Fluorescent product formation and changes in structure of DNA reacted with peroxidizing arachidonic acid

Calf thymus DNA was reacted with peroxidizing arachidonic acid at 37 C for 76 hr. Fluorescent DNA products increased with reaction time. These products had characteristic fluorescence spectra with maximum excitation at 315 nm and maximum fluorescence at 420 nm. Structural changes occurred in the DNA reacted with peroxidizing arachidonic acid, as observed by decreased melting point, decreased hyperchromicity, partial resistance to hydrolysis by deoxyribonuclease and by decreased template activity for rat liver RNA polymerase.     

Free radical reactions of peroxidizing lipids with amino acids and proteins: An ESR study

Free radical transfer from oxidizing methyl linoleate to amino acids and proteins was studied in dry model systems incubated for periods up to 20 days. Electron spin resonance was used to study free radical production. Free radicals were detectable in the amino acids lysine, arginine, histidine, tryptophan, and cysteine. Reduced glutathione and, to a limited extent, cystine also gave free radical signals. Free radicals produced in proteins primarily showed central singlet lines, attributable to carbon-centered radicals, with g=2.004±0.001. Sulfhydryl proteins also exhibited downfield shoulders at g≄2.015 and 2.023 that were essentially identical to peaks observed in cysteine and reduced glutathione. The field positions of sulfur resonance in cysteine and proteins suggested a sulfur-oxygen complex rather than thiyl radicals. This report is part of ScD Thesis, MIT, 1974 (KMS).     

Free radical polymerization of p-methyl styrene

An experimental investigation is reported of the free-radical synthesis kinetics of poly(p-methyl styrene) in cyclohexane at low monomer conversion in the temperature range 50°–70°C using AIBN initiator. The p-methyl styrene monomer contained greater than 97% paraisomer. Isothermal conversion/time curves were obtained using glass ampoule reactors and gravimetry and molecular weight distribution and weight-average molecular weights were measured by s.e.c. and low angle laser light scattering photometry (LALLSP). Transfer to small molecules (monomer, cyclohexane, —) was found to be small or negligible with virtually all of the polymer chains formed by termination by combination. Predicted and measured weight-average molecular weights are in good agreement for polymer synthesized at low conversions.     

Free radical desorption in continuous emulsion polymerization

A mathematical model for continuous emulsion polymerization which accounts for the desorption of radicals from polymer particles is presented. The desorption factor has been incorporated into the Sato-Taniyama model and the resulting systems of equations solved iteratively. The effects of desorption on variables such as concentration of particles, polymerization rate, and average number of radicals per particle are illustrated. Fit of the model to experimental data is presented and discussed.     

Free radical bulk polymerization in cylindrical molds

Bulk styrene homopolymerization in cylindrical molds was studied in order to simulate the reactive injection process when the reaction kinetics was much slower than the filling process. Mathematical models were built and implemented, allowing the analysis of certain kinetic phenomena, such as the gel‐effect, and the relevance of natural convection. Based on a detailed kinetic mechanism, the polymer properties (average molecular weight and polydispersity) and monomer conversion were calculated as functions of spatial coordinates and time. The results obtained show that polymer properties and monomer conversion may be very heterogeneous inside the cylindrical mold, although insensitive to variations of the diffusion coefficient, so that defects are expected to appear as a consequence of the heterogeneity of polymer properties inside the mold. Experiments confirmed the simulation results. Simulations indicate that heterogeneities may be expected to increase when the reaction rates are one order of magnitude higher, as in acrylic acid polymerizations.     

Free radical polymerization models for simulating reactive processing

The generally accepted kinetic mechanism for free radical copolymerization was simplified by various assumptions and restrictions to give several realistic and easily evaluated models for the simulation of industrial molding. Six assumptions, including conversion-dependent rate coefficients and constant comonomer concentration ratios, were used to obtain a simplified model. Special cases of this simplified model were obtained by the following additional constraints: (1) Restriction C, consecutive inhibition and radical generation reactions; (2) Restriction I, constant initiator decomposition rate; (3) Restriction Z, zero termination rate for free radicals; and (4) Restriction K or P, all rate coefficients independent of conversion or only polymerization rate coefficient dependent on conversion. For various combinations of these restrictions, the time and concentration variables in the simplified model are separated and solved; the separate solutions are then combined in various ways to give models capable of predicting a wide variety of behavior. Many of these models have analytical solutions that greatly facilitate the evaluation of rate constants. Models based on restrictions KCI, PCI, and PCZ are shown to give good agreement with isothermal DSC data plotted as reaction rate versus time and, in a more sensitive test, as reaction rate divided by monomer concentration versus fractional conversion. Because of their predictive ability and ease of evaluating constants. Models PCI and PCZ are recommended for simulating industrial processing; they are particularly well suited for simulating compression molding of sheet molding compound.     

