Die durch die Anwesenheit von Eisen(III)-ionen bedingten Phasengleichgewichte kristalliner Aluminiumhydroxide des Nordstrandits,Hydrargillits und Bayerits

The investigation of ageing processes of coprecipitated aluminium and iron hydroxides—Al_0,5Fe_0,5(OH)₃, initially amorphous, reveals the major influence of Fe³⁺-ions on the transformation steps among the aluminium hydroxides.By combined X-ray and IR examination it has been found that the ageing of amorphous aluminium hydroxide in the presence of iron ions leads to the surprising coexistence of all known, well defined crystalline trihydroxide species of aluminium, namely nordstrandite, gibbsite and bayerite. Iron ions for their part transform from amorphous stage of hydroxide at the beginning into hydrohematite.The change in temperature orpH conditions of the milieu, or the change of both the parameters results in only one or two modifications from those aluminium hydroxides mentioned above.

     

Deferoxamine Iron Chelation Increases δ-Aminolevulinic Acid Induced Protoporphyrin IX in Xenograft Glioma Model

Exogenous administration of δ-aminolevulinic acid (δ-ALA) leads to selective accumulation of protoporphyrin IX (PpIX) in brain tumors, and has shown promising results in increasing extent of resection in fluorescence-guided resection (FGR) of brain tumors. However, this approach still suffers from heterogeneous staining and so some tumor margins may go undetected because of this variation in PpIX production. The aim of this study was to test the hypothesis that iron chelation therapy could increase the level of fluorescence in malignant glioma tumors. Mice implanted with xenograft U251-GFP glioma tumor cells were given a 200 mg kg⁻¹ dose of deferoxamine (DFO), once a day for 3 days prior to δ-ALA administration. The PpIX fluorescence observed in the tumor regions was 1.9 times the background in animal group without DFO, and 2.9 times the background on average, in the DFO pre-treated group. A 50% increase in PpIX fluorescence contrast in the DFO group was observed relative to the control group (t-test P-value = 0.0020). These results indicate that iron chelation therapy could significantly increase δ-ALA-induced PpIX fluorescence in malignant gliomas, pointing to a potential role of iron chelation therapy for more effective FGR of brain tumors.     

Die Bildung von kristallinem Böhmit in gemeinsam gefällten AlFe(III)-Hydroxiden unter hydrothermalen Bedingungen

Under mild hydrothermal conditions originally amorphous aluminium hydroxide coprecipitated with iron(III)ions as Al_0,5Fe_0,5(OH)₃ transforms into aluminium hydroxide crystalline phases which are not observed in products of ageing of pure aluminium hydroxide.By X-ray diffraction analysis, IR spectroscopic studies and microscopic observations it has been found that due to the presence of iron(III) hydroxide it is possible to stabilize the trihydoxide of aluminium i.e. bayerite until 130–140°C. Moreover, with increasing temperature well crystallized boehmite is obtained instead of the usually formed pseudoboehmite.Experiments revealed that the formation of crystalline boehmite does not take place as a process of pseudoboehmit crystallites growth but only as a result of bayeriteboehmite transformation.

     

Studies on oxine and its derivatives : The sensitivity and selectivity of some 7-substituted 8-hydroxyquinoline-5-sulphonic acids and some 2-substituted 8-hydroxyquinoline-4-carboxylic acids towards certain metals

A number of new derivatives of 8-hydroxyquinoline containing both solubilising groups and groups which might sterically hinder chelation have been prepared, viz. 8-hydroxy-7-morpholino-methylquinoline-5-sulphonic acid, 8-hydroxy-7-piperidinomethylquinoline-5-sulphonic acid, 8-hydroxy-2-(3,4-dimethoxyphenyl)-quinoline-4-carboxylic acid, 8-hydroxy-2-n-hexylquinoline-4-carboxylic acid and 8-hydroxy-2-(i-ethylpropyl)-quinoline-4-carboxylic acid. The limiting sensitivities of the reactions of these reagents towards copper, nickel, aluminium, zinc, magnesium, gallium, indium, thallium, yttrium, cadmium, cobalt and iron have been investigated     

