The Unseen Beauty (and function) of Chiral Molecules
As Charissa notes, chirality, or the “handedness” of molecules, plays a major role in biology. Many molecules, from sugars to amino acids to odorants, are chiral molecules; they can exist as mirror images, known more formally by scientists as enantiomers or optical isomers. Take glucose, for instance. The chemical formula of glucose is C6H12O6. Enantiomers of glucose all share this formula, but differ structurally. The atoms in L-glucose and D-glucose are arranged differently, resulting in two molecules are mirror images of each other.
The concept of chirality comes up in the classroom quite frequently. Initially, it may be somewhat difficult for students of biology to see this structural difference. Using the hand example that Charissa mentioned, however, generally eliminates any confusion. Just like your right hand cannot be superimposed on your left hand, L-glucose cannot be superimposed on D-glucose. With that initial confusion resolved, students then typically move to another question. So what?
For living organisms, the function of enantiomers can differ dramatically. Naturally occurring glucose almost always is D-glucose. In fact, our cells cannot utilize L-glucose as an energy source. In the classroom, we can use this example to emphasize the specificity of enzymes, molecules that catalyze chemical reactions within our cells. When describing the specificity of enzymes, we often use the lock-and-key analogy. Enzymes interact with substrates in a very specific way, much like locks interact with keys. To use an analogy more related to chirality, however, let’s think about a pair of gloves. The glove designed for your right hand will not fit on your left hand. Similarly, L-glucose will not “fit” into the active site of an enzyme that has evolved to catalyze chemical reactions involving D-glucose.
The odorants mentioned by Charissa represent another fascinating example of the role enantiomers play in our daily lives. Let’s look at two examples. Spearmint and caraway plants both produce carvone (C10H14O). These plants, however, synthesize two different enantiomers of this compound. Evolution has resulted in two different biosynthetic pathways, which, in turn, produce molecules that are mirror images of each other. Moreover, the odor receptors in our olfactory system have evolved to differentiate between these molecules. As Charissa wrote, “One has the zing of mint, the other the earthiness of cumin.” In a similar fashion, our odor receptors can distinguish enantiomers of limonene (C10H16). To us, D-limonene smells like oranges, whereas L-limonene smells like lemons.
As we can see from these few examples, the “handedness” of molecules matters. Perhaps an image showing D-glucose and L-glucose does not have the same visual allure as a photograph of Edith Sitwell’s hand holding a chiral shell, but both images matter. Both images allow us to think more intently about structure and function, and about the beauty of our everyday experiences. I am sure that visitors to Chirality: Defiant Mirror Images (Charissa's exhibit) will appreciate the artistry of the included works. I hope they also will leave the exhibition with an appreciation of the biological importance of asymmetrical symmetry.
Charissa's Update: Chirality: Forms and Formalisms of Art-and-Science Hybrid
The Scottish physicist Lancelot Law Whyte (1896-1972) published an article titled “Chirality” in the art-sci-tech journal Leonardo in 1975. Whyte included a photograph of the poet and literary critic Edith Sitwell holding a helical shell. The shell in Sitwell’s hand has a dextral chiral form, meaning it has a right-handed coiling shape. It was the Whyte family Christmas card from 1958.
The word “chirality” comes from the Greek word kheir, meaning, “hand.” Human hands and feet are chiral: regardless of how you orient them, they resist superimposition. They are defiant forms that, while mirroring each other, refuse to overlap symmetrically.
Chirality is most frequently used in the sciences to describe the “handedness” of molecules, their organization in space as mirror images that cannot be superimposed on one another.
Like our hands, these molecular compounds are symmetrical mirror images of each other but if layered one atop the other, their relationship becomes asymmetrical.
Edibles, smells, and drugs provide examples of chirality. Take sugar, for example. We need sugar in our diet, but if we were to eat a mirror image of sugar, the same atoms arranged in the left-hand form, then we would go hungry. Food chemists have used this logic to develop zero-calorie artificial sweeteners. They sweeten your tea, but provide no nutrition or calories. Spearmint and the spice caraway are chiral molecules. One has the zing of mint, the other the earthiness of cumin. Certain drugs are chiral. Ibuprofen is a well-known chiral pain reliever, but in its non-superimposable mirror image it is deadly. One form may be helpful the other may be inactive or even toxic (http://www.rowland.harvard.edu/rjf/fischer/background.php.).
Chirality, simply put, is inspiring. I am fascinated by its possibility now in art and in the history of science within art: its potential as a new mode of form and formalism in contemporary art and the lively overlapping in Whyte’s article from forty years ago. It is intriguing to me that Whyte published a scientific essay in Leonardo, a journal with a large readership of artists, using a photograph of a shell in the hand of Edith Sitwell, a member of the mid-century London literati. In bringing these elements together – the scientific form of chirality, the photograph of Sitwell’s hand, and the art-sci-tech audience of Leonardo – Whyte forged new conceptual territory for all disciplines involved.
Whyte was part of a group of scientists, including Conrad Waddington, Joseph Needham, Joseph Woodger, J.D. Bernal, Dorothy Wrinch, Julian Huxley, Lancelot Hogben, et. al. in 1930s England who came together for assorted causes, scientific and political in nature. They gathered in various collective formations – The Theoretical Biology Club, Biotheoretical Gathering, The Tots and Quots – to advance a third-way for biology beyond the mechanism/vitalism debate and to forge an anti-fascist front against the rise of the Third Reich. Another one of their shared investments was the popularization of science: bringing science to a mass audience through accessible prose, tantalizing pictures, and modern art. Members of this group interacted with artists and architects of the London Bauhaus, a brief incarnation of the German design school in the middle of the 1930s in England which included Walter Gropius, László Moholy-Nagy, and György Kepes, among others.
In spring 2016 I will be doing archival research to tease out an “aesthetics of holism” in the London Bauhaus: how these scientists’ ideas about theoretical biology, politics, and art gelled alongside the integrated art-sci-tech design philosophies of members of the Bauhaus in mid-1930s England. For now, I am doing my own part in bringing these ideas to contemporary art in the twenty first century.
I am curating an exhibition, Chirality: Defiant Mirror Images, which opens October 24 at Gray Matters Gallery in Dallas, Texas. Artists Ellen Levy, Jeff Gibbons, Luke Harnden, Trent Straughan, Alan and Michael Fleming, and Steve Oscherwitz will be showing two-, three-, and four-dimensional work in this show. There will be instantiations of chirality in digital painting, interactive digital art, drawing, robotic art, and sculpture. This exhibition plays out the unique agency of chiral forms – their asymmetrical symmetry, how they look alike and act differently, and their ability to spin light out into space (or optical activity) – when introduced to the realm of art. Invoking “agency” in terms of the dynamics of chiral form, the exhibition sets in relief new models of form-making, individuation, and social action.
My goal in curating Chirality: Defiant Mirror Images is to refresh the formal language of art by introducing the concept of chirality. I hope to inject a mutational and living sense of form and formalism to the art world – that art is a matter of becoming and passing on rather than being and permanence.