Enhanced electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry of long‐chain polysaccharides

Abstract

A novel strategy was developed to extend the application of electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (MS) to the analysis of long-chain polysaccharides. High molecular weight polydisperse maltodextrins (poly-alpha(1-4) glucose) and dextrans (poly-alpha(1-6) glucose) were chosen as model compounds in the present study. Increased ionization efficiency of these mixtures in the positive ion mode was achieved upon modification of their reducing end with nitrogen-containing groups. The derivatization method is based on the formation of a new C--N bond between 1,6-hexamethylenediamine (HMD) and the reducing end of the polysaccharide, which exists in solution as an equilibrium between the hemiacetal and the open-ring aldehyde form. To achieve the chemical modification of the reducing end, two synthetic pathways were developed: (i) coupling of HMD by reductive amination and (ii) oxidation of the hemiacetal to lactone, followed by ring opening by HMD to yield the maltodextrin lactonamide of 1,6-hexanediamine (HMMD). Amino-functionalized polysaccharides were analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FTICR-MS) in the positive ion mode by direct flow injection. The hexamethylenediamine (HMD) and maltodextrin lactonamide of 1,6-hexanediamine (HMMD) moieties provide increased proton affinities which dramatically improve the detection of the long-chain polysaccharides by FTICR-MS. The present approach allowed for identification of single components in mixtures with prominent heterogeneity in the degree of polymerization (DP), without the need for chromatographic separation prior to MS. The high mass accuracy was essential for the unambiguous characterization of the species observed in the analyzed mixtures. Furthermore, molecular components containing up to 42 glucose residues were detected, representing the largest polysaccharide chains analyzed so far by ESI FTICR-MS.

Attachment of Chloride Anion to Sugars: Mechanistic Investigation and Discovery of a New Dopant for Efficient Sugar Ionization/Detection in Mass Spectrometers

“…15 The successful application of this method to the analysis of carbohydrates in different biological systems has already been reported 10. 16–18 However, as already mentioned, physicochemical properties of carbohydrates tend to decrease their ionizabilities,4, 16, 17 a problem that is usually overcome by functionalization of the sample or by implementation of front‐end chromatographic methods 18–21…”

Synthesis of Hyperbranched Glycoconjugates by the Combined Action of Potato Phosphorylase and Glycogen Branching Enzyme from Deinococcus geothermalis

“…Purification of the above described mixture was possible with Amberlite IR-120 (H + ) resin. This strong cation-exchange resin was able to adsorb amine functionalized molecules [51,52]. The unreacted and partly reacted core molecules could therefore be separated from the product in a yield of 45% to 61%.…”

Synthesis and structural characterization of amino-functionalized polysaccharides

“…For the synthesis of HMD-linked maltodextrin, the procedure previously described by us was used [16]. Briefly, a 50 mL round-bottom flask equipped with teflon-coated magnetic stirrer and refrigerant was loaded with 1.44 g (12 mM) of HMD, 1.02 g (0.3 mM) of Dex3000, 0.35 mL of glacial AcOH and 10 mL of DMF.…”

“…Q-TOF Micro mass spectrometer is interfaced to a PC running the MassLynx software to control the instrument, acquire and process the MS data. All mass spectra were recorded in the positive ion mode previously shown [15,16,18] to be advantageous for neutral oligosaccharide analysis. The ion source temperature was kept at 80 0 C. For all experiments nitrogen at about 50 L h -1 flow rate was used as a desolvation gas.…”

“…This type of copolymers can be synthesized in many ways [12][13][14]; however, one of the most efficient methods is based on coupling of a functionalized hydrophobic block to a hydrophilic moiety. This procedure can be successfully applied for polyasaccharide modification at the reducing end, as described by us previously [15,16].…”