Glucose reactions with acid and base catalysts in hot compressed water at 473 K

The effects of the homogeneous catalysts (H(2)SO(4) and NaOH) and heterogeneous catalysts (TiO(2) and ZrO(2)) on glucose reactions were examined in hot compressed water (473 K) by a batch-type reactor. From the homogeneous catalyst studies, we confirmed that the acid catalyst promoted dehydration, while isomerization of glucose to fructose was catalyzed by alkali. Anatase TiO(2) was found to act as an acid catalyst to promote formation of 5-hydroxymethylfuraldehyde (HMF). Zirconia (ZrO(2)) was a base catalyst to promote the isomerization of glucose. The effects of the additives were also confirmed through fructose reactions.     

Efficient microwave-assisted synthesis of 5-hydroxymethylfurfural from concentrated aqueous fructose

Studies on the HCl-catalysed microwave-assisted dehydration of highly concentrated aqueous fructose (27 wt %) to 5-hydroxymethylfurfural (HMF) revealed a significant increase in the fructose conversion rate over the conventional heated systems. Water, being the most benign solvent and therefore ideal for green and sustainable chemistry, normally is a poor solvent for the dehydration process resulting in low HMF selectivities and yields. However, reaction at 200 °C with microwave irradiation with a short reaction time of only 1 s resulted in good HMF selectivity of 63% and fructose conversion of 52%, while prolonged irradiation for 60 s (or more) resulted in nearly full fructose conversion (95%) but lower HMF yield (53%). Decreasing the fructose concentration significantly improved the HMF selectivity, but possibly made the production route less attractive from an industrial point of view due to the resultant low throughput.     

Effect of Formic Acid on Conversion of Fructose to 5-Hydroxymethylfurfural in Aqueous/Butanol Media

Acid-catalyzed dehydration of carbohydrates into 5-hydroxymethylfurfural (HMF), a valuable biomass-derived intermediate, has received increasing attention. Efficient methods for HMF production are needed for successful commercialization of HMF in the near future. A new process for the dehydration of sugars into 5-hydroxymethylfurfural in aqueous/butanol media enhanced by using formic acid was developed. The effects of formic acid concentration, reaction temperature, and reaction time on the fructose conversion and HMF yield showed the significant influences of these process variables. The optimum conditions were found to be 2.5?mol/L formic acid concentration, 170°C and 70?min. Under such conditions, a fructose conversion of 98.3% with a HMF yield of 69.2% was achieved. The application of the butanol solvent and formic acid led to the conversion of fructose to HMF with high yield. The catalytic system in this study has prospects for commercial application due to its less corrosion and convenient downstream separation.     

5-(Hydroxymethyl)-2-furfural: a selective inhibitor of DNA polymerase lambda and terminal deoxynucleotidyltransferase

5-(Hydroxymethyl)-2-furfural (HMF), a pyrolysate of carbohydrate isolated from instant coffee (Coffea arabica L.), selectively inhibits the activities of mammalian DNA polymerase lambda (pol lambda) and terminal deoxynucleotidyltransferase (TdT) which are family X pols, in vitro. The compound influenced neither the activities of replicative DNA polymerases such as alpha, delta, and epsilon, nor even the activity of pol beta which is from the same family and thought to have a very similar three-dimensional structure to the pol beta-like region of pol lambda. Since parts of HMF such as furan, furfuryl alcohol, and 2-furaldehyde did not influence the activities of any enzymes tested, the substituted form of furan with a hyroxymethyl group and a formyl group might be important for the inhibition of pol lambda and TdT. The inhibitory effect of HMF on intact pol lambda (i.e., residues 1-575), a truncated pol lambda lacking the N-terminal BRCA1 C-terminus domain (133-575, del-1 pol lambda) and another truncated pol lambda lacking the N-terminal proline-rich region (245-575, del-2 pol lambda) was dose-dependent, and 50% inhibition was observed at a concentration of 26.1, 10.3, and 4.6 microM, respectively. The IC(50) value of HMF for TdT was the same as that for del-2 pol lambda (5.5 microM). The HMF-induced inhibition of both pol lambda and TdT activities was competitive with respect to both the DNA template-primer and the dNTP substrate. On the basis of these results, HMF was suggested to bind to the pol beta-like region of pol lambda and TdT.     

