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Modeling the influence of complexation on the water activity of ionic surfactants. We present a systematic study of the complexation of sodium dodecyl sulfate (SDS) with eight aqueous salts by means of isothermal titration calorimetry (ITC) and potentiometric titrations. The molar binding ratio of the anions to SDS was systematically varied. The dependence of the complexation heat and the magnitude of the heat of dilution on the ion concentration were found to agree well with theoretical predictions derived from a simple three-site binding model. These results allow us to determine the relative stability of the complex formed and the energy of transfer between the two species as functions of the ion concentration. Moreover, our measurements allow us to provide information on the structure of the complex, as SDS is a weak, nonionic surfactant. From the molar binding ratio, the intrinsic molar water activities of the different complexes were deduced from the equation of state of water in the electrolyte. It is found that complexation has a significant influence on the water activity of the mixtures, as the aqueous salt exerts a considerable stabilization effect. The molar water activities of the mixtures formed under the conditions of our experiments are significantly higher than that of pure water, and show a highly nonlinear dependence on the salt concentration. These results are in good qualitative agreement with the predictions of a theoretical model for ionic surfactants in aqueous solutions, based on the concept of the "dipole mesh" of the molecule, in which a particle follows the electric field due to the surrounding ions and carries a constant dipole moment which is screened according to the Debye-Hückel law.Hoffmann and Dodds-Walls, 2008) were the most frequently used drug combinations. In general, the most common combination drug was levofloxacin with an injectable agent. However, the trend towards non-injection therapy was noted with the increase in the number of prescriptions of combination therapies containing ampicillin and levofloxacin or ampicillin and trimethoprim. Although levofloxacin was the most frequently prescribed injectable combination agent, there was also an increase in the number of prescriptions of trimethoprim and ampicillin. The prescribing of multiple antibiotic agents in combination with each other, especially within the same injection, has been reported previously (Zhang et al., [




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