Flow-injection analysis of silicate rocks for total iron and aluminium

A flow-injection method is described for the spectrophotometric determination of total iron and aluminium in silicate rocks. Rock samples are opened up by fusion with a mixture of lithium carbonate and boric acid, the melt is taken up in 1M hydrochloric acid and the resulting solution is used for the determination of both iron and aluminium. The flow system for the determination of iron needs no particular reagents, involving simply measurement of the absorbance of the chloro-complex of iron(III) at 335 nm. The system for aluminium consists of the reduction of iron(III) to iron(II), colour development with Xylenol Orange (XO), destruction of XO-chelates other than that of aluminium by addition of EDTA and subsequent measurement of the absorbance of the aluminium-XO complex at 506 nm. The systems permit semi-automatic, rapid analysis of silicate rocks for iron and aluminium. Results obtained for standard rocks were in good agreement with the recommended values. The precision ranged from 0.1 to 0.9% for iron and from 0.3 to 0.7% for aluminium.     

An Untargeted Metabolomics Approach for Correlating Pulse Crop Seed Coat Polyphenol Profiles with Antioxidant Capacity and Iron Chelation Ability

Pulse crop seed coats are a sustainable source of antioxidant polyphenols, but are typically treated as low-value products, partly because some polyphenols reduce iron bioavailability in humans. This study correlates antioxidant/iron chelation capabilities of diverse seed coat types from five major pulse crops (common bean, lentil, pea, chickpea and faba bean) with polyphenol composition using mass spectrometry. Untargeted metabolomics was used to identify key differences and a hierarchical analysis revealed that common beans had the most diverse polyphenol profiles among these pulse crops. The highest antioxidant capacities were found in seed coats of black bean and all tannin lentils, followed by maple pea, however, tannin lentils showed much lower iron chelation among these seed coats. Thus, tannin lentils are more desirable sources as natural antioxidants in food applications, whereas black bean and maple pea are more suitable sources for industrial applications. Regardless of pulse crop, proanthocyanidins were primary contributors to antioxidant capacity, and to a lesser extent, anthocyanins and flavan-3-ols, whereas glycosylated flavonols contributed minimally. Higher iron chelation was primarily attributed to proanthocyanidin composition, and also myricetin 3-O-glucoside in black bean. Seed coats having proanthocyanidins that are primarily prodelphinidins show higher iron chelation compared with those containing procyanidins and/or propelargonidins.     

Determination of aluminium using high performance chelation ion chromatography

The suitability of high performance chelation ion chromatography (HPCIC) using postcolumn reaction for the separation and determination of dissolved aluminium in complex samples was investigated. Use of a chelating ion-exchanger allowed for differentiation between kinetically labile and kinetically stable species of aluminium. Separation through a combination of chelation and cation-exchange was achieved using a 200 x 4.0 mm id column packed with particles of silica functionalised with iminodiacetic acid, with nitric acid-potassium chloride eluents. A temperature anomaly causing a five-fold increase in column efficiency for aluminium is believed to be a result of localised temperature effects in the particular type of instrument used. Postcolumn reagents investigated for the photometric detection included Tiron, Pyrocatechol Violet, Chrome Azurol S, and Eriochrome Cyanine R. The lowest detection limit (2.7 microg/L for a 100 microL sample volume) was achieved using 0.25 mM Eriochrome Cyanine R in 0.2 M hexamine (pH 6.1) with 1 mM cetyltrimethylpyridium bromide (CTAB). The optimised HPCIC system was applied successfully to the quantification of labile aluminium in paper mill process water.     

