44 results on '"Ruth Edge"'
Search Results
2. Anti- and pro-oxidative mechanisms comparing the macular carotenoids zeaxanthin and lutein with other dietary carotenoids - a singlet oxygen, free-radica I in vitro and ex vivo study
- Author
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Fritz Boehm, Ruth Edge, and T. George Truscott
- Subjects
Lutein ,Radical ,chemistry.chemical_element ,Q1 ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Oxygen ,03 medical and health sciences ,chemistry.chemical_compound ,Dalton Nuclear Institute ,QD ,Physical and Theoretical Chemistry ,Carotenoid ,030304 developmental biology ,chemistry.chemical_classification ,0303 health sciences ,Singlet oxygen ,organic chemicals ,food and beverages ,QR ,0104 chemical sciences ,Zeaxanthin ,ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute ,chemistry ,Xanthophyll ,Hydroxyl radical - Abstract
The interactions of dietary carotenoids, and particularly the xanthophylls in the macula, with singlet oxygen and three different oxy-radicals, (hydroxyl radical, nitrogen dioxide and the superoxide radical anion) are compared using pulsed laser and γ-techniques. The results give possible molecular mechanisms for the switch from anti-oxidant (protection) by carotenoids to pro-oxidant (damage) by carotenoids. The participation of oxygen in radical mechanisms in the presence of different carotenoids is compared for the different radicals. It is shown that the mechanistic role of oxygen differs very significantly for anti-/pro-oxidation by hydroxyl radicals when compared to nitrogen dioxide. Lutein was found to be an extremely good cell protector against hydroxyl radicals at all oxygen concentrations, including under physiological conditions.
- Published
- 2020
3. Active Intermediates in Copper Nitrite Reductase Reactions Probed by a Cryotrapping-Electron Paramagnetic Resonance Approach
- Author
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Derren J. Heyes, Muralidharan Shanmugam, Nigel S. Scrutton, Ruth Edge, and Tobias M. Hedison
- Subjects
Reaction mechanism ,Nitrite Reductases ,chemistry.chemical_element ,010402 general chemistry ,Photochemistry ,Crystallography, X-Ray ,01 natural sciences ,Redox ,Catalysis ,law.invention ,Metal ,Electron transfer ,law ,redox enzyme ,Manchester Institute of Biotechnology ,Catalytic Domain ,Dalton Nuclear Institute ,Electron paramagnetic resonance ,Research Articles ,metalloenzymes ,biology ,010405 organic chemistry ,Chemistry ,Electron Spin Resonance Spectroscopy ,Temperature ,Active site ,General Chemistry ,General Medicine ,ResearchInstitutes_Networks_Beacons/manchester_institute_of_biotechnology ,Copper ,0104 chemical sciences ,electron paramagnetic resonance ,ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute ,copper center ,visual_art ,biology.protein ,visual_art.visual_art_medium ,copper nitrite reductase ,Oxidation-Reduction ,Research Article - Abstract
Redox active metalloenzymes catalyse a range of biochemical processes essential for life. However, due to their complex reaction mechanisms, and often, their poor optical signals, detailed mechanistic understandings of them are limited. Here, we develop a cryoreduction approach coupled to electron paramagnetic resonance measurements to study electron transfer between the copper centers in the copper nitrite reductase (CuNiR) family of enzymes. Unlike alternative methods used to study electron transfer reactions, the cryoreduction approach presented here allows observation of the redox state of both metal centers, a direct read‐out of electron transfer, determines the presence of the substrate/product in the active site and shows the importance of protein motion in inter‐copper electron transfer catalyzed by CuNiRs. Cryoreduction‐EPR is broadly applicable for the study of electron transfer in other redox enzymes and paves the way to explore transient states in multiple redox‐center containing proteins (homo and hetero metal ions)., Metalloenzyme catalysis: Through the use of cryoreduction and annealing, a method of studying electron transfer in redox active metalloenzymes is developed. Combined with electron paramagnetic resonance spectroscopy, active states in the catalytic cycle of the copper containing nitrite reductases are probed.
- Published
- 2020
4. An Electron Paramagnetic Resonance (EPR) spectroscopy study on the γ-irradiation sterilization of the pharmaceutical excipient l-histidine: Regeneration of the radicals in solution
- Author
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Christopher J. Wedge, Claudio Vallotto, Ruth Edge, Helen E. Williams, Damien Martin Murphy, Mark E. Newton, and Zoë J. Ayres
- Subjects
0301 basic medicine ,Free Radicals ,Radical ,Deamination ,Pharmaceutical Science ,Excipient ,Spin-trapping ,010402 general chemistry ,Photochemistry ,01 natural sciences ,law.invention ,Excipients ,Fenton reaction ,03 medical and health sciences ,Electron paramagnetic resonance (EPR) ,law ,medicine ,Organic chemistry ,QD ,Histidine ,Dalton Nuclear Institute ,Electron paramagnetic resonance ,Dissolution ,Active ingredient ,Spin trapping ,Chemistry ,Electron Spin Resonance Spectroscopy ,Sterilization ,Sterilization (microbiology) ,0104 chemical sciences ,ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute ,030104 developmental biology ,Gamma Rays ,Irradiation ,Powders ,medicine.drug - Abstract
The effects of γ-radiation sterilization on the parenteral excipient L-histidine were analysed by means of EPR spectroscopy. The irradiation process was found to induce the formation of a deamination radical which was persistent in the solid state. The nature and reactivity of the radicals following dissolution in water was evaluated using spin-trapping EPR experiments. The deamination radical was found to regenerate in solution in the presence of trace metals, potentially leading to radical induced degradation reactions occurring up to an hour after the dissolution process. Understanding this process is significant for the improved design of parental pharmaceutical formulations in which unwanted radical reactions after γ‐radiation sterilization could lead to degradation of active ingredients.
- Published
- 2017
5. Photochemistry and photopolymerisation of substituted 2-methylanthraquinones and novel 2-acryloxymethylanthraquinone in radiation curing
- Author
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Christopher M. Liauw, Ruth Edge, Norman S. Allen, Michele Edge, Hazira Hamzah, Suppiah Navaratnam, and Fernando Catalina
- Subjects
Tertiary amine ,Photochemistry ,General Chemical Engineering ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Anthraquinone ,Photopolymerisation ,chemistry.chemical_compound ,flash photolysis ,Benzophenone ,Laser photolysis ,Dalton Nuclear Institute ,Triplet state ,2-Methylanthraquinones ,2-Ethylanthraquinone ,General Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Intersystem crossing ,ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute ,chemistry ,Flash photolysis ,0210 nano-technology ,Phosphorescence ,laser photolysis - Abstract
Anthraquinones have been the subject of numerous photochemical studies and their photopolymerization activities have been examined under various conditions to improve more efficient photochemical systems. This article involves further detailed investigations into the photophysical, photochemistry and photopolymerisation properties of 4 commercial derivatives of 2-substituted anthraquinone, namely, 2-Bromomethylanthraquinone (2BA), 2 Chloromethylanthraquinone (2CA), 2 Ethylanthraquinone (2EA), 2 Hydroxymethylanthraquinone (2HA) and one novel synthesized anthraquinone, 2 Acryloxymethylanthraquinone (2AA). 2AA is synthesized from 2HA. The results from both spectroscopic and analysis studies proved the 2AA to having the ester link. Absorption spectroscopy and solvent shift data are used to characterise their spectral activity. Luminescence studies involving fluorescence and phosphorescence analysis indicates efficient intersystem crossing to triplet state and n-π* nature of the lowest excited triplet state. The polymerisation activity was studied using methyl methacrylate (MMA) and analysis of the cure rate was measured using the gravimetric method. All the compounds are shown to be highly dependent on the structure. However, the rate of polymerisation (Rp) was reduced in the presence of amine. This is consistent with other results, proving the behaviour of derivatives with n-π* configuration. Hardness tests for all compounds took place using a different formula of acrylated resin/monomer systems. The excited state characteristics of the methyl derivatives have also been examined using micro and nanosecond flash photolysis. Triplet absorption spectra of all the anthraquinone derivatives show a significant red shift in the region of 340–370 nm with increasing solvent polarity due to stabilisation of the lowest triplet state by solvent reorganization. Hydrogen atom abstraction takes place in 2 propanol, forming a semiquinone radical. In the presence of the tertiary amine, triethylamine, all anthraquinone derivatives show the formation of intermediary species related to either the exciplex or the radical ion pair. Under aerobic conditions, the first decay rate for all anthraquinone derivatives increases and showed oxygen to be a good quencher with a bimolecular rate constant of around 2 × 10 mol. dm s. Relative to benzophenone, the molar absorption coefficient, ε, and quantum yield of intersystem crossing, Φisc were calculated, and it is summarised that the value for Φisc for all compound is less than 1.00 and controls to a major extent their photochemical activities., The authors thank the University of Sains Malaysia for funding Hazira Mazah.
- Published
- 2018
6. Singlet Oxygen and Free Radical Reactions of Retinoids and Carotenoids-A Review
- Author
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T. George Truscott and Ruth Edge
- Subjects
0301 basic medicine ,retinoids ,Physiology ,Radical ,Clinical Biochemistry ,chemistry.chemical_element ,Review ,010402 general chemistry ,Hydrogen atom abstraction ,Photochemistry ,01 natural sciences ,Biochemistry ,Oxygen ,singlet oxygen ,03 medical and health sciences ,chemistry.chemical_compound ,polycyclic compounds ,Dalton Nuclear Institute ,Molecular Biology ,Carotenoid ,neutral free radicals ,chemistry.chemical_classification ,hydrogen abstraction ,hydroxyl radical ,Chemistry ,Singlet oxygen ,organic chemicals ,carotenoids ,Cell Biology ,Polyene ,lycopene ,radical cations/anions ,0104 chemical sciences ,030104 developmental biology ,ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute ,pro-/anti-oxidants ,Hydroxyl radical ,Limiting oxygen concentration ,xanthophylls - Abstract
We report on studies of reactions of singlet oxygen with carotenoids and retinoids and a range of free radical studies on carotenoids and retinoids with emphasis on recent work, dietary carotenoids and the role of oxygen in biological processes. Many previous reviews are cited and updated together with new data not previously reviewed. The review does not deal with computational studies but the emphasis is on laboratory-based results. We contrast the ease of study of both singlet oxygen and polyene radical cations compared to neutral radicals. Of particular interest is the switch from anti- to pro-oxidant behavior of a carotenoid with change of oxygen concentration: results for lycopene in a cellular model system show total protection of the human cells studied at zero oxygen concentration, but zero protection at 100% oxygen concentration.
