Original scientific paper
On the inhibitory properties of oximes I. action of oximes on the chemiluminescence of luminol
Jelka Matković
; Institut za medicinska istraživanja i medicinu rada Jugoslavenske akademije znanosti i umjetnosti; Zagreb
K. Weber
; Institut za medicinska istraživanja i medicinu rada Jugoslavenske akademije znanosti i umjetnosti; Zagreb
D. Fleš
; Institut za medicinska istraživanja i medicinu rada Jugoslavenske akademije znanosti i umjetnosti; Zagreb
N. Paulić
; Institut za medicinska istraživanja i medicinu rada Jugoslavenske akademije znanosti i umjetnosti; Zagreb
Abstract
It has been found that oximes with widely different chemical structure are effective inhibitors of the luminol reaction catalysed by organophosphorus compounds (esters of phosphoric or thiophosphoric acid, insecticides. nerve gases) or various complexes with iron. The reaction mechanism of the inhibition is closely related to the reactivation of cholinesterase inhibited by organo-phosphorus compounds with oximes. The reactivation of the inhibited cholinesterase is generally considered as due to the chemical interaction of oximes with inhibitor (organophosphorus compounds). The mechanism of the inhibition of luminol reaction probably consist of the interaction of inhibitor (oxime) with catalyst (organophosphorus compound. complex of iron). The study of inhibition of the luminol reaction with oximes provides a means for a simple evaluation of inhibitory properties of various oximes. The results of the measurements of inhibitory effect of 16 oximes on the luminol reaction catalysed by hemoglobin or potassium ferricyanide are described in this paper. By means of photoelectric measurements the relationship between the intensity (G) of chemiluminescence of luminol (in alkaline solutions in the presence of hydrogen peroxide and appropriate catalyst). and reaction time (t) with or without oximes (Fig. 1, 2, 3, and 4) was established. Maximal intensity of chemiluminescence (Gm) was used as a relative value of the maximal velocity of luminol reaction. From the relationship between maximal velocity and oxime concentration, the concentration for 50% inhibition (i1/2) can be determined. These concentrations are listed in Tables 1 and 2. It is evident that these concentrations are within relatively broad range, between 6,5,10-5 M and 5,9,10-3 M, and that they depend upon the nature and concentration of inhibitors used in the reaction. lt was further found that the yellow colour of some oximes in the alkaline solution has an insignificant role in the process of inhibition caused by oximes. This fact has been established by quantitative measurement of light absorption of oxime solution at various wave lengths (Curves 3 and 4, Fig. 7), followed by the numerical interpretation of the obtained results taking into account the spectral distribution of emitted light of luminol (Curve 2, Fig. 7) and the sensitivity of the photoelement (Curve I, Fig. 7). Spectral curves obtained as a result of these proceedings are shown in Fig. 8. It is evident that the absorption of light by oximes does not influence the luminescence appreciably. Tables 3 and 4 show the experimentally determined i1/2 and mathematically corrected i1/2 concentrations of P3AM and P4AM. The inhibition of the luminol reaction with oximes represents a competitive inhibition (Fig. 9 and JO) as shown by means of kinetic analysis (13. 14). The dissociation constant (Ki) of the compound obtained by the chemical combination of oximes (DAM and C-4-dioxime) with catalysts (hemoglobin or K3[Fe(CN)6]) was determined by the use of Dixon equation (2). The constant of inhibition, according to the equation (3) or (4), decreases when the concentration of substrate increases, what is in agreement with the theory of competitive inhibition. The possible influence of the ionic state of some oximes on the mechanism of inhibition is discussed. Ions of oximes (I- and Br-) evidently have no influence on the velocity of the luminol reaction. The results of the studies of the influence of oximes on the luminol reaction catalyzed by organophosphorus compounds will be published elsewhere.
Keywords
Hrčak ID:
182522
URI
Publication date:
21.9.1960.
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