The Arabidopsis Mitochondrial Glutaredoxin GRXS15 Provides [2Fe-2S] Clusters for ISCA-Mediated [4Fe-4S] Cluster Maturation

Iron-sulfur (Fe-S) proteins are crucial for many cellular functions, particularly those involving electron transfer and metabolic reactions. An essential monothiol glutaredoxin GRXS15 plays a key role in the maturation of plant mitochondrial Fe-S proteins. However, its specific molecular function is not clear, and may be different from that of the better characterized yeast and human orthologs, based on known properties. Hence, we report here a detailed characterization of the interactions between Arabidopsis thaliana GRXS15 and ISCA proteins using both in vivo and in vitro approaches. Yeast two-hybrid and bimolecular fluorescence complementation experiments demonstrated that GRXS15 interacts with each of the three plant mitochondrial ISCA1a/1b/2 proteins. UV-visible absorption/CD and resonance Raman spectroscopy demonstrated that coexpression of ISCA1a and ISCA2 resulted in samples with one [2Fe-2S]²⁺ cluster per ISCA1a/2 heterodimer, but cluster reconstitution using as-purified [2Fe-2S]-ISCA1a/2 resulted in a [4Fe-4S]²⁺ cluster-bound ISCA1a/2 heterodimer. Cluster transfer reactions monitored by UV-visible absorption and CD spectroscopy demonstrated that [2Fe-2S]-GRXS15 mediates [2Fe-2S]²⁺ cluster assembly on mitochondrial ferredoxin and [4Fe-4S]²⁺ cluster assembly on the ISCA1a/2 heterodimer in the presence of excess glutathione. This suggests that ISCA1a/2 is an assembler of [4Fe-4S]²⁺ clusters, via two-electron reductive coupling of two [2Fe-2S]²⁺ clusters. Overall, the results provide new insights into the roles of GRXS15 and ISCA1a/2 in effecting [2Fe-2S]²⁺ to [4Fe-4S]²⁺ cluster conversions for the maturation of client [4Fe-4S] cluster-containing proteins in plants.     

The Mechanisms of Making Molecules to Order

The mechanisms of formation of a [2]catenane and one of its molecular components have been investigated. While the synthesis of the tetracationic cyclophane, [BBIPYBIXYCY] ⁴⁺ from bipyridine (BP) and 1,4-bis(bromomethyl)benzene (BBB) , directed by the template, 1,5–bis[2(2–hydroxyethoxy)ethoxy]naphthalene (1/5BHEEN) becomes less efficient (23 to 5%) under ultra-high pressure reaction conditions (12 kbars), the self-assembly of {[2]-[BPP34C10]-[BBIPYBIXYCY] catenane}⁴⁺ from BP and BBB in the presence of BPP34C10 can be achieved with increased efficiency (18 to 42%) at 12 kbars. This difference in the trends of the yields can be ascribed to the enhanced templating action of BPP34C10 relative to that of 1/5BHEEN when two moles of BP and two moles of BBB are being employed to construct the tetracationic cyclophane. The self-assembly of the [2]catenane from BP, BBB , and BPP34C10 has been followed by ¹H NMR spectroscopy in D₇-DMF solution. On the basis of this spectroscopic evidence and supporting chemical data, the formation of {[2]-[BPP34C10]-[BBIPYBIXYCY] catenane} ⁴⁺ from two moles of BP , two moles of BBB , and one mole of BPP34C10 is believed to proceed via the monoquatemary intermediate, [MBXYBIPY] ⁺, which has not been isolated, and the dicationic species, [BBIPYXY] ²⁺, which has been isolated and shown to be an intermediate in the self-assembly process leading to the [2]catenane, presumably via the [BXYBBIPYXY] ³⁺ trication — the final intermediate which again has not been isolated.     

