Lobry De Bruyn-Alberda Van Ekenstein Research Articles

Insight into formation of various rare sugars in compressed hot phosphate buffer

Galactose, glucose, xylose, arabinose, maltose, and lactose were treated in 10 mmol/L sodium phosphate buffer at 140 °C using a tubular reactor under pressurized conditions. Each sugar was isomerized or epimerized to its corresponding ketose and C-2 positional epimer. Isomerization/epimerization resulted in production of various yields of rare sugars (0.8–27 mol%). Yield of rare keto-disaccharide (21–27 mol%) was higher than that of rare monosaccharide (5.8–16 mol%). Rare keto-monosaccharide yield was also different between hexose (13–16 mol%) and pentose (5.8–8.9 mol%). Although disaccharides were partially hydrolyzed to form corresponding monosaccharides, degrees of hydrolysis for these disaccharides were small (~1 mol%). During the treatment, organic acids were formed as byproducts, resulting in a drop in pH. Isomerization and epimerization hardly proceeded for all sugars at a pH lower than 6.3. This means that isomerization by Lobry de Bruyn-Alberda van Ekenstein transformation progressed well only when pH was > 6.3 regardless of kind of sugar.

Efficient Alkaline Isomerization of Lactose to Lactulose in the Presence of an Organogermanium Compound.

Lactulose, a disaccharide widely used in pharmaceuticals and functional foods, is produced by lactose isomerization. Lactose and lactulose have an aldose–ketose relationship. Less than 25 % conversion of lactose into lactulose is achieved using the Lobry de Bruyn–Alberda van Ekenstein transformation with heating, whereas the conversion is increased to 80 % by the addition of an approximately equimolar concentration of the organogermanium compound 3-(trihydroxygermyl)propanoic acid (THGP) to the reaction mixture. To further understand this phenomenon, in this study, we analyzed the affinity between THGP and sugar isomers using 1H nuclear magnetic resonance spectroscopy. For the dimethyl derivative of THGP with lactose and lactulose, the complex formation ratios at 0.1 M (1:1 mixing ratio) were 14 and 59 %, respectively, with complex formation constants of 1.8 and 43 M–1, respectively. The complex formation capacity was approximately 24-fold higher for lactulose than for lactose. Moreover, THGP is considered to protect lactulose from alkaline degradation, resulting in high production yield of lactulose. Therefore, we concluded that high affinity for the isomerization product may promote isomerization and that promotion of sugar isomerization using an organogermanium compound is an effective method for converting lactose to lactulose.

Interaction of saccharides and sugar alcohols with well cement

This paper reports on experimental investigations into the reactions of various saccharides and sugar alcohols in well (Portland) cement slurries at 90°C. At elevated temperatures the important element in saccharide chemistry is the overriding of a low activation energy barrier for the purpose of ring opening/cleavage and the formation of anionic molecules in cement slurries. The resulting experiments show a joint three-step reaction sequence for saccharides and sugar alcohols, accompanied by one set acceleration and two retardations of the cement hydration. The step-wise setting courses are explained by the spontaneous anion formation of polyhydroxy compounds owing to the Lobry de Bruyn–Alberda van Ekenstein rearrangement (keto-enol tautomerism) and charge neutralisation, as well as by well-known traditional organic–inorganic interactions. Furthermore the paper underlines the high relevance of temperature adjustment and cement aging on the course of setting of well cements.

Quantification of Lactulose and Epilactose in the Presence of Lactose in Milk using a dual HPLC analysis

The valuable lactose derivatives lactulose and epilactose can be derived from lactose either by the Lobry de Bruyn-Alberda van Ekenstein transformation during heat treatments or by enzymatic conversion using cellobiose 2-epimerases (EC 5.1.3.11). The chromatographic determination of lactose, lactulose, and epilactose in milk is challenging, due to the variable ratio of the three saccharides and their similar retention properties. In this work, a dual high-performance liquid chromatography (HPLC) analysis for the quantification of lactose, lactulose, and epilactose in milk samples was developed and validated. The samples originated from an enzymatic lactose conversion using the cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus. Application of this enzyme led to the formation of high lactulose concentrations (28.0 g/L) in milk. The dual HPLC analysis utilized a combination of two chromatographic separation techniques, configured in two parallel systems. After precolumn derivatization, the samples were analyzed as follows: Method 1 determined the concentration of lactose and epilactose using a C18 column with an ion-pair reagent as eluent, coupled with a UV detector. Method 2 determined the concentration of lactulose using a trimodal stationary phase (hydrophilic interaction, anion- and cation-exchange properties) with acetonitrile/ammonium formiate buffer as eluent, coupled with an evaporative light scattering detector. Both methods were validated in terms of linearity, precision and recovery. The revealing detection limits in the milk samples were 3.32 mg/L for lactose, 4.73 mg/L for epilactose and 139 mg/L for lactulose. The dual HPLC analysis presented allows accurate lactose, lactulose, and epilactose separation in complex food matrices such as milk.

