Results 1 - 10 of 9177
Results 1 - 10 of 9177. Search took: 0.033 seconds
|Sort by: date | relevance|
[en] A comparative analysis of the copper and iron ions bonds exchange energies was conducted for various variants of orderings and distributions of iron ions among crystallographic positions in ludwigite Cu2FeBO5. Analysis showed that the exchange bonds of iron ions play a key role in the formation of magnetic order. The magnetic ordering strongly depends on the distribution of iron ions among the positions. In the case when the Fe3+ is in the same position as in Fe3BO5, the most favorable magnetic structure is similar to the magnetic structure of ludwigite Fe3BO5. In other cases, the type of magnetic ordering is different.
[en] Investigated bay gamma-resonance spectroscopy (GRS) chelation of iron ions with sinthetic LDOPA-melanin and melanin isolated from the beans black grapes, hedera helix and sambucus nigra. It is found that melanin effectively chelate iron ions in both its two and in the tri valent state. The main part of the coordinated ions Fe''3+ ions are part of polynuclear (n≥2) clusters and with fast relaxation spin-spin iteraction gives paramaqnetic dublet GR-spectra. The presence of magnetic relaxation spectra indicates that part of the lokal points in melanin separated. The value of the parameters GR-spectra of the samples are characteristic of high-spin complex ions Fe''2+ and Fe''3+ with octahedrial ligand environment. It is expected that the ability of vegetable melanins effectiveli bing prooksidant Fe''2+ ions may be one of the possible mechanisms of their antioksidant and radioprotective properties.
[en] Highlights: • Reactive oxygen species were major drivers of evolution. • Reductive stress may not be a very useful concept. • Major antioxidant defences include restriction of O2 levels and sequestration of iron ions into non-redox active forms. • These defences allowed aerobic life to evolve but led to a battle between host and pathogens for iron. The first life forms evolved in a highly reducing environment. This reduced state is still carried by cells today, which makes the concept of “reductive stress” somewhat redundant. When oxygen became abundant on the Earth, due to the evolution of photosynthesis, life forms had to adapt or become extinct. Living organisms did adapt, proliferated and an explosion of new life forms resulted, using reactive oxygen species (ROS) to drive their evolution. Adaptation to oxygen and its reduction intermediates necessitated the simultaneous evolution of select antioxidant defences, carefully regulated to allow ROS to perform their major roles. Clearly this “oxidative stress” did not cause a major problem to the evolution of complex life forms. Why not? Iron and oxygen share a close relationship in aerobic evolution. Iron is used in proteins to transport oxygen, promote electron transfers, and catalyse chemical reactions. In all of these functions, iron is carefully sequestered within proteins and restricted from reacting with ROS, this sequestration being one of our major antioxidant defences. Iron was abundant to life forms before the appearance of oxygen. However, oxygen caused its oxidative precipitation from solution and thereby decreased its bioavailability and thus the risk of iron-dependent oxidative damage. Micro-organisms had to adapt and develop strategies involving siderophores to acquire iron from the environment and eventually their host. This battle for iron between bacteria and animal hosts continues today, and is a much greater daily threat to our survival than “oxidative stress” and “redox stress”.
[en] The currently available data for electron impact excitation of the iron ions, Fe I-Fe VIII, are assessed and listed according to their sources. Methods and approximations employed and the transitions considered are also given. 21 refs., 1 fig., 3 tabs
[en] Two rhodamine-based sensors RDI-1, RDI-2 was designed and synthesized by incorporation of the rhodamine 6G fluorophore and 2-formyl imidazole as the recognizing unit via the imine linkages. RDI-1, RDI-2 exhibits very high selectivity and an excellent sensitivity towards Fe(III) ions in aqueous buffer solution on compared with other probes. The color change from colorless to pink and turn-on fluorescence after binding with iron (III) was observed. Based on jobs plot and ESI-MS studies, the 1:1 binding mode was proposed. Live cell imaging experiments with each probe showed that these probes widely applicable to detect Fe3+ in living cells. -- Highlights: • Two rhodamine based probes was synthesized and used to recognize iron (III). • The chemosensors can be applied to detect iron(III) ions by color and turn-on fluorescent changes. • The very low detection limit was reported. • The applicability of these probes for live cell fluorescence imaging was studied
[en] Fluorescent organic molecules that respond to changes in the Fe2+ concentration with selectivity to other abundant di-valent metal ions will offer the ability to understand the dynamic fluctuations of the Fe2+ ion in interesting media. The use of 6-Br-ppmbi, derived from 2-pyridin-2-yl-benzimidazole, for metal ion-selective fluorescence recognition was investigated. Screening of the main group and transition metal ions showed exclusive selectivity for Fe2+ ions even in the presence of competing metal ions. In addition, the requirement for low concentrations of probe molecules to detect certain amounts of Fe2+ ions make this sensor unique compared to previously reported Fe2+ ion sensors
[en] We develop the methodology of quadrupole splitting distribution (QSD) analysis by evaluating the influences of absorber thickness, absorber texture, and the asumed Lorentzian width on the extracted QSD. We then present the first study to describe the Moessbauer spectra of members of a mineral family in terms of QSDs. The Fe2+ QSD and its characteristics (average QS, peak QS, skewness, and standard deviation) show gradual trends with changing Fe/(Fe+Mg) in a synthetic Al-deficient phlogopite-annite series. Al-deficient natural samples of phlogopite and annite show similar behaviour. The Fe2+ QSDs can be interpreted as population distribuitions of local distortion environments (LDEs) and, as such, contain much information that will become more accessible as theoretical calculations linking particular LDEs to corresponding QS values are developed. (orig.)
[en] Fe3+ can react with penicillamine to form Fe2+, the amount of Fe2+ is directly proportional to the addition of penicillamine in system, and then Fe2+ reacted with the chromogenic reagent of phenanthroline to form a stable complex which its maximum absorption wavelength is 511nm. The content of penicillamine is determinated by measuring the absorbance of the stable orange red complex. The method for the indirect determination of penicillamine using Fe(II)-phenanthroline spectrophotometry has been established. The method is used to the determination of penicillamine in tablets, and the results are satisfactory. (paper)