- Published
- 2017
7. Seeking the mechanism responsible for fluoroquinolone photomutagenicity: a pulse radiolysis, steady-state, and laser flash photolysis study
- Author
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Sonia Soldevila, Virginie Lhiaubet-Vallet, Francisco Bosca, M. Consuelo Cuquerella, and Ruth Edge
- Subjects
Photochemistry ,DNA damage ,Free radicals ,Context (language use) ,Lasers, Solid-State ,Biochemistry ,Structure-Activity Relationship ,chemistry.chemical_compound ,QUIMICA ORGANICA ,Ciprofloxacin ,Physiology (medical) ,Animals ,DNA Breaks, Single-Stranded ,Carcinogenicity ,Photolysis ,Chemistry ,Photodissociation ,Deoxyguanosine ,Acetylation ,DNA ,Solutions ,Kinetics ,Covalent bond ,Radiolysis ,Flash photolysis ,Cattle ,Steady state (chemistry) ,Genotoxicity ,Pulse Radiolysis ,Mutagens ,Fluoroquinolones - Abstract
The mechanism responsible for the remarkable photomutagenicity of fluoroquinolone (FQ) antibiotics remains unknown. For this reason, it was considered worthwhile to study in detail the interactions between DNA and a dihalogenated FQ such as lomefloxacin (LFX; one of the most photomutagenic FQs) and its N-acetyl derivative ALFX. Studies of photosensitized DNA damage by (A)LFX, such as formation of DNA single-strand breaks (SSBs), together with pulse radiolysis, laser flash photolysis, and absorption and fluorescence measurements, have shown the important effects of the cationic character of the piperazinyl ring on the affinity of this type of drug for DNA. Hence, the formation of SSBs was detected for LFX, whereas ALFX and ciprofloxacin (a monofluorated FQ) needed a considerably larger dose of light to produce some damage. In this context, it was determined that the association constant (K-a) for the binding of LFX to DNA is ca. 2 x 10(3) M-1, whereas in the case of ALFX it is only ca. 0.5 x 10(3) M-1. This important difference is attributed to an association between the cationic peripheral ring of LFX and the phosphate moieties of DNA and justifies the DNA SSB results. The analysis of the transient species detected and the photomixtures has allowed us to establish the intermolecular processes involved in the photolysis of FQ in the presence of DNA and 2'-deoxyguanosine (dGuo). Interestingly, although a covalent binding of the dihalogenated FQ to dGuo occurs, the photodegradation of FQ center dot center dot center dot DNA complexes did not reveal any significant covalent attachment. Another remarkable outcome of this study was that (A)LFX radical anions, intermediates required for the onset of DNA damage, were detected by pulse radiolysis but not by laser flash photolysis. (C) 2013 Elsevier Inc. All, rights reserved., We thank Professor Suppiah Navaratnam for his help. We acknowledge the Spanish government for Grants CTQ2010-19909 and CTQ2012-32621 and the Generalitat Valenciana for Grants PROMETEOII/2013/005.
- Published
- 2014
8. Magnetic field effect on singlet oxygen production in a biochemical system
- Author
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P. J. Hore, Yan Liu, Peter Gast, Ruth Edge, Christiane R. Timmel, and Kevin B. Henbest
- Subjects
Photosynthetic reaction centre ,Photosynthetic Reaction Center Complex Proteins ,Rhodobacter sphaeroides ,Photochemistry ,Catalysis ,Oxidative damage ,Magnetics ,chemistry.chemical_compound ,Nuclear magnetic resonance ,Materials Chemistry ,Cell-Free System ,Singlet Oxygen ,biology ,Singlet oxygen ,Metals and Alloys ,General Chemistry ,Magnetic field effect ,equipment and supplies ,biology.organism_classification ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Yield (chemistry) ,Ceramics and Composites ,human activities - Abstract
The yield of singlet oxygen sensitized by chemically modified, carotenoidless bacterial photosynthetic reaction centres and the ensuing oxidative damage are both shown to be magnetic field-dependent.
- Published
- 2016
9. Interactions of dietary carotenoids with activated (singlet) oxygen and free radicals: Potential effects for human health
- Author
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Ruth Edge, Fritz Böhm, and George Truscott
- Subjects
Lutein ,Free Radicals ,Radical ,Xanthophylls ,Photochemistry ,Redox ,Antioxidants ,chemistry.chemical_compound ,Electron transfer ,Zeaxanthins ,Animals ,Humans ,chemistry.chemical_classification ,Clinical Trials as Topic ,Reactive oxygen species ,Quenching (fluorescence) ,Singlet Oxygen ,Singlet oxygen ,Carotenoids ,Diet ,Oxidative Stress ,Radical ion ,chemistry ,Reactive Oxygen Species ,human activities ,Food Science ,Biotechnology - Abstract
Molecular mechanisms associated with the anti-/pro-oxidative properties of carotenoids (CARs) are described in organic solvents, micro-heterogeneous environments and model lipid membranes and in cellular suspensions. Singlet oxygen is important in the skin and eye and CARs are efficient singlet oxygen (SO) quenchers with corresponding rate constants near diffusion controlled (typically app. 10¹⁰ M⁻¹ s⁻¹) with lycopene (LYC) exhibiting the most efficient quenching in organic solvents. However, in membrane environments there is little or no difference in the quenching efficiency between the dietary CARs. Furthermore, aggregation of CARs, particularly those in the macula (lutein and zeaxanthin), markedly reduces SO quenching efficiency. Free radical interactions with CARs leads to at least three processes, electron and hydrogen atom transfer and adduct formation. The most studied is electron transfer where the CAR loses an electron to become a radical cation. The reactivity/lifetime of such CAR radicals may lead to a switch from anti- to pro-oxidant behaviour of CARs. These reactions are related to CAR redox potentials with LYC being the lowest (most easily oxidised) allowing LYC to reduce/repair all other CAR radical cations and LYC 'sacrificed' where mixtures of CARs are present in oxidative environments. Such redox-controlled reactions may lead to deleterious as well as beneficial health effects.
- Published
- 2012
10. Origin of Impurities Formed in the Polyurethane Production Chain. 1. Conditions for Chlorine Transfer from an Aryl Isocyanide Dichloride Byproduct
- Author
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June Callison, John M. Winfield, David Collison, Eric J. L. McInnes, Ruth Edge, Joseph J. W. McDouall, Kimberly R. de Cuba, David Lennon, Robert H. Carr, Willem van der Borden, and Klaas van der Velde
- Subjects
General Chemical Engineering ,Isocyanide ,Aryl ,Photodissociation ,chemistry.chemical_element ,General Chemistry ,Photochemistry ,Isocyanate ,Industrial and Manufacturing Engineering ,Adduct ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Chlorine ,Methylene ,Electron paramagnetic resonance - Abstract
Phenyl and 4-methylphenyl isocyanide dichlorides are models for byproduct that may be formed in the later stages of certain polyurethane production chains. Photochemical electron paramagnetic resonance (EPR) studies (λ > 310 nm), using the spin trap, N-tert-butyl-α-phenylnitrone, confirm a previously made suggestion that ArN═CCl2 can behave as a chlorine radical source. EPR spectra recorded during and after irradiation and supported by simulations evolve over time and indicate formation of the short-lived spin trap–Cl• adduct and a longer lived benzoyl-N-tert-butylnitroxide radical. Photolysis of C6H5N═CCl2, either alone or mixed with methylene diaryl isocyanate species, in o-C6H4Cl2, a polyurethane process solvent, led to the formation of mixtures containing dichloro- and trichlorobiphenyl isomers.
- Published
- 2012
11. Reduction of oxidized guanosine by dietary carotenoids: A pulse radiolysis study
- Author
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Ruth Edge, Parimal Gaikwad, T. George Truscott, Suppiah Navaratnam, and B.S. Madhava Rao
- Subjects
Radical ,Biophysics ,Guanosine ,macromolecular substances ,Photochemistry ,Biochemistry ,Electron Transport ,chemistry.chemical_compound ,Astaxanthin ,polycyclic compounds ,Organic chemistry ,Molecular Biology ,Carotenoid ,chemistry.chemical_classification ,organic chemicals ,Tryptophan ,food and beverages ,Nucleosides ,Carotenoids ,biological factors ,Diet ,Zeaxanthin ,Kinetics ,chemistry ,Xanthophyll ,Radiolysis ,Pulse Radiolysis - Abstract
Time-resolved pulse radiolysis investigations reported herein show that the carotenoids β-carotene, lycopene, zeaxanthin and astaxanthin (the last two are xanthophylls – oxygen containing carotenoids) are capable of both reducing oxidized guanosine as well as minimizing its formation. The reaction of the carotenoid with the oxidized guanosine produces the radical cation of the carotenoid. This behavior contrasts with the reactions between the amino acids and dietary carotenoids where the carotenoid radical cations oxidized the amino acids (tryptophan, cysteine and tyrosine) at physiological pH.
