Limonene Enantiomeric Ratios from Anthropogenic and Biogenic Emission Sources

Emissions from volatile chemical products (VCPs) have been identified as contributors to air quality degradation in urban areas. Limonene can be a tracer compound for VCPs containing fragrances in densely populated regions, but limonene is also emitted from conifers that are planted in urban areas. This creates challenges for using limonene to estimate VCP emissions. In this study, the -/+ enantiomeric ratios of limonene from VCP and conifer emission sources were quantified to evaluate if this measurement could be used to aid in source apportionment and emission inventory development. Samples were analyzed using a gas chromatograph equipped with a chiral column and mass spectrometry. The results demonstrate that limonene exhibits distinct enantiomeric ratios when sourced from VCPs versus conifers. (+)-Limonene was dominant in VCP sources (>97%), which was not universally true for conifer sources. The results were compared to those of air samples collected outside at two locations and indoors. The levels of (-)-limonene in outdoor air in Irvine and Portland and in indoor air were 50%, 22%, and 4%, respectively. This suggests outdoor limonene had both VCP and plant emission sources while indoor air was dominated by VCP sources. This study demonstrates the potential utility of enantiomeric analysis for improving VCP emission estimates in urban areas.

Enantioselective synthesis of 6-methyloctanal and 8-methyldecanal, the characteristic aroma components in yuzu Citrus junos, and analysis of their enantiomeric compositions in yuzu essential oil

6-Methyloctanal and 8-methyldecanal are the characteristic aroma components of yuzu Citrus junos. However, their absolute configurations and enantiomeric compositions in yuzu essential oil have not been analyzed. A concise enantioselective synthesis of both aldehydes was successfully carried out to determine their absolute configurations and enantiomeric compositions. Both aldehydes in yuzu essential oil were found to be (S)-form with high enantiomeric excess.

Sulcatol: Enantiospecific Attractant for Monarthrum mali (Coleoptera: Curculionidae: Scolytinae), Leptostylus asperatus (Coleoptera: Cerambycidae) and Associated Predators

In 2014-2019, we conducted six experiments in north-central Georgia in an attempt to verify the aggregation pheromone response of the ambrosia beetle Gnathotrichus materiarius (Fitch) (Coleoptera: Curculionidae: Scolytinae: Scolytini: Corthylina) to sulcatol known to be produced by male G. materiarius; we failed to catch any G. materiarius. However, we did find that another corthyline ambrosia beetle species Monarthrum mali (Fitch) was attracted to (R)-(-)-sulcatol, whereas the longhorn beetle Leptostylus asperatus (Haldeman) (Coleoptera: Cerambycidae: Lamiinae) was attracted to (S)-(+)-sulcatol. Attraction of both species was unaffected by the respective antipodes. Ethanol enhanced attraction of both species to traps baited with sulcatol. In at least one experiment, attraction to ethanol-baited traps was enhanced by sulcatol for Xylosandrus crassiusculus (Motschulsky), Xyleborus spp., and Hypothenemus spp. but reduced for Cnestus mutilatus (Blandford) (Coleoptera: Curculionidae: Scolytinae). Additionally, traps baited with ethanol and racemic sulcatol [50% (S)-(+): 50% (R)-(-)] caught the greatest numbers of four species of beetle predators: Coptodera aerata Dejean (Coleoptera: Carabidae), Colydium lineola Say (Coleoptera: Zopheridae), Madoniella dislocata (Say), and Pyticeroides laticornis (Say) (Coleoptera: Cleridae). Ethanol but not sulcatol attracted Temnoscheila virescens (F.) (Coleoptera: Trogossitidae). Information on interspecific relationships within forested communities may help us to better determine the roles of these species in maintaining stable and resilient forested ecosystems.

Enantiomeric composition of nicotine in tobacco leaf, cigarette, smokeless tobacco, and e-liquid by normal phase high-performance liquid chromatography

Evaluating the source of nicotine in e-liquid is a problem. Tobacco-derived nicotine contains predominantly (S)-(-)-nicotine, whereas tobacco-free nicotine products may not. Thus, we developed a new normal phase high-performance liquid chromatography method to determinate the enantiomeric composition of nicotine in 10 kinds of flue-cured tobacco, 3 kinds of burley, 1 kind of cigar tobacco, 2 kinds of oriental tobacco, 5 kinds of Virginia cigarette, 5 kinds of blend cigarette, 10 kinds of e-liquid, and 4 kinds of smokeless tobacco. The amount of (R)-(+)-nicotine ranged from ~0.02% to ~0.76% of total nicotine. An e-liquid sample had the highest level of (R)-(+)-nicotine. The extraction and purification processes used to obtain commercial (S)-(-)-nicotine from the tobacco do not decrease the amount of (R)-(+)-nicotine in tobacco. So the amount of (R)-(+)-nicotine in samples in our work were the same as tobacco samples.

Determination of Volatile Flavour Profiles of Citrus spp. Fruits by SDE-GC-MS and Enantiomeric Composition of Chiral Compounds by MDGC-MS

INTRODUCTION

Citrus fruits are known to have characteristic enantiomeric key compounds biosynthesised by highly stereoselective enzymatic mechanisms. In the past, evaluation of the enantiomeric ratios of chiral compounds in fruits has been applied as an effective indicator of adulteration by the addition of synthetic compounds or natural components of different botanical origin.

OBJECTIVE

To analyse the volatile flavour compounds of Citrus junos Sieb. ex Tanaka (yuzu), Citrus limon BURM. f. (lemon) and Citrus aurantifolia Christm. Swingle (lime), and determine the enantiomeric ratios of their chiral compounds for discrimination and authentication of extracted oils.

METHODOLOGY

Volatile flavour compounds of the fruits of the three Citrus species were extracted by simultaneous distillation extraction and analysed by gas chromatography-mass spectrometry. The enantiomeric composition (ee%) of chiral camphene, sabinene, limonene and β-phellandrene was analysed by heart-cutting multidimensional gas chromatography-mass spectrometry.

RESULTS

Sixty-seven (C. junos), 77 (C. limon) and 110 (C. aurantifolia) volatile compounds were identified with limonene, γ-terpinene and linalool as the major compounds. Stereochemical analysis (ee%) revealed 1S,4R-(-) camphene (94.74, 98.67, 98.82), R-(+)-limonene (90.53, 92.97, 99.85) and S-(+)-β-phellandrene (98.69, 97.15, 92.13) in oil samples from all three species; R-(+)-sabinene (88.08) in C. junos; and S-(-)-sabinene (81.99, 79.74) in C. limon and C. aurantifolia, respectively.

CONCLUSION

The enantiomeric composition and excess ratios of the chiral compounds could be used as reliable indicators of genuineness and quality assurance of the oils derived from the Citrus fruit species. Copyright © 2017 John Wiley & Sons, Ltd.