Conversion of biomass into 5-hydroxymethylfurfural using solid acid catalyst

5-Hydroxymethylfurfural (HMF) was produced from monosaccharide (fructose and glucose), polysaccharide (inulin) and the Jerusalem artichoke juice by a simple one-pot reaction including hydrolysis and dehydration using solid acid under mild condition. Hydrated niobium pentoxide (Nb(2)O(5)·nH(2)O(2)) after pretreatment showed high catalytic activities for dehydration of mono- and polysaccharide to HMF at 433 K in water-2-butanol (2:3 v/v) biphasic system, giving high HMF yield of 89% and 54% from fructose and inulin, respectively. The HMF yield was up to 74% and 65% when inulin and Jerusalem artichoke juice were hydrolyzed by exoinulinase. The solid acid made the process environment-friendly and energy-efficient to convert carbohydrates into bio-fuels and platform chemicals.     

Acidic resin-catalysed conversion of fructose into furan derivatives in low boiling point solvents

Conversion of fructose into furan derivatives 5-hydroxymethylfurfural (HMF) and 5-methoxymethylfurfural (MMF) is performed in tetrahydrofuran (THF) and methanol–organic solvent systems, catalysed by an acidic resin Amberlyst-15. The melted fructose can be converted into HMF on the surface of the solid resin catalyst in the presence of THF as an extracting phase, which is a good solvent for HMF and other by-products. The solid resin catalyst can be reused eleven times without losing its catalytic ability, with an average HMF yield of approximately 50%. Upon the addition of methanol, the generated HMF can further react with methanol to form MMF, and the total yield of HMF and MMF could be promoted to 65%. GC–MS analysis confirms the formation of a small amount of methyl levulinate in methanolorganic solvent system.     

Dehydration of fructose to 5-hydroxymethylfurfural by rare earth metal trifluoromethanesulfonates in organic solvents

The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) was investigated by using various rare earth metal trifluoromethanesulfonates, that is, Yb(OTf)₃, Sc(OTf)₃, Ho(OTf)₃, Sm(OTf)₃, Nd(OTf)₃ as catalysts in DMSO. It is found that the catalytic activity increases with decreasing ionic radius of rare earth metal cations. Among the examined catalysts, Sc(OTf)₃ exhibits the highest catalytic activity. Fructose conversion of 100% and a HMF yield of 83.3% are obtained at 120 °C after 2 h by using Sc(OTf)₃ as the catalyst. Moreover, the catalytic dehydration of fructose was also carried out in different solvents, for example, DMA, 1,4-dioxane, and a mixture of PEG-400 and water. The results show that among the solvents DMSO is the most efficient in promoting the dehydration of fructose to HMF, and no rehydration byproducts such as levulinic acid and formic acid are detected.     

Production of 5-hydroxymethylfurfural in ionic liquids under high fructose concentration conditions

Acid-promoted, selective production of 5-hydroxymethylfurfural (HMF) under high fructose concentration conditions was achieved in ionic liquids (ILs) at 80 °C. A HMF yield up to 97% was obtained in 8 min using 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) catalyzed with 9 mol % hydrochloric acid. More significantly, an HMF yield of 51% was observed when fructose was loaded at a high concentration of 67 wt % in [C₄mim]Cl. Water content below 15.4% in the system had little effect on HMF yield, whereas a higher water content was detrimental to both reaction rate and HMF yield. In situ NMR analysis suggested that the transformation of fructose to HMF was a highly selective reaction that proceeded through the cyclic fructofuranosyl intermediate pathway. This work increased our capacity to produce HMF, and should be valuable to facilitate cost-efficient conversion of biomass into biofuels and bio-based products.     

