MIT Reports to the President 1997-98
The Francis Bitter Magnet Laboratory (FBML) has continued to make notable advances in several areas of science and engineering involving high magnetic fields. The research program in Magnetic Resonance (nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR)) has continued to grow and remains the largest effort at the FBML. The program is funded primarily by the NIH and DOE, and involves ~20 NMR and EPR magnets and spectrometers.
A few of this year's highlights:
During the past year, Prof. Cory's research group continued to develop novel NMR methods, instrumentation and applications. These included:
NMR microscopy--We completed the construction of a high field NMR microscope with resolution of a few microns. We are currently using this to explore questions in developmental biology.
2-D diffusive scattering--We completed a set of studies to demonstrate that correlated, multi-vector scattering measurements are not only feasible by NMR, but that they provide information that is unavailable by other means. As a first example, we used these methods to measure the eccentricity of the average pore volume in a pore glass.
MAS gradient studies--We continue to explore applications of the combination of magic angle sample spinning and magnetic field gradients. We have shown that this is an excellent means of investigating compartmentation in biological samples. Some initial solid state studies have also been completed.
NMR investigations of quantum information processing--A large part of our efforts has been directed towards exploring quantum information processing by NMR. These studies include the implementation of quantum computers, studies of decoherence via quantum error correction, exploration of quantum coherence and entangled states, and the first demonstration of fully coherent quantum feedback control. This work includes strong collaborations with Dr. T. Havel (Harvard Medical School), Prof. Seth Lloyd (Mechanical Engineering), and a group at Los Alamos headed by Dr. Raymond LaFlamme.
We have completed the construction of a modest scale MRI setup for environmental transport studies. This is now being used by Professors P. Culligan (Civil and Environmental Engineering), K. Czerwinski (Nuclear Engineering) and their students.
HIGH FREQUENCY ELECTRON PARAMAGNETIC RESONANCE (EPR)
The capabilities of the 140 GHz EPR spectrometer have been dramatically extended by incorporating a four-phase microwave pulse forming network and amplifier. The greater microwave power and phase switching capability now allow us to perform more sophisticated pulsed EPR techniques. In particular, we are working on developing new pulsed multiquantum EPR experiments for measuring long-range distances (10-30 Å) in spin labeled proteins and peptides. We have also added a 140 GHz pulsed Electron-Nuclear Double Resonance (ENDOR) capability. The increased sensitivity, resolution and orientation selection available in the ENDOR experiment at this high frequency/field has enabled us to determine in detail the electronic structure of the tyrosyl radical of ribonucleotide reductase. ENDOR studies of the Fe-S cluster active site of the protein putidaredoxin have also been initiated. The paramagnetic Fe-S cluster precludes the characterization of the active site structure by NMR techniques due to the very large paramagnetic shifts and broadenings of the NMR resonances. High frequency ENDOR spectroscopy, however, is uniquely suited to study the active sites of such paramagnetic enzymes and proteins.
STRUCTURAL STUDIES OF ALZHEIMER'S DISEASE -AMYLOID
Amyloidoses are a group of peptide or protein misfolding disorders characterized by the accumulation of insoluble fibrillar protein material in extracellular spaces. Sixteen different peptides are known to form amyloid-like aggregates. The aggregation of these peptides is involved in several diseases. -amyloid (A) is involved in Alzheimer's disease, the conversion of the prion protein PrPc to PrPsc leads to the transmissible spongiform encephalopathy, and the synuclein protein is responsible for Parkinson's disease.
During the last year, we worked on methods to obtain large amounts of fibrillar peptide material. Fibril preparation is crucial for obtaining narrow lines, maximizing spectral resolution, and optimizing signal intensities. Fibril formation is also important for the biological relevance of the structural model. Furthermore, a uniformly 13C, 15N labeled 9mer peptide (A34-42) that resembles the C-terminal part of A has been synthesized. High-resolution AFM (Atome Force Microscopy) images indicate that this fragment forms regular fibrils as well.
Currently, we are working on methods of obtaining structural information on uniformly labeled samples to determine the three-dimensional fold of a protein. This includes measurement of NH-NH dipolar interactions that yield the relative orientations of backbone/backbone and backbone/side chain amides. Furthermore, we want to introduce proton-proton distances into the structure calculation protocol by performing 1H,1H recoupling experiments in perdeuterated peptides.
SOLID STATE NMR STUDIES OF MEMBRANE PROTEINS
During the past year, we have focused both on methodology for studying membrane proteins in general and on the structure of one particular membrane protein--bacteriorhodopsin (bR).
In methodology, we presented an approach to 3D spectroscopy of solids that will be useful in resolving and assigning resonances in membrane proteins. We plan to develop this technique further. We addressed methods of measuring torsion angles in proteins which we plan to apply to the study of retinal conformation in bR. We also described an approach to recoupling the shift anisotropy and the heteronuclear dipolar interaction in rotating solids, a technique that could be used in heteronuclear correlation spectroscopy. In addition, the desire to assign a set of resonances to the nitrogens of Arg82 stimulated the development of a new approach to performing frequency selective cross polarization.
