A quantum chemical approach using classical concepts to characterization and descriptive analysis of various reactions of metal ions and organic compounds

• Quantum chemical descriptors combining with the four-element theory establish feasible models.
• Quantum four-element model provides a general meaning for chemical reactivity of metal ions and organic compounds.
• Reactions in aqueous solutions — hydration, diffusion, deprotonation, precipitation, redox reaction, and complexation
• Reactions onto solid surfaces — adsorption, ion exchange reaction, and sorption by organoclay
• Biological activity — median effective concentrations measured from Photobacterium phosphoreum and Chlorella valgaris

Combined with the calculation of quantum chemical reactivity indices and the concept of the four-element theory, four major types of chemical interactions involved in various reactions can be integrated. This theoretical approach was applied to predict many kinds of reactions of metal ions and organic compounds in aqueous solutions — such as, hydration, diffusion, deprotonation, precipitation, redox reaction, and complexation; onto solid surfaces — such as, adsorption, ion exchange reaction, and sorption by organoclay; and for biological activity — such as, median effective concentrations measured from Photobacterium phosphoreum and Chlorella vulgaris. Results of analysis revealed that the quantum four-element model – which is constructed on the basis of 1) electronic chemical potential − μ+ and μ− (electron flow), 2) condensed local softness s+max and s−max (polarization), 3) atomic partial charge ρ+max(H) and − ρ−max (electrostatic interaction), and 4) the inverse of apolar surface area 1/APSA (hydrophilic interaction) – provides a general meaning for chemical reactivity and has great potential to probe mechanism of action.