Chemomechanics: chemical kinetics for multiscale phenomena

Abstract

The purpose of this critical review is to introduce the reader to an increasingly important class of phenomena: enormous changes in rates of simple chemical reactions within macromolecules as they are stretched by interactions with the environment. In these chemomechanical, or mechanochemical, phenomena the effect of the macromolecular environment can be visualized as a spring (harmonic or anharmonic) bridging and pulling apart a pair of atoms of the macromolecule. Being able to predict how the parameters of this spring affect the kinetics of the reactions occurring between the constrained atoms may create revolutionary opportunities for designing new reactions, molecules and materials that would capture large-scale deformations to drive useful chemistry or, conversely, that would propel autonomous micro- and nanomechanical devices by coupling them to the concerted motion of atoms that convert reactants into products. Although chemists have long studied and exploited coupling between molecular strain and reactivity in small molecules, a quantitative understanding of the relationship between large-scale (>50 nm) strain and localized reactivity presents unique conceptual and experimental challenges. Below we discuss both the phenomenology and the interpretive framework of chemomechanical phenomena (102 references).

Model studies of force-dependent kinetics of multi-barrier reactions

“…S1 and S2), in accord with the simplest model of singlebarrier force-dependent kinetics. 54 To confirm the conclusion that reduction of disulphides E1, E2, E4, and E6 is limited by the force-dependent kinetics of the formation of the zwitterionic intermediate, rather than the force-independent hydrolysis of the zwitterionic intermediate, as in the strain-free disulphide, we calculated (at the B3LYP/6- 53 ) the activation free energy of the first step in reduction of Et 2 S 2 by PPh 3 and PPh 2 CH 3 ( Fig. 3a) as a function of the stretching force applied across the terminal C atoms of Et 2 S 2 , using previously described methodology.…”

Interplay Between Mechanochemistry and Sonochemistry

“…Mechanistic frameworks should be investigated in these cases, although, unfortunately, space limitations prevent in-depth analysis. Our readers are referred to recent and comprehensive works such as those by Boulatov and associates [17], and RibasArino/Marx [18]. They largely deal with attempts to understand chemical reactivity under mechanical loads in general and some models may certainly be extrapolated to ultrasound-induced forces.…”

The renaissance of continuum mechanics

“…A recent excellent study was carried out by Freund (2009), who established a theoretical model to characterize the resisting force when a molecular bond is separated forcibly. Such a kinetic model at the molecular level is considered to be an important constituent in multiscale modeling which in addition includes continuum mechanics models both at the macromolecular level (where statistical mechanics is usually adopted to obtain the averaged properties) and the microscopic level (Huang and Boulatov, 2011). By chemomechanics, mechanics meets chemistry also in biology (Girard et al, 2007;Wilson et al, 2013) and in engineering (Hu and Hueckel, 2007).…”