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The mechanisms of the sulphur-only and catalytic vulcanization of polybutadiene: An EPR and DFT study. Eur Polym J 2015. [DOI: 10.1016/j.eurpolymj.2014.11.012] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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2
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Reaction Mechanisms in Irradiated, Precipitated, and Mesoporous Silica. J Phys Chem A 2013; 117:3304-18. [DOI: 10.1021/jp310683e] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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3
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Mechanical degradation of elastomers in the presence of silica and inhibitors using a new design of mechano reactor. Polym Degrad Stab 2013. [DOI: 10.1016/j.polymdegradstab.2012.08.026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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4
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The origin of the radiobiological damage in cells stored in cryostatic conditions. Radiat Phys Chem Oxf Engl 1993 2012. [DOI: 10.1016/j.radphyschem.2011.12.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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6
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7
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γ-Radiation Induced Functional Modification of Silica and Radiation Vulcanization of SBR-Silica Composites. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/masy.201150312] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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8
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Detailed analytical study of radiolysis products of simple organic compounds as a methodological approach to investigate prebiotic chemistry—Part 2. Radiat Phys Chem Oxf Engl 1993 2011. [DOI: 10.1016/j.radphyschem.2010.09.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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9
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Detailed analytical study of radiolysis products of simple organic compounds as a methodological approach to investigate prebiotic chemistry—Part 1. Radiat Phys Chem Oxf Engl 1993 2011. [DOI: 10.1016/j.radphyschem.2010.09.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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10
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Synthesis of spin labelled silica and EPR molecular dynamics study at silica-polymer interfaces. J PHYS ORG CHEM 2011. [DOI: 10.1002/poc.1826] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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gamma-irradiation of PEGd,lPLA and PEG-PLGA multiblock copolymers: II. effect of oxygen and EPR investigation. AAPS PharmSciTech 2008; 9:1110-8. [PMID: 18987978 DOI: 10.1208/s12249-008-9150-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2008] [Accepted: 09/25/2008] [Indexed: 11/30/2022] Open
Abstract
The purpose of this research was to evaluate how the presence of oxygen can affect irradiation-induced degradation reactions of PEGd,lPLA and PEG-PLGA multiblock copolymers submitted to gamma irradiation and to investigate the radiolytic behavior of the polymers. PEGd,lPLA, PEG-PLGA, PLA, and PLGA were irradiated by using a (60)Co irradiation source in air and under vacuum at 25 kGy total dose. Mw and Mn were evaluated by gel permeation chromatography. The stability study was carried out on three samples sets: (a) polymer samples irradiated and stored in air, (b) polymer samples irradiated and stored under vacuum, and (c) polymer samples irradiated under vacuum and stored in air. The thermal and radiolytic behavior was investigated by differential scanning calorimetry and electron paramagnetic resonance (EPR), respectively. Samples irradiated in air showed remarkable Mw and Mn reduction and Tg value reduction due to radiation-induced chain scission reactions. Higher stability was observed for samples irradiated and stored under vacuum. EPR spectra showed that the presence of PEG units in multiblock copolymer chains leads to: (a) decrease of the radiolytic yield of radicals and (b) decrease of the radical trapping efficiency and faster radical decay rates. It can be concluded that the presence of oxygen during the irradiation process and the storage phase significantly increases the entity of irradiation-induced damage.
