Fumigant Activity of 6 Selected Essential Oil Compounds and Combined Effect of Methyl Salicylate And Trans-Cinnamaldehyde Against Culex pipiens pallens

Antibiotics-Free Compounds for Chronic Wound Healing

The rapid rise in the health burden associated with chronic wounds is of great concern to policymakers, academia, and industry. This could be attributed to the devastating implications of this condition, and specifically, chronic wounds which have been linked to invasive microbial infections affecting patients' quality of life. Unfortunately, antibiotics are not always helpful due to their poor penetration of bacterial biofilms and the emergence of antimicrobial resistance. Hence, there is an urgent need to explore antibiotics-free compounds/formulations with proven or potential antimicrobial, anti-inflammatory, antioxidant, and wound healing efficacy. The mechanism of antibiotics-free compounds is thought to include the disruption of the bacteria cell structure, preventing cell division, membrane porins, motility, and the formation of a biofilm. Furthermore, some of these compounds foster tissue regeneration by modulating growth factor expression. In this review article, the focus is placed on a number of non-antibiotic compounds possessing some of the aforementioned pharmacological and physiological activities. Specific interest is given to Aloevera, curcumin, cinnamaldehyde, polyhexanide, retinoids, ascorbate, tocochromanols, and chitosan. These compounds (when alone or in formulation with other biologically active molecules) could be a dependable alternative in the management or prevention of chronic wounds.

Repellency and insecticidal activity of seven Mugwort (Artemisia argyi) essential oils against the malaria vector Anopheles sinensis

Anopheles sinensis is the main vector of malaria with a wide distribution in China and its adjacent countries. The smoke from burning dried mugwort leaves has been commonly used to repel and kill mosquito adults especially in southern Chinese provinces. In this study, the essential oils of mugwort leaves collected from seven provinces in China were extracted by steam distillation and their chemical compositions were analyzed. Among a total of 56–87 chemical constituents confirmed by GC–MS analyses, four compounds, eucalyptol, β-caryophyllene, phytol and caryophyllene oxide, were identified with appearances from all seven distilled essential oils. The effectiveness varied in larvicidal, fumigant and repellent activities against An. sinensis from these seven essential oils with different geographic origins. The essential oil from Hubei province showed the highest larvicidal activity against the 4th instar larvae of An. sinensis, with a median lethal concentration at 40.23 µg/mL. For fumigation toxicity, essential oils from 4 provinces (Gansu, Shandong, Sichuan and Henan) were observed with less than 10 min in knockdown time. The essential oil distilled from Gansu province displayed the highest repellent activity against Anopheles mosquitoes and provided similar level of protection as observed from DEET. Eucalyptol was the most toxic fumigant compound and phytol showed the strongest larvicidal activity among all tested mugwort essential oil constituents.

Chemical composition, antibacterial, antioxidant and insecticidal activities of moroccan Thapsia transtagana essential oil

INTRODUCTION

The use of chemical products to neutralize microorganisms has always been a subject of discussion and research for alternative solutions, indeed, the use of essential oils has been a promising natural methodology.

METHODS

In our study we used the essential oils from different parts of Thapsia transtagana (Apiaceae), obtained by hydrodistillation, were identified and using Gas chromatography-mass spectrometry (GC-MS) and Gas Chromatography-Flame Ionization Detection (GC/FID) methods and evaluated against several bacteria of Gram- and Gram + bacteria. Disk diffusion, Minimum Inhibitory Concentration (MIC) and Minimum Microbicidal Concentration (MMC) methods have been used. Free radical-scavenging activity and insecticidal activity of Thapsia transtagana essential oils were also identified.

RESULTS

Majority products from different parts of Thapsia transtagana essential oil identified by GC-MS and GC/FID methods are 2,6-Dimethylnaphthalene, Pinane and Hexahydrofarnesyl acetone. The highest activity was found against Staphylococcus aureus using inflorescence essential oil with minimal inhibitory concentration value for 0,56 μg/μL. Insecticidal activity was also the subject of this study, roots and inflorescence essential oils demonstrated to have a remarkable potent against Acanthoscelides obtectus and Sitophilus oryzae using contact assessment, inhalation assessment and ingestion assessment tests. Insecticidal activity assay results showed a significant enhancement of mortality in both test insect pest on increasing the dose and exposure period. In the other hand, the different essential oils of Thapsia transtagana were evaluated for their radical scavenging activities by means of the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) assay. The strongest scavenging activity was observed in inflorescences essential oil fraction scavenged radicals effectively at 100% using 500 mgL-1 concentration.

