The vibrational overtone induced unimolecular dissociation of HMHP (HOCH(2)OOH) and HMHP-d(2) (HOCD(2)OOH) into OH and HOCH(2)O (HOCD(2)O) fragments is investigated in the region of the 4nu(OH) and 5nu(OH) bands. The unimolecular dissociation rates in the threshold region, corresponding to the 4nu(OH) band, exhibit measurable differences associated with excitation of the OH stretch of the alcoh...

To understand the underlying mechanisms of significant differences in dissociation rate constant among different inhibitors for HIV-1 protease, we performed steered molecular dynamics (SMD) simulations to analyze the entire dissociation processes of inhibitors from the binding pocket of protease at atomistic details. We found that the strength of hydrogen bond network between inhibitor and the ...

The S-D bond dissociation dynamics of thiophenol-d1 (C6H5SD) pumped at 266, 243, and 224 nm are examined using the velocity map ion imaging technique. At both 266 and 243 nm, distinct peaks associated with X and A states of the phenylthiyl radical (C6H5S*) are observed in the D+ image at high and low kinetic energy regions, respectively. The partitioning of the available energy into the vibrati...

The ultraviolet photolysis of jet-cooled mass-selected ketenyl radicals has been investigated using the technique of fast radical beam photofragment translational spectroscopy. The C̃P(A9) – X̃ A9 photofragment yield cross section spans 33 400–48 000 cm and exhibits resolved resonances and broad continua. Dissociation produces both ground and excited state CH radicals in association with ground s...

High-level ab initio electronic structure calculations are used to interpret the fragmentation dynamics of CHBr(2)COCF(3), following excitation with an intense ultrafast laser pulse. The potential energy surfaces of the ground and excited cationic states along the dissociative C-CF(3) bond have been calculated using multireference second order perturbation theory methods. The calculations confi...

Self-consistent correlation potentials for H(2) and LiH for various inter-atomic separations are obtained within the random phase approximation (RPA) of density functional theory. The RPA correlation potential shows a peak at the bond midpoint, which is an exact feature of the true correlation potential, but lacks another exact feature: the step important to preserve integer charge on the atomi...

In the present study, the pH-dependent free radical-scavenging activity of betanin in the Trolox equivalent antioxidant capacity (TEAC) assay was determined. It was found that at a pH > 4 betanin is about 1.5-2.0-fold more active than some anthocyanins considered very good free radical scavengers as determined in the TEAC assay. The increase in the TEAC values of betanin with increasing pH is d...

The bond dissociation energy of a series of metallocenium ions, i.e., the energy difference of the reaction MCp2(+) → MCp(+) + Cp· (with M = Ti, V, Cr, Mn, Fe, Co, and Ni), was studied by means of multiconfigurational perturbation theory (CASPT2, RASPT2, NEVPT2) and restricted coupled cluster theory (CCSD(T)). From a comparison between the results obtained from these different methods, and a de...

The emission from the acidic form of the green fluorescence protein (GFP) changes with increasing time and temperature from t-1/2 to t-3/2 asymptotics. It is shown that a model of proton diffusion along a one-dimensional hydrogen-bond network within the protein, with a switch (Thr203) allowing for proton escape, explains the data quantitatively. From a comparison of the model with experiment, w...

An ab initio computational study on a series of sulfoxides is reported. The SO bond dissociation energy (BDE) of sulfoxides in which the sulfur atom is included in a formally aromatic ring (e.g., thiophene sulfoxide) is found to be decreased by as much as 25 kcal/mol, compared to DMSO. A complementary effect is observed for sulfoxides in which the sulfur is included in a formally antiaromatic r...