Addition Of Biphenyl Research Articles

Degradation of polychlorinated biphenyls (PCBs) by four bacterial isolates obtained from the PCB-contaminated soil and PCB-contaminated sediment

We investigated the PCB-degrading abilities of four bacterial strains isolated from long-term PCB-contaminated soil (Alcaligenes xylosoxidans and Pseudomonas stutzeri) and sediments (Ochrobactrum anthropi and Pseudomonas veronii) that were co-metabolically grown on glucose plus biphenyl which is an inducer of the PCB catabolic pathway. The aim of study was to determine the respective contribution of biomass increase and expression of degrading enzymes on the PCB degrading abilities of each isolate. Growth on 5 g l−1 glucose alone resulted in the highest stimulation of the growth of bacterial strains, whereas grown on 10 mg l−1, 100 mg l−1, 1 g l−1, or 5 g l−1 biphenyl did not effected the bacterial growth. None of the strains used in this study was able to grow on PCBs as the sole carbon source. Cells grown on glucose exhibited enhanced degradation ability due to an increased biomass. Addition of biphenyl at concentrations of 1 or 5 g l−1 did not increase total PCB degradation, but stimulated the degradation of highly chlorinated congeners for some of the strains. The degradation of di- and tri-chlorobiphenyls was significantly lower for cells grown on 5 g l−1 biphenyl independently on glucose addition. The highest degradation of the PCBs was obtained for A. xylosoxidans grown in the presence of glucose. Thus A. xylosoxidans appears to be the most promising among the four bacterial isolates for the purpose of bioremediation.

Adaptation mechanisms of bacteria during the degradation of polychlorinated biphenyls in the presence of natural and synthetic terpenes as potential degradation inducers

In this study, we examined the effect of polychlorinated biphenyls (PCBs) in the presence of natural and synthetic terpenes and biphenyl on biomass production, lipid accumulation, and membrane adaptation mechanisms of two PCB-degrading bacterial strains Pseudomonas stutzeri and Burkholderia xenovorans LB400. According to the results obtained, it could be concluded that natural terpenes, mainly those contained in ivy leaves and pine needles, decreased adaptation responses induced by PCBs in these strains. The adaptation processes under investigation included growth inhibition, lipid accumulation, composition of fatty acids, cis/trans isomerization, and membrane saturation. Growth inhibition effect decreased upon addition of these natural compounds to the medium. The amount of unsaturated fatty acids that can lead to elevated membrane fluidity increased in both strains after the addition of the two natural terpene sources. The cells adaptation changes were more prominent in the presence of carvone, limonene, and biphenyl than in the presence of natural terpenes, as indicated by growth inhibition, lipid accumulation, and cis/trans isomerization. Addition of biphenyl and carvone simultaneously with PCBs increased the trans/cis ratio of fatty acids in membrane fractions probably as a result of fluidizing effects of PCBs. This stimulation is more pronounced in the presence of PCBs as a sole carbon source. This suggests that PCBs alone have a stronger effect on bacterial membrane adaptation mechanisms than when added together with biphenyl or natural or synthetic terpenes.

The effect of polychlorinated biphenyls (PCBs) on the membrane lipids of Pseudomonas stutzeri

In this study we examined the effect of polychlorinated biphenyls (PCBs) on biomass production of a PCB-degrading Pseudomonas stutzeri, and on the fatty acid profile of its major membrane lipids. Growth based on biomass weight was stimulated when PCBs were added at the time of inoculation, but PCB addition three days after inoculation led to a significant decrease in biomass. Simultaneous addition of PCBs plus biphenyl or PCBs plus carvone negatively affected P. stutzeri biomass (addition of biphenyl or carvone at the time of inoculation and PCBs to three-day-old culture). In the presence of PCBs alone the amount of the prevalent fatty acids C16:0 and C17-cyclopropyl fatty acid (C17-CP) of P. stutzeri in total and neutral lipids was significantly reduced. When PCBs were added together with carvone (carvone at the time of inoculation and PCBs after three days) a significant reduction of these fatty acids was obtained, but, in addition, oleic, cis-vaccenic, and cyclononadecanic (C19-CP) acids were increased. When PCBs were combined to biphenyl the prevalent fatty acids were reduced and oleic, cis-vaccenic, and cyclononadecanic acids were increased in total and neutral lipids. Addition of 3-chlorobenzoic acid led to a significant growth inhibition and to the production of oleic and cis-vaccenic acids in the membrane fraction phosphatidylcholine.

