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Mazur M.,Slovak University of Technology in Bratislava | Valko M.,Slovak University of Technology in Bratislava | Rhodes C.J.,Fresh lands Environmental Actions
Journal of Sol-Gel Science and Technology | Year: 2017

Abstract: The influence of the hydration and drying process on the line shape and signal intensity of the electron paramagnetic resonance spectra recorded from Cu(II) ions present in silica xerogels calcined at various temperatures was investigated. The experimental Cu(II) electron paramagnetic resonance spectra were found to consist of a superimposition of three individual subspectra (Γ1, Γ2 and Φ), which reflect different local environments in which the Cu(II) ions were located. The results demonstrate that: (i) Within experimental error, the spin Hamiltonian parameters of each individual subspectrum remain, in the course of the experiments, identical. (ii) The hydration process changed the relative contribution from the individual subspectra (Γ1, Γ2 and Φsignificantly, and increased the overall electron paramagnetic resonance signal intensity by a factor of more than ten, as compared with the non-hydrated silica xerogels. (iii) On re-drying the hydrated silica xerogel samples, the original line shape and original signal intensity values were restored. Thus, measurement of the relative contributions of the individual subspectra can be used as a sensitive method with which to monitor the hydration/drying process in silica xerogels. As a caveat, we conclude that the influence of the hydration/drying process should be taken into account in the interpretation of Cu(II) electron paramagnetic resonance spectra of calcined silica xerogel samples, which provides the real novelty of the present report. Graphical Abstract: Relative contribution of subspectra (Γ1, Γ2 and Φ) to Cu(II) EPR spectra of silica xerogels calcined at the temperatures quoted and then hydrated for 15 min and for 3 days. [InlineMediaObject not available: see fulltext.] © 2017 Springer Science+Business Media New York


Rhodes C.J.,Fresh lands Environmental Actions | Dintinger T.C.,Fresh lands Environmental Actions | Dintinger T.C.,Public Health England
Progress in Reaction Kinetics and Mechanism | Year: 2012

A series of group 1 and group 2 element cation-exchanged samples of zeolite X were prepared and exposed to a beam of spin-polarised, positive muons (of energy 28MeV/c) from a particle accelerator. Longitudinal field repolarisation measurements were made which identified, in each case, both diamagnetic and paramagnetic muon fractions. One of the paramagnetic components revealed a hyperfine field compatible with values reported previously for free muonium atoms (1585 G), while a secondary component was detected showing roughly half the hyperfine coupling measured for atomic muonium, leading to the conclusion that the muonium had become chemically-bound within the zeolite structure, probably via a single-electron bond to a coordinatively unsaturated aluminium atom. A significant ''lost fraction'' was also indicated along with superhyperfine and anisotropic components that repolarised in weaker magnetic fields (0-100 G). As a general trend, the muonium atom yield was found to increase in order of the increasing radius/charge (r/z) ratio, though it is constant within the experimental errors, while the chemically bound muonium was formed in similar proportion in all samples (14.1±1.9% of the total muonium polarisation), with the exception of HX and the parent NaX (from which the other zeolite samples were prepared by cation-exchange), in which it was absent. Along with data from zero-field experiments which were also undertaken, this is interpreted in terms of an entrapment or effective ''scavenging'' of radiolytic electrons by the cations (in the order Na +>K +; Mg 2+>Ca 2+>Sr 2+>Ba 2+) whose combination with positive muons is therefore impeded, thus reducing the yield of muonium atoms. Results for LiX are anomalous since the muonium yield is greater than expected, possibly due to a greater degree of covalency in the Li-O bonding than pertains for the other cations. These results may have some implications for zeolites that suffer longterm radiation exposure/damage when they are used to clean radioactive cations (e.g. Cs +, Sr 2+) from the waters of nuclear power stations and as materials whose cation-exchange capacity has been deliberately enhanced by prior exposure to ionising radiation. © 2012 Science Reviews 2000 Ltd.


