Solubilization of Charged Porphyrins in Interpolyelectrolyte Complexes: A Computer Study

Abstract

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+) in the interpolyelectrolyte complex (IPEC) cores of co-assembled nanoparticles. We studied the stoichiometric mixtures of 137 A10+B25 and 137 A10−B25 chains with moderately hydrophobic A blocks (DPD interaction parameter aAS=35) and hydrophilic B blocks (aBS=25) with 10 to 120 P+ added (aPS=39). The P+ 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+ molecules easily solubilize in IPEC cores, where they partly replace PE+ and electrostatically crosslink PE− blocks. As the large P+ rings are apt to aggregate, P+ molecules aggregate in IPEC cores. The aggregation, which starts at very low loadings, is promoted by increasing the number of P+ 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+ in the mixture and on their association number, AS. If AS is lower than the ensemble average ⟨AS⟩n, the copolymer chains released from IPEC preferentially concentrate at the core-shell interface, thus increasing AS, which approaches ⟨AS⟩n. If AS>⟨AS⟩n, they escape into the bulk solvent.

Self-Assembly of Symmetric Copolymers in Slits with Inert and Attractive Walls

“…The effective pair interactions acting between beads i and j are "soft" and do not diverge at short distances r ij , which means that the DPD beads also behave as "soft" objects and can interpenetrate each other. The conservative force includes the (i) soft and spatially limited non-electrostatic repulsion, (ii) electrostatic interaction between charged particles, if the system contains the electrically charged particles, and (iii) bonding force, if the polymers, surfactants, or larger molecules (e.g., porphyrins) are present [59][60][61][62][63]. Flexible polymer chains are modeled as strings of interacting beads connected by elastic springs (usually described by the harmonic spring potential with the spring constant K and the equilibrium distance r 0 between two neighboring beads), emulating the covalent bonds.…”

DPD Modelling of the Self- and Co-Assembly of Polymers and Polyelectrolytes in Aqueous Media: Impact on Polymer Science

“…The most important results of the simulation study are reproduced in Figure 10. The other example of the fine tuning of electrostatic vs. non-electrostatic intera parameters [231] concerns the study of the solubilisation of ionic porphyrin deriva (PR) in the interpolyelectrolyte complex (IPEC) cores of block PE micelles. The PR bilisation in nanoparticles finds practical applications in medicine (in photodynamic apy), but, surprisingly, the embedding of ionic porphyrin derivatives in IPEC comp In summary, the simulation study of the P2VP-b-PEO self-assembly, based on the simplifying assumption that the average ionisation of P2VP units is proportional to the pH-dependent ionisation degree, α, which can be enumerated from the definition of the dissociation constant, K A ap (of protonated beads behaving as independent univalent acids),…”

“…The other example of the fine tuning of electrostatic vs. non-electrostatic interaction parameters [231] concerns the study of the solubilisation of ionic porphyrin derivatives (PR) in the interpolyelectrolyte complex (IPEC) cores of block PE micelles. The PR solubilisation in nanoparticles finds practical applications in medicine (in photodynamic therapy), but, surprisingly, the embedding of ionic porphyrin derivatives in IPEC complexes almost escaped the interest of researchers.…”

Stereocomplex Crystallized Nanomedical System for Enhanced Type I PDT and Synergistic Chemo-Phototherapy

“…Figure 1F exhibits a higher fluorescence intensity of the PX-SC-PEG micelle than that of free PX in PBS with an increase in irradiation time, which may be attributed to the reduced PX aggregation. 36 Interestingly, the total ROS content in the PX-SC-FA micelle appears extremely high among these groups. Several ROS detection probes were used to distinguish ROS types.…”