Different approaches to the study of chelating agents for iron and aluminium overload pathologies

Our objective is to illustrate the activity of the groups operating in Italy involved in identification and study of new chelating agents, mainly intended for treatment of human pathology correlated with metal overload. The objective of “chelation therapy” is removal of toxic metal ions from the human body or attenuation of their toxicity by transforming them into less toxic compounds or by dislocating them from the site at which they exert a toxic action. Because most of this research activity is related to chelating agents for iron and aluminium, diseases related to these two metal ions are briefly treated. Iron overload is the most common metal toxicity disease worldwide. The toxicity of aluminium in dialysis patients was a serious problem for haemodialysis units in the seventies and eighties of the last century. In particular, this review focuses on research performed by the group at Cagliari and Ferrara, and by that at Padova. The former is studying, above all, bisphosphonate and kojic acid derivatives, and the latter is investigating 3,4-hydroxypyridinecarboxylic acids with differently substituted pyridinic rings.

Merging zones in flow injection analysis: Part 5. Simultaneous determination of aluminium and iron in plant digests by a zone-sampling approach

A flow injection procedure is proposed for the simultaneous determination of aluminium and iron in plant material. The method is based on a flow configuration involving zone sampling and merging zones. Aluminium is determined spectrophotometrically with eriochrome cyanine R as reagent and iron by atomic absorption spectrometry. The advantages of this method over other procedures already reported are discussed. The effects of reagent composition for the aluminium determination are described in detail. The zone-sampling approach permits an easier pH control in the aluminium determinations so interferences caused by variations in sample acidity are avoided without the need for very concentrated buffers. The merging zones configuration greatly reduces the consumption of reagents. The proposed method permits the analysis of about 120 samples (240 determinations) per hour, with good precision (r.s.d. < 2%) in both the aluminium and iron channels. The results agree with those obtained by inductively-coupled argon plasma spectrometry.     

Spectrofluorimetric determination of trace amounts of aluminium with 5-bromo-salicylaldehyde salicyloylhydrazone

The fluorescent reagent 5-bromo-salicylaldehyde salicyloylhydrazone (5-Br-SASH) was synthesized and its ionization constants were established spectrophotometrically. The fluorescent reaction of this reagent with aluminium was studied. Based on this chelation reaction, a spectrofluorimetric method was developed for the determination of aluminium in acetic acid-ammonium acetate buffer solution of pH 5.4. Under these conditions, the A1-5-Br-SASH complex has excitation and emission maxima at 370 and 460 nm, respectively. The linear range of the method is from 0 to 120 ppb and the detection limit is 1.1 ppb of aluminium. The molar ratio of aluminium to the reagent is 1:3. Interferences of other ions were studied. The method was successfully applied to the determination of aluminium in glucose injection and common beverages.     

Separation of large amounts of iron(III) from cobalt,nickel, and aliminum by combined ion exchange-solvent extraction

A method is described for the cation-exchange separation of large amounts of iron(III) from cobalt, nickel, and aluminium. On the strongly acidic Dowex 50-X8, iron(III) is not adsorbed from an 80% tetrahydrofuran-20% 3 M hydrochloric acid mixture, while cobalt, nickel, and aluminium are retained; a quantitative separation is thus possible. Cobalt and nickel or aluminium are then separated by elution with 90% tetrahydrofuran-10% 6 M hydrochloric acid. In these mixtures combined ion exchange-solvent extraction appears to occur; both ion exchange and liquid-liquid extraction are. effective simultaneously.     

