NaBH_(4) was widely regarded as a low-cost hydrogen storage material due to its high-mass hydrogen capacity of approximately 10.8%(mass)and high volumetric hydrogen capacity of around 115 g·L^(–1).However,it exh...NaBH_(4) was widely regarded as a low-cost hydrogen storage material due to its high-mass hydrogen capacity of approximately 10.8%(mass)and high volumetric hydrogen capacity of around 115 g·L^(–1).However,it exhibits strong stability and requires temperatures above 500℃ for hydrogen release in practical applications.In this study,two polyhydric alcohols,xylitol and erythritol(XE),were prepared as a binary eutectic sugar alcohol through a grinding-melting method.This binary eutectic sugar alcohol was used as a proton-hydrogen carrier to destabilize NaBH_(4).The 19NaBH_(4)-16XE composite material prepared by ball milling could start releasing hydrogen at 57.5℃,and the total hydrogen release can reach over 88.8%(4.45%(mass))of the theoretical capacity.When the 19NaBH_(4)-16XE composite was pressed into solid blocks,the volumetric hydrogen capacity of the block-shaped composite could reach 67.2 g·L^(–1).By controlling the temperature,the hydrogen desorption capacity of the NaBH_(4)-XE composite material was controllable,which has great potential for achieving solid-state hydrogen production from NaBH_(4).展开更多
Xylitol and erythritol have been reported in numerous previous and recent studies as potential antidiabetic sweeteners,however,it is not certain which one is most effective in this regard.In the present study,the effe...Xylitol and erythritol have been reported in numerous previous and recent studies as potential antidiabetic sweeteners,however,it is not certain which one is most effective in this regard.In the present study,the effects of xylitol and erythritol were comparatively investigated on blood glucose,insulin level,dyslipidemia,pancreatic islet morphology andβ-cell function,and redox imbalance in a type 2 diabetes(T2D)model of rats.Seven-week-old male Sprague-Dawley rats were randomly divided into 8 groups:Normal Control(NC),Diabetic Control(DC),Diabetic Xylitol 5%(DX5),Diabetic Xylitol 10%(DX10),Diabetic Xylitol 20%(DX20),Diabetic Erythritol 5%(DE5),Diabetic Erythritol 10%(DE10),and Diabetic Erythritol 20%(DE20).T2D was induced in the diabetic groups initially by feeding 10%fructose solution to induce insulin resistance followed by an intraperitoneal injection of streptozotocin(40 mg/kg body weight)dissolved in citrate buffer(pH 4.5)to induce partial pancreaticβ-cells dysfunctions.The animals in NC group were fed with normal drinking water and injected with citrate buffer only.After the confi rmation of diabetes,the xylitol and erythritol with above-mentioned concentrations were supplied to the respective animal groups when the animals in NC and DC groups were supplied with normal drinking water.After 8 weeks intervention period,the body weight,fl uid and water intake,blood glucose,serum alanine aminotransferase,aspartate aminotransferase,CK-MB and creatinine were signifi cantly decreased,while the serum insulin level,serum lipids,glucose tolerance ability,pancreatic islet morphology andβ-cell function,pancreatic and serum redox imbalance were improved in the most xylitol and erythritol fed groups compared to the DC group,when effects were better for xylitol compared to erythritol.The data of this study suggests that xylitol has better antioxidant and antidiabetic effects compared to erythritol.Therefore,xylitol can be used as a preferrable dietary anti-diabetic sweetener or supplement over erythritol for the management of diabetes and its associated complications.展开更多
The electrodeposition of lead in alkaline solutions containing xylitol （1, 2, 3, 4, 5-pentahydroxypentane） was studied. The lead electrodeposition and the chemical stability of xylitol in alkaline solutions were inv...The electrodeposition of lead in alkaline solutions containing xylitol （1, 2, 3, 4, 5-pentahydroxypentane） was studied. The lead electrodeposition and the chemical stability of xylitol in alkaline solutions were investigated by cyclic voltammetry. Apparent activation energy, apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetry. Initial stages of lead electrocrystallization were determined by chronoamperometry. Voltammograms of a AISI 316 stainless steel electrode in xylitol solution exhibit no current in the potential range of-1.3 V to 0.75 V （vs Hg/HgO）, implying that xylitol is stable to oxidation and reduction. The apparent activation energy, apparent transfer coefficient and exchange current density were calculated to be 35.15 kJ/mol, 1.56 and 9.65x10^-5 A/m^2. Analysis of the chronoamperometric responses implies three-dimensional growth of nuclei, with the type of nucleation depending on overpotential.展开更多
