The Nature of Smell
Current theories of odour are discussed. The complexity of odour detection in animals and humans is amazing and odour detection is still underutilized in medicine today.
The sense of smell is one of God's great gifts. For man it can be a great source of pleasure which can heighten our experiences. Even unpleasant smells can warn us of problems. Minute quantities of illicit and criminal substances can be detected by trained dogs, which benefits mankind. In 1974, while still a Chemistry Professor at Columbia University and Barnard College, I published a paper in the prestigious journal Nature on theory of odour. At that time, the receptors for odour had not been yet found. It was not until the 1980's that this was done by Richard Axel and Linda Buck. They characterized over one hundred receptors in the upper nasal passages. Two years ago they received the Nobel Prize in Medicine for this work. These receptors were lock and key shape type receptors. In 1974, I had discussed the various theories of odour at that time. These included Amoore's limited number of shape receptors, Wright's theory which connected molecular vibrational frequencies with odour type and another theory based on lipid solubility. I also described a correlation between boiling points and odour classification. This implied that the intermolecular attraction between molecules related somewhat to the attraction between the molecule and some receptor. With Buck's discovery it seemed that the major problem was solved.
Then along came Professor Turin of England who did not feel that the shape theory was adequate despite the receptor characterization. He decided to re-invent the vibrational theory of Wright. He submitted a paper to Nature like I had done years before. He in addition got the BBC to run a documentary on his theory. The science behind his paper was at best speculative and the paper was rejected. He tried repeatedly to counter the objections but to no avail. Meanwhile the BBC documentary went on the air and he became overnight "expert" in the field. Turin was determined and continued to push his ideas despite the resistance. He had a book written by Chandler Burr called "The Emperor of Scent" which documented all his trials and tribulations and makes him out to be an anti-establishment hero. Turin was and is correct that one does not have the real ability to predict for a given new molecule what it will smell like. However neither can his theory do this.
Until the actual active sites of the receptors are characterized, one would not be able to describe a predictive theory. Also, because there are so many receptors, it may be an ensemble of interactions which produces the given effect. Nature can be quite complex and this might be necessary to differentiate so many different smells. Turin did eventually get his paper in another journal and he wrote his own book. Now the encyclopedias often mention his theory. He has gotten people to think about why this sense is so complex. So while I got my article in Nature, Turin did not, but he did get the sweet smell of "success".
