Mechanisms of antioxidant action. Effect of the polymer medium on the antioxidant efficiency of the dithiolates

Peroxide decomposing antioxidants (e.g. nickel dithiophosphates and thiophosphoryl disulphides) control hydroperoxide formation during processing and on exposure to light. However, these additives are more efficient u.v. stabilizers in polypropylene (PP) than in low density polyethylene (LDPE). It is suggested that this difference results from the more rapid formation of hydroperoxides in the more oxidisable substrate under normal processing conditions. In contrast, nickel xanthates are completely destroyed in PP under the same processing conditions and the transformation products obtained in this case are less effective u.v. stabilizers than the original xanthates. Nickel dialkyl dithiophosphates stabilise both LDPE and PP very effectively, while nickel alkyl xanthates are much less effective u.v. stabilisers in both matrices. However, the difference between the efficiencies of the two dithiolates is much less in the case of LDPE. The nickel dithiophosphates and xanthates effectively synergise with the commercial u.v. absorber Cyasorb u.v. 531 (HOBP) but they show antagonism towards a typical chain breaking antioxidant, Irganox 1076, during u.v. exposure. They are however synergists under thermal oxidative conditions.     

The effect of processing on the light stability of stabilized and unstabilized polyethylene

It is shown that antioxidants previously reported to be u.v. stabilizers can be distinguished by their mode of action into two categories. These are melt stabilizers, which destroy hydroperoxides during the processing operation, and u.v. stabilizers, which have the additional ability to destroy hydroperoxides during u.v. exposure. The interdependence of the chemical changes occurring during processing and on u.v. exposure are demonstrated.     

THE EFFECTS OF HOST-CELL REACTIVATION ON ASSAY OF U.V.-IRRADIATED HAEMOPHILUS INFLUENZAE TRANSFORMING DNA

Abstract— The host cell reactivation (HCR) mechanism in Haemophilus influenzae cells is inhibited by sub-microgram concentrations of acriflavine (as is already known to be true for Escherichia coli ). Exposure of these cells to similar concentrations of the drug during bacterial transformation increases the apparent ultraviolet light (u.v.) sensitivity of previously irradiated transforming DNA, indicating a repair of this DNA after uptake by the cells under normal conditions. Repair is inhibited by applying acriflavine at any time up to one hour after competent cells contact the irradiated transforming DNA. The fraction of the u.v. damage repaired by HCR is very different for different genetic markers. Those markers which are most u.v. sensitive when assayed in the absence of acriflavine are most poorly repaired, suggesting that this is the reason for their higher sensitivity. For all markers the fraction of the damage repairable by in vitro photoreactivation is approximately constant, and strongly overlaps the damage repairable by HCR. The degree of HCR achieved can be altered by experimental treatment of the H. influenzae DNA prior to transformation. Thus treatment of irradiated DNA with an enzyme from Micrococcus lysodeikticus –known to attack u.v. damaged, but not undamaged DNA–prevents subsequent intracellular repair of the same u.v. lesions whose repair is inhibited by acriflavine. Similarly, partial replacement of the thymine in transforming DNA by 5-bromouracil (BU) strongly inhibits repair of subsequent u.v. damage. As in bacteriophage, the BU effect is relieved if the u.v. exposure occurs in the presence of cysteamine. It is clear that intracellular repair must be considered in interpreting experiments with u.v.-irradiated transforming DNA.     

Poly-α-methyleneglutaronitrile. Characteristic features of some anionic polymers

For (initiator)/(monomer) ratios exceeding 10^-3, the anionic polymerization of α-methyleneglutaronitrile in homogeneous solution in DMF (initiated by lithium-naphthalene at -35° or by diphenylmethyl-lithium at -70°) leads to fairly white polymers with yields higher than 75 per cent. Infra-red and u.v. spectrometric studies and flash pyrolysis experiments show that the nitrile functions are involved in the polymerization only to a very small extent. On the other hand, molecular weight and sedimentation measurements and hydrodynamic behaviour of the polymer in DMF solution suggest a broad polydispersity for the samples, and a very high branching density for their higher molecular weight fractions. These characteristic features are to be correlated with those of anionic polyacrylonitrile; they may be tentatively attributed to transfer to polymer at the acidic methylene group a to the nitrile function.     