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EPR investigation on radiation-induced graft copolymerization of styrene onto polyethylene: Energy transfer effects. Radiat Phys Chem Oxf Engl 1993 2007. [DOI: 10.1016/j.radphyschem.2007.02.032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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17
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Polymers-gamma ray interaction. Effects of gamma irradiation on modified release drug delivery systems for oral administration. Int J Pharm 2004; 269:343-51. [PMID: 14706246 DOI: 10.1016/j.ijpharm.2003.09.027] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The aim of this work is to verify the efficiency of two kinds of matrix tablets formulations containing PEO or PVA as retarding polymer. Moreover, since in the last years the exposure to ionizing radiation is a more and more used method to reduce bacterial charge in pharmaceutical products, the effects of gamma irradiation on these two kinds of polymers has been evaluated. The study is performed on matrix tablets containing diltiazem HCl, as model drug, and polyethylene oxides (PEO) of two different molecular weights or polyvinylalchool (PVA) of medium degree of hydrolysis, as drug release modulators. Dissolution of the matrices, release of diltiazem and morphological behaviour of the samples, before and after exposure to increasing doses of gamma irradiation, are investigated in order to verify their stability. The results show that the ionizing radiation does not modify significantly the dissolution trend of the PVA samples; on the contrary, the dissolution and the morphological behaviour of the PEO matrices is strongly affected by the radiation dose received. In particular, the dissolution rate of the irradiated PEO tablets dramatically increases as a function of the irradiation dose and the swelling process, which characterised the non-irradiated PEO samples, was replaced by a rapid erosion process responsible for the quickly dissolution of the matrices. The changes of the dissolution and morphological PEO tablets performances could be explained by a breaking of the polymeric chains (shown by EPR studies) as a consequence of the exposure to gamma rays. These chemical-structural modifications of the polymers are responsible for the reduced efficacy of the PEO systems in controlling the drug release rate.
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19
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The radiation chemistry of acyclic hydrofluoro and perhalogenated ether and hydrocarbon compounds. J Fluor Chem 2003. [DOI: 10.1016/s0022-1139(03)00008-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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20
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Radiation-induced free radical reactions in polymer/drug systems for controlled release: an EPR investigation. Radiat Phys Chem Oxf Engl 1993 2003. [DOI: 10.1016/s0969-806x(02)00404-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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21
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Chemical and physical stability of hydroxypropylmethylcellulose matrices containing diltiazem hydrochloride after gamma irradiation. J Pharm Sci 2003; 92:131-41. [PMID: 12486689 DOI: 10.1002/jps.10271] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In recent years, the exposure to gamma-radiation is an increasingly used method to sterilize or to reduce bacterial charge in drug-delivery devices. The aim of this study was to investigate whether the ionizing radiation may be responsible for drug inactivation or for the alteration of the functional excipient used to modulate drug release from a controlled-release delivery system. In this work, we investigated the physical and dissolution stability of prolonged release matrix tablets containing diltiazem hydrochloride, as a model drug, and hydroxypropylmethylcellulose (HPMC) of two different viscosity grades, as the retarding polymer, before and after exposure to increasing doses of gamma-rays. The results show that gamma-irradiation induces chemical modifications in the structure of the active agent, and also of the hydrophilic polymer. The electronic paramagnetic resonance analysis of gamma-irradiated diltiazem has afforded evidence of carbon radicals stemming from C-H bond ruptures and sulphur radicals, the latter being formed mainly after admission of air at room temperature. The major radical products in the HPMC polymer radiolysis have been reckoned with chain scission events in agreement with the results of viscosity measurements that show a progressive decrease of the average molecular weight with increasing the radiation dose. The elaboration of the viscosity data has led to linear relationships between the eta(o)/eta ratio and the radiation dose D which were rationalized with the following equation under the assumption of a Mark-Houwink Sakurada coefficient a approximately equal 1: eta(o)/eta = (1 + uy(o) D)(a). In this equation, D is gamma-radiation dose, eta(o) and eta are the reduced viscosities before and after the irradiation respectively, u is the number average degree of polymerization, and y(o) is the chain scission radiolytic yield. From the linear relationships G(chain scissions) = 1.2 x 10(-6) and 1.4 x 10(-6) moles/J have been obtained for the two HPMC polymer samples M100 and M4 of different molecular weight used in the experiments. These changes could be responsible for the alteration of the drug-release mechanism and reduced polymer efficacy in controlling drug release.