Efficient Conversion of D-Glucose to D-Fructose in the Presence of Organogermanium Compounds.

D-Glucose and D-fructose are isomers of commonly consumed monosaccharides. The ratio of conversion of D-glucose to D-fructose by glucose isomerase (xylose isomerase) is not more than 50 %. However, addition of an equimolar ratio of the organogermanium compound poly-trans-[(2-carboxyethyl)germasesquioxane] (Ge-132) or its derivative increases the conversion ratio to 80 %. In contrast, use of the Lobry de Bruyn–Alberda van Ekenstein transformation with heating results in a lower conversion ratio, less than 30 %, whereas addition of an equimolar concentration of Ge-132 or its derivative to this reaction mixture increases the ratio to 73 %. Therefore, in this study, we aimed to further analyze the affinity between organogermanium compounds (i.e., Ge-132 and its derivatives) and sugar using 1H-nuclear magnetic resonance (NMR) spectrometry. For the dimethyl derivative of Ge-132, the complex formation ratios at 0.25 M (mixing ratio 1:1) were 19 and 74 % for D-glucose and D-fructose, respectively. Additionally, the complex formation constants between monosaccharides and Ge-132 were 1.2 and 46 M-1 for D-glucose and D-fructose, respectively. The complex formation capacity was approximately 40-fold higher for D-fructose than for D-glucose. Therefore, we concluded that the high affinity for the product of isomerization may promote isomerization, and that promotion of sugar isomerization using organogermanium compounds is an effective method for conversion of D-glucose to D-fructose.

Kinetics of Nε-(carboxymethyl)lysine formation in aqueous model systems of sugars and casein

This study investigated the formation of Nε-carboxymethyllysine (CML) in two caseinate solutions containing: (1) glucose, (2) lactose, each heated at 120°C and 130°C. At both heating temperatures, CML concentration in lactose-caseinate solution was higher than in glucose-caseinate solution. In both solutions, more CML was formed at 130°C than at 120°C. Using multiresponse modelling, two degradation routes for the sugars were confirmed: (1) isomerisation of glucose or lactose and subsequent degradation via Lobry de Bruyn–Alberda van Ekenstein (LA) arrangement; (2) the Maillard reaction between the reducing sugar and lysine residues. Modelling results suggested that CML was not formed from oxidation of the reducing sugars, but from the Maillard reaction via the Amadori rearrangement product. Since CML appeared to be thermally unstable under the current study conditions, it may not be a perfect indicator for heat damage of processed foods. This is the first study in which CML formation was linked to available information on the Maillard reaction via multiresponse modelling.

HPLC Determination of Lactulose in Heat Treated Milk

Lactulose (4-O-β-d-galactopyranosyl-d-fructose), formed from lactose (4-O-β-d-galactopyranosyl-d-glucose) by the Lobry de Bruyn–Alberda van Ekenstein rearrangement during severe heat treatments, is considered a useful indicator of heat-induced modifications in milk. Its chromatographic determination in milk is particularly troublesome due to the concomitant presence of a lactose amount two orders of magnitude larger than the lactulose amount and to a similar retention time of the two compounds. In this work, four HPLC methods have been compared with the aim to develop a more accurate analytical procedure to determine lactulose in milk, together with lactose. The developed method is based on a Carrez precipitation followed by a HPLC separation on two in-series amino-based columns, using CH3CN:H2O 75:25 (v:v) as the mobile phase at 1 ml/min flow rate and a refractive index as the detector. The linearity test for the quantitation of lactulose has been carried out over the range 0.060–1.006 mg/ml, the limit of detection, is 0.013 mg/ml (256 ng injected) and the limit of quantitation is 0.028 mg/ml (556 ng injected). The proposed method, simple, cheap and time-saving, allows an accurate lactulose–lactose separation, with conventional HPLC equipment.

Development of a chemical strategy to produce rare aldohexoses from ketohexoses using 2-aminopyridine

Rare sugars are monosaccharides that are found in relatively low abundance in nature. Herein, we describe a strategy for producing rare aldohexoses from ketohexoses using the classical Lobry de Bruyn–Alberda van Ekenstein transformation. Upon Schiff-base formation of keto sugars, a fluorescence-labeling reagent, 2-aminopyridine (2-AP), was used. While acting as a base catalyst, 2-AP efficiently promoted the ketose-to-aldose transformation, and acting as a Schiff-base reagent, it effectively froze the ketose–aldose equilibrium. We could also separate a mixture of Sor, Gul, and Ido in their Schiff-base forms using a normal-phase HPLC separation system. Although Gul and Ido represent the most unstable aldohexoses, our method provides a practical way to rapidly obtain these rare aldohexoses as needed.

