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| CHRYS WESDEMIOTIS |
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Professor
B.S., 1972, Technical University of Berlin
M.S., 1976, Technical University of Berlin
Ph.D., 1979, Technical University of Berlin
Postdoctoral fellow, 1980-1981, Cornell University
Greek Army, 1981-1983
Senior research associate, 1983-1989, Cornell University |
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Office: KNCL 112
(330) 972-7699 |
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Lab: KNCL 110, 114
(330) 972-8219 |
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| Email: wesdemiotis@uakron.edu |
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| Website: http://gozips.uakron.edu/~wesdemi |
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| Research Interests |
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Mass Spectrometry and Tandem Mass Spectrometry:
Fundamental Studies and Analytical Applications to Macromolecules
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| Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) offer the potential to combine interests in gas phase ion chemistry, instrumentation development, and chemical analysis. Our research explores these areas with studies on reactive intermediates relevant to biology and medicine, the development of new methods for molecular structure characterization, and applications of MS and MS/MS in the materials science and biological fields. |
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| Radicals relevant to biology and medicine |
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| Protein backbone radicals with the unpaired electron at the a-C atom of a glycyl residue have been implicated as intermediates in several biological processes, both detrimental and beneficial. The chemical properties of these species are largely unknown, but are of fundamental interest as they could provide the insight needed for a better understanding of their in vivo reactivity. Our group uses mass spectrometry techniques to produce such reactive intermediates in form of their metal ion complexes in the gas phase, so that their intrinsic dissociations and bimolecular reactions can be studied. The metal ion provides the charge necessary for mass spectrometric experiments. Peptide radicals are examined as model systems of the more complex protein radicals encountered in biology. Figure 1 provides examples of radicals currently investigated. |
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| Fig. 1. Li+ complex of the Li-carboxylate of AG• radical (left) and dimeric Cu+ complex of GG and an a-backbone radical (right). |
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| New methods for molecular structure characterization |
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| The stabilities and reactivities of molecular or quasimolecular ions are diagnostic of molecular structure. We are investigating the dissociations (i.e. unimolecular chemistry) of protonated and metalated biomolecules, in particular peptides, in order to understand their decomposition mechanisms and develop new approaches for determining their structures and sequences (Figure 2). Studies are also conducted on the thermochemistry of noncovalent interactions between metal ions and biomolecules. The bond energies of these interactions, which are determined experimentally by kinetic methods and calculated at suitable levels of theory, are sequence-specific and, thus, structurally informative; they also unveil insight about the biological functions of the metal ions involved. |
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Fig. 2. Singly charged dilithiated peptides give rise to tandem mass spectra that identify conclusively the peptide sequence. This is illustrated for dilithiated alanyl-leucine enkephalin. |
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| Mass spectrometry characterization of synthetic polymers |
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| Mass spectrometry provides the accurate molar mass of a compound (which reveals the compound’s composition) as well as the masses of fragments from the compound (which identify the compound’s primary structure). These data are obtained with unsurpassed sensitivity, selectivity, specificity, and speed. Our group employs mass spectrometry methods to characterize the repeat units, end groups, and molecular weights of new synthetic polymers. An illustrative example is given in Figure 4, which shows the MALDI mass spectrum of a star-branched polymer, synthesized by R.P. Quirk and coworkers via reaction of silane-terminated polystyrene (PS) arms with a polyhedral oligomeric silsesquioxane (POSS) core. The major distributions identified, A, B, and C, correspond to unreacted arm, dimerized arm, and 7-armed star, respectively, while the minor ones (D and E) represent 6- and 8-armed stars. |
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| Fig. 4. MALDI mass spectrum of a star-branched polymer prepared by hydrosilation of a vinyl-substituted POSS core with a silane-terminated PS of Mn = 2,000. |
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| A series of studies focuses on the acquisition, interpretation, and classification of the tandem mass spectra of important polymer classes. Knowledge of the fragmentation behavior of polymer ions is the first step in the development of tandem mass spectrometry strategies for the characterization of the sequences and architectures of complex polymers and copolymers. Considerable research efforts are also devoted to the development of selective degradation / mass spectrometry techniques for the characterization of polymers that are not analyzable directly by mass spectrometry or other spectroscopic means. Mild thermal degradation is employed to cleave large or complex polymer systems to smaller oligomers that can subsequently be identified by MS and MS/MS, to thereby gain structural data about the original polymer. This approach is analogous to the digestion / MS experiments performed on complex biological samples. The polymers studied by our group include (a) amphiphilic networks, stars, polymer brushes, and copolymers that are too large to be desorbed and detected intact; (b) polymers that cannot be ionized readily, and (c) polymers that are too large to give resolved oligomers for determination of their repeat units and end groups. Figures 8-9 show results on a tricomponent amphiphilic membrane (Figure 8), synthesized by J.P. Kennedy and coworkers. The products detected by MS (Figure 9) and MS/MS after mild pyrolysis at 275o C are polyglycol (distributions A-H) and polydimethylsiloxane (distribution I) oligomers; such products conclusively identify the building components of the membrane and provide valuable structural insight about a polymer network whose structure is very challenging to determine otherwise. |
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| Fig. 8. Proposed architecture of a tricomponent amphiphilic membrane composed of poly(ethylene glycol) and polydimethylsiloxane strands, crosslinked by poly(pentamethylcyclopentasiloxane) (PD5) domains. |
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| Fig. 9. MALDI mass spectrum of the pyrolysis products from the polymer shown in Fig. 8. All peaks are [M+Na]+ ions. |
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| Selected Publications |
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Wesdemiotis, C.; Pingitore, F.; Polce, M.J.; Russel, V.M.; Kim, Y.; Kausch, C.M.; Connors, T.H.; Medsker, R.E.; Thomas, R.R. Characterization of a poly(fluorooxetane) and poly(fluorooxetane-co-THF) by MALDI mass spectrometry, size exclusion chromatography, and NMR spectroscopy, Macromolecules 2006, 39, 8369-8378.
