Williams softness parameter

The Williams softness parameter (s, R or R (W)) is defined as the ratio of the ionization potential to the ionic function, ZVr where Z is the ionic charge and r the ionic radius of the cation (Williams and Hale 1966 Williams et al. 1982) ... 

Williams, M.W., and J.E. Turner. 1981. Comments on softness parameters and metal ion toxicity./. Inorg. Nucl. Chem. 43 1689-1691. 

Williams and Turner (1981) used a compilation of intraperitoneal-dosed mouse LD50 data available in the literature to develop a QSAR for the Pearson and Mawby softness parameter (Op) to predict the LD50 value of 25 mono-, di-, and trivalent cations to mice (Table 5.1). The 25 cations used to develop the Williams and Turner (1981) QSAR are listed in Table 5.15. 

Williams et al. (1982) and Turner et al. (1983) Pearson and Mawby Softness Parameter (Op) QSARs... 

Table 5.19 lists the 21 QSARs that only used the Pearson and Mawby softness parameter (Op) to predict cation toxicity. Two of these QSARs are duplicates. The Turner et al. (1983) QSAR with r =0.360 is a duplicate of the Williams et al. (1982) QSAR with the same r value. The Turner et al. (1985) QSAR with r =0.879 is a duplicate of the Turner et al. (1983) QSAR with the same r value. The Jones and Vaughn (1978) QSAR for Ag+, Am, Cd " and Hg had the highest perhaps because of their proximity in the periodic table. The Turner et al. (1983) QSAR for Mn +, cm+, Ni +, Cu +, zm+, Cd +, Hg +and Pb " had the second highest r, perhaps because Mn +, Co +, NE+, and Zn " were in row 4 of the periodic table and Cd +, Hg + and Pm+ were in close proximity. For the Jones and Vaughn (1978) and Turner et al. (1983) references with 4 and 3 QSARs, respectively, the r decreased as the number of divalent cations increased (Table 5.18). The Babich et al. (1986) and Magwood and George (1996) QSARs both had high r and almost identical cations. The Babich et al. (1986) QSAR had almost identical cations to those used for the Turner et al. (1983) QSAR with r =0.879 (Table 5.18). The Enache et al. (1999) QSAR also had a high r. However, the Mendes et al. (2010) QSAR with a high r was the best for the highest number (18) of cations (Table 5.19).

The Pearson-Mawby softness parameter played a central role in this work. Since the use of this parameter does not permit the comparison of ions with different oxidation numbers (Ahrland 1968), the analyses in Turner et al. (1983) and Williams et al. (1982) were confined largely to the application of equation 2 to groups of ions of a given charge. For the 14 divalent ions used in the mouse experiment (Williams et al. 1982), a correlation represented by r = 0.36 was found with standard error s = 0.57. One aim of the present study is to demonstrate a predictive ability for toxicity which can be used for ions of any oxidation number and which is hence independent of ap. 

Source Data from M.W. Williams, D. Hoeschele, J.E. Turner, K.B. Jacobson, N.T. Christie, C.L. Paton, L.H. Smith, H.R. Witschi, and E.H. Lee, Chemical Softness and Acute Metal Toxicity in Mice and Drosophila. Toxicol. Appl. Pharmacol. 63 (1982) 461-469 and J.E. Turner, E.H. Lee, K.B. Jacobson, N.T. Christie, M.W. Williams, and J.D. Hoeschele, Investigation of Correlations between Chemical Parameters of Metal Ions and Acute Toxicity in Mice and Drosophila. ScL Total... 

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