Formation Of Iron Complexes Research Articles

Antioxidant activity of Spathodea campanulata (Bignoneaceae) extracts

Spathodea campanulata is used in traditional medicine in Africa as diuretic and anti-inflammatory. Although few studies have reported the mechanism of antioxidant action, this study evidenced the antioxidant activity of S. campanulata bark and flower extracts and their possible mechanism of action. Ethanol extracts of S. campanulata bark and flowers showed antioxidant activity on lipid peroxidation of liver microsome induced by Fe3+-ascorbic acid. Bark extract was 5 times more efficient than flower extract. The antioxidant activity of flower extract, previously complexed with increasing concentrations of Fe3+ (20 - 100 μM) which resulted in antioxidant activity loss, was shown to be related to iron complex formation. In contrast, the antioxidant activity of bark extract was not inhibited by the previous incubation with Fe3+, although complexation was demonstrated by spectral analysis of the solution. These results suggest an antioxidant mechanism other than Fe3+ complex formation. Therefore, the antioxidant mechanisms of S. campanulata flower and bark extracts are distinct from each other, reflecting the extract heterogeneous composition and the mechanism of action.

Effect of pH on Complex Coacervate Core Micelles from Fe(III)-Based Coordination Polymer

The effect of pH on iron-containing complex coacervate core micelles [Fe(III)-C3Ms] is investigated in this paper. The Fe(III)-C3Ms are formed by mixing cationic poly(N-methyl-2-vinylpyridinium iodide)-b-poly(ethylene oxide) [P2MVP(41)-b-PEO(205)] and anionic iron coordination polymers [Fe(III)-L(2)EO(4)] at stoichiometric charge ratio. Light scattering and Cryo-TEM have been performed to study the variations of hydrodynamic radius and core structure with changing pH. The hydrodynamic radius of Fe(III)-C3Ms is determined mainly by the corona and does not change very much in a broad pH range. However, Cryo-TEM pictures and magnetic relaxation measurements indicate that the structure of the micellar cores changes upon changing the pH, with a more crystalline, elongated shape and lower relaxivity at high pH. We attribute this to the formation of mixed iron complexes in the core, involving both the bis-ligand and hydroxide ions. These complexes are stabilized toward precipitation by the diblock copolymer.

N-Heterocyclic Carbene Ligands as Mimics of Imidazoles/Histidine for the Stabilization of Di- and Trinitrosyl Iron Complexes

N-heterocyclic carbenes (NHCs) are shown to be reasonable mimics of imidazole ligands in dinitrosyl iron complexes determined through the synthesis and characterization of a series of {Fe(NO)(2)}(10) and {Fe(NO)(2)}(9) (Enemark-Feltham notation) complexes. Monocarbene complexes (NHC-iPr)(CO)Fe(NO)(2) (1) and (NHC-Me)(CO)Fe(NO)(2) (2) (NHC-iPr = 1,3-diisopropylimidazol-2-ylidene and NHC-Me = 1,3-dimethylimidazol-2-ylidene) are formed from CO/L exchange with Fe(CO)(2)(NO)(2). An additional equivalent of NHC results in the bis-carbene complexes (NHC-iPr)(2)Fe(NO)(2) (3) and (NHC-Me)(2)Fe(NO)(2) (4), which can be oxidized to form the {Fe(NO)(2)}(9) bis-carbene complexes 3(+) and 4(+). Treatment of complexes 1 and 2 with [NO]BF(4) results in the formation of uncommon trinitrosyl iron complexes, (NHC-iPr)Fe(NO)(3)(+) (5(+)) and (NHC-Me)Fe(NO)(3)(+) (6(+)), respectively. Cleavage of the Roussin's Red "ester" (μ-SPh)(2)[Fe(NO)(2)](2) with either NHC or imidazole results in the formation of (NHC-iPr)(PhS)Fe(NO)(2) (7) and (Imid-iPr)(PhS)Fe(NO)(2) (10) (Imid-iPr = 2-isopropylimidazole). The solid-state molecular structures of complexes 1, 2, 3, 4, 5(+), and 7 show that they all have pseudotetrahedral geometry. Infrared spectroscopic data suggest that NHCs are slightly better electron donors than imidazoles; electrochemical data are also consistent with what is expected for typical donor/acceptor abilities of the spectator ligands bound to the Fe(NO)(2) unit. Although the monoimidazole complex (Imid-iPr)(CO)Fe(NO)(2) (8) was observed via IR spectroscopy, attempts to isolate this complex resulted in the formation of a tetrameric {Fe(NO)(2)}(9) species, [(Imid-iPr)Fe(NO)(2)](4) (9), a molecular square analogous to the unsubstituted imidazole reported by Li and Wang et al. Preliminary NO-transfer studies demonstrate that the {Fe(NO)(2)}(9) bis-carbene complexes can serve as a source of NO to a target complex, whereas the {Fe(NO)(2)}(10) bis-carbenes are unreactive in the presence of a NO-trapping agent.

