Analysis of oligosaccharides by MEKC with aminobenzoic alkyl esters as derivatization agents

Reversed-phase separation methods for glycan analysis

Reversed-phase chromatography is a method that is often used for glycan separation. For this, glycans are often derivatized with a hydrophobic tag to achieve retention on hydrophobic stationary phases. The separation and elution order of glycans in reversed-phase chromatography is highly dependent on the hydrophobicity of the tag and the contribution of the glycan itself to the retention. The contribution of the different monosaccharides to the retention strongly depends on the position and linkage, and isomer separation may be achieved. The influence of sialic acids and fucoses on the retention of glycans is still incompletely understood and deserves further study. Analysis of complex samples may come with incomplete separation of glycan species, thereby complicating reversed-phase chromatography with fluorescence or UV detection, whereas coupling with mass spectrometry detection allows the resolution of complex mixtures. Depending on the column properties, eluents, and run time, separation of isomeric and isobaric structures can be accomplished with reversed-phase chromatography. Alternatively, porous graphitized carbon chromatography and hydrophilic interaction liquid chromatography are also able to separate isomeric and isobaric structures, generally without the necessity of glycan labeling. Hydrophilic interaction liquid chromatography, porous graphitized carbon chromatography, and reversed-phase chromatography all serve different research purposes and thus can be used for different research questions. A great advantage of reversed-phase chromatography is its broad distribution as it is used in virtually every bioanalytical research laboratory, making it an attracting platform for glycan analysis.

Graphical Abstract

Direct conversion of cellulose and hemicellulose to fermentable sugars by a microbially-driven Fenton reaction

The aim of this work was to develop a microbially-driven Fenton reaction that fragments cellulose and hemicellulose, degrades cellodextrins and xylodextrins, and produces short-chain oligosaccharides and monomeric sugars in a single bioreactor. The lignocellulose degradation system operates at neutral pH and does not require addition of conventional lignocellulose-degrading enzymes, thus avoiding problems associated with enzyme accessibility and specificity. The ability to produce useful bioproducts was demonstrated by production of the bioplastic polyhydroxybutyrate with the xylan degradation products as starting substrate.

Activation of an Otherwise Silent Xylose Metabolic Pathway in Shewanella oneidensis

Shewanella oneidensis is unable to metabolize the sugar xylose as a carbon and energy source. In the present study, an otherwise silent xylose catabolic pathway was activated in S. oneidensis by following an adaptive evolution strategy. Genome-wide scans indicated that the S. oneidensis genome encoded two proteins similar to the xylose oxido-reductase pathway enzymes xylose reductase (SO_0900) and xylulokinase (SO_4230), and purified SO_0900 and SO_4230 displayed xylose reductase and xylulokinase activities, respectively. The S. oneidensis genome was missing, however, an Escherichia coli XylE-like xylose transporter. After 12 monthly transfers in minimal growth medium containing successively higher xylose concentrations, an S. oneidensis mutant (termed strain XM1) was isolated for the acquired ability to grow aerobically on xylose as a carbon and energy source. Whole-genome sequencing indicated that strain XM1 contained a mutation in an unknown membrane protein (SO_1396) resulting in a glutamine-to-histidine conversion at amino acid position 207. Homology modeling demonstrated that the Q207H mutation in SO_1396 was located at the homologous xylose docking site in XylE. The expansion of the S. oneidensis metabolic repertoire to xylose expands the electron donors whose oxidation may be coupled to the myriad of terminal electron-accepting processes catalyzed by S. oneidensis Since xylose is a lignocellulose degradation product, this study expands the potential substrates to include lignocellulosic biomass.

IMPORTANCE

The activation of an otherwise silent xylose metabolic system in Shewanella oneidensis is a powerful example of how accidental mutations allow microorganisms to adaptively evolve. The expansion of the S. oneidensis metabolic repertoire to xylose expands the electron donors whose oxidation may be coupled to the myriad of terminal electron-accepting processes catalyzed by S. oneidensis Since xylose is a lignocellulose degradation product, this study expands the potential substrates to include lignocellulosic biomass.

Recent developments in sample preparation for chromatographic analysis of carbohydrates

Carbohydrates are a very important group of compounds due to their roles as structural materials, sources of energy, biological functions and environmental analytes; they are characterized by their structural diversity and the high number of isomers they present. While many advances have been made in carbohydrate analysis, the sample preparation remains difficult. This review aims to summarize the most important treatments which have been recently developed to be applied prior to the analysis of carbohydrates by chromatographic techniques. Due to the multiplicity of structures and matrices, many different techniques are required for clean-up, fractionation and derivatization. A number of new techniques which could be potentially adequate for carbohydrate characterization have also been revised.

