Water-soluble Azo Initiator Research Articles

Antioxidative and free radical scavenging effects of ecdysteroids from Serratula strangulata.

The antioxidative and free radical scavenging effects of four ecdysteroids, 20-hydroxyecdysone (E1), 25-deoxy-11,20-dihydroxyecdysone (E2), 24-(2-hydroxyethyl)-20-hydroxyecdysone (E3), and 20-hydroxyecdysone-20,22-monoacetonide (E4), isolated from the Chinese herb Serratula strangulata have been investigated in vitro. These ecdysteroids could protect human erythrocytes against oxidative hemolysis induced by a water-soluble azo initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH). They could also inhibit the peroxidation of rat liver microsomes induced by hydroxyl radicals, as monitored by the formation of thiobarbituric acid reactive substances (TBARS), and prevent radical-induced decrease of membrane fluidity as determined by fluorescence polarization. They reacted with galvinoxyl radicals in homogeneous solution, and the pseudo-first-order rate constants were determined spectrophotometrically by following the disappearance of galvinoxyl radicals. Compounds E1 and (or) E3 were the most active in both antioxidative and radical-scavenging reactions.

One-electron oxidation of “photo-Fenton” reagents and inhibition of lipid peroxidation

The “photo-Fenton” reagent, 2-mercaptopyridine N-oxide (MPO), which releases a hydroxyl radical on ultraviolet irradiation, has been found to act as an antioxidant. In the peroxidation of linoleate initiated by a water-soluble azo-initiator, MPO has about one-third the activity of the water-soluble vitamin E analogue Trolox C. In contrast, the oxygen-containing analogue, 2-hydroxypyridine N-oxide (HPO), does not have measurable antioxidant activity in this system. Both reagents react with hydroxyl radical with second order rate constants very close to the diffusion-controlled limit. With the less oxidising dithiocyanate radical anion, MPO reacts approximately 50 times more rapidly than HPO at pH>7. The more reducing properties of MPO result in its activity as an antioxidant and make it less suitable than HPO as a source of hydroxyl radicals for investigation of oxidative stress in biological systems.

Antioxidant effects of resveratrol and its analogues against the free-radical-induced peroxidation of linoleic acid in micelles.

The antioxidant effect of resveratrol (3,4',5-trihydroxy-trans-stilbene) and its analogues, that is, 4-hydroxy-trans-stilbene (4-HS), 3,5-dihydroxy-trans-stilbene (3,5-DHS), 4,4'-dihydroxy-trans-stilbene (4,4'-DHS), 3,4-dihydroxy-trans-stilbene (3,4-DHS), 3,4,5-trihydroxy-trans-stilbene (3,4,5-THS) and 3,4,4'-trihydroxy-trans-stilbene (3,4,4'-THS), against the peroxidation of linoleic acid has been studied in sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) micelles. The peroxidation was initiated thermally by a water-soluble azo initiator 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH), and the reaction kinetics were studied by monitoring the formation of linoleic acid hydroperoxides. The synergistic antioxidant effect of these compounds with alpha-tocopherol (vitamin E) was also studied by following the decay kinetics of alpha-tocopherol and the reaction intermediate, the alpha-tocopheroxyl radical. Kinetic analysis of the antioxidant process demonstrates that these compounds are effective antioxidants in micelles used either alone or in combination with alpha-tocopherol. The antioxidative action involves trapping the propagating lipid peroxyl radical and reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol. It was found that the antioxidant activity of resveratrol analogues depends significantly on the position of the hydroxyl groups, the oxidation potential of the molecule and the reaction medium. Molecules with ortho-dihydroxyl and/or para-hydroxyl functionalities possess high activity.