The electrodeposition of antimony in alkaline solutions containing xylitol was investigated using cyclic voltammetry,linear sweep voltammetry and chronoamperometry.The antimony electrodeposition and the chemical stabi...The electrodeposition of antimony in alkaline solutions containing xylitol was investigated using cyclic voltammetry,linear sweep voltammetry and chronoamperometry.The antimony electrodeposition and the chemical stability of xylitol in alkaline solutions were studied by cyclic voltammetric technique.Apparent activation energy,apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetric technique.Initial stages of antimony electrocrystallization were determined by chronoamperometry.Xylitol in alkaline solutions exhibits high chemical stability and there is no redox in solutions when the potential ranges from-1.20 V to ＋0.60 V（vs Hg/HgO）.There is no other redox reaction but hydrolysis occurring on stainless steel in the potential range of-1.75 V to 1.25 V（vs Hg/HgO） while the xylitol decomposition maybe take place on antimony electrode when potential is more negative than-1.70 V（vs Hg/HgO）.Cyclic voltammograms with different scan rates indicate that the antimony electrodeposition process is an electrocrystallization which is a completely irreversible electrode process.The apparent activation energy,apparent transfer coefficient and exchange current density were calculated to be 46.33 kJ/mol,0.64 and 4.40×10-6 A/m2,respectively.The analyses of the chronoamperometric responses support the view of a three-dimensional growth under progressive nucleation.The average diffusion coefficient of antimony was calculated to be 1.53×10-6 cm2/s.展开更多
The directly selective hydrogenolysis of xylitol to ethylene glycol(EG) and 1,2-propylene glycol(1,2-PDO)was performed on Cu–Ni–ZrO_2 catalysts prepared by a co-precipitation method. Upon optimizing the reaction con...The directly selective hydrogenolysis of xylitol to ethylene glycol(EG) and 1,2-propylene glycol(1,2-PDO)was performed on Cu–Ni–ZrO_2 catalysts prepared by a co-precipitation method. Upon optimizing the reaction conditions(518 K, 4.0 MPaH_2 and 3 h), 97.0% conversion of xylitol and 63.1% yield of glycols were obtained in water without extra inorganic base. The catalyst still remained stable activity after six cycles and above 80% total selectivity of glycols was obtained when using 20.0% xylitol concentration. XRD, TEM and ICP results indicated that Cu–Ni–ZrO_2 catalysts possess favorable stability. Cu and Ni are beneficial to the cleavage of C–O and C–H bond, respectively. To reduce the hydrogen consumption, isopropanol was added as in-situ hydrogen source and 96.4% conversion of xylitol with 43.6% yield of glycols were realized.展开更多
The objective of the study was to analyse Streptococcus mutans biofilms grown under different dietary conditions by using multifaceted methodological approaches to gain deeper insight into the cariogenic impact of car...The objective of the study was to analyse Streptococcus mutans biofilms grown under different dietary conditions by using multifaceted methodological approaches to gain deeper insight into the cariogenic impact of carbohydrates. S. mutans biofilms were generated during a period of 24 h in the following media： Schaedler broth as a control medium containing endogenous glucose, Schaedler broth with an additional 5% sucrose, and Schaedler broth supplemented with 1% xylitol. The confocal laser scanning microscopy（CLSM）-based analyses of the microbial vitality, respiratory activity（5-cyano-2,3-ditolyl tetrazolium chloride, CTC） and production of extracellular polysaccharides（EPS） were performed separately in the inner, middle and outer biofilm layers. In addition to the microbiological sample testing, the glucose/sucrose consumption of the biofilm bacteria was quantified, and the expression of glucosyltransferases and other biofilm-associated genes was investigated. Xylitol exposure did not inhibit the viability of S. mutans biofilms, as monitored by the following experimental parameters： culture growth, vitality, CTC activity and EPS production. However,xylitol exposure caused a difference in gene expression compared to the control. Gtf C was upregulated only in the presence of xylitol.Under xylitol exposure, gtf B was upregulated by a factor of 6, while under sucrose exposure, it was upregulated by a factor of three.Compared with glucose and xylitol, sucrose increased cell vitality in all biofilm layers. In all nutrient media, the intrinsic glucose was almost completely consumed by the cells of the S. mutans biofilm within 24 h. After 24 h of biofilm formation, the multiparametric measurements showed that xylitol in the presence of glucose caused predominantly genotypic differences but did not induce metabolic differences compared to the control. Thus, the availability of dietary carbohydrates in either a pure or combined form seems to affect the cariogenic potential of S. mutans biofilms.展开更多
Promoters are the most important tools to control and regulate the gene expression in synthetic biology and metabolic engineering. The expression of target genes in Escherichia coli is usually controlled by the high-s...Promoters are the most important tools to control and regulate the gene expression in synthetic biology and metabolic engineering. The expression of target genes in Escherichia coli is usually controlled by the high-strength inducible promoter with the result that the abnormally high transcription of these genes creates excessive metabolic load on the host, which decreases product formation. The constitutive expression systems are capable of avoiding these defects. In this study, to enrich the application of constitutive promoters in metabolic engineering, four promoters from the glycolytic pathway of E. coli were cloned and characterized using the enhanced green fluorescent protein as reporter. Among these promoters, Pgap Awas determined as the strongest one, the strength of which was about 8.92% of that of the widely used inducible promoter PT7. This promoter was used to control the expression of heterologous xylose reductase in E. coli for xylitol synthesis so as to verify its function in pathway engineering. The maximum xylitol titer(40.6 g·L-1) produced by engineered E. coli under the control of the constitutive promoter Pgap Awas obviously higher than that under the control of the inducible promoter PT7,indicating the feasibility and superiority of promoter Pgap Ain the metabolic engineering of E. coli.展开更多