Rapid and highly selective conversion of biomass into value-added products in hydrothermal conditions: chemistry of acid/base-catalysed and oxidation reactions

An overview of recent advances in research on selective conversion of carbohydrates into products with hydrothermal chemistry is given. Conversion methods tend to use acid- or base-catalysed reactions and oxidation reactions. Conversion products that can be selectively produced include acetic acid, formic acid, lactic acid, levulinic acid, 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (2-FA). Future conversion paths and possible new products that can be formed with hydrothermal chemistry include aldol/reverse condensation, dehydration, benzilic acid rearrangement, keto-enol tautomerization, Lobry de Bruyn–Alberda van Ekenstein transformation and oxidation reactions.

Aldose–ketose interconversion in pyridine in the presence of aluminium oxide

The reaction rate of the Lobry de Bruyn–Alberda van Ekenstein transformation of aldoses to ketoses in boiling pyridine was strongly increased by the addition of aluminium oxide. In addition to aldose–ketose transformation, 2-epimers of the starting aldoses and 3-epimers of the primarily produced ketoses were formed to some extent, as reported also when these reactions are carried out without aluminium oxide. The relative amounts of the primary ketose and the starting aldose in the reaction mixtures may be explained on the basis of their stability, predicted from reported free energy calculations. Isomerisation of ketoses to aldoses was much slower than the reverse reaction. The relative free energies are also in these cases important, the very stable xylo-2-hexulose gave only 7% and 6% of the aldoses gulose and idose, respectively, after boiling for 7 h in pyridine in the presence of aluminium oxide.

Ni/SiO2 catalysts prepared with ethylenediamine nickel precursors: Influence of the pretreatment on the catalytic properties in glucose hydrogenation

Nickel catalysts prepared with different metal loadings (5, 10, and 20 wt% Ni) by impregnation with nickel ethylenediamine complexes revealed small nickel particles (mean diameter: 2–3 nm) after reduction, even for high metal loadings (20 wt%). When used in the hydrogenation of glucose, these catalysts show almost no nickel leaching compared to a commercial Ni/SiO2 catalyst (prepared by precipitation, 67 wt% Ni), but they are slightly less active (TOF: 2 to 10 × 10−3 s−1) than a commercial nickel/silica catalyst (TOF: 14 × 10−3 s−1) and revealed lower yields to sorbitol (3–42% compared to 60%). The catalytic results depend on the pretreatment conditions performed. When the catalysts are calcined before reduction, higher conversion (19–45%) and selectivity to sorbitol (81–92%) are obtained than when they are directly reduced without calcination pretreatment (conversion: 10–16% and selectivity to sorbitol: 21–59%) after 5 h of reaction time, respectively. The difference was ascribed to the fact that complete decomposition of the nickel ethylenediamine precursor was achieved only when calcination pretreatment was performed. Indeed, when the catalysts were directly reduced, X-ray photoelectron spectroscopy (XPS) revealed a nitrogen-compound probably responsible for lower conversion and higher selectivities to fructose and mannose, indicating Lobry de Bruyn-Alberda van Ekenstein rearrangement. However, no nickel sintering was observed in contrast to the catalyst calcined before reduction.

Isomerisation of aldoses in pyridine in the presence of aluminium oxide

Addition of aluminium oxide to boiling pyridine solutions of D-xylose, L-arabinose, D-mannose and D-glucose strongly increased the reaction rate of the aldose-ketose transformation. The maximum content of 2-ketose was reached after less than 2h for the aldopentoses and 3h for the aldohexoses. D-Threo-2-pentulose (xylulose) was prepared from D-xylose, and isolated as its O-isopropylidene derivative, the yield was nearly twice that compared to that usually obtained in the classical Lobry de Bruyn-Alberda van Ekenstein transformation in pyridine.

Preparation of Mannac Containing Chitooligomers By Isomerisation and their Binding to Nkr-P1 Protein

4-O-(2-Acetamido-2-deoxy-β-D-glucopyranosyl)-2-acetamido-2-deoxy-D-mannopyranose (2) was prepared from diacetylchitobiose (1) by Lobry de Bruyn-Alberda van Ekenstein rearrangement under catalysis of Ca(OH)2. The disaccharide 2 shows about ten times higher affinity than 1 towards NKR-P1 protein acting as a crucial activating receptor of rat natural killer cells (leukocytes). Chitotriose (3) can be epimerized analogously to give GlcNAcβ1-4GlcNAcβ1-4ManNAc (4) and its binding properties to NKR-P1 are also about ten times higher than those of 3.

