Allosteric control of olefin isomerization kinetics via remote metal binding and its mechanochemical analysis

Abstract

Allosteric control of reaction thermodynamics is well understood, but the mechanisms by which changes in local geometries of receptor sites lower activation reaction barriers in electronically uncoupled, remote reaction moieties remain relatively unexplored. Here we report a molecular scaffold in which the rate of thermal E-to-Z isomerization of an alkene increases by a factor of as much as 104 in response to fast binding of a metal ion to a remote receptor site. A mechanochemical model of the olefin coupled to a compressive harmonic spring reproduces the observed acceleration quantitatively, adding the studied isomerization to the very few reactions demonstrated to be sensitive to extrinsic compressive force. The work validates experimentally the generalization of mechanochemical kinetics to compressive loads and demonstrates that the formalism of force-coupled reactivity offers a productive framework for the quantitative analysis of the molecular basis of allosteric control of reaction kinetics. Important differences in the effects of compressive vs. tensile force on the kinetic stabilities of molecules are discussed.

Coumarin Dimer Is an Effective Photomechanochemical AND Gate for Small-Molecule Release

“…Note that the energy of Int and TS 2 above f max (3.2 nN in the illustrated example, red scheme) cannot be quantified relative to the dimer because the dimer does not exist at such forces. The energy of coumarins relative to the dimer coupled to an infinitely compliant stretching potential is similarly undefined. , In all panels, red arrows indicate the extrinsic stretching force. The underlying data are tabulated in suppdata.mat (Supporting Information).…”

“…The energy of coumarins relative to the dimer coupled to an infinitely compliant stretching potential is similarly undefined. 55,73 In all panels, red arrows indicate the extrinsic stretching force. The underlying data are tabulated in suppdata.mat (Supporting Information).…”

Dual Friction Force/Fluorescence Microscopy

“…Remaining challenges are the improvement of the zero-point correction in hover mode, registration robustness and accuracy (as images in AFM and optical microscopy are often slightly different due to the nature of AFM as a scanning microscopy), and the normalization of the fluorescence intensity so that samples with different thicknesses can be compared. The technique can be combined with other instruments such as hyperspectral microscopy to correlate the force and the resulting structural change in the polymer for mechanistic studies and also can be applied to other mechanochromic materials, or more generally to mechanochemistry , and mechanobiology in the future.…”

Modulating Transition Metal Reactivity with Force

“…We note that a challenge with higher forces is the kinetic instability of the E FPL. For example, greater forces of extension (+241 pN) are accessible with the E(2,2) ligand, but the excessive strain generated within in the macrocycle leads to rapid (Δ G ≠ =20.0 kcal/mol) Z/E isomerization upon metal complexation [15,16] …”