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Gamma irradiation effects and EPR investigation on poly(lactide-co-glycolide) microspheres containing bupivacaine. FARMACO (SOCIETA CHIMICA ITALIANA : 1989) 2002; 57:427-33. [PMID: 12088056 DOI: 10.1016/s0014-827x(02)01220-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effects of gamma radiation on the stability of microspheres made of a polylactide-co-glycolide 50:50 copolymer (PLGA) and loaded with 40% bupivacaine (BU) were studied. The radiolysis mechanisms of BU and BU-loaded microspheres were investigated by using electronic paramagnetic resonance (EPR) analysis. Microspheres were prepared by means of a spray drying method. Gamma Irradiation was carried out in the open, at the dose of 25 kGy, by using a 60Co source. The stability of BU-loaded microspheres was evaluated over a 1-year period on the basis of drug content and dissolution profile. Non-irradiated microspheres were stable over the whole period under consideration. Immediately after irradiation the amount of BU released after 24 h from irradiated microspheres increased from 17 to 25%; in the following 3 months of storage it increased to about 35%, and then it kept constant for 1 year. Radicals generated by BU irradiation were identified by EPR analysis; the sensitivity to gamma radiation of BU was about four times lower than that of PLGA. Furthermore, the EPR spectra of loaded microspheres showed that the relative abundance of BU radicals plus PLGA radicals was proportionate to the electronic fractions of the components; this implies that no spin transfer BU/PLGA had occurred during gamma irradiation.
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First electron spin resonance identification of a nitrogen peroxy radical as intermediate in the photooxidation of 2,2,6,6-tetramethylpiperidine derivatives. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j150650a034] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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24
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Electron spin resonance study of transient radicals in .gamma.-irradiated organic inclusion compounds. II. Palmitic acid urea clathrate. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100649a032] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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25
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ESR of intermediate radicals in thermolysis mechanisms: peroxidic perfluoro polyethers. J Am Chem Soc 2002. [DOI: 10.1021/ja00327a017] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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26
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EPR spin labelling studies of molecular dynamics in elastomer-silica composites. RESEARCH ON CHEMICAL INTERMEDIATES 2002. [DOI: 10.1163/156856702320267109] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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27
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EPR evidence of a triplet biradical in the photolysis of nifedipine. RESEARCH ON CHEMICAL INTERMEDIATES 2002. [DOI: 10.1163/156856702320267136] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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28
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The mechanism of action of crosslinking additives in polyethylene vulcanisation: an EPR investigation. RESEARCH ON CHEMICAL INTERMEDIATES 2002. [DOI: 10.1163/156856702320267037] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Gamma irradiation effects on stability of poly(lactide-co-glycolide) microspheres containing clonazepam. J Control Release 2001; 75:317-30. [PMID: 11489319 DOI: 10.1016/s0168-3659(01)00401-1] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
This work was aimed at evaluating the effects of gamma irradiation on the stability of microspheres made of a poly(lactide-co-glycolide) copolymer (PLGA) and loaded with 15% w/w of clonazepam (CLO). The influence of CLO on PLGA radiolysis mechanisms and the identification of possible irradiation markers were also investigated. Microspheres were prepared by means of a spray-drying method. gamma Irradiation was carried out either under vacuum or in air, at a dose of 25 kGy, by using a 60Co source. The stability of CLO loaded microspheres was evaluated over a 6-month period on the basis of drug content and dissolution profile. Radiolysis mechanisms were investigated by using electronic paramagnetic resonance (EPR) analysis. The microspheres irradiated under vacuum were stable over the considered period of time. After irradiation in air, CLO release rate increased by approximately 10%, and did not change further in the following period of storage. The EPR analysis showed some radicals arising from both the polymeric matrix and the active ingredient. Polymer/CLO spin transfer reactions suggest that CLO had a radio-stabilising effect on the polymeric matrix. In the loaded microspheres, the intensity in time of the CLO radical signal is sufficient for its possible use as irradiation marker.