Debaryomyces nepalensis NCYC 3413, halotolerant yeast isolated from rotten apple, was capable of utilizing components of hemicellulose hydrolysate such as glucose, galactose, mannose, xylose and arabinose. The organis...Debaryomyces nepalensis NCYC 3413, halotolerant yeast isolated from rotten apple, was capable of utilizing components of hemicellulose hydrolysate such as glucose, galactose, mannose, xylose and arabinose. The organism utilizes xylose as a sole carbon source and produces xylitol. The Plackett-Burman design was applied to determine the specific medium components affecting xylitol production and found that xylose, K2HPO4, and ZnSO4 were critical in augmenting xylitol production. These significant parameters were further optimized using response surface methodology. The optimum concentrations of xylose, K2HPO4, and ZnSO4 were found to be 100 g/l, 10.6 g/l and 8.9 mg/l respectively. Under these optimal conditions the xylitol production increased from 27 g/l to 36 g/l with a yield of 0.44 g/g (57% increase in total yield). In addition, formation of the by product (glycerol) was decreased under optimal conditions.展开更多
The novel covalently modified glassy carbon electrode with poly(xylitol) was prepared using an electropolymerization technique for the simultaneous determination of uric acid(UA), xanthine(XA) and hypoxanthine(HX). Th...The novel covalently modified glassy carbon electrode with poly(xylitol) was prepared using an electropolymerization technique for the simultaneous determination of uric acid(UA), xanthine(XA) and hypoxanthine(HX). This new electrode presents an excellent electrocatalytic activity towards the oxidation of UA, XA and HX by cyclic voltammetry(CV) method. The oxidation peaks of the three compounds were well defined and had enhanced the peak currents. The separation potentials of the oxidation peak potentials for UA-XA and XA-HX were 380 and 370 mV in CV, respectively. Using differential pulse voltammetry(DPV) method, the calibration curves in the ranges of 5-55, 1.3-75.3 and 4-59 μmol/L were obtained for HX, XA and UA, respectively. The lowest detection limits(S/N=3) were 4.5, 0.75 and 3.75 μmol/L for HX, XA and UA, respectively. The practical application of the modified electrode was demonstrated by the determination of UA, XA, HX in human urine samples.展开更多
[Objective] The aim was to select the optimum conditions of xylitol Candida tropicalis conversion production. [Method] The effect of cell culture time,conversion time,conversion pH value,conversion initial sugar conce...[Objective] The aim was to select the optimum conditions of xylitol Candida tropicalis conversion production. [Method] The effect of cell culture time,conversion time,conversion pH value,conversion initial sugar concentration,speed and inoculation rate were determined respectively.[Result] Optimum fermentation conditions were obtained as follows:cell culture 16 h,conversion time 10 h,conversion pH value 5.5,conversion initial sugar concentration 20 g/L,conversion shaking speed 150 r/min,inoculation rate 10% (volume ratio). The yield of xylitol has increased to 90%. [Conclusion] This study had provided basis for the further study on xylitol.展开更多
Xylose reductase (EC 1.1.1.21) of Candida tropicalis IEC5-ITV, an indigenous xylitol-producing strain, was partially purified by reversed micelles and characterized, an 8.1 fold purification factor being obtained. The...Xylose reductase (EC 1.1.1.21) of Candida tropicalis IEC5-ITV, an indigenous xylitol-producing strain, was partially purified by reversed micelles and characterized, an 8.1 fold purification factor being obtained. The XR present in the crude extract exhibited its highest specific activity at pH 6.0 and 40℃, while in that obtained by reverse micelles, this occurs at pH 6.0 and 30℃. XR before and after extraction is stable within a range of 30 to 40℃, pH 7 after one hour of incubation under these conditions. After two months’storage at –18℃, the enzyme obtained by reverse micelles lost 76.60% specific activity. The estimated molecular weight by PAGE-SDS was 32.42 kD. KM for xylose was higher for the XR extracted by reverse micelles (0.026 M) than that obtained for the enzyme before extraction (0.0059 M), while KM for cofactor NADPH was lower after than before extraction (1.85 mM to 12.0 mM respectively). There was no activity with NADH as a cofactor. Variations in pH and temperature optima, as well as kinetic parameters before and after partial XR purification by reverse micelles are probably due to an alteration in enzyme molecule structure caused by the solvents used during extraction.展开更多