Characterization of the bottom sediments contaminated with polychlorinated biphenyls: Evaluation of ecotoxicity and biodegradability

At the locality of the former producer of PCBs Chemko Strážske in East Slovakia, a large amount of PCBs (the commercial mixture DELOR 103, an equivalent of AROCLOR 1242) is still persisting in sediments and negatively influences health of the population. The objective of this work was to provide a study of ecotoxicity and genotoxicity of PCBs in contaminated sediments. Toxicity of the PCB-contaminated sediments sampled from Zemplínska šírava and Strážsky canal (surroundings of the former producer of PCBs) was determined applying a standard aquatic plant toxicity test using Lemna minor. The endpoints for the test were frond numbers and frond areas. The sediment sampled from Zemplínska šírava was more toxic to L. minor than the one sampled from Strážsky canal. The results on genotoxicity showed that both sediments were not mutagenic toward the standard strains of the Ames test, Salmonella typhimurium TA98 and TA100. This work deals also with biodegradation of PCBs in two samples of the above mentioned contaminated sediments: a) in the natural sediments by autochthonous microbial consortium and b) in the bioaugmented sediments inoculated by allochthonous bacterial strains, two bacterial isolates from long-term PCB-contaminated soil Pseudomonas stutzeri and Alcaligenes xylosoxidans. Both approaches were applied under the biostimulation conditions, with addition of glucose or biphenyl as co-substrates, as well. The highest PCB degradation was observed in the bioaugmented sediment inoculated with bacterial strain P. stutzeri. Addition of biphenyl, as the co-substrate and the inducer, positively affected degradation of PCBs. The bphA1 gene, encoding enzyme biphenyldioxygenase, responsible for the start of PCB degradation, was identified in genome of P. stutzeri, a potential PCB-degrader isolated from long-term PCB-contaminated soil, but not in genome of A. xylosoxidans.

Reactivity between Biphenyl and Precursor of Solvated Electrons in Tetrahydrofuran Measured by Picosecond Pulse Radiolysis in Near-Ultraviolet, Visible, and Infrared

The initial decrease of solvated electrons in tetrahydrofuran (THF) upon addition of biphenyl was investigated by picosecond pulse radiolysis. Transient absorption spectra derived from the biphenyl radical anion (centered at 408 and 655 nm) and solvated electrons of THF (infrared) were successfully measured in the wavelength region from 400 to 900 nm by the extension of a femtosecond continuum probe light to near-ultraviolet using a second harmonic generation of Ti:sapphire laser and a CaF2 plate. From the analysis of kinetic traces at 1300 nm considering the overlap of primary solvated electrons and partial biphenyl radical anion, C37, which is defined by the solute concentration to reduce the initial yield of solvated electrons to 1/e, was found to be 87 +/- 3 mM. The rate constant of solvated electrons with biphenyl was determined as 5.8 +/- 0.3 x 10(10) M(-1) s(-1). We demonstrate that the kinetic traces at both 408 nm mainly due to biphenyl radical anion and 1300 nm mainly due to solvated electrons are reproduced with high accuracy and consistency by a simple kinetic analysis. Much higher concentrations of biphenyl (up to 2 M) were examined, showing further increase of the initial yield of biphenyl radical anion accompanying a fast decay component. This observation is discussed in terms of geminate ion recombination, scavenging, delayed geminate ion recombination, and direct ionization of biphenyl at high concentration.

