ISSN:
1431-4630
Keywords:
Key words Pyrazine
;
Odour threshold
;
Structure
;
Molecular modelling
;
Theoretical receptor
Source:
Springer Online Journal Archives 1860-2000
Topics:
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Abstract The odour thresholds (i.e. the lowest concentration at which an odour can be detected) of 80 alkylpyrazines, most of them synthesized, were determined by gas chromatography-olfactometry. Trimethylpyrazine (1) had the lowest threshold (50 ng/l air) amongst mono-, di-, tri- and tetramethylpyrazine. Substitution of the methyl group in position 2 of 1 by an ethyl group yielded 2-ethyl-3,5-dimethylpyrazine (2) showing a 4500-fold lower odour threshold than 1. The thresholds of 2-ethenyl-3,5-dimethylpyrazine (3), 2,3-diethyl-5-methylpyrazine (4) and 2-ethenyl-3-ethyl-5-methylpyrazine (5) were as low as that of 2. The threshold of 3-ethenyl-2-ethyl-5-methylpyrazine was 8000 times higher than that of 5, indicating that an ethenyl group was only tolerated in position 2, but not in position 3. A further increase in the odour threshold was found when the ethenyl or the ethyl group was located in position 5. Substitution of the ethyl group of 2 by a (Z)-1-propenyl group increased the threshold only by a factor of 5, whereas the (E)-isomer and the 2-propenyl group enhanced the threshold by factors of 160 and 27000, respectively. Also a propyl, butyl, pentyl, isobutyl or hexyl group in position 2 of 2 was too bulky, and in these molecules the odour threshold was at least 2200 times higher than that of 2. The geometrical structure of a theoretical receptor was obtained by superimposing the minimized structures of pyrazines with low thresholds (Chem-X force-field minimization). Sterically forbidden regions in the resulting model were found by superimposing pyrazines with high thresholds.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002170050422
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