Sensitive determination of carbohydrates labelled withp-nitroaniline by capillary electrophoresis with photometric detection using a 406 nm light-emitting diode

p-Nitroaniline was explored as a derivatising reagent for UV absorbance detection of carbohydrates after separation by CE. This derivatising agent has three advantages: first, it has excellent water solubility; second, it has high molar absorptivity; and third, it is possible to obtain sensitive detection using a UV or blue light-emitting diode (LED) as the light source. The labelling reaction took less than 30 min to complete with high reaction yield. The separation process was modelled and optimised using an artificial neural network. Nine carbohydrates were separated by a CE system within 16 min using a 0.17 M boric acid buffer at pH 9.7. On-column LED detection at 406 nm allowed the detection of carbohydrates with good detection limits (<1.1 microM or 8.8 fmol) and reproducible quantification in the concentration range of 2.6-200 microM. This method was applied successfully to the determination of component carbohydrates in some food samples.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.

Capillary electrophoresis separation of a mixture of chitin and chitosan oligosaccharides derivatized using a modified fluorophore conjugation procedure

A capillary electrophoresis (CE) method was developed for the simultaneous analysis of small chitin and chitosan oligosaccharides. For detection purposes, the oligomers were derivatized with 8-aminopyrene-1,3,6-trisulfonic acid (APTS), a well known fluorophore for oligosaccharides analysis. The detection was performed by laser-induced fluorescence (LIF) with an argon ion laser having an excitation wavelength of 488 nm and with emission monitored at 520 nm. Derivatization parameters such as reaction time and conditions were examined. Separation conditions were also varied by testing a range of buffer pHs and concentrations. The best conditions were found using an 80 mM borate buffer at pH 8.4. This CE-LIF optimized method was used for the analysis of an enzymatically produced oligo-chitosan sample composed of a complex mixture and having an average degree of polymerization of 3.7 monomer units and 80% deacetylation. The oligo-chitosan sample was treated with a chitin deacetylase-like enzyme, the products were derivatized with APTS, and then analyzed without purification. The goal was to determine whether the deacetylase-like enzyme could increase the extent of deacetylation of the oligo-chitosan sample.

Derivatization of carbohydrates for chromatographic, electrophoretic and mass spectrometric structure analysis

Carbohydrates, either alone or as constituents of glycoproteins, proteoglycans and glycolipids, are mediators of several cellular events and (patho)physiological processes. Progress in the "glycome" project is closely related to the analytical tools used to define carbohydrate structure and correlate structure with function. Chromatography, electrophoresis and mass spectrometry are the indispensable analytical tools of the on-going research. Carbohydrate derivatization is required for most of these analytical procedures. This review article gives an overview of derivatization methods of carbohydrates for their liquid chromatographic and electrophoretic separation, as well as the mass spectrometric characterization. Pre-column and on-capillary derivatization methods are presented with special emphasis on the derivatization of large carbohydrates.

Fluorescent labeling of pectic oligosaccharides with 2-aminobenzamide and enzyme assay for pectin

Oligogalacturonides [oligomers composed of (1-->4)-linked alpha-D-galactosyluronic acid residues] with degrees of polymerization (DP) from 1 to 10, and a tri-, penta-, and heptasaccharide generated from the backbone of rhamnogalacturonan I (RG-I) were labeled at their reducing ends using aqueous 2-aminobenzamide (2AB) in the presence of sodium cyanoborohydride in over 90% yield. These derivatives were analyzed by high-performance anion-exchange chromatography (HPAEC) and structurally characterized by electrospray-ionization mass spectrometry (ESIMS) and by 1H and 13C NMR spectroscopy. The 2AB-labeled oligogalacturonides and RG-I oligomers are fragmented by endo- and exo-polygalacturonase and by Driselase, respectively. 2AB-labeled oligogalacturonide is an exogenous acceptor for galacturonosyltransferase of transferring galacturonic acid from UDP-GalA. Thus, the 2AB-labeled oligogalacturonides and RG-I oligomers are useful for studying enzymes involved in pectin degradation and biosynthesis and may be of value in determining the biological functions of pectic fragments in plants.

