Radical initiators dihydrochloride

The addition of carbon-based radicals has been shown to be successful in water.3 Thus, radical additions of a 2-iodoalkanamide or 2-iodoalkanoic acid to alkenols using the water-soluble radical initiator 4,4 -azobis(4-cyanopenta-noic acid) or 2,2/-azobis(2-methylpropanamidine) dihydrochloride carried out in water generated y-lactones (Scheme 7.3). 

ABTS radical anions were used according to the method of (Kim et al., 2003). In brief, 1.0 mM of 2, 2 -azobis (2-amidino-propane) dihydrochloride (AAPH), a radical initiator, was mixed with 2.5 mM ABTS in phosphate-buffered saline (pH 7.4) and the mixed solution was heated in a water bath at 68 °C for 13 min. The resulting blue-green ABTS solution was adjusted to the absorbance of 0.650 + 0.020 at 734 nm with additional phosphate-buffered saline. 20 il of sample were added to 980 (iL of the ABTS radical solution. The mixture incubated in a 37°C water bath under restricted light for 10 min. A control (20 iL 50% methanol and 980 mL of ABTS radical solution) was run with each series of samples. The decrease of the absorbance at 734 nm was measured (Cary 50 Scan UV-Visible apparatus) at an endpoint after 10 min. Total antioxidant capacity of plant parts is expressed as mg / g of dry weight of vitamin C equivalents (VCEAC). The radical stock solution had to be freshly prepared and all measurements of the tested samples were repeated at least three times. 

The antioxidant effect of different types of lignins has been evaluated by their capacity to inhibit human erythrocyte haemolysis induced by AAPH [2,2 -az-obis(2-amidopropane) dihydrochloride], a peroxyl radical initiator (Fig. 8.10) [150], or by hydrogen peroxide [151]. 

The pH responsive gel used in the project is based on the monomer methacrylic acid (MAA) The gels are synthesised via a free-radical mechanism. The synthesis was carried out in an aqueous environment using 2,2 -azobis (2-methylpropionamidine) dihydrochloride (AMPA) and N,N -methylene bisacrylamide (MBA) which are water-soluble free radical initiator and crosslink agent respectively (Scheme 1). The polymerizations were carried out in water (20%w/v MAA 0.03%w/v MBA 0.06%w/v AMPA) under a nitrogen atmosphere. The polymerization was initiated thermally at 70°C, and gelation occurred in less than one hour. Residual monomer was removed from the gels by alternate soaking in water and methanol. 

A number of kinetic studies were carried out to elucidate the interaction between a-tocopherol and ascorbic acid in liposomes. By using either water-soluble or oil-soluble diazo radical initiators, the effect of radicals can be compared when they are produced either in the phospholipid bilayer or in the aqueous phase. Oxidation of a soybean phosphatidylcholine liposome in the presence of radicals produced in the water phase with a water-soluble radical initiator [2,2 -azobis(2-amidinopropane) dihydrochloride, (AAPH)], showed an induction period with both a-tocopherol (vitamin E) and ascorbic acid (vitamin C) (Figure 10.9). With a mixture of vitamin E and vitamin C, the length of the induction was close to the sum of the individual induction periods. This result indicates an additive effect in suppressing oxidation by both vitamin E and vitamin C. Vitamin C apparently traps radicals in the water phase. When oxidation was induced by radicals produced in the lipid phase with an oil-soluble radical initiator [2,2 -azobis(2,4-dimethylvaleronitrile), (AMVN)] incorporated into the membrane, ascorbic acid alone had no effect, while a-tocopherol had a greater effect because it is lipophilic. However, the mixture... 

Ebselen suppressed the oxidation of methyl linole-ate emulsions in aqueous dispersion induced by iron (10 xM Fe ), the spontaneous oxidation of rat brain and hver homogenates, but did not suppress the oxidation of these homogenates induced by 10 mM of the free radical initiator, 2,2 -azobis(amidinopropane) dihydrochloride (Noguchi et al. 1992). 

