Nanoparticle formation of an antimicrobial peptide induced by sulfated β-cyclodextrin: Application to alkaloid encapsulation

The association of polyanionic β-cyclodextrin (βCD) derivatives with the nonaggregating polycationic antimicrobial peptide Dhvar4 was studied in water at 296 K without a buffer to explore their potential for forming nanoparticles capable of encapsulating bioactive isoquinoline alkaloids. The βCD bearing sulfobutyl ether moieties formed a 1:1 inclusion complex with Dhvar4, exhibiting a binding constant of (1.1 ± 0.3) × 105 M–1. In contrast, βCD substituted with SO₃⁻ groups (S13βCD) promoted the self-assembly into nanoparticles with a narrow and uniform size distribution. When Dhvar4 was present in large excess relative to S13βCD, positively charged nanoparticles were produced. Conversely, negatively charged nanoparticles were obtained at S13βCD/Dhvar4 charge ratios above 2.5, which maintained their size for at least 30 days. The incorporation of pharmaceutically active isoquinoline alkaloids had minimal impact on the properties of nanoparticles formed in the presence of a >35 molar% excess of S13βCD over Dhvar4. Encapsulation efficiencies of 99 % and 72 % were achieved for coralyne and sanguinarine, respectively. Job plot and isothermal titration calorimetry measurements demonstrated that each S13βCD macrocycle could bind ∼13 molecules of these alkaloids. The present findings lay the groundwork for future biological validation and applications of nanoparticles composed of three types of biomedically important compounds.