The direct reaction of seven pyridinium
oximes with the
organophosphorus compounds (OPCs)
crotylsarin,
cyclosarin, and
VX was studied by spectrophotometry. This method allows to quantify different parameters: (a) the half-life times (t (1/2)) of the
oxime-OPC reactions on the basis of the changes in the absorption at the zwitterion (
betaine) peak maximum, (b) the first- and second-order rate constants (k (1), k (2)), and (c) the maximum reaction velocities (v (max)). The results of the study show that the reaction velocity of the
nerve agents with any of the
oximes investigated decreased in the order
crotylsarin >
cyclosarin >
VX. The comparison of the reaction rates of the three therapeutically used
oximes (2-PAM,
obidoxime,
HI 6) with the respective OPC gave the highest rate for
crotylsarin and
cyclosarin with
obidoxime and to a similar degree with
HI 6, while in the case of
VX the most reactive
oxime was
HI 6. The reaction velocity of the
nerve agents with the monopyridinium
oxime 2-PAM was lower as compared to the bispyridinium
oximes (
obidoxime,
HI 6). The results obtained with the two
sarin analogues indicate that the direct reaction with
2-PAM,
obidoxime, or
HI 6 could be used for non-
corrosive decontamination purposes, especially, if sensitive
biological surfaces like skin, mucous membranes, or
wounds are considered. However, in view of the concentrations of
nerve agents and
oximes, which could be expected during OPC
poisoning in man, the maximum reaction velocities would not be high enough to contribute markedly to the detoxication of
nerve agents in vivo.