Free radical polymerization of nitropropyl acrylates and methacrylates. I. Heat of polymerization

The heat of polymerization ΔH_p, of nitropropyl(meth)acrylate monomers has been studied by differential scanning calorimetry (DSC) in dynamic and isothermal modes. DSC showed that ΔH_p of 2‐nitropropyl(meth)acrylate was surprisingly smaller than that of propyl(meth)acrylate but similar to that of 2,2‐dinitropropyl(meth)acrylate. According to molecular structure analysis by a PM3 Hamiltonian in a MOPAC program, the contributing main factor to the lowering of ΔH_p of 2‐nitropropyl (meth)acrylate was found to be the hydrogen bond between the O(?C) and the H atom attached at position C6. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2929–2935, 2001     

Free radical polymerization of methyl methacrylate at high temperatures

Free-radical polymerization of methyl methacrylate in a tubular reactor has been conducted at above-Tg temperatures. A salient feature of these experiments is the very efficient control of reactor temperature by vapor-liquid equilibrium of the polymerizing mixture via monomer evaporation. The system pressure thus provides a powerful control variable, restricting the temperature in the entire reactor by changing the monomer evaporation rate. In the range of our experimental conditions, the temperature and pressure in the reactor follow the Antoine equation closely. High temperature runs also reduce the length requirement of the reactor. However, molecular weight averages of the products are not impressive, unless slow-burning initiators are used. Modeling of above-Tg reactions has been attempted at two-levels of sophistication. A plug-flow model gives predictions in good agreement with our experimental temperatures and conversion data. The predicted molecular weights are also consistent with the experimentally observed values. However, the more elaborate rheokinctic model suggests that the superficial agreement between model and experiment is due to initiator burn-out, which limits the final conversion to within 40 percent. The liquid layer next to the reactor wall can never be so viscous as to form a stagnant deposit, due to this conversion limitation. The velocity profiles are thus not very much distorted, and a plug-flow model is adequate. With a slow-burning initiator and a sufficiently long reactor, skewing of velocity profile and reactor channeling will eventually emerge. Hence, the rheokinetic model must be evoked to model the system under such conditions.     

Free radical polymerization engineering—I: A new method for modeling free radical homogeneous polymerization reactions

This paper deals with a new appraisal of free radical polymerization modeling. Classical properties of the distribution of polymerization degrees and methods for studying them thanks to the z-transform are recalled. When simple mechanisms are involved, the kinetics may be represented by a “detailed analytic” model relying on macromolecule balances. This is no longer possible when complex processes are occurring, e.g. transfer to polymer, β-scission, terminal double bond propagation… In order to deal with these more complex cases, a “tendency model” is proposed, relying on balances of quantities such as free radicals, macromolecules and the moments of the distribution of polymerization degrees. The quality of the polymer is described by chemical characters such as double bonds, long and short branching points, terminal double bonds… for which kinetic equations are established. Equations are given for calculating the moments of free radicals and those of instantaneously produced macromolecules via various processes. The simplicity and the usefulness of the method are illustrated by several examples and a comparison is made, when possible, with the detailed approach. Finally, equations are given, making it possible to calculate the quality of polymer produced in any kind of reactor and for different states of segregation.     

原子转移自由基聚合合成聚丙烯酸

通过调节反应体系的pH值,利用原子转移自由基聚合(ATRP)的方法,合成了聚丙烯酸,并采用黏度法测定其相对分子质量.实验结果表明,反应体系的pH值对热反应及产物的相对分子质量有着显著影响.     

Free radical polymerization with long chain branching: continuous polymerization of vinyl acetate in t-butanol

Vinyl acetate was polymerized in a continuous stirred tank reactor (CSTR) at 60°C in t-butanol solution. Mean residence times ranged from 1.35 to 7.2 hr; steady state conversions ranged from 15 to 61%. Molecular weights $\text{M}$_n and $\text{M}$_w were measured and interpreted in terms of a kinetic model developed from batch studies and the state of local mixing in the reactor. Good macroscopic mixing was confirmed by tracer studies and measurements of conversion vs time during the start-up period and at steady state. The molecular weights obtained at high conversions agreed more closely with predictions based upon a locally segregated state than with those based on complete molecular mixing. However, calculations based on agitation and diffusion rates raised serious questions about the validity of the segregation model for this polymerization. Other factors, some chemical and some related to the agitation, may be important, but the problem of predicting molecular structure remains unresolved.     

