Studies Of The Electrochemical Activity Of Thiobensoalides At The Mercuty Electrode
STUDIES OF THE ELECTROCHEMICAL ACTIVITY OF THIOBENSOALIDES AT THE MERCUTY ELECTRODE
B. Marczewska, A. Persona
Department of Analytical Chemistry and Instrumental Analysis, Faculty of Chemistry, Maria Curie-Sklodowska University,
Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland
So far electrochemical techniques are used very rarely in the investigation of pesticides. The aim of that study has been to test the electrochemical proprieties of 25 (N-phenyl) –2,4-dihydroxybenzenocarbothioamide derivatives with different substitutes at the anilide ring on mercury electrode. Thobensoanilides are known to have a strong biological activity. Previous works confirmed high bacteriostatic and mycostatic proprieties of these compounds. For this substances were determined Minimal Inhibitory Concentration (MIC) [1]. They are comparatively less toxic for higher organismus.
The result of measurement of all examined thibenzoanilides is that they undergo the absorption on the surface of the mercury electrode. The courses of the capacity versus the potential curves of this substances show similarity. They also show the similarity to the courses of differential capacity curves obtained in the presence of thiourea. This is probably connected with the presence of –C=S group and their specific adsorption on mercury electrode.
Some peaks are noticed on the curves obtained by square wave polarography method. They show electrode processes. In the range from –0.1 to –0.7 V two peaks are observed. They are different in size and shape. They can be also observed on the cyclic voltammetric curves. The potentials of these peaks depend on pH solutions. With the increase of pH, the values of the peaks move towards the more negative values. It should be noted that similary curves are obtained from solution in the presence of S² ion [2]. In the researching system, the electrode process is probably connected with the reaction of the RS- ion of thiobenzotioanilide with mercury and extract Hg(SR) and/or Hg (SR) which undergo the reduction in the following way:
Hg(SR)2+ 2H+ + 2e = Hg + 2HSR ; HgSR + H+ +e= Hg + HSR
Ten tiobenzonsnilides were carefully examined at pH=4 and 8 using square wave polarography and chronovoltamperometric method (Table1.). They have different toxic features which affect the fungi being chosen.
Table 1.Values ΔE of peaks sw of chosen thiobesoanilides with the different value of MIC
Factor MIC
ΔE/mV (pH=4)
ΔE/mV (pH=8)
5.3
326
338
13.6
320
272
26.6
162
216
26.4
250
210
87.3
196
160
115.0
126
136
It turns out that there is dependence among compounds with value of MIC from 5.3 to 115. The more toxic substance have the bigger distances between the values of the peaks sw and cathode peaks potentials in chronovoltamperometric curves. That fact helps to assume that these differences can be utilised in predefining, which thiobesoanilide is more or less toxic. It should be underlined that character of researching is rather qualitative and needs further description, however the initial measurement of the fungicide abilities can be very useful for the indication of the substances which is worth undergoing toxicological research.
References
1. K.Jóźwiak, H.Szumiło, B.Senczyna and A.Niewiadomy, SAR and QSAR in Eviromend Reserch, 10(1999) 509.
2. W.I.Gorochowskaja and W.M.Gorochowskij, Oscylopolarografia praktyczna, Wysszaja Skoła , Moskwa 1973.
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