Water-soluble Radical Initiator Research Articles

AIBA as Free Radical Initiator for Abrasive-Free Polishing of Hard Disk Substrate

In order to optimize the existing slurry for abrasive-free polishing (AFP) of a hard disk substrate, a water-soluble free radical initiator, 2,2′-azobis (2-methylpropionamidine) dihydrochloride (AIBA) was introduced into H2O2-based slurry in the present work. Polishing experiment results with AIBA in the H2O2 slurry indicate that the material removal rate (MRR) increases and the polished surface has a lower surface roughness. The mechanism of AIBA in AFP was investigated using electron spin-resonance spectroscopy and UV–Visible analysis, which showed that the concentration of hydroxyl radical (a stronger oxidizer than H2O2) in the slurry was enhanced in the present of AIBA. The structure of the film formed on the substrate surface was investigated by scanning electron microscopy, auger electron spectroscopy and electrochemical impedance spectroscopy technology, showing that a looser and porous oxide film was found on the hard disk substrate surface when treated with the H2O2-AIBA slurry. Furthermore, potentiodynamic polarization tests show that the H2O2-AIBA slurry has a higher corrosion current density, implying that a fast dissolution reaction can occur on the substrate surface. Therefore, we can conclude that the stronger oxidation ability, loose oxide film on the substrate surface, and the higher corrosion-wear rate of the H2O2-AIBA slurry lead to the higher MRR.

SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL ACTIVITY OF THIOUREA CONTAINING POLYMERS

N-acryloyl-N-phenylthiourea (APTU) is synthesized by reacting acryloyl chloride with phenylthiourea in the presence of triethylamine (TEA) as a base and characterized by FT-IR, 1H-NMR and mass spectra. The acrylic polymers from different feed ratios of ethylacrylate (EA), methylmethacrylate (MMA), styrene (St) and APTU have been prepared by emulsion polymerization in water containing sodium lauryl sulfate as a surfactant and ammonium persulfate as a water-soluble radical initiator. The polymers are characterized by FT-IR spectroscopy. The solubility is tested in various polar and non-polar solvents. The molecular weight and polydispersity are determined using gel permeation chromatography (GPC).Thermal behavior of the prepared polymers is also investigated by thermogravimetrical analysis (TGA). The polymers are tested for their antimicrobial activities against selected microorganisms.

Phase Transfer Catalyzed Polymerization of Styrene and Graft Copolymerization of Styrene onto Gelatin

The use of tetrabutylammonium bromide (TBAB), as phase transfer catalyst during polymerization of styrene in the presence of water-soluble radical initiator, potassium persulfate (KPS), and graft copolymerization of styrene onto gelatin, a water soluble polymer, using a water-insoluble radical initiator, benzoyl peroxide (BPO), has been explored in a water-benzene biphasic system. The percentage conversion (Pc) of styrene to polystyrene and percent grafting (Pg) of styrene onto gelatin was studied as a function of various reaction parameters. Under optimum reaction conditions, maximum Pc (76%) was obtained at [KPS] = 12.9 × 10−4 moles/L, [Sty] = 4.3 ×10−3 moles/L, and maximum Pg (87%) was obtained at [BPO] = 4.6× 10−4 moles/L, [Sty] = 13.88 × 10−3 moles/L using [PTC] = 2.89 × 10−4 moles/Lin 10 mL each of water and benzene in 120 min at 60 °C. The graft copolymer, Gel-g-poly(Sty), was characterized by IR, Thermogravimetric Analysis, Scanning Electron Microscopy and swelling behaviour in different solvents. Metal uptake and degradation studies of the grafted sample were also carried out. The grafted sample showed maximum uptake for Cu2+ (88%), Ni2+ (80%) and Fe2+ (50%). Degradation studies of Gel-g-poly(Sty) were carried out by soil burial test and UV radiations. Photo-degradation showed better degradation (5.26% wt. loss) in 32 h of exposure to UV radiations as compared to soil burial degradation (8.46% wt. loss) in 30 days. Gelatin-styrene graft copolymers can thus be used as bio- and photo-degradable materials for environmental management.

