Understanding Mechanochemistry

• Applicant: Professor Dr. Dominik Marx
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: from 2009 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 101803318

Final Report Abstract

At the heart of covalent mechanochemistry is the idea to utilize external mechanical forces in order to activate specific chemical bonds toward enabeling and controlling distinct chemical reactions. Thus, mechanochemistry adds another dimension to thermochemical, photochemical and electrochemical means of activation. Experimentally, the well-established class of approaches based on ball milling in a broad sense have been enriched more recently by developing dedicated sonochemical ensemble techniques as well as single-molecule force-probe methodologies. In the present project, conceptual foundations of the activation of chemical reactions using external mechanical forces have been developed based on the notion of what we call “force-transformed potential energy surfaces”, being Legendre transforms of isometrically constrained potentials. A particular isotensional computational approach, the so-called EFEI (“External Force is Explicitly Included”) method, has been devised in order to make readily use of the powerful machinery of structural optimization techniques as broadly provided by essentially all quantum chemistry program packages. The EFEI approach allows one to compute rigorously how the molecular structure of reactants, transition states and intermediates get distorted (or force-transformed) upon applying constant external forces as a function of their magnitude and directionality in dependence on the specific sites where the force acts on the molecular skeleton. EFEI even offers the possibility to compute the full pathway of chemical reactions along reaction coordinates as a function of force and to evaluate how the electronic structure responds to mechanochemical activation in the Born-Oppenheimer picture. Moreover, EFEI has been generalized to ab initio molecular dynamics which opens up a broad avenue to efficiently compute the mechanical response of multi-dimensional free energy landscapes, thus yielding “force-transformed free energy surfaces”, when combined with enhanced sampling strategies and rare event techniques such as metadynamics, thermodynamic integration or transition path sampling. Within this conceptual and computational framework, the force response of numerous chemical reactions has been explored including various electrocyclic ring-opening reactions, enzymatic disulfide bond-breaking reactions as well as mechanical manipulations of metal/molecule junctions and corresponding hybrid interfaces. In addition to providing a wealth of specific molecular insights, fundamental phenomena such as the force-induced confluence of reaction pathways, stress-induced steric hindrance mechanisms, metal-assisted mechanocatalysis, and surface peeling have been discovered.

Publications

• Understanding Covalent Mechanochemistry, Angew. Chem. Int. Ed. 48, 4190–4193 (2009)
  J. Ribas–Arino, M. Shiga, and D. Marx
  
• Mechanochemical Transduction of Externally Applied Forces to Mechanophores, J. Am. Chem. Soc. 132, 10609–10614 (2010)
  J. Ribas–Arino, M. Shiga, and D. Marx
  
• Force–Transformed Free–Energy Surfaces and Trajectory–Shooting Simulations Reveal the Mechano–Stereochemistry of Cyclopropane Ring–Opening Reactions, Angew. Chem. Int. Ed. 50, 7105–7108 (2011)
  P. Dopieralski, J. Ribas–Arino, and D. Marx
  
• The Janus-faced role of external forces in mechanochemical disulfide bond cleavage, Nat. Chem. 5, 685–691 (2013)
  P. Dopieralski, J. Ribas–Arino, P. Anjukandi, M. Krupicka, J. Kiss, and D. Marx
  
• Disfavoring Mechanochemical Reactions by Stress-Induced Steric Hindrance, J. Chem. Theory Comput. (Letter) 11, 841–846 (2015)
  M. Krupicka and D. Marx
  
• Nanomechanics of Bidentate Thiolate Ligands on Gold Surfaces, Phys. Rev. Lett. 114, 075501–1-5 (2015)
  M. E. Zoloff Michoff, J. Ribas–Arino, and D. Marx
  
• Peeling by Nanomechanical Forces: A Route to Selective Creation of Surface Structures, Phys. Rev. Lett. 115, 036102–1-5 (2015)
  P. Seema, J. Behler, and D. Marx
  
• Force–Induced Reversal of β–Eliminations: Stressed Disulfide Bonds in Alkaline Solution, Angew. Chem. Int. Ed. 55, 1304–1308 (2016)
  P. Dopieralski, J. Ribas–Arino, P. Anjukandi, M. Krupicka, and D. Marx
  
• Unclicking the Click: Metal–Assisted Mechanochemical Cycloreversion of Triazoles is Possible, Angew. Chem. Int. Ed. 56, 7745–7749 (2017)
  M. Krupicka, P. Dopieralski, and D. Marx
  
• Unexpected mechanochemical complexity in the mechanistic scenarios of disulfide bond reduction in alkaline solution, Nat. Chem. 9, 164–170 (2017)
  P. Dopieralski, J. Ribas–Arino, P. Anjukandi, M. Krupicka, and D. Marx