Jomova K.,Constantine the Philosopher University | Jenisova Z.,Constantine the Philosopher University | Feszterova M.,Constantine the Philosopher University | Baros S.,Constantine the Philosopher University | And 4 more authors.
Journal of Applied Toxicology | Year: 2011

Arsenic (As) is a toxic metalloid element that is present in air, water and soil. Inorganic arsenic tends to be more toxic than organic arsenic. Examples of methylated organic arsenicals include monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)]. Reactive oxygen species (ROS)-mediated oxidative damage is a common denominator in arsenic pathogenesis. In addition, arsenic induces morphological changes in the integrity of mitochondria. Cascade mechanisms of free radical formation derived from the superoxide radical, combined with glutathione-depleting agents, increase the sensitivity of cells to arsenic toxicity. When both humans and animals are exposed to arsenic, they experience an increased formation of ROS/RNS, including peroxyl radicals (ROO), the superoxide radical, singlet oxygen, hydroxyl radical (OH) via the Fenton reaction, hydrogen peroxide, the dimethylarsenic radical, the dimethylarsenic peroxyl radical and/or oxidant-induced DNA damage. Arsenic induces the formation of oxidized lipids which in turn generate several bioactive molecules (ROS, peroxides and isoprostanes), of which aldehydes [malondialdehyde (MDA) and 4-hydroxy-nonenal (HNE)] are the major end products. This review discusses aspects of chronic and acute exposures of arsenic in the etiology of cancer, cardiovascular disease (hypertension and atherosclerosis), neurological disorders, gastrointestinal disturbances, liver disease and renal disease, reproductive health effects, dermal changes and other health disorders. The role of antioxidant defence systems against arsenic toxicity is also discussed. Consideration is given to the role of vitamin C (ascorbic acid), vitamin E (α-tocopherol), curcumin, glutathione and antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase in their protective roles against arsenic-induced oxidative stress. © 2011 John Wiley & Sons, Ltd.


Mazur M.,Slovak University of Technology in Bratislava | Husarikova L.,Slovak University of Technology in Bratislava | Valko M.,Slovak University of Technology in Bratislava | Rhodes C.J.,Fresh Lands Environmental Actions
Applied Magnetic Resonance | Year: 2016

The various stages of the tetraethyl orthosilicate-based sol–gel process were investigated using electron paramagnetic resonance (EPR) spectroscopy with Cu(II) cations as a spin probe. The latter were introduced to the starting reaction mixture in the form of various copper(II) salts containing anions of different basicity (CuCl2, Cu(ac)2, or CuSO4). At the various defined stages of the sol–gel process, the experimental EPR spectra, recorded at both ambient and liquid nitrogen temperature, were found to be a superimposition of three main types of individual subspectra (Γ1, Γ2, and Φ), which reflect the different local environment in which the Cu(II) ions were located. The spin Hamiltonian parameters of each individual subspectrum remained identical, within experimental error, throughout the various stages of the sol–gel process. In contrast, the relative proportion of the individual subspectra varied significantly as the sol–gel process proceeded, from which the liquid-state to solid-state transition could be monitored as it occurred in the sol–gel reaction medium. Identical results were obtained, irrespective of the nature of the copper(II) salt employed. The results demonstrate that the EPR method provides an effective means with which to monitor the sol-to-gel transition from the viscous, colloid suspension to the final viscoelastic gel. © 2015, Springer-Verlag Wien.


Rhodes C.J.,Fresh lands Environmental Actions
Chemical Papers | Year: 2016

A critical review of zeolites and their use in practical applications is presented. Specificallyconsidered are their role as media for selective light-induced oxidations using molecular O2, and the relationship between this phenomenon and the surface electric fields that exist in zeolites. Methods for the determination of the strength of zeolite surface fields are discussed using sorbed molecules such as CO (with IR detection), spin-probes, di-tert-butyl nitroxide, and NO (measured using EPR spectroscopy). Relationship between the surface fields and molecular reorientation energetics for free radicals sorbed in zeolites, obtained using muonium as a spin-label, is explored. Finally, results obtained from exposing the naturally occurring zeolite, clinoptilolite, to high energy electrons as a means for activating materials toward selective removal of radioactive caesium and strontium cations from wastewaters of nuclear power plants are presented. © Institute of Chemistry, Slovak Academy of Sciences 2015.