Linear Chain Ferromagnetic Charge Transfer Compounds

Charge transfer complexes possessing a … DADA … structure with both the donor, D, and acceptor, A, being S = 1/2 radicals may exhibit cooperative magnetic phenomena. The complex [Fe(C₅Me₅)₂]⁺·[TCNQ]⁻· exhibits metamagnetic behavior. The similarly structured [TCNE]⁻· and [C₄(CN)₆]⁻· complexes are ferromagnets, whereas the [DDQ]⁻· salt is a paramagnet. The high temperature magnetic susceptibility obeys the Curie-Weiss expression with θ = + 30, + 30, and + 3 for the [TCNE]⁻·, [C₄(CN)₆]⁻·, and [TCNQ]⁻· salts, respectively. The ferromagnetic [TCNE]⁻· salt exhibits zero field Zeeman split ⁵⁷Fe Mossbauer spectra with an internal field of 425.6 kOe at 4.23 K. After reviewing the current papers discussing ferromagnetism in molecular (organic) compounds, a qualitative model consistent with the necessary bulk spin alignment required for a ferromagnet is presented.     

Spiroheterocyclic system. Part IV: Novel azo dye sulpha drugs of spiroheterocyclic naphthenes

Novel azo-dyes have been synthesized by diazotization of 4-amino benzene-4′-(substituted heterocyclo) sulphonamide derivatives and coupling with 1-oxa-4-thia-spiro[4,4]nonan-2-one (I) and/or with l-oxa-4-thia-spiro[4,5]decan-2-one (I′) in acid medium to give the corresponding 3-azo-(4′-substituted benzenesulphonamido)-l-oxa-4-thia-spiro[4,4]nonan-2-one (II-IX) and/or l-oxa-4-thia-spiro[4,5]decan-2-one (II′-IX′] as spiro-ligands. Treatment of these ligands with metal salts of iron (Fe³⁺), copper (Cu²⁺) and mercury (Hg²⁺) as chlorides in ethanolic solution furnished the corresponding metal chelates (II_a-c-IX_a-c) and/or (II′_a-c-IX′_a-c). The compounds were tested in vitro for antimicrobial activity to study the structure-activity relationship.     

Dual chemosensing properties of new ferrocene-based receptors towards fluoride and copper(II) ions

The new ferrocene based receptors N-[4-ferrocenyl-2-methyl-4-oxobut-1-enyl]-N′-phenylthiourea (1), N-[4-ferrocenyl-2-methyl-4-oxobut-1-enyl]-N′-[4-nitrophenyl]thiourea (2) were synthesized and characterized. Fluorescence titrations of receptors 1 and 2 with various transition metal ions showed selective response to Cu²⁺ ions and the emission intensities quenched significantly. Electrochemical titrations with anions revealed that receptors 1 and 2 sensed the F⁻ anion in high selectivity with a cathodic shift of 100 mV.     

Spectrophotometric and electrochemical behavior of a novel azocalix[4]arene derivative as a highly selective chromogenic chemosensor for Cr

In this study, a novel azocalix[4]arene derivative, 5,11,17-tris[(1-naphtyl)azo]-25,26,27,28-tetrahydroxy-calix[4]arene (NAC4) bearing napthyl groups on the upper rim was synthesized. Its complexation behavior for alkali, alkaline-earth and various heavy metal ions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Hg²⁺, Ni²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Co²⁺, Fe²⁺, Cr³⁺, Ag⁺) was investigated by spectroscopic and voltammetric methods. This chemosensor exhibits decreased absorbance in the presence of Hg²⁺ and a unique absorbance quenching effect only for Cr³⁺. In addition, a new absorption band centered at 565 nm with the formation of the 1:1 host–guest complex (Cr³⁺-NAC4) was observed in the case of Cr³⁺, leading to an obvious color change from light orange to dark lilac. In voltammetric experiments, Cr³⁺ ions decreased voltammetric peaks of NAC4, whereas no significant changes occurred in the presence of the other metal ions. The Benesi–Hildebrand method was used to determine a logarithmic value of 3.76 for the association constant of the complex between Cr³⁺ and NAC4.     

Synthesis,crystal structure and magnetic properties of a three-dimensional cyano-bridged heterometallic complex {NiII(Me6-[14]ane-N4)}2[WIV(CN)8] · 6H2O

Self-assembly of [W(CN)₈]⁴⁻ and {Ni(Me₆-[14]ane-N₄)}²⁺ (Me₆-[14]ane-N₄ = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) leads to a novel three-dimensional cyano-bridged complex {Ni(Me₆-[14]ane-N₄)}₂[W(CN)₈] · 6H₂O (1), which was characterized by IR, elemental analysis, ICP, TGA and SC-XRD. Magnetic behavior of the complex shows a characteristic of combination of zero-field splitting of Ni²⁺ in an axially distorted octahedral surrounding and a weak antiferromagnetic interaction between Ni²⁺ ions through the diamagnetic [W(CN)₈]⁴⁻ bridges.     