POLYCATIONIC SALTS. 3. SYNTHESIS, STYRENE BASED TRIALKYLAMMONIUM SALTS AND THEIR POLYMERIZATION1-2 1, 2

A number of styrene-based vinylbenzyltrialkylammonium chloride salts were prepared via the Menshutkin reaction of vinylbenzylchloride with selected tert. amines. The vinylbenzyltrinalkylammonium salts were obtained in most cases in nearly quantitative yields. The lower members of the vinyl-benzyltrialkylammonium salts, such as vinylbenzyltrimethyl-ammoniumchloride, vinylbenzyl-triethylammonium chloride are highly water soluble. Vinylbenzyldimethyl(n-octyl or n-dodecyl) ammonium chloride were insoluble in water, but soluble in methanol. These monomers were polymerized and copolymerized in water using water-soluble azo initiators for water soluble monomers or in methanol with 2,2-azobisisobutyronitrile to polyelectrolytes of extremely high molecular weights. Vinylbenzyltri-n-alkylammonium chlorides were also copolymerized and crosslinked with the water soluble crosslinking agent: N,N'di(vinylbenzyl)-N,N,N',N′-tetramethylethylene diammonium dichloride. Monomers and polymers were characterized by 15N NMR spectroscopy. With N,N'-di(vinylbenzyl)-N,N,N',N'-tetramethylethylene-diammonium dichloride, vinylbenzyltri-n-alkylammonium chlorides were polymerized to randomly crosslinked polycations with unusual properties. The polymers were evaluated for their effectiveness a bile acid sequestering agents. 1 Polycationic Salts 1: P. Zarras and O. Vogl, Polymer Preprints, ACS Division of Polymer Chemistry, 34(2), 424 (1993). 2 Polycationic Salts 2: P. Zarras and O. Vogl, Prog. Polym. Sci., 24(3), 485 (1999).

Synthesis and Characterization of New Surface Active Azo Initiators for Radical Reactions

The synthesis of a water soluble azo initiators from 2,2’-azodiisobutyronitrile (AIBN) was performed in three steps: reaction of dinitrile with aromatic alcohols in the presence of HCl to form bisiminoesters hydrochlorides which are hydrolyzed to the esters and final regioselective sulfonation of the aromatic esters. The thermal decomposition of the azo initiators obtained leads to formation of two surface active radicals which can start the chain reaction.

Synergistic antioxidant effect of green tea polyphenols with α-tocopherol on free radical initiated peroxidation of linoleic acid in micelles

The antioxidant effect of the main polyphenolic components extracted from green tea leaves, i.e., (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCG) and gallic acid (GA), against peroxidation of linoleic acid has been studied in sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) micelles. The peroxidation was initiated thermally by a water-soluble azo initiator 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AMPAD) and the reaction kinetics were followed by formation of linoleic acid hydroperoxides and consumption of the antioxidant. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants in micelles used either alone or in combination with α-tocopherol (vitamin E). The antioxidative action may involve trapping the initiating radicals in the bulk water phase, trapping the propagating lipid peroxyl radicals on the surface of the micelle and regenerating α-tocopherol by reducing α-tocopheroxyl radical. The antioxidant activity of these green tea polyphenols depends significantly on the microenvironment of the reaction medium, the oxidation potential and the size of the molecule.

Latex Blends of Fluorinated and Fluorine-Free Acrylates: Emulsion Polymerization and Tapping Mode Atomic Force Microscopy of Film Formation

Latex based upon fluorinated acrylates such as perfluorooctylethyl methacrylate (FMA) and perfluorooctylethyl acrylate (FA) and fluorine-free acrylates such as n-butyl methacrylate (BMA) was prepared by means of emulsion polymerization in the presence of octadecyltrimethylammonium bromide (C18TAB) and 2,2‘-azobis(2-amidinopropane) dihydrochloride (V50) as water-soluble azo initiator. Reaction calorimetric studies revealed that acetone addition, preferably 15−25 wt %, was the key to achieve high monomer conversion and to produce stable latex with average particle sizes varying between 50 and 300 nm. Monomer conversion was increased, and latex particle size was reduced when 2 wt % n-butyl acrylate (BA) was added together with fluorine-containing monomers. The reaction enthalpy of FMA was determined to be 62 kJ/mol with respect to 75 kJ/mol for the more reactive FA. Stable poly(perfluorooctylethyl methacrylate)/poly(n-butyl methacrylate) (PFMA/PBMA) latex blends were formed. According to tapping mode atomic force microscopy, PBMA formed a dense film at 65 °C containing PFMA nanoparticles dispersed in the PBMA matrix. Annealing at 100 °C caused accumulation of PFMA at the surface and formation of a gradient film containing a surface layer with high fluorine content. Such latex blends are of interest in water-, oil-, and soil-repellent coatings.

