Kinetics and mechanism of the reaction of [RuIII(edta)(H2O)]- with HOBr to form an intermediate RuV=O complex in aqueous solution

The interaction of [Ru(III)(edta)(H(2)O)](-) (1) (edta = ethylenediaminetetraacetate) with the oxygen transfer agent HOBr, was studied kinetically as a function of [HOBr] and temperature (5-35 degrees C) at a fixed pH of 6.2. Spectroscopic evidence is reported for the formation of a high valent intermediate (edta)Ru(V)=O complex. Water soluble 2,2'-azobis(3-ethylbenzithiazoline-6-sulfonate) (ABTS) was employed as a trap for this intermediate in order to gain further mechanistic information. Reactions were carried out under pseudo-first conditions for [ABTS] > [HOBr] > [1], and were monitored as a function of time for the formation of the one-electron oxidation product ABTS(*+). The reported kinetic data are interpreted in terms of a suggested reaction mechanism and discussed in reference to data reported before.     

New method for the synthesis of N-tert-alkoxyarylaminyl radicals

The reactions of 2,4-diaryl-6-tert-butylnitrosobenzenes with 2,2'-azobis[2-(methoxycarbonyl)propane] (5a), 2,2'-azobis(2-cyano-4-methylpentane) (5b), and 2,2'-azobis(2-cyano-4-methyl-4-methoxypentane) (5c) in refluxing benzene gave stable N-tert-alkoxy-2,4-diaryl-6-tert-butylphenylaminyls, which were successfully isolated as radical crystals in 13-52% yields after column chromatography. The radical yields depended on the reaction time and the molar ratio of azo compounds to nitroso compounds. In the same manner, acetyl- and cyano-group-carrying N-tert-alkoxyarylaminyls were generated by the reaction of 2-phenyl-4-(4-acetylphenyl)-6-tert-butylnitrosobenzene and 2-phenyl-4-(4-cyanophenyl)-6-tert-butylnitrosobenzene with 5a and 5b, and they were isolated as radical crystals. X-ray crystallographic analyses were performed for two radicals, and their molecular structures were discussed in detail. The magnetic properties were measured for the two isolated radicals with SQUID in the temperature range 1.8-300 K. One radical showed a weak ferromagnetic interaction (theta = 0.2 K) between the radicals, and the other showed a weak antiferromagnetic interaction (theta = -3.8 K). The ferromagnetic interaction was analyzed based on the X-ray crystallographic structure.     

Inhibition of free radical initiated peroxidation of human erythrocyte ghosts by flavonols and their glycosides

The in vitro peroxidation of human erythrocyte ghosts was used as a model to study the free radical-induced damage of biological membranes and the protective effect of flavonols and their glycosides, i.e., quercetin (Q), quercetin galactopyranoside (QG), quercetin rhamnopyranoside (QR), rutin (R), morin (MO), kaempferol (K) and kaempferol glucoside (KG). The peroxidation was initiated by a water-soluble free radical initiator 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AMPAD) at physiological temperature, and monitored by oxygen uptake. Kinetic analysis of the peroxidation process demonstrates that these flavonols and their glycosides are effective antioxidants against AMPAD-initiated oxidative damage of human erythrocyte ghosts, and that the flavonols bearing ortho-dihydroxyl groups possess significantly higher antioxidant activity than those bearing no such functionalities and the glycosides are less active than their parent aglycones.     

Soap-free synthesis for producing highly monodisperse, micrometer-sized polystyrene particles up to 6 microm

A soap-free emulsion polymerization method with the use of an amphoteric initiator, currently proposed by the authors for producing highly monodisperse, micrometer-sized polymer particles, was examined in the polymerization of styrene with a 2,2'-azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine] hydrate initiator and an NH(4)OH/NH(4)Cl pH buffer. The pH buffer was used to control the electric surface potential of particles to maintain a stable dispersion of particles and to prevent generation of new particles during the polymerization. Addition of monomer to the reaction system during polymerization could enlarge the average size of polymer particles to 5.7 microm with a coefficient of variation of 1.5%, which is much less than the standard criteria of monodispersity, 10%.     

