Simultaneous Determination of Molar Absorption Coefficients and Equilibrium Constants for Monomer-Dimer Equilibria

摘要

The majority of methods for measuring dimerication constants requires that the pure monomer spectrum be known. This spectrum is obtained by successive dilution of a dye solution until Beer's law is obeyed. In practice, there is a limit where the absorbance of the solution is too small to measure precisely. Frequently, the dye is diluted with alcoholic-aqueous solutions to foster monomer formation. We have devised a general scheme to compute molar absorption coefficients and dimerization constants based on Monahan's method. Absorbances are measured for a series of dye concentrations. A nonlinear least-squares program then finds the best-fit monomer and dimer molar absorption coefficients. Absorbances are remeasured at various temperatures or with different dye concentrations and the calculation repeated. The mean molar absorption coefficients are computed from all the measurements; these values are then used to compute the dimerization constants at each temperature.