Characterization of calcium phosphate as a gene carrier (I): Electrochemical properties

Calcium phosphate (CaPi) precipitation method has been used for decades in gene transfection. The underlying mechanism of this technique has been obscure. In the present study, electrochemical approaches were employed to elucidate the surface ionization and complexation phenomena in this colloidal dispersion. Potentiometric and conductometric titrations were carried out to characterize the ionizable CaPi colloid surfaces. The end points were determined to be at pH 4.32 and 9.88, respectively. Surface charge titration and zeta potential measurements were employed to estimate the point of zero charge (pzc) and isoelectric point (iep) of the CaPi precipitates. The pzc and iep of the CaPi precipitates were found to be at pH 7.09 and pH 7.0, respectively. Addition of pPyMT-1 and pSV2neo plasmid DNA results in a shift of both pzc and iep to higher values of 7.18 and 7.15, respectively. H(+) and OH(-) are the potential determining ions, which are shown to play important roles in determining the magnitude of the surface charge by their reactions with surface sites of CaPi.