Solubilization of Charged Porphyrins in Interpolyelectrolyte Complexes: A Computer Study

Using coarse-grained dissipative particle dynamics (DPD) with explicit electrostatics, we performed (i) an extensive series of simulations of the electrostatic co-assembly of asymmetric oppositely charged copolymers composed of one (either positively or negatively charged) polyelectrolyte (PE) block A and one water-soluble block B and (ii) studied the solubilization of positively charged porphyrin derivatives (P [Formula: see text]) in the interpolyelectrolyte complex (IPEC) cores of co-assembled nanoparticles. We studied the stoichiometric mixtures of 137 A [Formula: see text] B [Formula: see text] and 137 A [Formula: see text] B [Formula: see text] chains with moderately hydrophobic A blocks (DPD interaction parameter [Formula: see text]) and hydrophilic B blocks ([Formula: see text]) with 10 to 120 P [Formula: see text] added ([Formula: see text]). The P [Formula: see text] interactions with other components were set to match literature information on their limited solubility and aggregation behavior. The study shows that the moderately soluble P [Formula: see text] molecules easily solubilize in IPEC cores, where they partly replace PE [Formula: see text] and electrostatically crosslink PE [Formula: see text] blocks. As the large P [Formula: see text] rings are apt to aggregate, P [Formula: see text] molecules aggregate in IPEC cores. The aggregation, which starts at very low loadings, is promoted by increasing the number of P [Formula: see text] in the mixture. The positively charged copolymers repelled from the central part of IPEC core partially concentrate at the core-shell interface and partially escape into bulk solvent depending on the amount of P [Formula: see text] in the mixture and on their association number, [Formula: see text]. If [Formula: see text] is lower than the ensemble average [Formula: see text] , the copolymer chains released from IPEC preferentially concentrate at the core-shell interface, thus increasing [Formula: see text] , which approaches [Formula: see text]. If [Formula: see text] , they escape into the bulk solvent.