Chemically Fueled Transient Geometry Changes in Diphenic Acids

Abstract

Transient changes in molecular geometry are key to the function of many important biochemical systems. Here, we show that diphenic acids undergo out-of-equilibrium changes in dihedral angle when reacted with a carbodiimide chemical fuel. Treatment of appropriately functionalized diphenic acids with EDC (<i>N</i>-(3-dimethylaminopropyl)-<i>N</i>′-ethylcarbodiimide hydrochloride) yields the corresponding diphenic anhydrides, reducing the torsional angle about the biaryl bond by approximately 45°, regardless of substitution. In the absence of steric resistance, the reaction is well-described by a simple mechanism; the resulting kinetic parameters can be used to derive important properties of the system, such as yields and lifetimes. The reaction tolerates steric hindrance ortho to the biaryl bond, although the competing formation of (transient) byproducts complicates quantitative analysis.

Substituent Effects on Transient, Carbodiimide-Fueled Geometry Changes in Diphenic Acids

“…Gas-phase DFT geometry optimizations at the B97-D3(BJ)/TZV(2d,2p) level, summarized in Table 1, were carried out to understand the changes in geometry expected for these systems. The benzene rings of the diphenic acids are approximately orthogonal in most cases, as measured by the torsional angle (φ acid ) between the two rings, except for DP-Ac1 (as previously reported 29 ) and DP-Ac6. The smaller φ acid for DP-Ac1 (R = H) is unsurprising given that it is less sterically hindered.…”

“…The net result is the formation of a transient covalent bond that can be coupled to nonequilibrium behavior. 15 In previous work, 29 we demonstrated chemically fueled geometry changes using the water- soluble diphenic acids DP-Ac1-DP-Ac3 in Figure 1a. On reaction with EDC, they form (intramolecular) anhydrides, giving rise to significant changes in the twist about the biaryl bond as shown in Figure 1b.…”

“…Transient anhydrides were indeed generated, but the systems were not kinetically well-behaved under our original conditions, preventing analysis of structure-property effects. 29 Here, we report the expanded series of diphenic acid derivatives in Figure 1a. Suitable conditions for quantitative mechanistic analysis of EDC-fueled anhydride formation have been identified.…”

Chemically Fueled Transient Geometry Changes in Diphenic Acids

“…Consequently, they can be used to form intramolecular bonds, a potentially useful tool for inducing changes in geometry. Here, we demonstrate a simple system that undergoes significant changes in the twist about a single bond on treatment with a chemical fuel . Our focus is the water-soluble diphenic acids shown in Figure a.…”