PCB-degrading potential of aerobic bacteria enriched from marine sediments

The main objective of this work was to study catabolic potential of marine sediment bacteria in aerobic degradation of polychlorinated biphenyls (PCBs). Marine sediment samples were collected at urban areas of the Croatian Adriatic coast, and microcosm enrichment experiments were performed in seawater mineral salts (SMS) medium with the addition of biphenyl as the only carbon source. After two to four subcultures, all enriched mixed cultures demonstrated the capability to use biphenyl, indicating that biphenyl-utilizing bacteria are widespread in coastal marine sediments. PCB-degrading activity of the enrichment cultures as well as that of their biphenyl-utilizing members were further studied in SMS medium with the addition of PCB mixtures containing di- to heptachlorinated congeners. GC-MS analyses of the extracted cultures suggested that, although they differed in PCB-degrading capabilities, all of the enrichment cultures expressed activity toward at least some of the lower chlorinated congeners (di- to tetrachlorobiphenyls). Biphenyl-utilizing bacteria isolated from the most active PCB-degrading mixed cultures showed little taxonomic diversity (six out of seven isolates belonged to the genus Rhodococcus and one to the genus Sphingomonas). All isolated Rhodococcus strains (R. erythropolis and R. ruber) showed substantial PCB-degrading activity, suggesting that these bacteria might play an important role in aerobic PCB degradation in polluted marine sediment.

Study of the biodegradation process of polychlorinated biphenyls in liquid medium and soil by a new isolated aerobic bacterium ( Janibacter sp.)

We have isolated and characterised a novel aerobic bacterial strain, designated MS3-02, belonging to the genus Janibacter sp. The capability of this new strain to degrade polychlorinated biphenyls (PCBs) in a commercial mixture (Aroclor 1242) in liquid medium and in soil (sterile and non sterile soil), under laboratory scale, has been evaluated. MS3-02 was isolated from the soil around of an incinerator, located in the east of Madrid (Spain). Gas-chromatographic analysis showed that MS3-02 was able to reduce most peaks observed in the chromatogram between 70% and 100% after seven days of incubation in a culture mineral medium containing yeast extract, but without the addition of biphenyl. The presence of biphenyl in the culture medium decreased the rate of PCB degradation by this bacterium. Comparing the performance of the MS3-02 in liquid culture medium and in soil, degradation was less efficient in sterile soil and still less efficient in non sterile soil. Under the best conditions (sterile soil and 20 weeks of incubation) MS3-02 was able to reduce, between 50% and 100%, nine of the main gas-chromatographic peaks in Aroclor 1242.

Metabolism of 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene by Alcaligenes denitrificans

Metabolism of 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE), a persistent metabolite of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT), by an Alcaligenes denitrificans was optimal under `non-shaking' conditions, was accelerated by adding 1 g glucose l−1, and inhibited by 1 g sodium acetate l−1 or 1 g sodium succinate l−1. Addition of biphenyl, in the vapor form, to the reaction mixture did not enhance DDE metabolism. During the reaction, accumulation of conventional metabolites, 1-chloro-2,2-bis(4-chlorophenyl)ethylene (DDMU) and 4-chlorobenzoate, was not observed.

Sequential anaerobic-aerobic biodegradation of PCBs in soil slurry microcosms.

Many industrial locations have identified the need for treatment of polychlorinated biphenyl (PCB) wastes and remediation of PCB-contaminated sites. Biodegradation of PCBs is a potentially effective technology for treatment of PCB-contaminated soils and sludges; however, a practicable remediation technology has not yet been demonstrated. In laboratory experiments, soil slurry microcosms inoculated with microorganisms extracted from PCB-contaminated Hudson River sediments have been used for anaerobic dechlorination of weathered Aroclor 1248 in contaminated soil with a low organic carbon content. Anaerobic incubation was then followed by exposure to air, addition of biphenyl, and inoculation with Pseudomonas sp. LB400, an aerobic PCB degrader. The sequential anaerobic-aerobic treatment constituted an improvement compared to anaerobic or aerobic treatment alone by reducing the total amount of PCBs remaining and decreasing the tendency for end products to accumulate in humans. A 70% reduction of PCBs was observed during sequential treatment with products containing fewer chlorines and having a shorter half-life in humans than the original PCBs. The aerobic treatment alone was also quite effective as a stand-alone treatment reducing the PCBs by 67%. The results represent a case in which anaerobic river sediment organisms have been successfully transferred to a matrix free of river or lake sediments.