Egg Yolk Phosvitin and Functional Phosphopeptides—Review

Phosphopeptides are among the most interesting biomolecules with characteristic molecular structure and functions. They usually contain clusters of phosphoserines, which can effectively bind calcium and iron, and inhibit formation of insoluble calcium phosphates or iron complexes. Therefore, phosphopeptides can increase calcium or iron bioavailability and prevent lipid oxidation in foods. Milk protein casein has been currently used by industry to produce phosphopeptides. Egg yolk phosvitin is considered as the most phosphorylated protein found in the nature. Phosvitin from egg yolk can be much better source for producing phosphopeptides with varying sizes and functions than casein because it contains much greater number of phosphates in the molecule than casein. However, still phosvitin has not been subjected to considerable attention with regard to bioactive peptides production.

Thermodynamic remarks on chelating ligands for aluminium related diseases

Attention is devoted to the role of chelating agents in the treatment of aluminium related diseases. In fact, in spite of the actions that have drastically reduced the occurrence of dialysis diseases, they so far constitute a cause of great medical concern. Being aluminium chelators strictly related to iron chelators, a comparison is made of the complex formation properties of these two hard metal ions towards ligands characterized by charged oxygen donor groups. Empirical correlations between aluminium(III) and iron(III) complex formation constants, and their behavior are discussed in terms of structural and thermodynamic stabilities. Insertion of proper substituents to enhance the chelator binding capacity is debated on the bases of substituent effects on protonation and complex formation constants.

Solution Properties of Azidokojatoiron(III) Complexes

The formation of iron(III) complexes with chelating azidokojate anions L− was investigated in aqueous solutions as a function of the pH and the c(Fe3+):c(HL) molar ratio. Based on the stability constants, the distribution among the above complexes, [Fe(H2O)6]3+, and [Fe(H2O)5(OH)]2+ were calculated in solutions of various compositions. The complexes are redox stable in aqueous solutions both in the dark and in visible laboratory light. Properties of the investigated azidokojic acid and its iron(III) complexes are compared with those required for therapeutic applications as alternative iron chelators.

Discrimination of Mononuclear and Dinuclear Dinitrosyl Iron Complexes (DNICs) by S K-Edge X-ray Absorption Spectroscopy: Insight into the Electronic Structure and Reactivity of DNICs

In addition to probing the formation of dinitrosyl iron complexes (DNICs) by the characteristic Fe K-edge pre-edge absorption energy ranging from 7113.4 to 7113.8 eV, the distinct S K-edge pre-edge absorption energy and pattern can serve as an efficient tool to unambiguously characterize and discriminate mononuclear DNICs and dinuclear DNICs containing bridged-thiolate and bridged-sulfide ligands. The higher Fe-S bond covalency modulated by the stronger electron-donating thiolates promotes the Fe → NO π-electron back-donation to strengthen the Fe-NO bond and weaken the NO-release ability of the mononuclear DNICs, which is supported by the Raman ν(Fe-NO) stretching frequency. The Fe-S bond covalency of DNICs further rationalizes the binding preference of the {Fe(NO)(2)} motif toward thiolates following the trend of [SEt](-) > [SPh](-) > [SC(7)H(4)SN](-). The relative d-manifold energy derived from S K-edge XAS as well as the Fe K-edge pre-edge energy reveals that the electronic structure of the {Fe(NO)(2)}(9) core of the mononuclear DNICs [(NO)(2)Fe(SR)(2)](-) is best described as {Fe(III)(NO(-))(2)}(9) compared to [{Fe(III)(NO(-))(2)}(9)-{Fe(III)(NO(-))(2)}(9)] for the dinuclear DNICs [Fe(2)(μ-SEt)(μ-S)(NO)(4)](-) and [Fe(2)(μ-S)(2)(NO)(4)](2-).

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.