Antioxidant synergism of tea polyphenols and α-tocopherol against free radical induced peroxidation of linoleic acid in solution

Peroxidation of linoleic acid was initiated by a water soluble azo initiator 2,2′-azo(2-amidinopropane)dihydrochloride (AAPH) in tert-butyl alcohol–water solution and inhibited by α-tocopherol and polyphenols extracted from green tea, i.e. (–)-epicatechin (EC), (–)-epigallocatechin (EGC), (–)-epicatechin gallate (ECG), (–)-epigallocatechin gallate (EGCG) and gallic acid (GA), either alone or in combination. The reaction kinetics were followed by oxygen uptake, formation of linoleic acid hydroperoxides and consumption of the antioxidants. It was found that the tea polyphenols could slow the rate of peroxidation with an activity sequence of EGCG > EGC ≈ ECG > EC ≈ GA, but no definite inhibition period was observed. On the other hand, the tea polyphenols could significantly increase the inhibition period of α-tocopherol and protect the latter from depletion with an activity sequence of EGCG ECG ≈ EGC > GA > EC when they were used in combination. A synergistic antioxidation mechanism involving the recycling of α-tocopherol by the tea polyphenol is proposed.

Decarboxylation of [1-13C]Leucine by Peroxyl Radicals

The decarboxylation of [1-13C]leucine by peroxyl radicals (ROO.) has been studied by using combined gas chromatography/isotope ratio mass spectrometry (GC/IRMS) to follow the production of 13CO2. Peroxyl radicals were obtained by thermal decomposition of a water soluble azo initiator, 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH). The decarboxylation rates measured by GC/IRMS were dependent on [1-13C]leucine and AAPH concentrations. The leucine partial order was found to be constant over a 60 min. period (0.6) but the AAPH partial order was found to be variable during the same period, from 1.0 (t = 0) to 0.50 (t = 60 min.). The identification of the products of reaction between leucine and peroxyl radicals requires the use of combined gas chromatography/mass spectrometry using the selected-ion monitoring mode. Methyl-3 butanoate was identified from comparison of its mass spectrum with that of a standard. © 1997 John Wiley & Sons, Ltd.

Decarboxylation of [1-13C]Leucine by Peroxyl Radicals

The decarboxylation of [1-13C]leucine by peroxyl radicals (ROO.) has been studied by using combined gas chromatography/isotope ratio mass spectrometry (GC/IRMS) to follow the production of 13CO2. Peroxyl radicals were obtained by thermal decomposition of a water soluble azo initiator, 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH). The decarboxylation rates measured by GC/IRMS were dependent on [1-13C]leucine and AAPH concentrations. The leucine partial order was found to be constant over a 60 min. period (0.6) but the AAPH partial order was found to be variable during the same period, from 1.0 (t = 0) to 0.50 (t = 60 min.). The identification of the products of reaction between leucine and peroxyl radicals requires the use of combined gas chromatography/mass spectrometry using the selected-ion monitoring mode. Methyl-3 butanoate was identified from comparison of its mass spectrum with that of a standard. © 1997 John Wiley & Sons, Ltd.

Amphotericin B protects cis-parinaric acid against peroxyl radical-induced oxidation: amphotericin B as an antioxidant.

The antifungal effects of amphotericin B are believed to be due to two possibly interrelated mechanisms: an increase in permeation by binding to sterols in cellular membranes and a prooxidant effect causing oxidative damage in target cells. However, the seven conjugated double bonds in amphotericin B raise the possibility that it could be highly susceptible to autoxidation, causing an antioxidant effect. In the present study, we investigated the prooxidant and antioxidant properties of amphotericin B in a model system in which oxidation of a reporter molecule, cis-parinaric acid, was induced by azo initiators of peroxyl radicals. Since interactions of amphotericin B with sterols are essential for its pharmacological and toxic actions, we also studied the effects of cholesterol on the prooxidant and antioxidant properties of amphotericin B. Amphotericin B caused a noncollisional quenching of a characteristic fluorescence of cholesteryl cis-parinarate integrated in liposomes, suggesting the formation of amphotericin B-cholesteryl cis-parinarate complex. This effect of amphotericin B was ablated by increasing concentrations of cholesterol. We found that amphotericin B inhibited oxidation of cis-parinaric acid complexed with human serum albumin [using a water-soluble azo initiator, 2,2'-azobis(2aminopropane)dihydrochloride] and in liposomes [using a lipid-soluble azo initiator, 2,2'-azobis(2,4-dimethylvaleronitrile)]. The inhibitory effect of amphotericin B on 2,2'-azobis(2,4-dimethylvaleronitrile)-induced peroxidation of cis-parinaric acid in liposomes was also diminished by cholesterol. The antioxidant effect of amphotericin B in this model system suggests that amphotericin B does not exert its pharmacological and toxicological responses through a prooxidant effect to cause damage in target cells.