The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 10: intramolecular reactions involving alk-4-enols and 1,4-dicyanobenzene

Our study of the photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction has been extended to include alk-4-enols. Irradiation of acetonitrile solutions of the alk-4-enols, 6-methyl-5-hepten-2-ol (16) and 5-methyl-5-hexen-2-ol (17), and the aromatic, 1,4-dicyanobenzene (1), leads to cyclized 1:1 (alk-4-enol:aromatic) adducts. The addition of biphenyl (5) to the irradiation mixture, serving as a codonor, increases the yields and the efficiency of formation of the adducts. The structures assigned to the products trans-2-(isopropyl 4-cyanophenyl)-5-methyltetrahydrofuran (18, 29%) and cis-2-(isopropyl 4-cyanophenyl)-5-methyltetrahydrofuran (19, 24%) from 16 (reaction [5]), and r-2-(methyl 4-cyanophenyl)-2,t-5-dimethyltetrahydrofuran (20, 13%), r-2-(methyl 4-cyanophenyl)-2,c-5-dimethyltetrahydrofuran (21, 7%), r-3-(4-cyanophenyl)-3,t-6-dimethyltetrahydropyran (22, 11%), and r-3-(4-cyanophenyl)-3,c-6-dimethyltetrahydropyran (23, 2%), from 17 (reaction [6]), rests mainly upon analysis of the 1H and 13C nuclear magnetic resonance spectra. The structures of 19, 22, and 23 were firmly established by X-ray crystallography. The observed ratio of regioisomers indicates a strong preference for 1,5-exo-trig, relative to 1,6-endo-trig, cyclization of the intermediate alk-4-enol radical cation. The mechanistic implication of these results is discussed. Keywords: photoinduced electron transfer, radical ions, cyclization of radical cations, intramolecular reactions of radical cations.

The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 8: methanol–2-carene, and 1,4-dicyanobenzene

The structure and reactivity of the radical cation of (+)-2-carene ((1S,6R)-3,7,7-trimethyl-cis-bicyclo[4.1.0]hept-2-ene (3)) have been studied. The radical cation was generated by photoinduced single electron transfer to the first electronically excited singlet state of 1,4-dicyanobenzene in acetonitrile–methanol (3:1). The 1:1:1 (methanol:2-carene:1,4-dicyanobenzene) adducts were formed: trans-3-(4-cyanophenyl)-4-(1-methoxy-1-methylethyl)-1-methylcyclohexene(14), and cis- (15) and trans-3-(4-cyanophenyl)-6-(1-methoxy-1-methylethyl)-3-methylcyclohexene (16) in a combined yield of 80%. The efficiency of the reaction and the yield of products were increased by the addition of biphenyl, serving as a codonor. These photo-NOCAS adducts formally result from cleavage of the three-membered ring of the 2-carene radical cation, at the C1—C7 bond, forming the tertiary carbocation and allylic radical. Reaction of the cation with methanol and coupling of the allylic radical with the 1,4-dicyanobenzene radical anion at the ipso position, followed by loss of cyanide ion, completes the sequence. There was no evidence for cleavage of the C1—C6 bond under these conditions; however, when the irradiation was carried out in acetonitrile (no methanol) the (+)-2-carene was partially racemized. Racemization is indicative of C1—C6 bond cleavage. The results of abinitio molecular orbital calculations (STO-3G) provide insight into the extent of C1—C7 bond cleavage in the radical cation. The calculated spin and charge distribution, on the 2-carene radical cation global minimum (3a+•), is consistent with the observed regiospecificity of adduct formation. Keywords: photoinduced electron transfer, radical ions, molecular orbital calculations, bond cleavage, 2-carene.

Development of field application vectors for bioremediation of soils contaminated with polychlorinated biphenyls

Field application vectors (FAVs), which are a combination of a selective substrate, a host, and a cloning vector, have been developed for the purpose of expressing foreign genes in nonsterile, competitive environments in which the gene products provide no advantage to the host. Such gene products are exemplified by the enzymes for the cometabolism of polychlorinated biphenyls (PCBs) through the biphenyl degradation pathway. Attempts to use highly competent PCB-cometabolizing strains in the environment in the absence of biphenyl have not been successful, while the addition of biphenyl is limited by its human toxicity and low water solubility. Broad-substrate-specificity PCB-degradative genes (bphABC) were cloned from a naturally occurring isolate. Pseudomonas sp. strain ENV307, into broad-host-range plasmid pRK293. The resulting PCB-degrading plasmids were transferred to the FAV host Pseudomonas paucimobilis 1IGP4, which utilizes the nontoxic, water-soluble, nonionic surfactant Igepal CO-720 as a selective growth substrate. Plasmid stability in the recombinant strains was determined in the absence of antibiotic selection. PCB-degrading activity was determined by resting cell assays. Treatment of contaminated soil (10, 100, or 1,000 ppm of Aroclor 1242) by surfactant amendment (1.0% [wt/wt]Igepal CO-720 in wet soil) and inoculation with recombinant isolates of strain 1IGP4 (approximately 4 x 10(6) cells per g of soil) resulted in degradation of many of the individual PCB congeners in the absence of biphenyl.(ABSTRACT TRUNCATED AT 250 WORDS)

