(R)-(+)-Limonene

Physicochemical Characteristics of Four Limonene-Based Nanoemulsions and Their Larvicidal Properties against Two Mosquito Species, Aedes albopictus and Culex pipiens molestus.[Pubmed:33126682]

Insects. 2020 Oct 28;11(11). pii: insects11110740.

Negative impacts on the environment from the continuous use of synthetic insecticides against mosquitoes has driven research towards more ecofriendly products. Phytochemicals, classified as low-risk substances, have been recognized as potential larvicides of mosquitoes; however, problems related to water solubility and stability are limiting factors for their use in mosquito control programs in the field. In this context, many researchers have focused on formulating essential oils in nanoemulsions, exploiting innovative nanotechnology. In the current study, we prepared 4 (R)-(+)-Limonene oil-in-water nanoemulsions using low and high energy methods, and we evaluated their physicochemical characteristics (e.g., viscosity, stability, mean droplet diameter, polydispersity index) and their bioactivity against larvae of two mosquito species of great medical importance, namely, Cx. pipiens molestus and Ae. albopictus. According to the dose-response bioassays with the limonene-based nanoemulsions and pure limonene (dissolved in organic solvent), the tested nanoformulations improved the activity of limonene against Ae. albopictus larvae, while the performance of limonene was either the same or better than limonene against Cx. pipiens molestus, depending on the applied system. Overall, we achieved the production of limonene-based delivery nanosystems, with sufficient lethal properties against mosquito larvae to consider them promising larvicidal formulations applicable to mosquito breeding sites.

Trap Assays of the Walnut Twig Beetle, Pityophthorus juglandis Blackman (Coleoptera: Curculionidae: Scolytinae), Reveal an Effective Semiochemical Repellent Combination.[Pubmed:33106973]

J Chem Ecol. 2020 Dec;46(11-12):1047-1058.

Thousand cankers disease (TCD), is an invasive insect-disease complex caused by the walnut twig beetle, Pityophthorus juglandis, and fungal pathogen, Geosmithia morbida. Semiochemical interruption is a viable option for protecting walnut trees from P. juglandis attack. The goal of this study was to test beetle responses to potential repellent compounds. The results of five, flight-intercept assays are reported. Assays 1-3 tested four compounds at variable release rates: (S)-(-)-verbenone, (R)-(+)-verbenone, racemic chalcogran, and racemic trans-conophthorin. Trapping results indicated that the highest release rate tested for each compound was the most effective in reducing the number of beetles caught. (S)-(-)-Verbenone was the least effective, reducing P. juglandis trap catches by 66%. (R)-(+)-Verbenone reduced the number of P. juglandis by 84%. Neither enantiomer of verbenone performed as well as chalcogran or trans-conophthorin, which both reduced the number of beetles caught by ca. 98%. Following individual assays, the most effective compounds were tested in subtractive-combination assays. Combinations of high release rates for (R)-(+)-verbenone, trans-conophthorin, and two stereoisomers of limonene (tested in a previous study) were tested in two assays. The subtractive-combination assays were inconclusive in that trap catches were similar across all treatments. All combination treatments were highly effective, achieving approximately 99% reduction in the number of beetles caught. Based on the trapping results, commercial availability, and cost of the semiochemicals tested, we conclude that a combination of (R)-(+)-Limonene, trans-conophthorin, and (R)-(+)-verbenone constitutes an effective tool for reducing P. juglandis trap catches.

The Flower Essential Oil of Dalea mutisii Kunth (Fabaceae) from Ecuador: Chemical, Enantioselective, and Olfactometric Analyses.[Pubmed:33096831]

Plants (Basel). 2020 Oct 21;9(10). pii: plants9101403.

