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Structure-activity relationships on the odor detectability of homologous carboxylic acids by humans.

Cometto-Muñiz JE, Abraham MH - Exp Brain Res (2010)

Bottom Line: Odor thresholds and interindividual differences in olfactory acuity among these young, normosmic participants were lower than traditionally thought and reported.No significant effects of gender on odor detectability were observed.We discuss the mechanistic implications of this model for the process of olfactory detection.

View Article: PubMed Central - PubMed

Affiliation: Chemosensory Perception Laboratory, Department of Surgery Otolaryngology, University of California, San Diego, 9500 Gilman Dr, Mail Code 0957, La Jolla, CA 92093-0957, USA. ecometto@ucsd.edu

ABSTRACT
We measured concentration detection functions for the odor detectability of the homologs: formic, acetic, butyric, hexanoic, and octanoic acids. Subjects (14 ≤ n ≤ 18) comprised young (19-37 years), healthy, nonsmoker, and normosmic participants from both genders. Vapors were delivered by air dilution olfactometry, using a three-alternative forced-choice procedure against carbon-filtered air, and an ascending concentration approach. Delivered concentrations were established by gas chromatography (flame ionization detector) in parallel with testing. Group and individual olfactory functions were modeled by a sigmoid (logistic) equation from which two parameters are calculated: C, the odor detection threshold (ODT) and D, the steepness of the function. Thresholds declined with carbon chain length along formic, acetic, and butyric acid where they reached a minimum (ODTs = 514, 5.2, and 0.26 ppb by volume, respectively). Then, they increased for hexanoic (1.0 ppb) and octanoic (0.86 ppb) acid. Odor thresholds and interindividual differences in olfactory acuity among these young, normosmic participants were lower than traditionally thought and reported. No significant effects of gender on odor detectability were observed. The finding of an optimum molecular size for odor potency along homologs confirms a prediction made by a model of ODTs based on a solvation equation. We discuss the mechanistic implications of this model for the process of olfactory detection.

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Related in: MedlinePlus

Trends in odor detection thresholds as a function of the variable carbon chain length for the acids and five other homologous series (Cometto-Muñiz and Abraham 2008, 2009a, b, 2010; Cometto-Muñiz et al. 2008; see text). Bars, sometimes hidden by the symbol, indicate SE
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Fig5: Trends in odor detection thresholds as a function of the variable carbon chain length for the acids and five other homologous series (Cometto-Muñiz and Abraham 2008, 2009a, b, 2010; Cometto-Muñiz et al. 2008; see text). Bars, sometimes hidden by the symbol, indicate SE

Mentions: Previous work on odor sensitivity has indicated that the maximum molecular length of an odorant in a homologous series is very important, and it appears that there is an optimum value where odor potency is highest and, thus, ODT is lowest (Abraham et al. 2002). A plot of C (i.e., log ODT) against the maximum length of the carboxylic acid, in Angstroms, clearly shows a minimum around 9 Å (Fig. 4). In addition to molecular length, other factors that could determine high olfactory sensitivity for certain odorants include behavioral relevance and/or frequency of occurrence of the odorant in the chemical environment (Laska et al. 2005). Aside from the acids, human odor studies with homologous acetates (Cometto-Muñiz et al. 2008), alkylbenzenes (Cometto-Muñiz and Abraham 2009a), and aldehydes (Cometto-Muñiz and Abraham 2010) have revealed a minimum in ODT for hexyl acetate, butyl benzene, and octanal, respectively. For n-alcohols (Cometto-Muñiz and Abraham 2008) and 2-ketones (Cometto-Muñiz and Abraham 2009b), the decrease in ODTs with chain length reached a plateau with 1-butanol (continuing to 1-octanol) and 2-heptanone (continuing to 2-nonanone), respectively, and did not significantly rebound. Additional testing with larger homologs (e.g., 1-decanol and 2-undecanone) is needed to confirm or discard the possibility that thresholds might also rebound within alcohols and ketones, as seen for the other three series. Figure 5 illustrates the data discussed above and reveals that the human sense of smell is particularly sensitive to aldehydes and to medium and long chain acids, compared to the other four series.Fig. 4


Structure-activity relationships on the odor detectability of homologous carboxylic acids by humans.

