Motivated by the use of chitosan (Ch), and cellulose acetate (AC) as organic matrices in several therapeutic drugs, a theoretical study has been elaborated through the density functional theory method (DFT) to investigate the interaction mechanism between two essential ions for the human body Ca2+, K+ and two organic matrices chitosan (Ch), and cellulose acetate (AC). Many physical and chemical aspects have been carried out after the achievement of structural optimization. This involves structural parameters, molecular electrostatic potential (MEPs), interaction energy, reactivity indexes, frontier molecular orbitals (FMOs), quantum theory atoms in molecules (QTAIM) analysis and non-covalent interaction (NCI) analysis. The results of FMOs, MEPs and reactivity index studies have revealed that the site of interaction can be predicted. The calculation of electron interaction energies shows that those ions interact with the matrix of AC and Ch. Concretely, the Ca2+ ion interacted efficiently with the AC matrix. The structural analysis results show that the interaction of Ch and ions appear spontaneously (ΔG < 0) while the interaction of AC and ions (ΔG > 0), requires more energy to occur. Finally, the QTAIM analysis data indicates that the interactions of AC -ions and Ch-ions are non-covalent presenting an electrostatic character.