Originally posted April 22, 2011
The portrait drawn in over 50 years of studying the colors of chemicals
April 05, 2011
1Publications of Harry B. Gray by color.
Harry Gray (who was my postdoctoral advisor and is Gretchen’s doctoral advisor) recently celebrated his 75th birthday. A couple of weeks ago the group threw him a big bash at Caltech’s faculty club. Much of the organization was arranged by Gretchen with some help from our good friend, Paul. From all that I have heard, the evening was an absolute success. Group alumni from all over the world came out for the party. I was disappointed not to be able to make the trip back to Pasadena. But, I was fortunate enough to be able to work on a little gift for Harry. Before I say any more about this gift, I wanted to write a little bit about Harry and try (really all I can hope to do is try) to put Harry’s career into perspective and attempt to describe what he has meant to the field of chemistry.
Shades of Gray
Harry is a tremendous story teller. In fact, he may be a better story teller than he is a chemist … which is saying something. Harry was recently interviewed for the Voices of Inorganic Series by Rich Eisenberg, who is, among other most impressive things (professor at Rochester, Editor-in-Chief of Inorganic Chemistry, titan of the field), a Gray-group alum. Harry starts off the interview with going into his passion for colors. He tells us about the things he was always curious about. Where do colors come from? What are the physics/chemistry that makes colors possible? Harry tells a fabulous story from his childhood about his first forays into the world of color chemistry. When he was about 12, Harry started to wonder what kind of dyes gave color to his mother’s clothing. Being ever the intrepid explorer, Harry wrote to a chemical company, under the guise of being a chemistry professor, and ordered some sulfuric and nitric acid to be sent to his home. Having fooled some salesmen, Harry proceeded to dissolve his mother’s shirts in acid in order to extract their dyes. I love this story so much. It really encapsulates my perceptions of him and his science: Harry is passionate about his curiosities and will not be contained by any constraints. Harry was also never much into discovering phenomena but was concerned with being able to describe why these phenomena occur (i.e. people already knew that Prussian Blue was blue – Harry wanted to know WHY it was blue). Also … Harry is very mischievous!
(I should note that studying the color of a chemical has much much more worth than satisfying one scientist’s curiosity. Chemical colors are often an indication of the types of reactions that they make possible. Chlorophyll makes photosynthesis possible because it is green. Your blood is red because oxygen is bound to hemoglobin. Now, color is not an absolute determinant of chemical reactivity. But understanding chemical colors can help us to understand reactivity. And, as Harry has shown, the keen scientist can use the colors of chemicals to manipulate molecules in some truly incredible ways.)
Golden Years
Harry started his academic career as a graduate student at Northwestern University (also where I did my PhD). Harry worked with Fred Basolo and Ralph Pearson, two of the scientists responsible developing the modern field of inorganic chemistry because they helped to develop an understanding of WHY inorganic reactions occur. (The reactions of inorganic chemicals are responsible for an enormous range of materials that affect our every day lives – plastics, pharmaceuticals, respiration, photosynthesis, and on and on ad infinitum. For a brief primer on inorganic chemistry with respect to metal-ligand complexes, see here.) Specifically, Harry worked on understanding very basic reactions of platinum complexes, most of which are a beautiful yellow or yellow-orange color. The work from the Basolo and Pearson groups on platinum chemistry was essential for explaining the “trans-effect”, a universal staple of undergraduate instruction of inorganic chemistry. The trans-effect encompasses a series of observations that allow us to predict how platinum (and other) compounds will react. The chemistry behind the trans-effect is responsible for the way cisplatin(one of the most widely used anti-cancer pharmaceuticals) reacts with DNA.
An image showing how the anti-cancer drug cisplatin disrupts DNA. The reaction that attaches cisplatin to DNA is controlled by the chemistry described by the trans-effect. Image Source
Copenhagen Blue
After his PhD at Northwestern, Harry went to Copenhagen to work with Carl Ballhausen in order to develop a model/theory that could describe metal-ligand bonding. For the time, crystal field theory was state-of-the-art. This theory held that the shape of a metal complex plays a major role in determining multiple properties of that complex (bonding, molecular vibrations, and color). The problem with this theory is that, while it very generally described properties of inorganic compounds, it didn’t always give realistic predictions of these properties. Since Harry wouldn’t stand for not accurately knowing where a molecule’s color came from, he decided that something must be done about this. Harry and Carl’s work took crystal field theory and tweaked it with molecular orbital theory spawning a new approach called ligand-field theory. (Lots of theory … I know). One of the first papers they wrote together helped to describe the brilliant blue color of the vanadyl ion (VO2+). (It seemed all too appropriate that this work was carried out in Copenhagen as the term Copenhagen blue refers to a bluish-Gray color.)
The mineral cavansite [Ca(VO)Si4O10 4H2O] gets its blue color from the vandal ion, which Harry helped to explain. Image Source
(Non)Innocent Years
Harry started at his first independent position, Columbia University, after leaving Copenhagen. In the short time that he was at Columbia (during which he also held a joint appointment at the Rockefeller University) most of his group’s work seemed to focus on metal complexes with sulfur-based ligands. Depending on the metal used and the specific type of ligand attached to the metal, these complexes are capable of having a rainbows-worth of colors. Red nickel complexes. Orange/Yellow gold complexes. Green rhenium complexes. Blue/violet vanadium complexes. Harry’s work explained the chemistry that produced these colors.
In a show of how research is cyclical, these molecules (that Harry worked with in the 1960s and which people before him had also worked with) have recently come back in vogue in chemical research. These types of ligands can have profound effects on enhancing the types of chemistry that the molecules can perform. Because of this, they are classified as non-innocent. There are a lot of current studies that are looking to exploit ligand non-innocence to perform all sorts of new reactions (H2 production, CO2 conversion, etc.).