The pH Dependence of Lipid Peroxidation Using Water-Soluble Azo Initiators

We report here the pH dependence of the rate of lipid peroxidation of methyl linoleate/Triton mixed micelles using a series of water-soluble azo initiators. The cationic initiators 2,2′-azobis(2-amidinopropane) (ABAP) and 2,2′-azobis[2-(2-imidazolin-2-yl)propane] (ABIP) exhibit similar behavior, in which increased pH results in dramatically enhanced rates of peroxidation. Rate data for ABAP and ABIP were fitted to a single proton equilibrium, which yielded apparent kinetic pK a values for the rate of approximately 7 and 6, respectively. The azo initiator 4,4′-azobis(4-cyanopentanoic acid) (ABCPA), which yields a negatively charged radical upon thermolysis at neutral pH, was also studied. In contrast to the effects observed with ABAP and ABIP, peroxidation rates with ABCPA exhibit an inverse pH dependence, in which the rates of peroxidation increase with decreasing pH, with an apparent pK a of approximately 5. By comparison, methyl linoleate oxidation rates with 2,2′-azobis(2-cyanopropane) (ABCP) display minimal changes over the pH range 5 to 7.5. Two alternatives can be advanced to account for this behavior, including either a buffer effect which is specific to the cationic initiators or an altered amidinium pK a (∼ 6 to 7) in either the initial carbon-centered radical or the subsequent peroxyl radical generated upon thermolysis of ABAP or ABIP. In the latter case, the kinetic pH dependence could thus reflect an enhanced competence of neutral radicals over charged radicals to partition into the micelles and initiate peroxidation.

Synergistic Interactions between Vitamin A and Vitamin E against Lipid Peroxidation in Phosphatidylcholine Liposomes

Interactions between α-tocopherol and all-transretinol in suppressing lipid peroxidation were studied in a unilamellar liposomal system of phosphatidylcholine from either egg or soybean, in which peroxidation was initiated by the water-soluble azo initiator 2,2′-azobis(2-amidino-propane)hydrochloride and peroxidation was measured as production of conjugated diene hydroperoxides. While all-transretinol alone was poorly effective, the combination of all-transretinol with α-tocopherol caused an inhibition period far beyond the sum of the inhibition periods observed with individual antioxidants, providing evidence of synergistic interactions. Furthermore, the inhibition rate calculated in the presence of both all-transretinol and α-tocopherol,Rinh(E+A), was lower thanRinh(E)observed with α-tocopherol alone, suggesting that the extension of the inhibition time cannot be ascribed only to the antioxidant activity of α-tocopherol. The extent of synergism was linear with a molar ratio all-transretinol/α-tocopherol ranging from 0.1 to 1.0, whereas a drop was observed at a ratio of 2.0. Synergistic antioxidant interactions between all-transretinol and α-tocopherol were also evident when peroxidation was evaluated as production of malondialdehyde. A time course study, in which peroxidation of liposomes and depletion of antioxidants were concomitantly monitored, while showing that most of α-tocopherol was consumed to bring about the inhibition period, indicated that autooxidative reactions substantially contributed to the rapid depletion of all-transretinol, when the antioxidants were allowed to act separately. On the other hand, when α-tocopherol and all-transretinol were combined, the consumption of both antioxidants was significantly delayed, indicating reciprocal protection. Regeneration mechanisms cannot be accounted for by our results. The observed synergism between all-transretinol and α-tocopherol does not appear as the result of specific structural interactions in the lipid bilayer. Combination of all-transretinol with butylated hydroxytoluene, which reduced markedly all-transretinol oxidation, resulted in a synergistic antioxidant activity greater than that observed with comparable amounts of α-tocopherol. In light of the known antioxidant mechanism of retinoids, the data suggest that by limiting autooxidation of all-transretinol, α-tocopherol strongly promotes its antioxidant effectiveness. The concerted radical scavenging action in turn results in a synergistic protection of the lipid system against peroxidative stress and, ultimately, slows down the α-tocopherol consumption.

