Water-soluble Initiator Research Articles

Inverse Emulsion Polymerization of Acrylamide Initiated by Oil- and Water-soluble Initiators: Effect of Emulsifier Concentration

The nature of the reaction loci in inverse emulsion polymerization of acrylamide (AAm) initiated by oil (2,2′-azoisobutyronitrile, AIBN)- and water-soluble (ammonium peroxodisulfate, APS) initiators was investigated. The rate of polymerization (Rp,max, Interval 2) increases with increasing the emulsifier concentration up to a certain critical concentration and then decreases. The rate of polymerization and the polymerization rate per particle are somewhat larger in the APS-initiated polymerization than in the AIBN-initiated one. For both initiators the polymerization rate per particle is proportional to the particle size and decreases with increasing the emulsifier concentration and the decrease is much more pronounced at the high emulsifier concentrations. The similar kinetic dependences for both initiators were discussed in terms of the formation of monomeric or oligomeric radicals with the similar nature, mobility via the reaction system and partitioning between the oil and water phases. The similar radicals carrying the initiator fragment were formed by the addition of one or two (or several) units to the primary radicals (SO4•− or 2-cyanoisopropyl). The estimated average number of radicals per particle (n̅) is much below 0.5. The low radical concentration in the polymer particles was discussed in terms of the desorption of monomeric and emulsifier radicals. The desorption of radicals was confirmed by both the Nomura model (Nmodel, k′des,N) and the Ugelstad approach (the solution of population balance for the particle with n̅, Tmodel, k′des,T). The k′des,T’s were found to be much larger than the k′des,N’s. The differences in the k′des’s were discussed in terms of the desorption (surface active) monomeric radicals (the polymerization within the outer spheres of polymer particles) and emulsifier (the chain transfer to emulsifier) radicals. The radical entry rate decreases with increasing the emulsifier concentration or decreasing the particle size.

Pineal graft in old rats improves erythrocyte resistance to peroxyl radical-induced hemolysis

Pineal graft from young to old rats was performed and red blood cell hemolysis, induced by the water-soluble radical initiator 2,2'-azobis (2-amidino-propane) dihydrochloride (AAPH), was evaluated 6 months after graft. Pineal graft modified the hemolysis curve kinetic profile in grafted rats versus age-matched controls, the 50% hemolysis time as well as the lag time were longer, whereas the maximal amount of hemolysis was lower, and it occurred over a longer period of time. Thiobarbituric acid reactive substances production was lower in pineal-grafted rats than in controls and the age-related decrease of erythrocyte membrane fluidity was prevented by pineal graft. The present findings support an important physiological role of pineal gland in preventing age-related alterations of erythrocyte membranes and suggest a possible antioxidant action of melatonin.

Preparation of fluoroacrylate nanocopolymer by miniemulsion polymerization used in textile finishing

AbstractLatex based on fluoroacrylate (TAN) and other comonomers was prepared via miniemulsion polymerization in the presence of stearyl trimethyl ammonium chloride (STAC) and 2, 2′‐azobis (2‐amidinopropane) dihydrochloride (ABAP) as a water soluble initiator. Light transmittance studies demonstrated that the light transmittance of prepared emulsions increases with the amount of TAN, STAC, cosolvent DPM, and hydrophobe DM. Given suitable reaction temperature and quantities of TAN, STAC, DPM, and DM, a copolymer emulsion of fluoroacylate with a particle size of 50 nm was produced. The water repellency tested on polyester fabrics displayed greater effectiveness than that of commercial products with higher fluorine content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1466–1472, 2004

Synthesis of saccharidic polymer colloids via free radical mini‐emulsion polymerization

AbstractPolymer colloids based on 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D‐glucofuranose (3‐MDG) and butyl acrylate (BA) were prepared via free radical mini‐emulsion polymerization. The kinetic and colloidal features of the copolymerization were investigated. The final particle size (D) of the sugar latexes is inversely proportional to the concentration of the anionic emulsifier (sodium dodecyl sulphate, SDS) and the non‐ionic one (alkyl polyglucoside, APG). It was also found that D is independent of the concentration of either the water‐soluble initiator (potassium persulfate, KPS), or the oil‐soluble initiator (2,2′‐azobisisobutyronitrile, AIBN). The rate of mini‐emulsion polymerization is lower in comparison with the conventional emulsion polymerization under the same conditions. The polymerization rate (Rp) and the total number of particles (Np) are proportional to the 0.72th and 0.93th power of the SDS, and to the 1.40th and 2.22th of the APG concentration. Following reaction orders, 0.79/0.06 were obtained for Rp/Np versus the concentration of KPS, and 0.22/−0.01 for AIBN, respectively. Copyright © 2004 John Wiley & Sons, Ltd.

