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Reactive oxygen species comprise oxygen-based free radicals and non-radical species such as peroxynitrite and electronically excited (singlet) oxygen. These reactive species often have short lifetimes, and much of our understanding of their formation and reactivity in biological and especially medical environments has come from complimentary fast reaction methods involving pulsed lasers and high-energy radiation techniques. These and related methods, such as EPR, are discussed with particular reference to singlet oxygen, hydroxy radicals, the superoxide radical anion, and their roles in medical aspects, such as cancer, vision and skin disorders, and especially pro- and anti-oxidative processes.

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.

Managing certain by-products of the nuclear fuel cycle, such as the radioactive isotopes of caesium: 134Cs, 135Cs and 137Cs is challenging due to their environmental mobility and radioactivity. While a great many materials can isolate Cs+ ions from neutral or basic aqueous solutions via ion exchange, few of these, with the exception of ammonium phosphomolybdate (AMP), function effectively in acidic media. The use of AMP, and its porous composite in polyacrylonitrile (PAN) for management of Cs radioisotopes in various nuclear wastes have been known for decades and are well studied, yet the effects of radiation on the physiochemical properties of such composites have only received limited attention to date. In a previous publication, we demonstrated that a 100 kGy gamma irradiation dose has negligible effect on the ion exchange performance of AMP and AMP&ndash, PAN with respect to capacity or kinetics under the Cs+ concentrations and acidity found in spent nuclear fuel (SNF) recycling. As a continuation of this prior study, in this publication we explore the effects of gamma irradiation on the physiochemical properties of AMP and AMP&ndash, PAN using a range of characterisation methods. The effects of the same gamma dose on the oxidation state of Mo in AMP and AMP&ndash, PAN, the thermal degradation of both AMP and AMP&ndash, PAN, combined with a first study into the high-temperature degradation AMP, are reported. The implications of irradiation, its possible mechanism, the conditions present in SNF recycling, and for the end-of-life disposal or recycling of these materials are also discussed.

Gamma irradiation-induced defects at doses of 0.5 and 5 MGy were studied in lithium sodium-borosilicate (LiNaBSi) and sodium barium-borosilicate (NaBaBSi) glasses, used for high-level radioactive waste immobilisation in the UK and India, respectively. X-band electron paramagnetic resonance (EPR), Raman and UV-Vis-nIR spectroscopies were used to characterise the glasses before and after irradiation. EPR and UV-Vis-nIR absorption spectroscopies revealed the formation of boron-oxygen hole centres (BOHC), electrons trapped at alkali cations or ET centres and peroxy-radicals (PORs) as defects common to both glasses. In addition, E− or polaron centres were observed in NaBaBSi glasses, possibly related to formation of elemental sodium colloids. Time-dependent thermal annealing at a range of temperatures, including those relevant to canister centreline cooling (CCC), which may be of relevance to geological disposal in future technical assessments, was carried out to study thermal stability of these radiation-induced defects. It was observed that PORs are the most thermally-stable defects in both glasses. The influence of glass composition on the segregation of sodium and the possible formation of metal colloids upon irradiation have been discussed.

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.

Carotenoid pigments, particularly β-carotene and lycopene, are consumed in human foodstuffs and play a vital role in maintaining health. β-carotene is known to quench singlet oxygen and can have strong antioxidant activity. As such, it was proposed that β-carotene might reduce the risk of cancer. Epidemiological studies found inverse relationships between cancer risk and β-carotene intake or blood levels. However, clinical trials failed to support those findings and β-carotene supplementation actually increased lung cancer incidence in male smokers. Early experimental animal studies found dietary β-carotene inhibited UV-induced skin cancers. Later studies found that β-carotene supplementation exacerbated UV-carcinogenic expression. The discrepancies of these results were related to the type of diet the animals consumed. Lycopene has been associated with reduced risk of lethal stage prostate cancer. Other carotenoids, e.g., lutein and zeaxanthin, play a vital role in visual health. Numerous studies of molecular mechanisms to explain the carotenoids’ mode of action have centered on singlet oxygen, as well as radical reactions. In cellular systems, singlet oxygen quenching by carotenoids has been reported but is more complex than in organic solvents. In dietary β-carotene supplement studies, damaging pro-oxidant reactivity can also arise. Reasons for this switch are likely due to the properties of the carotenoid radicals themselves. Understanding singlet oxygen reactions and the anti-/pro-oxidant roles of carotenoids are of importance to photosynthesis, vision and cancer.

