzed for cell biomass, remaining sugar and D-xylitol concentration. The production of biomass and xylitol was monitored through dry-mass weight of mycelium and by HPLC, respectively. Findings: From the results of the utilization of single carbon source, fermentation of D-xylose produced the highest xylitol yield, which was 0.101 g xylitol/g D-xylose consumed, with the xylitol titre of 1.139 g/l was obtained (equivalent to 0.482 g xylitol/g biomass). However, the highest cell growth was observed when fermentation were conducted using a mixture of D-xylose and D-glucose at the ratio of 3:1, which resulted the biomass yield of 0.239 g biomass/g D-xylose (equivalent to 0.211 g xylitol/g biomass). Total amount of 44.94% of added D-xylose was consumed during the fermentation. Applications/Improvements: This paper shown that the addition of glucose had resulted higher biomass growth of A.niger PY11, thus subsequently increased the bioconversion of xylose to xylitol.

The Effect of pH Control on Acetone–Butanol–Ethanol Fermentation by Clostridium acetobutylicum ATCC 824 with Xylose and d-Glucose and d-Xylose Mixture

d-Glucose, l-arabinose, d-mannose, d-xylose, and cellobiose are saccharification products of lignocellulose and important carbon sources for industrial fermentation. The fermentation efficiency with each of the five sugars and the mixture of the two most dominant sugars, d-glucose and d-xylose, was evaluated for acetone–butanol–ethanol (ABE) fermentation by Clostridium acetobutylicum ATCC 824. The utilization efficacy of the five reducing sugars was in the order of d-glucose, l-arabinose, d-mannose, d-xylose and cellobiose. d-Xylose, the second most abundant component in lignocellulosic hydrolysate, was used in the fermentation either as sole carbon source or mixed with glucose. The results indicated that maintaining pH at 4.8, the optimal pH value for solventogenesis, could increase d-xylose consumption when it was the sole carbon source. Different media containing d-glucose and d-xylose at different ratios (1:2, 1:5, 1.5:1, 2:1) were then attempted for the ABE fermentation. When pH was at 4.8 and xylose concentration was five times that of glucose, a 256.9% increase in xylose utilization and 263.7% increase in solvent production were obtained compared to those without pH control. These results demonstrate a possible approach combining optimized pH control and d-glucose and d-xylose ratio to increase the fermentation efficiency of lignocellulosic hydrolysate.

Xylans are a valuable alternative resource: Production of d-xylose, d-lyxose and furfural under microwave irradiation

The influence of microwave irradiation on hydrolysis of xylan and simultaneous epimerization of the d-xylose to d-lyxose has been studied. An acidic solution of xylan was treated with catalytic amount of sodium molybdate and the composition of the reaction mixture was analyzed. Short reaction times of hydrolysis and subsequent epimerization reaction provided an equilibrium reaction mixture of d-xylose and d-lyxose (1.6:1) without significant formation of undesirable side products. Obtained pentoses can be reduced to the corresponding alditols (d-xylitol and d-lyxitol) in very good yields (88% and 85%) or can be further dehydrated to furfural (53%). Combined use of Mo(VI) catalyst and microwave irradiation allows better conversions and substantial reduction of reaction times (400-fold) compared to that obtained by conventional heating. Studied stereospecific transformation of xylan proceeds with high selectivity, short reaction times and very good yields that makes this approach attractive also for preparative purposes.

Direct conversion of xylan into alkyl pentosides

Xylan has been used as a raw material in the synthesis of butyl, octyl and decyl glycosides. Mixtures of d-xylose-, l-arabinose- and d-glucose-based surfactants were obtained under smooth conditions with high yields in a one-pot process. The surface activities of octyl and decyl glycosides thus obtained have been studied and compared with that of pure alkyl d-xylosides. The results have confirmed that the new synthetic approach described in this paper is a potentially economical and efficient method for the preparation of environmentally friendly surfactants.

Identification and inactivation of pleiotropic regulator CcpA to eliminate glucose repression of xylose utilization in Clostridium acetobutylicum

d-xylose utilization is a key issue for lignocellulosic biomass fermentation, and a major problem in this process is carbon catabolite repression (CCR). In this investigation, solvent-producing bacterium Clostridium acetobutylicum ATCC 824 was metabolically engineered to eliminate d-glucose repression of d-xylose utilization. The ccpA gene, encoding the pleiotropic regulator CcpA, was experimentally characterized and then disrupted . Under pH-controlled conditions, the ccpA-disrupted mutant (824ccpA) can use a mixture of d-xylose and d-glucose simultaneously without CCR. Moreover, this engineered strain produced acetone, butanol and ethanol (ABE) at a maximal titer of 4.94, 12.05 and 1.04 g/L, respectively, which was close to the solvent level of maize- or molasses-based fermentation by wild type C. acetobutylicum. Molar balance analysis for improved process of mixed sugars utilization also revealed less acid accumulation and more butanol yield by the engineered strain as compared to the wild type. This study offers a genetic modification strategy for improving simultaneous utilization of mixed sugars by Clostridium, which is essential for commercial exploitation of lignocellulose for the production of solvents and biofuels.