Formation of iron complexes from trifluoroacetic acid based liquid chromatography mobile phases as interference ions in liquid chromatography/electrospray ionization mass spectrometric analysis

Two unexpected singly charged ions at m/z 1103 and 944 have been observed in mass spectra obtained from electrospray ionization mass spectrometric analysis of liquid chromatography effluents with mobile phases containing trifluoroacetic acid (TFA) that severely interfered with sample analysis. Accurate mass measurement and tandem mass spectrometry studies revealed that these two ions are composed of three components; clusters of trifluoroacetic acid, clusters of mass 159 and iron. Formation of these ions is inhibited by removing TFA from the mobile phases and using formic acid in its place, replacing the stainless steel union with a titanium union or by adding a small blank fused‐silica capillary column between the chromatography column and the electrospray tip via a stainless steel union without any adverse effects to chromatographic separation, peak broadening or peptide identifications. Copyright © 2011 John Wiley & Sons, Ltd.

Characterization of Iron Dinitrosyl Species Formed in the Reaction of Nitric Oxide with a Biological Rieske Center

Reactions of nitric oxide with cysteine-ligated iron-sulfur cluster proteins typically result in disassembly of the iron-sulfur core and formation of dinitrosyl iron complexes (DNICs). Here we report the first evidence that DNICs also form in the reaction of NO with Rieske-type [2Fe-2S] clusters. Upon treatment of a Rieske protein, component C of toluene/o-xylene monooxygenase from Pseudomonas sp. OX1, with an excess of NO(g) or NO-generators S-nitroso-N-acetyl-D,L-pencillamine and diethylamine NONOate, the absorbance bands of the [2Fe-2S] cluster are extinguished and replaced by a new feature that slowly grows in at 367 nm. Analysis of the reaction products by electron paramagnetic resonance, Mössbauer, and nuclear resonance vibrational spectroscopy reveals that the primary product of the reaction is a thiolate-bridged diiron tetranitrosyl species, [Fe(2)(μ-SCys)(2)(NO)(4)], having a Roussin's red ester (RRE) formula, and that mononuclear DNICs account for only a minor fraction of nitrosylated iron. Reduction of this RRE reaction product with sodium dithionite produces the one-electron-reduced RRE, having absorptions at 640 and 960 nm. These results demonstrate that NO reacts readily with a Rieske center in a protein and suggest that dinuclear RRE species, not mononuclear DNICs, may be the primary iron dinitrosyl species responsible for the pathological and physiological effects of nitric oxide in such systems in biology.

Iron(II) Complexes with Tetradentate Bis(aminophenolate) Ligands: Synthesis and Characterization, Solution Behavior, and Reactivity with O2

Tetradentate bis(aminophenolate) ligands H(2)salan(X) and H(2)bapen(X) (where X refers to the para-phenolate substituent = H, Me, F, Cl) react with [Fe{N(SiMe(3))(2)}(2)] to form iron(II) complexes, which in the presence of suitable donor ligands L (L = pyridine or THF) can be isolated as the complexes [Fe(salan(X))(L)(2)] and [Fe(bapen(X))(L)(2)]. In the absence of donor ligands, either mononuclear complexes, for example, [Fe(salan(tBu,tBu))], or dinuclear complexes of the type [Fe(salan(X))](2) are obtained. The dynamic coordination behavior in solution of the complexes [Fe(salan(F))(L)(2)] and [Fe(bapen(F))(L)(2)] has been investigated by VT (1)H and (19)F NMR spectroscopy, which has revealed equilibria between isomers with different ligand coordination topologies cis-α, cis-β and trans. Exposure of the iron(II) salan(X) complexes to O(2) results in the formation of oxo-bridged iron(III) complexes of the type [{Fe(salan(X))}(2)(μ-O)] or [{Fe(salan(X))(L)}(2)(μ-O)]. The lack of catalytic activity of the iron(II) salan and bapen complexes in the oxidation of cyclohexane with H(2)O(2) as the oxidant is attributed to the rapid formation of stable and catalytically inactive oxo-bridged iron(III) complexes.

Formation of dinitrosyl iron complexes in cardiac mitochondria

It has been established that, in the presence of S-nitrosothiols, cysteine, and mitochondria, dinitrosyl iron complexes (DNIC) coupled to low-molecular-weight ligands and proteins are formed. The concentration of DNIC depended on oxygen partial pressure. It was shown that, under the conditions of hypoxia, the kinetics of the formation of low-molecular DNIC was diphasic. After the replacement of anaerobic conditions of incubation to aerobic ones, the level of DNIC came down; in this case, protein dinitrosyl complexes became more stable. We proposed that iron- and sulfur-containing proteins and low-molecular-weight iron complexes are the sources of iron for DNIC formation in mitochondrial suspensions. It was shown that a combination of DNIC and S-nitrosothiols inhibited effectively the respiration of cardiomyocytes.

