Arbor Dianae

Transferring Electrons for Work or Pleasure

In addition to his well-known books on neurology such as An Anthropologist on Mars, Oliver Sacks wrote an engaging memoir of his childhood and his love of chemistry in his formative years. Not only does it describe part of his own own intellectual development, but Uncle Tungsten, Memories of a Chemical Childhood offers one of the most accessible histories of chemistry ever written, providing fascinating insights into the intellectual developments of an entire field of study. Students in John Bullock’s Foundations of Physical Science used one particular chapter out of this book as an entry to the study of magnetism, electricity, and batteries. In it Sacks describes his own experiences in reproducing the metallic “trees” discovered by alchemists. For example, placing copper wire in a solution of silver nitrate, would result in “shining, almost fractal, arborescent growth” of metallic silver on the wire (see above).

These changes result from a simple oxidation-reduction (redox) reaction in which electrons are transferred from dissolved silver ions to metallic copper. Such redox reactions are the source of the electric current provided by all batteries and fuel cells (and the electron transport chain). As part of the investigation of these topics, students used readily available materials such as aluminum cans and copper wire to construct simple electrochemical cells. Pictured below, students hook two such cells together to form a battery with a potential of about 3 volts; here they are using it to power a dc motor.

Footnote: In Uncle Tungsten, Oliver Sacks explains his peculiar use of footnotes as a sort homage to Dmitri Mendeleev, the nineteenth-century Russian chemist who, being unable to resist the temptation to include seemingly endless examples of tangential materials in his texts, used them promiscuously. Sacks characteristically included the following note to provide some explanation for the names of the metallic trees he was so fond of:

“These names for metallic trees came from the alchemical notion of the correspondence between the sun, the moon, and the five (known) planets with the seven metals of antiquity. Thus gold stood for the sun, silver for the moon (and the moon goddess, Diana), mercury for Mercury, copper for Venus, iron for Mars, tin for Jupiter (Jove), and lead for Saturn.”

In the Classroom: Electrochemical Biosensors

Undergraduate Carly Flynn (concentrating in Science and Dance) and Post-Bac Katie Giarra (shown at right, Princeton, 2009) gave the first student presentation of the term in Chemistry 3 this week. The two explained the theory behind the operation of electrochemical glucose meters. These devices, used by millions of diabetics all over the world, employ enzymes bound to the anode of a small disposable electrochemical cell whose current output is directly proportional to blood glucose levels. They explained the background theory and led a discussion that included questions concerning sources of error in the measurements and strategies to minimize them, as well as recent developments in the field.

Fun in Philly

Chemistry professors Janet Foley and John Bullock presented research findings at the 244th National Meeting of the American Chemical Society, which was held in beautiful Philadelphia, PA this August. Janet’s talk, “Photochemical reactivity of two gold(I) dinuclear complexes, cis/trans-(AupNBT)2dppee“, focused on her recent work with an unusual gold photoprocess that involves a highly unusual, low-energy, chloride abstraction from solvent molecules. Some of the work was done by then Bennington undergraduate, Angela Herring.

John presented a poster on work done in collaboration with colleagues at Monash University (Melbourne, Australia) and the University of Lethbridge (Alberta, Canada) on the electrochemistry of an unusual series of triaryl phosphines, PPh3-n(dipp)n, which range from the least to the most sterically hindered such compounds known. These studies provide insight into the steric contributions to activation barriers of electrochemical oxidation processes in general. The poster can be viewed here.