Photochemical [2+2] cycloaddition of the olefinic double bonds in the supramolecular rectangle [Ru4(η6-p-cymene)4(μ-oxalato)2(μ-4,4′-bipyridylethylene)2]4+

Self-assembly of 4,4′-bipyridylethylene (bpe) bidentate connector with the dinuclear arene ruthenium clip [Ru₂(η⁶-p-cymene)₂(μ-oxalato)Cl₂] in the presence of silver triflate affords the cationic organometallic rectangle [Ru₄(η⁶-p-cymene)₄(μ-oxalato)₂(μ-bpe)₂]⁴⁺ ([1][CF₃SO₃]₄). Upon UV irradiation of a methanol solution of [1]⁴⁺, dimerisation of the olefinic double bonds of the two parallel bpe ligands occurs, thus giving rise to the [2+2] cycloaddition derivative [Ru₄(η⁶-p-cymene)₄(μ-oxalato)₂(μ-tpcb)]⁴⁺ ([2][CF₃SO₃]₄) (tpcb = tetrakis(4-pyridyl)cyclobutane). The [2+2] photodimerisation reaction was followed by ¹H NMR spectroscopy. Moreover, the molecular structure of these two systems was deduced by one-dimensional and two-dimensional NMR experiments (¹H, ¹³C, ROESY, COSY, HSQC). These data suggest the formation of only the rctt-tetrakis(4-pyridyl)cyclobutane isomer.     

Mass spectrometry of triglycerides: I. Structural effects

Mass spectra of several triglycerides of specific structure or with specific deuterium labeling have been measured with a low resolution mass spectrometer. With saturated triglycerides the abundances of ions characteristic of the component acids, [M-RCO₂]⁺, increase with increasing chain length, and [M-RCO₂CH₂]⁺ decrease with increasing chain length. Unsaturation in the acyl moiety causes the abundant formation of [RCO-1]⁺. Structures have been suggested for a number of the main peaks obtained from saturated triglycerides, and high resolution spectra of one triglyceride agree with the postulated structures. The peaks, [RCO+74]⁺, [RCO+115]⁺ and [RCO+128+14n]⁺, represent structures which contain the glyceryl portion of the triglyceride, since in case of the replacement of its hydrogens with deuteriums, these peaks are shifted accordingly. Evidence which indicates the possibility of determining the location of unsaturation by the interruption of homology of the [RCO+128+14n]⁺ series, brought about by the addition of deuterium to the unsaturated linkages, is introduced. Further evidence is also presented, which indicates that the [M-RCO₂CH₂]⁺ ions arise from the positions 1 and 3 and, in agreement with earlier studies from other laboratories, it is thus possible to identify the acyl groups attached to the 1 and 2 positions of the glyceryl moiety. Presented in part at the AOCS Meeting, New Orleans, April 1970. Part V of a series on Mass Spectrometry of Lipids. For IV see Lipids 4:421–427 (1969).     

Ketone bodies,glucose and glutamine as lipogenic precursors in human diploid fibroblasts

