Poly(vinyldiaminotriazine) nanoparticle adsorption of small drug molecules in aqueous phase and the role of synergistic interaction between hydrogen bonding and hydrophobic affinity

Poly(vinyldiaminotriazine) nanoparticles adsorbed 5-fluorouracil, thymine, theobromine, and xanthine in aqueous phase. Each drug molecule formed triple hydrogen bonds with a diaminotriazine moiety at the nanoparticle surface. Adsorption isotherm studies suggested monolayer adsorption while the adsorption capacity was strongly dependent on the drug compositions/structures (0.053 mmol/g 5-fluorouracil, 0.094 mmol/g thymine, 0.0078 mmol/g theobromine, and 0.0065 mmol/g xanthine). The drug compositional/structural effects were also reflected in the adsorption kinetics. In addition to neutral pH adsorption, studies were performed at pH below the polymer’s pKa and above the drugs’ pKa, separately. Reducing hydrophobicity of the hydrogen bonding sites by protonating the diaminotriazine moieties at pH 4.5 resulted in more than 3 times decrease in adsorption capacities whereas deprotonating the drug molecules at pH 9 increased the adsorption capacity due to electrostatic attraction between the negatively charged drugs and the positively charged nanoparticles, which was supported by strong dependency of the adsorption capacity on ionic strength. The adsorption was reversible for all the four drugs. While increasing temperature caused faster desorption, reducing hydrophobicity of the diaminotriazine moieties by protonation at pH 4.5 had a stronger effect on both cumulative desorption and burst release. The results of this study demonstrated an important role of synergistic interaction between hydrogen bonding and hydrophobic affinity in poly(vinyldiaminotriazine) nanoparticle adsorption of the drugs in the aqueous phase.