Professor of Physicsdurbin@purdue.edu
Office: Physics 180
Telephone: (765) 494-6426
Fax: (765) 494-0706
B.A. Physics 1976 University of Chicago
M.S. Physics 1977 University of Illinois, Urbana
Ph.D. Physics 1983 University of Illinois, Urbana
NSF Presidential Young Investigator Award 1987
While the static structures of simple proteins like myoglobin and hemoglobin are fairly well understood, their biological activity is likely to also depend on their dynamic vibrational properties. A new x-ray synchrotron technique is being exploited to measure the vibrational spectrum of iron atoms in the heme group, the major functional structure in myoglobin and several other important proteins. Utilizing the extremely high brightness of an undulator x-ray source at the Advanced Photon Source (APS) at Argonne National Laboratory, an x-ray beam whose energy is very close to the Mossbauer nuclear resonance (14.4 keV) and having meV energy resolution is incident on the Mb specimen. If a vibrational mode has an energy equal to the difference between the x-ray beam and the nuclear resonance, the resonance can be excited, with subsequent deexcitation which can be detected as Fe fluorescence. By monitoring this fluorescence as the x-ray energy is scanned through the resonance, an approximate map of the Fe vibrational density of states is obtained. This is especially important because the modes are specific to Fe, so there is no interference from the other parts of the protein; this provides an excellent complement to other Raman scattering and other vibrational probes.
This work is done in colaboration with Tim Sage and Paul Champion of Northeastern University, and Ercan Alp and Wolfgang Sturhahn at the Advanced Photon Source.
One of the major new opportunities due to intense, high brightness synchrotron sources of x-rays is the ability to image x-rays using various x-ray optical elements. This project extends the well-known Kirkpatrick-Baez imaging method to fluorescence to obtain an image of element distribution from small samples. A prototype has been assembled by graduate student Alex Bakulin, and is now in the testing stages. This could have a significant impact on standing wave measurements, XAFS studies, and other x-ray probes. The mirrors are coated with multilayers fabricated by collaborators at the Advanced Photon Source - Al Macrander, Chian Liu, and Jenny Erdmann. Some of the characterization is being done with Terrence Jach at NIST (Gaithersburg).
Holography was originally proposed by Gabor in 1948 as a technique which could allow one to "see" an atom inside its host structure. Recent developments by Thomas Gog and others have brought this somewhat closer to reality, in that holographic images can now be obtained by measuring the total yield of x-ray fluorescence from a specimen under suitable synchrotron irradiation. These initial results have been limited by relatively low count rates and long data collection times. We have been developing new methods for collecting the total x-ray fluorescence from a holographic specimen, so that data can be obtained from 100 to 1000 times faster than before. A long-range goal might be to holographically image the Fe atom centered in the heme group of myoglobin, for example.
Working closely with Professor Roberto Colella and others, the goal of this project is the construction of a specialized beam line at the Advanced Photon Source This beam line is under construction, and will soon be the only beam line at the Advanced Photon Source which can have two insertion devices operating simultaneously - a standard undulator for hard x-rays, and an elliptically polarized undulator for soft x-rays. This is funded by the DOE, and will serve the research needs of the X-ray Physics Group, which also includes Roberto Colella (Purdue), Don Bilderback and Qun Shen (Cornell), Terrence Jach (NIST), John Arthur (Stanford), Al Thompson (Berkeley), and Simon Moss (Houston).
|PHYS 670F||Advanced Graduate Lab||Spring 2000|
|PHYS 645||Electronic Theory of Solids I||Fall 93|
|PHYS 590A||X-Ray Physics||Fall 94, Spr 93|
|PHYS 470I||Industrial Physics Lab||Fall 99, 98|
|PHYS 460||Quantum Mechanics I||Spring 95|
|PHYS 350||Intermed. Lab I: Optics||Fall 85|
|PHYS 342||Modern Physics||Spr 97-99,92,90|
|PHYS 330||Intermed. Elect. & Magnetism||Spr 94, Fall 90,89|
|PHYS 271||Electricity & Magnetism||Fall 95,96,97|
|PHYS 271L||Electricity & Magnetism Lab||Fall 95,96,97|
|PHYS 261||Electricity & Optics (T.A.)||Spring 96|
|PHYS 221||General Physics II||Spring 91|
|PHYS 163||Mechanics, Heat & Kinetic Theory||Spr 87,88,89|
|PHYS 162||Particles, Kinematics, & Conservation Laws||Fall 86,87,88|