Incorporation of [¹⁴C] from acetoacetate, D(-)- and L(+)-3-hydroxybutyrate, glucose, glutamine, acetate and palmitate in cellular lipids were studied in cultures in human diploid fibroblasts (HDF). The results showed that acetoacetate was 2–10 times more effective as a lipogenic precursor than was either D- or L-3-hydroxybutyrate. Its extent of incorporation into lipids was 2- to 8-fold more than the other precursors examined under conditions when the overall rates of nonsaponifiable and saponi-fiable lipogenesis as measured by³H₂O incorporation were essentially unchanged. Acetoacetate supported both saponifiable and nonsaponifiable lipid syntheses with half-saturation values (K_m app.) of 185 μM and 30 μM, respectively. Glucose stimulated acetoacetate incorporation into lipids whereas, conversely, acetoacetate inhibited [¹⁴C] glucose incorporation into lipids. The presence of low density lipoproteins (LDL) cholesterol (@40 μg cholesterol/mL) inhibited the incorporation of [¹⁴C] from acetoacetate 56% into nonsaponifiable lipids; the inhibition was consistently higher (75%) when [¹⁴C] glucose or glutamine were the precrusors. The loss of 3-hydroxy-3-methyl-glutaryl CoA (HMG CoA) reductase activity upon addition of LDL-cholesterol was greater than the suppression of [¹⁴C] incorporation from acetoacetate or glucose into nonsaponifiable lipids. In the presence of glucose, [¹⁴C] acetoacetate was incorporated into 3-βOH sterols (digitonin precipitable). 7.7±1.1 times more effectively than was [¹⁴C] glucose. The results suggest that HDF would be a suitable model to investigate the effects of various precrusors of HMG CoA on the rate of cholesterol biosynthesis.     

Anionic polymerization of ethylene oxide with cryptates as counterions: 2

A kinetic study of the anionic polymerization of ethylene oxide has been made in tetrahydrofuran at 20°C, with the cryptate Cs⁺ + [TC] as counterion, [TC] being a spheroidal macrotricyclic ligand. Conductance measurements have been made on THF solutions of ?₄BCs + [TC]. Ionic associations higher than cryptated ion pairs are negligible for living end concentrations lower than 3 × 10^?4 moll^?1. k_± and the alkoxide ion pair dissociation constant K_D were determined from both sets of kinetic data obtained with and without added salt knowing the value of k_? from kinetic data performed with K⁺ + [222] as counterion. Free alkoxide ions are about twenty times more reactive than cryptated caesium ion pairs.     

Mass Spectrometry of the Lithium Adducts of Diacylglycerols Containing Hydroxy FA in Castor Oil and Two Normal FA

Castor oil can be used in industry. The molecular species of triacylglycerols containing hydroxy fatty acids (FA) in castor oil have been identified. We report here the identification of twelve diacylglycerols (DAG) containing hydroxy FA in castor oil using positive ion electrospray ionization mass spectrometry of the lithium adducts. They were RR (diricinolein, R is ricinoleate), RL, RS, R‐diOH18:0, R‐diOH18:1, R‐diOH18:2, R‐triOH18:0, R‐triOH18:1, R‐triOH18:2, diOH18:0‐diOH18:1, diOH18:1‐diOH18:1 and diOH18:1‐diOH18:2. The MS² fragment ions, [M + Li ? FA]⁺ and [FA + Li]⁺, from the lithium adducts of DAG containing hydroxy FA (one or two hydroxy FA), were used for the identification. The additional fragment ions from the neutral losses of FA lithium salts [M + Li ? FALi]⁺ were used for the identification of eleven DAG containing two normal FA in a soybean oil bioconversion product. The MS² fragment ions from the neutral losses of FA lithium salts [M + Li ? FALi]⁺ were not detected from the DAG containing hydroxy FA. The DAG containing FA with more hydroxyl groups than the other FA on the same DAG molecule tended to have a prominent fragment ion [FA + Li]⁺ and an undetectable fragment ion [M + Li ? FA]⁺ while the FA was the more hydroxylated FA. Also the less hydroxylated FA of a DAG tended to have a prominent fragment ion [M + Li ? FA]⁺ and an undetectable fragment ion [FA + Li]⁺ while the FA was the less hydroxylated FA.     

Radical polymerisation of ethyl acrylate in the presence of molecular oxygen

Oxygen as a promoter of radical polymerisation of ethyl acrylate was studied in the aqueous medium. Cu²⁺ was chosen as the catalyst for the ascorbic acid (AA)—0₂ redox reaction, constituting a three component initiating system. The rate of polymerisation, R_p, was observed to increase, remain constant and then decrease with increasing [Cu²⁺]. R_p increased with [O₂] upto ～ 6.5 × 10^?4M and thereafter remained constant. [AA] > 1.2 × 10^?3M did not influence the rate. R_p always increased with monomer [M] at fixed [Cu²⁺], [O₂] and [AA]. However, the order with respect to [M] increased with increasing [Cu²⁺]. The rate of polymerisation increased with ionic strength, μ and decreased with [H₂SO₄]. There was an initial increase in R_p followed by a decrease with increasing temperature. Conditions were identified where R_p depended only on [Cu²⁺] and [M] or [M] only for industrial exploitation. Kinetic chain length of the polymers obtained under various experimental conditions were determined viscometrically.     

