Partition coefficients of quinones and hydroquinones and their relation to biochemical reactivity

Some major effects of ring substituents on the partition coefficients of quinone headgroups are described. Attention is drawn to the large differences in partition coefficients in cyclohexane/water of the two major freely diffusing redox forms, the quinone, Q, and the hydroquinone, QH2. Methoxy substituents cause a marked increase of the cyclohexane/water partition coefficient of the hydroquinone, but this effect is absent in the quinone and is also not seen in measurements in octanol/water. The relation between partition coefficients and biochemical specificity of quinone binding sites is explored.