On the nature of a compound formed from dinitrosyl-iron complexes with cysteine and responsible for a long-lasting vasorelaxation

The nature of a compound able to induce long-lasting (⩾20 min) relaxation of rat abdominal aorta rings after addition of rapidly (within several minutes) disappeared mono- and binuclear dinitrosyl iron complexes with cysteine (M- and B-DNICs, respectively) (10 μmol) to the Krebs medium has been investigated. It has been found that long-lasting vasorelaxation is not induced either by S-nitrosocysteine formed upon decomposition of DNICs or by accumulation of free nitric oxide molecules or nitrite remaining in the incubation medium. Long-term air bubbling of the Krebs medium initially containing М-DNIC is accompanied by conversion of the complex first into B-DNIC, which represents a Roussin’s red salt cysteine ester and then into a more stable diamagnetic compound Х, which displays an intense absorption band at 278 nm. Compound X is decomposed after treatment with the strong bivalent iron chelator bathophenanthroline disulfonate (BPDS) and N-methyl- d-glucamine dithiocarbamate (MGD). The MGD-induced decomposition of compound Х is concomitant with the formation of EPR-detectable mononitrosyl iron complexes with MGD. Treatment of compound X with cysteine results in its decomposition and the appearance of optical absorption bands characteristic of М- and B-DNICs. Evidently, compound Х, has an iron-nitrosyl origin similar to that of М- and B-DNICs and its formation in oxygenated DNIC solutions is determined by the lowering cysteine content in them. It is hypothesized that compound X represents a cysteine ester of nitrosyl iron complexes, namely, a black Roussin’s salt cysteine ester responsible for long-lasting vasorelaxation initiated by addition of М- and B-DNICs that are rapidly decomposed to compound X to the incubation medium.

LACK of IRON Binding by Pixantrone IS ASSOCIATED with Reduced PRODUCTION of Reactive Oxygen SPECIES and Myoctye Cytotoxicity IN VITRO.

Abstract 4806 IntroductionPixantrone (PIX), an aza-anthracenedione, which has successfully completed a phase 3 trial (J Clin Oncol 2009; 27:15s, No. 8523) was designed to enhance clinical efficacy while significantly decreasing cardiotoxicity compared to doxorubicin (DOX) and mitoxantrone (MIT). Multidose administration, in animal models of equitoxic doses of PIX, MIT, and DOX, with or without prior therapy with DOX, resulted in minimal evidence for PIX cardiotoxicity compared with the severe histologic lesions seen with these other agents (Cavaletti et al: Investigational New Drugs 2007; 3:187-95). Both DOX and MIT contain a dihydroquinone structural element known to interact with iron. Additionally, DOX contains an aliphatic ketone which, once metabolized to the corresponding secondary alcohol metabolite doxorubicinol, is implicated in release of free iron and the chronic cardiotoxicity observed with DOX. In contrast, PIX has a nitrogen containing heterocycle which replaces the dihydroquinone, forming an aza-anthracenedione structure. PIX also does not contain an aliphatic ketone and cannot form metabolites analogous to doxorubicinol. MethodsTo validate the proposed mechanisms underlying the observed differences in cardiotoxicity, we used established spectrophotometric techniques to quantify iron:drug interactions that are thought to be mechanistic for chronic doxorubicin cardiotoxicity (Menna et al: Cardiovasc Toxicol 2007; 7:80–85). ResultsAdding increasing amounts of iron to drug solution, we observed that DOX and MIT underwent changes in visible range absorbance patterns, characteristic of drug:iron complex formation, confirming the expected 1:3 Fe(II)-drug ratio for both DOX and MIT. In contrast, no spectrophotometric changes were observed with iron added to PIX, clearly demonstrating that PIX does not bind iron. In vitro studies using H2C9 rat myocardial cells indicate that PIX (ID50 >50 μg/ml) is far less toxic than DOX (ID50= 1 μ/ml). Moreover, PIX does not induce significant reactive oxygen species (ROS) production in the H2C9 cells compared to DOX. ConclusionThese results demonstrate that PIX does not bind iron and that its inability to bind iron and its reduced propensity to generate ROS may be the mechanism for reduced PIX cardiotoxicity in animal models compared to DOX or MIT. Disclosures:McKennon:Cell Therapeutics, Inc: Employment. Singer:Cell Therapeutics, Inc: Employment.