- Published
- 2010
12. Primary Photoprocesses in a Fluoroquinolone Antibiotic Sarafloxacin
- Author
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Fernando Lorenzo, Ruth Edge, Suppiah Navaratnam, and Norman S. Allen
- Subjects
Aqueous solution ,Photochemistry ,Chemistry ,Radical ,Quantum yield ,Protonation ,General Medicine ,Biochemistry ,Anti-Bacterial Agents ,Ciprofloxacin ,Absorption band ,Radiolysis ,Flash photolysis ,Spectrophotometry, Ultraviolet ,Physical and Theoretical Chemistry ,Absorption (chemistry) - Abstract
The photophysical properties of the fluoroquinolone antibiotic sarafloxacin (SFX) were investigated in aqueous media. SFX in water, at pH 7.4, shows intense absorption with peaks at 272, 322 and 335 nm, (epsilon=36800 and 17000 dm3 mol(-1) cm(-1), respectively). Both the absorption and emission properties of SFX are pH-dependent; pKa values for the protonation equilibria of both the ground (5.8 and 9.1) and excited singlet states (5.7 and 9.0) of SFX were determined spectroscopically. SFX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Laser flash photolysis and pulse radiolysis studies have been carried out in order to characterize the transient species of SFX in aqueous solution. Triplet-triplet absorption has a maximum at 610 nm with a molar absorption coefficient of 17,000+/-1000 dm3 mol(-1) cm(-1). The quantum yield of triplet formation has been determined to be 0.35+/-0.05. In the presence of oxygen, the triplet reacts to form excited singlet oxygen with quantum yield of 0.10. The initial triplet (3A*) was found to react with phosphate buffer to form triplet 3B* with lower energy and longer lifetime and having an absorption band centered at 700 nm. SFX triplet was also found to oxidize tryptophan to its radical with concomitant formation of the anion radical of SFX. Hence the photosensitivity of SFX could be initiated by the oxygen radicals and/or by SFX radicals acting as haptens.
- Published
- 2009
13. Single and double reduction of C60 in 2:1 γ-cyclodextrin/[60]fullerene inclusion complexes by cyclodextrin radicals
- Author
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Yongmin Zhang, Suppiah Navaratnam, Yali Wang, René V. Bensasson, Annamaria Quaranta, Edward J. Land, and Ruth Edge
- Subjects
chemistry.chemical_classification ,Aqueous solution ,Fullerene ,Cyclodextrin ,Absorption spectroscopy ,010405 organic chemistry ,Chemistry ,Radical ,Kinetics ,General Physics and Astronomy ,010402 general chemistry ,Solvated electron ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Radiolysis ,Physical and Theoretical Chemistry - Abstract
Spectroscopic and chemical properties of γ-CD radicals, resulting from the abstraction by HO radicals of hydrogen atoms, have been investigated using pulse radiolysis. The reactions of γ-CD radicals with C60 in 2:1 γ-CD/C60 inclusion complexes have been studied in aqueous solutions. It has been demonstrated that the γ-CD radicals are reducing species producing C60- monoanion radicals, as well as doubly reduced C602-, well characterised by their absorption spectra in the near IR. The oxidation potential of γ-CD radical is estimated to be more negative than −390 mV vs. NHE. The kinetics of the C60 reduction by γ-CD radicals have been determined and compared with kinetics by other reducing species including the solvated electron (eaq-) and CO2- radicals. It was observed that the method of preparation of the 2:1 γ-CD/C60 inclusion complexes modifies the C60 reduction mechanism.
- Published
- 2008
14. A pulse-radiolysis approach to fast reductive cleavage of a disulfide bond to uncage enzyme activity
- Author
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Ruth Edge, Salvador Tomas, Christopher A. Hunter, Julia A. Weinstein, Jonathan Best, Suppiah Navaratnam, Jonathan P. Waltho, and Lilia Milanesi
- Subjects
Kinetics ,Molecular Conformation ,Photochemistry ,Biochemistry ,chemistry.chemical_compound ,Catalytic Domain ,Physiology (medical) ,Papain ,Cysteine ,Disulfides ,Sulfhydryl Compounds ,Binding site ,chemistry.chemical_classification ,Binding Sites ,biology ,Carica ,Plant Extracts ,Biological activity ,Enzyme assay ,Models, Chemical ,chemistry ,Spectrophotometry ,Yield (chemistry) ,Radiolysis ,Thiol ,biology.protein ,Pulse Radiolysis - Abstract
The essential thiol of the enzyme papain has been caged by linking to an aromatic thiol. The resulting caged protein is inactive but enzymatic activity is fully restored upon chemical cleavage of the protective disulfide bond. We have exploited the chemistry of this disulfide bond to uncage papain by pulse radiolysis. We have shown that up to 10% of the enzyme activity can be restored by reductive pulse radiolysis. This approach has been tested on a small-molecule model system, and experiments on this model compound show that pulse radiolysis of the mixed cysteine-aromatic disulfide results in selective reduction of the disulfide bond to generate a thiol in 10-20% yield, consistent with the radiolytically restored activity of the caged papain quantified by the biochemical assay.
- Published
- 2008
15. Primary Photophysical Properties of Moxifloxacin- A Fluoroquinolone Antibiotic
- Author
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Ruth Edge, Suppiah Navaratnam, Norman S. Allen, and Fernando Lorenzo
- Subjects
Photochemistry ,Ultraviolet Rays ,Moxifloxacin ,Molecular Conformation ,Analytical chemistry ,Quantum yield ,Solvated electron ,Biochemistry ,chemistry.chemical_compound ,Physical and Theoretical Chemistry ,Triplet state ,Aza Compounds ,Photolysis ,Singlet oxygen ,Lasers ,Reproducibility of Results ,Water ,General Medicine ,Hydrogen-Ion Concentration ,Anti-Bacterial Agents ,chemistry ,Excited state ,Radiolysis ,Quinolines ,Quantum Theory ,Flash photolysis ,Spectrophotometry, Ultraviolet ,Phosphorescence ,Fluoroquinolones - Abstract
The photophysical properties of the fluoroquinolone antibiotic moxifloxacin (MOX) were investigated in aqueous media. MOX in water, at pH 7.4, shows two intense absorption bands at 287 and 338 nm (epsilon = 44,000 and 17,000 dm(3) mol(-1) cm(-1), respectively). The absorption and emission properties of MOX are pH-dependent, pK(a) values for the protonation equilibria of both the ground (6.1 and 9.6) and excited singlet states (6.8 and 9.1) of MOX were determined spectroscopically. MOX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Phosphorescence from the excited triplet state in frozen ethanol solution has a quantum yield of 0.046. Laser flash photolysis and pulse radiolysis studies have been carried out to characterize the transient species of MOX in aqueous solution. On laser excitation, MOX undergoes monophotonic photoionization with a quantum yield of 0.14. This leads to the formation of a long-lived cation radical whose absorption is maximum at 470 nm (epsilon(470) = 3400 dm(3) mol(-1) cm(-1)). The photoionization process releases hydrated electron which rapidly reacts (k = 2.8 x 10(10) dm(3) mol(-1) s(-1)) with ground state MOX, yielding a long-lived anion radical with maximum absorption at 390 nm (epsilon(390) = 2400 dm(3) mol(-1) cm(-1)). The cation radical of MOX is able to oxidize protein components tryptophan and tyrosine. The bimolecular rate constants for these reactions are 2.3 x 10(8) dm(3) mol(-1) s(-1) and 1.3 x 10(8) dm(3) mol(-1) s(-1), respectively. Singlet oxygen sensitized by the MOX triplet state was also detected only in oxygen-saturated D(2)O solutions, with a quantum yield of 0.075.
- Published
- 2008
16. The sulphate radical is not involved in aqueous radiation oxidation processes
- Author
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Suppiah Navaratnam, Ruth Edge, K. Clarke, T. G. Truscott, and Edward J. Land
- Subjects
Radiation ,Aqueous solution ,Chemistry ,Inorganic chemistry ,Oxidizing agent ,chemistry.chemical_element ,Photochemistry ,Oxygen ,Adduct - Abstract
The H 2 O 2 /persulphate systems are of enormous environmental and commercial importance with the sulphate radical (SO 4 − ) being assumed as the oxidizing/bleaching species. We show that under normal conditions (air-saturated) no SO 4 − is produced and, most likely, a much longer-lived species, the adduct of O 2 and the persulphate radical, is formed.
- Published
- 2008
17. A Dual Sensor Spin Trap for Use with EPR Spectroscopy
- Author
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Stuart T. Caldwell, Ruth Edge, Caroline Quin, and Richard C. Hartley
- Subjects
Cyclopropanes ,chemistry.chemical_classification ,Free Radicals ,Molecular Structure ,Spin trapping ,Radical ,Organic Chemistry ,Electron Spin Resonance Spectroscopy ,Nitroxyl ,Photochemistry ,Biochemistry ,Cyclopropane ,law.invention ,Nitrone ,chemistry.chemical_compound ,Phenols ,chemistry ,law ,Phenol ,Molecule ,Nitrogen Oxides ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Spin Trapping - Abstract
Redox active metal ions, carbon-centered radicals, and oxygen-centered radicals are important to oxidative stress. A radical detector combining a nitrone spin trap, a phenol, and a cyclopropane radical clocklike unit was prepared and used with EPR spectroscopy to detect and distinguish between hydroxyl radicals, methyl radicals, and iron(III) ions. Iron(III) reacts with the phenol unit inducing opening of the cyclopropane ring and cyclization to generate a stable nitroxyl radical.
- Published
- 2007
18. Carotenoid Radical Anions and Their Protonated Derivatives
- Author
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Ruth Edge, Suppiah Navaratnam, Ali El-Agamey, T. George Truscott, and Edward J. Land
- Subjects
Anions ,chemistry.chemical_classification ,Aqueous solution ,Octoxynol ,Organic Chemistry ,Protonation ,Hydrogen-Ion Concentration ,Photochemistry ,Carotenoids ,Biochemistry ,Kinetics ,chemistry.chemical_compound ,Reaction rate constant ,chemistry ,Astaxanthin ,Methanol ,Canthaxanthin ,Protons ,Physical and Theoretical Chemistry ,Carotenoid - Abstract
In this study, we report the protonation reactions for astaxanthin and canthaxanthin radical anions in methanol, alkaline methanol, and aqueous 2% Triton X-100 at different pH values. The pKa values for the corresponding alpha-hydroxy radical derivatives of astaxanthin, canthaxanthin, and beta-apo-8'-carotenal were estimated in 2% Triton X-100. Also, the effects of the microenvironment and the structure of the carotenoids on the protonation rate constant are discussed.
