Research in the Harbison group

The nuclear magnetic resonance (NMR) frequencies of atoms such as 1H, 13C, 31P, and so on, are exquisitely sensitive to their environment. That environment includes electrons in closed shells, open shells and bonds, and other nuclei in constant motion, and also depends on the orientation of these objects relative to the large magnetic field we apply to the sample. We use the NMR frequency to probe the structure of DNA and RNA, as well as the chemistry and dynamics of hydrogen bonding.

However, to understand these NMR frequencies we must also be able to interpret them. An ever-more-important aspect of our research is therefore to use high-level quantum chemical methods to calculate molecular structures, and all sorts of spectra. We do these 'computer experiments' on everything from diatomic molecules, to endohedral fullerenes (atoms or molecules trapped in buckyball cages), to DNA. This work not only will help understand the structure and function of the molecules that make up the genetic code, and enzyme active sites, but it may also have impact in areas as apparently unrelated as quantum computing and medical imaging (MRI).

Here are some specific topics

Basis set development for NMR/NQR

Quantum chemistry programs are now widely available and relatively easy to use. Most give the capability for calculating NMR chemical shieldings, J couplings, and quadrupole interactions. Unfortunately, we recently discovered that the standard basis sets used in these programs do not allow for phenomena unique to NMR nuclei. NMR nuclei are non-spherical, and their higher order multipoles (magnetic dipole, electric quadrupole) polarize the core orbitals, making them no spherical. So, for example, a quadrupolar nucleus, with spin = 1 or higher, makes the s orbitals slightly non-spherical by adding a tiny amount of d character. By making a small adjustment to the input program, discussed in our Publications section, we can correct for this basis set problem, and reduce errors in some cases from ~15% to less than 1%.

NMR, gas-phase infrared, and quantum chemistry on peroxide explosives.

The explosive DADP, TATP and HMTD are easily synthesized by the wannabe terrorist, and extremely dangerous. We have done a number of studies characterizing these materials, with the intention of making them easier to detect and forensically analyze.

Gas-phase NMR

It surprises many chemists that NMR is possible in the gas-phase; it's actually quite easy. Gas-phase NMR has several advantages. It essentially eliminated intermolecular interactions, allowing direct comparison of quantum calculations and experiment. And it reveal an NMR interaction the spin-rotation coupling, that is essentially invisible in liquid state NMR, and absent in solid-state NMR. We are doing some of the first gas-phase 2D NMR work to improve the information content of our spectra.

People in our group

Some recent papers

J. Persons, G. S. Harbison (2007) The 14N quadrupole coupling in hexamethylenetriperoxidediamine (HMTD) Magn. Reson. Chem. 45, 905 - 908.

M. Shortridge, K. A. Mercier, D. S. Hage, G. S. Harbison, R. Powers (2008) Estimating Protein-Ligand Binding Affinity Using High-Throughput Screening by NMR, J. Combinator. Chem. 10, 948 - 958.

A. S. Lipton, R. W. Heck, W. A. de Jong, A. R. Gao, X. Wu, A. Roehrich, G. S. Harbison, P. D. Ellis (2009) The Low Temperature 65Cu NMR Spectroscopy of the Cu+ Site in Azurin J. Am. Chem. Soc., 131, 13992 - 13999.

M. N. Kinde-Carson, C. Ferguson, N. A. Oyler, G. S. Harbison, G. A. Meints (2010) Solid State 2H NMR Analysis of Furanose Ring Dynamics in DNA Containing Uracil J. Phys. Chem. B, 114, 3285 - 3293.

G. S. Harbison (2011) Thermal averaging of the spin-rotation coupling in small molecules leads to an isotropic NMR shielding J. Magn. Reson., 12, 299 - 303.

G. S. Harbison (2012) Nuclear Quadrupole Resonance, in Methods in Materials Research, Elton N. Kaufmann, ed., Wiley, NY, in press.

B. Worley, G. Richard, G. S. Harbison, R. Powers (2012) 13C NMR Reveals No Evidence of n-* Interactions in Proteins PLoS One, submitted.


Written by Gerry Harbison, who is solely responsible for its content. Comments, questions, snide remarks, or breathless adulation can be sent to Gerry at :
 gerry@setanta.unl.edu
.

 Last updated 4/20/2012 2:49 PM