Fourth Annual Maria Goeppert Mayer Symposium

UNIVERSITY OF CALIFORNIA, SAN DIEGO -- More than 100 people attended the Fourth Annual Maria Goeppert Mayer Symposium held here on March 6. "That makes this the best-attended of the series," said co-organizers Kim Baldridge, Senior Principal Scientist at SDSC and Adjunct Associate Professor of Chemistry in the Department of Chemistry and Biochemistry, and Tammy Dwyer, Associate Professor of Chemistry at the University of San Diego.

In addition to four invited speakers, the symposium featured over twenty posters presented by fifteen different research groups representing universities and research institutions from UC Santa Barbara to Arizona State University.

The symposium, originated by Baldridge, is organized each year at UC San Diego to honor the work of Maria Goeppert Mayer (1906-1972), who was awarded the Nobel Prize in physics in 1963 while a professor at UCSD. The conference commemorates her role as a leading scholar and her unflagging pursuit of excellence in science, broadly defined. This year's symposium was sponsored by SDSC and the UCSD Department of Chemistry and Biochemistry, and also by the National Biomedical Computational Resource.

As has become traditional the invited symposium speakers came from different schools and departments. "What links their work is its interdisciplinary cast," according to Baldridge. "In each case, speakers tell us not only about their own investigations but also about the connections their studies have to the major scientific issues of our time. The presence of these larger connections tends to unite often disparate studies and set listeners thinking." Baldridge reflects, "Maria Mayer was a broad-thinking pioneer who did not let the conventional boundaries in the physical sciences inhibit her pursuits. As such, her work connected together and impacted on many disciplines. The goal and result of the symposium is in harmony with this unconstrained view."

Clathrates and Climate
The first speaker was Miriam Kastner, Professor of Geophysics at the Scripps Institution of Oceanography (SIO), who has been studying the frozen gas hydrates, called clathrates, that are found on the ocean bottom and in the sediment just below it, along continental margins.. First noted by Sir Humphrey Davy in 1810, their significance and omnipresence was revealed by Roger Revelle and others as the science of oceanography was pursued over the postwar decades.

Methyl hydrate, the most common clathrate, is a form of ice crystal lattice consisting of "cages" of water with "guest molecules" of methane inside. Kastner and her associates at SIO have worked for a number of years to clarify the full phase diagrams of the clathrates, which are the largest component of the shallow geosphere, with a worldwide carbon mass of 10 Gigatonnes--more than oil, gas, peat, coal, and other carbon-dominated components.

Kastner discussed what various global warming scenarios might mean in terms of destabilization and decomposition of the clathrates, which would send methane and other greenhouse gases bubbling up through the ocean and into the atmosphere. Such events have happened when landslides on the continental margins destabilize the local ices, but a worldwide occurrence of destabilization could have serious climatic consequences, depending upon how fast the release occurred. According to Kastner, the clathrates, which might seem like minor oceanic constituents, nevertheless have the potential to exert great leverage on the earth's atmosphere, owing simply to their sheer volume.

Artificial Photosynthesis and Nanotechnology
The second speaker was Ana Moore, Associate Professor in the Department of Chemistry and Biochemistry at Arizona State University (ASU). Moore is part of a large, multidisciplinary team gathered in the ASU Center for the Study of Early Events in Photosynthesis, whose ultimate scientific objective is elucidation of the basic principles governing the biochemical and biophysical processes of photosynthetic energy storage.

As Moore explained, their objective is being realized through investigation of the most significant early events of photosynthesis in plant and bacterial systems; specific studies include light absorption and excitation transfer in photosynthetic antennas, structure and assembly of photosynthetic complexes, pigment-protein interactions, and the mechanisms of biological electron transfer reactions. In particular, Moore's group is exploring artificial, biomimetic photosynthetic systems to learn more about the natural process and to find applications of the clever photochemistry of natural photosynthesis in artificial systems. As she put it, "Nature is not in a hurry, but humanity is."

