In an ode addressed to his friend Fabullus, the Roman poet Catullus speaks of a fragrance so pleasing that “when you smell it you will beg the gods to make you all nose.” Would that the recipe for such a scent had been transmitted through the ages! Even today, however, it is not possible to document chemical composition with adequate fidelity to reconstruct an odor perfectly. Catullus writes that the gods of love gave the perfume to his girlfriend. Suppose such gods existed and could list the ingredients of its aroma. The list would contain hundreds—perhaps thousands—of chemical structures and their relative proportions. Very likely, many of the structures would stand for compounds that are currently unknown, but they could be synthesized in the laboratory. Would that knowledge permit me to reproduce the odor? This chapter argues that the answer remains uncertain. The current state of chemical knowledge can neither account for why an odor smells the way it does nor what determines its intensity. The recipe for replicating a sensory experience—what is essential and what is superfluous—remains obscure. The sense of smell challenges chemical understanding. On the one hand, given the structure of a new molecule a chemist can predict its spectroscopic properties over a wide domain of electromagnetic frequencies. A mixture ordinarily displays a spectrum that superimposes the spectra of its individual components, unless they physically interact with each other. In the chemical senses, on the other hand, perceptions of mixtures often cannot be inferred from their constituents, even though the components do not interact at the molecular level. Moreover, no one can reliably predict the organoleptic properties (taste or smell) of a new molecule from its structure. Even if that were possible, the English language does not offer a vocabulary with which to describe new smells, except by analogy to odors that are already familiar. The poverty of descriptors means that, in talking about olfactory stimuli, many people allude to direct experiences. These allusions call on memories of characteristic odors of familiar objects, which represent “unitary percepts.”
Use of Nanomaterials in Cryobiology and Cryomedicine
