Selective hydrolysis of borage oil with Candida rugosa lipase: Two factors affecting the reaction

A 46% γ-linolenic acid (GLA)-containing oil was produced by selective hydrolysis of borage oil (GLA content, 22%) at 35°C for 15 h in a mixture containing 50% water and 20 units (U)/g reaction mixture of Candida rugosa lipase. The GLA content was not raised over 46%, even though the hydrolysis extent was increased by extending the reaction time and by using a larger amount of the lipase. However, 49% GLA-containing oil was produced by hydrolysis in a reaction mixture with 90% water. This result suggested that free fatty acids (FFA) that accumulated in the mixture affected the apparent fatty acid specificity of the lipase in the selective hydrolysis and interfered with the increase of the GLA content. To investigate the kinetics of the selective hydrolysis in a mixture without FFA, glycerides containing 22, 35, and 46% GLA were hydrolyzed with Candida lipase. The result showed that the hydrolysis rate decreased with increasing GLA content of glycerides, but that the release rate of GLA did not change. Thus, it was found that the apparent fatty acid specificity of the lipase in the selective hydrolysis was also affected by glyceride structure. When 46% GLA-containing oil was hydrolyzed at 35°C for 15 h in a mixture containing 50% water and 20 U/g of the lipase, GLA content in glycerides was raised to 54% at 20% hydrolysis. Furthermore, GLA content in glycerides was raised to 59% when the hydrolysis extent reached 60% using 200 U/g of the lipase. These results showed that repeated hydrolysis was effective to produce the higher concentration of GLA oil. Because film distillation was found to be extremely effective for separating FFA and glycerides, large-scale hydrolysis of borage oil was attempted. As a result, 1.5 kg of 56% GLA-containing oil was obtained from 7 kg borage oil by repeated reaction.     

Microstructure of Strontium Titanate Thin Film Grown by the Hydrothermal-Electrochemical Method

Microstructures of SrTiO₃ thin films grown on Ti substrates by the hydrothermal-electrochemical method have been studied by transmission electron microscopy. The grown films consisted of a thin surface layer having an isotropic polycrystalline structure and a thick inner layer having a columnar structure. Pores of the order of several tens of nanometers were found at boundaries of columnar grains constituting the inner layer. A 20- or 30-nm-thick polycrystalline layer of Ti oxides contaminated with a small amount of Sr was also found at the SrTiO₃ film/Ti substrate interface. During the film growth at this interface, the observed pores are considered to act as short-circuit paths for mass transport from the film surface to the interface.     

E.s.r. studies on oxidation processes in irradiated polyethylene: 1. Diffusion of oxygen into amorphous parts at low temperatures

Oxidation processes in irradiated polyethylene were studied by e.s.r. By utilization of the characteristic feature of power saturation of the e.s.r. spectrum of peroxide radicals, quantitative measurement of the process of the reaction of oxygen with allylic radicals trapped in the amorphous part of the polyethylene were made and the data were analysed based on the diffusion-controlled process theory. Diffusion equations were solved by computer simulation method. Diffusion of the oxygen into the amorphous part of the polyethylene is discussed and diffusion constants at low temperature are estimated. Related values such as the activation energy of the diffusion process and the solubility constant, are also estimated.     

Free radicals trapped in polyethylene matrix: 1. Location of the alkyl radicals in irradiated polyethylene

Two types of alkyl radicals were found to be trapped in irradiated crystals grown from polyethylene solution. One of them corresponds to the broad sextet pattern of the e.s.r. spectrum and the other corresponds to the sharp sextet pattern. The free radicals attributed to the broad sextet began to disappear at a lower temperature than the temperature at which the free radicals attributed to the sharp sextet disappeared. When butadiene molecules were brought into contact with the specimen, the decay of the free radicals corresponding to the broad sextet was accelerated. When the specimen was subjected to fuming nitric acid treatment, no broad sextet was observed. The mat of the crystals, was aligned so that the c-axes of its crystallites were perpendicular to its surface. The broad sextet showed no anisotropy when the angle between the direction of applied magnetic field and that of the c-axis of the crystallite was varied. On the other hand, the sharp component of the spectrum showed apparent anisotropy. Consequently, it can be concluded that the broad component comes from the free radicals trapped in the lamellar surface and the sharp component is attributed to the free radicals trapped in the inner part of the crystallite. Hence, the locations of these two types of free radicals have been clarified with much more certainty than before.     

Fatty acids in echinoidea: Unusualcis-5-olefinic acids as distinctive lipid components in sea urchins

Open tubular gas liquid chromatographic (GLC) analyses of fatty acids from total lipids of 12 species of Echinoidea collected at several locations along the Pacific coast of Japan showed the same unusualcis-5-olefinic acids in all species, i.e.,cis-5-octadecenoic acid (5–18∶1),cis-5-eicosenoic acid (5–20∶1), all-cis-5,11- and 5,13-eicosadienoic acids (5,11- and 5,13–20∶2), allcis-5,11,14-eicosatrienoic acid (5,11,14–20∶3) and all-cis-5,11,14,17-eicosatetraenoic acid (5,11,14,17–20∶4). The structural analysis of partially purified 5,11,14,17–20∶4 was undertaken by reductive ozonolysis with GLC and gas chromatographic-mass spectrometric analyses of the products.¹³C-Nuclear magnetic resonance analyses of the totals and fractions of fatty acid methyl esters from the sea urchin lipids did not show any occurrence of fatty acids having an isolated olefinic bond in the 2, 3 or 4 positions. The 5-olefinic acids were concentrated on the polar lipids rather than neutral lipids. The branched and odd chain fatty acid contents of mud-feeding sea urchins were found to be relatively greater proportions of total fatty acids than in algae feeders.     