Atom transfer radical addition in the presence of catalytic amounts of copper(I/II) complexes with tris(2-pyridylmethyl)amine

Highly efficient atom transfer radical addition of polyhalogenated compounds to alkenes catalyzed by copper(I/II) complexes with tris(2-pyridylmethyl)amine in the presence of a radical initiator [2,2'-azobis(2-methylpropionitrile)] was reported.     

Design and Synthesis of 3-Triazolo-coumarins and Their Applications in Scavenging Radicals and Protecting DNA

In this study, we synthesized a series of 3-triazolo-coumarins and evaluated their antioxidant activities respectively by two methods: trapping 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical(ABTS^+·) and oxidation of DNA which was induced by Cu²⁺/glutathione(GSH), ·OH and 2,2'-azobis(2-amidinopropane hydrochloride)(AAPH). Among the nine 3-triazolo-coumarins, compounds 6c and 6f―6i were synthesized for the first time, which exhibited the capability of terminating radical propagation-chains in oxidation of DNA induced by AAPH. In this study, we found that phenethylamine moiety, hydroxyl and ortho-methoxy are the key groups to enhance the antioxidant activities of compounds.     

Synthesis and characterization of amphoteric latex particles

Stable monodisperse amphoteric latex particles were prepared by the semibatch surfactant-free emulsion copolymerization of methyl methacrylate and methacrylic acid (MAA) initiated by 2,2'-azobis(2-amidinopropane) dihydrochloride (V-50). These submicron particles have a net positive charge, which is attributed to the ionized amino group at low pH. In contrast, they become negatively charged owing to the ionized carboxyl group at high pH. There exists a pH at which these particles exhibit a net charge of zero (pI). At a constant level of V-50, the pI value of these latices decreases with increasing amount of MAA used in the polymerization recipe. The effect of pH on the colloidal stability of these amphoteric latices toward the addition of the negatively charged latex was investigated. The resultant coagulation kinetics was used to study the electrostatic interaction between the amphoteric particles and negatively charged particles.     

The direct synthesis of thioesters using an intermolecular radical reaction of aldehydes with dipentafluorophenyl disulfide in water

The combination of the water-soluble radical initiator, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044), and surfactant, cetyltrimethylammonium bromide (CTAB), was found to be the most suitable condition for the effective direct synthesis of useful active thioesters (pentafluorophenyl thioesters) in water.     

Reaction of [RuIII(edta)(H2O)]- with H2O2 in aqueous solution. Kinetic and mechanistic investigation

The reaction of [Ru(III)(edta)(H(2)O)](-) (1) (edta = ethylenediaminetetraacetate) with hydrogen peroxide was studied kinetically as a function of [H(2)O(2)], temperature (5-35 degrees C) and pressure (1-1300 atm) at a fixed pH of 5.1 using stopped-flow techniques. The reaction was found to consist of two steps involving the rapid formation of a [Ru(III)(edta)(OOH)](2-) intermediate which subsequently undergoes parallel heterolytic and homolytic cleavage to produce [(edta)Ru(V)=O](-) (45%) and [(edta)Ru(IV)(OH)](-) (55%), respectively. The water soluble trap, 2,2'-azobis(3-ethylbenzithiazoline-6-sulfonate) (ABTS), was employed to substantiate the mechanistic proposal. Reactions were carried out under pseudo-first conditions for [ABTS] > [HOBr] > [1], and were monitored as a function of time for the formation of the one-electron oxidation product ABTS* (+). A detailed mechanism in agreement with the rate and activation parameters is presented, and the results are discussed with reference to data reported for the corresponding [Fe(III)(edta)(H(2)O)](-)/H(2)O(2) system.     

A novel and efficient methodology for the C-C bond forming radical cyclization of hydrophobic substrates in water

[reaction: see text]. The combination of water-soluble radical initiator 2,2'-azobis[2-(2-imidazolin-2-yl)propane] (VA-061), water-soluble chain carrier 1-ethylpiperidine hypophosphite (EPHP), and surfactant cetyltrimethylammonium bromide (CTAB) was found to be the most suitable condition for effective radical cyclization in water for a variety of hydrophobic substrates.     

