Pulse radiolysis synthesis

PULSE-CHASE EXPERIMENTS N-END RULE PULSE RADIOLYSIS PURINE NUCLEOSIDASE PURINE NUCLEOSIDE PHOSPHORYLASE PUTRESCINE CARBAMOYLTRANSEERASE PUTRESCINE N-METHYLTRANSEERASE PUTRESCINE OXIDASE Putrescine synthesis,... 

When the irradiation of metal ion solutions is performed in the presence of the ligands CO or PPhs, metal reduction, ligandation, and aggregation reactions compete, leading to reduced metal complexes and then to stable molecular clusters, such as Chini clusters Pt3(CO)6] with m = 3-10 (i.e., 9-30 Pt atoms) [97], or other metal clusters [98]. The synthesis is selective and m is controlled by adjusting the dose m decreases at high doses). The mechanism of the reduction has been determined recently by pulse radiolysis [99]. Molecular clusters [Pt3(CO)6]5 have been observed by STM [100]. 

Schuchmann MN, Naumov S, Schuchmann H-P, von Sonntag J, von Sonntag C (2005) 4-Amino-3Ff-pyrimidin-2-one ("isocytosine") is a short-lived non-radical intermediate formed in the pulse radiolysis of cytosine in aqueous solution. Radiat Phys Chem 72 243-250 Schulte-Frohlinde D, Hildenbrand K (1989) Electron spin resonance studies of the reactions of OH and SO4 radicals with DNA, polynucleotides and single base model compounds. In Minisci F (ed) Free radicals in synthesis and biology. Kluwer, Dordrecht, pp 335-359 Schulte-Frohlinde D, Behrens G, Onal A (1986) Lifetime of peroxyl radicals of poly(U), poly(A) and single- and double-stranded DNA and the rate of their reaction with thiols. Int J Radiat Biol 50 103-110... 

Application of pulse radiolysis to polymers and polymerization was motivated at first by the success of radiation-induced polymerization as a novel technique for polymer synthesis. It turned out that a variety of monomers could be polymerized by means of radiolysis, but only a little was known about the reaction mechanisms. Early studies were, therefore, devoted to searching for initiators of radiation-induced polymerization such as radicals, anions and cations derived from monomers or solvents. Transient absorption spectra of those reactive intermediates were assigned with the aid of matrix isolation technique. Thus the initiation mechanisms were successfully elucidated by this method. Propagating species also were searched for enthusiastically in some polymerization systems, but the results were rather negative, because of the low steady state concentration of the species of interest. 

Ulanski P, Kadlubowski S, Rosiak JM (2002) Synthesis of poly(acrylic acid) nanogels by preparative pulse radiolysis. Radiat Phys Chem 63(3-6) 533-537... 

While steady-state radiolysis enables the synthesis of stable metal clusters in view of their characterization and the study of their physicochemical properties, pulse radiolysis allows the real-time kinetic and spectral study of transient clusters during the aggregation mechanism. For instance, the first steps of silver clusters nucleation have been studied by the teams of A. Henglein, " E. Janata and J. Belloni using pulse radiolysis, and some of the corresponding rate constants in water have been determined ... 

At the Institute for the Organic Synthesis and Photoreactivity (ISOF) is operating a 12 MeV (maximum energy with no load) Vickers L-band (1.3 GHz) traveling wave electron linear accelerator. The LINAC was put in operation mainly to be used as energy source for pulse radiolysis studies. 

In the case of benzene, one possible species absorbing in the region of 275 m/Lt is phenol. By measuring the absorption of phenol vapor in one atm. of air at 24 °C. in a Cary spectrophotometer, we found the absorption coefficient to be 4-5 X 103M 1 cm."1 at 275.7 m/ however, the absorption peak at 275.7 was very sharp, the absorption reaching zero by about 280 m/. We do not know how much the 50 fold increase in pressure used in the pulsed-radiolysis experiment would affect the width of the absorption, but it is very unlikely that phenol is the only absorbing species. In a recent study (10) on the synthesis of benzene oxide (A) in isooctane solution, this compound was found to have a maximum absorption at 271 m/x, and to be in equilibrium with oxepin (B), with a maximum at 305 m/x. 

