The Nose as a Stereochemist. Enantiomers and Odor

Bentley, Ronald

doi:10.1021/cr050049t

Cited by 133 publications

(83 citation statements)

References 101 publications

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“…A modified IETS mechanism appropriate to proteins was recently described (26), suggesting a testable model applicable to olfactory receptors. Finally, it was objected that enantiomers with identical vibrations should always smell the same, whereas some smell different (38). Given that proteins are chiral, a shape-only theory cannot account for the identical odors of most enantiomer pairs.…”

Section: Discussionmentioning

confidence: 99%

Molecular vibration-sensing component in Drosophila melanogaster olfaction

Franco

Turin

Mershin

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

176

218

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A common explanation of molecular recognition by the olfactory system posits that receptors recognize the structure or shape of the odorant molecule. We performed a rigorous test of shape recognition by replacing hydrogen with deuterium in odorants and asking whether Drosophila melanogaster can distinguish these identically shaped isotopes. We report that flies not only differentiate between isotopic odorants, but can be conditioned to selectively avoid the common or the deuterated isotope. Furthermore, flies trained to discriminate against the normal or deuterated isotopes of a compound, selectively avoid the corresponding isotope of a different odorant. Finally, flies trained to avoid a deuterated compound exhibit selective aversion to an unrelated molecule with a vibrational mode in the energy range of the carbon-deuterium stretch. These findings are inconsistent with a shape-only model for smell, and instead support the existence of a molecular vibrationsensing component to olfactory reception.

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Section: Discussionmentioning

confidence: 99%

Molecular vibration-sensing component in Drosophila melanogaster olfaction

Franco

Turin

Mershin

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

176

218

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“…This is less surprising when we recognize that the conformational space explored by an odorant is likely to Figure 11. Type 2, nootkatones: (a) (4R,4aS,6R)-(C)-nootkatone smells of grapefruit (0.8 ppm) and (b) (4S,4aR,6S )-(K)-nootkatone is 'woody, spicy' (600 ppm) (Bentley 2006). Note also that the (C) enantiomer is approximately 750 times more potent than the (K) enantiomer (Eliel & Wilen 1993).…”

Section: How Might Flexibility Affect Olfaction?mentioning

confidence: 99%

Odour character differences for enantiomers correlate with molecular flexibility

Brookes

Horsfield

Stoneham

2008

J. R. Soc. Interface.

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The olfactory system sensitively discerns scents from many small molecules as the brain analyses signals from nasal receptors. These receptors are selective to some degree, though the mechanism for selectivity is still controversial. Enantiomers, chiral pairs of left-and right-handed structures, are an important class of molecules in assessing proposed mechanisms. We show that there is a correlation between molecular (structural) flexibility and whether or not the left-and right-handed enantiomers smell the same. In particular, for the fairly extensive class of enantiomers with six-membered ring flexibility, enantiomers do not smell the same. There are, of course, significant experimental uncertainties, which we discuss here. We discuss models of receptor selectivity, both those based on shape and those where discrimination is based on other factors, such as electron affinity, proton affinity or vibration frequencies. The differences in scent of these enantiomers appear to be consistent with simple generalizations of a 'swipe card' model in which, while the shape must be good enough, critical information for actuation is a separate factor.

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“…[14] Most of the processes related to the interaction of a chiral ligand, such as a drug, with enzymes or protein receptors are characterized by marked enantioselectivity. [15] In particular, those underlying the sense of taste or smell [16] are often enantioselective: the two enantiomers of limonene smell different. The S form smells of lemon while the R form smells of orange.…”

Section: Introductionmentioning

confidence: 99%

Chirality Recognition between Neutral Molecules in the Gas Phase

2008

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Noncovalent interactions are particularly intriguing when they involve chiral molecules, because the interactions change in a subtle way upon replacing one of the partners by its mirror image. The resulting phenomena involving chirality recognition are relevant in the biosphere, in organic synthesis, and in polymer design. They may be classified according to the permanent or transient chirality of the interacting partners, leading to chirality discrimination, chirality induction, and chirality synchronization processes. For small molecules, high-level quantum chemical calculations for such processes are feasible. To provide reliable connections between theory and experiment, such phenomena are best studied in vacuum isolation at low temperature, using rotational, vibrational, electronic, and photoionization spectroscopy. We review these techniques and the results which have become available in recent years, with special emphasis on dimers of permanently chiral molecules and on the influence of conformational flexibility. Analogies between the microscopic mechanisms and macroscopic phenomena and between intra- and intermolecular cases are drawn.

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The Nose as a Stereochemist. Enantiomers and Odor

Cited by 133 publications

References 101 publications

Molecular vibration-sensing component in Drosophila melanogaster olfaction

Molecular vibration-sensing component in Drosophila melanogaster olfaction

Odour character differences for enantiomers correlate with molecular flexibility

Chirality Recognition between Neutral Molecules in the Gas Phase

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