Hao Chen 391 Clippinger Laboratories 740-593-0719 740-593-0148 (Fax) chenh2@ohio.edu Hao Chen Group

Information

Mass spectrometry is a fascinating analytical and biological technology. Our research focuses on the new mass-spec innovation based on newly discovered ion chemistry and novel instrumentation. The current projects are:

1. Liquid sample DESI —- the Study of Electrochemistry, Protein Conformation and Reaction Kinetics by Mass Spectrometry

We have extended the desorption electrospray ionization (DESI),¹ an ambient ionization method, to the direct analysis of liquid samples. Due to its direct sampling and ionization properties, this Liquid Sample DESI-MS is versatile and has unique applications. For instance, it allows us to study electrochemistry, protein conformations, fast reaction kinetics, atmospheric pressure ion/molecule (or ion/ion) reactions, single droplet microextraction, etc.^2-6

• One of our recent effort is being devoted to coupling of electrochemistry (EC)^2,3 with mass spectrometry using DESI as the interface for bioanalytical applications and for the investigation of mechanisms of reaction chemistry. For example, the generation of the perylene radical cation from the electro-oxidation of perylene and the electrolytic reduction of disulfide bonds of insulin in cell followed with online detection by DESI-MS.
• Due to the fast ionization feature, it can also been used to generate native protein ions from solutions with high sensitivity and to probe protein conformational changes in solution.⁵ For instance, the ionization of cytochrome c from water produce abundance native protein ions using DESI while traditional ESI gives unfolded ions.
• Based on the capability of desorption electrospray ionization (DESI) for direct and fast ionization of a high-speed liquid jet stream, we developed a microsecond time-resolved mass spectrometric method for fast kinetic study.⁷ The fast reaction of 2,6-dichlorophenolindophenol (DCIP) and L-ascobic acid (L-AA) was used to demonstrate this concept, and the pseudo-first order reaction rate constant was successfully measured with the time resolution down to 300 µs. The good agreement of the MS measured value of (116±3) s^-1 with that measured by stopped-flow optical method (105±2) s^-1 validates the feasibility of such as DESI-MS approach.
• Liquid sample DESI can be used to directly ionize large proteins (up to 150 kDa) and noncovalent protein complexes (> 45 kDa) preserving weak non-covalent interactions.⁸ Doping the DESI spray solvent with supercharging reagents resulted in the increased multiple charges without protein denaturation or complex dissociation.

2. Selenium Chemistry for Biological Thiol Derivatization

Selenium reagents such as ebselen can be used to selectively and rapidly derivatize thiol peptides/proteins for mass spectrometric analysis.⁹ This reaction is highly selective, rapid, reversible and efficient. For instance, the Cysteine¹²¹ residue of β-lactoglubin A can be labeled using ebselen with quantitative conversion in 30 s

3. Protein footprinting using fast photolytic oxidation of protein (FPOP) method with various oxidants.

Chemical footprinting of proteins has long been proven to be an efficient method for probing protein-protein interactions. FPOP¹⁰ achieves protein oxidation on a microsecond timescale, making it a strong candidate for protein footprinting. The objective of this project is to develop new FPOP methods with novel laser-generated oxidative chemical probes such as the highly oxidative sulfate radial anion SO₄-▪.

Tandem mass spectrometry is invaluable for chemical structure elucidation via examination of fragment ions after the activation and dissociation of gaseous precursor ions. Recently, an ambient ion thermal dissociation method11 has been established which allows the isolation and re-ionization of neutral fragments of peptide/protein ions at atmospheric pressure outside of the mass spectrometer. This method can also be used to seek green chemistry approaches in reaction methodology.¹² For instance, ionic Borsche-Drechsel cyclization is feasible without the need for conventional acid catalysts.

Center for Intelligent Chemical Instrumentation (CICI)

1. Takats, Z.; Wiseman, J. M.; Gologan, B.; Cooks, R. G. Science, 2004, 306, 471.
2. Miao, Z.; Chen, H. J. Am. Soc. Mass Spectrom. 2009, 20, 10.
3. Li, J.; Dewald, H. D.; Chen, H. Anal. Chem., 2009, 81, 9716.
4. Zhang, Y.; Chen, H. Int. J. Mass Spectrom. 2010, 289, 98.
5. Miao, Z.; Wu, S.; Chen, H. J. Am. Soc. Mass Spectrom. 2010, 21, 1730.
6. Sun. X; Miao, Z.; Yuan, Z.; Harrington, P. B.; Colla, J.; Chen, H. Int. J. Mass Spectrom. 2010, 301, 102.
7. Miao, Z.; Chen, H.; Liu, P.; Liu, Y. Anal. Chem. 2011, 83, 3994-3997.
8. Ferguson, C. N.,;Benchaar, S. A.; Miao, Z.; Loo, J. A.; Chen, H. Anal. Chem. 2011, In press.
9. Xu, K.; Zhang, Y.; Tang, B.; Laskin, J.; Roach, P. J.; Chen, H. Anal. Chem. 2010, 82, 6926.
10. Gau, B.; Chen, H.; Zhang, Y.; Gross, M. L. Anal. Chem. 2010, 82, 7821.
11. Hao Chen, Livia S. Eberlin, R. Graham Cooks, J. Am. Chem. Soc. 2007, 129, 5880.
12. Chen, H.; Eberlin, L. S.; Nefliu, M.; Augusti, R.; Cooks, R. G., Angew. Chem. Int. Ed., 2008, 47, 3422.