Kinetics and mechanism of O-O bond cleavage in the reaction of [RuIII(edta)(H2O)]- with hydroperoxides in aqueous solution

The reactions of [Ru(III)(edta)(H(2)O)](-) (1) (edta = ethylenediaminetetraacetate) with tert-butylhydroperoxide ((t)BuOOH) and potassium hydrogenpersulfate (KHSO(5)) were studied kinetically as a function of oxidant concentration and temperature (10-30 degrees C) at a fixed pH of 6.1 using stopped-flow techniques. Kinetic results were analyzed by using global kinetic analysis techniques. The reaction was found to consist of two steps involving the rapid formation of a [Ru(III)(edta)(OOR)](2-) intermediate, which subsequently undergoes heterolytic cleavage to form [(edta)Ru(V)=O](-). Since [(edta)Ru(V)=O](-) was produced almost quantitatively in the reaction of 1 with the hydroperoxides (t)BuOOH and KHSO(5), the common mechanism is one of heterolytic scission of the O-O bond. The water soluble and easy to oxidize substrate 2,2'-azobis(3-ethylbenzithiazoline-6-sulfonate (ABTS), was employed to substantiate the mechanistic proposal. Reactions were carried out under pseudo-first order conditions for [ABTS] > [hydroperoxide] > [1], and were monitored as a function of time for the formation of the one-electron oxidation product ABTS (*+). The detailed suggested mechanism is consistent with the reported rate and activation parameters, and discussed in reference to the results reported for the reaction of [Ru(II)(edta)(H(2)O)](-) with H(2)O(2).     

A MORPHOLOGICAL STUDY OF POLY（DIVINYLBENZENE-co-ACRYLIC ACID） IN CROSSLINKING PRECIPITATION POLYMERIZATION

Divinylbenzene-80 （DVB-80） and polar monomer acrylic acid （AA） having hydrogen bonding at a total monomer loading of 5 vol% were precipitated-copolymerized in a variety of organic solvents with 2,2＇-azobis（isobutyronitrile） （AIBN） as initiator. The experiments were investigated from a two-dimensional matrix, i.e., the actual crosslinking degree of DVB varying from 0 to 80% and the solvent composition varying from 0 to 100% of toluene mixture with acetonitrile, when the mixture of acetonitrile and toluene was used as the reaction solvent. Under various reaction conditions, six distinct morphologies including soluble polymers, swellable microgels, coagulum, irregular microparticles, and nano-/micrometer microspheres were formed and the structures of these polymer architectures were described. A morphological map was utilized to discuss the effects of both crosslinking degree of DVB and composition of solvent on the transitions between morphology domains. The results demonstrated that the microspheres are formed by an internal contraction due to the marginal solvency of the continuous phase and the crosslinking of the polymer network through the covalent bonding from DVB as well as the interchain hydrogen-bonding between the carboxylic acid units.     

Efficient synthesis of thioesters and amides from aldehydes by using an intermolecular radical reaction in water

The combination of the water-soluble radical initiator, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044) and the surfactant, cetyltrimethyl-ammonium bromide (CTAB), was found to be the most suitable condition for the effective and direct synthesis of useful active thioesters (pentafluorophenyl thioesters) in water. In addition, the direct amidation of aldehydes was achieved by the addition of the amines to the thioesterification reaction mixture in water.     

Synthesis of polystyrene/poly[2-(dimethylamino)ethyl methacrylate-stat-ethylene glycol dimethacrylate] core-shell latex particles by seeded emulsion polymerization and their application as stimulus-responsive particulate emulsifiers for oil-in-water emulsions

Surfactant-stabilized polystyrene (PS) latex particles with a mean hydrodynamic diameter of 155 nm were prepared by aqueous emulsion polymerization using 2,2'-azobis(2-amidinopropane) hydrochloride as a cationic radical initiator. Seeded aqueous emulsion copolymerizations of 2-(dimethylamino)ethyl methacrylate (DMA) and ethylene glycol dimethacrylate (EGDMA) were conducted in the presence of these PS particles to produce two batches of colloidally stable core-shell latex particles, in which the shell comprised a cross-linked P(DMA-stat-EGDMA) overlayer. Both the PS and PS/P(DMA-stat-EGDMA) latexes were characterized in terms of their particle size, morphology, and composition using dynamic light scattering, electron microscopy, and FT-IR spectroscopy, respectively. Using the PS/P(DMA-stat-EGDMA) latex particles as a pH-responsive particulate ('Pickering'-type) emulsifier, polydisperse n-dodecane-in-water emulsions were prepared at pH 8 that could be partially broken (demulsified) on lowering the solution pH to 3. These emulsions were characterized in terms of their emulsion type, mean droplet diameter, and morphology using electrical conductivity and Mastersizer measurements, optical microscopy, and scanning electron microscopy (using critical point drying for sample preparation).     