超高效液相色谱/静电场轨道阱高分辨质谱法同时测定塑料食品接触材料中光稳定剂和抗氧化剂的特定迁移量

建立了超高效液相色谱/静电场轨道阱高分辨质谱同时测定塑料食品接触材料中多种光稳定剂和抗氧化剂特定迁移量的方法。采用30 g/L乙酸、体积分数分别为10%、20%、50%的乙醇和油类模拟物(异辛烷)这5种食品模拟物对塑料食品接触材料进行处理,对处理液进行超高效液相色谱/静电场轨道阱高分辨质谱分析,外标法定量。该方法测定的40种目标化合物在相应的范围内均具有良好的线性关系,相关系数均大于0.998,定量限为0.01~1.00μg/L。考察了上述5种食品模拟物中光稳定剂和抗氧化剂的特定迁移量,平均加标回收率为81.46%~94.53%,相对标准偏差为3.25%~9.99%。应用该方法对市售塑料食品接触材料进行了测定,结果在部分样品中检出了不同含量的光稳定剂和抗氧化剂。该方法灵敏度高,定量限低,满足塑料食品接触材料中光稳定剂和抗氧化剂特定迁移量的检测要求。     

DECREASED SURVIVAL RESULTING FROM LIQUID-HOLDING OF U.V.-IRRADIATED ESCHERICHIA COLI C AND SCHZZOSACCHAROMYCES POMBE

Abstract— Ultraviolet-irradiated cells of E. coli C and of haploid wild type yeast Schizosac-charomyces pombe , held in buffer at 22°-25°C for various periods of time prior to plating, show a lower survival than those plated immediately after irradiation. This 'negative liquid-holding effect' (NLHE) contrasts 'liquid-holding recovery' (LHR), found in a number of other E. coli strains and in Saccharomyces cerevisiae . NLHE was observed at all u.v. doses tested. The effect is maximal at holding temperatures in the range 25–30°C, it is very small at 5°C and (in E. coli C) at 44°C. NLHE and LHR resemble each other in several respects. In E. coli both effects are inhibitable by the dark repair inhibitors acriflavine, caffeine and potassium cyanide. They do not occur in nutrient broth, and they are much reduced if the irradiated cells were illuminated with photoreactivating light before holding. NLHE in S. pombe shows characteristics similar to those observed in E. coli C . Mutations leading to increased u.v. sensitivity in E. coli C and S. pombe can alter the liquid-holding response so that LHR is observed. Tetrad analysis of crosses between u.v.-sensitive and u.v.-resistant S. pombe strains indicates that a single chromosome region can control both u.v. sensitivity and liquid-holding response. Several possibilities explaining NLHE are discussed. From current knowledge about dark repair processes and from the similarities between NLHE and LHR in E. coli it seems likely that the two effects reflect slight changes in the efficiency of dark repair.     

Mechanisms of antioxidant action: Antioxidant behaviour of nickel complex u.v. stabilisers

The antioxidant mechanisms involved in the u.v. stabilising activity of two nickel complexes, nickel dibutyl dithiocarbamate (NiDBC) and nickel acetophenone oxime (NiOx), have been investigated both by oxygen absorption measurements and in peroxide decomposition studies. NiDBC gives rise to a powerful catalyst for non-radical hydroperoxide decomposition; the rate of the reaction is faster in the presence than in the absence of light although the overall mechanisms appear to be very similar. NiOx is decomposed by hydroperoxides in a series of stoichiometric reactions which involve the consumption of at least six molecules of hydroperoxide per molecule of NiOx. Again the reaction is catalysed by light but the mechanism, which does not involve free-radical formation, is the same in the presence and absence of light. NiOx also appears to have weak radical trapping properties. Attempts to show that NiDBC and NiOx might interact sacrificially with photo-excited states of molecules (triplet carbonyl and singlet oxygen) were unsuccessful; the rates of photo-destruction of both complexes were unaffected by the presence of ketones both in the presence and absence of oxygen. This work confirms earlier conclusions that the nickel complex u.v. stabilisers function by auto-synergistic mechanisms involving u.v. screening and conventional chain-breaking and preventive antioxidant processes which operate during thermal processing operations as well as during environmental exposure. Although excited state quenching processes may occur, they appear to be less important in the overall scheme than the well established antioxidant mechanism.     