Her group has experimented with porphyrin-carotenoid-quinone systems like those found in plant photosynthetic reaction centers, and most recently they have explored carotenoporphyrin-fullerene triads, some of which can produce ATP better than nature's own chloroplasts. Such complexes can be incorporated into a variety of devices now being developed under the rubric of "nanotechnology"--small energy-capture and transfer systems expected to have wide application in medicine, electronics, and other areas.

Electrostatics of DNA and Long Polymers in Solvent
The next speaker was Andrea Liu, Assistant Professor in the UCLA Department of Chemistry and Biochemistry, where she is the recipient of an NSF Early Career Development Award. Liu's degrees are in physics and her interests encompass the theoretical chemistry and statistical mechanics of complex fluids. With one of her students, Bae-Yuen Ha, Liu has recently asked the question: why do like-charged rods attract?

She notes that DNA, which is a strong acid (with negative charge every 1.7 angstroms along the helix), condenses into bundles of rods, some with toroidal loops, in vitro. The same behavior is observed for F-actin and the FD virus and, indeed, other acidic long polymers. Why do the rods bunch up, and what governs the size of the bundles? Both Poisson-Boltzmann statistics and Debye-Hueckel theory predict that the repulsive force between like-charged rods would keep them apart, so what is observed is counterintuitive. But, as Liu found, the mean behavior predicted by theory can be overwhelmed by the particular, complex, geometrical and electrostatic interactions of real life. As a theoretical problem, Liu and Ha found that attraction depends first of all on the Bjerrum length, the distance at which the electrostatic energy in a system is of the order of the thermal energy. For a system of two rods of infinite length in which the counterions modify the local charge only, the fluctuations in charge between two rods become correlated, resulting in a short-range attraction. The repulsive force depends on the average charge along a rod, but the attraction depends on the variance in that charge.

Liu and Ha extended the theoretical problem, which can be solved analytically, to cover many finite-length rods, and they studied the kinetics of bundle formation. The size of the bundles in any given solution is limited by the angles at which a rod bundle and an approaching rod interact. Thus, Liu has shown, careful attention to the detailed physics of such a problem can explain what initially seems so counterintuitive.

New Marine Siderophores: How Oceanic Bacteria Find Iron
The final speaker was Alison Butler, Professor of Chemistry at UC Santa Barbara. Her research interests are in the area of bioinorganic chemistry and metallobiochemistry, with an emphasis on the roles of metal ions in the catalytic activity of metalloenzymes.

It is well known that although the oceans are rich in a variety of metal ions, they are relatively poor in iron, an essential metal for life. Experiments distributing iron chloride dust over the ocean surface result in enormous blooms of bacteria, algae, and phytoplankton, supporting the notion that microorganism populations in the open ocean are limited by access to iron. Nonetheless, these species persist in this iron-poor environment. How then, Butler asks, do marine microorganisms acquire the transition metal ions they need for survival?

Nature has answered this question in an interesting but perplexing way. Rather than evolving new mechanisms that use the abundant metals in the ocean, these organisms have developed ways to prepare molecular complexes (siderophores) that are extremely selective for binding and concentrating iron. Several siderophores have been identified from natural marine sources. Butler notes that these molecules seem species-specific and may even form the basis for a chemotaxonomy for microbes. This species specificity raises even more questions. How do the organisms recover the secreted molecules from the seawater? Do the siderophores remain associated with the membranes of the organism in some species-specific manner? How can organisms recognize their siderophores? How do the organisms get the iron back out of the siderophore without wasting all of the energy it took to make the molecules and sequester the ions? Butler has made great strides toward answering a number of these questions using the techniques of bioinorganic chemistry and she is now looking to ecological and technological implications of her results.

After the invited talks, participants were served lunch as they wandered among the poster presentations in the SDSC Auditorium until late in the afternoon. "Every poster received a lot of interest," Baldridge said, "and many were connected to the topics of the talks." She and co-organizer Dwyer are predicting a still larger turnout at the fifth symposium next year. "Our hope is that we've launched a tradition that will continue to commemorate Mayer and be a credit to science in the community for a long time to come," Baldridge said.