Comparison of local molecular motions at chain end and inside of the polymer chain by use of spin trapping method

The spin trapping method was applied to the study of local molecular motion in polyethylene. Spin trapping reagent, 2,4,6-tri-t-butyl nitrosobenzene, was mixed with polyethylene and the free radicals produced by γ-irradiation and thermal degradation were stably trapped by spin trapping reagent. Temperature dependences of e.s.r. spectra of the stable nitroxide radicals trapped were observed and widths of extrema separation and correlation times at various temperatures were compared for the local motions at inside of chain and at chain end. Less mobile character of the molecular motion at inside of the molecular chain was confirmed. Diluent effects to the molecular motions were also studied.     

Relation between diffusion controlled decay of radicals and α-relaxation in polyethylene and polyoxymethylene

Diffusion controlled process theory was applied to the analysis of the data concerning decay reactions of free radicals in irradiated polyethylene and polyoxymethylene in detail. Diffusion constants of free radical sites were estimated from the data of the decay reactions and their time constants were calculated by using Stokes-Einstein relation. These time constants were plotted against the inverse temperature in the relaxation maps, which were arranged by Wada. In the case of polyethylene, the time constants of decay reactions of alkyl radicals trapped in the lamellar surface and the inner part of crystallites were in good agreement with the relaxation times of α′- and α-processes, respectively. However, it was found that the time constants of main chain radicals trapped in polyoxymethylene were closely related to α-relaxation processes. The activation energies of the decay reactions of free radicals were in good agreement with those of the corresponding relaxation processes in both cases. From these results, it was concluded that the decay reactions of the free radicals reflect the molecular motions associated with the respective relaxation processes. Concerning the decay reaction of free radicals in the inner crystallite of polyethylene, effects of lamellar thickness and crystal surface were also studied by using solution grown crystals, which were crystallized at various temperatures, and the fuming nitric acid treated materials. It was found that the diffusion constant of free radical sites and its activation energy were strongly dependent on the lamellar thickness and half-life of free radicals was a function of the amount of the fold surface; i.e., the reaction rate was much depressed as the lamellar thickness was increased and the amount of the fold surface was decreased.     

The mechanism of oxidative degradation of ABS resin. Part I. The mechanism of thermooxidative degradation

In this work the early stages of the thermal oxidation of ABS resin films for commercial utilization and purified samples were studied by means of infrared spectroscopy. The film samples were submitted to thermal oxidation in a Gear oven at 70–90°C. During the aging in the Gear oven the nitrile and phenyl absorbance did not change, but oxidative products containing hydroxyl or carbonyl groups were produced rapidly, and the butadiene content decreased gradually. Two parts of the oxidative reaction were easily distinguished by analysis of the degradation procedure in the differential method and in the half-time method. An activation energy of 10 kcal./mole or less was obtained for the initiation process, involving mainly the formation of hydroperoxides induced by radical formation, which was apparent in the commercial samples, whereas a value of 10–20 kcal./mole was obtained for the subsequent process, initiated by the decomposition of the hydroperoxides, which induces chain-carrier reactions. A reaction scheme is proposed, and kinetic expressions are developed therefrom. These expressions explain the experimental results very well.     

Electron spin resonance studies of γ-irradiated cellulose. II. Free radicals in accessible regions to water in cellulose I and cellulose II

The types of free radicals produced in the water-accessible regions of cellulose I and cellulose II fibers by γ-irradiation in nitrogen atmosphere at room temperature were studied by ESR spectroscopy. The ESR spectra of the irradiated cellulose I and II change by contacting the fibers with water, and after immersion in water the spectral shape depends on the orientation of the fiber axes to the magnetic field. These spectra are probably related to the free radicals generated in the highly ordered regions inaccessible to water in irradiated cellulosic fibers. The ESR spectrum of free radicals generated in decrystallized cellulose after irradiation consists of a singlet and a doublet. When the ESR spectra of free radicals formed in the highly ordered regions of cellulose I and II and the singlet and the doublet are combined in adequate ratio, the constructed spectra are similar to those of the radicals scavenged by water in the irradiated cellulose I and II fibers. From these facts, the spectra due to the free radicals in the water-accessible regions in irradiated cellulose I and II are considered to consist of the singlet and the doublet formed by free radicals in the typical amorphous regions and the spectra of other types of radicals generated in the semicrystalline regions.     

Molecular motion of isolated polybutadiene chains tethered on the fresh surface of polytetrafluoroethylene

The polybutadiene (PBD) chains tethered on the fresh surface of a polytetrafluoroethylene (PTFE) were produced by a block copolymerization of PTFE with 1,3-butadiene in vacuum at 77 K. The extremely low segmental density of the tethered chains was estimated by a spin labelling technique. The tethered chains can be regarded as ‘isolated polymer chains’. The PBD tethered chain has an unpaired electron at the chain end. We studied the molecular mobility of the PBD tethered chains by electron spin resonance (e.s.r.) spectroscopy, using the PBD chain end radical as a probe. The site exchange motion between two conformations at the chain end was observed in the temperature range 77–173 K and the rate of the exchange motion was determined by spectral simulations. The tethered chains are mobile even below 218 K which is a glass transition temperature of 1,4-PBD in the bulk. The high mobility of the PBD chains tethered on the PTFE surface is attributed to: the PBD chains have a very large space around the chains because of an extremely low segmental density on the PTFE surface. © 1997 Elsevier Science Ltd.