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.

This work investigates the evolution of the tensile and structural properties of fused filament fabrication (FFF), formed polymers under gamma irradiation. Commercial off-the-shelf print filaments of Poly(lactic acid) (PLA), Thermoplastic polyurethane (TPU), Chlorinated polyethylene elastomer (CPE), Nylon, Acrylonitrile butadiene styrene (ABS) and Polycarbonate (PC) were exposed to gamma-ray doses of up to 5.3 MGy. The suitability of FFF-formed components made from these materials for use in radiation environments is evaluated by considering their structural properties. We identify clear trends in the structural properties of all the materials tested and correlate them with changes in the chemical structure. We find that Nylon shows the best performance under these conditions, with no change in ultimate tensile strength and an increase in stiffness. However, some of our findings suggest that the effect of additives to this type of filament may result in potentially undesirable adhesive properties. The organic polymer PLA was notably more radiation-sensitive than the other materials tested, showing 50% decrease in Young’s Modulus and ultimate tensile strength at order of magnitude lower radiation dose. A mechanism is proposed whereby FFF-processed components would have substantially different radiation tolerances than bulk material.

Reducing radiation damage is important and dietary antioxidants that can protect cells from such damage are of value. Dietary lycopene, a carotenoid found in tomatoes, protects human lymphoid cell membranes from damage by γ-radiation. We report that such protective effects are remarkably reduced as the oxygen concentration increases - near zero at 100% oxygen from fivefold protection at 20% oxygen and, dramatically, from 50-fold protection at 0% oxygen. Such huge differences imply that under higher oxygen concentrations lycopene could lead to improved cancer therapy using γ-radiation. The cells are not efficiently protected from the superoxide radical by lycopene. Noncellular studies suggest molecular mechanisms for the oxygen effect.

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.

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.

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.

An effort has been made to bridge the gap between academic knowledge of polymeric seal degradation and industrial practices. A series of physical and mechanical properties that can be related to the sealing behavior of three commercial samples of nitrile rubber have been studied for their degradation when exposed to gamma radiation. For all samples the glass transition temperature (Tg) and retention factor (RF) were found to increase with total dose whilst percentage change in mass (ΔM%) was found to decrease. The ultimate uptake of carbon dioxide (CO2) did not appear to change with radiation dose but the kinetics of the absorption process were found to decrease, suggesting the formation of crosslinks. The crosslinks formed appear to be dependent on the original material composition and comparison against degradation of material properties supports the theory behind butadiene, BDN, content being linked to a propensity for crosslink clustering. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44618.

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.

