The sign that many disciplines share roots in chemistry is often a freehand curve of the potential function for a reaction, quickly drawn by the speaker, whether she or he is a biologist, mathematician, physicist, biochemist, or chemist. Examples of such curves were both the symbol and the subject for the Second Annual Maria Goeppert-Mayer Symposium on Chemistry, held March 8 at UCSD/SDSC. The symposium commemorates Maria Goeppert-Mayer's role as a leading scholar and her unflagging pursuit of excellence in science, and the four featured speakers focused again and again on the potential function as they discussed the ways in which their current research is interwoven with fundamental ideas in chemistry.

Kim Baldridge, principal scientist at SDSC, who has just finished a year as an NSF-sponsored visiting assistant professor in the UCSD Chemistry Department, founded the symposium last year and has continued as its organizer this year. More than 70 participants from UCSD and universities in Southern California attended.
"Our aim in setting up this symposium has been to honor the ability of the patient worker to capture the specific and particular, the tension between noise and signal, symmetry and asymmetry, order and disorder, that can open up some of the hardest problems to solution by means of a metadisciplinary approach," Baldridge says. "For me, and for most of the participants, this symposium has been a welcome exercise in interdisciplinary synergy." A poster session featuring work by 20 groups followed the morning's speaker session.

When Disorder Creates Order: Tuning in to Noise
The first speaker was Katja Lindenberg, UCSD professor of chemistry and associate director of the Institute for Nonlinear Studies. Lindenberg's title was borrowed from an article in Physics Today for March 1996 ("Tuning in to Noise," by Adi R. Bulsara and Luca Gammaitoni, pp. 39-45).

Lindenberg reviewed the statistical properties of noise. Although noise is defined as something undesirable, there are systems in which it is absolutely necessary. Such systems exhibit stochastic resonance or may be subject to noise-induced currents. Examples occur in DNA denaturation and in diffusion-limited chemical reactions. Correctly managed, Lindenberg concluded, noise can be the lever in creating order, or a kind of substrate upon which order is constructed, "not unwanted or undesired at all."

Randomness and Order in Amorphous and Crystalline Materials
The second speaker was Frances Hellman, a professor in the UCSD Physics Department. In her talk, Hellman noted that amorphousness may not be quite random, and crystalline may not be perfectly ordered. Hellman described a regime of vapor deposition growth which is proving important in the development of thin films for magneto-optic recording processes.
In this regime, it is possible to balance the depositional forces to control the texture of the growing film surface in such a way that the direction of magnetization can lie out of the plane of the film. To achieve this kind of control, it is necessary to recognize, first, that chemical vapor deposition cannot be automatically assumed to be producing a small sample identical to the original bulk material and, second, to distinguish the various geometries of order.

Ab Initio Energetics, Kinetics, and Dynamics of Gaseous and Gas Surface Reactions
The third speaker, Emily Carter, professor of chemistry at UCLA, discussed the way in which various computational techniques were used to determine how hydrogen is desorbed from the surface of silicon wafers during etching by hydrofluoric acid. The computational techniques ranged from ab initio (first-principles) calculations that take into account all interactions among the electrons in a system (such as a cluster of silicon atoms) to a Monte Carlo code that treats the kinetics of absorption and desorption statistically.
They enabled Carter's group to discover that hydrogen absorption onto a silicon surface was occuring along one energetic pathway, while desorption was accessing quite another pathway, and that the whole was therefore a nonequilibrium system in which desorption is catalyzed by small defects in the silicon crystal structure. The work enabled the group to reject several mechanisms proposed to explain the laboratory observations, and, as Carter pointed out, it was close attention to the sensitivity of the computational methods to ambiguities that proved fruitful.

Dimer-Selective Nuclear Receptor Ligands: Retinoid X Receptor Agonists and Antagonists
The fourth speaker was Stacie Canan Koch of the medicinal chemistry research program at Ligand Pharmaceuticals in San Diego. Koch described her laboratory's efforts to discover novel compounds with retinoid activity. The group has developed several classes of retinoid X receptor (RXR) active analogues. These include oxime compounds related to the RXR-selective retinoid Targretin (reg. TM of Ligand Pharmaceuticals) and novel 9-cis-retinoic acid analogues.

Many display potent activation of the RSRs and virtually complete receptor selectivity. RXR agonists can act as highly effective and benign chemopreventive agents in the NMU rat mammary carcinoma model. Other analogues have activities ranging from RXR agonist or partial agonist to RXR homodimer antagonist. She discussed the role of substituents and geometric isomers in imparting RXR activity in each of the series and presented selective syntheses, structural determinations, and biological activities of the analogues.
Copyright 1997 SDSCwire.