Analysis of sugar composition and pesticides using HPLC and GC–MS techniques in honey samples collected from Saudi Arabian markets

Honey is a complex foodstuff found in nature which is used without any processing. Honey has been in use in medicine as well as raw food since ancient times. Essentially, it is a blend of sugars especially fructose and glucose. The objectives of the study were to determine major sugar composition as well as pesticides contamination in honey samples. Further, Hydroxy-methyl-furfuraldehyde (HMF) level was also determined to ascertain the freshness of honey samples. A total of 14 samples were collected from local market and tested for fructose, glucose, sucrose, HMF and organochlorine pesticides using HPLC and GC–MS techniques respectively. The total sugars in the 14 honey samples were found ranging between 50.26 and 74.74 g/100 g of honey. The chromatographic results showed the presence of the sugars like fructose and glucose in all honey samples. The honey sample SH–11 was found to contain the highest amount of fructose (40.63%). On the other hand, the lowest amount of fructose with 29.08% was observed in SH–7. The HPLC analysis also revealed the presence of sucrose in two samples but under the permissible limit. The average ratio of fructose to glucose in these honey samples was 1.3. None of the sample has ratio below 1.0 indicating lesser chances for honey to crystallize on storage. Out of 14 honey samples, 13 samples were found negative for the presence of any of the 63 pesticides tested. Only sample No. 13, was found to contain 15.95 ppb hexachlorobenzene per kilogram of honey. The HMF was not detected in four samples but in remaining samples it was well below the maximum permissible limit. No pesticide and sugar adulteration was observed in any of the honey samples. The honeys collected from Saudi Arabian markets were found to confirm the standards set by the regional and international standardization organization, the GSO and Codex Alimentarius Commission respectively.     

Conversion of hexose into 5-hydroxymethylfurfural in imidazolium ionic liquids with and without a catalyst

Conversion of fructose and glucose into 5-hydroxymethylfurfural (HMF) was investigated in various imidazolium ionic liquids, including 1-butyl-3-methylimidazolium chloride (BmimCl), 1-hexyl-3-methylimidazolium chloride (HmimCl), 1-octyl-3-methylimidazolium chloride (OmimCl), 1-benzyl-3-methylimidazolium chloride (BemimCl), 1-Butyl-2,3-dimethylimidazolium chloride (BdmimCl), and 1-butyl-3-methylimidazolium p-toluenesulfonate (BmimPS). The acidic C-2 hydrogen of imidazolium cations was shown to play a major role in the dehydration of fructose in the absence of a catalyst, such as sulfuric acid or CrCl₃. Both the alkyl groups of imidazolium cations and the type of anions affected the reactivity of the carbohydrates. Although, except BmimCl and BemimCl, other four ionic liquids could only achieve not more than 25% HMF yields without an additional catalyst, 60–80% HMF yields were achieved in HmimCl, BdmimCl, and BmimPS in the presence of sulfuric acid or CrCl₃ in sufficient quantities.     

Efficient and selective conversion of sucrose to 5-hydroxymethylfurfural promoted by ammonium halides under mild conditions

The highly efficient and selective production of 5-hydroxymethylfurfural (HMF) from sucrose has been achieved in the presence of metal chlorides and ammonium halides under mild conditions. Notably, an 87% yield of HMF from sucrose was obtained with a catalyst system composed of CrCl(3) and NH(4)Br at 100°C for 1.0 h in N,N-dimethylacetamide (DMAc) solvent. The effect of the reaction temperature and time was investigated in detail, and a possible mechanism for this catalytic process has been proposed. In addition, NH(4)Br is an effective promoter in the conversion of glucose and fructose to HMF.     

3-(2-carboxyethyl)-4,6-dichloro-1H-indole-2-carboxylic acid: an allosteric inhibitor of fructose-1,6-bisphosphatase at the AMP site

3-(2-Carboxyethyl)-4,6-dichloro-1H-indole-2-carboxylic acid (MDL-29951), an antagonist of the glycine site of the NMDA receptor, has been found to be an allosteric inhibitor of the enzyme fructose 1,6-bisphosphatase. The compound binds at the AMP regulatory site by X-ray crystallography. This represents a new approach to inhibition of fructose 1,6-bisphosphatase and serves as a lead for further drug design.     