Redox properties of 8-quinolinol and implications for its mode of action

8-Quinolinol (oxine, 8-hydroxyquinoline) is a simple aromatic alkaloid with allelopathic, antibacterial, antifungal, and cytotoxic activities. Generally, it is assumed that 8-quinolinol toxicity depends on transition metal chelation that negatively affects their availability for metalloenzymes in the cell or reactive oxygen species generation (ROS), which are formed following reduction of molecular oxygen by autoxidation of the redox active metal central atom of the 8-quinolinol complex. On the contrary, beneficial effects of 8-quinolinol and its derivatives in the medication of certain degenerative diseases are known. In this context, the activity of 8-quinolinol derivatives is attributed to their antioxidant activity following iron complex formation. To address this controversial issue, we explore the possible anti- or pro-oxidant effects of 8-quinolinol and its iron complexes in the deoxyribose degradation assay, by cyclic voltammetry and in a biological assay. The antibacterial effects of 8-quinolinol and its complex with iron were evaluated on Curtobacterium flaccumfacies and Paenibacillus amylolyticus. 8-Quinolinol showed strong antioxidant activity in the deoxyribose degradation assay. This activity may not depend exclusively on iron chelation, but probably more on the notable reducing properties of 8-quinolinol; it proved to be a more efficient antioxidant than the flavonoids catechin and quercetin. By contrast, 8-quinolinol showed no pro-oxidative effects in the deoxyribose degradation assay, both in free form and in complex with iron, as it may occur with redox cyclers. Cyclic voltammetry confirmed this too. 8-Quinolinol significantly inhibited bacterial growth and respiration. Idiosyncratically, its 50:1 mixture with iron(III) ions was less active compared with free 8-quinolinol; it even caused a U-shaped nonlinear hormetic effect on growth and failed to inhibit respiration as totally as the pure mixture; the respiration was even accelerated compared with the control as a result of lower stress. Our results support the notion that complex formation with either iron or other transition metals affects the reducing power of 8-quinolinol, but, in contrast to general assumptions, this study finds no support that complex formation with iron represents the major mode of action.     

Particle shape in thixotropic aluminium and thorium molybdates gels

Summary Electron microscope examination of thixotropic aluminium and thorium molybdate gels shows that one hour after formation they are constituted by short fibrils of small axial ratio. The fibrils of the aluminium molybdate gels, with ageing at room temperature or with boiling, increase in diameter and length; the fibrous shape of the particles is maintained after two and a half years of ageing; all fibrils are crystalline by electron diffraction. The fibrils of the thorium molybdate gels, except in the gels containing hydrochloric acid, change with ageing at room temperature or with boiling, into plates of hexagonal, elliptical or rectangular profile; the fibrils and plates are crystalline and have the same electron diffraction pattern as the fibrils.This work was aided, in part, by grants from Conselho Nacional de Pesquisas and the Rockefeller Foundation.     

Design of iron chelators with therapeutic application

Iron is essential for the proper functioning of all living cells, however it is toxic when present in excess. Thus, using iron chelators as therapeutic agents, namely chelation therapy, has received increasing attention. The objective of this review is to discuss the factors which should be considered when designing clinically useful iron chelators, to present the application of iron chelators in the treatment of iron overload associated with β-thalassaemia major and sickle cell anaemia, and to highlight the potential applications in the treatment of neurodegenerative disorders and microbial infection. This article reviews recent knowledge centred on these themes and indicates the growing importance of the concept of iron chelation in medicine.     

The Fe(II) and Co(II) chelation complexes of 2,6-BIS(4-Ethyl-2-Pyridyl)-4-Phenyl-Pyridinl

A study has been made of the spectrophotometric constants of the new modified terpyridine chelation reagent, 2,6-bis(4-ethyl-2-pyridyl)-4-phenyl-pyridine (trivial name “ethyl-terosole”), as its Fe(II) and Co(II) complex cations. This new Iigand is outstanding for use in the trace quantity determination of iron. No advantage as compared to more sensitive ligands previously studied is provided by Co(II) chelation.     

Synthesis of certain pyridinyl and diazinyl hydrazones containing one or more ferroin groups, and their chromogenic reactions with iron, copper, cobalt and nickel

Fifteen new hydrazones with one or more ferroin groups were prepared, and their chelation and chromogenic properties with iron(II), copper(I), cobalt(II) and nickel(II) were investigated. Improved sensitivity in the spectrophotometric determination of cobalt, copper, and nickel is provided by several of the new compounds. Several others are capable of forming unusually stable and interesting binuclear iron(II) complexes.     