Superabsorbent polyacrylates are prepared by means of free-radical-initiated copolymerization of acrylic acid and its salts with a cross-linker (12,13). Two principal processes are used bulk, aqueous solution pol5unerization and suspension polymerization of aqueous monomer droplets in a hydrocarbon liquid continuous phase (14) (see Bulk and Solution Polymerizations Reactors Heterophase Polymerization). In either process, the monomers are dissolved in water at concentrations of 20-40 wt% and the polymerization is initiated by free radicals in the aqueous phase (15). The initiators, freeradical (qv) used include thermally decomposable initiators, reduction-oxidation systems, and photochemical initiators and combinations. Redox systems include persulfate/bisulfite, persulfate/thiosulfate, persulfate/ascorbate, and hydrogen peroxide/ascorbate. Thermal initiators include persulfates, 2,2 -azobis(2-amidinopropane)-dihydrochloride, and 2,2 -azobis(4-cyanopentanoic acid). Combinations of initiators are useful for polymerizations taking place over a temperature range. 

A number of water- and fat-soluble nitrogen compounds, e.g., 2,2 -azo-fe/.v(2-amidinopropane) dihydrochloride (ABAP), 2,2 -azo-te(2,4-dimethylvaleroni-trile) (AMVN), and 2,2 -azo-to(2-cyanopropane) (ABCP), form free radicals during decomposition that in the sample to be investigated initiate lipid peroxidation [16] ... 

Because the size of the emulsion droplets dictates the diameter of the resulting capsules, it is possible to use miniemulsions to make nanocapsules. To cite a recent example, Carlos Co and his group developed relatively monodisperse 200-nm capsules by interfacial free-radical polymerization (Scott et al. 2005). Dibutyl maleate in hexadecane was dispersed in a miniemulsion of poly(ethylene glycol)-1000 (PEG-1000) divinyl ether in an aqueous phase. They generated the miniemulsion by sonication and used an interfacially active initiator, 2,2 -azobis(A-octyl-2-methyl-propionamidine) dihydrochloride, to initiate the reaction, coupled with UV irradiation. 

Since the fatty acid chains in each lipid were 18 carbons and 16 carbons, respectively, it is reasonable that they could form a mixed lipid phase. Furthermore the bis-dienoyl substitution of 15 favors the formation of crosslinked polymer networks. Ohno et al. showed that the dienoyl group associated with the sn-1 chain could be polymerized by lipid soluble initiators, e.g. AIBN, whereas the dienoyl in the sn-2 chain was unaffected by AIBN generated radicals. Conversely, radicals from a water-soluble initiator, e.g. azo-bis(2-amidinopropane) dihydrochloride (AAPD), caused the polymerization of the sn-2 chain dienoyl group, but not the sn-1 chain. These data provide clear evidence for the hypothesis of Lopez et al. that the same reactive group located in similar positions in the sn-1 and sn-2 chains of polymerizable 1,2-diacyl phospholipids are positionally inequivalent [23]. 

As preliminary examples, AIBN was reported to give a 48 hr degradation of tetrazepam very similar to that obtained in 6 months accelerated degradation of tablets (28). Similarly, the water-soluble initiator 2,2 -azobis (2-amidinopropane) dihydrochloride was shown to accelerate the natural degradation of thymidine. In contrast, systems producing the more reactive hydroxy radicals (e.g., Fenton conditions) give mainly nonnatural degradation products (29). 

Radicals generated during peroxidation of lipids and proteins show reactivity similar to that of the hydroxyl radical however, their oxidative potentials are lower. It is assumed that the reactive alkoxyl radicals rather than the peroxyl radicals play a part in protein fragmentation secondary to lipid peroxidation process, or protein exposure to organic hydroperoxides (DIO). Reaction of lipid radicals produces protein-lipid covalent bonds and dityrosyl cross-links. Such cross-links were, for example, found in dimerization of Ca2+-ATPase from skeletal muscle sarcoplasmic reticulum. The reaction was carried out in vitro by treatment of sarcoplasmic reticulum membranes with an azo-initiator, 2,2/-azobis(2-amidinopropane) dihydrochloride (AAPH), which generated peroxyl and alkoxyl radicals (V9). 

Regarding the initiation process of polymerization, it can be started by y-radiation. It is a method that has been used for the synthesis of hydrogels of PEO as well as hydrogels based on vinyl monomers " in this latter case, azo-compounds such as 2,2-azo-isobutyroni-trile (AIBN)f or 2,2 -azobis (2-amidine-propane) dihydrochloride or V-SO, and aqueous salt solutions such as aqueous ammonium peroxodisulfate are also used. Among the monomers most used in the preparation of hydrogels through free-radical polymerization are 2-hydroxyethyl methacrylate (HEMA) and A-vinyl-2-pyrrolidone (VP). ... 