We also studied the effect of dynamics on peptide spectra by examining gramicidin-A in lipid bilayers. Our spectra indicate that the rotational diffusion of the peptide interferes with the proton decoupling. We developed a method to elucidate the dynamics of lipid bilayers without resorting to 2H labeling. A review of these developments appeared in Nature Structural Biology.
In addition, we studied protonated Schiff base model compounds that are models for the M state of bR. We have detailed methods for trapping the various photointermediates of bR and also described measurements of the 15N chemical shift of the L550 intermediate. In NMR spectra of several forms of bR, we observed two M intermediates that are possibly the switch that provides directionality to the proton pump in bR. Furthermore, we described the involvement of Arg in the proton pumping cycle of bR. In the M intermediate we find an Arg that exhibits a 25 ppm difference in the shifts between the nitrogens of Arg82. This effect appears in both wild type bR and the D85N mutant.
Our results demonstrate convincingly that we are able to measure distances in membrane peptides and proteins and explain the mechanism of the intensity losses in the spectra. The results establish the structure of the Schiff base in the L-intermediate of bR, the presence of two forms of M and the perturbation of an Arg in the formation of the M intermediate.
SOLID STATE NMR STUDIES OF PEPTIDES & PROTEINS
During the past year we made significant progress in developing methods that will be useful for determining the structure of large and/or insoluble proteins or peptides, and we have improved the resolution with new 3D sequences.
We continue to develop new and improved pulse sequences to perform dipolar recoupling, methods for controlling the bandwidth of the sequences--either spectrally selective or broadband--and for reintroducing chemical shift anisotropies. Resolution is always a problem in NMR spectra and we illustrated the possibility of significantly increasing the resolution via 3D 15N-13C-13C chemical shift correlation spectra. We have also employed 15N13C correlation spectra for assigning spectra of peptide and proteins, and nucleic acids. We described the resolution of a structural question in the 9-mer peptide that is part of a -amyloid. Specifically with powder experiments we established the configuration of the GG peptide bond as trans.
Our continued experiments on I3/2 nuclei via multiple quantum excitation could be widely applicable to biological systems. We published three papers concerned with spectroscopy of quadrupolar nuclei based on the development general approaches to spectroscopy of I3/2 spin systems. We recorded some of the initial spectra of 17O, discussed J-couplings in quadrupole spectra, and presented a new technique to measure distance using a ramped RF field. The approach should be useful for multiply labeled systems since only one spin pair at a time is recoupled.
The measurement of torsion angles and was the subject of additional research. Our initial approach relied on 1H,13C and 1H,15N dipolar couplings. Most recently, we have employed 15N,13C couplings in NCCN experiments.
A competing proposal was recently submitted to NIH for the next five-year funding cycle.
CENTER FOR MAGNETIC RESONANCE
The Center for Magnetic Resonance has completed its 22nd year of operation as a facility open to scientists needing access to high field NMR EPR and magnetic resonance imaging equipment. During this year, more than 80 projects were worked on by over 100 investigators, some from departments within MIT including Chemistry, Physics, and Nuclear Engineering, as well as users and collaborators from institutions outside of MIT such as Harvard University, Brandeis University and Brigham & Women's Hospital. Work resulted in close to 70 publications in print or in press.
Highlights of work conducted at the center include advances in high frequency dynamic nuclear polarization of proteins (DNP), high precision NH Bond distance measurements in a serine protease active site and protein structure determination of Human Z.
A competing proposal was recently submitted to NIH for the next five-year funding cycle.
MAGNET DESIGN & TECHNOLOGY
"Cryotribology and `Electromaglev'" is an HTS research program headed by Dr. Yukikazu Iwasa. Our focus centers on a new magnetic levitation system called "electromaglev" or "active-maglev" in which an HTS bulk sample, e.g., YBCO, is levitated stably in the DC magnetic field generated by electromagnets placed underneath the floating object. During the past two years, we completed a comprehensive theoretical and experimental study on lift, lateral and tilt stabilities, and other dynamic parameters. We hope to continue this work as a new 3-year program effective September 1, 1998.
We continued research on the key operational issue of protection for high temperature superconducting (HTS) magnets operating in the temperature range 10-60 K. In addition to this basic protection study, practical aspects of cryocooler-cooled operation will also be investigated. Small coils wound from silver-sheathed BSCCO-2223 tapes will be investigated in the temperature range 4.2-- 60 K. Accurate analytical models have been developed for low-Tc magnets in past research. However, these models do not apply well to high-temperature superconductors due to their wide current-sharing temperature regions and significant variation in thermophysical properties across these regions.
We developed a numerical NZP model for a three-dimensional, dry-wound, BSSCO-2223 superconducting magnet. The test magnet operates under quasi-adiabatic conditions at 20~K and above, in zero background field. It is contained in a stainless steel cryostat and cooled by a Daikin cryocooler. The NZP model is based on the two-dimensional transient heat diffusion equation. Quenches are simulated by a numerical code using the finite-difference method. Agreement between voltage traces obtained in the test magnet during heater-induced quenching events and those computed by the numerical NZP model is reasonable. The model is also used to simulate quenching in magnets similar to the test magnet. Specifically studied were effects of magnet inductance, for a given set of operating current and temperature, on the maximum temperature reached in one full turn of the conductor located at the magnet outermost layer driven normal with a heater. The simulation demonstrates that there is an operating current limit for a given magnet inductance and operating temperature below which the magnet can be considered self-protecting. The model indicates that thermal contact resistance has a dominant effect on propagation in the azimuthal direction (across layers).
