THEORY OF MEASUREMENT OF WEAK MOLECULAR COMPLEXES .I. GENERAL CONSIDERATIONS

Some aspects of the measurement of formation constants and other constants for weak molecular complexes are considered from the standpoint of basic binding theory. The theoretical minimum errors in the formation constant k and the extinction coefficient є are discussed as a function of the saturation fraction of the most dilute component, and it is shown in agreement with previous work that the most accurate values of either parameter are obtained when the saturation fraction lies between 0.2 and 0.8. Outside this region, the determined values become extremely uncertain, and in addition, insufficient data are available to adequately fit a given stoichiometric model. It is suggested that the criteria that the highest concentration of the excess component be not less than 0.1 /k are insufficient to assign a given stoichiometric model to the data, but apply instead to the smallest range of saturation fraction required to show that a line of finite limiting slope and/or intercept exists. To develop criteria by which a given stoichiometric model can be considered in 1:1 correspondence with the phenomenological equation fitting the data, the principles of information theory are applied to the binding process. It is concluded that of the order of 75% of the saturation curve is required to show the correspondence between the equation of the model and the equation fitting the data. Also discussed are various plotting forms and the errors arising from various rearrangements of the basic binding equation. © 1969, American Chemical Society. All rights reserved.