By means of related procedures grafting from and onto radical VFA polymerization with functionalized silica are also possible. It was found that these methods are ineffective for the synthesis of PVFA/silica hybrid materials [103]. Hence, radical copolymerization of VFA with vinylsilane-function-alized silica particles was chosen [99]. The functionalization of silica particles with VTS yields, with good reproducibility, hybrid particles (VTS-silica) with an average carbon content of 3.4 w/w-%. Co-polymerization of VFA with VTS-silica particles was performed in aqueous suspensions containing 2,2 -azobis-(2-amidinopropene) dihydrochloride (ABAC) as initiator. The... 

Although AIBN is a popular choice, other azo compounds can give superior results due to their varying half-life. Indeed, the nature of the substitution of a newly formed carbon radical plays an important role in their half-life, as can be seen from the following for 2, 2 -azobis(4-methoxy)-3,4-dimethylvaleronitrile (AMYN), with a t /2 in toluene of 1 h at 56 °C and 10 h at 33 °C. There are also hydrophilic azo compounds, such as 2, 2 -azobis(2-methylpropionamidine) dihydrochloride (APPH), with a t j2 in water of 10 h at 56 °C. Typically, 5-10 mol% of the initiator is added, either in one portion or via slow addition. There... 

The water-soluble azo-initiator A APH[2,2Azo-bis(2-amidinopropane)dihydrochloride] can be used to produce radicals in the aqueous phase, whereas the lipid-soluble AMVN [2,2 -azo-bis-(2,4-dimethylvaleronitrile)] can be used to produce radicals in the lipid phase. AAPH decomposes with a first-order rate constant of X,=6.6xlO Vmin at 37°C, and the flux of the free radicals is proportional to the AAPH concentration." ... 

When lipoprotein are subjected to the attack of peroxyl radicals, thermally induced from aqueous solutions of azo-initiator 2,2 -azobis (2methylpropionamidine).dihydrochloride (AAPH), the lipoperoxidation occurs according to a radical pathway (Litescu et al, 2002 Tache et al, 2011) leading to lipo-peroxides formation on the LDL layer. In our experiments the FTIR analysis was performed first on the LDL deposed on the solid support, then the LDL was subjected to free radicals attack for 10 minutes, allowed to dry on inert atmosphere and after that the oxidised LDL layer was once more assessed by FTIR. 

The lipophilic a-tocopherol and its hydrophilic analog Trolox also behave quite differently in linoleic acid micelles compared to phosphatidylcholine liposomes. With micelles of linoleic acid in SDS initiated with a water-soluble initiator [2,2 -azobis-(2-amidino propane) dihydrochloride, ABAP], a-toco-pherol was much less active than Trolox (Table 10.16). With phosphatidylcholine liposomes initiated with a lipid-soluble initiator AMVN, a-tocopherol and Trolox had about the same antioxidant activity. Linoleic acid and SDS form mixed micelles in the aqueous phase in which the polar antioxidant Trolox equilibrates more rapidly and becomes more effective than in liposomes. Also, Trolox can efficiently trap radicals from the water-soluble initiator ABAP. 

The g values reported for such complexes in 3-methyIpentane glass are around 2.05 [6]. Due to a S-S bonding g j in these species is expected to be directed along the S-S bond [31]. This is exactly what was found for the species in irradiated crystalline cystine dihydrochloride (g=2.06, 2.01, and 2.00), irradiated at 77 K and annealed to protonate the RSSR" anions formed initially [25, 42, 43]. RSH-complexed thiyl radicals also display characteristic electronic absorption spectra with strong maxima around 400 nm, and their own chemistry... 

Reversible atom transfer free radical polymerization of n-butyl acrylate was conducted in miniemulsion systems using the water-soluble initiator 2,2 -azobis(2-amidinopropane) dihydrochloride (V-50) and the hydrophobic ligand 4,4 -di(5-nonyl)-4,4 -bipyridine to form a complex with the copper ions [67, 80]. The resultant Cu(II) complex has a relatively large solubility in the continuous aqueous phase, but this should not impair its capability of controlling the free radical polymerization. This is because the rapid transport of the Cu(II) complex between the dispersed organic phase and the continuous aqueous phase assures an adequate concentration of the free radical deactivator. As a consequence, the controlled free radical polymerization within the homogenized monomer droplets can be achieved. 

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