Selective reduction of xylose to xylitol from a mixture of hemicellulosic sugars

The biocatalytic reduction of d-xylose to xylitol requires separation of the substrate from l-arabinose, another major component of hemicellulosic hydrolysate. This step is necessitated by the innate promiscuity of xylose reductases, which can efficiently reduce l-arabinose to l-arabinitol, an unwanted byproduct. Unfortunately, due to the epimeric nature of d-xylose and l-arabinose, separation can be difficult, leading to high production costs. To overcome this issue, we engineered an E. coli strain to efficiently produce xylitol from d-xylose with minimal production of l-arabinitol byproduct. By combining this strain with a previously engineered xylose reductase mutant, we were able to eliminate l-arabinitol formation and produce xylitol to near 100% purity from an equiweight mixture of d-xylose, l-arabinose, and d-glucose.

Induction of aldose reductase and xylitol dehydrogenase activities in Candida tenuis CBS 4435.

In this study the ability of various sugars and sugar alcohols to induce aldose reductase (xylose reductase) and xylitol dehydrogenase (xylulose reductase) activities in the yeast Candida tenuis was investigated. Both enzyme activities were induced when the organism was grown on D-xylose or L-arabinose as well as on the structurally related sugars D-arabinose or D-lyxose. Mixtures of D-xylose with the more rapidly metabolizable sugar D-glucose resulted in a decrease in the levels of both enzymes formed. These results show that the utilization of D-xylose by C. tenuis is regulated by induction and catabolite repression. Furthermore, the different patterns of induction on distinct sugars suggest that the synthesis of both enzymes is not under coordinate control.

Effect of molecular structure on the conductivity of amorphous carbohydrate–water–KCl mixtures in the supercooled liquid state

The effect of carbohydrate structure on the conductivity of low water content amorphous carbohydrate–water, and carbohydrate–water–KCl mixtures, has been measured using both direct current and alternating current techniques at temperatures in the supercooled liquid and glassy range, ranging from −40 to 80 °C. The structures included homologous mono-, di- and trisaccharides (glucose, maltose and maltotriose), a monosaccharide with no exocyclic hydroxymethyl group (xylose) and a second trisaccharide (raffinose). The KCl-mixtures contained 9.3% w/w water and 0.74% w/w KCl which resulted in calorimetric glass transition temperatures, T g, in the range −29–19 °C. At this concentration conduction due to KCl dominated that due to intrinsic conductors originating from the carbohydrates and water. In the supercooled liquid region, as temperature, T, is reduced to T g, the activation energy of the molar conductivity of KCl, Λ m, increased as described by a Vogel–Tamman–Fulcher-type equation, Λ m= Λ m0exp[ B/( T− T 0)], where Λ m0, B and T 0 are constants. Comparison of the molar conductivity of KCl in the carbohydrate mixtures at T g with that in aqueous solutions showed that conductivity is, to varying extents, uncoupled from viscosity. The uncoupling increased in the order d-xylose< d-glucose<maltose<maltotriose and raffinose. The results suggest that the primary structural characteristic determining conductivity is molecular weight, though the presence of the exocyclic hydroxymethyl group in the monosaccharide also has an effect. Whilst at T g the d-xylose mixture had the lowest conductivity, at a particular temperature the trisaccharide mixtures of maltotriose and raffinose had the lowest conductivities.

An approach to estimate the chemical structure of melanoidins

A blue pigment (Blue-M1, C27H31N4O13) was isolated from the reaction mixture of d-xylose and glycine in 60% ethanol (starting pH 8.1) stored at 26.5 °C for 48 h or 2 °C for 96 h under nitrogen. Its novel chemical structure, two pyrrolopyrrole rings combined with methine bridge, was elucidated. Involvement of 3-deoxyxylosone, xylosone and N-substituted pyrrole-2-aldehyde to the formation of Blue-M1 were proposed. Blue-M1 kept five hydroxyl groups belonging to 3-deoxyxylosone and xylosone. The chemical character of Blue-M1 was compared to that of a nondialyzable melanoidin preparation (Melanoidin-1) obtained from the reaction mixture of d-xylose and butylamine neutralized with acetic acid in methanol incubated at 50 °C for 7 days. The results indicated strong resemblance between both substances, suggesting that Blue-M1 would be a key intermediate in melanoidin formation. The possibility of occurrence of pyrrolopyrrole ring formation in colored advanced glycation end products (AGEs) was also discussed.