PHOTOREVERSION VON VIER GRUPPEN UV-INDUZIERTER MUTATIONEN ZUR GIFTRESISTENZ IM NICHTPHOTOREAKTIVIERBAREN E. COLI

Abstract— In the non-photoreaclivable bacterial strain E. coli B/phr^-/MC2 the photoreversion of four groups of u.v.-induced mutations were investigated. They lead to resistance to Chloramphenicol (2 mg/l; "C"), Penicillin (13 or 16 mg/l; "P13" and "P16") or Streptomycin (3 mg/l; "S"). The u.v.-dose curve is concave for the C-mutations (two to three hits), about linear for P13 and S, and they reach peaks and decrease at high u.v.-doses. Though no photoreactivation of killing (PR) is present there is photoreversion of all four types of mutations (PRM). At u.v.-doses below the peaks in average about 43 per cent mutations are photoreversible. At high u.v.-doses the curves with light-post treatment (L) cross the darkcurves (D). In the photoreactivable strain B/r (by the spontaneous mutation MC2 to Mitomycin-resistance strain B/phr^- was made about as u.v.-resistant as B/r is) the photoreversion of the mutation groups C, P13 and P16 (S was not investigated here) was much higher, in average about 77 per cent at low doses. It is assumed that the difference in PRM of about 34 per cent between both strains is due to a PRM-mechanism present in B/r but not in B/phr^-/MC2; this mechanism may be the photoreactivating enzyme that opens thymine-dimers. The PRM in B/phr-/MC2 must then be due to a second mechanism which is probably not the dimer opening enzyme. It may be the same mechanism as in the case of mutations of phage kappa which are induced by u.v. and reversed partially by light, both extra cellularly. The premutations giving this second type of PRM may perhaps be cytosine-hydrate in the DNA. Tn average about 23 per cent mutations of B/r are photostable. Since this ratio decreases with low u.v.-doses in the C-mutations and increases in P13 and in P16 probably two types of photostable premutations seem to exist.     

Liquid-holding effects in U.V.-irradiated phage T3

Abstract— Holding complexes of u.v.-irradiated (254 nm) T3 phage in E. coli B/r cells for several hours at 37°C in buffer, or broth with chloramphenicol, affects the phage survival in at least two different ways: (1) by enhancing excision repair, resulting under certain conditions in liquid-holding recovery (LHR), and (2) by destroying the phage (holding inactivation). LHR is most apparent in buffer containing 20 μg ml^-1 chloramphenicol (CAP). It is expressed by as much as a 10–fold increase in the fraction of complexes that display host-cell reactivation (resulting from excision repair), but the percentage of u.v. lesions repaired within repair-proficient complexes is slightly decreased. LHR is not observed if T3 infects the repair-deficient strain B_s-1. Holding inactivation is readily observed with unirradiated phage complexes in broth containing CAP. The response of irradiated-phage complexes to liquid-holding conditions is more complex: holding inactivation is less effective for irradiated than for unirradiated phage DNA (i.e. the irradiated DNA is to some extent ‘protected’), and processes leading to LHR are superimposed. Thus under certain holding conditions one observes the paradoxical phenomenon that the viable titer of irradiated phage is several times higher than that of unirradiated phage. The nature of holding inactivation is not known, nor is the mechanism by which irradiated DNA is partially protected against it. Holding inactivation does not require protein synthesis; it is rather enhanced at high CAP concentration and seems to be favored by otherwise active cell metabolism. At high CAP concentrations (200–400 μg ml^-1, as compared to 20 μg ml^-1) irradiated-phage complexes show neither LHR nor protection against holding inactivation. Likewise they fail to undergo some step by which the phage DNA becomes insensitive to repair inhibition by caffeine.     

The chemical and physical changes occurring during U.V. degradation of high impact polystyrene

Dynamic-mechanical measurements, i.r. spectroscopy and oxygen absorption techniques have been used to study structural changes in high impact polystyrene during its photo-oxidation under artificial weathering conditions. It was found, using a viscoelastometric technique, that the damping peak at ?80° (corresponding to the β-transition temperature of polybutadiene) disappeared completely after irradiation for 14 hr; this was accompanied by a sharp increase in the complex modulus at 20°. A parallel change was observed in the rate of formation of carbonyl and hydroxyl groups as measured by i.r. spectroscopy. The results indicate that the polybutadiene part of the resin is selectively attacked by u.v. light during the initial stages of the process. Similar results have been reported for ABS [1].     

MISCHKLONE U.V.-INDUZIERTER MUTANTEN BEIM PHAGEN KAPPA

Abstract— Clear-plaque mutations of phage k of Serratia are induced by extracellular u.v.-irradiation in a 2–hit process. The 2–hit-nature cannot be due to induction of one hit in each of the two DNA-strands since replating the contents of 97 wildtype plaques of u.v.-survivors (u.v.-dose 4.5 min) revealed only 1 case of heterozygosity; at least 20 cases would have been expected if phage with 1–hit-mutations formed phages looking like wildtype. On the other hand, only 1 case of heterozygosity was observed among replatings of 94 c -mutants induced by the u.v.-dose 4.5 min (survival 10^-3); most of the plaques contained pure c -type. The pure c -mutant clones are very probably due to 'recessive' lethal lesions in the nonpremutated DNA-strand. This is indicated by the dose dependence of the frequency of heterozygotes; at a dose of 3 min u.v. (survival 1.2 × 10^--²) 9 heterozygotes were observed among 95 mutants tested. From these numbers the rate of induction by u.v. of the recessive lesions's can be calculated. The data at the higher dose are in satisfactory agreement with the calculated rate. Also other types of plaque mutations (e, t, b ) showed heterozygosity. Two cases of abnormal heterozygosity were observed; one contained 2 stable mutant types ( c and b ), another one wildtype, c -tm and l -type.     