Objective:To evaluate the level of salivary Mutatis streptococci(MS) after rinsing with xylitol, fluoride,and a combination of xylitol and fluoride solutions,compared with distilled water. Methods:Eighty healthy 8-9 y...Objective:To evaluate the level of salivary Mutatis streptococci(MS) after rinsing with xylitol, fluoride,and a combination of xylitol and fluoride solutions,compared with distilled water. Methods:Eighty healthy 8-9 years old subjects with high level of MS(】 10~5 CFU/mL) were equally divided into 4 groups.Subjects rinsed their moutlis for 1 min with 10 mL of 0.05%(w/v) sodium fluoride(NaF),12.5%(w/v) xylitol or 0.05%(w/v) NoF + 12.5%(w/v) xylitol 3 times daily over 10 weeks.Distilled water rinsed group served as a control.Paraffin-stimulated whole saliva samples were collected at baseline,5 weeks,and 10 weeks after rinsing to determine the level of salivary MS by culturing on Mitis Salivarius Bacitracin agar.The statistical significance was calculated by Kruskol Wallis,Mann Whitney U,and Wilcoxon signed-rank tests at a significant level of P【 0.05.Results:Significant reductions in MS count were observed in subjects using 0.05%NaF + 12.5%xylitol over other groups within 5 weeks and after 10 weeks and 12.5%xylitol alone after 10 weeks compared with baseline.Conclusions:The present study provides evidence for the inhibitory effect of xylitol,used in combination with fluoride,delivered in the form of mouthrinse, on salivary MS in the group of schoolchildren.展开更多
Small-scale biorefinery from sugarcane bagasse offers new possibilities to the sugar and ethanol industries.The aim of this study was to evaluate the feasibility of a small-scale biorefinery for the production of xyli...Small-scale biorefinery from sugarcane bagasse offers new possibilities to the sugar and ethanol industries.The aim of this study was to evaluate the feasibility of a small-scale biorefinery for the production of xylitol from sugarcane bagasse.The liquid fraction from the autohydrolysis treatment was selected as the source of sugars for xylitol and two scenarios were analyzed for the residual solid:ethanol or pellet production.A technical-economic analysis of alternatives was applied.The internal rate of return(IRR)was used to compare the selected proposals.The highest IRR values were obtained when processing 70,000 dry tons per year of bagasse.The results showed promising prospects for a small-scale biorefinery with capacities above 20,000 dry tons per year(xylitol and pellets),and above 50,000 dry tons per year(xylitol and ethanol).展开更多
Xylitol is an alternative sweetener which has been previously reported to have many beneficial effects such as prevention from dental caries, reduction of visceral fat and increased synthesis of collagen. However, its...Xylitol is an alternative sweetener which has been previously reported to have many beneficial effects such as prevention from dental caries, reduction of visceral fat and increased synthesis of collagen. However, its role in body weight loss management has not been uncovered before. This study sought to investigate the effects of xylitol on body weight loss management, blood glucose and lipid profile on diet-induced obesity (DOI) mice. Fifteen male mice were subjected to high fat diet (60 kcal%) and normal drinking water for 28 days and then randomly divided into three (control, glucose and xylitol) groups. Each group of mice was then fed with normal diet for another 28 days with supplied normal drinking water (control);glucose solution 10% and xylitol solution 10%. Body weight loss was found to be significantly high in xylitol mice (2.56 ± 0.21, p = 0.003) compared to the other two groups. Lowest blood glucose level was found in the control group mice with the mean 7.65 ± 0.10 (p = 0.001). Xylitol mice had also showed the lowest total cholesterol level (4.20 ± 0.90, p = 0.000) than the other groups, but highest in HDL level (2.72 ± 0.14, p = 0.000). In conclusion, these findings proved that xylitol has the potential to reduce body weight, lowering the blood glucose but yet increase the HDL level.展开更多
Antibiotic-loaded poly (methyl methacrylate) bone cements (ALPBCs) are widely used as an agent to decrease the occurrence of periprosthetic joint infection (PJI). Most often, the antibiotic used in an ALPBC is gentami...Antibiotic-loaded poly (methyl methacrylate) bone cements (ALPBCs) are widely used as an agent to decrease the occurrence of periprosthetic joint infection (PJI). Most often, the antibiotic used in an ALPBC is gentamicin, tobramycin, or vancomycin. In many recent clinical studies, it has been reported that the pathogens that commonly present in PIJ are becoming resistant to these antibiotics. As such, a new generation of antibiotics is emerging, among which is daptomycin. Literature reports with a clinically relevant medium-dose daptomycin-loaded cement show that the daptomycin release rate from cylindrical specimens is low. Incorporation of a poragen, such as dextrose, glycine, or particulate xylitol, into the cement powder has been shown to be an effective way to increase daptomycin release rate. There are, however, no studies on modeling of daptomycin release from specimens of either a daptomycin-loaded cement or a daptomycin-poragen-loaded cement. In the present work, we determine the profiles of daptomycin release from cylindrical medium-dose daptomycin-xylitol-loaded cement specimens, as a function of the particulate xylitol loading. We used these results and relationships that have been shown to model antibiotic release from ALPBC specimens to obtain the best-fit relationship for the present cements. Through this approach, we demonstrated that, regardless of the xylitol loading, the daptomycin release profile is a mixture of initial burst followed by a slow Fickian diffusion.展开更多
基金support from the National Natural Science Foundation of China(52201255)the Natural Science Foundation of Jiangsu Province(BK20210884)the Innovation,and Entrepreneurship Program of Jiangsu Province(JSSCBS20211007).