The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction (Part 4): methanol–olefins, methyl 4-cyanobenzoate

Dicyanobenzene-1,4 (1) and -1,2 are known to undergo substitution upon irradiation, in the presence of an olefin, in acetonitrile–methanol (3:1) solution. The products are 1:1:1 (methanol:olefin:aromatic) adducts, substituted on the aromatic ring with loss of a cyano group. This reaction, referred to as the photo-NOCAS (nucleophile–olefin combination, aromatic substitution) reaction, has been shown to be fairly general with regard to the olefin and the nucleophile that can be incorporated. Less is known about the scope of the reaction incorporating other electron-withdrawing substituted aromatic molecules. The purpose of this study was to determine if methyl 4-cyanobenzoate (10) would also take part in this reaction, to form 4-substituted aromatic esters. Irradiation of acetonitrile–methanol solutions of 10 and olefins 2,3-dimethyl-2-butene (2) and 1-methylcyclohexene (5) gave cyclic imine esters, 11 and 13, respectively, instead of photo-NOCAS products. The photo-NOCAS products were obtained when the codonor biphenyl (4) was added to the irradiation mixture. Formation of the cyclic imine ester is attributed to excitation of the charge-transfer complex formed between 10 and the olefin. The addition of biphenyl (4) serves to generate the contact radical ion pair (CRIP) upon irradiation of the charge-transfer complex between 10 and 4. This CRIP can dissociate to the solvent-separated radical ions, the radical cation of 4 can accept an electron from the olefin, and the olefin radical cation can go on to give the photo-NOCAS products. Irradiation of a solution of 10 and 2 in nonpolar solvent (benzene) gave the oxetane, believed to arise from the exciplex. In addition to photo-NOCAS products from 10, 4-cyanophenylketones 17 and 23 are also formed by attack of the β-alkoxyalkyl radical at the carboxyl carbonyl. The differences in behaviour between 1,4-dicyanobenzene (1) and methyl 4-cyanobenzoate (10) under these reaction conditions are described and explained.

Kinetics of Biphenyl and Polychlorinated Biphenyl Metabolism in Soil

The metabolism of C-labeled PCBs (polychlorinated biphenyls), which comprised the Aroclor 1242 mixture, was greatly enhanced by the addition of biphenyl (BP) to soil. After 49 days, only 25 to 35% of the original PCBs remained in the soil, and 48 to 49% was converted to CO(2) (including soil carbonates) in treatments enriched with BP; by contrast, 92% of the PCBs remained and less than 2% was converted to CO(2) in the unenriched control. Although the mineralization of PCBs in soils inoculated with Acinetobacter strain P6 was not greater than that in uninoculated BP-enriched soils, the initial and maximum mineralization rates and the disappearance of more highly chlorinated PCBs were greater with Acinetobacter strain P6. The mineralization of BP was consistent with kinetic models based upon linear-no growth and exponential growth; lower cell densities (<10/g) of BP-oxidizing bacteria gave a better fit for exponential growth, whereas the highest cell density (10/g) gave a better fit for linear-no growth. The numbers of BP-oxidizing bacteria declined exponentially upon depletion of the substrate. Since the mineralization of the chlorinated cometabolites was brought about by microorganisms (commensals) other than BP oxidizers, CO(2) production could not be fit to either of the two growth models. However, CO(2) production from the highest-density inoculum could be fit to a first-order (no-growth) sequential-reaction series. Although the population dynamics of the commensals could not be determined, the rate-limiting step in the cometabolic-commensal metabolism of PCBs to CO(2) had to be the initial oxidation, since the rate of CO(2) production was directly related to the population density of BP oxidizers.