- Published
- 2006
19. Monomeric Azaheterofullerene Derivatives RC59N: Influence of the R Moiety on Spectroscopic and Photophysical Properties
- Author
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Ruth Edge, Annamaria Quaranta, Otto Vostrowsky, Andreas Hirsch, Frank Hauke, René V. Bensasson, Suppiah Navaratnam, Sydney Leach, and Winfried Leibl
- Subjects
Singlet Oxygen ,Absorption spectroscopy ,Photochemistry ,Chemistry ,Singlet oxygen ,Spectrum Analysis ,Organic Chemistry ,General Chemistry ,Chlorobenzenes ,Catalysis ,chemistry.chemical_compound ,Ultraviolet visible spectroscopy ,Excited state ,Moiety ,Fullerenes ,Singlet state ,Triplet state ,Ground state ,Toluene - Abstract
We have synthesised nine monomeric azaheterofullerene (AZA) derivatives, RC(59)N, with a wide variety of different side chains R and investigated their spectroscopic and photophysical properties in toluene and o-dichlorobenzene (ODCB). Measurements include their ground-state absorption spectra, molar absorption coefficient (epsilon(G)), fluorescence spectra, fluorescence quantum yields (Phi(F)), singlet-state lifetimes (tau(F)), triplet-state absorption spectra, triplet molar absorption coefficients (epsilon(T)), singlet oxygen (Phi(Delta)), and triplet state (Phi(T)) quantum yields. The replacement of a carbon by a nitrogen atom in the C(60) sphere strongly affects most of the spectroscopic and photophysical properties. The chemical nature of the R moiety has definite effects on these properties in contrast with minor effects on the chemical nature of the addends in [6,6]-ring bridged monoadduct methano[60]fullerene derivatives. These effects concern properties of the ground state, singlet excited state, and triplet states of our nine RC(59)N derivatives and in particular the values of photophysical parameters epsilon(G), epsilon(T), Phi(Delta), and Phi(T), which are significantly lower than those of analogous monoadduct [6,6]-ring bridged methano[60]fullerene derivatives.
- Published
- 2006
20. Photophysical studies of six amphiphilic 2:1 cyclodextrin:[60]fullerene derivatives
- Author
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Ruth Edge, Edward J. Land, Yongmin Zhang, Salvatore Filippone, André Rassat, Juan Yang, Michael Brettreich, Suppiah Navaratnam, Andreas Hirsch, Pierre Sinaÿ, René V. Bensasson, Annamaria Quaranta, and David J. McGarvey
- Subjects
chemistry.chemical_classification ,Fullerene ,Absorption spectroscopy ,Cyclodextrin ,Singlet oxygen ,General Physics and Astronomy ,Photochemistry ,chemistry.chemical_compound ,chemistry ,Radiolysis ,Moiety ,Flash photolysis ,Physical and Theoretical Chemistry ,Triplet state - Abstract
In search of a simple internal complexation of C 60 in cyclodextrins, six 2:1 cyclodextrin:[60]fullerene conjugates involving different types of linkers have been synthesised. Using spectrophotometry, laser flash photolysis and pulse radiolysis, we have investigated spectroscopic and photophysical properties of these 2:1 cyclodextrin [60]fullerene monoadduct conjugates ( CDF ), including ground and triplet state absorption spectra, triplet molar absorption coefficients ( e T ), quantum yields of triplet ( Φ T ) and singlet oxygen formation ( Φ Δ ) in water and toluene, in order to probe the possibility of 2:1 inclusion complexes of C 60 between two cyclodextrins. In water, the CDF spectroscopic and photophysical properties indicate hydrophobically driven self-assemblies of the amphiphilic conjugates into spherical micelles with no evidence for the presence of a 2:1 inclusion complex, while in toluene they show no sign of aggregation. It is observed that formation of aggregates in water does not prevent scavenging of HO radical by the C 60 moiety of the CD–C 60 conjugates.
- Published
- 2006
21. Photolysis of carotenoids in chloroform: enhanced yields of carotenoid radical cations in the presence of a tryptophan ester
- Author
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Ali El-Agamey, David J. McGarvey, T. George Truscott, Ruth Edge, Edward J. Land, and Marc Burke
- Subjects
chemistry.chemical_classification ,chemistry.chemical_compound ,Radiation ,Chloroform ,chemistry ,organic chemicals ,Photodissociation ,Radiolysis ,Tryptophan ,food and beverages ,Photochemistry ,Carotenoid - Abstract
The presence of an acetyl tryptophan ester gives rise to enhanced yields of carotenoid radical cations in chloroform following 355 nm laser excitation of the carotenoid, even though the tryptophan does not absorb at this wavelength. The increase is attributed to positive charge transfer from semi-oxidized tryptophan itself generated by light absorbed by the carotenoid. The mechanism of these radical processes has been elucidated by pulse radiolysis studies.
- Published
- 2005
22. Oxygen Effect on Protection of Human Lymphoid Cells Against Free Radicals by the Carotenoid Lycopene
- Author
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Ruth Edge, Fritz Boehm, and Terence George Truscott
- Subjects
0301 basic medicine ,chemistry.chemical_classification ,030109 nutrition & dietetics ,Radical ,chemistry.chemical_element ,Photochemistry ,Biochemistry ,Oxygen ,Nitrogen ,Lycopene ,03 medical and health sciences ,chemistry.chemical_compound ,Cell killing ,chemistry ,Physiology (medical) ,Radiolysis ,Limiting oxygen concentration ,Carotenoid - Abstract
Carotenoids are known to act as dietary antioxidants and so are of wide interest for their health benefits. Dietary lycopene, the carotenoid pigment in tomatoes, has been shown to protect against human lymphoid cell membrane damage from free radicals produced by gamma radiation and also by the nitrogen dioxide radical, generated photolytically. This protective effect is dramatically reduced as the oxygen concentration increases, particularly for damage due to gamma radiolysis – becoming near zero at 100% oxygen from 5-fold protection at 20% oxygen and 50-fold protection at zero per-cent oxygen. The effect is less pronounced for nitrogen dioxide-induced cell killing falling from 17-fold protection in the absence of oxygen to 9-fold at 100% oxygen. Non-cellular gamma radiation and laser studies were also carried out to support the molecular mechanisms suggested for the effect of oxygen. The remarkable reduction in protection by lycopene against gamma radiation at high oxygen concentrations could be exploited to enhance radiation procedures for therapy and preliminary studies have also been undertaken for irradiations with high energy protons.
- Published
- 2016
23. Efficiencies of fragmentation of glycosaminoglycan chloramides of the extracellular matrix by oxidizing and reducing radicals: potential site-specific targets in inflammation?
- Author
-
Ruth Edge, Almabrok Akeel, Stephen W. Martin, Sambulelwe Sibanda, A.W. Paterson, Saphwan Al-Assaf, and Barry J. Parsons
- Subjects
Inflammation ,Free Radicals ,Hypochlorous acid ,Heparin ,Reducing agent ,Radical ,Inorganic chemistry ,Hypochlorite ,Photochemistry ,Solvated electron ,Biochemistry ,Extracellular Matrix ,Oxidative Stress ,chemistry.chemical_compound ,chemistry ,Physiology (medical) ,Oxidizing agent ,Animals ,Humans ,Hydroxyl radical ,Hyaluronic Acid ,Fragmentation (cell biology) ,Oxidation-Reduction ,Glycosaminoglycans - Abstract
Hypochlorous acid and its conjugate base, hypochlorite ions, produced under inflammatory conditions, may produce chloramides of glycosaminoglycans, these being significant components of the extracellular matrix (ECM). This may occur through the binding of myeloperoxidase directly to the glycosaminoglycans. The N–Cl group in the chloramides is a potential selective target for both reducing and oxidizing radicals, leading possibly to more efficient and damaging fragmentation of these biopolymers relative to the parent glycosaminoglycans. To investigate the effect of the N–Cl group, we used ionizing radiation to produce quantifiable concentrations of the reducing radicals, hydrated electron and superoxide radical, and also of the oxidizing radicals, hydroxyl, carbonate, and nitrogen dioxide, all of which were reacted with hyaluronan and heparin and their chloramides in this study. PAGE gels calibrated for molecular weight allowed the consequent fragmentation efficiencies of these radicals to be calculated. Hydrated electrons were shown to produce fragmentation efficiencies of 100 and 25% for hyaluronan chloramide (HACl) and heparin chloramide (HepCl), respectively. The role of the sulfate group in heparin in the reduction of fragmentation can be rationalized using mechanisms proposed by M.D. Rees et al. (J. Am. Chem. Soc. 125:13719–13733; 2003), in which the initial formation of an amidyl radical leads rapidly to a C-2 radical on the glucosamine moiety. This is 100% efficient at causing glycosidic bond breakage in HACl but only 25% efficient in HepCl, the role of the sulfate group being to favor the nonfragmentary routes for the C-2 radical. The weaker reducing agent, the superoxide radical, did not cause fragmentation of either HACl or HepCl although kinetic reactivity had been demonstrated in earlier studies. Experiments using the oxidizing radicals, hydroxyl and carbonate, both potential in vivo species, showed significant increases in fragmentation efficiencies for both HACl and HepCl, relative to the parent molecules. The carbonate radical was shown to be involved in site-specific reactions at the N–Cl groups, reacting via abstraction of Cl, to produce the same amidyl radical produced by one-electron reductants such as the hydrated electron. As for the hydrated electrons, the data support fragmentation efficiencies of 100 and 29% for reaction of carbonate radicals at N–Cl for HACl and HepCl, respectively. For the weaker oxidant, nitrogen dioxide, no fragmentation was observed, probably because of a low kinetic reactivity and low reduction potential. It seems likely therefore that the N–Cl group can direct damage to extracellular matrix glycosaminoglycan chloramides, which may be produced under inflammatory conditions. The in vivo species, the carbonate radical, is also much more likely to be site-specific in its reactions with such components of the ECM than the hydroxyl radical.