The photoenolization of the quinone (286) can be carried by irradiation at 313 or 365 nm in acid solution. The steady state irradiation has identified the product as the unstable hydroxylated compound (287) which is formed via the enol (288). The presence of this intermediate was detected in a laser flash study of the reaction. The quinones (289) undergo cyclization when irradiated with visible light.The mechanism by which the compounds (289) are transformed into the derivatives (290) involves the production of an excited state that is either a zwitterion or a biradical. After the transfer of a hydrogen the intermediate (291) is formed. It is within this species that cyclization occurs to give the final products. (2+2)-Cyclo-adducts such as (292) and oxetanes can be obtained by the photochemical addition of quinones to homobenzvalene. Interest in the photo-SET in quinone systems has led to the synthesis of the pyropheophytin substituted naphthoquinone dyads (293). A pulse radiolysis study of vitamin K in solution has been reported. 

Metal nanoparticles can be prepared in a myriad of ways, e.g., by pulse radiolysis [110], vapor synthesis techniques [111], thermal decomposition of organometallic compounds [112], sonochemical techniques [113,114], electrochemical reduction [115,116], and various chemical reduction techniques. Some of the most frequently used reducing agents include alcohols [117,118], citrate [119,120], H2 [121], borohydrides [122], and, more recently, superhydride [123]. The chosen experimental conditions determine the size, size distribution, shape, and stability of the particles. Because naked metal particles tend to aggregate readily in solution, stabilizing the nanoparticles is the key factor for a successful synthesis. Sometimes the solvent can act as a stabilizer, but usually polymers and surfac-... 

Microemulsion-mediated materials synthesis employs three basic methods, as illustrated in Fig. 3 [17]. The microemulsion-plus-trigger method (Fig. 3, method a) is based on a single microemulsion. The fluid system is activated in some way in order to initiate the reactions that eventually lead to particle formation. Pulse radiolysis and laser photolysis have served as triggers for the preparation of nanosize gold particles [41]. In the case of metal oxides, temperature elevation can provide the needed trigger action hydrated metal ions solubilized... 

Takacs E (1992) Radiat Phys Chem 40 75 Takdcs E, Wojndrovits L, Foldvary Cs, Borsa J, Sajo I (2001) Res Chem Intermed 27 837 Takamuku S, Yamamato Y (1991) Pulse radiolysis study related to organic synthesis. In Tabata Y (ed) Pulse radiolysis. CRC, Boca Raton, pp 431-450 Theard L (1965) J Phys Chem 69 3292 Tilquin B (2008) Radiosterilization of drugs. In Spotheim-Maurizot M, Mostafavi M, Douki T, Belloni J (eds) Radiation chemistry from basics to applications in material and life sciences. EDP Sciences, Paris, pp 151-163... 

Remarkably few isolable complexes exhibit silver-silver covalency. The ionization potential [144] and bond length (2.5310(10) A) [145] of singly bonded Ag-Ag have been determined by spectroscopic studies on supersonic beams. Small clusters Ag ( = 2-5) have been synthesized and studied in an argon matrix [146], and the gas-phase synthesis and reaction chemistry of mixed-valent silver(0/I) clusters have been studied by mass spectrometry [147]. Pulse radiolysis of Ag+ solutions or glasses in water and ethanol has allowed the study of unstable clusters as intermediates in metal colloid formation thus, the absorption and EPR spectra of [Ag2], [Ag4], and [Ag4] have been recorded [148]. These are fully delocalized Ag(0,I) ions in which partial occupation of silver 5s-orbital combinations leads to net metal-metal bonding. 

Two basic approaches have been used in the preparation of metallic colloidal dispersions disintegration of the macroscopic metallic elements or synthesis of particles from metal salts using appropriate reducing agents, ultrasonics, pulse and laser radiolysis [ ] ... 

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