CONCLUSION

Its essential oils were proved to have strong antimicrobial, insecticidal and antioxidant activities that allows it to be used by the pharmaceutical and cosmetic industries as natural preservative.

Chemical and Enantioselective Analysis of the Essential Oils from Different Morphological Structures of Ocotea quixos (Lam.) Kosterm

The traditional Ecuadorian spice Ishpingo, characterized by a strong cinnamon-like aroma, is constituted by the dry cupules of Amazonian species Ocotea quixos. Nevertheless, bark and leaves also present aromatic properties and are sometimes used as substitutes. In the present study, the essential oils, distilled from these morphological structures, are comparatively analyzed for their chemical and enantiomeric compositions. A total of 88 components were identified with 2 orthogonal GC columns, whereas 79, corresponding to more than 94%, were also quantified with at least 1 column. Major compounds were (E)-methyl cinnamate in cupules (35.9-34.2%), (E)-cinnamaldehyde in bark (44.7-47.0%), and (E)-cinnamyl acetate (46.0-50.4%) in leaves. For what concerns the enantioselective analysis, 10 chiral terpenes and terpenoids were detected, of which 6 were present as enantiomeric pairs in at least 1 essential oil, the others being enantiomerically pure. Both quantitative and enantioselective analyses were submitted to Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA), where their results confirmed significative difference among the three products.

Synergistic terpene combinations as larvicides against the dengue vector Aedes aegypti Linn

Most of the essential oils (EO) known for mosquitocidal activity contain terpenes as part of their chemical constituents. In this study, four monoterpenes namely γ-terpinene (T), R-(+)-limonene (L), carvacrol (C), and trans-anethole (A) were screened against late third instar Aedes aegypti Linn. larvae singly and in combination to find out the synergistic interaction. The monoterpenes γ-terpinene, R-(+)-limonene, trans-anethole, and carvacrol showed larvicidal activity with LC₅₀ values of 9.76, 11.88, 50.19, 48.57 ppm and LC₉₀ values of 16.99, 17.78, 65.21, 75.02 ppm, respectively for Ae. aegypti when tested individually. Prepared binary combinations at LC₂₀ values and studied the synergistic interactions based on cotoxicity factor (CTF) and found that all the binary combinations showed synergistic interactions (CTF > 20). Further, the binary (1:1), ternary (1:1:1), and quaternary (1:1:1:1) terpene combinations on equal weight basis were prepared, evaluated against Ae. aegypti larvae and synergistic interactions were studied by Wadley's method. Among the eight combinations two combinations viz. LC (LC₅₀ 10.42 ppm) and LA (LC₅₀ 11.86 ppm) were showing synergistic interactions (R > 1.5) and others were exhibiting additive effect (1.5 ≥ R > 0.5) and none of the combinations showed antagonism (R < 0.5). Among the two methods used the Wadley's method found suitable when combinations were made on an equal weight basis. The two binary combinations found in this study are promising synergistic mixtures which has scope in designing mosquito larvicidal EOs by enriching the EOs with terpenes or by producing EO combinations with these terpenes as chemical constituents in the correct proportions.

Dehydrogenative β-Arylation of Saturated Aldehydes Using Transient Directing Groups

An unprecedented cross-dehydrogenative-coupling (CDC) reaction of saturated aldehyde β-C-H with arenes to form cinnamaldehydes via the cleavages of four C-H bonds has been developed. The reaction possesses complete E-stereoselectivity for the C═C double bond. The protocol is featured by atom and step economy, mild reaction conditions, and convenient operation.

Resistance to insecticides and synergistic and antagonistic effects of essential oils on dimefluthrin toxicity in a field population of Culex quinquefasciatus Say