- Published
- 2013
24. ABSTRACTS
- Author
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T. G. Truscott, Tadeusz Sarna, Malgorzata Barbara Rozanowska, Ruth Edge, and Edward J. Land
- Subjects
Melanin ,chemistry.chemical_classification ,Chemistry ,Organic chemistry ,General Medicine ,Physical and Theoretical Chemistry ,Photochemistry ,Biochemistry ,Carotenoid - Published
- 1999
25. Relative One-Electron Reduction Potentials of Carotenoid Radical Cations and the Interactions of Carotenoids with the Vitamin E Radical Cation
- Author
-
David J. McGarvey, Ruth Edge, L Mulroy, Edward J. Land, and T. G. Truscott
- Subjects
chemistry.chemical_classification ,Lutein ,General Chemistry ,Photochemistry ,Biochemistry ,Catalysis ,Lycopene ,Zeaxanthin ,chemistry.chemical_compound ,Electron transfer ,Colloid and Surface Chemistry ,chemistry ,Radical ion ,Astaxanthin ,Canthaxanthin ,Carotenoid - Abstract
Pulse radiolysis studies have been used to determine the electron-transfer rate constants between various pairs of carotenoids, one of which is present as the radical cation. These dietary carotenoids include those of importance to vision, namely zeaxanthin and lutein. These results have suggested the order of relative ease of electron transfer between six carotenoids. Additional experiments, involving electron transfer between astaxanthin (ASTA), β-apo-8‘-carotenal (APO), and vitamin E (TOH), lead to the following order in terms of relative ease of electron transfer for the seven carotenoid radical cations studied: astaxanthin > β-apo-8‘-carotenal > canthaxanthin > lutein > zeaxanthin > β-carotene > lycopene, such that lycopene is the strongest reducing agent (the most easily oxidized) and astaxanthin is the weakest, and the radical cations of the visual carotenoids, lutein (LUT) and zeaxanthin (ZEA), are reduced by lycopene (LYC) but not by β-carotene (β-CAR). Work on 7,7‘-dihydro-β-carotene (77DH) and...
- Published
- 1998
26. Radiolytic and Photolytic Production of Free Radicals and Reactive Oxygen Species: Interactions with Antioxidants and Biomolecules
- Author
-
Ruth Edge
- Subjects
chemistry.chemical_classification ,Reactive oxygen species ,Antioxidant ,Singlet oxygen ,Radical ,Biomolecule ,medicine.medical_treatment ,Analytical chemistry ,Photochemistry ,chemistry.chemical_compound ,Radical ion ,chemistry ,Radiolysis ,medicine ,Flash photolysis - Abstract
This chapter discusses a variety of free radicals and other reactive oxygen species that are biologically and medically relevant. Radiolytic and/or photochemical methods of production for each reactive oxygen species are shown and for each type of reactive oxygen species some antioxidant and/or biomolecule interactions are discussed. Additionally, the techniques of laser flash photolysis and pulse radiolysis are described in detail and a comparison of the two techniques is made.
- Published
- 2013
27. Corrigendum to 'Seeking the mechanism responsible for the fluoroquinolone photomutagenicity: A pulse radiolysis, steady-state and laser flash photolysis study' [Free Radic. Biol. Med. 67 (2014) 417–425]
- Author
-
Ruth Edge, Francisco Bosca, M. Consuelo Cuquerella, Sonia Soldevila, and Virginie Lhiaubet-Vallet
- Subjects
Pulse (signal processing) ,Chemistry ,law ,Physiology (medical) ,Radiolysis ,Flash photolysis ,Steady state (chemistry) ,Laser ,Photochemistry ,Biochemistry ,law.invention - Published
- 2016
28. Interactions of dietary carotenoids with singlet oxygen (1O2) and free radicals: potential effects for human health
- Author
-
T. George Truscott, Fritz Böhm, and Ruth Edge
- Subjects
chemistry.chemical_classification ,Lutein ,Quenching (fluorescence) ,Free Radicals ,Singlet Oxygen ,Singlet oxygen ,organic chemicals ,Radical ,food and beverages ,Photochemistry ,Carotenoids ,General Biochemistry, Genetics and Molecular Biology ,Antioxidants ,Zeaxanthin ,chemistry.chemical_compound ,chemistry ,Food ,Xanthophyll ,Photoprotection ,polycyclic compounds ,Humans ,Carotenoid ,Oxidation-Reduction - Abstract
The dietary carotenoids provide photoprotection to photosynthetic organisms, the eye and the skin. The protection mechanisms involve both quenching of singlet oxygen and of damaging free radicals. The mechanisms for singlet oxygen quenching and protection against free radicals are quite different - indeed, under some conditions, quenching of free radicals can lead to a switch from a beneficial anti-oxidant process to damaging pro-oxidative situation. Furthermore, while skin protection involves β-carotene or lycopene from a tomato-rich diet, protection of the macula involves the hydroxyl-carotenoids (xanthophylls) zeaxanthin and lutein. Time resolved studies of singlet oxygen and free radicals and their interaction with carotenoids via pulsed laser and fast electron spectroscopy (pulse radiolysis) and the possible involvement of amino acids are discussed and used to (1) speculate on the anti- and pro-oxidative mechanisms, (2) determine the most efficient singlet oxygen quencher and (3) demonstrate the benefits to photoprotection of the eye from the xanthophylls rather than from hydrocarbon carotenoids such as β-carotene.
- Published
- 2011
29. The reduction potential of the β-carotene + /β-carotene couple in an aqueous micro-heterogeneous environment
- Author
-
Edward J. Land, Ruth Edge, Marc Burke, T. George Truscott, and David J. McGarvey
- Subjects
Photosynthetic reaction centre ,Free Radicals ,Spectrophotometry, Infrared ,medicine.medical_treatment ,Photosynthetic Reaction Center Complex Proteins ,Biophysics ,β-Carotene ,One-electron reduction potential ,Photochemistry ,Photosynthesis ,Biochemistry ,Electron Transport ,Structural Biology ,beta-Carotene ,Cations ,Genetics ,medicine ,Cysteine ,Molecular Biology ,Carotenoid ,Micelles ,chemistry.chemical_classification ,Aqueous solution ,Carotene ,Tryptophan ,Water ,Cell Biology ,Hydrogen-Ion Concentration ,Oxidants ,beta Carotene ,Electron transport chain ,Solutions ,Radical ion ,chemistry ,Reducing Agents ,Thermodynamics ,Tyrosine ,Pulse Radiolysis - Abstract
There is a resurgence of interest in the role of electron transfer reactions involving beta-carotene in photosynthesis. There is also current debate on the health benefits of dietary carotenoids and the possible deleterious effects on certain sub-populations such as smokers. The impact of dietary carotenoids on health may well be also related to radical reactions. A key parameter in biological systems is therefore the one-electron reduction potential of the carotenoid radical cation, now reported for the first time in a model biological aqueous environment. The value obtained is 1.06+/-0. 01 V and is sufficiently high to oxidise cell membrane proteins, but is low enough to repair P(680).+ in the photosynthetic reaction centre.
- Published
- 2000
30. Lack of Visible Chromofore Development in the Pulse RadiolysisOxidation of 5,6-dihydroxyndole-2-carboxylic Acid Oligomers: DFT Investigation and Implications for Eumelanin Absorption Propertiess
- Author
-
Alessandra Napolitano, Lucia Panzella, Vincenzo Barone, Orlando Crescenzi, Alessandro Pezzella, Ruth Edge, Marco d'Ischia, Edward J. Land, Suppiah Navaratnam, A., Pezzella, L., Panzella, O., Crescenzi, A., Napolitano, S., Navaratman, R., Edge, E. J., Land, Barone, Vincenzo, M., D’Ischia, Pezzella, Alessandro, Panzella, Lucia, Crescenzi, Orlando, Napolitano, Alessandra, Navaratnam, S., Edge, R., Land, E. J., Barone, V., and D'Ischia, Marco
- Subjects
Indoles ,Time Factors ,Absorption spectroscopy ,Semiquinone ,Polymers ,IONIZATION MASS-SPECTROMETRY ,Photochemistry ,Oligomer ,GAS-PHASE ,AQUEOUS-SOLUTION ,Absorption ,DENSITY-FUNCTIONAL THEORY ,chemistry.chemical_compound ,BIOMIMETIC CONDITIONS ,Settore CHIM/02 - Chimica Fisica ,Melanins ,Chemistry ,Organic Chemistry ,Chromophore ,Quinone methide ,SOLVATION MODELS ,Quinone ,POLARIZABLE CONTINUUM MODEL ,MOLECULAR-DYNAMICS ,Radiolysis ,Quantum Theory ,DENSITY-FUNCTIONAL THEORY, POLARIZABLE CONTINUUM MODEL, IONIZATION MASS-SPECTROMETRY, AQUEOUS-SOLUTION, GAS-PHASE, EXCITATION-ENERGIES, TD-DFT, BIOMIMETIC CONDITIONS, MOLECULAR-DYNAMICS, SOLVATION MODELS ,Spectrophotometry, Ultraviolet ,EXCITATION-ENERGIES ,Absorption (chemistry) ,Pulse Radiolysis ,TD-DFT ,Oxidation-Reduction - Abstract
The structural factors underlying the peculiar optical properties and visible chromophore of eumelanin biopolymers are largely uncharted. It is known that synthetic eumelanins from 5,6-dihydroxyindole are black and display a featureless UV-visible absorption spectrum, whereas those from 5,6-dihydroxyindole-2-carboxylic acid (1) are lighter in color and exhibit a distinct band around 310 nm, but the origin of this difference has never been addressed in detail. Recently, we showed that 5,6-dihydroxyindole dimers generate on pulse radiolysis oxidation strongly absorbing transients with intense maxima in the 500-600 nm region, which have been attributed to planar extended quinone methide species. We now report the unexpectedly different behavior of three oligomers from 1, namely, the 4,4'-biindolyl 2, the 4,7'-biindolyl 3, and the 4,7':4',7''-terindolyl 4. Pulse radiolysis oxidation of 2-4 led initially to semiquinone intermediates exhibiting similar absorption maxima at 360-380 nm. Semiquinone absorption decay followed second-order kinetics (2k = 1.4 x 10(8), 3.2 x 10(8), and 1.4 x 10(8) M(-1) s(-1) for 2, 3, and 4, respectively) but did not lead to significant chromophore development in the visible region. Similar absorption traces were obtained from monomer 1. DFT calculations predicted 5,6-dihydroxyindolyl-5,6-indolequinone structures with significant dihedral twists across the interunit single bonds for the most stable two-electron oxidation products of 2 and 3. The computed absorption spectra consistently featured strong bands around 310 nm but little or no absorption in the visible region. It is suggested that the effective conjugation length in oligomeric/polymeric eumelanin components from 1 may be controlled by hindered rotation around inter-ring bonds preventing planarization of the continuous array of indole units. This may provide an explanation for the difference in the absorption properties of polymers from the two key eumelanin monomers.