Electrochemical oxidation of <Emphasis Type="Italic">p</Emphasis>-sulfonated calix[8]arene

The water-soluble p-sulfonated sodium salt of calix[8]arene (III) was synthesized. The product was characterized by FT-IR, NMR and UV–Vis spectra.Then the electrochemical behaviors of p-sulfonated sodium salt of calix[8]arene in NaAc+HAc (pH = 4) buffer solution was studied. In aqueous solution, p-sulfonated calix[8]arene can be oxidized when the potential is more than 0.7 V vs SCE. It was confirmed that the reaction was a two-electron irreversible electrochemical reaction. The transfer coefficient, α, was measured as 0.7. At 25°, the diffusion coefficient of p-sulfonated calix[8]arene was determined as 8.6 × 10⁻⁷ cm² s⁻¹. The diffusion activation energy of p-sulfonated calix[8]arene was 18.9 kJ mol⁻¹ at pH = 4.     

Selective Extraction of Fe3+ Cation by Calixarene-Based Cyclic Ligands

Abstract

The selective liquid-liquid extraction of Fe³⁺ cation from the aqueous phase to the organic phase was carried out by using p-tert-butylcalix[4]arene [L₁], ca-lix[4]arene [L₂], p-nitro-calix[4]arene [L₃], calix[4]arene p-sulfonic acid [L₄], p-(diethylamino)methylcalixt4]arene [L₅], tetramethyl-p-tert-butylcalix[4]arene tet-raketone [L₆], 25,27-dimethyl-26,28-dihydroxy-p-tert-butylcalix[4]arene diketone [L₇], calix[4]arene-bearing dioxime group on the lower rim [L₈], and a monooxime [L₉]. The effect of varying pH upon the extraction ability of calixarenes substituted with electron-donating and electron-withdrawing groups at their p-position was examined. Observed results were compared with those found for unsubstituted calix[4]arene.     

Viscosity‐molecular weight relationship for cellulose solutions in either NMMO monohydrate or cuen

The intrinsic viscosities, [η], of nine cellulose samples, with molar masses from 50 × 10³ to 1 390 × 10³ were determined in the solvents NMMO*H₂O (N‐methyl morpholin N‐oxide hydrate) at 80°C and in cuen (copper II‐ethlenediamine) at 25°C. The evaluation of these results with respect to the Kuhn–Mark–Houwink relations shows that the data for NMMO*H₂O fall on the usual straight line in the double logarithmic plots only for M ≤ 158 10³; the corresponding [η]/M relation reads log ([η]/mL g⁻¹) = –1.465 + 0.735 log M. Beyond that molar mass [η] remains almost constant up to M ≈ 10⁶ and increases again thereafter. In contrast to NMMO*H₂O the cellulose solutions in cuen behave normal and the Kuhn–Mark–Houwink relation reads log ([η]/mL g⁻¹) = −1.185 + 0.735 log M. Possible reasons for the dissimilarities of the behavior of cellulose in these two solvents are being discussed. The comparison of three different methods for the determination of [η] from viscosity measurements at different polymer concentrations, c, demonstrates the advantages of plotting the natural logarithm of the relative viscosities as a function of c. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Extraction of Pb2+ with p-tert-butylcalix [4]-, [5]-, [6]Arene Carboxylic Acid Ligands and their Monomeric Counterpart: A Thermodynamic Approach