Our work on developing a "permanent" HTS magnet system is continuing. The system combines the simplicity and ease of operation of a ferromagnetic permanent magnet with the strength, capability and versatility in field generation of an electromagnet. Once energized and producing a desired field, the system, without being coupled to a cooling source, can maintain the field for a long period. This HTS magnet is particularly suitable for an on-board or portable unit requiring a constant field and where "permanence" means a duration of hours, days, weeks, months, or even years. The systemís other features are "recooling" and "recharging" capabilities designed to have the system re-cooled while maintaining its constant field to make the field literally permanent, and recharged if its upper operating temperature is exceeded and the field decays.
THIN FILM MAGNETISM, SUPERCONDUCTIVITY AND TUNNELING
In condensed matter physics, in particular magnetism, our research has resulted in significant contributions both fundamentally as well as for industrial application. Several issues of interfacial spin transport and magnetic excitations were addressed in the past year's research emphasis. Now we are even closer to verifying the fundamental theoretical predictions of certain exotic magnetic compounds (which are technologically important materials), using our new molecular beam epitaxy (MBE) system. Our research in these materials has already shown the possibility of a four level memory/logic element - a first of such kind of thin film tunnel device. International collaborative research is taking place with scientists and professors from the University of Paris at Orsay, the University of Eindhoven and the Ukrainian Academy of Sciences. Exchange of scientists and graduate students are part of this program.
In the area of semiconductors, our continued research in collaboration with Hewlett-Packard Company has been valuable, in search of far future material for atomically resolved storage (> Terabytes/in2). We are exploring the materials with the right properties and giving HP the fundamental information necessary for their program. There is also continued collaboration with other companies such as IBM, Seagate, Read-Rite and Motorola in the field of magnetism.
Currently, there are three graduate students and two postdocs taking part in the research. Among the four high school students and four undergraduates who took part in the research activities, one high school student was a finalist in Westinghouse Science Competition and one undergraduate won the best BS senior thesis award in Materials Science Department. Another undergraduate is currently doing research at Los Alamos National Lab, taking a term off from MIT. Our research during this past year has resulted in several research publications, many invited talks and two patents. The PI received the IBM Research Partnership Award for the third year in a row. He also participated in the National Research Council's survey of research thrust for the next 10 years in the area of magnetism in USA. The PI has been invited by Joseph Fourier University (France) to be a distinguished visiting professor in their university.
MOSSBAUER SPECTROSCOPY LABORATORY
The Mossbauer Spectroscopy laboratory continued to operate as a user facility under the direction of Dr. Georgia Papaefthymiou.
Primary investigations included studies of: (a) large iron complexes of nanometer-size dimensions that delineate the molecular/solid state boundary; (b) nanoscale magnetic particles on silica or plolymeric supports, leading to the development of advanced nanocomposite materials for magnetic and catalytic applications; and (c) nanostructured iron-palladium alloy films developed as hydrogen separation membranes in high temperature chemical reactors.
The results were presented at the "International Conference for the Applications of the Mossbauer Effect" held in Rio de Janeiro, Brazil in September of 1997. Various aspects of this research were published in the Journal of Applied Physics, the Journal of Magnetism and Magnetic Materials and in Hyperfine Interactions.
During the past year, FBML resources were consolidated into one building. We now boast an upgraded space for two 750 MHz NMR magnets, as well as space for the wide bore 750 MHz magnet to be built under Dr. Yukikazu Iwasa.
Newly renovated facilities have recently been provided for Prof. Cory's research group, including a wet lab and a computer lab.
Extensive renovation is taking place on the second floor to prepare office space for Professor Jacquelyn Yanch, Prof. David Cory and their students.
Professors Keith Nelson and Andrei Tokmakoff of the Department of Chemistry have moved into temporary lab space on the first floor pending completion of their permanent laser lab facility in the Chemistry Department. Additional Chemistry faculty are also considering moving to the Magnet Lab while their current lab space undergoes renovation.
EDUCATION AND PERSONNEL
The Laboratory contributes to undergraduate education by participation in the Undergraduate Research Opportunities Program (UROP), a program that encourages and supports research-based intellectual collaborations of MIT undergraduates with Institute faculty and research staff. In addition, the laboratory has 25 full-time graduate and 15 postdoctoral students performing research.
For several years now, we have been pursuing the development of an Imaging Center here at the Magnet Lab. These plans are being revised in conjunction with the Harvard/MIT HST program.
Once construction is complete on the second floor magnet hall, instruments currently housed on the fourth and fifth floors will be relocated in order to create a comprehensive "Center for Magnetic Resonance."
A new classroom is being designed to replace one lost to construction of office space on the second floor. Work is scheduled to begin in early 1999.
Robert G. Griffin
MIT Reports to the President 1997-98