The synthesis of metal(II) complexes of a bis(thiosemicarbazonato) ligand derived from 1,2-cyclohexanedione are reported. The compounds have been characterised by a range of techniques including reverse-phase HPLC, cyclic voltammetry, NMR, UV/Vis, IR, Raman and EPR spectroscopy. Xray crystal structures of the proligand and two copper(II) complexes have been obtained, and the electronic structures have been analysed by using DFT calculations. DFT calculations have also been used to map the potential energy surface of a related bis(thiosemicarbdzone) proligand and predict solution-phase one-electron reduction potentials of the copper(H) complex by using three polarisable continuum Solvation models. Electrochemistry experiments show that the copper(II) complex undergoes quasi-reversible one-electron reduction at biologically accessible potentials and is within the range proposed for the complex to be hypoxia-selective. In addition, UV/Vis spectroelectrochemistry experiments have been used to characterise the reduced copper(l) anion, and the reaction between the anion and dioxygen has been characterised by experiments and theory, Observation of this oxidation reaction has important implications for the proposed mechanisms of hypoxia selectivity of bis(thiosemicarbazonato)copper(H) complexes, The copper-64 radiolabelled complex has been prepared in aqueous solution which demonstrates the potential of rise of these complexes as medical imaging agents. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The effect of γ-radiation on a variety of model vitreous wasteforms applied to, or conceived for, immobilisation of UK intermediate and high level radioactive wastes was studied up to a dose of 8 MGy. It was determined that γ-irradiation up to this dose had no significant effect upon the mechanical properties of the wasteforms and there was no evidence of residual structural defects. FTIR and Raman spectroscopy showed no evidence of radiation directly affecting the silicate network of the glasses. The negligible impact of this γ-irradiation dose on the physical properties of the glass was attributed to the presence of multivalent ions, particularly Fe, and a mechanism by which the electron–hole pairs generated by γ-irradiation were annihilated by the Fe2+–Fe3+ redox mechanism. However, reduction of sulphur species in response to γ-radiation was demonstrated by S K-edge XANES and XES data.

Two series of extended carbon chain butadiynyl and hexatriynyl complexes, [Mo{(C≡C)nC≡CSiMe3}(bpy)(η-C7H7)] (n = 1, 2; bpy = 2,2′-bipyridine) and [Mo{(C≡C)nC≡CR}(dppe)(η-C7H7)] (n = 1, R = H, SiMe3; n = 2, R = SiMe3; dppe = Ph2PCH2CH2PPh2), have been prepared and structurally characterized. The redox chemistry of these complexes has been investigated by cyclic voltammetry, and the 17-electron radical cations resulting from one-electron oxidation have been characterized by spectroelectrochemical IR and UV–visible methods and EPR spectroscopy. DFT calculations on the H-terminated model complexes [Mo{(C≡C)nC≡CH}(L2)(η-C7H7)]z+ (L2 = bpy, dppe) reveal a largely metal-centered HOMO (z = 0) with a modest increase in carbon chain character with increasing chain length. Spin density calculations for the 17-electron radical cations (z = 1) show large coefficients of spin density at the metal center, consistent with the remarkably high stability of the experimental complexes. However, both DFT theoretical and exper...

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.

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.

The cycloheptatrienyl molybdenum alkynyl complex [Mo(C≡CH)(dppe)(η-C7H7)], 1 (dppe = Ph2PCH2CH2PPh2), undergoes oxidative dimerization on reaction with [FeCp2]PF6 in thf at −78 °C to give the bis(vinylidene) [{Mo(dppe)(η-C7H7)}2(μ-C═CH-CH═C)][PF6]2, [2][PF6]2. Deprotonation of [2][PF6]2 with KOBut yields butadiyndiyl-bridged [{Mo(dppe)(η-C7H7)}2(μ-C≡C-C≡C)], 3, which undergoes in situ aerial oxidation to give [{Mo(dppe)(η-C7H7)}2(μ-C4)][PF6], [3]PF6, as the major product. The cyclic voltammogram of [3]PF6 exhibits a series of four redox processes indicative of sequential formation of [{Mo(dppe)(η-C7H7)}2(μ-C4)]n+ (n = 0, 1, 2, 3, 4) with the comproportionation constant, KC, for [3]PF6 of 1.9 × 107. Spectroscopic investigations on [3]PF6 by IR, Raman, NIR, and EPR spectroscopy reveal properties characteristic of a d5/d6 mixed valence complex with a localized electronic structure and an estimated intramolecular electron transfer rate in the range 108–1010 s–1. The experimental NIR spectrum of [3]PF6 is cons...