Preparation and Characterizations of C60/Polystyrene Composite Particle Containing Pristine C60Clusters

Fullerene/polystyrene (C60/PS) nano particle was prepared by using emulsion polymerization. Styrene and fullerene were emulsified in aqueous media in the presence of poly(N-vinyl pyridine) as an emulsion stabilizer, and polymerization was initiated by water soluble radical initiator, potassium persulfate. The obtained nano particles have an average diameter in the range of 400-500 nm. The fullerene contents in the nano particle can be controlled up to 15 wt % by varying the feed ratio, which was confirmed by themogravimetric analysis (TGA) and elemental analysis (EA). The structure and morphologies of the C60/PS nano particles were examined by various analytical techniques such as dynamic light scattering (DLS), scanning electron microscope (SEM), transmission electron microscope (TEM), electron diffraction (ED) pattern, X-ray powder diffraction (XRD), and UV spectroscopy. Unlike conventional C60/PS particles initiated by organic free radical initiators, in which the fullerene is copolymerized forming a covalent bond with styrene monomer, the prepared C60/PS nano particles contain pristine fullerene as secondary particles homogeneously distributed in the polystyrene matrix.

Concentration and time dependent cytoprotective effects of anthocyanins against oxidative hemolysis induced by water and lipid soluble free radical initiators: an <i>in vitro</i> study

The non-enzymatic, free radical-mediated peroxidation of erythrocyte membranes is now correlated with a variety of pathological conditions, and considered as a primary event associated with hematotoxicity of variety of drugs and chemicals that induce erythrocyte hemolysis. The plant derived polyphenols including anthocyanins have been suggested to enhance red blood cell resistance to oxidative stress both in vitro and in vivo. The present study was designed to investigate the concentration and time dependent anti-hemolytic activity of anthocyanins using in vitro models of azo compounds-induced erythrocyte membrane peroxidative damage. Three different concentrations (1, 0.1 and 0.01 mg/ml) of anthocyanins solution were incubated with erythrocytes suspension 30 min before addition of either water soluble (AAPH) or lipid soluble (AMVN) free radical initiators. The level of hemoglobin released into the solution was determined spectrophotometrically, both in presence and absence of anthocyanins. Moreover, the most effective concentration was selected to be added at different time intervals (zero time, 2 and 3 hours) post challenge with either AAPH or AMVN and the extent of hemolysis was determined as mentioned before. The results showed that anthocyanins, concentration dependently attenuated hemolysis induced by azo compounds, and substantial cytoprotective effects of anthocyanins were observed when they added simultaneously with azo compounds, while delayed addition of anthocyanins for 2 and 3 h diminished but not abolished the protective effect of anthocyanins. In conclusion, anthocyanins can effectively display concentration and time dependent cytoprotective properties against azo compounds-induced peroxidative hemolytic damage.

Protective Effect of <i>Aloe vera (Aloe barbadensis</i> Miller) on Erythrocytes Anion Transporter and Oxidative Change

The purpose of this study was to evaluate the ability of aqueous extract of Aloe barbadensis Miller (Aloe vera) on oxidative damage and Anion Exchanger 1 (AE1, also known as Band 3) expression in human erythrocytes exposed to the water soluble free radical initiator 2.2’-azobis-2-amidinopropano dihydrochloride (AAPH). In addition, total phenolic compounds in the extracts were determined as catechin equivalent and the various antioxidant activities were compared to natural and synthetic standard antioxidants such as BHA and ascorbic acid. Since Aloe vera extract did not cause a consumption of the cytosolic antioxidant, glutathione (GSH) when it was direct incubated with GSH in basic aerated aqueous solution, this indicates that Aloe vera extract does not proceed auto oxidation at this experimental condition. Furthermore, Aloe vera extract prevent the consumption of GSH, in radical treated RBCs. It also inhibit consumption of GSH when it was direct incubated with AAPH. Aloe vera gel extract inhibits the generation of diphenyl-2-picrylhy-drazyl (DPPH) and the scavenging activity was increased in a dose dependent manner. Aloe vera extract was shown the similar reducing power than standards BHT and ascorbic acid. Biochemical analysis by SDS-PAGE and western blotting showed that AAPH-induced oxidative stress increased the susceptibility of AE1 to proteolytic degradation. Of note, our data evidenced that Aloe vera treatment was able to partially restore the normal RBC membrane protein profiles in a dose-dependent manner. These results clearly demonstrate the antioxidative activity of Aloe vera gel extract that might be ascribed to a synergistic action of the bioactive compounds contained therein.