文摘NaBH_(4) was widely regarded as a low-cost hydrogen storage material due to its high-mass hydrogen capacity of approximately 10.8%(mass)and high volumetric hydrogen capacity of around 115 g·L^(–1).However,it exhibits strong stability and requires temperatures above 500℃ for hydrogen release in practical applications.In this study,two polyhydric alcohols,xylitol and erythritol(XE),were prepared as a binary eutectic sugar alcohol through a grinding-melting method.This binary eutectic sugar alcohol was used as a proton-hydrogen carrier to destabilize NaBH_(4).The 19NaBH_(4)-16XE composite material prepared by ball milling could start releasing hydrogen at 57.5℃,and the total hydrogen release can reach over 88.8%(4.45%(mass))of the theoretical capacity.When the 19NaBH_(4)-16XE composite was pressed into solid blocks,the volumetric hydrogen capacity of the block-shaped composite could reach 67.2 g·L^(–1).By controlling the temperature,the hydrogen desorption capacity of the NaBH_(4)-XE composite material was controllable,which has great potential for achieving solid-state hydrogen production from NaBH_(4).
基金supported by funding from the Research office,University of KwaZulu-Natal,Durbanthe National Research Foundation,Pretoria,South Africa(112430)。
文摘Xylitol and erythritol have been reported in numerous previous and recent studies as potential antidiabetic sweeteners,however,it is not certain which one is most effective in this regard.In the present study,the effects of xylitol and erythritol were comparatively investigated on blood glucose,insulin level,dyslipidemia,pancreatic islet morphology andβ-cell function,and redox imbalance in a type 2 diabetes(T2D)model of rats.Seven-week-old male Sprague-Dawley rats were randomly divided into 8 groups:Normal Control(NC),Diabetic Control(DC),Diabetic Xylitol 5%(DX5),Diabetic Xylitol 10%(DX10),Diabetic Xylitol 20%(DX20),Diabetic Erythritol 5%(DE5),Diabetic Erythritol 10%(DE10),and Diabetic Erythritol 20%(DE20).T2D was induced in the diabetic groups initially by feeding 10%fructose solution to induce insulin resistance followed by an intraperitoneal injection of streptozotocin(40 mg/kg body weight)dissolved in citrate buffer(pH 4.5)to induce partial pancreaticβ-cells dysfunctions.The animals in NC group were fed with normal drinking water and injected with citrate buffer only.After the confi rmation of diabetes,the xylitol and erythritol with above-mentioned concentrations were supplied to the respective animal groups when the animals in NC and DC groups were supplied with normal drinking water.After 8 weeks intervention period,the body weight,fl uid and water intake,blood glucose,serum alanine aminotransferase,aspartate aminotransferase,CK-MB and creatinine were signifi cantly decreased,while the serum insulin level,serum lipids,glucose tolerance ability,pancreatic islet morphology andβ-cell function,pancreatic and serum redox imbalance were improved in the most xylitol and erythritol fed groups compared to the DC group,when effects were better for xylitol compared to erythritol.The data of this study suggests that xylitol has better antioxidant and antidiabetic effects compared to erythritol.Therefore,xylitol can be used as a preferrable dietary anti-diabetic sweetener or supplement over erythritol for the management of diabetes and its associated complications.
