Statistical physics study of the interaction of the 5, 10, 15, 20-tetrakis (4-tolylphenyl) porphyrin (H2TTPP) with magnesium ion: New microscopic interpretations

Abstract

In this article, Tetraphenylporphyrin molecules were synthesized and used as biosensor for Magnesium ion. The metallization of porphyrin is a fundamental step which needs to be studied and educated. In fact, adsorption isotherms of magnesium nitrate on porphyrin coated onto Quartz crystal are achieved at four temperatures. Then, statistical physics treatment has been applied to deduce new microscopic interpretations for the experimental data. The main contribution of this analytical treatment is to deduct some physicochemical parameters related to the adsorption process which could not be achieved by means of empirical models. A Layer by Layer adsorption model with two energies was found to be the best model to reproduce the experimental isotherms of magnesium ion on porphyrin. In this model, seven parameters affecting the adsorption process were adjusted, namely the number of ions per site, the density of receptor sites, the two energetic parameters, the cohesion pressure, the covolume and the number of layers. The adsorption mechanisms were characterized by an energetic investigation which demonstrated that the magnesium ion was physisorbed onto porphyrin. Via the exploitation of our advanced model, three classical thermodynamic functions have been investigated and interpreted. Keywords: Adsorption isotherms, Quartz Crystal Microbalance, Porphyrin complexation, Layer by Layer model, Thermodynamic properties