Formation of methemoglobin and metmyoglobin using 8‐aminoquinoline derivatives or sodium nitrite and subsequent reaction with cyanide

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Abstract
The kinetics of the oxidation of hemoglobin (Hb) and myoglobin (Mb) by sodium nitrite, 8-[(4-amino-1-methylbutyl)amino]-6-methoxy-quinoline diphosphate (primaquine), 6-methoxy-8-(6-diethvlaminohexylamino)-4-meihyl-quinoline dihydrochloride (WR6026) and 8-[(4-amino-1-methylbutyl)amino]-2,6-diniethoxy-4-methyl-5-[(3-trifluoromethyl)phenoxy]quinoline succinate (WR238,605) were studied at pH values ranging from 7.4 to 7.6 and at 37 ± 1°C. The reaction between Hb and primaquine, WR6026 and WR238,605 resulted in precipitation, as did the reaction between Mb and WR238,605. The reaction between nitrite ion (NO2−) and Hb showed a lag period followed by an autocatalytic phase. The data in this study are consistent with and substantiate the proposed mechanism for the Hb–NO2− oxidation reaction. The reaction between Mb and NO2− at higher NO2− concentrations also showed a lag period followed by an autocatalytic period, while at lower NO2− concentrations no lag period was seen. The data suggest a shift in rate constant at these lower NO2− concentrations. The reaction between Mb and both WR6026 and primaquine followed a two-term rate law with oxidant-dependent and -independent terms. Concentration–effect curve data, along with these results, suggest the presence of a catalytic pathway. The rates of formation of cyanomethemoglobin and cyanometinyoglobin complexes from cyanide ion and methemoglobin (MHb) and metmyoglobin (MMb), respectively, were followed in the presence of the heme oxidants. The rate constants were all within a narrow range and suggest that complexation of cyanide by MHb and MMb is not affected by the presence of oxidants.

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