The perturbational treatment of H-bonded systems reduces the discussion of H-bond properties to that of proton donor and proton acceptor properties. Among the variety of interaction contributions within perturbation theory it is simply the electrostatic interaction which mainly seems to control H-bond strength and stereochemistry of H-bonds. The easy accessible classical and clear electrostatic...

Sequential Monte Carlo/Quantum Mechanical calculations of the interaction energy of hydrogen-bonded methanol in liquid water gives the same result for methanol acting either as the proton donor or the proton acceptor. For the complex-optimized cases methanol acting as the proton acceptor, CH3HO· · ·H2O, is more stable than the proton donor, CH3OH· · ·OH2, by ∼ 0.5 kcal/mol. In the case of metha...

The dynamical behavior and the temperature dependence of the kinetic isotope effects (KIEs) are examined for the proton-coupled electron transfer reaction catalyzed by the enzyme soybean lipoxygenase. The calculations are based on a vibronically nonadiabatic formulation that includes the quantum mechanical effects of the active electrons and the transferring proton, as well as the motions of al...

We study the hydrogen tunneling problem in a model system that represents the active site of the biological enzyme, soybean lipoxygenase-1. Toward this, we utilize quantum wavepacket dynamics performed on potential surfaces obtained by using hybrid density functional theory under the influence of a dynamical active site. The kinetic isotope effect is computed by using the transmission amplitude...

A theoretical investigation of proton-coupled electron transfer in ruthenium polypyridyl complexes is presented. The three reactions studied are as follows: (1) the comproportionation reaction of [(bpy)(2)(py)Ru(IV)O](2+) and [(bpy)(2)(py)Ru(II)OH(2)](2+) to produce [(bpy)(2)(py)Ru(III)OH](2+); (2) the comproportionation reaction of [(tpy)(bpy)Ru(IV)O](2+) and [(tpy)(bpy)Ru(II)OH(2)](2+) to pro...

One of the key problems of molecular bioenergetics is the understanding of the function of redox-driven proton pumps on a molecular level. One such class of proton pumps are the heme-copper oxidases. These enzymes are integral membrane proteins in which proton translocation across the membrane is driven by electron transfer from a low-potential donor, such as, e.g. cytochrome c, to a high-poten...

This paper presents a theoretical formulation for electron transfer coupled to the motion of multiple protons. This theory is applied to proton-coupled electron transfer ~PCET! through amidinium– carboxylate salt bridges, where the electron transfer reaction is coupled to the motion of two protons at the proton transfer interface. The rate for the donor–~amidinium–carboxylate!–acceptor system i...

Proton-transfer reactions across and at the surface of biological membranes are central for maintaining the transmembrane proton electrochemical gradients involved in cellular energy conversion. In this study, fluorescence correlation spectroscopy was used to measure the local protonation and deprotonation rates of single pH-sensitive fluorophores conjugated to liposome membranes, and the depen...

Photoactivation of attractant phototaxis receptor sensory rhodopsin I (SRI) in Halobacterium salinarum entails transfer of a proton from the retinylidene chromophore's Schiff base (SB) to an unidentified acceptor residue on the cytoplasmic half-channel, in sharp contrast to other microbial rhodopsins, including the closely related repellent phototaxis receptor SRII and the outward proton pump b...