The role of iron on the degradation and mineralization of organic compounds using conventional Fenton and photo-Fenton processes

The role of iron on the degradation of different organic compounds, differing in their structure (aliphatic versus aromatic) and iron complex formation capacity, by conventional and photo-Fenton processes was investigated. Results show that these chemical characteristics can affect the degree of treatment in terms of COD and TOC removals. While aromatics exhibited a fast and great reduction in the COD by the conventional Fenton process, aliphatic compounds, apart from acetic acid, required the presence of UV light to enhance treatment results. EDTA and oxalic acid responded very positively to UV irradiation in both COD removal and mineralization, reaching the highest values showed by aromatics; and results depended on the intensity of the UV light applied. Phenol and 4-nitrophenol responded favourably to UV irradiation in terms of mineralization and slightly in COD removal. Reductions in the COD were almost total (95.99%), while only an 80% of reduction in the TOC was achieved, for the best photo-Fenton treatment of oxalic acid, phenol and nitrophenol. 60% COD and 40% TOC removals were achieved correspondingly in the case of EDTA. Acetic acid showed almost no mineralization and low COD removal (≈20%) when treated by a conventional Fenton process; and did not enhanced results when assisting the treatment with UV light. Photo-regeneration of ferrous ion and photo-decarboxylation of iron carboxylates are assessed in the framework of these results.

Nutrition classics. The American Journal of Medicine, Volume 31, 1961. Syndrome of iron deficiency anemia, hepatosplenomegaly, hypogonadism, dwarfism and geophagia.

SUMMARY A syndrome occurring in males, characterized by severe irondeficiency anemia, hypogonadism, dwarfism, hepatosplenomegaly, and geophagia, has been observed in villagers in Iran suffering from malnutrition. Eleven such patients, studied in detail, are described. Despite hepatosplenomegaly, results of the liver function tests were uniformly normal except for the serum alkaline phosphatase, which was consistently elevated. The anemia was not associated with blood loss, hookworm infestation, or intestinal malabsorption, and patients responded promptly to oral iron therapy. Although the diet contained adequate amounts of iron, it is believed that the predominantly wheat diet, with its high phosphate content, interfered with absorption because of the formation of insoluble iron complexes. Correction of the anemia resulted in marked decrease in the size of the liver and spleen. Prolonged follow-up of patients receiving a well balanced diet indicates that the endocrine abnormalities of growth and sexual development are reversible. The relationship of geophagia (which occurred in nearly all patients) to this syndrome is not clear and is discussed. The possibility of zinc deficiency is considered as an explanation of hypogonadism, dwarfism, and changes in alkaline phosphatase.

Formation of mononuclear nitrosyl intermediates during hydrolysis of [Na2[Fe2(μ-S2O3)2(NO)4]·4H2O, a donor of nitrogen monoxide

One of the effects of endogenous NO is the formation of dinitrosyl iron complexes (DNICs), which, along with nitrosothiols, have been identified in all life forms, i.e., in the cells of bacteria, plants, and mammals [1]. Nitrosyl nonheme iron complexes have been identified by EPR as products of interaction of NO with some iron‐sulfur proteins and other iron-containing proteins [2‐5]. DNICs are intermediates in the iron-catalyzed decomposition and formation of S- nitrosothiols [6] and are considered as NO reservoirs and transporters in vivo. These results initiated the development of methods of synthesis and study of the physical and chemical properties of synthetic DNIC analogues [7] with the aim of their practical use as NO donors in medicine and biology [8, 9]. In the present paper, we report the results of the mass spectral and electrochemical studies of the products of hydrolysis of the tetranitrosyl iron thiosulfate complex Na 2 [Fe 2 ( µ -S 2 O 3 ) 2 (NO) 4 )] · 4 H 2 O (TNIC) in aqueous solutions. Study of the antimetastatic effect of the TNIC on three experimental models—melanoma B16, LL carcinoma, and AKATOL—showed that the complex inhibits metastatic growth. The combined administration of a low ineffective dose of the TNIC with cisplatin (or adriablastin) in leukemia P 388‐bearing mice leads to 100% survival among the laboratory animals [10]. Studying the TNIC decomposition products in solutions and determining the structure and properties of intermediates formed during hydrolysis are important for an understanding of molecular genetic mechanisms of action of exogenous NO donors of this class.

