CSU Los Angeles -- October 15, 2003

Work by Cal State L.A.'s Chemistry Professor Featured in this Week's Science Magazine

Chemistry research by Matthias Selke, associate professor of chemistry at California State University, Los Angeles, is featured in this week's issue of Science.

The study, "Phosphadioxirane: A Peroxide from an Ortho-Substituted Arylphosphine and Singlet Dioxygen," is the result of Selke's work, conducted with post-doctoral student Ruomei Gao, graduate students David G. Ho and Ha-Yong Chung, and undergraduate Jeff Celaje, since 2001. The issue's Perspective by Alexander Greer, Department of Chemistry and Graduate Center, CUNY/Brooklyn College, provides commentary on the study.

Oxygen exists in air as O2, the dioxygen molecule. The reaction of the dioxygen molecule with a class of organic phosphorous compounds called phosphines is one of the better known reactions in all of chemistry. The primary adduct has never been observed or isolated.

The team of chemists used a higher energy form of dioxygen, singlet dioxygen, which allowed them to carry out reactions at very low temperature (- 80 C). The singlet dioxygen molecule is reactive enough to accomplish this type of chemistry at extremely low temperatures.

Selke's team was able to observe the primary adduct between the phosphine and singlet oxygen by nuclear magnetic resonance spectroscopy, and establish its structure.

"There had been a fair amount of speculation how the O2 is bound to the phosphorous when they initially react, and we established that it is in the form of a triangle, with each oxygen atom forming a bond to the phosphorus atom," said Selke.

As noted in Greer's commentary, until the 1970s, scientists believed that compounds containing O2 in such a triangle couldn't exist. Later, says Selke, it was discovered that it was indeed possible for a carbon atom to be connected to O2 in this fashion. This compound, called dimethyldioxirane is now widely used as a reagent for oxidation reactions. Since then, researchers have been searching for compounds where the O2 is bound in a triangle to other atoms such as phosphorus, sulfur or nitrogen.

"Until our work," Selke continues, "all attempts were unsuccessful. Our phosphine worked because we designed the overall molecule to block, or at least slow down, the unwanted reactions that would destroy the compound.

"We also found that our compound can transfer one of the oxygen atoms to certain other organic molecules. This is very useful because the molecule can therefore be used as an oxidant and/or to study how such processes occur. One of the reasons that has precluded observations of compounds like ours is that usually they are so reactive that you can never observe them even at low temperature. Slowing this reactivity down, and possibly using it in a controlled fashion, is a desirable goal both to understand how oxidation processes occur and to make reagents that can do controlled oxidations."

Contact: Carol Selkin, Media Relations Director (323) 343-3044


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