Vapour pressure QSAR models

Based on the EPI generated values for solubility (log Sol), octanol-water partitioning (log Kow), vapour pressure (log VP) and Henry s Law constants (log HLC) new linear QSAR models are build by estimating the relationships between the EPI generated data and available experimental data for up to 65 organophosphor insecticides, the general formula for the descriptors, Du to be used being... 

The compound-specific data required for exposure assessments comprise the 1-octanol/water partition coefficient (log water solubility (S ), vapour pressure (p ), Henry s law constant (H, H ), soil sorption coefficient hydrolysis half-life time, photolysis half-life time and information on biodegradability (OECD, 1993c). These parameters generally relate to steady-state conditions - conditions that are rarely met in the real environment. The experimental data underlying the QSAR models are preferably determined by standardized protocols, but, even then, the absolute values are of variable reliability and precision, which clearly affects the accuracy of the predictions based on the acquired QSARs. The endpoints discussed in the following sections were selected because of their consideration in regulatory evaluation schemes in, for example, the EU (EEC, 1990). 

Table 4.4 Examples of QSAR models for estimating vapour pressure p. ...

The PROPERTIES option provides measured values taken from the literature or values calculated from QSAR models for 10 molecular descriptors that relate to the chemicals physical and chemical properties molecularweight, parachor, molar refraction, molar volume, boiling point, vapour pressure, water solubility, log P, heat of vapourization, and log S (see Lyman et al. 1982, for a detailed discussion of these parameters). The user may alter the value for any parameter in order to see how that may affect values of other parameters in the system. The option also generates connectivity indices which are highly useful in describing and comparing molecular structural characteristics (Kier and Hall 1976). 

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