Nano-HPLC-mass spectrometry and MEKC for the analysis of oligosaccharides from human milk

The separation of oligosaccharides derivatized with various esters of aminobenzoic acid by means of reversed-phase nano-HPLC (nHPLC) with on-line ESI mass spectrometry and off-line MALDI-TOF mass spectrometry as well as MEKC is described. For this purpose methyl, ethyl and butyl aminobenzoates and heptyloxyaniline were used as derivatization agents for homologous maltodextrins and oligosaccharides from human milk. Four different C(18) stationary phases were tested for this purpose because the type of stationary phase was shown to have a dramatic effect on the performance of the separation. Optimal results were obtained using n-butyl aminobenzoate as label and an encapsulated ODS stationary phase. The on-line coupling of nHPLC to ESI MS allowed to separate and identify various oligosaccharides from human milk. This technique enabled the exact attribution of the molecular structure to a signal in the chromatogram. In a second approach oligosaccharides were separated by nHPLC and subsequently fractionated. The fractions were analyzed by MALDI-TOF mass spectrometry. The results obtained by this approach confirmed the ESI MS data. An analogous separation profile was obtained by using sodium dodecyl sulfate in MEKC, which proves that the retention mechanisms of both techniques are identical.

Ion-pair RP-HPLC determination of sugars, amino sugars, and uronic acids after derivatization with p-aminobenzoic acid

A new, selective, and sensitive ion-pair RP-HPLC method for the simultaneous determination of three classes of natural organic compounds, i.e., carbohydrates, amino sugars, and uronic acids, in environmental samples is presented. p-Aminobenzoic acid is used for precolumn derivatization of the analytes, enabling fluorescence (lambda(ex) 313 nm, lambda(em) 358 nm) or photometric detection (303 nm). The dependence of the derivatization yield on the reaction conditions is examined. Derivatives of lactose, galactose, glucose, mannose, xylose, arabinose, galacturonic acid, glucuronic acid, N-acetylglucosamine, and glycerinealdehyde were separated on a RP-C18 column with hydrophilic end capping within 35 min, applying TBAHSO4 as the ion-pair reagent. The concentration detection limits range between 20 and 30 microg L(-1) ((1-2) x 10(-7) M) for fluorescence detection and between 30 and 75 microg L(-1) for UV detection. A good linearity is achieved in the concentration range from 50 microg L(-1) to 100 mg L(-1) (r2 > 0.99). The described method has been applied for the determination of mono-/disaccharides, uronic acids, and amino sugars in soil solutions and in landfill leachates.

Analysis of carbohydrates in wood and pulps employing enzymatic hydrolysis and subsequent capillary zone electrophoresis

An efficient method for determining the carbohydrate composition of extractive-free delignified wood and pulp is described here. The polysaccharides in the sample are first hydrolyzed using a mixture of commercially available preparations of cellulase and hemicellulase. The reducing saccharides in the hydrolysate thus obtained are subsequently derivatized with 4-aminobenzoic acid ethyl ester and thereafter quantitated by capillary zone electrophoresis (CZE) in an alkaline borate buffer with monitoring of the absorption at 306 nm. All reducing sugars (i.e., neutral monosaccharides and uronic acids) which occur as structural elements in the polysaccharides of wood and pulp can be quantitated in a single such analytical run, which can also determine the contents of 4-deoxy-beta-L-threo-hex-4-enopyranosyluronic acid (HexA) residues present in pulps obtained from alkaline processes. CZE analyses were performed using linear regression of standard curves over a concentration range spanning approximately three orders of magnitude. Carbohydrate constituents constituting approximately 0.1% of the dry mass of the sample could be quantitated. The overall precision of this analytical procedure--involving enzymatic hydrolysis, derivatization and CZE--was good (RSD=2.2-7.5%), especially considering the heterogeneity of the wood and pulp samples. The total yield of carbohydrates (93-97%) obtained employing the procedure developed here was consistently higher than that obtained upon applying the traditional procedure for carbohydrate analysis (85-93%) (involving acid hydrolysis and gas chromatographic analysis) to the same pulps. The trisaccharide HexA-xylobiose was the only HexA-containing saccharide detected using the conditions for enzymatic hydrolysis developed here (i.e., 30 h incubation at pH 4 and 40 degrees C); whereas mixtures of HexA-xylobiose and HexA-xylotriose were obtained when the incubation was performed at pH 5 or 6.