Ionic Liquid Matrix for Direct UV-MALDI-TOF-MS Analysis of Dermatan Sulfate and Chondroitin Sulfate Oligosaccharides

Abstract

Polyanionic oligosaccharides such as dermatan sulfate (DS) and chondroitin sulfate (CS) exhibit poor ionization efficiencies and tend to undergo thermal fragmentation through the loss of SO 3 under conventional ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI) conditions. A new ionic liquid matrix (ILM), a guanidinium salt of α-cyano-4-hydroxycinnamic acid, facilitates direct UV-MALDI mass spectrometric (MS) analysis of underivatized DS and CS oligosaccharides up to a decasaccharide in their common form as sodium salts. The resulting mass spectra show very low extent of fragmentation through an SO 3 loss. The new ILM is suitable for MALDI-MS analysis of mixtures containing oligosaccharides with different numbers of sulfo groups.The use of room-temperature ionic liquids as matrices is a fast growing area of matrixassisted laser desorption/ionization mass spectrometry (MALDI-MS) method development. Ionic liquid matrices (ILMs) have a number of advantages over conventional crystalline matrices including the homogeneity of the analyte-matrix mixture and high vacuum stability of the matrix. 1,2 ILMs have been shown effective in MALDI-MS analysis of several classes of biological molecules including peptides and proteins, 3 phospholipids, 4 oligonucleotides, 5 and neutral oligosaccharides. 6 The goal of this work was to develop a facile MALDI-timeof-flight (TOF)-MS method for the characterization of glycosaminoglycan (GAG)-derived oligosaccharides using an ILM.When analyzed by mass spectrometry, GAG-derived oligosaccharides have a tendency to fragment through the loss of SO 3 (Δ −102 m/z). In electrospray ionization (ESI) mass spectrometry, these polysulfated, polycarboxylated oligosaccharides often result in several peaks, corresponding to intact oligosaccharide and fragments due to the SO 3 loss, 7 each of which can be sodiumcationized, protonated, or both and have various charge states. 8 The advantage of MALDI is that multiply charged species are not observed in the reflector mass spectra, 9 simplifying data interpretation as compared to the ESI mass spectra. However, due to their thermal lability, poor ionization efficiency, and a tendency to undergo extensive Na/H exchange, polyanions such as GAG-derived oligosaccharides are rarely analyzed by MALDI-MS, and methods for such analysis are scarce.To date, a very few methods have been reported for MALDI-MS analysis of underivatized GAG-derived oligosaccharides. 10-12 A peptide complexation method described by Juhasz and Biemann 13,14 allows the detection of polysulfated oligosaccharides by MALDI-MS in a form of noncovalent complexes with basic peptides, (Gly-Arg) n , where n exceeds the number of sulfo groups in the oligosaccharide by one. While this method is sensitive and affords MALDI mass spectra in which SO 3 loss is suppressed, 15 it is limited by the availability of synthetic peptides. Recently, we reported a successful MALDI-MS analysis of sodium salts of an octasulfated disaccharide and an octasulfated pentasaccharide in their uncomp...

ESI-MS differential fragmentation of positional isomers of sulfated oligosaccharides derived from carrageenans and agarans

“…As shown in Figure 3 Table 2), under Ϫ40 eV collision energy demonstrated that compounds G4S-AOH (3) and G3S-AOH (8) had higher abundances of [M-Na] Ϫ (100% for both cases) while G6S-AOH (7) and G2S-AOH (6) underwent more facile glycosidic fragmentations, giving rise to relative abundances of 57.9% and 33.5% for molecular ion, respectively (Table 2). In accordance with these observations, B 1 relative intensities were consequently lower for G4S-AOH (3,16.4%) and G3S-AOH (8,10.0%) than for G6S-AOH (7,36.7%) and G2S-AOH (6, 100%). We also observed that G2S-AOH …”

“…The earlier studies [13,14] in this field were mostly conducted using FAB ionization. More recently, a number of combinations of ionization techniques (MALDI [15][16][17] and ESI [18 -22] and mass analyzers (TOF [15][16][17]22] quadrupoles and/or ion traps [8 -12, 18 -22] have been utilized. Sulfated oligosaccharides produced from glycosaminoglycans (hyaluronan sulfate, chondroitin sulfate [11,12], heparan sulfate [22], heparin [13, 14, 19 -23], dermatan sulfate [16], mucin [8,9], and mucopolysaccharides [24] have served as models for the improvement of the knowledge of mass spectrometric methods involving these types of molecules.…”

Structural Analysis of Bikunin Glycosaminoglycan

“…Spectra were internally calibrated with bovine insulin, hen egg lysozyme, and cytochrome C. Sinapinic acid was used for the analysis of bikunin PG, and bis-1,1,3,3-tetramethylguanidinium Rcyano-4-hydroxycinnamate (G 2 CHCA) was used for the analysis of bikunin pG. 43 The negative-ion ESI-FTICR mass spectra of bikunin GAG mixture were acquired on a 7T Bruker Apex IV QeFTMS instrument fitted with an Apollo II electrospray ion source. Bikunin GAG sample was dissolved in 50% aqueous methanol to a concentration of 0.1 mg/mL and directly infused using nanospray through a pulled fused silica tip (model FS360-75-15-D-5, New Objective, Woburn, MA) at a flow rate of 10 μL/h.…”

Ionic liquids in sample preparation

“…Besides proteins and peptides, ILs were also used as matrices for the MALDI-MS analysis of other molecules, such as amino acids, oligonucleotides [110,111], carbonaceous compounds [112], dermatan sulfate and chondroitin sulfate oligosaccharides [113], uncomplexed highly sulfated oligosaccharides [114,115], aflatoxins [116], chlorosulfolipids [117], and phospholipids [118,119]. Generally speaking, these ILs have different advantages over a traditional matrix.…”