The relative conductance of two different electroactive thiol molecules (containing ferrocene and viologen headgroups) inserted into an n-alkanethiolate background SAM was tracked over time using a scanning tunneling microscope. Both types of inserted molecules exhibited stochastic variation in their conductance. This phenomenon of “blinking” thus appears to be quite general, despite the fact that these two molecules are structurally different from one another and from molecules in which this phenomenon had been studied previously. This behavior is most simply rationalized as conformational and/or orientational changes of one or a small collection of molecules over time.

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The toxicity of several compounds isolated from Asarum heterotropoides root steam distillate to third-instar larvae of Culex pipiens pallens Coquillett, Aedes aegypti (L.), and Ochlerotatus togoi Theobald was examined using a direct contact mortality bioassay. Safrole was the most toxic constituent to Cx. p. pallens and Ae. aegypti larvae, whereas terpinolene was most toxic to Oc. togoi. However, LC50 values of these three mosquito larvae to both essential oils as well as the remainder of the 26 compounds identified in A. heterotropoides were considerably greater than for fenthion or temephos. However, we suggest that constituents of A. heterotropoides root steam distillate merit further study as potential mosquito larvicides due to global efforts to reduce the level of highly toxic synthetic pesticides in the aquatic environment.

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