A simple design for an in situ, three-electrode spectroelectrochemical cell is reported that can be used in commercial Q- and W-band (ca. 34 and 94 GHz, respectively) electron paramagnetic resonance (EPR) spectrometers, using standard sample tubing (1.0 and 0.5 mm inner diameter, respectively) and within variable temperature cryostat systems. The use of the cell is demonstrated by the in situ generation of organic free radicals (quinones and diimines) in fluid and frozen media, transition metal ion radical anions, and on the enzyme nitric oxide synthase reductase domain (NOSrd), in which a pair of flavin radicals are generated.

Two series of bis-phosphine-substituted cyclopentadienyl molybdenum alkynyl complexes, [Mo(C≡CR)(CO)(dppe)Cp′] and trans-[Mo(C≡CR)(CO)(PMe3)2Cp′] (R = Ph or C6H4-4-Me, dppe = Ph2PCH2CH2PPh2, Cp′ = Cp or Cp*), have been prepared and structurally characterized. One-electron oxidation to the 17-electron radical cations has been investigated by cyclic voltammetry and, for selected Cp* derivatives, by spectroelectrochemical IR and UV–visible methods. Through a combination of experimental measurements (IR and EPR spectroscopy) and DFT-based calculations some important differences between the two series of complexes [Mo(C≡CR)(CO)(dppe)Cp′] and trans-[Mo(C≡CR)(CO)(PMe3)2Cp′] have been established. In particular, the change in molecular geometry leads to enhanced alkynyl character in the HOMO of [Mo(C≡CR)(CO)(dppe)Cp′] when compared with the largely metal-centered HOMO of trans-[Mo(C≡CR)(CO)(PMe3)2Cp′].

The first examples of vinylidene complexes of the cycloheptatrienyl tungsten system [W(C=CHR)(dppe)(η-C₇H₇)](+) (dppe = Ph₂PCH₂CH₂PPh₂; R = H, 3; Ph, 4; C₆H₄-4-Me, 5) have been synthesised by reaction of [WBr(dppe)(η-C₇H₇)], 1, with terminal alkynes HC≡CR; a one-pot synthesis of 1 from [WBr(CO)₂(η-C₇H₇)] facilitates its use as a precursor. The X-ray structure of 4[PF₆] reveals that the vinylidene ligand substituents lie in the pseudo mirror plane of the W(dppe)(η-C₇H₇) auxiliary (vertical orientation) with the phenyl group located syn to the cycloheptatrienyl ring. Variable temperature ¹H NMR investigations on [W(C=CH₂)(dppe)(η-C₇H₇)][PF₆], 3, estimate the energy barrier to rotation about the W=C(α) bond as 62.5 ± 2 kJ mol⁻¹; approximately 10 kJ mol⁻¹ greater than for the molybdenum analogue. Deprotonation of 4 and 5 with KOBu(t) yields the alkynyls [W(C≡CR)(dppe)(η-C₇H₇)] (R = Ph, 6; C₆H₄-4-Me, 7) which undergo a reversible one-electron oxidation at a glassy carbon electrode in CH₂Cl₂ with E(½) values approximately 0.12 V negative of Mo analogues. The 17-electron radicals [6](+) and [7](+) have been investigated by spectroelectrochemical IR, UV-visible and EPR methods. The electronic structures of representative vinylidene (3) and alkynyl (6) complexes have been investigated at the B3LYP/Def2-SVP level. In both cases, electronic structure is characterised by a frontier orbital with significant metal d(z²)character and this dominates the structural and spectroscopic properties of the system.

The design and study of organometallic mixed-valence complexes is complicated by the mixing of metal d and bridging ligand π orbitals, which often makes the assignment of metal oxidation states amb...

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.

International audience; Reaction of [PdMe2(tmeda)] with pyridyl-N-di(tert-butyl)phosphinoimine spontaneously affords an unusual bimetallic palladium(I) ligand-based biradical complex, which behaves as a "masked" form of Pd0 in its reactions with neutral ligands and chlorobenzene.

