  The global descriptors of chemical activity:ionization potential IP, electron
affinity EA, chemical potential mu, absolute electronegativity chi, molecular
hardness eta and softness S,electrophilicity index omega for cyanides X(CN)k
with X=H, Na, K, Ag, Cu, Ca, Hg, Cd, Zn in the gas phase and water medium have
been determined by taking advantage of the quantum-chemical computations.To
this aim, the HOMO and LUMO energy levels were calculated using DFT B3LYP
method and QZVP (Valence Quadruple-Zeta Polarization) basis set, which enables
precise calculations for hydrogen cyanide and its salts containing both light
(H, Na, Ca) and heavy (K, Ag, Cu, Cd, Hg, Zn) atoms.The results obtained
indicate that while the EA-parameter roughly determines the LD50 values for the
cyanides considered, the omega-descriptor is related rather to the product of
cyanide LD50 and hydrolysis n-degree.Hence,the theoretical LD50CN(omega)
function proposed is interconnected with the nLD50 collective variable, whereas
LD50(EA)directly approximates LD50 indicating that the toxicity of cyanides
decreases with increasing EA, omega-values.The calculations carried out suggest
that some of the LD50(Exp)experimentally determined are incorrect (AgCN) or
inaccurate (Cd(CN)2) and require revision.Comparison of the theoretically
estimated LD50(omega) with NOAEL toxicity parameters indicates that they are
well correlated in contrast to LD50(EA) and LD50(Exp), exhibiting lower and
marginal degrees of correlation, respectively.