- Published
- 2009
31. A mechanistic study of the C-P bond cleavage reaction of 1,2-(PH2)2-C6H4 with nBuLi/Sb(NMe2)3
- Author
-
Eric J. L. McInnes, Robert J. Less, Dominic S. Wright, Ruth Edge, Vesal Naseri, and Robert E. Mulvey
- Subjects
Inorganic Chemistry ,chemistry.chemical_classification ,Deprotonation ,Base (chemistry) ,Chemistry ,law ,Radical ,Photochemistry ,Electron paramagnetic resonance ,Medicinal chemistry ,Bond cleavage ,Homolysis ,law.invention - Abstract
In situ 31P NMR spectroscopic studies of the reaction of the primary diphosphine 1,2-(PH2)2-C6H4 with the mixed-metal base system nBuLi/Sb(NMe2)3, combined with X-ray structural investigations, strongly support a mechanism involving a series of deprotonation steps followed by antimony-mediated reductive C–P bond cleavage. The central intermediate in this reaction is the tetraphosphide dianion [C6H4P2]22− ([4]) from which the final products, the 1,2,3-triphospholide anion [C6H4P3]− (3) and [PhPHLi] (8·Li), are evolved. An EPR spectrocopic study suggests that homolytic C–P bond cleavage is likely to be involved in this final step.
- Published
- 2008
32. Photoreactivity of biologically active compounds. XIX: excited states and free radicals from the antimalarial drug primaquine
- Author
-
S Kristensen, Ruth Edge, Hanne Hjorth Tønnesen, Suppiah Navaratnam, and Roger H. Bisby
- Subjects
Free Radicals ,Radical ,Biophysics ,Primaquine ,Photochemistry ,chemistry.chemical_compound ,Antimalarials ,medicine ,QD ,Radiology, Nuclear Medicine and imaging ,Reactivity (chemistry) ,Biphenyl ,Radiation ,Fenbufen ,Photolysis ,Radiological and Ultrasound Technology ,Chemistry ,other ,Photochemical Processes ,Kinetics ,Deuterium ,Models, Chemical ,Excited state ,Flash photolysis ,Sodium azide ,Oxidation-Reduction ,medicine.drug - Abstract
The formation and reactivity of excited states and free radicals from primaquine, a drug used in the treatment of malaria, was studied in order to evaluate the primary photochemical reaction mechanisms. The excited primaquine triplet was not detected, but is likely to be formed with a short lifetime (50 ns) and with a triplet energy250 kJ/mol as the drug is an efficient quencher of the fenbufen triplet and the biphenyl triplet, and forms (1)O(2) by laser flash photolysis ((PQ)Phi(Delta)=0.025). Primaquine (PQ) exists as the monocation (PQH(+)) in aqueous solution at physiological pH. PQH(+) photoionises by a biphotonic process and also forms the monoprotonated cation radical (PQH(2+)*) by one electron oxidation by HO* (k(q)=6.6 x 10(9) M(-1) s(-1)) and Br*(2)(-) (k(q)=4.7 x 10(9) M(-1) s(-1)) at physiological pH, detected as a long-lived transient decaying essentially by a second order process (k(2)=7.4 x 10(8) M(-1) s(-1)). PQH(2+)* is scavenged by O(2), although at a limited rate (k(q)=1.0 x 10(6) M(-1) s(-1)). The reduction potential (E degrees) of PQH(2+)*/PQH(+) is+1015 mV, as measured versus tryptophan (TRP*/TRPH). Primaquine also forms PQH(2+)* at pH 2.4, by one electron oxidation by Br*(2)(-) and proton loss (k(q)=2.7 x 10(9) M(-1) s(-1)). The non-protonated cation radical (PQ(+)*) is formed during one electron oxidation with Br*(2)(-) at alkaline conditions (k(q)=4.2 x 10(9) M(-1) s(-1) at pH 10.8). The estimated pK(a)-value of PQH(2+)*/PQ(+)* is pK(a) approximately 7-8. Primaquine is not a scavenger of O*(2)(-) at physiological pH. Thus self-sensitization by O*(2)(-) is eliminated as a degradation pathway in the photochemical reactions. Impurities in the raw material and photochemical degradation products initiate photosensitized degradation of primaquine in deuterium oxide, prevented by addition of the (1)O(2) quencher sodium azide. Photosensitized degradation by formation of (1)O(2) is thus important for the initial photochemical decomposition of primaquine, which also proceeds by free radical reactions. Formation of PQH(2+)* is expected to play an essential part in the photochemical degradation process in a neutral, aqueous medium.
- Published
- 2008
33. Direct observation of NH2* reactions with oxygen, amino acids, and melanins
- Author
-
V. Johnson, K. Clarke, T. G. Truscott, Suppiah Navaratnam, E. J. Land, and Ruth Edge
- Subjects
chemistry.chemical_classification ,Melanins ,Quenching (fluorescence) ,Hydroxyl Radical ,Radical ,Spectrum Analysis ,Amino radical ,chemistry.chemical_element ,Hydrogen Peroxide ,Photochemistry ,Oxygen ,Amino acid ,Melanin ,Ammonia ,chemistry.chemical_compound ,Kinetics ,Reaction rate constant ,chemistry ,Physical and Theoretical Chemistry ,Amines ,Amino Acids ,Pulse Radiolysis ,Oxidation-Reduction - Abstract
We report the direct observation of the quenching of the weakly absorbing transient due to the amino radical by oxygen and, hence determine, by a totally direct method, the corresponding rate constant (k = (1.1 +/- 0.1) x 10(9) dm3 mol(-1) s(-1)). We also report the rate constants for the reactions of the amino radical with several amino acids and models of black eumelanin and blond/red phaeomelanin. These reactions lead to a mechanism, based on free radicals, that can explain why ammonia is useful in commercial hair (melanin) bleaching, avoiding excessive amino acid (hair protein) damage.
- Published
- 2008
34. Spectroelectrochemical and computational studies on the mechanism of hypoxia selectivity of copper radiopharmaceuticals
- Author
-
Jennifer C. Green, Jonathan R. Dilworth, Eric J. L. McInnes, Jason P. Holland, Ruth Edge, David Collison, and Peter J. Barnard
- Subjects
Thiosemicarbazones ,Time Factors ,Inorganic chemistry ,chemistry.chemical_element ,Electrons ,Protonation ,Crystallography, X-Ray ,Photochemistry ,Electrochemistry ,Redox ,Catalysis ,Dissociation (chemistry) ,law.invention ,law ,Organometallic Compounds ,Animals ,Humans ,Hypoxia ,Electron paramagnetic resonance ,Chemistry ,Organic Chemistry ,Electron Spin Resonance Spectroscopy ,General Chemistry ,Hydrogen-Ion Concentration ,Copper ,Oxygen ,Zinc ,Density functional theory ,Protons ,Radiopharmaceuticals ,Selectivity ,Oxidation-Reduction ,Algorithms - Abstract
Detailed chemical, spectroelectrochemical and computational studies have been used to investigate the mechanism of hypoxia selectivity of a range of copper radiopharmaceuticals. A revised mechanism involving a delicate balance between cellular uptake, intracellular reduction, reoxidation, protonation and ligand dissociation is proposed. This mechanism accounts for observed differences in the reported cellular uptake and washout of related copper bis(thiosemicarbazonato) complexes. Three copper and zinc complexes have been characterised by X-ray crystallography and the redox chemistry of a series of copper complexes has been investigated by using electronic absorption and EPR spectroelectrochemistry. Time-dependent density functional theory (TDDFT) calculations have also been used to probe the electronic structures of intermediate species and assign the electronic absorption spectra. DFT calculations also show that one-electron oxidation is ligand-based, leading to the formation of cationic triplet species. In the absence of protons, metal-centred one-electron reduction gives the reduced anionic copper(I) species, [Cu(I)ATSM](-), and for the first time it is shown that molecular oxygen can reoxidise this anion to give the neutral, lipophilic parent complexes, which can wash out of cells. The electrochemistry is pH dependent and in the presence of stronger acids both chemical and electrochemical reduction leads to quantitative and rapid dissociation of copper(I) ions from the mono- or diprotonated complexes, [Cu(I)ATSMH] and [Cu(I)ATSMH(2)](+). In addition, a range of protonated intermediate species have been identified at lower acid concentrations. The one-electron reduction potential, rate of reoxidation of the copper(I) anionic species and ease of protonation are dependent on the structure of the ligand, which also governs their observed behaviour in vivo.
