Mechanism of thermal decomposition of peroxide radicals formed in polytetrafluoroethylene by γ-ray irradiation

Thermal decomposition of polymer peroxide radicals formed in γ-irradiated polytetrafluoroethylene, ～CF₂CF(OO·)CF₂～ (radical I) and ～CF₂CF₂(OO～) (radical II), was studied by mass spectral analysis of the gas evolved in comparison with their photolysis with ultraviolet light. In the thermal decomposition of radicals I and II, CO₂ was the most abundant component, with smaller amount of CO, CF₂O, and gases present. In the photolysis, CO instead of CO₂ was the most abundant in the case of radical I, while in the case of radical II, CO₂ was again the main product. When a labeled polymer peroxide radical, ～CF₂CF(¹⁸O-¹⁸O·)CF₂～, was treated with heat or ultraviolet light, C¹⁸O¹⁶O was detected as a main component. In the treatment with ultraviolet light, a large amount of C¹⁸O comparable to that of C¹⁸O¹⁶O was also obtained. The mechanism of main-chain scission of radicals I and II is discussed.     

Pharmacological activities of synthetic human cholecystokinin-33 of which tyrosine was sulfated by arylsulfotransferase

The pharmacological activities of synthetic human CCK-33, in which a tyrosine molecule was sulfated by arylsulfotransferase, were investigated in the rat and the guinea-pig. The activities were compared with those of non-sulfated CCK-33 (CCK-33NS), CCK-8 and CCK-4. CCK-33 was about 100 fold more potent than non-sulfated CCK-33(CCK-33NS) but was about 20 fold less potent than CCK-8 in the contraction of the isolated gallbladder of the guinea-pig. In rat pancreatic secretion, intravenous CCK-33 and CCK-8 showed almost the same activity. The potency of each was about 1000 fold more than the individual potency of CCK-33NS, non-sulfated CCK-8 (CCK-8NS) and CCK4. There were no significant differences in gastric acid stimulatory activities among CCK-33, CCK-8, CCK-4, but the activities of CCK-33NS and CCK-8NS were less than those of CCK-33 and CCK-8, respectively. CCK-33 and CCK-8 produced a reduction in the intake of powder chow in doses of 10(-8) and 3 x 10(-8) mol/kg i.p., but CCK-33NS, CCK-8NS and CCK-4 did not. In conclusion, the activities of synthetic human CCK-33 are almost the same as those of CCK-8 on exocrine pancreatic secretion, gastric acid secretion and food intake, but less than CCK-8 on isolated gallbladder contraction.     

Preparation of telechelic oligomers by controlled thermal degradation of isotactic poly(1-butene) and poly(propylene-ran-1-butene)

It was found that telechelic isotactic oligo(1-butene) and telechelic oligo(propylene-ran-1-butene) could be isolated as nonvolatile oligomers from polymer residues resulting from the thermal degradation of isotactic poly(1-butene) and poly(propylene-ran-1-butene), respectively. Their structures were determined by ¹H and ¹³C NMR with attention being paid to their reactive end groups. The maximum average number of terminal vinylidene groups per molecule (f_TVD) was 1.8, indicating that about 80 mol% were α,ω-diene oligomers having two terminal vinylidene groups. This useful new telechelic oligomer had a lower polydispersity than the original polymer, in spite of its lower molecular weight and T_m. The composition of end groups of nonvolatile oligomers obtained by thermal degradation of poly(propylene-ran-1-butene) could be explained by the differences in bond dissociation energy and activation energy of elementary reactions during thermal degradation, based on the monomer composition of the original polymer.     

Kinetics of the γ-radiation-induced polymerization of ethylene in liquid carbon dioxide

The γ-radiation-induced polymerization of ethylene with the use of liquid carbon dioxide as a solvent, was studied from the viewpoint of kinetics. The polymerization was carried out at conversions less than 10% under the pressure ranging from 100 to 400 kg./cm.², dose rates 1.3 × 10⁴?1.6 × 10⁵ rad/hr., and temperatures of 20–90°C. The concentration of carbon dioxide varied up to 84.1 mole-%. The polymerization rate and the polymer molecular weight were observed to increase with reaction time. This observation, however, becomes less pronounced with increasing concentration of carbon dioxide and with rising temperature. The exponents of the pressure and the dose rate were determined to be 2.3 and 0.85 for the rate, and 2.0 and ?0.20 for the molecular weight, respectively. From the kinetic considerations for these results, the effect of carbon dioxide on the initiation and termination reaction in the polymerization was evaluated.     

A spider toxin binding protein from bovine brain: its purification and N-terminal amino acid sequence determination.

A 60kDa spider toxin binding protein from bovine brain was solubilized with digitonin and purified up to 5800-folds over starting crude homogenate. The purification procedure entailed DEAE-cellulose, concanavalin-A affinity, 1-naphthylacetyl spermine affinity and high performance liquid chromatography. The purified protein owned a very high affinity for ligand 125I-JSTX-3 binding Kd 15.6nM and Bmax 6.5nM. The amino acid composition of the protein was determined. The N-terminal amino acid sequence analysis yielded a unique sequence: NH2-X-Pro-X-Val-Tyr-Phe-Lys-Glu-Gln-Phe-Leu-Asp-Gly-Asp-X.     

Short-chain branching in γ-radiation-induced polymerization of ethylene

In an attempt to elucidate the mechanism of chain-branch formation in the polymerization of ethylene, the effect of reaction conditions on short-chain branching in γ-radiationinduced polymerization of ethylene was investigated by using infrared spectroscopy. The concentration of methyl groups, i.e., the frequency of short-chain branching, increases with temperature and pressure and is independent of ethylene conversion to polymer and radiation intensity. The number of methyl groups per polymer molecule increases almost proportionally with the degree of polymerization. These facts indicate that short-chain branching occurs mainly by the mechanism of intramolecular hydrogen transfer. The effect of pressure on the rate of chain branching can be postulated by considering the transition state to be six-membered rings in hydrogen transfer reactions. The activation energy of chain branching is found to exceed that of propagation by 6 kcal./mole.