Studies on extraction equilibrium constants at different temperatures and thermodynamic parameters of solvent extraction of Pb²⁺ ion with carboxylic acid derivatives of different ring size calixarenes and structure related monomeric compound have been carried out. The extraction equilibrium constants corresponding to calix[n]arene (n?=?4, 5, 6) derivatives decrease in the order [5]arene > [6]arene > [4]arene. In all cases, the complexation process is primarily enthalpy driven. The favorable enthalpic contribution for extraction of Pb²⁺ is in the order hexamer ≈ monomer > tetramer > pentamer. However, the unfavorable entropic loss follows the order: monomer > hexamer > tetramer > pentamer. Overall stability of the host-guest complex is the function of entropy-enthalpy compensation and the free energy of complexation is minimum for the pentamer, followed by tetramer ≈ hexamer and monomer. Although the carboxylic acid derivative of calix[4]arene is more preorganized than the calix[5]arene derivative, extraction of Pb²⁺ ion with the tetramer passes through greater entropic loss than that with the pentamer and the degree of preorganization of calix[4]arene derivative is far from perfect for the complexation and extraction of Pb²⁺ ion. As compared to tetrameric and hexameric counterparts, the structural features of the carboxylic acid derivative of calix[5]arene prior to complexation contribute much to interact with the Pb²⁺ ion and form a thermodynamically stable complex. Supplementary materials are available for this article. Go to the publisher's online edition of Solvent Extraction and Ion Exchange to view the supplemental file.     

Reactivity studies of 2,3,5,6-Tetra(2-pyridyl) pyrazine (tppz) with first-row transition metal ions

Reactions of 2,3,5,6-tetra(2-pyridyl) pyrazine (tppz) with [ML₆][X]₂ (L = CH₃CN, H₂O;X = [BF₄]⁻, [ClO₄]⁻, [NO₃]⁻ [BArF]⁻(BArF - B[3,5-C₆H₃(CF₃)₂]₄) lead to the high-yield formation of mononuclear [M(tppz)₂]²⁺, (M = Mn^II, Fe^II, Co^II, and Ni^II) and dinuclear [Ni₂(tppz)(CH₃CN)₆]⁴⁺ species. The new compounds were fully characterized by X-ray crystallographic, spectroscopic, and magnetic susceptibility measurements. Surprisingly, the 2:1 M:tppz reactions did not lead to isolation of the dinuclear species except in the case of Ni(II). It was further noted that even in the case of the Ni reactions, the nuclearity of the product depends on the choice of anions and the reaction conditions. Magnetic measurements of the mononuclear species [Co(tppz)₂]²⁺ revealed thermally induced spin-crossover behavior from a high-spin S = 3/2 at higher temperatures to a low-spin S = 1/2 complex at lower temperatures. The dinuclear compound [Ni₂(tppz)(CH₃CN)₆]⁴⁺ exhibits a weak anti-ferromagnetic interaction through the bridging tppz ligand.     

Highly efficient extraction of tetra- and hexavalent plutonium using DGA functionalized pillar[5]arene in RTIL: Understanding speciation,thermodynamics and radiolytic stability

DGA functionalized pillar[5]arene (P5DGA) in ionic liquid was demonstrated as highly efficient system for the extraction of plutonium from acidic aqueous solution in tetravalent and hexavalent oxidation state. The extraction followed ‘cation-exchange’ mechanism via [Pu.P5DGA]⁴⁺ and [PuO₂.P5DGA]²⁺, as extracted species for Pu⁴⁺ and PuO₂²⁺, respectively. Evaluation of thermodynamic parameters (ΔG, ΔH and ΔS) showed the feasibility and spontaneity of the extraction process. The process was exothermic and primarily ‘enthalpy driven’, since entropy change was found negative. P5DGA-RTIL solvent system showed good radiolytic stability even at 1000 kGy of gamma dose.     

The association constant of macrocyclic ether–cation interactions in 1,4-dioxane/water mixtures. III. Effect of temperature on the binding

The association constant, K_a of Na⁺ with [12]crown-4, [15]crown-5 and [18]crown-6 crown ethers were determined in a binary mixture, 1,4-dioxane/water (50/50) using a Na⁺ ion selective electrode at different temperatures. K_a values were determined with the relationship, 1/K_a [L_o]^n+m–1 = (1–nP′)ⁿ(1–mP′)^m/P′, for various stoichiometries, (n:m), where P′ is the mole fraction of the complexed cation. The exothermic association constants and the thermodynamic data for cation–macrocycle complexes explained in terms of Eigen–Winkler binding mechanism are given. The binding power found for Na⁺, however, was the highest with [18] crown-6.