A convenient method to prepare emulsified polyacrylate nanoparticles from for drug delivery applications

We describe a method to obtain purified, polyacrylate nanoparticles in a homogeneous powdered form that can be readily reconstituted in aqueous media for in vivo applications. Polyacrylate-based nanoparticles can be easily prepared by emulsion polymerization using a 7:3 mixture of butyl acrylate and styrene in water containing sodium dodecyl sulfate as a surfactant and potassium persulfate as a water-soluble radical initiator. The resulting emulsions contain nanoparticles measuring 40-50 nm in diameter with uniform morphology, and can be purified by centrifugation and dialysis to remove larger coagulants as well as residual surfactant and monomers associated with toxicity. These purified emulsions can be lyophilized in the presence of maltose (a non-toxic cryoprotectant) to provide a homogeneous dried powder, which can be reconstituted as an emulsion by addition of an aqueous diluent. Dynamic light scattering and microbiological experiments were carried out on the reconstituted nanoparticles. This procedure allows for ready preparation of nanoparticle emulsions for drug delivery applications.

Radical-Initiator-Induced Solid-State Polymerization of Butadiyne Nanocrystals in Water and Their Dispersion Stabilization

Butadiyne nanocrystals in water are usually polymerized by UV or gamma-ray irradiation to give polydiacetylene (PDA) nanocrystals. In this study, we confirmed that solid-state polymerization of 1,6-di(N-carbazolyl)-2,4-hexadiyne (DCHD) and 5,7-dodecadiyn-1,12-diyl bis[N-(butoxycarbonyl-methyl)carbamate] (4BCMU) could be stimulated by water-soluble radical initiators. The radical initiators used were potassium peroxodisulfate, three kinds of azo-type compounds and a redox initiator. In all cases, the solid-state polymerization was confirmed by color change into blue indicating that PDA modified by the radical residues at the end was formed. However, nanocrystal cohesion occurred especially when the concentration of the initiators was high or the dispersion was kept for a long time. In order to improve the dispersion stability, two kinds of surfactants, i.e., sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTMAC), were added to the DCHD nanocrystal aqueous dispersion. As a result, when anionic SDS was added, the solid-state polymerization of nanocrystals proceeded without coagulation and quantitative conversion was confirmed for all initiators. Cationic DTMAC has no effect on dispersion stabilization. PDA nanocrystal surfaces in water are negatively charged in nature and electric interaction of nanocrystals with the cations results in decrease of surface charge and aggregation of nanocrystals.

Functionalization of Polymer Nanoparticles by Thiol−Ene Addition

Syndiotactic 1,2-polybutadiene nanoparticles (volume average diameter 13 nm) were functionalized in aqueous dispersion by free radical mercaptan addition. By appropriate choice of both water-soluble radical initiator and mercaptan concentration, nanoparticles with a degree of functionalization of up to 85% were prepared using 3-mercaptopropionic acid methyl ester and 3-mercaptopropionic acid. Only a minor portion of double bonds formed cycles instead of the desired thiol−ene addition products. The composition and structure of the nanoparticles were elucidated by combination of elemental analysis, NMR, IR, DLS, and TEM. Highly hydrophilic mercaptans (3-mercaptopropanesulfonic acid sodium salts), in contrast, only reacted with surface accessible double bonds to afford stable and redispersible nanoparticles solely stabilized with covalently bound moieties on their surface. Analogous grafting of the tripeptide glutathione was demonstrated.