Conjugated linoleic acid modulates hepatic lipid composition in mice

Conjugated linoleic acid (CLA) is a chemoprotective fatty acid that inhibits mammary, colon, forestomach, and skin carcinogenesis in experimental animals. We hypothesize that the ubiquitous chemoprotective actions of dietary CLA in extrahepatic tissues are dependent upon its role in modulating fatty acid composition and metabolism in liver, the major organ for lipid metabolism. This study begins to evaluate the role of CLA in lipid metabolism by determining the modulation of fatty acid composition by CLA. Female SENCAR mice were fed semipurified diets containing 0.0% (Diet A), 0.5% (Diet B), 1.0% (Diet C), or 1.5% (Diet D) CLA (by weight) for six weeks. Mice fed Diets B, C, and D exhibited lower body weights and elevated amounts of extractable total lipid in livers compared with mice fed diets without CLA (Diet A). Analyses of the fatty acid composition of liver by gas chromatography revealed that dietary CLA was incorporated into neutral and phospholipids at the expense of linoleate in Diets B, C, and D; oleate increased and arachidonate decreased in neutral lipids of CLA diet groups. In addition, increasing dietary CLA was associated with reduced linoleate in hepatic phospholipids. In an in vitro assay, CLA was desaturated to an unidentified 18:3 product to a similar extent as linoleate conversion to γ-linolenate (9.88, and 13.63%, respectively). These data suggest that CLA may affect metabolic interconversion of fatty acids in liver that may ultimately result in modified fatty acid composition and arachidonate-derived eicosanoid production in extrahepatic tissues. In addition to determining how dietary CLA modulates eicosanoid synthesis, further work is needed to identify enzymatic products that may result from desaturation of CLA.     

Effects of conjugated linolenic acid and conjugated linoleic acid on lipid metabolism in mice

The effects of two isomers of conjugated linolenic acid (CLnA), α‐eleostearic acid (α‐ESA) and punicic acid (PA), on body fat and lipid metabolism were investigated, compared with a conjugated linoleic acid (CLA) mixture (primarily cis9,trans11‐ and trans10,cis12‐18:2) and α‐linolenic acid (ALA), a non‐conjugated octadecatrienoic acid, in the present study. ICR mice were fed either a control diet or one of four experimental diets supplemented with 1% α‐ESA, 1% PA, 1% CLA mixture and 1% ALA in the form of triacylglycerols (TAG) for 6 weeks. The weights of perirenal and epididymal adipose tissues were significantly decreased while the liver weight was significantly increased in mice fed CLA, compared with the control. In contrast to CLA, the tissue weights in α—ESA‐, PA‐ and ALA‐fed mice were not affected. No significant differences were observed in TAG, total cholesterol, high‐density lipoprotein and low‐density lipoprotein cholesterol levels among the five groups. The liver TAG level was significantly decreased in mice fed α‐ESA and PA while it was significantly increased in mice fed the CLA mixture. These results indicate that CLnA and CLA have differential effects on body fat mass and liver TAG levels in mice.     

伴有水解缩合反应的种子乳液聚合动力学(I)模型

伴有水解缩合反应的自由基种子乳液聚合反应是制备有机-无机杂化乳胶粒的一种新方法，水解缩合反应和自由基聚合这两种反应在乳液体系中的动力学耦合过程决定了聚合产物的微结构和应用性质。通过单体的分配系数建立了单体在乳液体系中各相的分配模型，进而建立了考虑单体分配的自由基种子乳液共聚合的动力学模型。针对功能基团在乳液各相中水解缩合反应的特点，结合自由基种子乳液共聚合的动力学模型，建立了伴有水解缩合反应的自由基种子乳液聚合动力学模型。该模型反映了反应过程中的物质传递规律、非均相反应特点、自由基共聚合和水解缩合反应间的耦合关系。     

Microsomal desaturation-elongation of linoleic acid following parenteral feeding with lipid emulsions in the rat

The effect of total parenteral nutrition (TPN) with lipid emulsion to supply either 27.5% or 2% total calories on in vitro desaturation-elongation of 18∶2(n−6) by liver microsomes was studied in the rat. The emulsion lipid contained ca. 50% 18∶2(n−6) plus 8% 18∶3(n−3) or 77% 18∶2(n−6) plus 0.5% 18∶3(n−3). The reaction rate was influenced by the in vitro substrate concentration and inhibited above 50 μmol 18∶2(n−6)/mg microsomal protein. At maximum rates of desaturation-elongation, the formation of triene and tetraene (n−6) fatty acids was reduced in rats given either of the two emulsions. The rate of (n−6) pentaene formation was increased in rats given the emulsion with low 18∶3(n−3) but not in rats given the emulsion with 8% 18∶3(n−3). Analyses of the microsomal lipid indicated increased free cholesterol in all rats that received TPN. Esterified cholesterol was increased only in rats given 27.5% TPN calories as lipid. Microsomal total phospholipids and phospholipid class distributions were not altered by TPN. The data are consistent with reports of reduced levels of long-chain desaturation-elongation metabolites of 18∶2(n−6) in tissue phospholipids following infusion of parenteral lipid. The data suggest that the mechanism may include alterations in other metabolic pathways such as cholesterol, in addition to desaturase enzyme activities, and may be influenced by both the quantity and fatty acid composition of the lipid infused.     