Mechanistic aspects of thiyl radical-promoted acyl radical cyclization of formylenoate-cyclization versus oxidation

Treatment of formylalkenoates 1 and 7 with 2,2'-azobis(2-methylpropanenitrile) (AIBN) in the presence of dioxygen gave oxygenated carboxylic acids 5, 6, 8, 9 instead of acyl radical cyclization products, through preferential reaction of the corresponding acyl radicals with dioxygen rather than intramolecular attack to an enoate moiety. The reaction of 1 with AIBN in the absence of dioxygen recovered starting 1 in 98% yield.     

纳米TiO_2粒子静电吸附引发剂及其原位锚固丙烯酸丁酯聚合

调节体系酸碱度使分散于水分散液中的纳米TiO2粒子表面带负电,进而通过静电作用高效稳定吸附上偶氮盐类引发剂2,2′-偶氮二异丁脒二氯化氢(AIBA).实验发现引发剂在TiO2粒子表面的静电吸附存在一个稳定吸附上限,其值在pH=10的体系中为0.084mmol/g(相对于TiO2的量).进一步通过原位乳液聚合在TiO2粒子表面就地引发丙烯酸丁酯(BA)的锚固聚合,制备得到了PBA/TiO2复合乳胶.对聚合动力学和聚合产物的观察发现,吸附引发剂在其中起到重大作用,只有当引发剂用量略低于稳定吸附上限时,反应过程稳定性和聚合产物分散性才较好.此时聚合反应阻聚期短、反应速率快、单体转化率高、实验重现性好.热重分析(TGA)和红外光谱分析(FTIR)结合抽提实验证实,通过原位乳液聚合可在TiO2粒子表面锚固上13.5%的不可抽提PBA聚合物.动态激光粒度分析(DLS)发现,原位锚固改性对TiO2粒子软团聚体具有稳定的解团聚作用,可有效提高纳米TiO2粒子在体系中的分散性和分散稳定性.这一化学改性作用与超声分散所带来的物理性的可逆解软团聚作用有着本质区别.     

Preparation of micrometer-sized polymer particles with control of initiator dissociation during soap-free emulsion polymerization

A previously proposed method of soap-free emulsion polymerization employing an amphoteric initiator, 2,2'-azobis [N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate (VA-057), was extended to synthesize micrometer-sized polystyrene particles with low polydispersity in an acidic region of pH from 3.3 to 4.6. A buffer system of CH3COOH/CH3COONa was used for the adjustment of pH, which was aimed at effective promotion of particle coagulation in early stage of the polymerization. In these experiments, CH3COOH concentration was varied from 20 to 360 mM at a CH3COONa concentration of 10 mM. Polymer particles with an average size of 1.8 microm and low polydispersity were obtained at the CH3COOH concentration of 40 mM for the concentrations of 1.1 M styrene monomer and 10 mM initiator. To more precisely control dispersion stability of particles, experiments in which pH was stepwisely changed during the polymerization were also carried out. This polymerization method could enhance the average size of particles to 2.2 microm while retaining the monodispersity of particles. Furthermore, combination of pH stepwise change and monomer addition during the polymerization could produce particles with an average size of 3.0 microm and low polydispersity.     

Diiron amido-imido complex [(CpFe)2(mu2-NHPh)(mu2-NPh)]: synthesis and a net hydrogen atom abstraction reaction to form a bis(imido) complex

A reaction between [CpFeCl]x and LiNHPh (1 equiv to Fe) produces a new paramagnetic Fe(II)-Fe(III) mu2-amido-mu2-imido complex [(CpFe)2(mu2-NHPh)(mu2-NPh)] (1), which, upon interaction with 2,2'-azobis(2,4-dimethylvaleronitrile), undergoes a net N-H hydrogen atom abstraction reaction to give a diamagnetic Fe(III)-Fe(III) mu2-imido dimer [CpFe(mu2-NPh)]2 (2). The molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction.     

