Comment pubs.acs.org/est
Professor Einstein and the Quantum Mechanics
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during chloramination of drinking water. Just as predictive models removed the need for environmental chemists to measure octanol−water partition coefficients or Henry’s law constants, it is now possible to imagine a day when many of the constants that we carefully measure in the lab will be accessible with the click of a mouse. Despite the promise of molecular simulation, many environmental chemists still view these unfamiliar tools with skepticism. Some caution on the part of potential users is justified by failed attempts to apply them to complex systems when reaction mechanisms were incompletely understood. This is particularly true when multiple reaction pathways are possible or when heterogeneous reactions occur on mineral surfaces. As a result of these real and perceived limitations, many applications of these powerful tools still seem like glorified structure activity relationships in which a parameter like the energy of the highest occupied molecular orbital has replaced the Hammett coefficient. As algorithms improve and software increasingly becomes user-friendly, I expect to see more compelling uses of molecular models. Just as it should have been obvious to the experimental fluid mechanics researchers of 1960s that the heyday of the flume was over, the time when graduate students spend years measuring equilibrium or rate constants under simple laboratory conditions is coming to an end. I am hopeful that our liberation from these tedious exercises will open up opportunities to address complex problems that seem intractable today. For example, with a means of accurately predicting transformation rates in the troposphere, we should be able make more sensible recommendations about the hazards posed by the thousands of chemicals that are routinely released to the environment. An ability to simulate heterogeneous reactions could free us from the trial-and-error mentality that still dictates much of the current research on the design of catalysts and membranes. And simulations might help toxicologists realize the goal of eliminating the need for animal testing. There is a bright future ES&T’s budding Professor Einsteins. It is time for our quantum mechanics to lead the way.
side from being the son of the most famous scientist of the twentieth century, Hans Albert Einstein was a brilliant researcher in his own right. As vividly told in a new biography by Robert Ettema and Cornelia Mutel (ASCE Press, 2104), Einstein applied the latest research on turbulence to the complex problem of sediment resuspension and transport in flowing water bodies. Over the course of a career spanning four decades, he helped transform fluid mechanics from a discipline that relied upon empirical relationships to a modern science in which accurate predictions about complex natural phenomena could be made without resorting to laboratory experimentation. Although Einstein was not particularly interested in contaminants that might be present on those suspended sediments, I believe that his career is instructive to today’s environmental chemists. Einstein began his career as a doctoral student in Professor Eugen Meyer-Peter’s laboratory at the Swiss Federal Institute in Zurich. When he entered the research world in the early 1930s, his supervisors were responding to the need to predict water flow in complex systems through the construction of bigger and bigger flumes. During his tedious years measuring the movement of painted sand grains, Hans had an insight that set the stage for the rest of his career: he reasoned that it might be possible to circumvent empiricism by applying the tools of modern physics to describe the movement of particles in rivers. After completing his dissertation, Einstein moved to America where he helped lead a movement that modernized fluid mechanics. With new physicsbased models, researchers were free to dedicate their efforts to studying actual rivers and estuaries instead of tiny lab-scale models. Like the flume that Einstein and his students employed to test their predictions in the basement of my building at UC Berkeley, where he was a faculty member for 24 years, many of the state-of-the-art experimental facilities of the previous century are slowly rusting away or have been repurposed for research on other problems. I believe that environmental chemistry is poised to undergo a similar modernization. Starting about 10 years ago, chemists started to apply the latest developments in molecular simulations to predict chemical properties that previously had only had been accessible through experimentation. Early ab initio calculations provided researchers with parameters that could be used to predict phenomena such as the rates of dehalogenation of simple compounds on the surface of zerovalent iron and products of hydrocarbon combustion reactions. As computing power increased and algorithms for simulating large molecules and their solvation shells improved, it has become possible to accurately predict many important thermodynamic properties without ever entering a laboratory. For example, Li et al. (Environmental Science & Technology 2014, 48, 13808-13816; DOI: 10.1021/es504339r) recently predicted the rate of atmospheric oxidation of a family of short chain chlorinated parrafins for which analytical standards were not available. Similarly, Liu et al. (Environmental Science & Technology 2014, 48, 8653-8663; DOI: 10.1021/es500997e) used molecular simulations to gain new insights into the potential for different tertiary amines to serve as precursors for NDMA formation © 2015 American Chemical Society
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David L. Sedlak,* Editor-in-Chief AUTHOR INFORMATION
Corresponding Author
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[email protected]. Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS. The authors declare no competing financial interest. Published: February 20, 2015 2585
DOI: 10.1021/acs.est.5b00900 Environ. Sci. Technol. 2015, 49, 2585−2585
