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QUANTUM MECHANICAL STUDY OF THE COMPETITIVE HYDRATION BETWEEN PROTONATED QUINAZOLINE AND LI+, NA+, AND CA2+ IONS
Citation:
Sawunyama, P. AND G W. Bailey. QUANTUM MECHANICAL STUDY OF THE COMPETITIVE HYDRATION BETWEEN PROTONATED QUINAZOLINE AND LI+, NA+, AND CA2+ IONS. JOURNAL OF PHYSICAL CHEMISTRY A 105(42):9717-9724, (2001).
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
Hydration reactions are fundamental to many biological functions and environmental processes. The energetics of hydration of inorganic and organic chemical species influences their fate and transport behavior in the environment. In this study, gas-phase quantum mechanical calculations at the MP2/6-31G**//HF/6-31G* and B3LYP/6-311+G(2df,2p)//B3LYP/6-31G* levels of theory are used to interpret the local competition for water between protonated quinazoline (1,3-diazanaphthalene) and metal ions, i.e., Li+, Na+, and Ca2+, under very low water contents. Calculated enthalpies and free energies of hydration at 298.15 K, DeltaH(hyd)(298) and DeltaG(hyd)(298), respectively, for the reactions quinazoline + H2O --> quinazoline hydrate and Mz+ + H2O --> M(H2O)(z+) show that hydration of metal ions is more favorable than hydration of the quinazoline species. At the MP2/6-31G**//HF/6-31G* computational level, DeltaH(hyd)(298) values range from 0.4 kcal mol(-1) for neutral quinazoline to -11.1 and -10.5 kcal mol(-1) for NI and N3 protonated quinazoline monocations, respectively, while DeltaH(hyd)(298) = -39.3, -28.2, and -56.4 kcal mol(-1) for Li+, Na+, and Ca2+ ions, respectively. At the B3LYP/6-311+G(2df,2p)//B3LYP/6-31G* computational level, DeltaH(hyd)(298) = 6.9, -5.5, and -5.4 kcal mol(-1) for neutral,quinazoline, N1, and N3 protonated quinazoline monocations, respectively, while DeltaH(hyd)(298) values are -34.0, -23.4, and -55.7 kcal mol(-1) for Li+, Na+, and Ca2+ ions, respectively. Accordingly,
DeltaG(hyd)(298) values indicate that although metal cations hydrate spontaneously, quinazoline species do not. In addition to hydration, direct reaction between quinazoline species and metal cations is also explored.