Nitric oxide‐induced bacteriostasis and modification of iron‐sulphur proteins in Escherichia coli

The nitric oxide (NO) cytotoxicity has been well documented in bacteria and mammalian cells. However, the underlying mechanism is still not fully understood. Here we report that transient NO exposure effectively inhibits cell growth of Escherichia coli in minimal medium under anaerobic growth conditions and that cell growth is restored when the NO-exposed cells are either supplemented with the branched-chain amino acids (BCAA) anaerobically or returned to aerobic growth conditions. The enzyme activity measurements show that dihydroxyacid dehydratase (IlvD), an iron-sulphur enzyme essential for the BCAA biosynthesis, is completely inactivated in cells by NO with the concomitant formation of the IlvD-bound dinitrosyl iron complex (DNIC). Fractionation of the cell extracts prepared from the NO-exposed cells reveals that a large number of different protein-bound DNICs are formed by NO. While the IlvD-bound DNIC and other protein-bound DNICs are stable in cells under anaerobic growth conditions, they are efficiently repaired under aerobic growth conditions even without new protein synthesis. Additional studies indicate that L-cysteine may have an important role in repairing the NO-modified iron-sulphur proteins in aerobically growing E. coli cells. The results suggest that cellular deficiency to repair the NO-modified iron-sulphur proteins may directly contribute to the NO-induced bacteriostasis under anaerobic conditions.

Decoding plant responses to iron deficiency

Plants respond to iron deprivation by inducing a series of physiological and morphological responses to counteract the nutrient deficiency. These responses include: (i) the acidification of the extracellular medium, (ii) the reduction of ferric ion and (iii) the increased transport of ferrous ion inside of root cells. This iron transport system is present in strategy I plants and is strictly regulated; at low iron concentration the responses are induced whereas upon iron supply they are repressed. The mechanisms related with this process has been extensively studied, however, the specific cellular effectors involved in sensing iron deficiency, the cascade of components participating in signal transduction, and the way iron is metabolized and delivered, are yet poorly understood. Recently, it has been proposed nitric oxide (NO) as a signaling molecule required for plant responses to iron deficiency. NO is produced rapidly in the root epidermis of tomato plants that are growing under iron deficient conditions. Furthermore, it was demonstrated that NO is required for the expression and activity of iron uptake components in roots during iron deprivation. Here we propose and discuss a working hypothesis to understand the way NO is acting in plants responses to iron deficiency. We specifically highlight the cross talk between NO and plant hormones, and the interaction between NO, iron and glutathione for the formation of dinitrosyl iron complexes (DNICs). Finally, a potential role of DNICs in iron mobilization is proposed.Addendum to: Graziano M, Lamattina L. Nitric oxide accumulation is required for molecular and physiological responses to iron deficiency in tomato roots. Plant J 2007; 52:949-60.

Kinetic and characterization studies of iron(II) and iron(III) complex formation reactions with hydrazinopyridine

Reactions of iron(II) and iron(III) with hydrazinopyridine have been investigated. The metal-to-ligand ratio of the two complexes was determined to be 1 : 3 and the stability constants of [Fe(hypz)3]2+ and [Fe(hypz)3]3+ were evaluated as 2.51 × 102 L3 mol−3 and 1.94 × 103 L3 mol−3, respectively. The complex formation reactions were studied kinetically as a function of [hzpy] at various temperatures (15–37°C) at fixed pH (7.5) using stopped-flow techniques. Kinetic results suggest that the binding of hzpy with Fe(II) or Fe(III) takes place in two consecutive steps: a slow and [hzpy] dependent rate-determining step followed by [hzpy] independent ring closure. The activation parameters for both steps in the two systems have been calculated. The low (57 ± 1, 46 ± 2 kJ mol−1) as well as (21 ± 0.1, 21 ± 0.1 kJ mol−1) for the first and second steps, respectively, and the large negative values of (−81 ± 4, −110 ± 5 J K−1 mol−1) as well as (−197 ± 3, −197 ± 3 J K−1 mol−1) for the first and second steps for both Fe(II) and Fe(III) systems, respectively, indicate associative modes of activation for both ligand substitution processes. [Fe(hypz)3](PF6)2 and [Fe(hypz)3](PF6)3 were isolated as solids and characterized using CHN, IR, magnetic and UV-Visible measurements.