Almost a century ago Meyer [1] and Overton [2] laid the foundations for the use of partition coefficients as a measure of the way chemicals travel through and distribute themselves inside living systems. This work was followed by that of Meyer and Hemmi [3] in the 1930s and by Collander [4] in the early 1950s. So the time was ripe in the early 1960s for Fujita, Iwasa, and Hansch [5] to concentrate on the octanol/water system, and use log Pact as a hydrophobic parameter. Combining this parameter with Hammett-Taft electronic and steric parameters, they were successful in constructing quantitative structure-activity relationships (QSAR) which rationalized some simple biological end-points, such as growth rate of oat shoots and inhibition of fly head cholinesterase [6]. It is doubtful that either Hansch or Fujita could have foreseen the torrent of research papers their work would initiate through the following three decades. Just a list of the fields in which the log Poci of solutes háve found a role is impressive: 1) protein binding and specific roles of the solute in enzyme stabilization, denaturation or enan-tioselectivity [7—11]; 2) inhibition of bacteria [12-15], molds protozoa and organelles [17-20]; 3) action as mutagens, carcinogens, or antineoplastics [16-18]; 4) action as anesthetics, anticonvulsants, or pesticides [19-21]; 5) their effect on skin penetration, host-guest complexation and multiple drug resistance [22-24]; 6) in predicting behavior of dyes in photographic emulsions, histochemistry, and radiopaque media [25-27].

In the attempt to maintain a comprehensive database of measured log P values, references are made to over 500 different journals, and this does not include sources such as graduate degree theses, monographs, and private communications. It is safe to conclude that interest in the hydrophobic parameter is still on the rise with no end in sight.

Of course the number of reported measurements underestimates the level of use of log Poa as a hydrophobic parameter. Many QSAR are constructed using calculated log P values, and scarcely a month goes by without a report of several new methodologies for their estimation. Almost all of them have their strong and weak points. An adequate discussion of each would take far too much space, and so reference must be made to a recent review article [28], even though that is fast becoming out of date.

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