High-pressure pulse-radiolysis

Cohen FI, van EldikR, Masarwa M, Meyerstein D (1990) Mechanism of oxidation ofaquated copper(ll) ions by hydroxyl free radicals. A high-pressure pulse-radiolysis experiment. Inorg Chim Acta 177 31-34... 

The volume of activation which can provide very valuable information concerning the reaction mechanism is obtained by high-pressure pulse radiolysis (for a review in the area of transition metal ion chemistry, see van Eldik and Meyerstein 2000). 

Fig. 6 Schematic diagram of the electron beam window for high pressure pulse radiolysis. The electron beam enters from the right side.

A recent reinvestigation of the proton transfer to cobalt(i) macroeycle (raf-LCo(I), see Equation (3)) using a high-pressure pulse radiolysis technique led to observed accelerated reaction forming 20 when the pressure was increased. ... 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

Buxton GV, Mulazzani QG, Ross AB (1995) Critical review of rate constants for reactions of transients from metal ions and metal complexes in aqueous solutions. J Phys Ref Data 24 1035-1349 Cheek CH, Swinnerton JW (1964) The radiation-induced chain reaction between nitrous oxide and hydrogen in aqueous solutions. J Phys Chem 68 1429-1432 Christensen H, Sehested K (1980) Pulse radiolysis at high temperatures and high pressures. Radiat Phys Chem 16 183-186... 

Pulse Radiolysis A technique related to flash photolysis pulse radiolysis uses very short (nanosecond) intense pulses of ionizing radiation to generate transient high concentrations of reactive species. See Salmon, G. A. and Sykes, A.G., Pulse radiolysis, Methods Enzymol. 227, 522-534, 1993 Maleknia, S.D., Kieselar, J.G., and Downard, K.M., Hydroxyl radical probe of the surface of lysozyme by synchrotron radiolysis and mass spectrometry. Rapid Commun. Mass Spectrom. 16, 53-61, 2002 Nakuna, B.N., Sun, G., and Anderson, V.E., Hydroxyl radical oxidation of cytochrome c by aerobic radiolysis, Free Radic. Biol. Med. 37, 1203-1213, 2004 BataiUe, C., Baldacchino, G., Cosson, R.P. et al., Effect of pressure on pulse radiolysis reduction of proteins, Biochim. Biophys. Acta 1724, 432-439, 2005. 

The temperature dependence of the absorption spectrum of the solvated electron has been recorded not only in water but also in alcohols (Fig. 3). Measurements are performed using nanosecond pulse radiolysis with a specific cell for high temperature and high pressure in a temperature range up to around 600 K depending on the solvent. Indeed, by increasing the temperature, the decay of solvated electrons becomes faster for example, this decay is much faster in alcohols than in water, so, the data obtained with nanosecond set-up are limited at lower temperatures for alcohols compared with water. 

By now most of the studies were carried out using nanosecond pulse radiolysis techniques coupled with spectroscopic detection method, only a few were reported to use muonium reactions, ° steady state (7 )radiolysis, laser phtolysis, and picosecond pulse radiolysis. Since conventional pulse radiolysis techniques are well known, here we just briefly introduce the high temperature high pressure (HTHP)... 

Pulse radiolysis studies of liquids at high temperature must necessarily be carried out at pressures sufficiently high to prevent boiling. The first pulse radiolysis experiments at high temperature were conducted by Michael et al. [74] who determined the spectrum of Caq in the temperature range —4 to 390 °C which the use of small suprasil capillaries above 200 °C. 

It was some ten years before any systematic program of pulse radiolysis at high temperature had begun when Christensen and Sehested [75] had available a pulse radiolysis cell that enabled measurements to be made up to 320 °C and 140 bar. This work focused on the radiation chemistry of water at elevated temperatures because of its relevance to the radiation chemistry occurring in the primary cooling circuits of pressurized water reactors used for electricity generation. 

Most pulse radiolysis experiments are performed with solutions at ambient temperature. In other cases, the temperature of the sample is kept constant or it is varied by means of suitable thermostatic systems. The construction details of a variable-temperature (from ca. —160 to -t-150°C) cell housing adaptable to a pulse radiolysis flow system have been given [111]. An alternative method of carrying out pulse radiolysis studies on liquids at high temperature (up to 300 °C) is to enclose the whole assembly of cell, reservoir syringe, and flow system in a pressure vessel [112]. Only the cell is located within a heating block and the reservoir remains at ambient temperature. With this method, the sample in the cell can be changed remotely as in conventional experiments. 

A high-pressure cell, originally utilized in flash-photolysis experiments where limitations caused by low beam penetration do not exist, has been adapted for measurements up to 200 MPa in pulse radiolysis experiments to be performed at ambient temperature with a beam energy as low as 2 MeV [113]. 

This is a very fast reaction that, under some conditions, can even exceed rates of H abstraction (309). Cyclization of LO to epoxides is the dominant reaction in aprotic solvents (including neat lipids), when lipids are at low concentration (275) or highly dispersed on a surface (315, 316), at room temperature (147, 308, 317), and at low oxygen pressures (275, 278) and the reaction accelerates with increasing polarity of the aprotic solvent (308-310). However, the stability of LO is reduced considerably in polar solvents (309, 310). Although epoxyallylic radicals from cyclization have been observed in pulse radiolysis studies of LO in aqueous solutions (308), H abstraction and scission reactions are much faster. This pattern can be seen in the change of cyclic products yields when oxidation was conducted in different solvents (Table 8). The change in competition over time is also apparent. 

Kissner, R., Nauser, T, Bugnon, P, Lye, PG, and Koppenol, WH. 1997. Formation and properties of peroxynitrite as studied by laser flash photolysis, high-pressure stopped-flow technique, and pulse radiolysis. Chem Res Toxicol 10 1285-1292. 

Lipsky (237), Sandros (181), and Russian workers (238,239) observed triplet energy transfer from benzene to biacetyl for dilute benzene solutions. This indicates that the triplet lifetime in solution is also concentration dependent as is the case for o-xylene (240) where the lifetime Increased from a few nanoseconds to microseconds or more, on dilution. This has been confirmed for benzene (175,189) and further, additional evidence from photochemical (173) and pulse radiolysis (241) systems demonstrate the very short lifetime of the triplet state in pure benzene liquid. It is believed (175) that decay proceeds via the triplet excimer which is only inefficiently quenched by butene-2. Results of electron impact excitation (242) and pulse radiolysis (243) have indicated a triplet lifetime of 500 ps for gaseous benzene at low and high pressures. 

The role of FNO in atmospheric chemistry is related to the destruction of stratospheric ozone.244 246 The reaction F + NO has been extensively studied using different experimental techniques, including mass spectrometry, chemiluminescence, ESR, IR, and UV spectroscopy.241,247 251 The pressure dependence of the kinetics of FNO formation was recently studied by Pagsberg et al.25i in order to obtain the fall-off curve and the high- and low-pressure limiting rate constants. The reaction was initiated by pulse radiolysis of a SF6/NO gas mixture. In the presence of NO, the decay of the formed... 

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