Water-Soluble Copolymers. 67. Polyelectrolytes of N-Vinylformamide with Sodium 3-Acrylamido-3-methylbutanoate, Sodium 2-Acrylamido-2-methylpropanesulfonate, and Sodium Acrylate: Synthesis and Characterization

Copolymers of N-vinylformamide (NVF) with sodium 3-acrylamido-3-methylbutanoate (NaAMBA), sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS), and sodium acrylate (NaA) were prepared by free-radical polymerization in aqueous solution using 2,2'-azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride as the water-soluble azo initiator. Copolymer compositions were determined utilizing 13 C NMR by integration of the carbonyl resonances. Reactivity ratios were determined for NVF (M 1 )/NaAMBA (M 2 ) (the BAVF series) and NVF (M 1 )/NaAMPS (M 2 ) (the PSVF series). Both series, with r 1 and r 2 <1 and r 1 r 2 < 0.075, are representative of copolymers that display alternating tendencies. Microstructural data calculated statistically by the methods of Igarashi support these findings. Weight-average molecular weights range from 0.9 x 10 6 to 7.5 x 10 6 and were determined by low-angle laser light scattering in 1 M NaCl solution. The findings are compared to previous results obtained for the copolymerization of acrylamide with the various anionic comonomers.

Scavenging of free radicals by tenoxicam: a participating mechanism in the antirheumatic/antiinflammatory efficacy of the drug.

The radical scavenging activity of tenoxicam against hydroxyl (HO.), superoxide (O2.-), and peroxyl (LOO.) radicals, all of them involved in the inflammatory reactions, has been tested in different cell-free systems and by different techniques. Tenoxicam is a good scavenger of both HO. radicals (IC50 = 56.7 microM), as determined by Electron Spin Resonance (ESR) spectroscopy with the spin trapping (5,5-dimethyl-1-pyrroline N-oxide, DMPO) technique, and O2.- radicals generated by the phenazine methosulfate/reduced beta-nicotinamide adenine dinucleotide (PMS/NADH) system. The high reactivity of the drug towards HO. was confirmed by the rate constant of reaction with HO. (k approximately 10(10) M-1s-1), determined by competition kinetic studies with N,N-dimethyl-4-nitrosoaniline. In addition at a microM level (1-5 microM) it dose-dependently prevents the phycoerythrin peroxidation induced by the water-soluble azoinitiator 2,2-azobis (2-amidinopropane) dihydrochloride (ABAP), indicating a quenching effect on aqueous peroxyl radicals. The HO.-entrapping capacity was confirmed in models more close to the in vivo situation: tenoxicam inhibits the HO.-induced depolymerization of hyaluronic acid already at 15 microM and the HO.-driven lipid peroxidation in phosphatidylcholine liposomes (PCL) with an IC50 of 10 microM. In this membrane model it delays at 1-10 microM level the decomposition of phosphatidylcholine hydroperoxides to short-chain alkenals (markers: total carbonyl functions as 2,4-dinitrophenylhydrazones and conjugated dienes). The high susceptibility of the drug to HO. attack is also demonstrated by its extensive degradation (HPLC studies) when irradiated with HO. radicals. The antioxidant component of tenoxicam evidenced in this study sheds some light on the hitherto undefined mechanism of the antiinflammatory action of the drug.

The Effects of Vitamin C and Urate on the Oxidation Kinetics of Human Low-Density Lipoprotein

Oxidative modification of human low-density lipoprotein (LDL) is believed to play an important role in atherogenesis. Vitamin C (ascorbate) and urate are major water-soluble plasma antioxidants in humans. Urate levels (300-395 microM) in human serum are considerably higher than ascorbate levels (30-50 microM). In this study, we compared the ability of urate to protect human LDL from in vitro oxidation with that of ascorbate. LDL was subjected to in vitro oxidation at 30 degrees C with an O2 saturated solution (0.15 M NaCl/0.25 mM EDTA) and 15 mM of a thermally labile water soluble azo-initiator (ABAP or azobis-2-amidinopropane HCl). In parallel experiments, 50 microM ascorbate or 50 microM urate were present in the oxidation buffer. The consumption of alpha-tocopherol, gamma-tocopherol, urate or ascorbate and the formation of lipid hydroperoxides were measured as a function of time in the in vitro oxidation system. The rate of lipid hydroperoxide formation was found to be significantly increased after the LDL tocopherols (alpha-plus gamma-tocopherol) were totally consumed, i.e., after the lag phase. Urate (50 microM) was more effective than ascorbate (50 microM) in extending the lag phase. Moreover, urate was consumed more slowly than ascorbate under identical oxidation conditions. Urate was not, however, as effective as ascorbate in preventing the formation of lipid hydroperoxides before the lag phase. An empirical mathematical model was also developed to describe the oxidation kinetics of LDL alpha- and gamma-tocopherol in the presence or absence of urate or ascorbate.