Quirk, R.P.; Ocampo, M.; Polce, M.J.; Wesdemiotis, C. Functionalization of poly(styryl)lithium with thiiranes: sulfur extrusion vs ring-opening mechanisms, Macromolecules 2007, 40, 2352-2360.
He, J.; Zhou, L.; Soucek, M.D.; Wollyung, K.M.; Wesdemiotis, C. UV-curable hybrid films based on vinyl functionalized siloxane oligomer and acrylated polyester, J. Appl. Polym. Sci. 2007, 105, 2376-2386.
Wollyung, K.M.; Xu, K.; Cochran, M.; Kasko, A.M.; Mattice, W.L.; Wesdemiotis,
C.; Pugh, C. Synthesis and mass spectrometry studies of an amphiphilic
polyether-based rotaxane that lacks an enthalpic driving force for threading,
Macromolecules 2005, 38, 2574-2586.
He, J.; Nebioglu, A.; Zong, Z.; Soucek, M.D.; Wollyung, K.M.; Wesdemiotis, C. Preparation of a siloxane acrylic functional siloxane colloid for UV-curable organic-inorganic hybrid films, Macromol. Chem. Phys. 2005, 206, 732-743.
Quirk, R.P.; Kim, H.; Polce, M.J.; Wesdemiotis, C. Anionic synthesis of primary amine-functionalized polystyrenes via hydrosilation of allylamines with silyl hydride functionalized polystyrenes, Macromolecules 2005, 38, 7895-7906.
Arnould, M.A.; Vargas, R.; Buehner, R.W.; Wesdemiotis, C. Tandem mass spectrometry characteristics of polyester anions and cations formed by electrospray ionization, Eur. J. Mass Spectrom. 2005, 11, 243-256.
Quirk, R.P.; Pickel, J.M.; Arnould, M.A.; Wollyung, K.M.; Wesdemiotis, C. Efficient synthesis of w-(p-vinylbenzyl)polystyrene by direct functionalization of poly(styryl)lithium with p-vinylbenzyl chloride in hydrocarbon solvent with lithium 2,3-dimethyl-3-pentoxide, Macromolecules 2006, 39, 1681-1692.
Nagy, A.; Kennedy, J.P.; Wang, P.; Wesdemiotis, C.; Hanton, S.D. Extent of coverage of surfaces treated with hydrophobizing microemulsions: a mass spectrometry and contact angle study, Appl. Surf. Sci. 2006, 252, 3751-3759.
Wang, P.; Polce, M.J.; Bleiholder, C.; Paizs, B.; Wesdemiotis, C. Structural characterization of peptides via tandem mass spectrometry of their dilithiated monocations, Int. J. Mass Spectrom. 2006, 249-250, 45-59.
Quirk, R.P.; Kim, Y.J.; Wesdemiotis, C.; Arnould, M.A. Hydroxyl chain-end functionalization of polymeric organolithium compounds with oxetane, J. Polym. Sci. Part A: Polym. Chem. 2006, 44, 2684-2693.
Wesdemiotis, C.; Wang, P. Thermochemistry studies of biomolecules, In Mass Spectrometry Applied to Biomolecules; Lifshitz, C.; Laskin, J., Eds.; John Wiley & Sons: Hoboken, New Jersey, 2006, 567-617.
Wang, P.; Newkome, G.R.; Wesdemiotis, C. Mass spectrometry of organometallic assemblies: bis-terpyridine-Ru(II) connectivity, Int. J. Mass Spectrom. 2006, 255-256, 86-92. |
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