Optimization of Emulsion Polymerization for Submicron-Sized Polymer Colloids towards Tunable Synthetic Opals

Submicron-sized polymeric colloidal particles can self assemble into 3-dimensional (3D) opal structure which is a useful template for photonic crystal. Narrowly dispersed polymer microspheres can be synthesized by emulsion polymerization in water using water-soluble radical initiator. In this report, we demonstrate a facile and reproducible emulsion polymerization method to prepare various polymeric microspheres within 200 - 400 nm size ranges which can be utilized as colloidal photonic crystal template. By controlling the amount of monomer and surfactant, monodisperse polymer colloids of polystyrene (PS) and acrylates with various sizes were successfully prepared without complicated synthetic procedures. Such polymer colloids self-assembled into 3D opal structure exhibiting bright colors by reflection of visible light. The colloidal particles and the resulting opal structures were rigorously characterized, and the wavelength of the structural color from the colloidal crystal was confirmed to have quantitative relationship with the size of constituting colloidal particles as predicted by Bragg equation. The tunability of the structural color was achieved not only by varying the particle size but also by infiltration of the colloidal crystal with liquids having different refractive indices.

ChemInform Abstract: Radical Addition of 2-Iodoalkanamide or 2-Iodoalkanoic Acid to Alkenols Using a Water-Soluble Radical Initiator in Water. A Facile Synthesis of γ-Lactones.

Abstract Heating a mixture of 2-iodoacetamide and 5-hexen-1-ol in water at 75 °C in the presence of a water-soluble radical initiator, 4,4′-azobis(4-cyanopentanoic acid), provided γ-(4-hydroxybutyl)-γ-lactone in 95% yield. The use of 2-iodoacetic acid in place of 2-iodoacetamide also gave the same γ-lactone in 93 % yield.

Highly Unsaturated Fatty Acid might Act as an Antioxidant in Emulsion System Oxidized by Azo Compound

Now it is recognized that DHA is oxidatively stable fatty acid compared with linoleic acid (LA) in emulsified system, although DHA is oxidatively unstable in a bulk system. In fact, an emulsified mixture of DHA and LA behaves as in a bulk system, namely the oxidative stability of DHA becomes lower than that of LA. Therefore, in this study, tridocosahexaenoate (DDD) and glycerol trilinoleate (LLL) were separately emulsified using TritonX-100 as an emulsifier and DDD emulsion was mixed with the oxidizing LLL emulsion using a water-soluble radical initiator, 2,2'-azobis(2-aminopropane) dihydrochloride. As a result, DHA suppressed the oxidation of LA, while DHA was not significantly oxidized. This suppression ability was examined using glycerol trieicosapentaenoate, glycerol trilinolenate, or glycerol trioleate instead of DDD and it was found that this activity was increased with the increasing number of double bonds in the structure. Furthermore, the same type of experiment was carried out using a lipid-soluble radical initiator, 2,2'-azobisisobutyronitrile and the similar result was obtained. These results indicated that a highly polyunsaturated fatty acid might act as an antioxidant in an emulsion system oxidized by an azo compound.

Protection by Exogenously Added Coenzyme Q9 against Free Radical-Induced Injuries in Human Liver Cells

Reduced coenzyme Q10 (CoQ10H2) is known as a potent antioxidant in biological systems. However, it is not yet known whether CoQ9H2 could act as an antioxidant in human cells. The aim of this study is to assess whether exogenously added CoQ9 can protect human liver cells against injuries induced by a water-soluble radical initiator, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and a lipid-soluble radical initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). CoQ9-enriched cells were obtained by treatment of HepG2 cells with 10 µM CoQ9 liposomes for 24 h. CoQ9-enriched cells were exposed to 10 mM AAPH and 500 µM AMVN over 4 h and 24 h, respectively. The loss of viability after treatment with AAPH or AMVN was much less in CoQ9-enriched cells than in naive HepG2 cells. The decrease in glutathione and the increase in thiobarbituric acid-reactive substance after treatment with AAPH or AMVN were also suppressed in CoQ9-enriched cells. The incubation of CoQ9-enriched cells with AAPH or AMVN led to a decrease in cellular CoQ9H2 and reciprocal increase in cellular CoQ9 resulting from its antioxidant function. Taken together, it was demonstrated for the first time that exogenously added CoQ9 could prevent oxidative stress-mediated damage to human cells by virtue of its antioxidant activity.

