Abstract:
RATIONALE: Detection of hydrophobic peptides remains a major obstacle for matrix-assisted laser desorption/ionization
mass spectrometry (MALDI-MS). This stems from the fact that most matrices for MALDI are hydrophilic and therefore
have low affinities for hydrophobic peptides. Herein, 1-aminopyrene (AP) and AP-derived group of uniform materials
based on organic salts (GUMBOS) as novel matrices for MALDI-MS analyses of peptides were investigated for
hydrophobic and hydrophilic peptides.
METHODS: A number of solid-phase AP-based GUMBOS are synthesized with variable hydrophobicity simply by
changing the counterions. Structures were confirmed by use of
H NMR and electrospray ionization mass spectrometry
(ESI-MS). 1-Octanol/water partition coefficients (Ko/w) were used to measure the hydrophobicity of the matrices. A
dried-droplet method was used for sample preparation. All spectra were obtained using a MALDI-TOF mass
spectrometer in positive ion reflectron mode.
1
RESULTS: A series of AP-based GUMBOS was synthesized including [AP][chloride] ([AP][Cl]), [AP][ascorbate] ([AP][Asc])
and [AP][bis(trifluoromethane)sulfonimide] ([AP][NTf2]). The relative hydrophobicities of these compounds and α-cyano4-hydroxycinnamic
acid (CHCA, a common MALDI matrix) indicated that AP-based GUMBOS can be tuned to be much
more hydrophobic than CHCA. A clear trend is observed between the signal intensities of hydrophobic peptides and
hydrophobicity of the matrix.
CONCLUSIONS: MALDI matrices of GUMBOS with tunable hydrophobicities are easily obtained simply by varying the
counterion. We have found that hydrophobic matrix materials are very effective for MALDI determination of
hydrophobic peptides and, similarly, the more hydrophilic peptides displayed greater intensity in the more hydrophilic
matrix.