Free radical polymerization of vinyl acetate in the presence of liquid polysulfides

The free radical polymerization of vinyl acetate in the presence of a liquid polysulfide H(SCH₂CH₂OCH₂OCH₂CH₂S)_nH (thiocol) was investigated from the point of view of reaction mechanism and characterization of the resulting copolymers. It was shown that, besides the thiol end groups that were consumed very rapidly, the disulfide groups within the thiocol chain were also involved in chain transfer processes. The chain transfer constant of the thiocol S–S groups in the polymerization reaction was estimated from their rate of consumption versus the rate of monomer consumption (C_T = 0.89). The resulting copolymers, made up of randomly distributed thiocol sequences and PVAc blocks, were characterized by ¹H NMR, GPC, DSC and TGA measurements. The copolymers displayed only one glass transition each, which decreased as the PVAc block length decreased, while their thermal stability was lower than that of both thiocol and PVAc. The molecular weight of the copolymers increased with VAc conversion as a consequence of the insertion of PVAc blocks within the thiocol chain.     

Biocatalysis of linoleic acid to conjugated linoleic acid

CLA refers to a group of geometrical and positional isomers of linoleic acid (LA) with conjugated double bonds. CLA has been reported to have diverse health benefits and biological properties. Traditional organic synthesis is highly capital-intensive and results in an isomeric mixture of CLA isomers. Biotechnology presents new alternatives to traditional lipid manufacturing methods. The objective of this study was to examine the effect of protein isolation procedures on linoleate isomerase (LAI) recovery from microbial cells and biocatalysis of LA to CLA. Protein isolation experiments were carried out using Lactobacillus acidophilus L1 and two strains of Lactobacillus reuteri (ATCC 23272 and ATCC 55739). Under the same assay conditions, ATCC 55739 had the highest LAI activity among the microbial cultures examined in this study. Efficiency of cell lysis methods, which included various combinations of lysozyme and mutanolysin treatments in combination with sonication and osmotic rupture of cells with liquid nitrogen, was very low. Although treatment of cell material with a detergent (octylthioglucoyranoside) freed a significant amount of LAI activity into the solution, it was not sufficient to recover all the LAI activity from the residual cells. Crude LAI preparations produced mainly the cis-9,trans-11 CLA isomer. Time and substrate/protein ratio had a significant effect on biocatalysis of LA to CLA. It appears that the mechanism and kinetics of enzymatic conversion of LA to CLA are quite complex and requires further research using pure LAI preparations. Published with approval of the Director, Oklahoma Agricultural Experiment Station.     

Free radical polymerization in ionic liquids—Influence of the IL-concentration and temperature

The influence of the ionic liquid (IL) 1-ethyl-3-methylimidazoliumethylsulfate ([EMIM]EtSO₄) on the polymerization kinetics of methyl methacrylate was investigated. ILs are liquids with relatively high polarities and viscosities. These two characteristic properties are strongly correlated with the rate coefficients of propagation k_p and termination k_t of polymerizations carried out in ILs. The rate constant of termination k_t decreases when the concentration of ionic liquid, and thus the viscosity is increased, whereas the propagation rate coefficient k_p increases with increasing IL content. The viscosity of ILs can be varied by either working with mixtures of ILs with conventional organic solvents – here the IL [EMIM]EtSO₄ was mixed with dimethyl formamide (DMF) – or by variation of the temperature. The studies were carried out to determine the influence of the viscosity on the propagation and the termination reaction as well as the molecular weight distribution.     

Lipid binding properties of a factor necessary for linoleic acid desaturation

Suspension and centrifugation of crude microsomes of rat liver in low ionic strength solution separated a soluble protein fraction that is necessary for the full activity of the linoleic acid desaturase. The fraction partially purified through Sephadex G-150 still retains lipids which are mainly constituted by phosphatidylcholine. Linoleic acid predominates in the fatty acid composition. By NaCl gradient centrifugation and electrophoresis in gelatinized cellulose acetate, the factor behaves like a lipoprotein. The factor binds linoleic acid and linolyl-CoA that are desaturated to γ-linolenic acid when incubated with washed microsomes. Albumin does not replace the factor.