CEMWOQ Poster

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1. Induced Reaction Spontaneity in a Self-Assembling Nanosystem M.R. McTaggart and C. Malardier-Jugroot Royal Military College of Canada, Kingston ON Main image: High molar mass SMA nanosheet, lower layer and hydrogens removed for clarity Matt.McTaggart@rmc.ca @mattmctaggart Cecile.Malardier-Jugroot@rmc.ca Conclusion & plans for future work 1. Confinement affects reaction thermodynamics. Reactants in nano- structures may pack closer than in bulk, decreasing the energy necessary to reach ΔG‡. This should be considered when developing nanocontainers. 2. A system-level approach is crucial for analysis. An integrated system of water, polymer structure, and metals give rise to the effect. A variety of scales and techniques are required to build understanding of the effect. We have begun a systematic kinetics study s using pyrrole polymerization as a model. Because SMA produces a 1D and 2D conformer that support the same reaction, we hope to elucidate the role of dimension on the Arrhenuis equation. References & Further Reading 1. Malardier-Jugroot, Cecile, T. G. M. Van de Ven, and M. A. Whitehead. "Characterization of a novel self-association of an alternating copolymer into nanotubes in solution." Molecular Simulation 31.2-3 (2005): 173-178. 2. McTaggart, Matt, Cecile Malardier-Jugroot, and Manish Jugroot. "Self-assembled biomimetic nanoreactors I: Polymeric template." Chemical Physics Letters 636 (2015): 216- 220. 3. McTaggart, Matt, Cecile Malardier-Jugroot, and Manish Jugroot. "Self-assembled biomimetic nanoreactors II: Noble metal active centers." Chemical Physics Letters 636 (2015): 221-227. 4. Li, Xia, Matt McTaggart, and Cecile Malardier-Jugroot. "Synthesis and characterization of a pH responsive folic acid functionalized polymeric drug delivery system." Biophysical chemistry 214 (2016): 17-26. 5. Shah, Vishva, Cecile Malardier-Jugroot, and Manish Jugroot. "Mediating gold nanoparticle growth in nanoreactors: Role of template-metal interactions and external energy." Materials Chemistry and Physics 196 (2017): 92-102. SMA self-assembles in water, creating 2-3nm interior spaces Poly(styrene-alt-maleic acid), SMA, is an alternating co-polymer composed of hydrophobic styrene and hydrophilic maleic acid (Top). Using small angle neutron scattering (SANS) and transmission electron microscopy (TEM), our group discovered that its tertiary structure is chain length dependent. We have mapped nanostructure to dynamic light scattering for real-time monitoring of the assembly into nanotubes (Bottom) or nanosheets (Main Image). 6 kDa 20 40 100 200 350 ? ? 1000 nm 100 10 1 PtCl2 auto-reduces, coordinates π-π interaction sites & forms Pt-NPs Bright points in this HR- TEM image are platinum atoms coordinated to the assembly binding sites; dark patches are Pt NPs within the SMA nanostructure. The polymer assembly withstood several minutes’ exposure to a 300kV beam to achieve this shot. Platinum II chloride is insoluble in water and has a calculated dissociation energy of 308.4 kJ·mol-1. Ordinarily, an electron-donating agent would be used in concert with an organic template to reduce the salt to platinum metal nanoparticles. When introduced to SMA solution, PtCl2 spontaneously reduces to Pt, forming monodisperse nanoparticles and reinforcing the structure by co- ordinating its π-π interaction sites. Confinement by the nanosystem necessary for reaction Pyrrole polymerization is thermodynamically unfavourable but confinement within the SMA nanostructure provides access to a spontaneous reaction pathway. Solvation energy minimization drives low solubility molecules to become confined within the SMA structures. Quasi-elastic neutron spectrometry (right) revealed that the translational diffusion of pyrrole is equivalent to polypyrrole long before the reaction occurs. [PPy] = 0.0699t + 0.0435 R² = 0.9983 0 0.5 1 1.5 2 2.5 3 0 5 10 15 20 25 30 Absorbance, 465 nm Time (days) Pyrrole polymerization in SMA(6) at 50°C A decreased diffusion coefficient suggests that confined pyrrole packs at a higher density than the bulk liquid. The decreased volume and translational kinetic energy may be sufficient to diminish the activation energy demand to what is thermally available. MD modeling predicts an effective pressure greater than 10 MPa. The reaction schematic (left) illustrates the possible thermodynamic scenario. Pyrrole polymerization is typically a 1st order reaction but follows 0th order kinetics under confinement, meaning that the rate is no longer governed by reactant concentration or availability. This finding is consistent with a higher packing density: the probability of reaction is only limited by orientation and availability of sufficient ambient free energy for activation. Diffusion coefficient of pyrrole under confinement Internal reactivity affected by external 2D gold crystals Addition of AuCl to SMA solution produces single atomic layer gold crystals on the outer surface. Unlike platinum, gold is not in contact with the pyrrole during in its SMA confinement. Nevertheless, gold has a stronger catalytic effect than platinum on the polymerization process (below). This is consistent with the confinement model wherein the system starting thermodynamic state, and not activation energy, is affected. SMA (350) Pt-SMA (350) Au-SMA (350) SEM image of a gold sheet on SMA produced at RMC. Inset SAEM pattern showing hexagonal close-packed structure taken on the Titan- 300 TEM at CCEM.