Alcohol fermentation of sweet potato. I. Acid hydrolysis and factors involved

Factors affecting acid hydrolysis of sweet potato powder (SSP) to fermentable sugars were examined. These include HCl concentration, temperature, time, and levels of SPP. Maximum reducing sugar, reported as dextrose equivalent (DE), was detected after 24 min hydrolysis (1% SPP) in 0.034N HCl heated at 154°C. These samples also had 3.43% droxymethylfurfural (HMF) based on dry weight. A high level of HMF (9.2%) was detected in 1% SPP heated at 154° in 0.10N HCl for 18 min. The lowest concentration of HMF formed (1.8%), at maximal DE of 61%, was established in samples containing 5% SPP and heated at 154° in 0.034N HCl for 48 min. Aqueous extracts of uncured SPP, examined by HPLC, contained glucose, fructose and sucrose, but degraded SPP had only glucose and fructose. Products of degraded SPP, under appropriate conditions, could be used for alcohol fermentation.     

Isotopic discrimination between D-[1-(13)C]fructose and D-[2-(13)C]fructose in rat liver cells

When liver cells from either normal or hereditarily diabetic rats are exposed to (13)C-enriched D-fructose (10 mM) and unlabelled D-glucose (also 10 mM) in the presence of D(2)O, the output of (13)C-enriched D-glucose generated from D-[1-(13)C]fructose is significantly lower than that from D-[2-(13)C]fructose. This coincides with a higher generation of (13)C-enriched L-lactate and L-alanine from D-[1-(13)C]fructose, as compared to D-[2-(13)C]fructose. In absolute terms, the mean paired difference in the output of (13)C-enriched D-glucose generated from D-[1-(13)C]fructose versus D-[2-(13)C]fructose is not significantly different from the mean paired difference in the production of (13)C-enriched L-lactate and L-alanine from the same precursors, with an overall mean value of 7.01 +/- 1.59 micromol (n = 8; P < 0.005). It is proposed that these findings indicate isotopic discrimination at the phosphoglucoisomerase level between (12)C and (13)C for the carbon atom in position 1 (as compared to that in position 2) of D-fructose 6-phosphate.     

Analytical Procedures for Studying the Dehydration of D-Fructose

In order to study the kinetics of the dehydration of D-fructose, procedures for the qnantitation of fructose and its dehydration products, S-hydroxymethyI-2W furaldehyde (HMF), Ievulinic acid, and a “humin”, were developed. For many reaction conditions, these compounds, together with soluble polymers (up to 15%) that are humin precursors, account for at least 98% of the amount of initial D-fructose. Fructose, HMF, and levulinic acid were determined by g.l.c. of their O-trimethylsilyl derivatives. U.v. absorption and titration could also be used for the determination of HMF and levulinic acid. Humin was determined gravimetrically.     

贮存时间对不同蜜源蜂蜜中羟甲基糠醛含量增速的影响

为了更好控制蜂蜜在贮藏和流通过程中的羟甲基糠醛含量,研究了其在贮存过程中羟甲基糠醛的增长规律。本文对192个不同蜜源的蜂蜜在常温贮存期间的羟甲基糠醛含量进行了检测,统计了贮存时间和蜜源对羟甲基糠醛增长速率的影响,并分析了组分对羟甲基糠醛增率的相关性。结果表明,贮存450d内,蜂蜜的羟甲基糠醛增率与贮存时间呈正相关;椴树蜜、洋槐蜜、紫云英蜜和百花蜜的羟甲基糠醛增率无显著差异,且极显著高于枣花蜜;羟甲基糠醛增率与葡萄糖含量呈显著相关;果葡比极显著相关于酸度。     

Browning of model orange juice solution: factors affecting the formation of decomposition products

A model solution of orange juice was prepared and stored. Factors affecting browning and formation of such decomposition products as 3-hydroxy-2-pyrone (3OH2P), 5-hydroxymethylfurfural (HMF), furfural, 5-hydroxymaltol, and 2-furoic acid were examined. Ascorbic acid (AsA) was essential for browning, which was stimulated by amino acids and citric acid, and repressed by chelators and radical scavengers (RS). 3OH2P was derived from AsA. Its formation was stimulated by sugars and repressed by citric acid, chelating agents, and RS. HMF was derived from fructose. Furfural was derived from AsA, and its formation was stimulated by sugars and chelating agents and repressed by RS. 5-hydroxymaltol and 2-furoic acid were derived from fructose and AsA respectively. We did not find any decomposition products showing the same formation pattern as the browning, but a furfural solution with added amino acids turned brown like the model orange juice solution. It might be an indicator for the browning of orange juice.     

