Program Information

"Chemical Reactivity: In The Laboratory, Biology, and the Environment"

Location:

Lagerquist Hall, Mary Baker-Russell Music Building, Pacific Lutheran University
(Lagerquist is located in the MBR music building. Campus map and directions.)

Date and Time:

1:00 to 5:30 p.m., Saturday, November 9th, 2002

Speakers:

Professor Kristie A. Boering

Departments of Chemistry and of Earth and Planetary Science, University of California, Berkeley
http://www.cchem.berkeley.edu/~kabgrp/

Unusual kinetic isotope effects: From the molecular to the global scale

Abstract: Unusual kinetic isotope effects which cannot be explained by standard physical chemical treatments have been shown to influence the isotopic compositions of a variety of oxygen-containing compounds in Earth's atmosphere, such as ozone and stratospheric carbon dioxide. Recent theory and experiments investigating the nature of these isotope effects on a molecular level and their application to studies of stratospheric ozone depletion and global climate change from decadal to millennial time scales will be presented.

Professor James Collman

George A. and Hilda M. Daubert Professor of Chemistry
Department of Chemistry, Stanford University
http://www.stanford.edu/group/collman/

Functional analogs of the dioxygen reducing site in Cytochrome C Oxidase: The role of Copper-B

Abstract: Cytochrome c oxidase (CcO) is a multi-metallic enzyme that is responsible for the exothermic 4-electron reductionof oxygen during respiration. CcO contains at its active site: a myoglobin-like heme-a3 with a three-coordinate copper (CuB) on its distal face. Two other electron transfer centers, heme-a, and dimeric CuA provide the two additional electrons required to reduce oxygen. We have designed and synthesized porphyrin/copper complexes that closely resemble the active site of CcO. When adsorbed on an electrode, these synthetic analogs catalyze the 4-electron reduction of dioxygen to water without leaking partially reduced oxygen species: hydrogen peroxide, superoxide, and hydroxyl radicals. This electrocatalytic reaction takes place in water at pH 7 over the potential range of cytochrome c, which is the terminal electron source for CcO. A copper free analog also catalyzes the 4-electron reduction of oxygen. Thorough analysis of the differences in the electrocatalytic properties of the forms with and without Cu reveals the probable role of CuB in CcO during oxygen reduction. This distal copper suppresses release of cytotoxic superoxide and protects against inhibitors such as cyanide ion and carbon monoxide. Our kinetic analysis of these catalytic reactions shows that a hydroperoxide complex of Fe(III) develops before irreversible rupture of the O-O bond. In our system, as in CcO (according to dft calculations), this ferric hydroperoxo intermediate is formed in the turnover-determining step. This minimizes its steady-state concentration and hence the amount of this intermediate that can decompose with release of deleterious hydrogen peroxide. The possible role of a fifth electron source, a phenol, Try-244, that is found associated with CuB, will also be discussed. When our active site catalysts are dissolved in a lipid film on the electrode, the rate of electron transfer to the catalyst is slowed by diffusion of redox centers. Under such conditions where electron transfer becomes rate limiting (as it is in CcO) the copper-free catalyst no longer exhibits selective 4-e reduction of oxygen, but the iron-copper system is still an excellent mimic of CcO.

Professor David M. Golden

Mechanical Engineering Department, Stanford University
http://vonkarman.stanford.edu/tsd/Golden.html

Pressure dependent reactions for atmospheric and combustion models

Abstract: Reactions that are both temperature and pressure dependent are common. Many such reactions are of importance in understanding the chemistry of the atmosphere and/or of combustion. Often these reactions involve transformations with no intrinsic barriers. Rendering rate constants for these reactions into a form that can be used in complex models requires some knowledge of the potential energy surface, the mechanism of translational-vibrational energy transfer and master equation calculations. The reaction: HO + NO2 -> HONO2 is an important sink for the important HO radical in the atmosphere. However, it is now apparent that a second channel to form the much less stable HOONO exists. The ratio of these pathways as a function of pressure and temperature is an interesting example of the problem. The reaction: ClO + ClO -> ClOOCl is thought to be a crucial step in the formation of the Antarctic ozone “hole”. How well can we describe this process? The reaction HO + CO -> H + CO2 is the reaction that accounts for most of the heat release in combustion and is important in establishing HO concentrations in the atmosphere. This reaction has been studied over the temperature range 80 – 2000K and at various pressures with several different bath gases. Can we represent this data accurately? Finally, what do we mean by “accurately”? What is sufficient accuracy? When is perfection the enemy of good?

Professor John Brauman, 2002 Linus Pauling Medalist

J. G. Jackson-C. J. Wood Professor of Chemistry
Department of Chemistry, Stanford University
http://www.stanford.edu/dept/chemistry/faculty/brauman/

Reactivity and solvation in ionic reactions

Abstract: Simple correlations form the basis of much of our 'understanding' of chemical reactivity. Structural changes, including polar and steric effects are commonly invoked to explain chemical reactivity. In ionic reactions, however, these structural changes can also affect solvation.
We now have evidence that the solvation effects arising from these structural changes can be the major factor in the source of changes in reactivity. In particular much of the barrier that appears to arise in sterically hindered systems can be associated with solvent effects, rather than non-bonded repulsions.