UC San Diego

Nasal pungency thresholds (NPT) in man have been determined by Cometto-Muñiz and Cain for 44 varied compounds, including esters, aldehydes, ketones, alcohols, carboxylic acids, aromatic hydrocarbons and pyridine. With the exclusion of acetic acid, 43 of these NPT values are well correlated through the general linear free energy equation of Abraham, leading to the algorithm,

log(1/NPT) = -8.519 + 2.154 p₂ ^H + 3.522 ∑a^H ₂  + 1.397 ∑b₂ ^H  + 0.860 log L¹⁶                              (i)

n = 43, r² = 0.955, SD = 0.27, F = 201

where the independent variables are solute descriptors: p₂ ^H   is the dipolarity/polarizability, ∑a^H ₂   and ∑b₂ ^H   are the overall or effective hydrogen-bond acidity and basicity, and L¹⁶ is the solute Ostwald solubility coefficient on hexadecane at 25 °C. Surprisingly, the aliphatic aldehydes and carboxylic acids fit the correlation and with respect to nasal pungency thresholds in man for brief (1-3 s) presentations must be regarded as `nonreactive' compounds. It is suggested mere transport of the compound from the air stream to the receptor area largely determines the potency to produce pungency. Various chemical properties of the receptor area are deduced from the coefficients in Eq. i.