Tunneling recombination luminescence of glassy polyethylene adipate γ-irradiated at low temperature and effect of electron scavengers

The isothermal luminescence (ITL) from glassy polyethylene adipate (PEA) γ-irradiated at 77 K was observed over a long period of time, together with effect of the electron scavengers on it. The decay behavior of ITL is similar to that of polyethylene terephthalate or polycrystalline PEA obtained previously, so that the decay obeys the decay function I( t) = I 0/(1 + αt) m . The detailed discussion on the parameters included in the decay function is given. Differences in the parameters between different materials or different physical states are found not to be very large, except the parameter I 0. Addition of biphenyl into PEA enhances considerably the intensity of ITL and causes the luminescence center to exchange from the ester cation into the biphenyl cation. In the biphenyl doped PEA, the possibility of the triplet-triplet energy transfer from the excited ester group to the biphenyl and the positive charge transfer from the ester cation to the biphenyl are shown.

The photochemical preparation of ozonides by electron-transfer photo-oxygenation of epoxides

9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemistry of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis- and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trioxolane. The same stereochemical course is followed for the electron-transfer photo-oxygenation of more easily oxidized 2,3-dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3,5-bis(2'-naphthyl)-1,2,4-trioxolane. The corresponding trans-ozonide was prepared by ozonation of cis-1,2-bis(2'-naphthyl)ethene and stereochemically identified by Chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase. These stereochemical results have been interpreted in terms of a mechanism involving addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides.

Cosensitized electron transfer photo-oxygenation: The photochemical preparation of 1,2,4-trioxolanes, 1,2-dioxolanes and 1,2,4-dioxazolidines

9,10-dicyanoanthracene (DCA) sensitizes the electron transfer photo-oxygenation of epoxides, cyclopropanes and aziridines to yield 1,2,4-trioxolanes (ozonides), 1,2-dioxolanes and 1,2,4-dioxazolidines respectively. The addition of biphenyl (BP) as a cosensitizer can provide significantly enhanced rates of reaction of various substrates. An investigation of the stereochemistry of the photo-oxygenation of epoxides and aziridines has given support to a mechanism involving the addition of singlet oxygen as a dipolarophile to intermediate carbonyl and azomethine ylides. A mechanism for DCABP cosensitization is presented.

Cosensitization by 9,10-dicyanoanthracene and biphenyl of the electron-transfer photooxygenation of 1,1,2,2-tetraphenylcyclopropane

Electron-transfer photooxygenation of 1,1,2,2-tetraphenylcyclopropane with 9,10-dicyanoanthracene in oxygen-saturated acetonitrile yields 1,1,3,3-tetraphenyl-2-propen-1-o1 after reduction of the intermediate hydroperoxide. The rate of reaction is significantly increased by the addition of biphenyl as a cosensitizer.

Thermal and photo‐induced phenomena in γ‐irradiated poly(methyl methacrylate)

AbstractESR spectra and optical absorption spectra of γ‐irradiated poly(methyl methacrylate) (PMMA) at 77°K and the photo‐ and thermal bleaching behavior have been studied. γ‐Irradiation of PMMA yields a singles spectrum with a line width of 6 G which is bleachable with visible light. This species is assigned to the polymer cation. The unbleached species consists mainly of a four‐line spectrum and is assigned to a polymer radical having a different CH2 conformation from the usual nine‐line spectrum. On subsequent warming to room temperature, the spectrum changes into the nine‐line spectrum. γ‐Irradiation of PMMA containing biphenyl as an additive at 77°K gives biphenyl cation. Yield of polymer radical is reduced by the addition of biphenyl and 2‐methyltetrahydrofuran. A mechanism is proposed which is consistent with the experimental results.

Pulse radiolysis of hexamethylphosphoric triamide

The solvation of electrons in pure hexamethylphosphoric triamide (HMPT) has been observed by transient infra-red absorption following pulse radiolysis. Addition of biphenyl (ϕ2) and anthracene (A) provided evidence of scavengeable electrons, the yield corresponding to a G-value of about 2. The relatively high yield and the very low binding energy of solvated electrons in HMPT are ascribed to the polar and aprotic basic nature of this solvent.