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LSU Chemistry Sweeps STEM Rainmaker Awards

Rainmakers in Research Recognized

2107 LSU Rainmakers
At the LSU Rainmakers event were, left to right: Provost Rick Koubek, Campus Federal Credit Union President and CEO Dawn Harris, Associate Vice President for Research & Economic Development Stephen David Beck, Associate Professor Donghui Zhang, Associate Vice President for Research & Economic Development Gus Kousoulas, the Mary P. Poindexter Professor of Mass Communication Lance Porter, Assistant Professor Rendy Kartika, Vice President of Research & Economic Development Kalliat T. Valsaraj, Roy Paul Daniels Professor of Chemistry Kermit Murray, the Louise & Kenneth Kinney Professor of Black Drama and Playwriting Femi Euba, and Assistant Professor Benjamin Kahan. Photo Credit: Cody Willhite, LSU

Tip-Enhanced Laser Ablation Sample Transfer for Biomolecule Mass Spectrometry

Ghorai, S.; Seneviratne, C. A.; Murray, K. K. J. Am. Soc. Mass Spectrom. 2014.

http://dx.doi.org/10.1007/s13361-014-1005-x

Atomic force microscope (AFM) tip-enhanced laser ablation was used to transfer molecules from thin films to a suspended silver wire for off-line mass spectrometry using laser desorption ionization (LDI) and matrix-assisted laser desorption ionization (MALDI). An AFM with a 30 nm radius gold-coated silicon tip was used to image the sample and to hold the tip 15 nm from the surface for material removal using a 355 nm Nd:YAG laser. The ablated material was captured on a silver wire that was held 300 μm vertically and 100 μm horizontally from the tip. For the small molecules anthracene and rhodamine 6G, the wire was cut and affixed to a metal target using double-sided conductive tape and analyzed by LDI using a commercial laser desorption time-of-flight mass spectrometer. Approximately 100 fg of material was ablated from each of the 1 μm ablation spots and transferred with approximately 3% efficiency. For larger polypeptide molecules angiotensin II and bovine insulin, the captured material was dissolved in saturated matrix solution and deposited on a target for MALDI analysis.

GUMBOS matrices of variable hydrophobicity for matrix-assisted laser desorption/ionization mass spectrometry

Al Ghafly, Siraj, Das, Regmi, Magut, Galpothdeniya, Murray, Warner, Rapid Commun. Mass Spectrom. 2014, 28, 2307; DOI: 10.1002/rcm.7027.

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 1H 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.

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-cyano-4-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.