Rhodes C.J.,Fresh lands Environmental Actions
Annual Reports on the Progress of Chemistry - Section C | Year: 2010

The present review focuses mainly on the interaction between molecules and the surfaces of zeolites and opens with Electron Spin Resonance (ESR) spectroscopy in view of the desire to study radical intermediates in catalytic systems. In this aim too, the family of spectroscopic techniques known collectively as μSR (Muon Spin Rotation, Relaxation or Resonance) which employ spin-polarised positive muons, and can probe radicals in porous media, including zeolites, with a unique and remarkable sensitivity are paid due attention. All such methods have undergone appreciable developments in recent years, especially in regard to pulsed-techniques and theoretical methods for data acquisition and analysis. DFT calculations continue to prove their worth in the prediction and interpretation of hyperfine coupling constants in (paramagnetic) radical species. The broader characterization of less fleeting (diamagnetic) molecules hosted in zeolites, either as deliberately introduced probes or as formed during catalytic activity, has been greatly aided by developments in infra-red (IR) spectroscopy, UV/Resonance Raman methods, inelastic neutron scattering techniques and NMR, as are surveyed in their recent applications to this topic. © The Royal Society of Chemistry 2010.


Rhodes C.J.,Fresh lands Environmental Actions
Science Progress | Year: 2015

September 2015 saw the International Permaculture Conference1, held in London, followed by the Convergence2, which occupied 6 days at Gilwell Park, on the Essex-London border, where its practitioners gave presentations and workshops on various aspects of permaculture, which is a sustainable design system intended to emulate the principles of living ecosystems. While it has been emphasised3 that such terms as sustainable development, and sustainable agriculture, are really oxymorons, since neither untrammelled growth nor our present form of industrial food production can be maintained in perpetuity, permaculture4 has a value-added factor that extends beyond what might be merely maintained or sustained, which is the quality of regeneration. All sustainable solutions are unsustainable over the longer term, if they are not also intrinsically regenerative. Nature offers the ultimate example of a design that is both sustainable and regenerative, and it is logical to appeal to natural principles for solutions to many of our current problems. This is sometimes taken to mean that we need adopt more “simple” lifestyles, abandoning our technology in the process, but the reality is more complex. Within a broader perspective of regenerative design, permaculture identifies the elements of sustainable living which are harmonious with nature. Discordant practices which lead, e.g. to soil erosion3, fret the environment, and are neither sustainable nor regenerative, but degenerative. © 2015, Science Reviews 2000 Ltd, All right reserved.


Rhodes C.J.,Fresh Lands Environmental Actions
Annual Reports on the Progress of Chemistry - Section C | Year: 2011

The technique variously known as Electron Spin Resonance (ESR) or Electron Paramagnetic Resonance (EPR) continues to find important applications mainly in the Biomedical, Materials and Environmental Sciences. Among the advances which feature information gleaned through its agency, are studies of enzymes and membranes, conductive polymers and novel materials, fuel cells, antioxidants, environmental samples, catalysts and photocatalysts, spin-trapping agents, spin-probes and spin-labels. High-field methods are particularly useful in obtaining improved resolution of overlapping signals and the interpretation of many systems had benefited from the use of Density Functional Theory (DFT) calculations. © 2011 The Royal Society of Chemistry.


Rhodes C.J.,Fresh lands Environmental Actions
Progress in Reaction Kinetics and Mechanism | Year: 2015

Recent progress is surveyed in regard to the importance of molecular species containing unpaired electrons in catalytic systems, as revealed using ESR spectroscopy. The review begins with studies of enzymes and their role directly in biological systems, and then discusses investigations of various artificially created catalysts with potential human and environmental significance, including zeolites. Among the specific types of catalytic media considered are those for photocatalysis, water splitting, the degradation of environmental pollutants, hydrocarbon conversions, fuel cells, ionic liquids and sensor devices employing graphene. Studies of muonium-labelled radicals in zeolites are also reviewed, as a means for determining the dynamics of transient radicals in these nanoporous materials.


Rhodes C.J.,Fresh lands Environmental Actions
Chemical Speciation and Bioavailability | Year: 2014

Some of the prospects of using fungi, principally white-rot fungi, for cleaning contaminated land are surveyed. That whiterot fungi are so effective in degrading a wide range of organic molecules is due to their release of extra-cellular ligninmodifying enzymes, with a low substrate-specificity, so they can act upon various molecules that are broadly similar to lignin. The enzymes present in the system employed for degrading lignin include lignin-peroxidase (LiP), manganese peroxidase (MnP), various H2O2 producing enzymes and laccase. The degradation can be augmented by adding carbon sources such as sawdust, straw and corn cob at polluted sites.

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