Collander’s equation

Further analysis of equation 39 reveals a reason for the validity of Collander s equation that correlates partition coefficients in different solvent systems (111). Thus, in equation 39 the terms (IW-IQ) and (Jy-JQ) both reflect a variable characteristic of the solvents. For small changes in this variable they should be proportional to each other... 

Thus, Collander s equation 42, which was established from empirical studies (111), is theoretically derived from the extrathermo-dynamic treatment of solvent effects and is obtained as a result of the second approximation which takes into account the effects of solvation on the interaction term between R and x> x S we now regard the interaction of drugs (in water) with tfie bio-phase as a partitioning phenomenon, equation 42 becomes the basis for the use of the partition coefficient in octanol/water, P, as a model for the partition coefficient between biophase and water,... 

The analysis of the parameters representing the effect of the medium in terms of extrathermodynamical relations has shown (see above, section A.2) that the hydrophobic substituent constant it depends on the molecules from which it is derived. For example, hydrophobic constants derived from the octanol/water partition coefficients of aromatic molecules differ from those obtained from aliphatic molecules (112). Collander s equation (111) provides the empirical basis for the evaluation of logP values for the same molecule in different solvents. However, solvents with markedly different solvation properties (e.g., hydrogen bonding ability) do not conform to Collander s equation (see below, section C.3). 

Deviations from equation 42 are not attributed solely to solvent effects. Applying Collander s equation to many partition coefficients for various compounds in various solvent systems, Hansch (112, 121) found that deviations from the correlation can be classified on the basis of known chemical properties as hydrogen bond donors for those that were below the regression line and as hydrogen bond acceptors for those above the line. 

It is known that the RPLC retention parameters are often strongly correlated to the analyte s distribution coefficient in organic solvent/ water. Generally, the relationship between liquid/liquid (LL) distribution and RPLC retention are of the form of the dimensionless Collander-type equations, e.g., see Eq. (15.21)... 

In the case of parameters related to the effects of the medium Collander s relation (equation 42) has been shown to hold for many different compounds in many solvent systems (112-118). For example, partition coefficients between water and oleyl alcohol, isobutyl alcohol, and xylene correlate well with partition... 

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