Structure-activity relationships of larvicidal monoterpenes and derivatives against Aedes aegypti Linn.

In the search for larvicidal compounds against Aedes aegypti L. (Diptera: Culicidae), a collection of monoterpenes were selected and evaluated. R- and S-limonene exhibited the highest larvicidal potency (LC(50)=27 and 30 ppm, respectively), followed by γ-terpinene (LC(50)=56 ppm) and RS-carvone (LC(50)=118 ppm). Structural characteristics which may contribute to the understanding of the larvicidal activity of monoterpenes were empirically identified. The presence of heteroatoms in the basic hydrocarbon structure decreases larvicidal potency. Conjugated and exo double bonds appear to increase larvicidal potency. Replacement of double bonds by more reactive epoxides decreases the larvicidal potency. The presence of hydroxyls in the cyclic structure resulted in decreased potency, probably due to increased polarity indicanting that lipophilicity seems to play an important role in increasing the larvicidal potency in this set of compounds.

Toxic effects on and structure-toxicity relationships of phenylpropanoids, terpenes, and related compounds in Aedes aegypti larvae.

In the search for toxic compounds against Aedes aegypti L. (Diptera: Culicidae) larvae, a collection of commercially available aromatic and aliphatic diversely substituted compounds were selected and evaluated. p-Cymene exhibited the highest larvicidal potency LC50 = 51 ppm, whereas 1,8-cineole exhibited the lowest activity value LC50 = 1419 ppm. To aid future work on the search for larvicidal compounds, the structure-toxicity relationships of this collection have been evaluated. The presence of lipophilic groups results in an overall increase in potency. In general, the presence of hydroxyl groups resulted in less potent compounds. However, methylation of such hydroxyls led to an overall increase in potency. The most potent compounds showed comparably good larvicidal activity in A. aegypti larvae as other terpenes, which we assume to be the result of the increased lipophilicity.

Efficacy of instrumentation techniques and irrigation regimens in reducing the bacterial population within root canals.

The purpose of this study was to compare the in vitro intracanal bacterial reduction produced by using two instrumentation techniques and different irrigation methods. Root canals inoculated with Enterococcus faecalis were prepared by using the following techniques and irrigants: alternated rotary motions (ARM) technique, hand nickel-titanium files and 2.5% sodium hypochlorite (NaOCl) as irrigant; ARM technique and combined irrigation with 2.5% NaOCl and citric acid; ARM technique and combined irrigation with 2.5% NaOCl and 2% chlorhexidine gluconate; and Greater Taper rotary files, using 2.5% NaOCl as irrigant. Controls were instrumented by using the ARM technique and irrigated with sterile saline. Canals were sampled before and after preparation. After serial dilution, samples were plated onto Mitis-Salivarius agar, and the colony forming units that were grown were counted. All test techniques and solutions significantly reduced the number of bacterial cells within the root canal (p < 0.05). There was no significant difference between the experimental groups (p > 0.05). Nonetheless, all of them were significantly more effective than the control group (p < 0.05). These findings support the importance of using antimicrobial irrigants during the chemomechanical preparation, regardless of the solutions or instrumentation techniques used.