Ian Carmichael

Ian Carmichael

Director - Notre Dame Radiation Laboratory

University of Glasgow, Scotland, B.Sc.Hons (1971) Ph.D. (1974)

Phone: (574) 631-4502
Email: carmichael.1@nd.edu
Office: 321 Radiation Research Building

Theoretical Studies of Reactive Intermediates


Scientific Interests

Quantum Chemistry of Reactive Intermediates

Structure and properties of radicals, radical ions, and excited states in solution and on surfaces.

Magnetic Interactions in Molecular Species

EPR splittings; NMR spin-coupling constants and chemical shifts; nuclear quadrupolar couplings.

Theory of Radiation and Photochemical Transformations

Photophysical processes; dissociative electron attachment; transient absorption spectroscopy.

Radiation Damage in Macromolecular Crystallography

Specific damage mechanisms and mitigation strategies.

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Recent Accomplishments

Ds Plot

Radiation Damage in MX

OH-cleavage from tyrosine residues has been cited as a result of specific radiation damage incurred during protein crystallography at 100 K, but no clear mechanism for such phenolic C–O bond cleavage in tyrosine has been reported in the radiation chemistry literature.We have reinvestigated the initial report of Tyr -OH group loss in myrosinase and indeed find, at increasing doses, clear electron density loss was detectable local to Tyr -OH groups.However a systematic investigation performed on a range of protein crystal damage series deposited in the PDB has established that such electron density loss is not generally a dominant damage. Full Tyr aromatic ring displacement is instead proposed to account for instances of observable Tyr -OH electron density loss.

Understanding Dissociative Electron Attachment

Despite decades of gas-phase studies on dissociative electron attachment (DEA) to various molecules, as yet there has been no direct detection and characterization of the neutral radical species produced by this process. We use stepwise electron spectroscopy to directly measure and characterize the neutrals produced upon zero-electron-energy DEA to a model molecule, carbon tetrachloride. We observe the direct yield of the trichloromethyl radical and measure the appearance energies of all the other neutral species. Combined with high-level quantum chemical calculations this allows a comprehensive analysis of both the initial DEA event and the subsequent electron-impact ionizations under single-collision conditions. This work paves the way toward a complete experimental characterization of DEA processes, in turn providing a refined understanding of the low-energy electron-induced formation of radical species.

NMR Spin Couplings in Biomolecules

NMR J-couplings measured by selective 13-C labeling of twelve, structurally-diverse,β-(1–4) linked disaccharides were analyzed using parametrized equations obtained from density functional theory calculations, coupled with Fredholm theory and circular statistics. Our statistical program, MA’AT, allowed the modeling of the linkage torsional parameters, phi (φ) and psi (ψ),as a single von Mises distribution with mean positions in close accord to those of rotamer populations obtained from 1 μs aqueous molecular dynamics (MD) simulations and crystallographic database statistical analyses. An experimental means to validate the conformational preferences predicted from MD simulations is thus established.

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Selected Publications

Li, Z., A.R. Milosavljevic, I. Carmichael, and S. Ptasińska. "Characterization of Neutral Radicals from a Dissociative Electron Attachment Process."  Phys. Rev. Lett. 119 (2017) 053402. link.

Bury, C.S.,  I. Carmichael, and E.F. Garman. "OH Cleavage from Tyrosine: Debunking a Myth." J. Synchrotron Rad 24 (2017): 7-18. link

Zhang, W., T. Turney, R. Meredith, Q. Pan, L. Sernau, X. Wang, M.J. Hadad, A. Cosica, T. Klepach, X. Hu, R.J. Woods, I. Carmichael, and A.S. Serianni. "Conformational populations of β‑(1→4) O‑Glycosidic linkages using redundant NMR J‑couplings and circular statistics." J. Phys. Chem. B 121 (2017):3042-30. link

Li, Z., M.M. Dawley, I. Carmichael, and S. Ptasińska. "Electron Induced Fragmentation of Methylated Formamides." Int. J. Mass Spectrom 410 (2016): 36-46. link

Bury, C.S., I. Carmichael, J.E. McGeehan, and E.F. Garman. "Radiation Damage with Nucleoprotein Complexes Studied by Macromolecular X-ray Crystallography."  Radiat. Phys. Chem. 128 (2016): 118-25. link

Bury, C.S., J.E. McGeehan, A. Antson, I. Carmichael, M. Gerstel, M. Shevtsov, and E.F. Garman. "RNA Protects a Nucleoprotein Complex against Radiation Damage." Acta Crystallogr. D 72 (2016): 648-57. link

 

Full List of Publications

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