Redifferentiation of human hepatoma cells induced by green tea polyphenols

A novel approach for the treatment of cancer is the differentiation therapy in which cancer cells are induced to attain a mature phenotype when exposed to differentiation inducers. To examine the effects of polyphenols extracted from green tea, i.e. ( – )-epicatechin (EC), ( – )-epigallocatechin (EGC), ( – )-epicatechin gallate (ECG) and ( – )-epigallocatechin gallate (EGCG), on the proliferation and redifferentiation of human hepatoma cell line SMMC-7721, we measured the changes of cell growth, cell surface charge and cell morphography after treament with green tea polyphenols. It was found that the growth curve of treated cells was decreased remarkably, cell surface charge of treated cells was decreased and the microvilli on the surface of treated cells were reduced obviously. It confirmed that green tea polyphenols could reverse malignant phenotypic characteristics and induced redifferentiation of SMMC-7721 cells. The ability of green tea polyphenols to inhibit reactive oxygen species (ROS)-mediated oxidative damage of DNA was also assessedin vitro by measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular and linear forms. It was found that green tea polyphenols could significantly inhibit the oxidative damage of DNA induced by a water-soluble azo initiator 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH). However, they could promote the oxidative damage of DNA induced by H2O2 and Fe2+ at high concentrations. The relationship between the anti-cancer activity and antioxidation-prooxidation activity of green tea polyphenols is discussed.

Interfacial Energy Promotes Radical Heterophase Polymerization

Experimental evidence is presented that during the conditions of aqueous heterophase polymerization radical generation and subsequent polymerization are induced by the interfacial energy. A comprehensive study of the emulsion polymerization of styrene at 25 °C with various types of emulsifiers and with different nonredox initiators such as potassium peroxodisulfate, 2,2‘-azoisobutyronitrile, dibenzoyl peroxide, and poly(ethylene glycol)-azo-initiator reveals that the particular initiator−stabilizer combination has a strong influence on the achievable final conversion and the latex properties. The deceleration of the polymerization due to the low temperature allowed the recognition of basic differences in the behavior of monomer- and water-soluble initiators, especially at low conversions during the prenucleation period.

PHEMA hydrogels obtained by a novel low-heat curing procedure with a potential for in situ preparation.

In this work, we report on poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels obtained by a low heat curing reaction. These materials are suitable for in situ preparation and therefore endowed with a potential for several biomedical applications. The novel procedure adopted involves as the first step the synthesis of a soluble oligomeric PHEMA precursor containing polymerizable functions as side substituents. As the second step, the precursor is dissolved in equal amounts of 2-hydroxyethyl methacrylate (HEMA) and water, to form a viscous but still injectable syrup. A low temperature water soluble initiator is then added. The curing reaction starts promptly and is completed within few minutes. During the entire process the internal temperature never rises above 40 degrees C. Preliminary mechanical characterizations performed on the hydrogels in their water-swollen state and diffusion tests in absorption/desorption experiments clearly indicated that on all respects the novel hydrogels are comparable with conventional PHEMA hydrogels obtained according to literature from HEMA in the presence of divinyl crosslinkers. However, the much shorter curing time combined with the far lower curing temperature endow the new hydrogels with a higher potential in view of specific surgical requirements, and particularly for in situ preparation.

Synergistic inhibition of lipid peroxidation by vitamin E and a dopamine agonist, cabergoline

We examined antioxidant activity of cabergoline, a dopamine agonist, during the aerobic oxidation of phosphatidylcholine liposomes at 37°C. Cabergoline retarded the oxidation initiated with a lipid-soluble initiator significantly better than that with a water-soluble initiator, suggesting that cabergoline locates in the lipid layer of liposomal membranes. Cabergoline inhibited the oxidation of liposomal membranes synergistically with endogenous antioxidants such as ascorbic acid, ubiquinol-10 and vitamin E, and vitamin E was the most efficient synergist. These results suggest that cabergoline may have a neuroprotective effect on the substantia nigra of Parkinsonian patients because of its synergistic antioxidant activity with vitamin E as well as its action on dopamine receptor.