Determination of the Vapor Pressure Curve of a Liquid in the Presence of a Nonvolatile Solute

We present a modification of the data analysis for the classical physical chemistry experiment Determination of Enthalpy of Vaporization by the Boiling-Point Method. The vapor pressures of solutions of both ionic and molecular compounds are determined at different temperatures. In this experiment we show that the enthalpy of vaporization change is dependent on the type and amount of nonvolatile solute present. Sets of data collected for different concentrations of sodium chloride, urea, and sucrose solutions are analyzed in order to determine H_vap and S_vap for pure water and for solutions of ionic and molecular solutes.Students perform the data analysis taking into consideration the activity coefficient for the solution and the mole fraction of the solvent. Simultaneous data analysis is introduced and results are used to explain the meaning of the physical parameters determined using this method of data analysis.     

Tailored side‐chain architecture of benzil voltage stabilizers for enhanced dielectric strength of cross‐linked polyethylene

The synthesis and physico‐chemical properties of seven benzil‐type voltage stabilizers are reported. The benzil core is substituted with alkyl chains of different length that are linked to the benzil core via an ester, ether, or tertiary amine group. All additives can be melt‐processed with low‐density polyethylene (LDPE). Fourier‐transform infrared spectroscopy confirms that benzil compounds are not affected by the LDPE cross‐linking reaction induced by dicumyl peroxide. Moreover, a combination of gel content measurements, thermal analysis, and small‐angle X‐ray scattering indicates that the presence of benzil voltage stabilizers does not significantly alter the microstructure of cross‐linked polyethylene (XLPE). Electrical tree inhibition experiments under high‐voltage alternating current conditions show that all investigated additives substantially enhance the dielectric strength of the insulating material at a concentration of only 10 mmol kg^?1. The highest improvement in dielectric strength, of more than 70% with respect to reference XLPE, is obtained with voltage stabilizers, which carry short (methyl) side chains that are linked to the benzil core via an ester or tertiary amine group. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1047–1054     

Intracule functional models. Part III. The dot intracule and its Fourier transform

The dot intracule D(x) of a system gives the Wigner quasi-probability of finding two of its electrons with u.v = x, where u and v are the interelectronic distance vectors in position and momentum space, respectively. In this paper, we discuss D(x) and show that its Fourier transform d(k) can be obtained in closed form for any system whose wavefunction is expanded in a Gaussian basis set. We then invoke Parseval's theorem to transform our intracule-based correlation energy method into a d(k)-based model that requires, at most, a one-dimensional quadrature.     

Photoreactivation of killing in Streptomyces. 3. Action spectra for photolysis of pyrimidine dimers and adducts in S. griseus and S. griseus PHR-1

Abstract— Photolysis of tritium-labelled thymine-derived photoproducts by 254-nm ultraviolet radiation (u.v.) in conidia of Streptomyces griseus was measured by chromatography of cell hydrolysates. The relative photolysis cross-sections of uracilthymine dimer (UT○) at various wavelengths are the same as those of thymine-thymine dimer (TT○), and their ratios at 313, 365, 405 and 436 nm are 2:1:2:3. Except at 436 nm, these relative values agree very well with cross-sections previously reported for photoreactivation of u.v. killing in this organism, leading to the conclusion that photoreactivation in the wild type is due to repair of cyclobutane-type pyrimidine dimers. In a mutant showing restricted photoreactivation (S. griseus PHR-1), post-u.v. treatments at the above wavelengths did not affect UT○ and TT○ in the conidia, supporting the earlier suggestion that this organism does not contain active PR enzyme. Another u.v. photoproduct, the precursor of a pyrimidine adduct (PO-T) that appears in cell hydrolysates, was removed from both wild-type and mutant cells very efficiently at 313 nm. This is presumably a direct photochemical reaction. In addition, in wild-type cells, the precursor of PO-T appeared to be inefficiently removed photoenzymatically at all wavelengths. Removal of the precursor of PO-T appears to be biologically significant, however, only in the mutant.     

