Henry Eyring

American chemist

• Born: February 20, 1901; Colonia Juárez, Mexico
• Died: December 26, 1981; Salt Lake City, Utah

Twentieth-century chemist Henry Eyring helped develop the transition state theory of chemical reactions, an important contribution in the field of chemical kinetics, which deals with the speed of chemical reactions.

Primary field: Chemistry

Specialties: Physical chemistry; kinetics

Early Life

Born in the town of Colonia Juárez in Mexico on February 20, 1901, Henry Eyring was raised in a small but prosperous Mormon community not far from the United States border. His family had settled in the region about twenty years earlier, after leaving Utah to escape anti-Mormon sentiment. Although Eyring had a happy childhood, supported by his father’s career as a cattle rancher, the Mexican Revolution began the year he was born, and by 1912, his family joined nearly five thousand other Mormons from the area in relocating to El Paso, Texas, in an attempt to flee the violence. His family struggled in Texas until his father was able to buy land near Pima, Arizona. Despite the constant relocations and laborious tasks on the family farm, Eyring excelled in school, particularly in mathematics and science. In 1919, he began to study mining engineering at the University of Arizona, working odd jobs in his free time in order to send money home to his family.

Although Eyring had intended to pursue a career in mining, a summer job working in a mine exposed him to discouraging working conditions and he gave up the idea of a mining career. He opted for graduate school instead, earning a degree in metallurgy in 1924. Eyring moved to Berkeley, California in order to complete his PhD in chemistry at the University of California in 1927. At Berkeley, his interests and career finally matched up. He began to study the ionization of gases and the decomposition of certain chemicals in solvents. From here, his specialty in chemical kinetics emerged. Fellowships and teaching appointments afforded him enough money to support himself and his family while still pursuing serious scientific study. At the same time, Eyring was finding that his religious beliefs as a Mormon, although unpopular with some of his colleagues, were actually a fundamental aspect of his motivation and scientific curiosity. He began publishing actively in both religious and scientific scholarship as his career gained momentum in the 1930s.

Life’s Work

In 1929, Eyring temporarily relocated to Berlin, where he worked with Michael Polanyi, another successful chemist interested in chemical kinetics. Broadly speaking, the two were interested in studying the ways that temperature, catalysts, and other factors influenced chemical reaction rates. Eyring and Polanyi focused much of their work on reaction rates involving hydrogen, but their goal was not limited to any one chemical, and they intended to calculate a formula that could predict the role temperature played in all reaction rates. Although neither Eyring nor Polanyi would complete their research while together, the question became a defining one for both of their careers.

In 1930, Eyring returned to Berkeley to both continue his work and present some of his ideas to an American audience. He had begun, at this time, to make some basic predictions about hydrogen reactions that went against contemporary understandings of chemistry but ultimately proved to be true. These predictions, particularly the prediction that hydrogen and fluorine and would not react while at room temperature, attracted the attention of a leading chemist working at Princeton, and Eyring was offered a research position at the university. He and his wife, Mildred Bennion, relocated to New Jersey, where they remained for the next fifteen years.

While at Princeton, Eyring saw the most significant theories and research of his life come to fruition. His work focused on surface chemistry, the study of the point at which two chemically uniform materials interact with one another. In 1935, Eyring played a primary role in developing transition state theory. A transition state is the moment of highest energy in a chemical reaction. It is also the state at which colliding reactants form products. By looking at transition states, Eyring hoped to find constants across different types of reaction rates, a goal that he never accomplished. He found the complexity of transition states to be enormous and subject to seemingly endless thermodynamic influences. This may have been one of the reasons the Journal of Chemical Physics rejected Eyring’s first paper. However, Eyring was able to make two significant contributions. First, he realized that, even if reactants and products were not in a state of chemical equilibrium, they would still be in a state of quasi-equilibrium. This means that, even if the products are removed from the reaction, the flow of the reaction will continue.

From this realization, Eyring was able to write the Eyring equation (sometimes called the Eyring–Polanyi equation), a method of determining the exact influence of temperature on reaction rates. To complete this equation, a chemical reaction is repeated several times at different temperatures. The information from the reaction is then inserted into a formula based on a number of constants, including the Boltzmann constant, Planck’s constant, and the gas constant.

Eyring’s equation became an important working tool for chemists interpreting changes in the reaction rates of their experiments. Eyring’s own interests, however, remained broad, and he took advantage of his time at Princeton to work on a number of other issues, including the diffusion and viscosity of liquids. In 1944, Princeton became home to the Textile Research Institute, and Eyring conducted further work on the mechanical applications of different textiles. During this time, he and his wife raised three sons.

In 1946, the University of Utah approached Eyring and asked him to serve as dean of its graduate school. By this time, Eyring was not only a successful research scientist, but also a widely published author on religion and the intersection between spiritual questions and the natural sciences. He accepted the position. During his years at the University of Utah, Eyring was awarded the National Medal of Science (1966), and served as President of the American Chemical Society (1963). In the later years of his life, Eyring was known as much for his role in religious debate (both within and outside of the Mormon community) as he was for his research interests. He was still actively researching contemporary problems in chemistry when he died of cancer in 1981.

Impact

Transition state theory has perhaps been of greatest use to scientists studying the effects enzymes have on chemical reactions. When certain enzymes are present in biochemical reactions, they serve as a catalyst, and the transition state required for a reaction becomes even lower than it already was.

Prior to the research done by Eyring and his colleagues, the incredibly quick catalytic cycle in which enzymes affect biochemical reactions was difficult to understand in a broad sense, let alone to predict. Eyring’s ideas led to a greater understanding of the role of enzymes in chemical reactions, including the discovery that enzymes serve to regularize and stabilize the transition states of reactions.

There are a large number of practical applications for these ideas in modern science. The creation of HIV-1 protease inhibitors is perhaps the most widely known. By creating an enzyme catalyst responsive to the specific energies needed for the HIV virus to affect the human body, scientists have been able to create the most common and powerful medicine used in combating the major world health crisis of AIDS.

Bibliography

Eyring, Henry J. Mormon Scientist: The Life and Faith of Henry Eyring. Salt Lake City: Desert, 2008. Print. Biography of Eyring, written by his grandson. Focuses on the intersection of his religious faith and his scientific work. Includes detailed personal and autobiographical information. Illustrations, index.

Houston, Paul L. Chemical Kinetics and Reaction Dynamics. Mineola, NY: Dover, 2006. Print. Reviews the contemporary understanding of chemical kinetics, including many theories and methodologies directly related to Eyring’s work. Illustrations, bibliography, index.

Pilling, Michael J., and Paul W. Seakins. Reaction Kinetics. Oxford: Oxford UP, 1996. Print. Presents an introduction to the role that kinetics plays in the modern understanding of chemistry, with an emphasis on Eyring’s contribution to the field. Illustrations, bibliography, index.

Sole´, Ricard V. Phase Transitions. Princeton: Princeton UP, 2011. Print. Explains transition states as both a mathematical and chemical process, with an exploration of how theories of transition states relate to a broad range of other disciplines. Illustrations, bibliography, index.