Strictinin as an efficient antioxidant in lipid peroxidation

The antioxidant effect of strictinin (SOH), which was extracted from green tea leaves, against the peroxidation of linoleic acid in sodium dodecyl sulfate (SDS) and cetyl trimethylammonium (CTAB) micelles, against the peroxidation of low-density lipoprotein (LDL) and against oxidative hemolysis of human red blood cells (RBCs), has been studied. The peroxidation of linoleic acid and LDL, and oxidative hemolysis of RBCs were initiated thermally by a water-soluble azo initiator 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH), and the reaction kinetics in micelles and LDL were monitored by uptake of oxygen. The synergistic antioxidant effect of SOH with α-tocopherol (Vitamin E) was also studied by following the decay kinetics of α-tocopherol. Kinetic analysis of the antioxidation process demonstrates that SOH, used either alone or in combination with α-tocopherol, is an effective antioxidant against lipid peroxidation, but its effects significantly depend on the reaction medium.

Grafting of PVA in Miniemulsion Copolymerizations of n-Butyl Acrylate and Methyl Methacrylate Using Water-Soluble, Partially Water-Soluble, and Oil-Soluble Initiators

Miniemulsion copolymerizations of methyl methacrylate and n-butyl acrylate initiated with water-soluble (hydrogen peroxide, HPO), partially water-soluble (tert-butyl peroxide, TBHP), and oil-soluble (tert-butyl peroctoate, TBPO) initiators were carried out to study the grafting of poly(vinyl alcohol) (PVA) at the oil/water interface. The amounts of grafted PVA produced in miniemulsion polymerizations initiated with TBHP and TBPO were substantially less than those produced in the corresponding seeded emulsion polymerizations. Differences in the internal viscosities at the respective interfaces were proposed to explain these results. The amount of grafted PVA was determined as a function of the monomer to polymer (M/P) ratio in seeded emulsion polymerizations initiated with TBHP and was found to decrease with increasing M/P ratio. The grafting was followed as a function of conversion in miniemulsion polymerizations initiated with TBPO and where a continuous addition of SFS (sodium formaldehyde sulfoxylate) solution was utilized; the grafting was found to occur mainly in the later stages of the polymerization. Both results strongly support the idea that the different internal viscosities at the interface might affect the termination reactions between primary radicals and PVA macroradicals, thereby resulting in different amounts of grafting. The degree of hydrolysis (DH) of the serum PVA after the miniemulsion polymerizations was determined using FTIR and saponification. On the basis of the results, it was found that aqueous phase and interface grafting occurred in the HPO system; however, interface grafting dominated the TBHP system. In addition, the grafted PVA in the TBHP system was still water-soluble, implying that the grafted chains were short, owing to rapid termination reactions at the interface presumably.

Control Crystallization of Calcium Carbonate in Aqueous Solution with In-Situ Radical Polymerization of Sodium Acrylate as a Latent Inductor for Crystal Nucleation and Growth

Abstract Crystallization of CaCO3 with in-situ radical polymerization of sodium acrylate in aqueous solution was carried out by a double jet method to prevent heterogeneous nucleation at glass walls. The concentration of sodium acrylate was 1.71 mM and the feed ratio of sodium acrylate to calcium ions was 0.62. After addition of the calcium reactants into the aqueous solution of sodium acrylate was completed, an aqueous solution of potassium peroxodisulfate as a water-soluble radical initiator was added to the reaction mixture after incubation at 30 °C for several minutes (1, 3, or 20 min). Three different crystal polymorphs of CaCO3 (aragonite, vaterite, and calcite) were selectively induced by changing the time for adding the radical initiator to a calcium carbonate solution with sodium acrylate. Formation of crystalline CaCO3 in the presence of sodium acrylate with the radical initiator at different feed ratio of sodium acrylate to calcium ions was also studied. The higher concentration of sodium acrylate increased sizes of vaterite spherical particles. The present results indicate that the final crystalline phases are highly sensitive to the presence of the active additives at the very initial nucleation stage (within several minutes).

Inhibition of human low density lipoprotein oxidation by flavonols and their glycosides

Antioxidative effects of the flavonols and their glycosides, i.e., quercetin (Q), quercetin galactopyranoside (QG), quercetin rhamnolpyranoside (QR), rutin (R), morin (MO), myrecetin (MY), kaempferol (K) and kaempferol glucoside (KG), against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either by a water-soluble initiator 2,2′-azobis(2-amidino propane hydrochloride) (AAPH), or by cupric ion (Cu 2+). The reaction kinetics were monitored either by the uptake of oxygen and the depletion of α-tocopherol (TOH) presented in the native LDL, or by the formation of thiobarbituric acid reactive substances (TBARS). Kinetic analysis of the antioxidation process demonstrates that these flavonols and their glycosides are effective antioxidants against AAPH- and Cu 2+-initiated LDL peroxidation, 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.