A series of molybdenum alkynyl complexes [Mo(C≡CR)(dppe)(η-C7H7)] featuring a range of alkynyl substituents R with varying electron-donating and -withdrawing properties have been prepared. Oxidatio...

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.

For heparan sulfate (HS) to bind and regulate the activity of proteins, the polysaccharide must present an appropriate sequence and adopt a suitable conformation. The conformations of heparin derivatives, as models of HS, are altered via a change in the associated cations, and this can drastically modify their FGF signaling activities. Here, we report that changing the cations associated with an N-acetyl-enriched heparin polysaccharide, from sodium to copper(II), converted it from supporting signaling through the fibroblast growth factor receptor (FGF-1-FGFR1c) tyrosine kinase signaling system to being inhibitory in a cell-based BaF3 assay. Nuclear magnetic resonance and synchrotron radiation circular dichroism (SRCD) spectroscopy demonstrated that the polysaccharide conformation differed in the presence of sodium or copper(II) cations. Electron paramagnetic resonance confirmed the environment of the copper(II) ion on the N-acetyl-enriched polysaccharide was distinct from that previously observed with intact heparin, which supported signaling. Secondary structures in solution complexes of polysaccharides with FGF-1 (which either supported signaling through FGFR1c or were inhibitory) were determined by SRCD. This allowed direct comparison of the two FGF-1-polysaccharide complexes in solution, containing identical molecular components and differing only in their cation content. Subtle structural differences were revealed, including a reduction in the level of disordered structure in the inhibitory complex.

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.

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.

The carbonate radical (CO 3 (*-)) is of importance in biology and chemistry. We used pulse radiolysis to generate the CO 3 (*-) radical and show there is no reaction with oxygen. However, in the presence of ammonia the CO 3 (*-) radical is removed by NO (*), which itself arises from the scavenging of NH 2 (*) by oxygen, and the mechanism of this process is reported. The CO 3 (*-) radical shows complex decay patterns in the presence of ammonia, which can be understood as a balance between the radical-radical reaction CO 3 (*-) + CO 3 (*-) and CO 3 (*-) + NH 2 (*) (the amino radical). Also, we report reactivity with glycine and alanine and with melanin models. The CO 3 (*-) reacts with both dopa-melanin (DM, a model of black eumelanin) and with cysteinyl-dopa-melanin (CDM, a model of red/blond phaeomelanin). However, the reaction rate constant is much higher with CDM than with DM.

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.

The synthesis of zinc(II) and copper(II) complexes of an unsymmetrical bis(thiosemicarbazonato) ligand containing a reactive styrene group are reported. The compounds have been characterised by a range of techniques including reverse-phase HPLC, cyclic voltammetry, NMR, UV/Vis, electron paramagnetic resonance and fluorescence emission spectroscopy. Time-dependent density functional theory calculations have been used to assign the electronic absorption spectrum of [ZnIIATSM] and probe the nature of the fluorescent excited state. Electrochemistry experiments show that the copper(II) complex undergoes quasi-reversible one-electron reduction at biologically accessible potentials and is within the range proposed for the complex to be hypoxia-selective. The copper-64 radiolabelled complex has been prepared in aqueous solution and characterised by reverse-phase radio-HPLC. Cellular uptake in HeLa cells has been observed using confocal fluorescence microscopy.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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.

Raman spectroscopy and microscopy, along with all vibrational spectroscopic techniques, has proven itself to be a valuable analytical technique to quantitatively and qualitatively determine the molecular composition, properties of all kind of material systems. It has been successfully utilized in various fields of science, primarily due to the extraordinary versatility of sampling methods. The technique requires minimal sample preparation and can analyze samples of one monolayer thickness or of low sample concentration. Excellent spectral and spatial resolution and detailed fingerprinting can be derived from Raman spectra. Many technical issues such as fluorescence, poor sensitivity, or reproducibility have been overcome with the advances in instrumentation. Thus, its versatility of applications, rapidness of collection and easy analysis have made Raman spectroscopy an attractive analytical tool.