Novel Polymer Monolithic Column for Hydrophilic Compounds

A hydrophilic polymer-based monolithic column was prepared from water-soluble crosslinking agents for liquid chromatography. The column media were prepared with a diacrylate monomer, aqueous polyethylene glycol, methanol, and a water-soluble radical initiator. A fused silica capillary column, which was significantly modified by vinyl groups, was utilized as the outer column in order to control polymer shrinkage. We optimized the modification of the capillary column, composition of the monomer and porogen, and polymerization condition. The optimized column exhibited high hydrophilicity and achieved the baseline separation of nucleobases by using only a buffered solution as the mobile phase. Additionally, another column prepared from binary water-soluble crosslinking agents exhibited lower nonspecific adsorption of several proteins. Basically, we would show the possibility of a new type of polymer monolith prepared from water-soluble crosslinker and water-soluble porogenic solvent, and they can be used for chromatographic separation without non-specific hydrophobic interaction.

Effects of olive oil polyphenols on erythrocyte oxidative damage

Many studies have investigated the protective effects of oleuropein and hydroxytyrosol against cell injury, but few have investigated the protective effects of oleuropein aglycones 3,4-dihydroxyphenylethanol-elenolic acid (3,4-DHPEA-EA) and 3,4-dihydroxyphenylethanol-elenolic acid dialdehyde (3,4-DHPEA-EDA). The present work studied and compared the capacity of these four compounds, found at high concentrations in olive oil, to protect red blood cells (RBCs) from oxidative injury. The in vitro oxidative stress of RBCs was induced by the water-soluble radical initiator 2,2'-azo-bis(2-amidinopropane) dihydrochloride. RBC changes were evaluated either by optical microscopy or by the amount of hemolysis. All compounds were shown to significantly protect RBCs from oxidative damage in a dose-dependent manner. The order of activity at 20 microM was: 3,4-DHPEA-EDA > hydroxytyrosol > oleuropein > 3,4-DHPEA-EA. Even at 3 microM, 3,4-DHPEA-EDA and hydroxytyrosol still had an important protective activity. However, deleterious morphological RBC changes were much more evident in the presence of hydroxytyrosol than with 3,4-DHPEA-EDA. For the first time it was demonstrated that 3,4-DHPEA-EDA, one of most important olive oil polyphenols, may play a noteworthy protective role against ROS-induced oxidative injury in human cells since lower doses of this compound were needed to protect RBCs in vitro from oxidative mediated hemolysis.

Acceleration of Lipid Peroxidation in .ALPHA.-Tocopherol Transfer Protein-Knockout Mice Following the Consumption of Drinking Water Containing a Radical Initiator

To assess the antioxidative role of vitamin E (VE) in a mouse model of severe VE deficiency by using biomarkers, alpha-tocopherol transfer protein (alpha-TTP(-/-))-knockout mice were maintained on a VE-deficient diet for 28 weeks [KO group, n = 6]. Wild-type C57BL/6 mice were maintained on a diet containing 0.002% alpha-tocopherol [WT group, n = 6]. The animals were housed individually in a metabolic cage from the age of 9 weeks (Week 0) to 27 weeks. Urine was collected every week, and the levels of total hydroxyoctadecadienoic acid (tHODE), 7-hydroxycholesterol (t7-OHCh), and 8-iso-prostaglandin F(2alpha)(t8-isoPGF(2alpha)), which are biomarkers for lipid peroxidation, were measured by gas chromatography (GC)-mass spectrometry. From the age of 21 weeks (Week 12), three mice in each group were provided drinking water containing the water-soluble radical initiator 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIPH) until the end of the study (Week 19). Blood and tissue samples were collected, and the levels of the abovementioned biomarkers therein were assessed. AIPH consumption clearly elevated the plasma and erythrocyte levels of tHODE and t8-isoPGF(2alpha) in both the WT and KO groups except for the erythrocyte level of tHODE in the WT group. Furthermore, this elevation was more prominent in the KO group than in the WT group. Interestingly, AIPH consumption reduced the stereoisomer ratio of HODE (ZE/EE), which is reflective of the efficacy of a compound as an antioxidant in vivo; this suggests that free radical-mediated oxidation reduces the antioxidant capacity in vivo. The urine levels of tHODE, t7-OHCh, and t8-isoPGF(2alpha) tended to increase with AIPH consumption, but these individual levels fluctuated. It was clearly demonstrated by the proposed biomarkers that maintaining alpha-TTP(-/-) mice on a VE-deficient diet results in a severe VE deficiency and promotes lipid peroxidation.

