norHarmane containing ionic liquid matrices for low molecular weight MALDI-MS carbohydrate analysis: The perfect couple with α-cyano-4-hydroxycinnamic acid

ERRA-BALSELLS, ROSA; SALUM, MARÍA L.; SCHMIDT DE LEÓN, TOBÍAS

JOURNAL OF MASS SPECTROMETRY

JOHN WILEY & SONS LTD

Año: 2019

1076-5174

Cinnamic acid derivatives, particularly α-cyano-4-hydroxycinnamic acid (E-α-cyano-4-hydroxycinnamic acid or (E)-2-cyano-3-(4-hydroxyphenyl)prop-2-enoate; CHCA) has been extensively used especially for protein and peptide analysis. Together with the introduction of ionic liquid MALDI matrix (ILM) started the study of applications of IL prepared with CHCA and a counter organic base (i.e., aliphatic amines) in which CHCA moiety is the chromophore responsible of UV-laser absorption. Although the extensive studies of norharmane (9H-pyrido[3,4-b]indole; nHo) applications as matrix and its peculiar basic properties in the ground and electronic excited state, it was never tested nHo containing ILM in MALDI-MS experiments. This pyrido-indole compound was introduced as MALDI matrix twenty two years ago for different applications including low molecular weight (LMW) carbohydrates (neutral, acidic and basic carbohydrates). These facts encouraged us to use it as a base, for the first time, for ILM preparation. As a rational design of new IL MALDI matrices, E--cyanocinnamic acid.nHo and E-cinnamic acid.nHo were prepared and their properties as matrices studied. Their performance was compared with that of (i) the corresponding IL prepared with butylamine as basic component, (ii) the corresponding crystalline E--cyanocinnamic and E-cinnamic acid and (iii) the classical crystalline matrices (2,5-dihydroxybenzoic acid, DHB; nHo) used in the analysis of neutral/sulfated carbohydrates. The IL DHB.nHo was tested too. Herein we demonstrate the outstanding performance for the IL CHCA.nHo for LMW carbohydrate in positive and negative ion mode (linear and reflectron modes). Sulfated oligosaccharides were detected in negative ion mode and although the dissociation of sulfate groups was not completely suppressed the relative intensity (RI) of [M-Na]- peak was quite high. Additionally, to better understand the quite different performance of each IL tested as matrix the physical and morphological properties in solid state were studied (optical image; MS image).