Human diseases related to aluminium overload

Abstract  

In this paper attention is devoted to the role of aluminium in osteodistrophy and dialysis dementia. In fact, these diseases, in spite of the actions that have drastically reduced their occurrence, have so far constituted a cause of great medical concern. As a preliminary point, some aspects concerning the solution chemistry of aluminium are considered, then the medical problems are described and finally the chelation therapy of aluminium overload, giving some insight on the chelators recently proposed.     

The surface oxidation potential of melanosomes measured by free electron laser-photoelectron emission microscopy

A technique for measuring the photoionization spectrum and the photoelectron emission threshold of a microscopic structured material is presented. The theoretical underpinning of the experiment and the accuracy of the measurements are discussed. The technique is applied to titanium silicide nanostructures and melanosomes isolated from human hair, human and bovine retinal pigment epithelium cells, and the ink sac of Sepia officinalis. A common photothreshold of 4.5 +/- 0.2 eV is found for this set of melanosomes and is attributed to the photoionization of the eumelanin pigment. The relationship between the photoionization threshold and the electrochemical potential referenced to the normal hydrogen electrode is used to quantify the surface oxidation potential of the melanosome. The developed technique is used to examine the effect of iron chelation on the surface oxidation potential of Sepia melanosomes. The surface oxidation potential is insensitive to bound Fe(III) up to saturation, suggesting that the metal is bound to the interior of the granule. This result is discussed in relation to the age-dependent accumulation of iron in human melanosomes in both the eye and brain.     

Aluminium in the human brain

Abstract  

An inevitable consequence of humans living in the Aluminium Age is the presence of aluminium in the brain. This non-essential, neurotoxic metal gains entry to the brain throughout all stages of human development, from the foetus through to old age. Human exposure to myriad forms of this ubiquitous and omnipresent metal makes its presence in the brain inevitable, while the structure and physiology of the brain makes it particularly susceptible to the accumulation of aluminium with age. In spite of aluminium’s complete lack of biological essentiality, it actually participates avidly in brain biochemistry and substitutes for essential metals in critical biochemical processes. The degree to which such substitutions are disruptive and are manifested as biological effects will depend upon the biological availability of aluminium in any particular physical or chemical compartment, and will under all circumstances be exerting an energy load on the brain. In short, the brain must expend energy in its ‘unconscious’ response to an exposure to biologically available aluminium. There are many examples where ‘biological effect’ has resulted in aluminium-induced neurotoxicity and most potently in conditions that have resulted in an aluminium-associated encephalopathy. However, since aluminium is non-essential and not required by the brain, its biological availability will only rarely achieve such levels of acuity, and it is more pertinent to consider and investigate the brain’s response to much lower though sustained levels of biologically reactive aluminium. This is the level of exposure that defines the putative role of aluminium in chronic neurodegenerative disease and, though thoroughly investigated in numerous animal models, the chronic toxicity of aluminium has yet to be addressed experimentally in humans. A feasible test of the ‘aluminium hypothesis’, whereby aluminium in the human brain is implicated in chronic neurodegenerative disease, would be to reduce the brain’s aluminium load to the lowest possible level by non-invasive means. The simplest way that this aim can be fulfilled in a significant and relevant population is by facilitating the urinary excretion of aluminium through the regular drinking of a silicic acid-rich mineral water over an extended time period. This will lower the body and brain burden of aluminium, and by doing so will test whether brain aluminium contributes significantly to chronic neurodegenerative diseases such as Alzheimer’s and Parkinson’s.     

Titrages “thermochimiques” par formation de fluorures complexes de fer,aluminium, antimoine,etain et plomb

A thermochemical study of the titration of aluminium, iron, copper, lead, tin and antimony salts with sodium fluoride is described. The destruction of fluoride cumplexes by boric acid has been studied. The measurement apparatus consists of two thermistors and a bridge. Clear breaks were obtained for iron, aluminium, copper and lead but no separation of iron and aluminium was possible. The action of boric acid also gave clear breaks in the curves.