The Elucidation of Peroxyl Radical Reactions in Aqueous Solution with the Help of Radiation-Chemical Methods

Whenever free radicals are formed, independent of whether this occurs thermally, is induced by UV or ionizing irradiation, or takes place in redox reactions, they are converted rapidly into the corresponding peroxyl radicals in the presence of oxygen. Peroxyl radical reactions in aqueous environments are observed not only in aquatic systems (e.g., rivers, lakes and oceans) but also in the living cell and to a considerable degree even in the atmosphere (in water droplets). The peroxyl radical chemistry occurring in this medium is often very different from that observed in the gas phase or in organic solvents. In spite of the great importance of these reactions in medicine (for example in anti-cancer irradiation therapy and ischaemia) there have been comparatively few studies of peroxyl reactions in aqueous media. Radiation-chemical techniques such as pulse radiolysis offer the best means for carrying out such studies, so that it is not surprising that the majority of the information available in this area has been obtained with the help of radiation-chemical methods. The radiation chemistry of water can be con trolled in such a manner that the main products are ^˙OH radicals (90 % yield), which react with substrate molecules to give substrate radicals and in the presence of oxygen to give substrate peroxyl radicals. The experimental conditions can also be varied in such a way that HO/O radicals can be formed in 100 % yield and caused to react with substrates. We therefore have a simple access to these intermediates, which are extremely important in biological systems. A detailed product analysis, supported by kinetic studies carried out with the help of pulse radiolysis, has been used to clarify the chemistry of a series of peroxyl radicals, so that sufficient material is now available to justify a review of the variety of the peroxyl radical reactions studied by means of radiation-chemical methods. A more general survey of the physical properties of the peroxyl radicals and their unimolecular and bimolecular reactions will be followed by a discussion of selected examples of various classes of substance. Because of the great biological importance of radical-induced DNA damage this area will also be treated briefly.     

Voltammetric Detection of Free Sulfhydryl Compounds in Food Flours

Cyclic voltammetry has been applied to the rapid measurement of free SH‐compounds in food flours samples. The protocol is based on the electrochemical adaptation of the Ellman's test, where the DTNB reacts with SH‐compounds present in food flour extracts, resulting in the equimolar production of the electroactive compound TNBA which, in turns, reacts with phenylendiamine. The reaction is found to provide an analytical signal from which to quantify indirectly free sulfhydryl compounds in flours extracts.     

Variational transition state theory without the minimum-energy path

In this paper we propose a method for carrying out variational transition state theory calculations without first obtaining a converged minimum-energy path (MEP). We illustrate the method in two ways, first of all by employing an unconverged MEP and secondly by using a dynamically optimized distinguished reaction path. Preliminary tests of the algorithm for the reactions OH+H₂→H₂O+H and C₂H₅→C₂H₄+H are very encouraging. Received: 22 January 1997 / Accepted: 11 March 1997     

Copolymerization of acrylonitrile with itaconic acid in dimethylformamide: effect of triethylamine

The copolymerization of acrylonitrile (AN) in dimethylformamide (DMF) was retarded by the presence of itaconic acid (IA) comonomer. Addition of TEA helped overcome the retardation at enhanced concentrations of IA in the feed. The monomer reactivity ratios determined by both terminal and penultimate models revealed that the overall monomer reactivity’s are practically unaffected by the presence of TEA. The penultimate-unit effect for radicals terminated in AN was enhanced by the presence of TEA. Higher TEA concentrations helped regain the reactivities of AN and IA to AN-radical to the state in pure DMF. The penultimate model could explain the feed-copolymer composition profile for the whole range. Whereas IA systematically retarded the polymerization rate at all concentration regime in DMF, it increased the rate at higher IA concentration in DMF/TEA system. For a given IA concentration, the polymerization rate decreased as the solvent is enriched in TEA. The copolymers synthesized in the presence of TEA, manifested higher cyclization temperature and consequently lower char residue, attributed to the incorporation of TEA in the polymer by means of salt formation with IA moiety camouflaging the catalytic effect of the -COOH group in cyclization reaction. ¹³C-NMR studies confirmed the incorporation of the TEA molecules in the polymer chain.     

Conformations and base-catalyzed equilibrations of N-nitroso-decahydroquinolines and N-nitroso-2-methyldecahydroquinolines

Conformations of six title compounds were determined by¹³C-NMR spectroscopy. Equilibration of the 2-methyl-compounds gives as main products the derivatives of the amines least abundant in the product mixture of the catalytic hydrogenation.

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Konformation und Base-katalysierte Äquilibrierungen von N-Nitroso-decahydrochinolinen und N-Nitroso-2-methyl-decakydrochinolinen (Kurze Mitt.)

Zusammenfassung Die Konformationen der sechs Titelverbindungen wurden mittels¹³C-NMR Spektroskopie bestimmt. Äquilibrierung der 2-Methyl-verbindungen ergab als Hauptprodukte die Derivate der bei katalytischer Hydrierung in geringster Menge entstandenen Amine.

     

Capto-dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]

The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals.     

用含偶氮基的聚苯乙烯大分子引发剂合成两亲性嵌段共聚物

采用含偶氮基的聚苯乙烯预聚物（ＰＳ ＡＣＰＣ）作为引发剂，合成了苯乙烯（Ｓｔ）分别与甲基丙烯酸（ＭＡＡ）、甲基丙烯酸（β 羟丙酯）（ＨＰＭＡ）的嵌段共聚物，考察了ＰＳ ＡＣＰＣ引发第二单体的聚合反应行为，以及影响第二单体转化率和均聚物含量、共聚物组成的因素．用溶解性、凝胶渗透色谱（ＧＰＣ）、红外光谱（ＩＲ）、核磁共振（ＮＭＲ）、动态接触角（ＤＣＡ）等表征了嵌段共聚物．     

Influence of solvent polarity upon salt solubilities,II: Solubilities of two potassium carboxylates at 85°C in aqueous 1,4-dioxane

The solubilities of potassium acetate and benzoate in aqueous 1,4-dioxane at a temperature of 85°C are reported together with a quasi-thermodynamic general treatment of the experimental results.This brief contribution is a second report upon the results of systematic solubility measurements, commenced with Ref.¹, which have been performed by Dr.John A. McNaney during his abruptly truncated lifetime.     

SYNTHESES OF STYRENE-METHYL METHACRYLATE BLOCK COPOLYMER BY POLYAZOAMIDE AS INITIATOR

Polyazoamide(PAA) was used as initiator to prepare block copolymer P(MMA-b-St) byfree radical polymerization. The fraction of block copolymer was about 50%. The structureof the block-copolymer was characterized by IR and the results of ~1H-NMR and GPCshowed that the content of the block and the molecular weight (M_w) of the prepolymerand block copolymer could be controlled by varying the mol ratio of styrene/PAA andMMA/prepolymer. DSC and TEM results revealed that the block copolymer has twoseparated glass transition temperatures and phase separation within the domain structure.