Catalytic conversion of cellulose to 5-hydroxymethyl furfural using acidic ionic liquids and co-catalyst

Efficient catalytic conversion of microcrystalline cellulose (MCC) to 5-hydroxymethyl furfural (HMF), is achieved using acidic ionic liquids (ILs) as the catalysts and metal salts as co-catalysts in the solvent of 1-ethyl-3-methylimidazo-lium acetate ([emim][Ac]). A series of acidic ILs has been synthesized and tested in conversion of MCC to HMF. The effect of reaction conditions, such as reaction time, temperature, catalyst dosage, metal salts, water dosage, Cu(2+) concentration and various acidic ILs are investigated in detail. The results show that CuCl(2) in 1-(4-sulfonic acid) butyl-3-methylimidazolium methyl sulfate ([C(4)SO(3)Hmim][CH(3)SO(3)]), is found to be an efficient catalyst for catalytic conversion of MCC to HMF, and 69.7% yield of HMF is obtained. A mechanism to explain the high activity of CuCl(2) in [C(4)SO(3)Hmim][CH(3)SO(3)] is proposed. To the best of our knowledge, this report first proposes that the Cu(2+) and [C(4)SO(3)Hmim][CH(3)SO(3)] show better catalytic performance in catalytic conversion of MCC to HMF.     

Monosaccharide-H2O2 reactions as a source of glycolate and their stimulation by hydroxyl radicals

An analysis of the H(2)O(2)-induced breakdown and transformation of different keto-monosaccharides at physiological concentrations reveals that glycolate and other short-chained carbohydrates and organic acids are produced. Depletion of monosaccharides and glycolate synthesis occurs at increased rates as the length of the carbohydrate chain is decreased, and is significantly increased in the presence of trace amounts of Fe(2+) ions (10 microM). Rates of monosaccharide depletion (initial concentration of 3 mM) observed were up to 1.55 mmol h(-1) in the case of fructose, and 2.59 mmol h(-1) in the case of dihydroxyacetone, depending upon pH, H(2)O(2) concentration, temperature and the presence or absence of catalytic amounts of Fe(2+). Glycolate was produced by dihydroxyacetone cleavage at rates up to 0.45 mmol h(-1) in the absence, and up to 1.88 mmol h(-1) in the presence of Fe(2+) ions (pH 8). Besides glycolate, other sugars (ribose, glyceraldehyde, glucose), glucitol (sorbitol) and organic acids (formic and 2-oxogluconic acid) were produced in such H(2)O(2)-induced reactions with fructose or dihydroxyacetone. EPR measurements demonstrated the participation of the OH radical, especially at higher pH. Presence of metal ions at higher pH values, resulting in increased glycolate synthesis, was accompanied by enhanced hydroxyl radical generation. Observed changes in intensity of DEPMPO-OH signals recorded from dihydroxyacetone and fructose reactions demonstrate a strong correlation with changes in glycolate yield, suggesting that OH radical formation enhances glycolate synthesis. The results presented suggest that different mechanisms are responsible for the cleavage or other reactions (isomerisation, auto- or free-radical-mediated oxidation) of keto-monosaccharides depending of experimental conditions.     

Promotion by phosphate of Fe(III)- and Cu(II)-catalyzed autoxidation of fructose

Although the oxidative destruction of glucose and fructose has been studied by several investigators over the past century, the mechanism by which phosphate promotes these oxidation reactions is not known. A wide range of oxidation products have been used to monitor the oxidation of sugars and free radicals have been shown to be involved. The influence of phosphate concentration on the rate of production of free radicals and several sugar oxidation products has been studied. It was found that fructose is much more susceptible to autoxidation than glucose, galactose, or sucrose. The promotion of sugar oxidation by phosphate was found to be iron dependent. Addition of the iron chelators, diethylenetriaminepentaacetic acid (DTPA) and desferrioxamine completely suppressed the oxidation reactions, even at high concentrations of phosphate. Formaldehyde was positively identified as a product of fructose oxidation by HPLC analysis of its acetylacetone adduct. A mechanism is proposed in which phosphate cleaves the oxo bridges of the iron(III)-fructose complex, based on UV spectral analysis and magnetic susceptibility measurements, and thereby catalyzes the autoxidation of fructose.