Photoreactivation of killing in Streptomyces. II. Kinetics of formation and photolysis of pyrimidine dimers and adducts in S. coelicolor and S. griseus PHR-1

Abstract— A pyrimidine adduct, 6-4‘-[pyrimidine-2’-one] thymine (PO-T)?, observed in DNA hydrolysates of 254-nm ultraviolet (u.v.) irradiated conidia of Streptomyces coelicolor, increases linearly with u.v. dose up to 2 × 10⁵ ergs/mm². Yields of thymine dimer (T○) and uracil-thymine dimer (U○) level off at much lower doses. Initial relative rates of formation of these u.v. photoproducts are: 1:1.3:4.8 for PO-T, T○ and U○, respectively. Similar results were obtained with a Streptomyces griseus mutant, PHR-1. An equation is derived to estimate the ratio of the amount of PO-T to the total amount of thymine-derived photoproducts at low (biological) u.v. doses. The observed PO-T fractions compare well with the calculated values. Rapid photolysis of the precursor of PO-T was observed by post-u. v. treatment at 313 nm of conidia of S. coelicolor and of S. griseus PHR-1. The photolysis was much slower at 365 nm and did not occur at all at 405 nm. Pyrimidine dimers were not appreciably affected by post-u. v. treatment at the above wavelengths in these Streptomyces strains. Both of these strains are phenotypically photoreactivation-deficient, and the present results indicate that they do not possess active photoreactivating enzyme. In earlier papers[3,4,5], the pyrimidine adduct found in acid hydrolysates of DNA was loosely referred to as “uracil-thymine adduct (U-T adduct)”. Such terminology is not strictly correct. The pyrimidine adduct in acid hydrolysates is PO-T (sometimes called P₂B), which could theoretically result from removal of ammonia from a C-T adduct or removal of water from a U-T adduct (see [6]).     

RED LIGHT INTERACTIONS WITH BLUE AND ULTRAVIOLET LIGHT IN POLAROTROPISM OF GERMLINGS OF A FERN AND A LIVERWORT

Abstract— In polarotropism of the chloronema of the fern Dryopteris filix-mas (L.) Schott and of the germ tube of the liverwort Sphaerocarpos donnellii Aust. a phytochrome action in blue and u.v. was presumed[1, 2]. In the present paper this assumption was tested by simultaneously irradiating with red and blue, and red and near u.v. Red energy is given to shift the phytochrome photoequilibrium in favour of high P _fr/ P ^total concentrations. The data obtained by simultaneous irradiation are consistent with the predictions made under the assumption of a phytochrome involvement in the blue- and u.v.-mediated polarotropic response.     

U.V. INDUCED CONFORMATIONAL CHANGES IN TRANSFER RNA

Abstract— The quantum yields for the u.v. inactivation of the amino acid acceptor function of E. coli transfer RNA (for val, phe and lys) and for the loss of its conformation, as a function of exposure, have been determined following irradiation at 280, 265 and 254 nm. Our results suggest that u.v. damage produces a change in the conformation of transfer RNA which in turn inactivates it, and that the anticodon is not the u.v. sensitive site. Calculations indicate that a small number of photoproducts inactivate the transfer RNA.     

Diffusion mechanism of the synergism of u.v.-absorbers and antioxidants

The mechanism of synergism in mixtures of u.v.-absorbers with antioxidants is considered. The synergism is attributed to diffusion of the antioxidant from the deeper-lying layers of polymer film, protected from the action of light by a u.v.-absorber, towards surface layers where the photoreaction takes place. The effect of the antioxidant diffusion process on the duration of the induction period of the unbranched chain oxidation reaction of the polymer is analysed. The experimental investigation of the polybutadiene photo-oxidation process has verified the diffusion mechanism so allowing finding of the optimum relationship between the concentrations of u.v.-absorber and antioxidant and explanation of the observed enhancement of the effect of synergism in thicker polymeric films, for higher antioxidant diffusion coefficients and lower light intensities.     

Experimental study of a d.c. oxygen glow discharge by V.U.V. absorption spectroscopy

Vacuum ultraviolet absorption spectroscopy has been used to measure the concentration of oxygen molecules O₂(³), metastable singlet O₂(¹) molecules, atoms, and ozone in a d.c. glow discharge. The axial electric field, the electronic density, and the gas temperature are also determined. This set of measurements is presented for the positive column of a glow discharge created in a 1.6-cm-diameter Pyrex tube, for a pressure between 0.2 and 5 Torr and a d.c. current up to 80 mA.