Changes in free monosaccharides during storage of dried milk.

Changes in the monosaccharide fraction of dried skim milk stored under different conditions of temperature and humidity have been studied. The monosaccharide fraction of freshly spray-dried milk contained only galactose and glucose. Both monosaccharides increased during storage, and the formation of tagatose and 3-deoxypentulose was also detected. These changes suggest that lactose transformations during storage take place via condensation with proteins (Maillard reaction), isomerization (Lobry de Bruyn-Alberda van Ekenstein reaction), and hydrolysis

The Synthesis of Carbon-13 Enriched Monosaccharides Derived from Glucose and Mannose

Abstract A modified Kiliani-Fischer reaction is used to prepare multigram quantities of [1-13C]-enriched glucose and mannose which are converted chemically or enzymatically into other labeled monosaccharides. The simplest conversion is the synthesis of labeled fructose from labeled glucose using commercially available immobilized glucose isomerase. The equilibrium for this reaction provides a 1:l mixture of glucose and fructose which can be separated by chromatography. The equilibrium can be shifted toward fructose by treating the reaction with germanate ion. [1-13C]Mannose can be converted into more useful sugars using a modification of the Lobry de Bruyn-Alberda van Ekenstein transformation. In this reaction, D-[1-13C]mannose is treated with an aqueous solution of dilute alkali and phenylboronate to form a mixture of labeled fructose, mannose and glucose. Fructose can be converted to a mixture of methyl fructofuranosides by using trifluoroacetic acid in methanol. [2-13C]Dihydroxyacetone can be prepared ...

Effect of the protein, citrate and phosphate content of milk on formation of lactulose during heat treatment.

Milk ultrafiltrate and milks of varying protein, citrate and phosphate concentrations were heated in sealed containers. Protein was found not to be involved in the mechanism of formation of lactulose, but increasing the protein content of milk reduced the concentration of lactulose after heating. This was considered to be due to increased condensation of lactose and lactulose with amino groups of the protein. Less lactulose was formed in milk ultrafiltrate than in skimmed milk accorded the same heat treatment, which was attributed to the buffering capacity of the milk protein in skimmed milk. Activation energies for lactulose formation in skimmed milk and in ultrafiltrate were 128 and 131 kJ/mol respectively. Citrate and phosphate catalysed the formation of lactulose. It is proposed that the formation of free lactulose in heated milk and ultrafiltrate proceeds exclusively by the Lobry de Bruyn-Alberda van Ekenstein transformation with the naturally occurring phosphate and citrate acting as base catalysts.

Metal-ion catalysis of aldose-ketose isomerizations in acidic solutions

A comparative study has been made of the ability of metal ions to catalyze the Lobry de Bruyn-Alberda van Ekenstein transformation. An analytical enzymic assay system, which is highly sensitive and selective, was developed to monitor the rates of isomerization of hexose and triose phosphates. The metal ions catalyze the isomerization of hexose phosphates by virtue of their Lewis acid character with the first transition series being most effective. The metal ions also appear to have no ability to direct the course of the reactions. Amino acids also catalyze the isomerization apparently by virtue of the free carboxylate anion.

The Lobry De Bruyn-Alberda Van Ekenstein Transformation

This chapter discusses the Lobry de Bruyn-Alberda van Ekenstein transformation. The Lobry de Bruyn-Alberda van Ekenstein transformation has usually been considered to embrace both epimerization of aldoses and ketoses and aldose-ketose isomerization. Actually, Lobry de Bruyn and Alberda van Ekenstein observed all three reactions, so that an experimental basis for defining the transformation has existed from almost the time of its first recognition. The experimental limits of the transformation have never been extended beyond those established in the original investigations. The history of the mechanism of the Lobry de Bruyn-Alberda van Ekenstein transformation begins with the first description of its reactions. Thus, Lobry de Bruyn and Alberda van Ekenstein proposed that the transformation might take place by intramolecular transfer of hydrogen in hemiacetal intermediates, which they considered were formed from the aldoses by addition and removal of water. Soon after this, Wohl and Neuberg suggested the enediol intermediate for aldose-ketose isomerization. The enolization mechanism apparently won nearly immediate acceptance and it has since dominated the field. The first 30 years of the transformation seem to have been marked more by speculations on the mechanism than by experiments designed to elucidate it.