基金Project(2007CB613604)supported by the National Basic Research Program of China
文摘The electrodeposition of lead in alkaline solutions containing xylitol （1, 2, 3, 4, 5-pentahydroxypentane） was studied. The lead electrodeposition and the chemical stability of xylitol in alkaline solutions were investigated by cyclic voltammetry. Apparent activation energy, apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetry. Initial stages of lead electrocrystallization were determined by chronoamperometry. Voltammograms of a AISI 316 stainless steel electrode in xylitol solution exhibit no current in the potential range of-1.3 V to 0.75 V （vs Hg/HgO）, implying that xylitol is stable to oxidation and reduction. The apparent activation energy, apparent transfer coefficient and exchange current density were calculated to be 35.15 kJ/mol, 1.56 and 9.65x10^-5 A/m^2. Analysis of the chronoamperometric responses implies three-dimensional growth of nuclei, with the type of nucleation depending on overpotential.
文摘The electrodeposition of antimony in alkaline solutions containing xylitol was investigated using cyclic voltammetry,linear sweep voltammetry and chronoamperometry.The antimony electrodeposition and the chemical stability of xylitol in alkaline solutions were studied by cyclic voltammetric technique.Apparent activation energy,apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetric technique.Initial stages of antimony electrocrystallization were determined by chronoamperometry.Xylitol in alkaline solutions exhibits high chemical stability and there is no redox in solutions when the potential ranges from-1.20 V to ＋0.60 V（vs Hg/HgO）.There is no other redox reaction but hydrolysis occurring on stainless steel in the potential range of-1.75 V to 1.25 V（vs Hg/HgO） while the xylitol decomposition maybe take place on antimony electrode when potential is more negative than-1.70 V（vs Hg/HgO）.Cyclic voltammograms with different scan rates indicate that the antimony electrodeposition process is an electrocrystallization which is a completely irreversible electrode process.The apparent activation energy,apparent transfer coefficient and exchange current density were calculated to be 46.33 kJ/mol,0.64 and 4.40×10-6 A/m2,respectively.The analyses of the chronoamperometric responses support the view of a three-dimensional growth under progressive nucleation.The average diffusion coefficient of antimony was calculated to be 1.53×10-6 cm2/s.
基金financial supports provided by the National Natural Science Foundation of China (21406255)the Shanghai Science and Technology Committee (16dz1207200)the Youth Innovation Promotion Association CAS (2015231)
文摘The directly selective hydrogenolysis of xylitol to ethylene glycol(EG) and 1,2-propylene glycol(1,2-PDO)was performed on Cu–Ni–ZrO_2 catalysts prepared by a co-precipitation method. Upon optimizing the reaction conditions(518 K, 4.0 MPaH_2 and 3 h), 97.0% conversion of xylitol and 63.1% yield of glycols were obtained in water without extra inorganic base. The catalyst still remained stable activity after six cycles and above 80% total selectivity of glycols was obtained when using 20.0% xylitol concentration. XRD, TEM and ICP results indicated that Cu–Ni–ZrO_2 catalysts possess favorable stability. Cu and Ni are beneficial to the cleavage of C–O and C–H bond, respectively. To reduce the hydrogen consumption, isopropanol was added as in-situ hydrogen source and 96.4% conversion of xylitol with 43.6% yield of glycols were realized.
基金supported by the National Deutsche Gesellschaft fr Zahnerhaltung-GABA Scientific Fund, Germany
文摘The objective of the study was to analyse Streptococcus mutans biofilms grown under different dietary conditions by using multifaceted methodological approaches to gain deeper insight into the cariogenic impact of carbohydrates. S. mutans biofilms were generated during a period of 24 h in the following media： Schaedler broth as a control medium containing endogenous glucose, Schaedler broth with an additional 5% sucrose, and Schaedler broth supplemented with 1% xylitol. The confocal laser scanning microscopy（CLSM）-based analyses of the microbial vitality, respiratory activity（5-cyano-2,3-ditolyl tetrazolium chloride, CTC） and production of extracellular polysaccharides（EPS） were performed separately in the inner, middle and outer biofilm layers. In addition to the microbiological sample testing, the glucose/sucrose consumption of the biofilm bacteria was quantified, and the expression of glucosyltransferases and other biofilm-associated genes was investigated. Xylitol exposure did not inhibit the viability of S. mutans biofilms, as monitored by the following experimental parameters： culture growth, vitality, CTC activity and EPS production. However,xylitol exposure caused a difference in gene expression compared to the control. Gtf C was upregulated only in the presence of xylitol.Under xylitol exposure, gtf B was upregulated by a factor of 6, while under sucrose exposure, it was upregulated by a factor of three.Compared with glucose and xylitol, sucrose increased cell vitality in all biofilm layers. In all nutrient media, the intrinsic glucose was almost completely consumed by the cells of the S. mutans biofilm within 24 h. After 24 h of biofilm formation, the multiparametric measurements showed that xylitol in the presence of glucose caused predominantly genotypic differences but did not induce metabolic differences compared to the control. Thus, the availability of dietary carbohydrates in either a pure or combined form seems to affect the cariogenic potential of S. mutans biofilms.
