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Photolysis reaction of di-tert-butylperoxide was undertaken in various solvents by photoacoustic calorimetry (PAC) for the determination of the O-O bond dissociation enthalpy of this homolysis reaction and was very similar to a widely accepted value for the gas phase bond dissociation enthalpy. The procedure proposed in the study allows determination of solvation of free radicals energetics and indicates that the frequent assumption of canceling solvation enthalpies must be used with caution. This is based on thermodynamic cycle, and ECW model.

Mid-infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations are used for the structural characterization of protonated phosphorylated serine, threonine and tyrosine. The results have shown that IRMPD spectroscopy is good tool for structural characterization of small phosphorylated peptides.

Time-resolved photoacoustic calorimetry and quantum chemistry measurements are used to examine the energetic of sulfur-hydrogen bonds in thiophenol and para-substituted thiophenols. The data generated for the substituted thiophenols confirm that substituent effects are less definite on the S - H bond dissociation enthalpy of the relative phenols.

Examines the solvation enthalpies of various free radicals. Photolysis reaction of di-tert-butylperoxide using photoacoustic calorimetry; Solvation characteristic of phenoxy radicals; Measurement of the oxidation potential of A-H bond.

The structure of the sodiated peptide GGGGGGGG-Na+ or G8-Na+ was investigated by infrared multiple photon dissociation (IRMPD) spectroscopy and a combination of theoretical methods. IRMPD was carried out in both the fingerprint and N–H/O–H stretching regions. Modeling used the polarizable force field AMOEBA in conjunction with the replica-exchange molecular dynamics (REMD) method, allowing an efficient exploration of the potential energy surface. Geometries and energetics were further refined at B3LYP-D and MP2 quantum chemical levels. The IRMPD spectra indicate that there is no free C-terminus OH and that several N–Hs are free of hydrogen bonding, while several others are bound, however not very strongly. The structure must then be either of the charge solvation (CS) type with a hydrogen-bound acidic OH, or a salt bridge (SB). Extensive REMD searches generated several low-energy structures of both types. The most stable structures of each type are computed to be very close in energy. The computed energy barrier separating these structures is small enough that G8-Na+ is likely fluxional with easy proton transfer between the two peptide termini. There is, however, good agreement between experiment and computations in the entire spectral range for the CS isomer only, which thus appears to be the most likely structure of G8-Na+ at room temperature. [Copyright &y& Elsevier]

The demand for novel effective antioxidant-based drugs has led to the synthesis and evaluation of the antioxidant potential in several molecules derived from natural compounds. In this work the in vitro antioxidant activity of an abietic acid-derived catechol (methyl 11,12-dihydroxyabietate-8,11,13-trien-18-oate, MDTO) was evaluated. This substance, possessing important biological properties, is similar to carnosic acid, a natural antioxidant from rosemary or sage leaves. Aiming to understand the antioxidant activity of MDTO, the energetics of its O-H bond, using time-resolved photoacoustic calorimetry (TR-PAC), was investigated. On energetic grounds it is predicted that MDTO is a good free radical scavenger, although its activity is lower than that of quercetin, a very effective antioxidant, which was used for comparison. In agreement with these predictions, the DPPH(*) and ABTS(*+) radical scavenging activities are lower than those of quercetin. In addition, MDTO also reacts with HOCl, a powerful proinflammatory oxidant produced by activated neutrophils, and protects liposomes against iron-ascorbate-induced oxidation. The discussion of these results foresees potential applications of MDTO as an antioxidant.