In this work, we firstly tested five spatial repellent pyrethroids, meperfluthrin, dimefluthrin, heptafluthrin, metofluthrin and transfluthrin, to determine the susceptibility of pyrethroids to field strains of Culex quinquefasciatus using adult topical bioassay. The results showed that though field strains exhibited the highest resistance to dimefluthrin among the selected five pyrethroids, it still can be considered low resistance in the scale of Cui et al. (2006; 2007). Then, the aim of this study was to optimise the synergistic efficacy of essential oils combined with dimefluthrin and explore the major contribution composition of eucalyptus oil, basil oil and cinnamon oil as natural synergist of dimefluthrin against the field populations of C. quinquefasciatus. GC-MS analysis showed 1,8-cineole, eugenol and trans-cinnamaldehyde were the main chemical components of eucalyptus oil, basil oil and cinnamon oil, respectively. The results of bioactivity showed that eucalyptus oil and 1,8-cineole have highly fumigant knock-down activity to the adults, showing KT₅₀ (the median knockdown time) of 5.76 and 4.27 min at the concentration of 24.2 µL/L; basil oil and eugenol, cinnamon oil and trans-cinnamaldehyde have highly fumigant toxicity to the adults, showing LD₅₀ of 1.00 and 0.79, 1.26 and 1.03 µL/L, respectively. Three effective main essential oil components were selected to prepare binary mixtures, which combined with dimefluthrin against the field population of Culex quinquefasciatus. 1,8-cineole+eugenol (9:1, w/w), 1,8-cineole+trans-cinnamaldehyde (1:1, w/w) and trans-cinnamaldehyde+eugenol (9:1, w/w) combined with dimefluthrin (10:1, w/w) were the most synergistic interaction, showed SR (synergistic ratio) values of 1.2471, 1.5709 and 1.1969; KT₅₀ of 11.68, 9.51 and 10.67 min respectively, by quadrate box method. In addition, to validate the stable synergistic interaction of 1,8-cineole+trans-cinnamaldehyde (1:1, w/w) combined with dimefluthrin (10:1, w/w), the SR values were about 1.3, and KT₅₀ values were 38.72-50.26 min by simulated house method. Overall, our results pointed out the promising potential of these essential oils to increase the efficacy of dimefluthrin. It might be expected that these essential oils could be developed to a useful botanical synergist of dimefluthrin for the control of the field populations of C. quinquefasciatus.

Acaricidal Activity and Synergistic Effect of Thyme Oil Constituents against Carmine Spider Mite (Tetranychus Cinnabarinus (Boisduval))

Studies examining the use of essential oils as replacements for synthetic insecticides require an understanding of the contribution of each constituent present, interactions among these components, and how they relate to overall toxicity. In the present study, the chemical composition of commercial thyme oil was identified by gas chromatography-mass spectrometry. Thyme oil and blends of its major constituents were tested for their acaricidal activitities against carmine spider mites (Tetranychus cinnabarinus (Boisduval)) using a slide-dip bioassay. Natural thyme oil showed greater toxicity than any single constituent or blend of constituents. Thymol was the most abundant component (34.4%), and also possessed the strongest acaricidal activity compared with other single constituents. When tested individually, four constituents (linalool, terpinene, p-cymene and carvacrol) also had activity, while α-pinene, benzoic acid and ethyl gallate had almost no activity. The toxicity of blends of selected constituents indicated a synergistic effect among the putatively active and inactive constituents, with the presence of all constituents necessary to reach the highest toxicity. The results indicated that thyme oil and some of its major constituents have the potential to be developed into botanical acaricides.

Primary Screening of Plant Essential Oils as Insecticides, Fumigants, and Repellents Against the Health Pest Paederus fuscipes (Coleoptera: Staphylinidae)

The contact and fumigant toxicity as well as repellent activity of 10 plant essential oils were evaluated against Paederus fuscipes Curtis adults. Essential oils were identified through gas chromatography-mass spectrometry analysis. Results showed that wintergreen oil exhibited optimal contact and fumigant toxicity but had no significant repellent activity against P. fuscipes. The LC50 values of fumigant toxicity of wintergreen oil were 2.680 and 1.591 µL/L air after 1 and 8 h of exposure, respectively. The LC50 values of contact toxicity of wintergreen oil were 0.086 and 0.060 µL/adult after 1 and 8 h of exposure, respectively. Cinnamon oil exhibited the highest repellent activity. In particular, 0.1 µL/cm2 cinnamon oil showed 100% repellency against P. fuscipes even for 6 h. Moreover, 0.01 and 0.005 µL/cm2 cinnamon oil conferred 80% repellency against P. fuscipes for 8 and 4 h, respectively. Overall, wintergreen oil is the best candidate insecticide and fumigant, and cinnamon oil is optimal as a repellent. The low-dose, rapid action of wintergreen oil and the low-dose, persistent repellency of cinnamon oil are important factors that suggest their use as insecticides, fumigants, and repellents against P. fuscipes.