Structural effects of dinotefuran and analogues in insecticidal and neural activities

The insecticidal potencies of dinotefuran and analogues against the adult male American cockroach, Periplaneta americana (L) were measured by injection with or without metabolic inhibitors. The potency of dinotefuran was close to those of clothianidin and imidacloprid under the conditions used. The nerve-excitatory and nerve-blocking activities were measured with central nerve cords of P americana. The nerve-excitatory activity of dinotefuran was lower than that of imidacloprid, but was comparable with that of clothianidin. The nerve-blocking activity of dinotefuran was comparable with that of imidacloprid and slightly higher than that of clothianidin. Quantitative analyses showed that variations in the insecticidal activity were better correlated with variations in the nerve-blocking activity than with those in the nerve-excitatory activity when the contribution of the hydrophobic factor was allowed for.     

Determination of Total Iodine in Soils by Inductively Coupled Plasma Mass Spectrometry

A method for the determination of the total amount of iodine in soil by inductively coupled plasma mass spectrometry was developed. Iodine in soil was completely extracted by heating a mixture of 5 mL of 5% tetramethylammonium hydroxide solution and 100 mg of soil for 3 h in an oven at 70°C. Indium as an internal standard was added and the extract was diluted at least more than 10-fold. Iodine amount in the solution was determined by measuring the signal intensity of ¹²⁷I against that of ¹¹³In. When the method was tested by analyzing four reference soil samples (GSS-1, 4, 5, and 7), the iodine contents obtained were in good agreement with the certified values for the samples.     

Speciation of iodine in soils

In order to analyze the behavior and phytoxicity of iodine in soil, the chemical forms of soil iodine must be identified. Therefore, a method for quantitative speciation of iodine in soil was proposed. Iodine extracted from soil samples with tetrametBPyIammonium hydroxide (TMAH) was separated into humic and fnalvic acid fractions at pH4 1.5 after the addition of ascorbic acid into the TMAH extract to reduce iodate into iodide. Since the iodide in the TMAH extract was recovered in the fdvic acid fraction by this procedure, iodine contained in the haamic acid fraction was considered to be organically bound. Podine in the fulvic acid fraction was separated into organic iodine bound to fnlvic acids and the total inorganic iodine. Furthermore, iodine soluble from soil in 0.1 mol L^-1 potassium chloride was assumed to correspond to the amount of total iodide in soil, and from the difference in the concentration of total inorganic iodine and soluble iodide, the amount of iodate was calculated. By the application of this method, iodine in soil was separated into four fractions: organic iodine bound to humic acids, organic iodine bound to fulvic acids, iodate, and iodide. This speciation method was applied to two soils. It was found that s Barge proportion of iodine in soil occurred in an organicalPy bound form.     

Insecticidal activity and nicotinic acetylcholine receptor binding of dinotefuran and its analogues in the housefly, Musca domestica

The insecticidal activity of dinotefuran and 23 related compounds against the housefly, Musca domestica (L) was measured by injection with metabolic inhibitors. Dinotefuran was less active than imidacloprid and clothianidin by a factor of 10 in molar concentrations. Their binding activities to the fly-head membrane preparation were measured by using [125I]alpha-bungarotoxin ([125I]alpha-BGTX) and [3H]imidacloprid ([3H]IMI) as radioligands. The activity of some selected compounds measured with [3H]IMI was 10(4)-fold higher than that measured with [125I]alpha-BGTX. With [3H]IMI as a radioligand, dinotefuran was 13-fold less active than imidacloprid. The inhibitory effect of dinotefuran on the binding of [3H]IMI to the membrane preparation was in a competitive manner. Quantitative analysis of the insecticidal activity of the test compounds with the binding activity measured with [3H]IMI showed that the higher the binding activity, the higher was the insecticidal activity.