- Published
- 2008
35. Deep-red luminescence and efficient singlet oxygen generation by cyclometalated platinum(II) complexes with 8-hydroxyquinolines and quinoline-8-thiol
- Author
-
Nail M. Shavaleev, Suppiah Navaratnam, Julia A. Weinstein, Harry Adams, Jonathan Best, and Ruth Edge
- Subjects
Denticity ,Singlet oxygen ,Ligand ,Quinoline ,chemistry.chemical_element ,Chromophore ,Photochemistry ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Excited state ,Physical and Theoretical Chemistry ,Luminescence ,Platinum - Abstract
The synthesis and photophysical study of (C/\N)Pt(II)Q complexes, where C/\N is a bidentate cyclometalating ligand and Q is 8-hydroxyquinoline or quinoline-8-thiol, are presented. The compounds were obtained as a single isomer with N atoms of the C/\N and Q ligands trans-coordinated to the Pt(II) center as shown by X-ray crystallography. These chromophores absorb intensely in the visible region and emit in the deep-red spectral region from a quinolate-centered triplet intraligand charge-transfer excited state. The emission maxima are in the range 675-740 nm, with the quantum yields and lifetimes of up to 0.82% and 5.3 mus, respectively, in deoxygenated organic solvents at room temperature. These complexes are efficient photosensitizers of singlet oxygen in air-saturated solutions, with yields up to 90%.
- Published
- 2006
36. Spectral and photophysical studies of substituted indigo derivatives in their keto forms
- Author
-
Hugh D. Burrows, Raquel Rondão, Suppiah Navaratnam, Maria João Melo, Gundula Voss, Ruth Edge, and J. Sérgio Seixas de Melo
- Subjects
Indoles ,Light ,Photochemistry ,Indigo Carmine ,Indigo ,Physical Phenomena ,chemistry.chemical_compound ,Emission spectrum ,Physical and Theoretical Chemistry ,HOMO/LUMO ,Singlet Oxygen ,Chemistry ,Singlet oxygen ,Chemistry, Physical ,Plant Extracts ,Physics ,Temperature ,Internal conversion (chemistry) ,Atomic and Molecular Physics, and Optics ,Kinetics ,Intersystem crossing ,Spectrometry, Fluorescence ,Models, Chemical ,Spectrophotometry ,Excited state ,Protons ,Phosphorescence - Abstract
The spectral and photophysical properties of indigo derivatives with di-, tetra-, and hexa-substitution in their neutral (keto) form are investigated in solution. The study comprises absorption and emission spectra, together with quantitative measurements of quantum yields of fluorescence (phi(F)) and singlet oxygen formation (phi(Delta)) and fluorescence lifetimes. The energy difference between the HOMO and LUMO orbitals is dependent on the degree (number of groups) and relative position of substitution. The phi(F) and phi(Delta) values were found to be very lowor=10(-3). Because of the absence of transient triplet-triplet signal, the intersystem crossing yields (phi(T)) were estimated by assuming that all the triplet states formed give rise to singlet oxygen formation, that is, phi(Delta) approximately phi(T) . It was then possible from phi(IC)=1-phi(F)-phi(T) to estimate the S(1) approximately approximately --S(0) internal conversion yields and thus, with the other data, to determine the rate constants for all decay processes. From these, several conclusions are drawn. Firstly, the radiationless rate constants, k(NR) , clearly dominate over the radiative rate constants, k(F) , (and processes). Secondly, the main deactivation channel for the compounds in their keto form is the radiationless S(1) approximately approximately --S(0) internal conversion process. Finally, although the changes are relatively small, internal conversion yield seems to be independent of the overall pattern of substitution. A more detailed investigation of the decay profiles with collection at the blue and red emission of the fluorescence band of indigo and one di-substituted indigo reveals the decays to be bi-exponential and that at longer emission wavelengths these appear to be associated with both rise and decay times indicating that two excited species exist, which is consistent with a keto-excited form giving rise (by fast proton transfer) to the enol-form of indigo. Evidence is presented which supports the idea that intramolecular (and possibly some intermolecular) proton transfer can explain the high efficiency of internal conversion in indigo.
- Published
- 2006
37. Dopaquinone redox exchange with dihydroxyindole and dihydroxyindole carboxylic acid
- Author
-
Lucia Panzella, Edward J. Land, Christopher A. Ramsden, Suppiah Navaratnam, Patrick A. Riley, Alessandro Pezzella, Alessandra Napolitano, Ruth Edge, Marco d'Ischia, Edge, R., D'Ischia, M., Land, E. J., Napolitano, A., Navaratnam, S., Panzella, L., Pezzella, A., Ramsden, C. A., Riley, P. A., R., Edge, D'Ischia, Marco, E. J., Land, Napolitano, Alessandra, S., Navaratnam, Panzella, Lucia, Pezzella, Alessandro, C. A., Ramsden, and P. A., Riley
- Subjects
Nucleophilic addition ,Indoles ,Semiquinone ,Free Radicals ,Clinical Biochemistry ,DHICA ,Cell Biology ,Plant Science ,Photochemistry ,Cysteinyldopa ,Redox ,chemistry.chemical_compound ,Indolequinone ,Kinetics ,Reaction rate constant ,chemistry ,Models, Chemical ,Radiolysis ,Computer Simulation ,Agronomy and Crop Science ,Oxidation-Reduction ,Developmental Biology - Abstract
A pulse radiolytic investigation has been conducted to establish whether a redox reaction takes place between dopaquinone and 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid (DHICA) and to measure the rate constants of the interactions. To obviate possible confounding reactions, such as nucleophilic addition, the method employed to generate dopaquinone used the dibromide radical anion acting on dopa to form the semiquinone which rapidly disproportionates to dopaquinone. In the presence of DHI the corresponding indole-5,6-quinone (and/or tautomers) was also formed directly but, by judicious selection of suitable relative concentrations of initial reactants, we were able to detect the formation of additional indolequinone from the redox exchange reaction of DHI with dopaquinone which exhibited a linear dependency on the concentration of DHI. Computer simulation of the experimental time profiles of the absorption changes showed that, under the conditions chosen, redox exchange does proceed but not quite to completion, a forward rate constant of 1.4 x 10(6)/M/s being obtained. This is in the same range as the rate constants previously established for reactions of dopaquinone with cyclodopa and cysteinyldopa. In similar experiments carried out with DHICA, the reaction more obviously does not go to completion and is much slower, k (forward) =1.6 x 10(5)/M/s. We conclude that, in the eumelanogenic pathway, DHI oxidation may take place by redox exchange with dopaquinone, although such a reaction is likely to be less efficient for DHICA.
- Published
- 2006
38. Studies of carotenoid one-electron reduction radicals
- Author
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Ali El-Agamey, T. George Truscott, Suppiah Navaratnam, Edward J. Land, and Ruth Edge
- Subjects
chemistry.chemical_classification ,Anions ,Chemistry ,Reducing agent ,Octoxynol ,Radical ,Biophysics ,food and beverages ,Benzene ,Electrons ,Photochemistry ,Biochemistry ,Carotenoids ,chemistry.chemical_compound ,Kinetics ,Ketyl ,Radical ion ,Astaxanthin ,Xanthophyll ,One-electron reduction ,Solvents ,Hexanes ,Canthaxanthin ,Molecular Biology ,Oxidation-Reduction - Abstract
The relative reduction potentials of a variety of carotenoids have been established by monitoring the reaction of carotenoid radical anion (CAR1(*-)) with another carotenoid (CAR2) in hexane and benzene. This order is consistent with the reactivities of the carotenoid radical anions with porphyrins and oxygen in hexane. In addition, investigation of the reactions of carotenoids with reducing radicals in aqueous 2% Triton-X 100, such as carbon dioxide radical anion (CO2(*-)), acetone ketyl radical (AC(*-)) and the corresponding neutral radical (ACH(*)), reveals that the reduction potentials for beta-carotene and zeaxanthin lie in the range -1950 to -2100 mV and those for astaxanthin, canthaxanthin and beta-apo-8'-carotenal are more positive than -1450 mV. This illustrates that the presence of a carbonyl group causes the reducing ability to decrease. The radical cations have been previously shown to be strong oxidising agents and we now show that the radical anions are very strong reducing agents.
- Published
- 2006
39. Carotenoid Radicals and the Interaction of Carotenoids with Active Oxygen Species
- Author
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Ruth Edge and T. George Truscott
- Subjects
chemistry.chemical_classification ,Singlet oxygen ,Radical ,medicine.medical_treatment ,Carotene ,Photochemistry ,chemistry.chemical_compound ,chemistry ,Radical ion ,Astaxanthin ,Oxidizing agent ,medicine ,Carotenoid ,Alkyl - Abstract
Carotenoid radicals are generated from the interaction of a wide range of carotenoids with several oxy-radicals, such as CCl3O 2 • , RSO 2 • , NO 2 • and various aryl peroxyl radicals, while less strongly oxidizing radicals, such as alkyl peroxyl radicals, can lead to hydrogen atom transfer, thereby generating the neutral carotene radical. Comparison of the relative abilities of many pairs of carotenoids to donate/accept electrons: CAR1•++CAR2→CAR1+CAR2•+, has allowed the relative oxidation potentials to be established, showing that lycopene is the easiest carotenoid to oxidize to its cation radical and astaxanthin is the most difficult.