ATRP in Waterborne Miniemulsion via a Simultaneous Reverse and Normal Initiation Process

Atom transfer radical polymerization with simultaneous reverse and normal initiation process was conducted in a miniemulsion system with the use of highly active transition-metal complexes formed by hydrophobic ligands at concentrations 5−8 times lower than in a typical reverse ATRP process. The molecular weights were essentially determined by the concentration of alkyl halide (used in ∼5-fold excess to a standard radical initiator) and much less affected by the concentration of a standard radical initiator (e.g., AIBN) and/or CuII complex. Controlled polymerizations of methacrylate, acrylate, and styrene were demonstrated by a linear correlation between molecular weights and monomer conversions and relatively low polydispersities (Mw/Mn < 1.3). The resulting latexes showed good colloidal stability with an average particle sized around 250−300 nm. Oil-soluble initiator (e.g., AIBN) provided better control over polymerization than water-soluble initiator (e.g., VA-044). Well-defined waterborne 3-arm star p...

A novel antioxidant action of ethanolamine plasmalogens in lowering the oxidizability of membranes.

We have demonstrated a novel antioxidant action of ethanolamine plasmalogens both in protecting cholesterol from oxidation by free radicals and in lowering the oxidizability of membranes, along with the action of scavenging radicals, by the oxygen-uptake method using large unilamellar vesicles and the water-soluble azo-radical initiator, AAPH [2,2'-azobis-(2-amidino-propane) dihydrochloride].

Antioxidative polyphenols from berries of Pimenta dioica

The ethyl acetate-soluble part of allspice, berries of Pimenta dicica, showed strong antioxidant activity and radical-scavenging activity against 1,1diphenyl-2-picrylhydrazl (DPPH) radical. From the ethyl acetate-soluble part, two new compounds, 5-galloyloxy-3-4-dihydroxypentanoic acid and 5-(5-carboxmethyl-2-oxocyclopenty)3Z-penteny 6-O-galloy-beta-D-glucoside were isolated together with 11 known polyphenols by repeated column chromatography. Their structures were elucidated on the basis of MS and various NMR spectroscopic data. All isolated compounds were evaluated for antioxidative effects on oxidation of methyl linoleate under aeration and heating, anf on peroxidation of liposome induced by 2-2'-azobis-(2-amidinopropane)dihydrocloride (AAPH) as water-soluble initiator along with their radical-scavenging activity against DPPH. Quercetin and its glycoside showed remarkable activity for scavenging DPPH radical and inhibiting peroxidation of liposome. Two new compounds also exhibited strong DPPH radical-scavenging activity and inhibitory effect on the peroxidation od liposome as myricetin.

Antioxidant Activity and Incorporation in Soybean Phosphatidylcholine Membranes of Catechins Protecting .ALPHA.-Tocopherol against Lipid Peroxidation

The aim of the present paper is to correlate the relative antioxidant activity of catechins and their incorporation in soybean phosphatidylcholine (sPC) membranes. For the purpose the inhibition effect of the catechins (+)-catechin (C), (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC), and (-)-epigallocatechin gallate (EGCG) on α-Tocopherol (α-Toc) consumption was compared when the lipid oxidation was initiated in the aqueous medium by the water-soluble radical initiator 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) or in the lipid phase by the lipophilic 2,2′-azobis(4-methoxy-2, 4-dimethylvaleronitrile) (Meo-AMVN). The catechins C, EC, EGC, ECG and EGCG at a concentration of 15 μM were added exogenously to the water medium of multilamellar (MLV) liposomal suspensions or were incorporated in the lipid phase of MLV or unilamellar (ULV) liposomes, containing incorporated α-Tocopherol (α-Toc) at the same concentration. The α-Toc and catechin consumption were followed by high-performance liquid chromatography (HPLC) technique. The inhibition the accumulation of lipid hydroperoxides (LOOH) by catechins in ULV oxidized by AAPH also was studied. The antioxidant activity of catechins, expressed by the constant of inhibition kinh, and the parameters n and kclinh were determined. The galloylated catechins ECG and EGCG, inhibiting α-Toc consumption in greater extent in MeO-AMVN - than in AAPH-oxidation, were better incorporated in lipid membranes, and also had higher peroxyl radicals scavenging activity than the non-galloylated C, EC, and EGC. ECG being the most effective catechin protecting α-Toc against lipophilic radicals interacted most efficiently with PC layers as well as ECG was the strongest radical scavenger. In hydrophilic radicals-initiated oxidation EGCG incorporated in MLV layers protected α-Toc better than ECG, and was consumed faster than ECG when incorporated in ULV liposomes. EGCG was situated closer to the lipid/water interface than ECG. The EGCG derived radical was more prone to participate in side propagation reactions. The cis-form EC had higher affinity for lipid membranes than the trans-form C, as EC had greater effect sparing α-Toc consumption in MeO-AMVN oxidation than C. EGC, the least effective among the studied catechins to preserve α-Toc from oxidation, was worst incorporated in lipid layers, and its radical was unstable leading to side propagations. In conclusion, the catechins interacted with PC membranes, and preserved α-Toc from oxidation by cooperating with it to scavenge peroxyl radicals or by regenerating it from its radical.

