Cecil Dybowski, Francis Alison Professor
Francis Alison Professor
University of Delaware
035 Brown Lab
Newark, DE 19716
(b. 1946) B.S., 1969, Ph.D., 1973, University of Texas at Austin; Research Fellow in Chemical Engineering, 1973 – 1976, California Institute of Technology; Visiting Scientist, 1982, E. I. Du Pont de Nemours and Company; Professeur Associé, 1989, Université Pierre et Marie Curie; Visiting Professor of Chemical Engineering, 1998, University of California at Berkeley
Research in Professor Dybowski’s group focuses on spectroscopy, particularly NMR spectroscopy, of solid and solid-like materials. The spectroscopic analyses aid in understanding structure/function relations in pure crystalline solids, mixed solids, and phases at surfaces. The studies are motivated by practical problems such as pharmaceutical efficacy, catalytic function, and environmental contamination, but they also are intrinsically of scientific interest.
Recent work focuses on the NMR properties of heavy-atom spin-1/2 nuclei such as 207Pb, 199Hg, and 119Sn. NMR chemical shielding in these materials is sensitive to the local electronic environment, and relaxation of these nuclei often results from processes not seen for light nuclei. Experimentally the 207Pb and 199Hg chemical shifts in a variety of solids vary by thousands of ppm from one environment to another, making NMR spectroscopy a strong barometer of local structure. This sensitivity provides a means to address structural questions that arise in catalytic reactions or in devices like fuel cells.
To predict NMR chemical shieldings theoretically and connect measured quantities to structural features requires sophisticated computational chemistry. Our group does this with density functional calculations that include relativistic effects. The calculations semi-quantitatively predict trends in chemical shielding with structure. In particular, small changes in atom-atom distances or angles of vectors result in electronic effects observed as substantial changes in the NMR properties.
Relaxation times reflect the dynamic nature of a solid. We have observed that relaxation in materials like Pb(NO3)2 is efficient, with relaxation times of a few seconds for a crystalline solid containing a rare spin-1/2 nucleus. The experimental temperature dependence (1/T1 α T2) and the lack of magnetic-field dependence are explained by a theory developed in this laboratory for a novel relaxation mechanism involving Raman-like modulation of spin interactions that effectively relaxes the nuclear spins. The mechanism is effective for a variety of heavy nuclei, as we have observed it for nuclei in PbMoO4, PbC12, and SnF2.
- R. E. Taylor, S. Bai, and C. Dybowski "A Solid-State 199Hg NMR Study of Mercury Halides," J. Mol. Struct., (2011) 987, 193 – 198.
- W. Liu, W. D. Wang, W. Wang, S. Bai and C. Dybowski "Influence of Structure on the Spectroscopic Properties of the Polymorphs of Piroxicam," J. Phys. Chem. B, (2010) 114, 166141 – 16649.
- W. Liu, W. D. Wang, W. Wang, S. Bai, and C. Dybowski "Measurement of the Principal Values of the Chemical-Shift Tensors of Overlapped Protonated and Unprotonated Carbons with the 2D-SUPER Technique and Dipolar Dephasing (DD-SUPER)," J. Magn. Reson., (2010) 206, 177 – 181.
- S. Bai, O. Dmitrenko and C. Dybowski "15N and 13C NMR Chemical Shifts of 6-(Fluoro, Chloro, Bromo, and Iodo)purine 2'-Deoxynucleosides: Measurements and Calculations," Magn. Reson. Chem., (2010) 48, 61 – 67.
- S. Bai, G. Neue, P. A. Beckmann, C. Dybowski and A. J. Vega "119Sn Spin-Lattice Relaxation in α-SnF2," Phys. Rev. B, (2009) 79, 214302.
- R. E. Taylor, C. T. Carver, O. Dmitrenko, S. Bai and C. Dybowski "Revisiting HgCl2: A Solution- and Solid-State 199Hg NMR and ZORA-DFT Computational Study" J. Mol. Struct., (2009) 930, 99 – 109.
- A. Glatfelter, C. Dybowski, S. Bai, D. Kragten, M. J. Blake, S. Segarra and D. L. Perry "Infrared Studies of Lead(II) Halide-1,10-Phenanthroline Photosensitive Materials. Spectrochim," Acta A, (2009) 71, 1922 – 1926.
- O. Dmitrenko, S. Bai and C. Dybowski "Prediction of 207Pb NMR Parameters for the Solid Ionic Lead (II) Halides Using the Relativistic ZORA-DFT Formalism. Comparison with the Lead-containing Molecular Systems," Solid State Nucl. Magn. Reson., (2008) 34, 186 – 190.
- R. E. Taylor and C. Dybowski "Variable Temperature NMR Characterization of α-Glycine," J. Mol. Struct., (2008) 889, 376 – 382.
- O. Dmitrenko, S. Bai, P. A. Beckmann, S. van Bramer, A. J. Vega and C. Dybowski "The Relationship Between 207Pb Chemical Shift and Solid State Structure in Pb(II) Compounds," J. Phys. Chem. A, (2008) 112, 3046 – 3052.
- R. E. Taylor, A. D. French, G. R. Gamble, D. S. Himmelsbach, R. D. Stipanovic, D. P. Thibodeaux, P. J. Wakelyn and C. Dybowski "1H and 13C Solid-state NMR of Gossypium barbadense (Pima) Cotton," J. Mol. Struct., (2008) 878, 177 – 184.
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