Iron Oxide/PAMAM Nanostructured Hybrid Systems. Combined Computational and Experimental

SUPPORTING INFORMATION

Iron oxide/PAMAM nanostructured hybrid systems. Combined computational and experimental studies

S1.1 PAMAM and PAMAM-SAH structural features: Radius of Gyration

PAMAM and PAMAM-SAH dendrimer Radius of Gyration (Rg) vs. time is reported in Figure S.1. Rg has been also reported as average (together with standard deviation) calculated in the last 20 ns of each run (Figure S.2). In all cases the Rg value reaches a stable value. As expected, the average PAMAM-SAH Rg value is always higher than the PAMAMRg, if comparing same generation. In detail, as the number of succinic terminals increases, the dendrimer structure loses compactness, similarly to the PAMAM dendrimer at a neutral pH [4].

Figure S.1. Radius of Gyration for PAMAM (a) and PAMAM-SAH dendrimers throughout the simulation.

Figure S.2. Radius of gyration (average value and standard deviation) calculated in the last 20 ns of the MD simulations for PAMAM (black) and PAMAM-SAH (red) dendrimers.

S1.2 Dendrimer Magnetite Binging Mode

Figure S.3 depicts the binding mode characterizing the adsorption ofPAMAM and PAMAM-SAH dendrimers on magnetite (MAG).

PAMAM/MAG interaction is characterized by a binding energy mostly characterized by vdW contribution (Figure 4 of the main text). The dendrimer spreads over the MAG surface with external and internal branches involved in the contact surface. In case of PAMAM-SAH dendrimer the binding mode changes as the generation increases. In detail, PAMAM-SAH G2 exposes few succinic groups with respect to G3 and G4.TheG2 binding mode is still partially driven by vdW, with a behavior more similar to PAMAM dendrimers where the dendrimer spreads over the MAG particle to maximize the contact surface with an interaction mostly dominated by short range interactions.In case of PAMAM-SAH dendrimers, as the generation increases (PAMAM-SAH G3 and G4), the dendrimer adsorption surface is mostly characterized by succinic terminals in contact with the MAG nanoparticle.Dendrimer succinic groups occupy almost completely charged sites on the MAG surface, avoiding the dendrimer propensity to spread over the MAG surface interacting with both internal and external branches.

Figure S.3. Dendrimer MAG mode of binding for PAMAM and PAMAM-SAH. Representative snapshots taken at the end of each MD simulation are shown for G2, G3, and G4 dendrimers as representative cases of different binding modes. In PAMAM-SAH dendrimers succinic terminal groups are shown in red.

S1.3 Dendrimer Void Volume Calculation

The volume associated to the internal voids and cavities has been calculated by following the approach well described in by Maiti and coworkers in 2004[2].First, for each system the dendrimer solvent accessible volume (VSAS) which is the volume contained inside the solvent accessible surface area (ASAS), has been calculated in the last 20 ns of the MD trajectory. Figure S.4 reports VSAS1/3 as a function of probe radius used for calculating ASAS (by using the GROMACS tool g sas) for several generations of PAMAM (Figure S.4 a) and PAMAM-SAH (Figure S.4 b). Data reported in Figure S.4a for PAMAMG1,G2,G3, and G4 are in close agreement with data reported in Figure 13a in ref. [2] for same dendrimer generations. A fitting line is obtained by linear regression of VSAS1/3 values for larger probe radii (from 0.5 to 1 nm). The VSAS1/3 value extrapolated from the fitting line for a probe radius equal to 0 provides a measure of the dendrimer total volume including pores and internal voids. The deviation of calculated VSAS1/3 from the fitting line gives a measure of the volume characterizing internal voids, reported in Figure S.5 for several generations of PAMAM (Figure S.5a) and PAMAM-SAH (Figure S.5b) dendrimers. It is interesting to notice how the chosen probe radius does not effectively influences the calculated value of internal voids (Figure S.5a and b) for considered dendrimers.

Figure S.4. VSAS1/3 as a function of probe radius for several generation of PAMAM (a) and PAMAM-SAH (b) dendrimers. Each point in the picture indicate a calculated VSAS1/3. A regression line (continuous line) is obtained by fitting VSAS1/3 values for probe larger radii (from 0.5 to 1 nm). The extrapolated value for a probe radius equal to 0 from the fitting line provides a measure of the dendrimer total volume (including pores and internal voids).

Figure S.5. Dendrimer internal volume plotted as a function of the dendrimer generation for both PAMAM (a) and PAMAM-SAH (b). Several curves are plotted each corresponding to a different probe radius. The chosen probe radius between 0.1 and 0.3 does not affect the calculated value of internal volume.

From data shown in Figure S.5 and considering a MAG volume around 34 nm3, we can conclude that the dendrimer void volume is insufficient to incorporate the MAG particle in all cases for PAMAM and PAMAM-SAH except for PAMAM-SAH G4, which have an internal void volume of about 45 nm3. This indicates that a G4 PAMAM-SAH might be able to entrap the considered MAG particle, at least partially. However, the strong electrostatic interactions between MAG and dendrimer succinic terminals avoids the particle entrapment in the interior part of the dendrimer.

References

1. Maingi, V.; Jain, V.; Bharatam, P. V; Maiti, P. K. Dendrimer building toolkit: model building and characterization of various dendrimer architectures. J. Comput. Chem.2012, 33, 1997–2011.

2. Maiti, P. K.; Çagın, T.; Wang, G.; Goddard, W. A. Structure of PAMAM Dendrimers: Generations 1 through 11. Macromolecules2004, 37, 6236–6254.