基金Supported by the National High Technology Research and Development Program of China(863 Program)(2012AA02A704)the Major State Basic Research Development Program of China(973 Program)(2013CB733900)+1 种基金the National Natural Science Foundation of China(21176028,21376028)the National Research Foundation for the Doctoral Program of Higher Education of China(20121101110050)
文摘Promoters are the most important tools to control and regulate the gene expression in synthetic biology and metabolic engineering. The expression of target genes in Escherichia coli is usually controlled by the high-strength inducible promoter with the result that the abnormally high transcription of these genes creates excessive metabolic load on the host, which decreases product formation. The constitutive expression systems are capable of avoiding these defects. In this study, to enrich the application of constitutive promoters in metabolic engineering, four promoters from the glycolytic pathway of E. coli were cloned and characterized using the enhanced green fluorescent protein as reporter. Among these promoters, Pgap Awas determined as the strongest one, the strength of which was about 8.92% of that of the widely used inducible promoter PT7. This promoter was used to control the expression of heterologous xylose reductase in E. coli for xylitol synthesis so as to verify its function in pathway engineering. The maximum xylitol titer(40.6 g·L-1) produced by engineered E. coli under the control of the constitutive promoter Pgap Awas obviously higher than that under the control of the inducible promoter PT7,indicating the feasibility and superiority of promoter Pgap Ain the metabolic engineering of E. coli.
文摘Debaryomyces nepalensis NCYC 3413, halotolerant yeast isolated from rotten apple, was capable of utilizing components of hemicellulose hydrolysate such as glucose, galactose, mannose, xylose and arabinose. The organism utilizes xylose as a sole carbon source and produces xylitol. The Plackett-Burman design was applied to determine the specific medium components affecting xylitol production and found that xylose, K2HPO4, and ZnSO4 were critical in augmenting xylitol production. These significant parameters were further optimized using response surface methodology. The optimum concentrations of xylose, K2HPO4, and ZnSO4 were found to be 100 g/l, 10.6 g/l and 8.9 mg/l respectively. Under these optimal conditions the xylitol production increased from 27 g/l to 36 g/l with a yield of 0.44 g/g (57% increase in total yield). In addition, formation of the by product (glycerol) was decreased under optimal conditions.
基金Project(201215135) supported by the Natural Science Foundation of Jilin Province,China
文摘The novel covalently modified glassy carbon electrode with poly(xylitol) was prepared using an electropolymerization technique for the simultaneous determination of uric acid(UA), xanthine(XA) and hypoxanthine(HX). This new electrode presents an excellent electrocatalytic activity towards the oxidation of UA, XA and HX by cyclic voltammetry(CV) method. The oxidation peaks of the three compounds were well defined and had enhanced the peak currents. The separation potentials of the oxidation peak potentials for UA-XA and XA-HX were 380 and 370 mV in CV, respectively. Using differential pulse voltammetry(DPV) method, the calibration curves in the ranges of 5-55, 1.3-75.3 and 4-59 μmol/L were obtained for HX, XA and UA, respectively. The lowest detection limits(S/N=3) were 4.5, 0.75 and 3.75 μmol/L for HX, XA and UA, respectively. The practical application of the modified electrode was demonstrated by the determination of UA, XA, HX in human urine samples.
文摘[Objective] The aim was to select the optimum conditions of xylitol Candida tropicalis conversion production. [Method] The effect of cell culture time,conversion time,conversion pH value,conversion initial sugar concentration,speed and inoculation rate were determined respectively.[Result] Optimum fermentation conditions were obtained as follows:cell culture 16 h,conversion time 10 h,conversion pH value 5.5,conversion initial sugar concentration 20 g/L,conversion shaking speed 150 r/min,inoculation rate 10% (volume ratio). The yield of xylitol has increased to 90%. [Conclusion] This study had provided basis for the further study on xylitol.
文摘Xylose reductase (EC 1.1.1.21) of Candida tropicalis IEC5-ITV, an indigenous xylitol-producing strain, was partially purified by reversed micelles and characterized, an 8.1 fold purification factor being obtained. The XR present in the crude extract exhibited its highest specific activity at pH 6.0 and 40℃, while in that obtained by reverse micelles, this occurs at pH 6.0 and 30℃. XR before and after extraction is stable within a range of 30 to 40℃, pH 7 after one hour of incubation under these conditions. After two months’storage at –18℃, the enzyme obtained by reverse micelles lost 76.60% specific activity. The estimated molecular weight by PAGE-SDS was 32.42 kD. KM for xylose was higher for the XR extracted by reverse micelles (0.026 M) than that obtained for the enzyme before extraction (0.0059 M), while KM for cofactor NADPH was lower after than before extraction (1.85 mM to 12.0 mM respectively). There was no activity with NADH as a cofactor. Variations in pH and temperature optima, as well as kinetic parameters before and after partial XR purification by reverse micelles are probably due to an alteration in enzyme molecule structure caused by the solvents used during extraction.
