Report No xxxx - Instytut Fizyki JÄ drowej PAN

35 Cl-NQR STUDY OF ELECTRONIC STRUCTURE AND BIOLOGICAL
ACTIVITY OF SELECTED DDT-TYPE INSECTICIDES
K. Makiej, B. Nogaj
Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań,
Poland
INTRODUCTION
Insecticides belong to pesticides being a large group of compounds toxic to pests.
They are synthetic compounds and do not occur in the natural environment. An important
criterion of classification of pesticides is the acute toxicity defined as the lethal dose LD 50 per
os, so the dose causing death of a half of the number of target animals, expressed in mg/kg of
body weight [1]. Insecticides are characterised by low molecular mass and high biological
activity in insects. One of the best known insecticide is DDT – 1,1,1-trichloro-2,2-bis-(pchlorophenyl)ethane
[2,3]. It was commonly used in agriculture in the 40s through to the 60s
of the last century because of its high and selective toxicity. Its use was eventually abandoned
because of its exceptionally high stability in the environment and in living organisms,
following from its resistance to the effect of enzymes.
In this study an attempt was made to find a correlation between the chemical structure
and biological activity of selected DDT-type insecticides.
EXPERIMENTAL
The NQR spectra provide the information on NQR line frequency, quadrupole
coupling constant and asymmetry of the tensor of electric field gradient and on the basis of
them on the electron density in the vicinity of a given nucleus.
The electronic structure of the following DDT type insecticides has been studied by
35 Cl-NQR: DDT, DDD, DDE, DDA. The molecules of these compounds have the shape of a
wedge with the base of phenyl rings with Cl atoms at para positions (Fig.1).
Cl
R
Cl
Fig.1. The structural formula of DDT-type insecticides
RESULTS AND DISCUSSION
Table 1 presents the structural formula, 35 Cl-NQR frequencies and biological activity of the
insecticides studied (LD 50 for rats [4]). The two phenyl rings are constant elements of the
compounds differing only in the substituent R joining the rings. The mean 35 Cl-NQR ( ν 1, 2 )
frequency characterising the two Cl atoms at the para positions of the phenyl rings was
calculated for particular insecticides. This value was correlated with the parameter LD 50
obtaining a linear relation. The LD 50 parameter decreases with increasing mean frequency
ν 1,2 (Fig.2), which means that the biological activity of the insecticides increases with
increasing 35 Cl-NQR frequency on chlorine atoms at the phenyl rings.
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