Nanoreactors in vitro et silico

A talk given during the High Performance Computing Symposium, Queen's University, Kingston in June 2017.

Transcript

1. NANOREACTORS IN VITRO ET SILICO MATT MCTAGGART & CECILE MALARDIER-JUGROOT ROYAL MILITARY COLLEGE OF CANADA KINGSTON ON
2. NATURAL PROCESSES MAKE EXTENSIVE USE OF NANOSCALE REACTION SPACES • Enzyme-mediated reactions are fast, efficient, and specific • Nanoscale structure influences atomic scale function • Coordination under confinement enables bond formations despite unfavourable energetics 2
3. UNDERSTANDING HOW STRUCTURE AFFECTS REACTIVITY ENABLES REPLICATION • Experimental methods are limited by: • Access to small spaces and time scales • Complexity and dynamism averaged • Theoretical methods are limited by: • Expression of weak interactions • Coupling large force gradients to reactivity • Unexpected or unknown solvation physics 3
4. ACT 1: BIRTH OF A BUZZWORD
5. MEET THE PROTAGONIST: POLY(STYRENE-ALT-MALEIC ACID) • SMA is an amphiphilic polymer • Diacid group is responsive to pH • In 2004, DFT studies of SMA in the gas phase indicated that strong H-bonds form at pH 7 • Rigid, linear, and rotational periodicity 5 Malardier-Jugroot, C. et al. J. Phys. Chem. B 2005, 109, 7022-7032
6. H-BOND SUPPORTED ORGANIZATION PERMITS SELF-ASSEMBLY IN NEUTRAL WATER • Theoretical results encouraged experiment by small-angle neutron scattering and cryo-TEM • SANS revealed the characteristic peak for a hollow cylinder • Supported by cryo-TEM • Optimized nanotube model fit experiment 6 Malardier-Jugroot, C. J. et al. Langmuir 2005, 21, 10179-10187 I.D.: 25.6 Å O.D.: 39.4 Å
7. NANOTUBE TO NANOREACTOR • Attempted applications: • Organic molecule loading • Crystal growth templating • Pyrrole polymerizes spontaneously despite unfavourable energetics • Pt salt reduced to 2 nm crystals without reducing agent • Nanostructure drives the chemistry within 7 Groves, M.N. et al. Chem. Phys. Lett. 2014, 612, 309–312
8. ACT 2: SANS SPECTRUM SANS PEAK
9. FOLLOW-ON EXPERIMENT PRODUCES AN UNEXPECTED RESULT • SANS experiment to determine shape and size of Pt and Au crystals • Control run to confirm nanotubes; Mw increased from 40 to 350 kDa • However, the characteristic peak did not appear in it nor in the metal containing samples 9 McTaggart, M. et al. Chem. Phys. Lett. 2015, 636, 221–227 SMA(350) Pt-SMA(350) Au-SMA(350) SMA(40)
10. BACK TO THE BUILDER WINDOW • Parameters in the form function allow inaccurate interpretation of the SANS signal • Original optimization of the SMA chain used to model an alternative assembly: • Chain to chain: 8.5 Å • Bond to bond: 6.4 Å • Bond precession: 69° 10 McTaggart, M. et al. Chem. Phys. Lett. 2015, 636, 216-220
11. THE EVIDENCE CONVERGES • TEM confirms the DFT model which informs the theoretical form function that in turn interprets the SANS experimental data 11 Parameter SANS Model TEM SLDsolid (Å-2) 1.87e-06 SLDsolv (Å-2) 6.38e-06 Spacing s (Å) 6.99 8.5 6.9 Thickness t (Å) 12.34 n/a ~15 Layers n (N) 1.00 n/a n/a Bond-bond d (Å) n/a 6.4 3.3 Precession p (deg.) n/a 69 70 d p
12. APPLICATION TO A NEW PRIMARY STRUCTURE • Poly(isobutylene-alt-maleic acid) is a similarly alternating amphiphilic co- polymer • Its chain-chain distance was calculated to be 2.77 Å, a value exactly confirmed by TEM 12 Chan, A. et al. Mol. Simul. 2011, 37, 701–709 McTaggart, M et al. in preparation
13. ACT 3: BRINGING IT TOGETHER
14. COORDINATION CHEMISTRY • Spotted on TEM and x-ray • In the proposed mechanism: • PtCl2 dissociates within the nanoreactor core • Pt reduction is kinetically-driven • Strengthens nanostructure for use in more challenging environments • Highly ordered single-atom deposition on the SMA surface for catalysis 14 a. PtCl2 dissoc. to coord: 3.5 J·mol-1 Pt-C bond length: 2.22 Å b. Pt reduction: 308.4 kJ·mol-1 Pt-C bond length: 2.08 Å McTaggart, M. et al. in preparation
15. SOURCES OF THE FORCES • Water dynamics within and around the nanoreactor is a likely candidate force behind the thermodynamic changes observed • Current work joins molecular dynamics to quasi-elastic neutron scattering and spectroscopy 15
16. INSPIRING DISCOVERY • Availability of experimental and computational information was key to nanomaterial discoveries • Sustainable chemistry is likely to be more nuanced and complex • Coordination of effort promotes advances along a confluent path 16
17. • This case demonstrates that relatively simple gas-phase quantum mechanical modeling can predict or confirm structural properties of dynamic self-assembling materials in solution • Theoretical and experimental methods applied in concert can overcome the limitations of each in the investigation of complex systems 17 EPILOGUE
18. QUESTIONS & DISCUSSION CURRENT/FORMER CMJ LAB: ANITA CHAN DR. MICHAEL GROVES SUMMER LI VISHVA SHAH