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.

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.

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.

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.

The influence of side-chain structure on the mode of reaction of ortho-quinone amines has been investigated with a view, ultimately, to developing potential methods of therapeutic intervention by manipulating the early stages of melanogenesis. Four N-substituted dopamine derivatives have been prepared and quinone formation studied using pulse radiolysis and tyrosinase-oximetry. Ortho-quinones with an amide or urea side chain were relatively stable, although evidence for slow formation of isomeric para-quinomethanes was observed. A thiourea derivative cyclized fairly rapidly (k = 1.7/s) to a product containing a seven-membered ring, whereas a related amidine gave more rapidly (k approximately 2.5 x 10(2)/s) a stable spirocyclic product. The results suggest that cyclization of amides, ureas and carbamates (NHCO-X; X = R, NHR or OR) does not occur and is not, therefore, a viable approach to the formation of tyrosinase-activated antimelanoma prodrugs. It is also concluded that for N-acetyldopamine spontaneous ortho-quinone to para-quinomethane isomerization is slow.

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.

Porphyrins such as protoporphyrin IX (PP IX) and uroporphyrin I (UP I) can be phototoxic to human cells. To study the protective ability of antioxidants (beta-carotene, lycopene, ascorbic acid and alpha-tocopherol), against such porphyrin phototoxicity, membrane destruction experiments (Jurkat cells) and human cell cultures (fibroblasts) were performed. Both beta-carotene and lycopene and also the combination of beta-carotene, ascorbic acid and alpha-tocopherol offered cell protection against PP IX phototoxicity. Investigations of both cell membrane protection and of cell growth showed differences in terms of the protection afforded by the anti-oxidants. Thus, for PP IX, carotenoids alone, and in combination with ascorbic acid and alpha-tocopherol, showed higher protection factors in general than UP I. However, for membrane protection there was significant protection against UP I by the combination of beta-carotene, ascorbic acid and alpha-tocopherol but not by any of these anti-oxidants alone. The membrane protection against PP IX by beta-carotene, and especially lycopene, is significant presumably because of the high lipophilicity of all these molecules. However, the hydrophilic UP I will cause phototoxicity mainly via H(2)O(2), radical or singlet oxygen production in the aqueous phase, and these reactive species may be generated some distance from the cell membrane. This may lead to the little or no protection observed for UP I by the individual antioxidants. Nevertheless, a combination of beta-carotene, ascorbic acid and alpha-tocopherol offers membrane protection against the phototoxicity of both porphyrins. This is believed to occur as a result of synergistic processes. Our results suggest that the treatment of porphyria cutanea tarda and erythropoietic protoporphyria may be improved by the use of a combination of the antioxidants studied.

The radical cations of five dietary carotenoids have been shown to react with dopamelanin (a model of the black eumelanin) and cysteinyldopamelanin (a model of the red/yellow pheomelanin) in both micellar and homogeneous environments. It is suggested that such repair reactions show previously unidentified protective roles for melanin/carotenoid combinations, especially where the maintenance of the (small) carotenoid concentration is vital to avoid deleterious effects, such as in the retina of the eye.

Antioxidants like β-carotene, α-tocopherol and ascorbic acid should be able to protect human cells against damage due to ultraviolet light. Cultured human fibroblasts have been irradiated with UVA or UVB light after incubation with the antioxidants or combinations of them. The efficiency of the protection by the antioxidants in dietary concentrations is estimated by cell counting following cell culture. In the case of UVA irradiation we find synergistic effects of combinations with β-carotene as the main protector. On the other hand, only additive effects of the tested combinations are observed in the experiments with UVB light. Our experiments show a protective effect of dietary antioxidants against human tissue cell damage by ultraviolet light.

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...