基金Supported by Faculty of Dentistry,Mahidol University,2008
文摘Objective:To evaluate the level of salivary Mutatis streptococci(MS) after rinsing with xylitol, fluoride,and a combination of xylitol and fluoride solutions,compared with distilled water. Methods:Eighty healthy 8-9 years old subjects with high level of MS(】 10~5 CFU/mL) were equally divided into 4 groups.Subjects rinsed their moutlis for 1 min with 10 mL of 0.05%(w/v) sodium fluoride(NaF),12.5%(w/v) xylitol or 0.05%(w/v) NoF + 12.5%(w/v) xylitol 3 times daily over 10 weeks.Distilled water rinsed group served as a control.Paraffin-stimulated whole saliva samples were collected at baseline,5 weeks,and 10 weeks after rinsing to determine the level of salivary MS by culturing on Mitis Salivarius Bacitracin agar.The statistical significance was calculated by Kruskol Wallis,Mann Whitney U,and Wilcoxon signed-rank tests at a significant level of P【 0.05.Results:Significant reductions in MS count were observed in subjects using 0.05%NaF + 12.5%xylitol over other groups within 5 weeks and after 10 weeks and 12.5%xylitol alone after 10 weeks compared with baseline.Conclusions:The present study provides evidence for the inhibitory effect of xylitol,used in combination with fluoride,delivered in the form of mouthrinse, on salivary MS in the group of schoolchildren.
文摘Small-scale biorefinery from sugarcane bagasse offers new possibilities to the sugar and ethanol industries.The aim of this study was to evaluate the feasibility of a small-scale biorefinery for the production of xylitol from sugarcane bagasse.The liquid fraction from the autohydrolysis treatment was selected as the source of sugars for xylitol and two scenarios were analyzed for the residual solid:ethanol or pellet production.A technical-economic analysis of alternatives was applied.The internal rate of return(IRR)was used to compare the selected proposals.The highest IRR values were obtained when processing 70,000 dry tons per year of bagasse.The results showed promising prospects for a small-scale biorefinery with capacities above 20,000 dry tons per year(xylitol and pellets),and above 50,000 dry tons per year(xylitol and ethanol).
文摘Xylitol is an alternative sweetener which has been previously reported to have many beneficial effects such as prevention from dental caries, reduction of visceral fat and increased synthesis of collagen. However, its role in body weight loss management has not been uncovered before. This study sought to investigate the effects of xylitol on body weight loss management, blood glucose and lipid profile on diet-induced obesity (DOI) mice. Fifteen male mice were subjected to high fat diet (60 kcal%) and normal drinking water for 28 days and then randomly divided into three (control, glucose and xylitol) groups. Each group of mice was then fed with normal diet for another 28 days with supplied normal drinking water (control);glucose solution 10% and xylitol solution 10%. Body weight loss was found to be significantly high in xylitol mice (2.56 ± 0.21, p = 0.003) compared to the other two groups. Lowest blood glucose level was found in the control group mice with the mean 7.65 ± 0.10 (p = 0.001). Xylitol mice had also showed the lowest total cholesterol level (4.20 ± 0.90, p = 0.000) than the other groups, but highest in HDL level (2.72 ± 0.14, p = 0.000). In conclusion, these findings proved that xylitol has the potential to reduce body weight, lowering the blood glucose but yet increase the HDL level.
文摘Antibiotic-loaded poly (methyl methacrylate) bone cements (ALPBCs) are widely used as an agent to decrease the occurrence of periprosthetic joint infection (PJI). Most often, the antibiotic used in an ALPBC is gentamicin, tobramycin, or vancomycin. In many recent clinical studies, it has been reported that the pathogens that commonly present in PIJ are becoming resistant to these antibiotics. As such, a new generation of antibiotics is emerging, among which is daptomycin. Literature reports with a clinically relevant medium-dose daptomycin-loaded cement show that the daptomycin release rate from cylindrical specimens is low. Incorporation of a poragen, such as dextrose, glycine, or particulate xylitol, into the cement powder has been shown to be an effective way to increase daptomycin release rate. There are, however, no studies on modeling of daptomycin release from specimens of either a daptomycin-loaded cement or a daptomycin-poragen-loaded cement. In the present work, we determine the profiles of daptomycin release from cylindrical medium-dose daptomycin-xylitol-loaded cement specimens, as a function of the particulate xylitol loading. We used these results and relationships that have been shown to model antibiotic release from ALPBC specimens to obtain the best-fit relationship for the present cements. Through this approach, we demonstrated that, regardless of the xylitol loading, the daptomycin release profile is a mixture of initial burst followed by a slow Fickian diffusion.