Harry B. Gray – there is nothing about this man that is innocent.
Busy as a Beaver
Harry moved from Columbia to Caltech in the late 1960s. At this point in his career Harry was really able to comfortably spread his wings. There is really no way I can accurately describe all of Harry’s work while at Caltech (or really at his other stops either). But I do want to mention two different strains of research that have been part of his work for several decades now: bioinorganic chemistry and solar energy conversion.
Blue Blood
Along with Stephen Lippard and Richard Holm, Harry is generally credited with founding the field of bioinorganic chemistry (the study of the role that metals play in biology). Harry was first edged into this pursuit by colleagues in New York at the Rockefeller University. Harry broke into the field by studying the blue blood of lobsters (which is due to a protein called hemerythrin) and the blue copper protein, azurin. One of my favorite stories about the group at this time is that they would harvest their own hemerythrin and then used their research as an excuse to have a lobster-bake! Harry eventually shifted focus a little more towards heme proteins (cytochrome c, myoglobin, cytochrome P450) which are basically red in color. Along the way, Harry’s research has taught us all the power of direct questioning, good observation, and creative problem-solving.
The study of blue copper proteins have been a particularly fruitful endeavor for Harry. Hemerythrin and laccase are examples of how copper, while in a protein, can interact with oxygen in lots of different ways. Hemerythrin is the oxygen carrier in the blood of shellfish. Laccase is an enzyme that can convert oxygen into water. And azurin, which has been a work-horse of a protein for the group, has evolved for the sole purpose of shuttling electrons back and forth from one protein to another. Harry’s work on azurin highlights the fact that proteins can encapsulate metals within their interiors in very uncomfortable ways. But, this strain is what allows proteins to do such interesting things with metals.
If Harry’s formative years in bioinorganic were dominated by copper proteins, his most recent research has focused more on iron containing heme proteins. Cytochrome c is another ubiquitous electron transfer protein. Myoglobin delivers oxygen to our muscles. Cytochrome P450 enzymes are responsible for digesting most of the pharmaceuticals that we ingest. All of these different functionalities arise from the multiple ways that a protein can wrap itself around a single iron heme molecule. Harry’s research has pushed to understand the very precise chemistry of the iron heme in each of these examples.
The iron heme is capable of performing a vast array of different chemistries – all dependent upon the structure of the protein surrounding it.Image Source
Harry’s most important work in this field has to do with how metal-containing proteins carry electrons. Importantly his research continues to show us how electrons can move down the length of a protein from one spot to another. This science is vitally important for our understanding of how photosynthesis works. One process that occurs during photosynthesis requires an electron move from one spot on a protein to another. And the distance that this electron must travel, by most accounts, seems utterly unreasonable. Yet, the electron can move really rapidly over this distance. Using the protein azurin as a template, Harry’s group showed how specific protein structures can make electrons move really fast. And, to make all of these studies possible Harry exploited his knowledge of colors.
Blinded by the Light
One last note about Harry’s research. Recently, Harry has involved himself in a big push coming out of Caltech to develop cheap solar fuels. While some of this research may seem new, Harry has been studying photoinduced chemistry for a long time. In the late 1960s and early 1970s the group studied how the energy from light can displace a ligand from a metal, making the metal more reactive. In the 1980s a lot of focus was placed on the use of blue and green rhodium dimer compounds for the purpose of storing solar energy. In the late 80s and early 90s, the group worked to study the photochemistry of dimeric platinum complexes (yellow compounds that glow a gorgeous green color). And, the recent push is to design and understand materials made from cheap chemicals (cobalt, iron, and silicon instead the state-of-the-art platinum) that can be used to convert water into oxygen and hydrogen.
The Gray Scale
Harry has obviously had a huge impact on the course of science. His ability to excel while working on a very broad array of topics is most impressive. (Harry can be likened to the fox in Isaiah Berlin’s parable: “The Hedgehog and the Fox”. The role of the chemist as a fox has been discussed recently on the blogs In the Pipeline and The Curious Wavefuncion.) Harry has trained countless scientists, many of whom have had their own impressive careers. These inorganic chemists (my academic family) have made our field what it is today because of the way that Harry trained them. Mark Wrighton and Holden Thorpe have become chancellors at their respective institutions (Washington University in St. Louis and the University of North Carolina). Giants in the field of chemistry have come through Harry’s lab at one point or another: Rich Eisenberg, Ed Steifel, Mark Wrighton, Ed Solomon, Nate Lewis, Charles Lieber, Dan Nocera and others that I am sure I am neglecting. Harry has also trained the scientists whose research I want my own work to most emulate: Thomas Meade, Chris Chang, Yi Lu, Ivan Dmochowski, and Akif Tezcan.
A Career in Colors
For Harry’s gift, I wanted to put together something that represented his presence in the field, his cultivation of scientists, and his love of colors. So, I decided to put together a collage of Harry’s publication with each paper represented by a color of a chemical that was important to the work.
It is striking to see the breadth of topics Harry covered in this image. It’s also amazing to see how his research has progressed over the years. You see the yellows of the platinum complexes early on. You can see when Harry started studying the blue copper proteins in the 1970s. And you can see how his research focus in bioinorganic chemistry shifted from these blue copper proteins to the red heme containing proteins.
And he’s still going. Pushing science. Learning new things. Telling new stories. Harry’s most sage advice to young scientists is: “Don’t peak too soon!” I am sure that there is a lot more really exciting work to come out of Harry’s lab, and I am very much looking forward to continuing to learn chemistry from this true master of the field.
Thanks Harry
Cheers
-mrh