Effects of external electric fields on double proton transfer kinetics in the formic acid dimer

Abstract

Molecules can be exposed to strong local electric fields of the order of 10(8)-10(10) V m(-1) in the biological milieu. The effects of such fields on the rate constant (k) of a model reaction, the double-proton transfer reaction in the formic acid dimer (FAD), are investigated. The barrier heights and shapes are calculated in the absence and presence of several static homogenous external fields ranging from 5.14 × 10(8) to 5.14 × 10(9) V m(-1) using density functional theory (DFT/B3LYP) and second order Møller-Plesset perturbation theory (MP2) in conjunction with the 6-311++G(d,p) Pople basis set. Conventional transition state theory (CTST) followed by Wigner tunneling correction is then applied to estimate the rate constants at 25 °C. It is found that electric fields parallel to the long axis of the dimer (the line joining the two carbon atoms) lower the uncorrected barrier height, and hence increase the raw k. These fields also flatten the potential energy surface near the transition state region and, hence, decrease the multiplicative tunneling correction factor. The net result of these two opposing effects is that fields increase k(corrected) by a factor of ca. 3-4 (DFT-MP2, respectively) compared to the field-free k. Field strengths of ∼3 × 10(9) V m(-1) are found to be sufficient to double the tunneling-corrected double proton transfer rate constant at 25 °C. Field strengths of similar orders of magnitudes are encountered in the scanning tunneling microscope (STM), in the microenvironment of a DNA base-pair, in an enzyme active site, and in intense laser radiation fields. It is shown that the net (tunneling corrected) effect of the field on k can be closely fitted to an exponential relationship of the form k = aexp(bE), where a and b are constants and E the electric field strength.

Effect of external electric field on ground and singlet excited states of phenylalanine: A theoretical study

“…This proposition is further substantiated by some recent works which show that biological systems can experience a strong electric field with magnitude ranging from $10 8 to $10 10 Vm À1 [12,13].…”

“…Moreover, the ground and excited state of phenylalanine is envisaged to be influenced by the presence of external electric field, especially in the context of biological systems where the ions present in cellular environment, polar sugar-phosphate back bone and charged histones impart strong local electric field [12]. This proposition is further substantiated by some recent works which show that biological systems can experience a strong electric field with magnitude ranging from $10 8 to $10 10 Vm À1 [12,13].…”

Aβ self-association and adsorption on a hydrophobic nanosurface: competitive effects and the detection of small oligomers via electrical response

“…49 Aer energy minimization and 4 ns equilibration in the NPT ensemble, the systems were additionally equilibrated for 1 ns in the canonical (NVT) ensemble at 310 K. The volume of the simulation box was found to converge during the equilibration period (see Fig. 77,78 As our simulation box size in the x-direction is $100Å, the strength of the external eld applied along the x-direction ranged from about 9.7 Â 10 À5 to 4.4 Â 10 À4 a.u ( Table 1). Following this, a uniform electric eld of strength E x was applied in the direction parallel to the SWCNT axis (i.e.…”

TITAN: A Code for Modeling and Generating Electric Fields—Features and Applications to Enzymatic Reactivity

“…The seemingly endless potential of electric fields as a means for the control of chemical reactivity has sparked a lot of interest, not only from the biochemistry community, but also from organic chemists, as well as others . As a consequence, there is an increasing need for computational and theoretical chemists to extend their activities and expertise to this new research field.…”