Estudo do efeito isotópico sobre a solubilidade da 3- metilpiridina em H2O e D2O

Abstract

Experimental studies of 3-methylpiridyne/water and 3- methylpiridyne/heavy water binary mixtures show solubility differences. In this work Molecular Dynamics method was used to simulate 54 model systems. Each system corresponds to a point at a temperature vs molar fractions phase diagram. The systems were simulated in cubic boxes containing a mixture of 3- metylpiridyne/water/heavy water in compositions ranging from 0.1 to 0.9 (molar fraction of 3-methylpiridyne) and temperatures ranging from 280 to 380 K. The results indicate that the interactions that contribute most for the 3-metilpiridine solubility in water and heavy water are the H/D bonds with the N at the 3- methylpiridyne. Those H/D bonds tend to be more structured as we increase the organic molecule concentration and decrease the system temperature. The local concentration analyses show that the first hydration shell of the nitrogen site has the same quantities of water and heavy water. Despite that there are more H bonds than D bonds at the first hydration shell. From this result we conclude that there are structural differences on the shell favoring the H bonds. The magnitude of those differences seems to vary with the temperature and the composition of the system. Our studies of H/D bonds lifetime show that there are not significant differences between the H and D bonds with the N site.