The Nature of Smell
| The sense of smell is one of God's great gifts. For man it can be a great source of pleasure which can heighten his experiences. Even unpleasant smells can warn him of problems. Minute quantities of illicit and criminal substances can be detected by trained dogs. In 1974 while a Chemistry Professor at Columbia University-Barnard College, I published a paper in the journal Nature on theory of odour [Intermolecular Basis of Odour; A. Mazziotti, Nature 250 645--646 (1974)]. At that time the receptors for odour had not been discovered for 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. In 2004 they received the Nobel Prize in Medicine for this work. In 1974 I discussed the various theories of odour prominent at that time including 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. In my paper, I showed a correlation between boiling points and odour classification which implied that the intermolecular attraction (VanderWaals forces) between molecules related to a similar attraction between the odorant molecule and some receptor or collection of receptors. Professor Turin of England who did not feel that the shape theory was adequate, despite the receptor characterization, decided to revisit the vibrational theory of Wright. He submitted a paper to Nature as I had done years before. He also had the BBC create a documentary on his theory. The science behind his paper was felt to be speculative by the reviewers 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 it was a great success. Turin was determined and continued to push his ideas despite the resistance of the Nature editors. A book written by Chandler Burr called "The Emperor of Scent" documented all his trials and tribulations and protrays him as an anti-establishment hero. The book is an interesting read. Turin was and is correct that one does not have the ability to predict for a given new molecule what it will smell like. The nature of the interactions are as I had said years before quantum mechanical and depend not just on the electronic structure of the odour molecule and the receptor but also the vibrational and rotational components as well. He gives an example of how replacing regular hydrogen with a heavy isotope in a compound leads to a different odour for that compound. In my opinion this just verifies that all intermolecular forces- electronic, vibrational and rotational need to be accounted for in order to have a predictive theory of odour. While the receptors are now known it will not be until the actual active sites of the receptors are fully understood that one would be able to create a reasonable predictive model of odour. Also, because there are so many receptors it probably will be an ensemble of interactions which produces the given odour. Turin did publish his paper in another journal and continues his research. The theory of odour still has some new chapters to be written in the future. | ||||||||||||||||||||
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