Ethanol fermentation of mixed-sugars using a two-phase, fed-batch process: method to minimize D -glucose repression of Candida shehatae D -xylose fermentations

cells pre-grown on D-xylose simultaneously consumed mixtures of D-xylose and D-glucose, under both non-growing (anoxic) and actively growing conditions (aerobic), to produce ethanol. The rate of D-glucose consumption was independent of the D-xylose concentration for cells induced on D-xylose. However, the D-xylose consumption rate was approximately three times lower than the D-glucose consumption rate at a 50% D-glucose: 50% D-xylose mixture. Repression was not observed (substrate utilization rates were approximately equal) when the percentage of D-glucose and D-xylose was changed to 22% and 78%, respectively. In fermentations with actively growing cells (50% glucose and D-xylose), ethanol yields from D-xylose increased, the % D-xylose utilized increased, and the xylitol yield was significantly reduced in the presence of D-glucose, compared to anoxic fermentations (YETOH,xylose = 0.2–0.40 g g−1, 75–100%, and Yxylitol = 0–0.2 g g−1 compared to YETOH,xylose = 0.15 g g−1, 56%, Yxylitol = 0.51 g g−1, respectively). To increase ethanol levels and reduce process time, fed-batch fermentations were performed in a single stage reactor employing two phases: (1) rapid aerobic growth on D-xylose (μ = 0.32 h−1) to high cell densities; (2) D-glucose addition and anaerobic conditions to produce ethanol (YETOH,xylose = 0.23 g g−1). The process generated high cell densities, 2 × 109 cells ml−1, and produced 45–50 g L−1 ethanol within 50 h from a mixture of D-glucose and D-xylose (compared to 30 g L−1 in 80 h in the best batch process). The two-phase process minimized loss of cell viability, increased D-xylose utilization, reduced process time, and increased final ethanol levels compared to the batch process.

Simultaneous utilization of glucose and D-xylose by Candida shehatae in a chemostat

The kinetics of biomass formation, D-xylose utilization, and mixed substrate utilization were determined in a chemostat using the yeast Candida shehatae. The maximum growth rate of C. shehatae grown aerobically on D-xylose was 0.42 h−1 and the Monod constant, Ks, was 0.06 g L−1. The biomass yield, Y{X/S}, ranged from 0.40 to 0.50 g g−1 over a dilution rate range of 0.2–0.3 h−1, when C. shehatae was grown on pure D-xylose. Mixtures of D-xylose and glucose (∼1 : 1) were simultaneously utilized over a dilution rate from 0.15 to 0.35 h−1 at pH 3.5 and 4.5, but pH 3.5 reduced μmax and reduced the dilution rate range over which D-xylose was utilized in the presence of glucose. At pH 4.5, μmax was not reduced with the mixed sugar feed and the overall or lumped Ks value was not significantly increased (0.058 g L−1vs 0.06 g L−1), when compared to a pure D-xylose feed. Kinetic data indicate that C. shehatae is an excellent candidate for chemostat production of value added products from renewable carbon sources, since simultaneous mixed substrate utilization was observed over a wide range of growth rates on a 1 : 1 mixture of glucose and D-xylose.

Induction of aldose reductase and xylitol dehydrogenase activities in Candida tenuis CBS 4435

In this study the ability of various sugars and sugar alcohols to induce aldose reductase (xylose reductase) and xylitol dehydrogenase (xylulose reductase) activities in the yeast Candida tenuis was investigated. Both enzyme activities were induced when the organism was grown on d-xylose or l-arabinose as well as on the structurally related sugars d-arabinose or d-lyxose. Mixtures of d-xylose with the more rapidly metabolizable sugar d-glucose resulted in a decrease in the levels of both enzymes formed. These results show that the utilization of d-xylose by C. tenuis is regulated by induction and catabolite repression. Furthermore, the different patterns of induction on distinct sugars suggest that the synthesis of both enzymes is not under coordinate control.

The effect of mixtures of acetic acid and D-xylose on the growth rate of Candida blankii

The growth rate of the yeastCandida blankii in carbon-limited chemostat culture on a mixture of D-xylose and acetic acid as carbon sources was determined not only by the acetic acid concentration in the feed, but also by the ratio of xylose to acetic acid. The hypothesis is put forward that the inhibitory effect of acetic acid on the growth rate is determined, in part, by the specific rate of acetic acid metabolism.

Quinoxalines derived from D-xylose and o-phenylenediamine under acidic refluxed conditions.

Quinoxalines derived from d-xylose and o-phenylenediamine (OPD) in an acidic medium under reflux were studied, using GLC, GC-MS and NMR measurements.Three quinoxaline derivatives (XA-I, XA-II and G-2) were separated from the reaction mixture of d-xylose with OPD (0.2 mol, each) in a 46% total yield. Their approximate molar ratio was 3:3:2. Two newly isolated XA-I and XA-II derivatives were identified as 2-methyl-3-(2′- hydroxyethyl)quinoxaline and 2-(l ′,2,′3,′-trihydroxypropyOquinoxaline, respectively. The other was G-2 [2-(2′,3′-dihydroxypropyl)quinoxaline], which has previously been obtained from D- glucose or D-xylose in an alkaline solution. XA-I may be regarded as a partially reduced form of G-2 at the side chain of the quinoxaline, with XA-II as an oxidized form. A possible mechanism for quinoxaline formation is discussed.