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ESR study of the effects of a charge scavenger on the radiolysis of isotactic polypropylene. Radiat Phys Chem Oxf Engl 1993 1999. [DOI: 10.1016/s0969-806x(98)00242-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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33
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Excitation versus ionic mechanism in the solid state radiolysis of poly(perfluoroethers). Radiat Phys Chem Oxf Engl 1993 1999. [DOI: 10.1016/s0969-806x(98)00237-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Abstract
Gamma radiation treatment plays an increasingly important role in the sterilization/sanitization of pharmaceutical products. However, irradiation may affect the stability of the product and thus its safety of use. We investigated the influence of ionizing radiation on modified release microparticulate drug delivery systems made of two types of polylactide-co-glycolide copolymers (PLG): RG 503 and RG 503H; these polymers have identical molecular weights but different chemical structures. The effect of gamma radiation on polymer stability of the raw polymers (P) and related microspheres (Ms) was evaluated. Samples were irradiated at different irradiation doses (5, 15 and 25 kGy) using 60Co as radiation source. The microspheres were prepared using the spray drying technique. Degradation of PLG and related microspheres was evaluated during six months in terms of average molecular weight (Mw) loss by gel permeation chromatography (GPC) and variation in glass transition temperature (Tg) using differential calorimetry (DSC). The presence of free radicals in the product was tested by electron paramagnetic resonance (EPR). Both P and Ms showed a trend in decreasing their Mw at time 0 as a function of irradiation dose. For RG503 the decay in Mw is always negligible for doses below 15 kGy while it is about 10% for 25 kGy. After 150 days Mw decay was 25% in the microspheres and 20% in the raw polymer. It was not possible to evaluate the radiation effect, at different storage times, for RG503H because this polymer resulted to be unstable even in the regular storage conditions without being irradiated. The concentration of radiation-induced free radicals was higher in RG 503H (both P and Ms) and they were more stable than the free radicals species observed in the case of polymer RG 503. Alterations and/or production of new radicals were observed on exposure of RG 503H microspheres to the light. Radiolytic degradation of RG 503 under vacuum is characterized by a prevalence of the chain scission events leading to a decrease of Mw. Some crosslinking can occur mainly in the post irradiation stage through the decay and coupling of the hydrogen abstraction radicals. A hydroperoxydative cycle, whose mechanism is suggested, is generated in the presence of oxygen.
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The fourth Castellani seminar Preface. Radiat Phys Chem Oxf Engl 1993 1996. [DOI: 10.1016/0969-806x(96)00018-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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37
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Radiation induced oxidation of isotactic polypropylene and mechanism of action of HALS stabilizers. Radiat Phys Chem Oxf Engl 1993 1996. [DOI: 10.1016/0969-806x(96)00024-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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39
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The mechanism of gamma radiolysis of DNA-PT(II) complexes. Radiat Phys Chem Oxf Engl 1993 1996. [DOI: 10.1016/0969-806x(96)00028-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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40
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ESR study of paramagnetic centres in irradiated platinum complexes. RESEARCH ON CHEMICAL INTERMEDIATES 1996. [DOI: 10.1163/156856796x00629] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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41
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ESR molecular dynamics study at the oxidation sites of polypropylene with nitroxyl spin labels and spin probes. RESEARCH ON CHEMICAL INTERMEDIATES 1996. [DOI: 10.1163/156856796x00647] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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42
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ESR study of radical processes in irradiated DNA: The effect of the complexation with cis-dichloro diamino Pt(II). RESEARCH ON CHEMICAL INTERMEDIATES 1996. [DOI: 10.1163/156856796x00034] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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43
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44
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Radiolysis mechanisms in clathrates systems: EPR spectroscopy investigation of the long chain carboxylic esters urea adducts. Radiat Phys Chem Oxf Engl 1993 1995. [DOI: 10.1016/0969-806x(94)e0023-c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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46
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Reactive intermediates of metal alkoxides II—an EPR investigation on irradiated titanium alkoxides. Radiat Phys Chem Oxf Engl 1993 1995. [DOI: 10.1016/0969-806x(94)e0020-j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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47
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Matrix isolation and ESR study of platinum(I) diolefin complexes—norbornadiene and (1,5-cyclooctadiene) platinum dichloride radical anions. Radiat Phys Chem Oxf Engl 1993 1995. [DOI: 10.1016/0969-806x(94)e0021-a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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48
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Free-radical and ion chemistry of fluoro derivatives: the mechanism of γ-radiolysis of perfluoropolypropene and perfluoropolytrimethylene oxides. J Fluor Chem 1993. [DOI: 10.1016/s0022-1139(00)80555-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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49
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Free radical and ion chemistry of fluoroderivatives: the mechanism of gamma radiolysis of perfluoropolyethers. J Fluor Chem 1991. [DOI: 10.1016/s0022-1139(00)83861-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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50
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