Radiation-induced adducts

EPR Parameters of Radiation-Induced Centers in NHtY and Their Oxygen Adducts... 

The experimental methodology in radiation-induced oxidation of benzene systems involved the measurement of rate constants and the transient absorption spectra by pulse radiolysis and the determination of yields of hydroxylated products on oxidation of the hydroxycyclo-hexadienyl radicals under steady-state conditions. The two commonly used oxidants — K3Fe(CN) "and IrCl " — convert quantitatively the OH adducts to the corresponding phenolic products. Thus, the pulse radiolysis technique in combination with product analysis using analytical techniques such as UV-VIS spectroscopy, HPLC, GC-MS, etc. under steady state conditions has provided valuable information in the understanding of the oxidation reaction mechanism of aromatics in... 

Another important aspect that has been well addressed " is on the radiation-induced degradation of benzene and its derivatives in aqueous solution. The Advanced Oxidation Processes (e.g. Oj-HjOj, HjOj-UV, electron beam) make use of the highly reactive OH radical in the degradation of water pollutants. Radiation chemical methods are superior to other methods (Fenton or photolysis) in the generation of peroxyl radicals from the reaction of OH adducts. 

Recently, Al-Sheikhly et al studied the radiation-induced destruction of benzene and dienes. Their pulse radiolysis work gave a rate constant k = 7.8 x 10 dm mol s to form the hydroxycyclo-hexadienyl radical, absorbing at 315 nm with a molar extinction coefficient of 4.2 x 10 dm mol cm (Fig. 1). The OH adduct... 

Alcock and coworkers studied the polymerization of butadiene (as well as of monoolefins, acetylene and aromatic olefins) trapped within the tunnel clathrate system of tris((9-phenylenedioxy)cyclotriphosphazene, induced by Co-y-radiation. The host was used in order to find if the concatenation and orientation of the monomer molecules under the steric forces generated within the host crystal lattice will lead to stereospecific polymerization. The clathrate was prepared by addition of liquid butadiene to the pure host at low temperature. The irradiation was conducted at low temperatures. Irradiation of pure butadiene (unclathrated bulk monomer) leads to formation of a mixture of three addition products f,2-adduct, cis- and trons-f,4-adducts. In contrast, the radiation-induced polymerization within the tunnel system of the host yielded almost pure trans-1,4-polybutadiene. A small percentage of f, 2-addition product was observed, but no evidence for the formation of c/s-f,4-adduct was found, confirming the earlier observation by Fin ter and Wegner. The average molecular weight was about 5000,... 

The type of base modification will determine which protein will come first and which system, BER or NER, will be used to cure the damaged DNA. NER is responsible for the removal of bulky adducts such as dimerized pyrimidine bases produced by UV radiation from sunlight, or benzo(a)pyren or psoralen adducts and others (Tab. 1). Bulky adducts are Table 1. Radiation-induced DNA damage recognition proteins in human cells. 

It is apparent from the present results that maleic anhydride forms an adduct of Type II with benzene and alkylbenzenes under the influence of silent discharge. The generally accepted path of formation of II in photochemical (6) or gamma-radiation induced (14) reaction is the following (benzene is used as substrate for convenience) ... 

Radiation induced copolymerization of hexafluoroacetone xcith a-olefins has been done over a broad temperature range. From these experiments, it was confirmed that ethylene can be copolymerized below its critical temperature to give an alternating copolymer. A radical mechanism is involved at relatively high temperatures below —10°C, the mechanism has been confirmed to be ionic and may be cationic. Propylene can be copolymerized in a way similar to that of ethylene however, the rate of copolymerization was much slower. Isobutylene did not copolymerize with hexafluoroacetone at 0°C. A 1 2 adduct compound was obtained as the main product. At low temperatures, copolymerization proceeds to some extent. 

The corresponding monohydroxy[ C]methyl derivatives, accessible through reaction of equimolar amounts of H CHO and alkyl cyanoacetates or dialkyl malonates readily eliminate water to give alkyl 2-cyano[3- C]acrylates till. =CN) and dialkyl [ " C]-methylenemalonates till. R = COOR ), respectively, which are highly valuable intermediates in Michael additions, Diels—Alder reactions and epoxidations. Unfortunately, carbon-14-labeled acrylates are unstable towards radiation induced polymerization. In order to circumvent this undesirable side effect, it has been recommended to run the formation in the presence of anthracene in order to trap the [ Clacrylates in situ as stable Diels-Alder adducts 112. These can be purified and stored briefly. Their subsequent thermolysis in the presence of maleic acid anhydride re-generates the acrylates 111 for immediate use in further reactions. ... 

The principle of MS/MS for direct analysis of a multicomponent system is shown in Figure 6.18, in which the first mass spectrometer (MS I) operates with soft ionisation (FI, FD, Cl, LD), and thus produces an ensemble of molecular ions (M + H+, M — H+, or adducts). For identification of molecule ABC only ABC+ is allowed to enter an interface or fragmentation zone for excitation by collisional activation, laser radiation or surface-induced dissociation. Within the time of one vibration (10-13s), ABC+ dissociates into fragments characterising the original molecule. They are separated and detected by MS II [226]. Soft ionisation with FI/FD produces low ion yields, which may be insufficient for MS/MS LVEI (typically at 20 V) can be an alternative. Complete analysis of a multicomponent system is carried out in some 20 min. 

Hankiewicz E (1995) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis II. Reactions of primary radicals with oxidants. Bull Pol Acad Sci Chem 43 41-49 Hankiewicz E (1996) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis - Part III. Consecutive reactions. Radiat Phys Chem 47 61-65 Hankiewicz E (1998) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis. IV. Reactions of primary radicals with reductants. Bull Pol Acad Sci Chem 46 455-464 Hankiewicz E, Bothe E, Schulte-Frohlinde D (1992) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis, part. I. Transformation reactions of two isomeric OH-adducts. Free Rad Res Commun 16 391-400... 

---