Cometto-Muñiz JE, Abraham MH - Exp Brain Res (2010)

Trends in odor detection thresholds as a function of the variable carbon chain length for the acids and five other homologous series (Cometto-Muñiz and Abraham 2008, 2009a, b, 2010; Cometto-Muñiz et al. 2008; see text). Bars, sometimes hidden by the symbol, indicate SE
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2964470&req=5

Fig5: Trends in odor detection thresholds as a function of the variable carbon chain length for the acids and five other homologous series (Cometto-Muñiz and Abraham 2008, 2009a, b, 2010; Cometto-Muñiz et al. 2008; see text). Bars, sometimes hidden by the symbol, indicate SE
Mentions: Previous work on odor sensitivity has indicated that the maximum molecular length of an odorant in a homologous series is very important, and it appears that there is an optimum value where odor potency is highest and, thus, ODT is lowest (Abraham et al. 2002). A plot of C (i.e., log ODT) against the maximum length of the carboxylic acid, in Angstroms, clearly shows a minimum around 9 Å (Fig. 4). In addition to molecular length, other factors that could determine high olfactory sensitivity for certain odorants include behavioral relevance and/or frequency of occurrence of the odorant in the chemical environment (Laska et al. 2005). Aside from the acids, human odor studies with homologous acetates (Cometto-Muñiz et al. 2008), alkylbenzenes (Cometto-Muñiz and Abraham 2009a), and aldehydes (Cometto-Muñiz and Abraham 2010) have revealed a minimum in ODT for hexyl acetate, butyl benzene, and octanal, respectively. For n-alcohols (Cometto-Muñiz and Abraham 2008) and 2-ketones (Cometto-Muñiz and Abraham 2009b), the decrease in ODTs with chain length reached a plateau with 1-butanol (continuing to 1-octanol) and 2-heptanone (continuing to 2-nonanone), respectively, and did not significantly rebound. Additional testing with larger homologs (e.g., 1-decanol and 2-undecanone) is needed to confirm or discard the possibility that thresholds might also rebound within alcohols and ketones, as seen for the other three series. Figure 5 illustrates the data discussed above and reveals that the human sense of smell is particularly sensitive to aldehydes and to medium and long chain acids, compared to the other four series.Fig. 4

Bottom Line: Odor thresholds and interindividual differences in olfactory acuity among these young, normosmic participants were lower than traditionally thought and reported.No significant effects of gender on odor detectability were observed.We discuss the mechanistic implications of this model for the process of olfactory detection.

View Article: PubMed Central - PubMed

Affiliation: Chemosensory Perception Laboratory, Department of Surgery Otolaryngology, University of California, San Diego, 9500 Gilman Dr, Mail Code 0957, La Jolla, CA 92093-0957, USA. ecometto@ucsd.edu

ABSTRACT
We measured concentration detection functions for the odor detectability of the homologs: formic, acetic, butyric, hexanoic, and octanoic acids. Subjects (14 ≤ n ≤ 18) comprised young (19-37 years), healthy, nonsmoker, and normosmic participants from both genders. Vapors were delivered by air dilution olfactometry, using a three-alternative forced-choice procedure against carbon-filtered air, and an ascending concentration approach. Delivered concentrations were established by gas chromatography (flame ionization detector) in parallel with testing. Group and individual olfactory functions were modeled by a sigmoid (logistic) equation from which two parameters are calculated: C, the odor detection threshold (ODT) and D, the steepness of the function. Thresholds declined with carbon chain length along formic, acetic, and butyric acid where they reached a minimum (ODTs = 514, 5.2, and 0.26 ppb by volume, respectively). Then, they increased for hexanoic (1.0 ppb) and octanoic (0.86 ppb) acid. Odor thresholds and interindividual differences in olfactory acuity among these young, normosmic participants were lower than traditionally thought and reported. No significant effects of gender on odor detectability were observed. The finding of an optimum molecular size for odor potency along homologs confirms a prediction made by a model of ODTs based on a solvation equation. We discuss the mechanistic implications of this model for the process of olfactory detection.

Show MeSH
Related in: MedlinePlus