An essential oil was distilled with 0.25% yield from fresh flowers of Dalea mutisii Kunth, a native species mainly growing in the Andean region of Ecuador. A total of 50 compounds were identified, and most of them were quantified. The chemical composition was characterized by the prevalence of monoterpene hydrocarbons (>90%). Major components were alpha-pinene (42.9%), beta-pinene (15.1%), beta-phellandrene (12.6%), myrcene (6.7%), and (Z)-beta-ocimene (5.4%). The essential oil was then submitted to enantioselective analysis, with a 2,3-diethyl-6-tert-butyldimethylsilyl-beta-cyclodextrin-based capillary column. An enantiomeric excess was measured for (1R,5R)-(+)-alpha-pinene (91.6%), (1R,5R)-(+)-beta-pinene (15.2%), (R)-(-)-alpha-phellandrene (4.8%), and (R)-(-)-beta-phellandrene (88.8%), whereas (R)-(+)-Limonene was enantiomerically pure. A gas chromatography-olfactometry (GC-O) analysis was additionally carried out on this pleasantly fragrant essential oil, following an aroma extract dilution analysis (AEDA) approach. Main odorants were alpha-pinene, beta-pinene, alpha-phellandrene, and (Z)-beta-ocimene, with dilution factors (FD) of 8, 4, 2, and 2, respectively.

Enhancing benchtop NMR spectroscopy by means of sample shifting.[Pubmed:32945292]

Analyst. 2020 Nov 9;145(22):7406-7411.

Benchtop NMR spectrometers have become widely available over the last decade. They are now used successfully in various branches of chemistry. Their popularity continues to grow due to their low price and almost zero running costs. However, benchtop spectrometers suffer from low resolution and sensitivity compared to the high-field spectrometers used in NMR labs for several decades. In this article we present a solution for boosting the sensitivity of benchtop NMR spectrometers in a multi-scan experiment and improving their capabilities in quantitative measurement. Our solution involves the synchronized shifting of a sample to preserve its high nuclear polarization during the measurement. We performed several experiments using different samples to confirm this improved performance: an 1H NMR experiment for 4,4-dimethoxy-2-butanone, and 13C NMR experiments for benzyl salicylate, the liquid pharmaceutical product Acerin (skin solution), and a mixture of m-anisaldehyde and (R)-(+)-Limonene.

Electrophysiological Responses of the Beech Leaf-Mining Weevil, Orchestes fagi, to Seasonally-Variant Volatile Organic Compounds Emitted by American Beech, Fagus grandifolia.[Pubmed:32914252]

J Chem Ecol. 2020 Oct;46(10):935-946.

The beech leaf-mining weevil, Orchestes fagi, is a common pest of European beech, Fagus sylvatica, and has recently become established in Nova Scotia, Canada where it similarly infests American beech, F. grandifolia. We collected volatile organic compounds (VOCs) emitted by F. grandifolia leaves at five developmental stages over one growing season and simultaneously analyzed them for volatile emissions and O. fagi antennal response using gas chromatography-electroantennographic detection (GC-EAD). Volatile profiles changed significantly throughout the growing season, shifting from primarily beta-caryophyllene, methyl jasmonate, and simple monoterpene emissions to dominance of the bicyclic monoterpene sabinene during maturity. Two VOCs dominant during bud burst, (R)-(+)-Limonene and geranyl-p-cymene, may be of biological relevance due to the highly specific oviposition period of O. fagi at this stage though antennal responses were inconclusive. Senescence showed a decrease in blend complexity with an increase in (Z)-3-hexenyl acetate and (Z)-3-hexen-1-ol as well as a resurgence of alpha-terpinene and geranyl-p-cymene. We present a novel electroantennal preparation for O. fagi. Antennae of both male and female O. fagi responded to the majority of detectable peaks for host volatiles presented via GC-EAD. Females displayed greater overall sensitivities and less specificity to host volatiles and it is hypothesized that this translates to more generalist olfaction than males. It is clear that olfactory cues are important physiologically though their implications on behaviour are still unknown. The results presented in this study provide a baseline and tools on which to connect the complex and highly time-specific phenology of both F. grandifolia and the destructive pest O. fagi through which olfactory-based lures can be investigated for monitoring systems.