Modeling kinetics of subcellular disposition of chemicals.
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Affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, North Dakota State University, Fargo, North Dakota 58105, USA. stefan.balaz@ndsu.edu
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Mentions: The dependencies of the concentrations or effects on lipophilicity profiles are most frequently measured after a constant exposure time for all chemicals. The profiles are different for individual distribution periods and will be described in detail below. To facilitate the discussion, an empirical equation describing all simulated profiles(2087) is introduced at this point:Equation 11 describes the multilinear dependencies with up to four linear parts and can be considered an extended form of the bilinear equation described by eq 9. The model partition coefficient was substituted by a reference partition coefficient using the Collander equation 1 in section . The first term on the right side is written in a way that emphasizes the substitution of the partition coefficients. The connection between the adjustable coefficients A, B, and C and the shape of the corresponding curves is outlined in Figure 17. The coefficients A and Bi determine the slopes of linear parts, as shown in the upper panel of Figure 17. The coefficients Ci are associated with the position of the curvatures. The Collander exponent β modulates the sharpness of the curvatures. The upper curve, which is characteristic for the mixed period of distribution, is described using the integer values of the coefficients A and Bi, which are selected from available combinations, summarized in Table 6. The lower curve is typical for open systems. The leftmost and rightmost linear parts still maintain the integer values that are specified in Table 6. However, the slopes of two linear parts that characterize the convex dip are no longer confined to the integer values and, consequently, the coefficients B1 and B2 are freely adjustable. The adjustable coefficients of eq 11, for the dependencies shown in Figure 17 and other cases discussed in sections −, were fitted to the experimental data using nonlinear regression analysis, deploying the Fletcher and Powell algorithm.(2090) 
View Article: PubMed Central  PubMed
Affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, North Dakota State University, Fargo, North Dakota 58105, USA. stefan.balaz@ndsu.edu