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.

Endomorphins, endogenous opioid peptides, provide antioxidant defense in the brain against free radical-induced damage

Oxidative stress has been considered to be a major cause of cellular injuries in a variety of chronic health problems, such as carcinogenesis and neurodegenerative disorders. The brain appears to be more susceptible to oxidative damage than other organs. Therefore, the existence of antioxidants may be essential in brain protective systems. The antioxidative and free radical scavenging effects of endomorphin 1 (EM1) and endomorphin 2 (EM2), endogenous opioid peptides in the brain, have been investigated in vitro. The oxidative damage was initiated by a water-soluble initiator 2,2′-azobis(2-amidinopropane hydrocholoride) (AAPH) and hydrogen peroxide (H2O2). The linoleic acid peroxidation, DNA and protein damage were monitored by formation of hydroperoxides, by plasmid pBR 322 DNA nicking assay and single-cell alkaline electrophoresis, and by SDS-polyacrylamide gel electrophoresis. Endomorphins can inhibit lipid peroxidation, DNA strand breakage, and protein fragmentation induced by free radical. Endomorphins also reacted with galvinoxyl radicals in homogeneous solution, and the pseudo-first-order rate constants were determined spectrophotometrically by following the disappearance of galvinoxyl radicals. In all assay systems, EM1 was more potent than EM2 and GSH, a major intracellular water-soluble antioxidant. We propose that endomorphins are one of the protective systems against free radical-induced damage in the brain.

Phenolic constituents and antioxidant properties of Xanthosoma violaceum leaves.

An extract of Xanthosoma violaceum leaves was subjected to a polyphenol profile determination, including total polyphenols, and antioxidant activity evaluation. Analysis of the extract resulted in the isolation of a new flavone C-glycoside, apigenin 6-C-beta-D-glucopyranosyl-8-C-beta-D-apiofuranoside (1), as well as known flavone C-glycosides, including vitexin (2), isovitexin (3), isovitexin 4'-O-rhamnopyranoside (4), apigenin 6-C-[beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside] (5), and apigenin 6,8-diC-beta-D-glucopyranoside (6). The antioxidant activity of the extract was assessed by means of two different in vitro tests: bleaching of the stable 1,1-diphenyl-2-picrylhydrazyl radical (DPPH test) and peroxidation induced by the water-soluble radical initiator 2,2'-azobis(2-amidinopropane) hydrochloride, on mixed dipalmitoylphosphatidylcholine/linoleic acid unilamellar vesicles (LP-LUV test). In both tests used, the extract and a fraction II showed a significant antioxidant/free-radical scavenging effect (fraction II, EC(50) = 11.6 microg/mL) in comparison to alpha-tocopherol (EC(50) = 10.1 microg/mL).

Biostability and biocompatibility of a surface-grafted phospholipid monolayer on a solid substrate

We have previously demonstrated phosphorylcholine monolayer chemically grafted onto a methacryloyl-terminated solid substrate by in situ polymerization. The in situ polymerization was carried out at the interface between a pre-assembled acrylated phospholipid monolayer produced by vesicle fusion and a methacryloyl-terminated substrate using a water-soluble initiator, 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AAPD). Herein, we examined the biostability and biocompatibility of a surface-grafted phospholipid monolayer (poly-PC) on a methacryloyl-terminated substrate using a “wash off’ test, in vitro protein adsorption and in vivo cage implantation for time intervals of 4, 7, 14 and 21 days, respectively. In order to compare the biostability and biocompatibility of phospholipid surfaces on solid substrates, we used two types of phospholipid surfaces: a physically adsorbed phospholipid monolayer (PC) and a poly-PC. Atomic force microscopy and water contact angle measurements indicated that the poly-PC surface was more stable in PBS, Triton X-100 and to EO gas sterilization than the PC surface. The adsorption of proteins such as albumin, fibrinogen, IgG and human plasma proteins on the poly-PC surfaces were significantly reduced, in vitro. Moreover, the poly-PC surface greatly reduced macrophage adhesion and the formation of foreign body giant cells, in vivo.