Synthesis and structures of (R)-cyclopentadienyl-binaphthoxy titanium(IV) complexes and catalytic properties for olefin polymerization

Two new chiral pre-ligands, (R)-3,3'-bis(tetramethylcyclopentadienyl)-2,2'-bismethoxy-1,1'-bisnaphthalene (1) and (R)-3-tetramethylcyclopentadienyl-2,2'-bismethoxy-1,1'-bisnaphthalene (2), were synthesized by reaction of (R)-3,3'-dilithium-2,2'-bismethoxy-1,1'-bisnaphthalene with 2,3,4,5-tetramethyl-2-cyclopentenone at room temperature. Treatment of the pre-ligands 1 and 2 with butyllithium and Me(3)SiCl first, and subsequently with TiCl(4) (2 and 1 equiv for 1 and 2, respectively) afforded a binuclear complex (R)-3,3'-bis[(tetramethylcyclopentadienyl)trichlorotitanium]-2,2'-bismethoxy-1,1'-bisnaphthalene (3) and a mononuclear complex (R)-3-(tetramethylcyclopentadienyl)trichlorotitanium-2,2'-bismethoxy-1,1'-bisnaphthalene (4) in moderate yields. Complexes 3 and 4 were further converted into constrained geometry complexes (R)-1,1'-bis{2,2'-naphthoxy-3,3'-bis[(tetramethylcyclopentadienyl)dibromotitanium]} (5) and (R)-1-(2-naphthoxy)-1'-(2'-naphthol)-3-(tetramethylcyclopentadienyl)dibromotitanium (6) by treatment with BBr(3). The pre-ligands 1 and 2 were characterized by (1)H and (13)C NMR and high resolution mass spectroscopy (HRMS), and the new titanium complexes 3-6 were characterized by (1)H and (13)C NMR and elemental analyses. Molecular structures of 4, 5, and 6 were determined by single-crystal X-ray diffraction analysis. Complexes 4, 5, and 6 all have a pseudo-octahedral coordination environment and adopt a three-legged piano stool geometry around the titanium atom in their solid state structures. When activated with Al(i)Bu(3) and Ph(3)CB(C(6)F(5))(4), the chiral complexes 5 and 6 show moderate catalytic activities for propylene, 1-hexene, and 5-ethylidene-2-norbornene (ENB) polymerization and ethylene/1-hexene copolymerization. The polymers produced by the chiral 5/(i)Bu(3)Al/Ph(3)CB(C(6)F(5))(4) catalyst system from the 1-hexene, and ENB polymerization and ethylene/1-hexene copolymerization with high comonomer contents exhibit optical activity.     

Spontaneous vesicle formation and phase behavior in mixtures of an anionic surfactant with imidazoline compounds

Unexpected colloidal assemblies form in aqueous mixtures of sodium dodecylbenzenesulfonate (SDBS) with the following imidazoline compounds: 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (V-44, which is a commonly used free-radical initiator), 2,2'-tetramethylenedi-2-imidazoline (TMI), and the main recombination product (RP) from the decomposition of V-44. All of these imidazoline compounds act as hydrotropes. As the molar ratio of imidazoline to SDBS increases, a gradual transition from micelles to vesicles to bilayers to precipitate is observed. V-44 decomposes slowly at 25 degrees C, and the phase diagrams of V-44/SDBS and RP/SDBS are similar. The vesicular region observed in mixtures of TMI/SDBS is larger in composition than that of V-44/SDBS and RP/SDBS mixtures. At equimolar compositions of SDBS and RP, a novel colloidal structure with multiple closely packed bilayers is observed. In these mixtures, small unilamellar vesicles (<80 nm in diameter) form spontaneously, although with time they coexist with a small amount of precipitate and their size increases steadily. The self-assembly of vesicles occurs over a wide range of compositions when the solution pH is lower than the pK(a) of the imidazoline moiety. Quasi-elastic light scattering, cryogenic transmission electron microscopy, nuclear magnetic resonance, and small-angle neutron scattering were used to determine the characteristic length scales and properties of the assemblies.