A Generic Single‐Step Synthesis of Monodisperse Core/Shell Colloids Based on Spontaneous Pickering Emulsification

Monodisperse core–shell colloids are widely applied in various fields such as biomedicine, catalysis, and optics, and are also important for fundamental studies in colloid and interface science. The synthesis of particles with a well-defined core–shell morphology still comprises several separate steps such as core preparation, its subsequent functionalization with a coupling agent and the deposition of one or several shells. This multi-step approach towards composite colloids has some serious drawbacks. First, both coupling chemistry and synthetic pathways need to be specifically designed for the materials involved. Second, multi-step reactions often require intermediate purifications or separations that not only reduce the net yield but also hamper the up-scaling of composite-colloid synthesis for applications such as those referred to above. In this communication we report a novel single-step synthesis of monodisperse latex-based core–shell colloids that completely relies on self-assembly of the components involved (Fig. 1). Recently we discovered that nano-particles may induce spontaneous emulsification of oil in water to thermodynamically stable, monodisperse Pickering emulsions. This novel emulsification phenomenon, first observed for magnetite (Fe3O4) nano-particles, turns out to be quite generic since also cobalt ferrite (CoFe2O4) and commercial silica particles (Ludox) lead to stable Pickering emulsions. It was also shown that using the chemically reactive oil (methacryloxypropyltrimethoxysilane, TPM), Pickering emulsions could be polymerized by addition of a radical initiator (potassiumpersulphate, KPS) resulting in stable colloidal dispersions (Fig. 2a and b). Here we investigate the use of such particle-stabilized emulsions (hereafter TPM-emulsions) in a seeded growth polymethylmethacrylate (PMMA) polymerization, to obtain in one single and simple step, PMMA colloids with various inorganic cores. Initially we focused on TPM-emulsions merely as a source for monodisperse inorganic cores to seed a surfactant-free PMMA polymerization. However, exploring what would happen when TPM-emulsions are prepared directly in the presence of methylmethacrylate (MM) we noticed that, surprisingly, MM does not interfere at all with the TPM emulsification. In fact, during the latter emulsification, MM remains present as a separate oil phase (Fig. 2c insert). Addition of a water-soluble radical initiator, however, not only induces polymerization of the TPM-emulsion droplets to solid spheres, but simultaneously also triggers the polymerization of PMMA shells onto these spheres. Thus the floating MM phase (Fig. 2) acts as a monomer source for this PMMA shell formation and, indeed, the shell thickness continues to grow until the whole MM phase is consumed. It turns out that, in addition, polymerized TPM-emulsions are also excellent seeds dispersions for growing polystyrene shells via surfactant free emulsion polymerization, as well as silica shells via the classical Stober synthesis, showing that the spontaneous Pickering emulsification allows for the preparation of polymeric as well as inorganic composite model colloids. C O M M U N IC A TI O N

Radical graft functional modification of cellulose with allyl monomers: Chemistry and structure characterization

Cotton cellulose was successfully functionalized via a free radical graft polymerization process. Potassium persulfate served as an effective water soluble radical initiator to generate cellulosic radicals. The polymeric radicals could react with allyl monomers such as allyl-dimethylhydantion (ADMH) to form surface grafted cellulose. The reaction sites generated by potassium persulfate were probably at carbon 3 and 4 in glucose ring via oxidative hydrogen abstraction. The cellulosic radicals can initiate grafting polymerization of ADMH with a maximum polymerization degree of about 12 based on LC–MS results. The radical graft polymerization mechanisms were proposed based on LC–ESI/MS analysis. The ideal covalent bonding between cellulose and poly (allyl-dimethylhydantion) (PADMH) ensured permanent graft of the monomers on cotton and durability of the expected functions on the treated cotton.