- Published
- 2006
40. Pulse radiolysis study of the interaction of retinoids with peroxyl radicals
- Author
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Ann Cantrell, T. George Truscott, Edward J. Land, Ruth Edge, Tadeusz Sarna, and Malgorzata Barbara Rozanowska
- Subjects
Antioxidant ,Free Radicals ,medicine.drug_class ,Octoxynol ,medicine.medical_treatment ,Detergents ,Retinoic acid ,free radicals ,Tretinoin ,Ascorbic Acid ,Photochemistry ,retinal ,Biochemistry ,Micelle ,vitamin A ,Antioxidants ,Lipid peroxidation ,chemistry.chemical_compound ,Retinoids ,Physiology (medical) ,Cations ,peroxyl radical ,retinoic acid ,medicine ,Humans ,Retinoid ,Vitamin A ,Micelles ,Chemistry ,pulse radiolysis ,Retinol ,lipid peroxidation ,ascorbate ,Bromine ,Lipids ,Carbon ,Peroxides ,Kinetics ,antioxidants ,Models, Chemical ,retinoid ,Spectrophotometry ,Radiolysis ,Microsome ,carbon tetrachloride ,Lipid Peroxidation ,Pulse Radiolysis ,retinol - Abstract
Vitamin A (retinol) and its derivatives-retinal and retinoic acid-are known for their ability to inhibit lipid peroxidation. Antioxidant actions of retinoids have been attributed to chain-breaking by scavenging of peroxyl radicals. Based on chemical analysis of retinoic acid degradation products formed during microsomal lipid peroxidation, it was previously suggested that retinoids interact with peroxyl radicals forming free carbon-centered radical adducts. However, it can be argued that such a mode of antioxidant action of retinoids is not sufficient to fully explain their effectiveness at inhibiting lipid peroxidation, which in many systems is comparable to, or even exceeds, that of alpha-tocopherol. In order to elucidate the mechanism of interaction of retinoids with peroxyl radicals, (trichloromethyl)peroxyl radical was generated by pulse radiolysis, and its interactions with retinoids solubilized in Triton X-100 micelles were followed by kinetic absorption spectroscopy. All retinoids--retinol, retinal, and retinoic acid--interacted with the peroxyl radical, and at least two transient products were detected. One of these products, absorbing at 590 nm, was identified as retinoid cation radical. Therefore, we postulate that, apart from formation of radical adducts, retinoids may also scavenge peroxyl radicals by electron transfer.
- Published
- 2004
41. Spectroscopic properties and reactivity of free radical forms of A2E
- Author
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Suppiah Navaratnam, Ruth Edge, Joan E. Roberts, Agnieszka Broniec, Albert R. Wielgus, Anna Pawlak, Tadeusz Sarna, T. George Truscott, and Edward J. Land
- Subjects
Free Radicals ,Radical ,retinal pigment epithelium ,free radicals ,Pyridinium Compounds ,Photochemistry ,Biochemistry ,Dissociation (chemistry) ,A2E ,chemistry.chemical_compound ,phototoxicity ,Retinoids ,Reaction rate constant ,Physiology (medical) ,Oxidizing agent ,oxidative stress ,Formate ,A2E radicals ,Spectrum Analysis ,pulse radiolysis ,Kinetics ,Radical ion ,chemistry ,Radiolysis ,retinal lipofuscin ,Pyridinium - Abstract
A pyridinium bisretinoid (A2E) is the only identified blue-absorbing chromophore of retinal lipofuscin that has been linked to its aerobic photoreactivity and phototoxicity. Pulse radiolysis has been used to study both the one-electron oxidation and the one-electron reduction of A2E in aqueous micellar solutions. The reduction to the semireduced A2E (lambda(max) broad and between 500 and 540 nm) was achieved with formate radicals and the subsequent decay of A2E* was slow (over hundreds of milliseconds) via complex kinetics. The long lifetime of the A2E* should facilitate its reactions with other biomolecules. For example, with oxygen, the A2E* produced the superoxide radical anion with a rate constant of 3 x 10(8) M(-1) s(-1). The A2E was also reduced by the NAD radical, the corresponding rate constant being 2.3 x 10(8) M(-1) s(-1). Other experiments showed that the one-electron reduction potential of A2E lies in the range -640 to -940 mV. The semioxidized form of A2E (lambda(max) 590 nm) was formed via oxidation with the Br2*- radical and had a much shorter lifetime than the semireduced form. With strongly oxidizing peroxyl radicals (CCl3O2*) our kinetic data suggest the formation of a radical adduct followed by dissociation to the semioxidized A2E. With milder oxidizing peroxyl radicals such as that from methanol, our results were inconclusive. In benzene we observed an efficient oxidation of zeaxanthin to its radical cation by the A2E radical cation; this may be relevant to a detrimental effect of A2E in vision.
- Published
- 2004
42. Formation and reactivity of free radicals in 5-hydroxymethyl-2-furaldehyde--the effect on isoprenaline photostability
- Author
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Suppiah Navaratnam, Jørgen Brustugun, Ruth Edge, and Hanne Hjorth Tønnesen
- Subjects
Absorption spectroscopy ,Free Radicals ,Photochemistry ,Radical ,Biophysics ,Quantum yield ,Electrons ,Buffers ,Solvated electron ,Phosphates ,chemistry.chemical_compound ,Cations ,Radiology, Nuclear Medicine and imaging ,Furaldehyde ,Radiation ,Radiological and Ultrasound Technology ,Singlet oxygen ,Spectrum Analysis ,Isoproterenol ,Oxygen ,Solutions ,Glucose ,chemistry ,Radiolysis ,Flash photolysis ,Hydroxyl radical - Abstract
Solutions of glucose are used as diluents for drugs in various drug infusions. When sterilized by heat small amounts of the substance 5-hydroxymethyl-2-furaldehyde (5-HMF) is produced from glucose. At a hospital ward such infusions may be exposed to irradiation; including UV-light. The photoreactivity of the furaldehyde is investigated. It is shown to photodestabilize the catecholamine isoprenaline. It is shown to be a producer, but also a consumer, of singlet oxygen. The excited triplet, cation and anion radical have been produced by pulse radiolysis and flash photolysis and their absorbance characteristics have been determined. The triplet absorption spectrum showed absorption bands at 320 and 430 nm with molar absorption coefficients of 4700 and 2600 M-1 cm-1, respectively. The anion radical showed absorption bands at 330 and 420 nm with molar absorption coefficients of 2000 and 300 M-1 cm-1, respectively. The cation radical had an absorption band at 320 nm with a molar absorption coefficient of 5000 M-1 cm-1. The quantum yield for the production of singlet oxygen, sensitized by the 5-HMF triplet, was determined to be 0.6, whilst the quantum yield for the triplet formation was 1.0. Aqueous solutions of 5-HMF were found to photoionize to yield the hydrated electron and the cation radical of 5-HMF in a biphotonic process. The influences of pH, buffer and glucose on the formation of transients were evaluated. The reactions between 5-HMF and the solvated electron, the hydroxyl radical and the superoxide were also studied.
- Published
- 2004
43. Characterisation of carotenoid radical cations in liposomal environments: interaction with vitamin C
- Author
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Edward J. Land, Marc Burke, Ruth Edge, and T. George Truscott
- Subjects
Lutein ,1,2-Dipalmitoylphosphatidylcholine ,Free Radicals ,Biophysics ,Ascorbic Acid ,Xanthophylls ,Photochemistry ,chemistry.chemical_compound ,Zeaxanthins ,Cations ,Radiology, Nuclear Medicine and imaging ,Carotenoid ,chemistry.chemical_classification ,Liposome ,Radiation ,Radiological and Ultrasound Technology ,Molecular Structure ,food and beverages ,Ascorbic acid ,beta Carotene ,eye diseases ,Zeaxanthin ,chemistry ,Radical ion ,Xanthophyll ,Radiolysis ,Liposomes ,Spectrophotometry, Ultraviolet - Abstract
Pulse radiolysis was used to generate the radical cations of beta-carotene and two xanthophylls, zeaxanthin and lutein, in unilamellar vesicles of dipalmitoylphosphatidyl choline. The rate constants for the reaction (repair) of these carotenoid radical cations with the water-soluble vitamin C were found to be similar (approximately 1x10(7) M(-1) s(-1)) for beta-carotene and zeaxanthin and somewhat lower (approximately 0.5x10(7) M(-1) s(-1)) for lutein. The results are discussed in terms of the microenvironment of the carotenoids and suggest that for beta-carotene, a hydrocarbon carotenoid, the radical cation is able to interact with a water-soluble species even though the parent hydrocarbon carotenoid is probably entirely in the non-polar region of the liposome.
- Published
- 2001
44. One-electron reduction potentials of dietary carotenoid radical cations in aqueous micellar environments
- Author
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Edward J. Land, Marc Burke, Ruth Edge, T. George Truscott, and David J. McGarvey
- Subjects
Free Radicals ,Radical ,Biophysics ,macromolecular substances ,β-Carotene ,One-electron reduction potential ,Photochemistry ,Biochemistry ,Dietary carotenoid ,chemistry.chemical_compound ,Electron transfer ,Lycopene ,Structural Biology ,Astaxanthin ,Cations ,Genetics ,Canthaxanthin ,Cysteine ,Molecular Biology ,Carotenoid ,Micelles ,chemistry.chemical_classification ,organic chemicals ,Tryptophan ,Water ,food and beverages ,Cell Biology ,Dipeptides ,Hydrogen-Ion Concentration ,Carotenoids ,Radical cation ,chemistry ,Radical ion ,Spectrophotometry ,Radiolysis ,One-electron reduction ,Tyrosine ,Pulse Radiolysis ,Oxidation-Reduction - Abstract
The one-electron reduction potentials of the radical cations of five dietary carotenoids (β-carotene, canthaxanthin, zeaxanthin, astaxanthin and lycopene) in aqueous micellar environments have been obtained from a pulse radiolysis study of electron transfer between the carotenoids and tryptophan radical cations as a function of pH, and lie in the range of 980–1060 mV. These values are consistent with our observation that the carotenoid radical cations oxidise tyrosine and cysteine. The decays of the carotenoid radical cations in the absence of added reactants suggest a distribution of exponential lifetimes. The radicals persist for up to about 1 s, depending on the medium.
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