Tocopherol-mediated peroxidation. The prooxidant effect of vitamin E on the radical-initiated oxidation of human low-density lipoprotein

Oxidation of human low-density lipoprotein (LDL) is implicated as an initiator of atherosclerosis. α-Tocopherol (α-TocH) may thus inhibit atherosclerosis beause it is the major and most active chain-breaking antioxidant in extracted LDL lipid. Our studies show, however, that α-TocH can be a strong prooxidant for the LDL itself, i.e., an aqueous dispersion of lipid-bearing particles. Thus, a steady flux (R g ) of alkylperoxyl radicals (ROO . ) generated from a water-soluble azo initiator induced lipid peroxidation in LDL which was faster in the presence of α-TocH than in its absence (for R g <2 NM S -1 ), insensitive to R g and [O 2 ], and inhibited by vitamin C, ubiquinol-10 (normally present in fresh LDL), and small phenolic antioxidants but not inhibited by the aqueous radical scavenger uric acid

A moderately water‐soluble azo initiator for emulsion polymerizations

The use of N,N'-dimethyldiazenecarboxamide as an initiator for the emulsion polymerization of methyl methacrylate is described. Polymerization was achieved with 85-90% conversion of monomer in both batch and semi-batch modes with no coagulation noted. Particle diameters were in the range 120-130 nm with a polydispersity of 1.05

Cholesterol : Free radical peroxidation and transfer into phospholipid membranes

Cholesterol, when sequestered in saturated liposomes of dimyristoylphosphatidylcholine (DMPC) or dipalmitoylphos-phatidylcholine (DPPC), undergoes peroxidation thermally initiated either by a lipid-soluble or a water-soluble azo initiator and in both cases the reaction is inhibited effectively by the water-soluble antioxidant, 6-hydroxy-2,5,7,8-tetra-methylchroman-2-carboxylate (Trolox). Quantitative kinetic methods of autoxidation show that the oxidizability, k p (2k t) 1 2 (where k p and 2 k t are the rate constants of radical chain propagation and termination, respectively) of cholesterol in DMPC or DPPC multilamellar liposomes, where k p (2k t) 1 2 is 3.0 • 10 −3 to 4.3 · 10 −3 M − 1 2 s − 1 2 at 37–45°C, is similar to that measured in homogeneous solution in chlorobenzene, where K p (2k t) 1 2 is 3.32-10 −3. However, its oxidizability in smaller unilamellar vesicles of DMPC or DPPC increases by at least 3-times that measured in multilamellar systems. Autoxidation/antioxidant methods show that cholesterol partitions directly from the solid state into DMPC or DPPC liposomes by shaking and this is confirmed by 31P and 2H quadrupole NMR spectra of deuterated cholesterol when membrane bound. Analytical studies indicate that up to 21 mol% cholesterol will partition into the membranes by shaking.

Investigation of the persulfate/itaconic acid interaction and implications for emulsion polymerization

AbstractItaconic acid, a carboxylated water‐soluble vinyl monomer, is shown to greatly induce the thermal decomposition of potassium persulfate initiator. From decomposition rate studies carried out at 50, 60, and 70°C, the rate constants for this interaction are found to be increased eight to 15 times as much over the values of rate constants from uninduced decompositions. The induction is found to be particularly sensitive to the concentration of the first anion of itaconic acid and is thought to lead to wastage of initiator radicals. As the polymerization temperature is increased from 50 to 70°C, this interaction between itaconic acid and persulfate leads to worsening monomer conversion levels in acrylate latexes made with both compounds. Employing a water‐soluble azo initiator in the presence of itaconic acid does not result in any induced decomposition of the former. Acrylate latexes prepared with these two compounds have monomer conversion levels which rise as the polymerization temperature is increased, as is expected in conventional emulsion polymerizations.