Journal of Photochemistry and Photobiology B: Biology
Synthesis and photoactivated insecticidal activity of tetraethynylsilanes
Introduction
Compared to traditional organophosphate and carbamate pesticides, the photoactivatable insecticides act through photodynamic pathways [1], [2], which are characterized by the great enhancement of their activities after absorption of light energy and have diverse biological effects including insecticidal, fungicidal, bactericidal, nematicidal, and herbicidal activities [3], [4]. The main classes of photodynamic sensitizers that have been used as photoinsecticides are xanthenes, porphyrins, phenothiazines, furanocoumarins, acridines, thiophenes, and polyacetylenes [5], [6].
In our work on arylene ethynylenes [7], [8], [9], [10], [11], [12], [13], we were interested in the preparation of tetraethynylsilanes (RCC)4Si, because of their ready accessibility and stability. The attachment of a fluorophore to the silicon atom enhances the quantum yield of photoluminescence (PL), and that several TETS exhibit high quantum yields in solution have been revealed [8], [9]. We envisaged such TETS could achieve high photoactivated insecticidal activities induced by four triple bonds on silicon. With this thought in mind, a series of TETS were synthesized and their photoactivated insecticidal activities against the 4th-instar larvae of Aedes albopictus (Skuse) were investigated, and the structure–activity correlation was also clarified [14].
Section snippets
General
All reactions were carried out under an atmosphere of argon with freshly distilled solvents, unless otherwise noted. Tetrahydrofuran (THF) was distilled from sodium/benzophenone. Other solvents such as toluene, diisopropylamine, and CH2Cl2 were distilled from CaH2. Solutions of LiHMDS and Grignard reagents in THF and diethyl ether were purchased and used without titration. A solution of n-BuLi in hexane was purchased and titrated by the Gilman method prior to use. Silica gel was used for column
Results and discussion
At 100 mg L−1, the mortality of 4th-instar larvae of A. albopictus (Skuse) in the light treatments was shown in Table 1, only three TETS 3, 8, 9 and α-terthienyl showed potent toxicity (100%), larvicidal activities of other eight TETS were very low (⩽38%) even at so high concentration (100 mg L−1). Unsubstituted TETS 3 gave a good insecticidal activity, when methoxy group was introduced at the terminal phenyl ring, the toxicities of TETS 4–6 were very low comparable to that of TETS 3, which
Conclusions
A series of TETS have been successfully synthesized in moderated yields, and their photoactivated insecticidal activities against the 4th-instar larvae of A. albopictus (Skuse) were determined. TETS 3, 8, 9 exhibited higher activities. When four thiophene rings were attached on the same silicon atom with the triple bond, TETS 8 displayed the highest photoactivated insecticidal activity. The relationship analysis between structure and activity showed the thiophene ring played a very important
Abbreviations
TETS tetraethynylsilanes NMR nuclear magnetic resonance SD standard deviation LC50 median inhibitory concentration
Acknowledgments
This work was supported by the Natural Science Foundation of Guangdong Province (No. 8451027501001447); the Scientific Research Foundation for Returned Scholars, Ministry of Education of China; the Key Project of Chinese Ministry of Education (No. 209092) and Transformation of Scientific and Technological Achievements from Department of Education of Guangdong province (cgzhzd0712).
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These authors contributed equally.