Biomedical Chemistry: Research and Methods 2019, 2(3), e00097

Spectrophotometric Determination of the Ionization Constants for the Oximes – Cholinesterases Reactivators at Different Temperatures

T.V. Schäfer*, A.A. Tyaptin, T.B. Pechurina

State Scientific Research Test Institute of the Military Medicine, 4 Lesoparkovaya str., Saint-Petersburg, 195043 Russia; *e-mail: schafer@yandex.ru

Keywords:oximes; absorbtion spectra; protolytic dissotiation; ionization constants; temperature effect

DOI:10.18097/BMCRM00097

The whole version of this paper is available in Russian.

The goal of study was the determination of the ionization constants for the oximes – cholinesterases reactivators in aqueous solutions at different temperatures. The wavelengths of absorption maxima of the protonated and deprotonated oxime groups, the molar extinction coefficients of the various oximes species, and the ionization constants for the oxime cholinesterases reactivators (isonitrosin, pralidoxime, dipyroxime, toxogonin, methoxime, carboxime and asoxime) were obtained using spectrophotometric data (wavelength 190 to 450 nm) in solutions (pH 5-12) at 20°C, 25°C and 37°C. The proportion of nucleophilic forms involved in the oxime-induced reactivation of phosphorylated cholinesterases was shown to be is positively dependent on the incubation medium pH value and temperature. A hypothesis that the temperature affects the oximes ability to reactivate phosphorylated cholinesterases has been proposed.
Figure 1. Structural formulas of oximes cholinesterase reactivators.
Figure 2. Absorbance spectra of monooximes (1.0·10−4 M, 37°C) in solutions with various pH (shown as numbers inside plots).
Figure 3. Absorbance spectra of bispyridinium dialdoximes (5.0·10−5 М, 37°C) in solutions with various pH (shown as numbers inside plots).
Figure 4. Fraction of oximate-ions (upper line) or sum of the fractions of monoprotonated and deprotonated forms of bispyridinium dialdoximes (bottom line), (mean ± SEM), in aqueous solutions, pH 7.3 (—●—) or 7.4 (- - ○ - -), at different temperatures. Data calculated according to equations 12–14.

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Table 1. Wavelengths corresponding to absorption maxima (λmax) of protonated and deprotonated oxime groups, nm

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Table 2. Molar absorption coefficients ε species of monooximes at at λmax of oximate-ion and ionization constants in aqueous solutions at different temperatures, (mean ± SEM)

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Table 3. Molar absorption coefficients ε species of bispyridinium dialdoximes at λmax of oximate-ion and ionization constants in aqueous solutions at different temperatures, (mean ± SEM)

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Table 4. Linear models characteristics of temperature dependence of the oximes pKa, pKa1, pKa2 values

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