|Alphabetical | By research field | By research focus|
Neutron Diffraction Studies of Metal Hydride Complexes
Our main research involves the neutron diffraction studies of metal hydride complexes, especially H atoms in metal clusters. The usual technique for structural determination, X-ray diffraction, is normally incapable of determining the positions of the hydride ligands reliably in such molecules, and over the years we have used the technique of neutron diffraction to accurately characterize such compounds. Examples include the discovery of five-coordinate hydrogen atoms in the cluster complex [H2Rh13(CO)24]3- (Fig. 1), and the more recent characterization of a H4Co4 cluster in the core of H4Co4(Cp*)4 (Fig. 2), Other recent results in the neutron structures of metal hydrides are given in the references below,[3-9] It is hoped that our investigations will lead to a better understanding of metal-hydrogen bonding, and this work has been summarized in a review article.
Neutron Diffraction Studies on Small Proteins
In an attempt to understand the unusual thermostability of proteins from hyperthermophiles such as Pyrococcus furiosus, we have recently been engaged in the neutron diffraction study of the small iron/sulfur protein rubredoxin isolated from this organism. Pyrococcus furiosus is a microorganism that lives in deep undersea vents (Fig 3), under conditions of extremely high temperature and pressure. We have recently published the 1.5-Å resolution neutron diffraction study of the wild-type protein as well as one of its mutants, which revealed details of its molecular structure at the atomic level (e.g., see Fig 4). In addition to finding a tight series of hydrogen bonds at the N-terminus of this protein that may explain part of its remarkable thermostability, we were also able to map out the H/D exchange behavior of the N-H bonds of the protein backbone.
Construction of a Single Crystal Diffractometer at the new Spallation Neutron Source
Finally, we are involved in the design and building of a Single Crystal Diffractometer
at the new high-intensity Spallation Neutron Source (SNS), currently under construction
at Oak Ridge National Laboratory in Tennessee. The significance of this project
is that the SNS is capable of delivering neutron beams with intensities 50-100
times higher than existing neutron sources. The concomitant reduction in crystal
size necessary for a structural analysis (currently one of the major disadvantages
of neutron diffraction) will hopefully make the technique much more accessible
to the practicing chemist or structural biologist. The ability to routinely
locate H atoms in biological macromolecules will make neutron diffraction an
extremely powerful technique in structural biology. The SNS itself is scheduled
for completion in late 2006, and our instrument by late 2008.
Chemistry Dept., USC College of Letters, Arts & Sciences