Facet-Dependent Lethality of a Contact Insecticide Crystal.

The activity of crystalline contact insecticides relies on the extraction of surface molecules by insect tarsi upon contact. Most crystals are inherently anisotropic, and surface molecules on symmetry independent faces are expected to have different free energies. The facet-dependent bioavailability and associated efficacy of insect lethality have not been investigated, however.

ROY Crystallization on Poly(ethylene) Fibers, a Model for Bed Net Crystallography.

Many long-lasting insecticidal bed nets for protection against disease vectors consist of poly(ethylene) fibers in which insecticide is incorporated during manufacture. Insecticide molecules diffuse from within the supersaturated polymers to surfaces where they become bioavailable to insects and often crystallize, a process known as blooming. Recent studies revealed that contact insecticides can be highly polymorphic.

Insecticidal and Repellent Properties of Rapid-Acting Fluorine-Containing Compounds against Mosquitoes.

The development of safe and potent insecticides remains an integral part of a multifaceted strategy to effectively control human-disease-transmitting insect vectors. Incorporating fluorine can dramatically alter the physiochemical properties and bioavailability of insecticides. For example, 1,1,1-trichloro-2,2-bis(4-fluorophenyl)ethane (DFDT)─a difluoro congener of trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)─was demonstrated previously to be 10-fold less toxic to mosquitoes than DDT in terms of LD values, but it exhibited a 4-fold faster knockdown.

Overcoming insecticide resistance in Anopheles mosquitoes by using faster-acting solid forms of deltamethrin.

Background: Controlling malaria-transmitting Anopheles mosquitoes with pyrethroid insecticides is becoming increasingly challenging because of widespread resistance amongst vector populations. The development of new insecticides and insecticidal formulations is time consuming and costly, however. A more active crystalline form of deltamethrin, prepared by heating the commercial crystalline form, previously was reported to be 12-times faster acting against susceptible North American Anopheles quadrimaculatus mosquitoes.

Crystallography of Contemporary Contact Insecticides.

The active forms of contact insecticides used for combatting mosquito-borne infectious diseases are typically crystalline solids. Numerous molecular crystals are polymorphic, crystallizing in several solid forms characterized by different physicochemical properties, including bioavailability. Our laboratory recently found that the activity of crystalline contact insecticides is inversely dependent on the thermodynamic stability of their polymorphs, suggesting that efficacy can be enhanced by the manipulation of the solid-state structure.

Imidacloprid Crystal Polymorphs for Disease Vector Control and Pollinator Protection.

Imidacloprid, the world's leading insecticide, has been approved recently for controlling infectious disease vectors; yet, in agricultural settings, it has been implicated in the frightening decline of pollinators. This argues for strategies that sharply reduce the environmental impact of imidacloprid. When used as a contact insecticide, the effectiveness of imidacloprid relies on physical contact between its crystal surfaces and insect tarsi.

A deltamethrin crystal polymorph for more effective malaria control.

Pyrethroid contact insecticides are mainstays of malaria control, but their efficacies are declining due to widespread insecticide resistance in mosquito populations, a major public health challenge. Several strategies have been proposed to overcome this challenge, including insecticides with new modes of action. New insecticides, however, can be expensive to implement in low-income countries.

Experimental evidence for the role of paramagnetic oxygen concentration on the decay of long-lived nuclear spin order.

Nuclear singlet lifetimes are often dependent on the quantity of paramagnetic oxygen species present in solution, although the extent to which quenching or removing molecular oxygen has on extending singlet lifetimes is typically an unknown factor. Here we investigate the behaviour of the singlet relaxation time constant as a function of the oxygen concentration in solution. An experimental demonstration is presented for a chemically inequivalent proton pair of the tripeptide alanine-glycine-glycine in solution.