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J Colloid Interface Sci. 2009 Sep 15;337(2):390-5. doi: 10.1016/j.jcis.2009.05.066. Epub 2009 Jun 2.

Calorimetric measurements of proton adsorption onto Pseudomonas putida.

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University of Washington, Department of Earth and Space Sciences, 070 Johnson Hall, Seattle, WA 98195, United States.


Having an understanding of the reactive nature of the bacterial surface is enhanced when its reactivity is considered in a thermodynamic framework. Towards this end, isothermal titration calorimetry was used to measure heats of proton adsorption onto Pseudomonas putida, a common gram negative soil bacterium. Proton adsorption generated large exothermic heats and proton uptake continued down to pH 2.5. Applying a surface complexation model to the calorimetric data allowed for the derivation of site-specific enthalpies and entropies of proton adsorption. The 4-site non-electrostatic model of Borrok et al. [D.M. Borrok, J.B. Fein, J. Colloid Interface Sci. 286 (2005) 110] was chosen to describe proton adsorption and enabled derivation of site-specific enthalpies of -2.4+/-0.3, -3.7+/-0.2, -9.0+/-0.6, and -36.0+/-1.2 kJ/mol for Sites 1-4, respectively. Entropies of proton adsorption were calculated to be 51+/-3, 75+/-1, 91+/-2, and 55+/-4 J/mol K, for Sites 1-4, respectively. Enthalpies and entropies of Sites 1 and 3 are consistent with that of multifunctional organophosphonic acids, Site 2 is consistent with multifunctional carboxylic acids, and Site 4 is consistent with an amine. Temperature dependence of the acidity constants for Sites 1-3 is predicted to be minimal; however, Site 4 is predicted to more substantially affected by temperature.

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