Puerarin and Conjugate Bases as Radical Scavengers and Antioxidants: Molecular Mechanism and Synergism with β-Carotene

The 4'-hydroxyl group of puerarin, a C-glycoside of the isoflavonoid daidzein, was shown, using 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radical cation and stopped-flow spectroscopy and by comparison with the 7-propylpuerarin (A ring derivative) and 4'-propylpuerarin (B ring derivative), to be a more efficient radical scavenger as compared to the 7-hydroxyl group by a factor of 2, a difference increasing upon deprotonation. The difference in radical scavenging agreed with the oxidation potentials (cyclic voltammetry in acetonitrile, 0.1 M Bu4NBF4 at 25 degrees C): E/mV=862+/-3 for puerarin, 905+/-10 for 7-propylpuerarin, and 1064+/-2 for 4'-propylpuerarin relative to ferrocene/ferricenium. In aqueous solution, the reduction potential was shown to decrease for increasing pH, and deprotonation of the 4'-hydroxyl group increased radical scavenging more than deprotonation of the 7-hydroxyl group. The 7-hydroxyl was found to be more acidic (pKa1=7.20+/-0.01 in puerarin and pKa=7.23+/-0.01 in 4'-propylpuerarin) than the 4'-hydroxyl group (pKa2=9.84+/-0.08 in puerarin and pKa=9.51+/-0.02 in 7-propylpuerarin); aqueous solution, ionic strength of 0.1, and 25 degrees C. In phosphatidyl choline liposome of pH 7.4, puerarin and beta-carotene each showed a modest antioxidant activity measured as prolongation of the lag phase for formation of conjugate dienes and using the water-soluble radical initiator APPH with effects of puerarin and beta-carotene being additive. For the lipophilic initiator AMVN, the antioxidative effect decreased for puerarin and increased for beta-carotene as compared to APPH and showed a clear synergism. A regeneration of beta-carotene, effective in the liposome lipid phase as antioxidant, from the cation radical by deprotonated forms of puerarin was demonstrated in 9:1 chloroform/methanol using laser flash photolysis with k2=2.7x10(4) L mol-1 s-1 for the bimolecular process between the cation radical and the puerarin dianion.

Highly Stable Polymerizable Vesicles in Anionic Surfactant/Ammonium Salt Mixtures in the Presence of Cross-linking Monomers for Convenient Preparation of Hollow Nanospheres

Spontaneous and stable vesicles are formed from vinylbenzyltrimethylammonium chloride (VBTAC) and sodium dodecyl sulfate (SDS) ranging in molar composition from 3:7 to 7:3 in the presence of 30 mol % divinylbenzene (DVB). Dynamic light scattering analysis and transmission electron microscope observations revealed that microparticles with diameters around 120 nm (30%) and 580 nm (70%) were formed. Trapping efficiency of the vesicles examined with D-(+)-glucose amounted to ca. 15%. These vesicles were capable of undergoing polymerization in the presence of water-soluble radical initiators such as 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride to fix the vesicular structure. Retention of the vesicle size and bimodal size distribution characteristics during the polymerization indicated that intravesicular polymerization prevailed over the intervesicular process. SDS was stably retained in the cross-linked vesicle and was not removed from the vesicle by exhaustive dialysis or ultrafiltration, due to the electrostatic interaction within the cross-linked polymeric framework produced from VBTAC and DVB. The resulting hollow nanospheres are readily redispersed in water without the aid of additional surfactants.