Membrane Depolarization by Hexacyanoferrate (III), Hexabromoiridate (IV) and Hexachloroiridate (IV)

Three artificial electron acceptors of different E_o and charge,hexacyanoferrate (III) (K₃Fe(CN)₆), hexachloroiridate (IV) (K₂IrCl₆),and hexabromoiridate (IV) (K₂IrBr₆), were compared with respectto their rate of reduction by roots of Zea mays L., the concomitantproton secretion, and to the effect on plasmalemma depolarization. It has been shown that these plasma membrane impermeable electronacceptors were reduced by a plasmalemma reductase activity.At low concentrations proton secretion was slightly inhibited,at higher concentrations, however, the rate of proton secretionwas stimulated. The root cell plasmalemma showed a transientdepolarization after addition of all three electron acceptors.The depolarization was concentration-dependent for the iridatecomplexes but not for hexacyanoferrate (III). For both iridatecomplexes maximum depolarization was reached at 50 µmoldm^–3. A hypothetical model as an explanation of the redox dependentproton secretion will be given. Key words: Hexachloroiridate (IV), hexabromoiridate (IV), hexacyanoferrate (III), plasmalemma redox, membrane potential, Zea mays     

Guanine complexes with dysprosium(III), thorium(IV) and uranium(IV) chlorides

By refluxing mixtures of guanine (guH) and DyCl₃, ThCl₄ or UCl₄ in ethanol-triethyl orthoformate, solid complexes of the Dy(guH)₂(gu)Cl₂ and M(gu)₂Cl₂ (M = Th, U) types were isolated. The insolubility of the new complexes in organic media, combined with the coordination number six suggested by the spectral evidence, favors polymeric configurations. Most likely structures involve a linear, chainlike, single-bridged polymeric backbone

The Dy³⁺ complex is probably a linear polymer, also containing terminal unidentate guanine ligands, whilst for M = Th⁴⁺, U⁴⁺ highly polymeric structures arising from cross-linking between linear polymeric

units seems most likely. IR evidence rules out participation of the O(6) oxygen of guanine in coordination, despite the hard acid character of the metal ions under study. Guanine apparently coordinates exclusively through ring nitrogens in the new metal complexes; N(9) and N(7). N(9) are, respectively, the most likely binding sites of terminal unidentate and bridging bidentate guanine. The chloro ligands present in the complexes seem to be exclusively terminal.     

Synthesis and characterisation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes [Ti(IV), Zr(IV), Hf(IV), La(III), Ce(III), Yb(III), Sn(II) and Fe(II)]

The preparation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes is described. These are of formula [M{η⁵-C₅H₄(BX)}Cl₃] [M = Ti and X = CAT (2a), CAT^t (2b) or CAT^tt (2c); X = CAT^tt and M = Zr (4a) or Hf (4b)], [M{η⁵-C₅H₄(BX)}₂Cl₂] [M = Zr, X = CAT (3a) or CAT^t (3c); or M = Hf, X = CAT (3b) or CAT^t (3d)], [M{(μ-η⁵-C₅H₃BCAT)₂ SiMe₂}Cl₂] [M = Zr (5a) or Hf (5b)], [M{η⁵-C₅H₃(BCAT)₂}Cl₃] [M = Zr (6a) or Hf (6b)], [M{η⁵-C₅H₄BCAT}₃(THF)] [M = La (7a), Ce (7b) or Yb (7c)], [Sn{η⁵-C₅ H₄(BCAT^t)}Cl](8) and [Fe{η⁵-C₅H₄(BCAT^t)}₂] (9). The abbreviations refer to BO₂C₆H₄-1,2 (BCAT) and the 4-Bu^t (BCAT^t) and the (BCAT^tt) analogues. The compounds 2a-9 have been characterised by microanalysis, multinuclear NMR and mass spectra. The single crystal X-ray structure of the lanthanum compound 7a is presented.     

Extraction of Np(IV), Pu(IV) and Am(III) by bidentate organophosphorus extractant

This paper summarizes the extraction of Np(IV), Pu(IV) and Am(III) with dihexyl-N,Ndiethyl carbamyl methylene phosphonate (DHDECMP)-diethyl benzene (DEB) in nitric acid.The distribution ratio of Np(IV), Pu(IV) and Am(III) was studied as a function of a number of parameters such as concentration of nitric acid, salting-out reagent in the aqueous phase, contact time and temperature. Stripping and separation of Np(IV), Pu(IV) and Am(III) from the pregnant organic phase were also studied. The suitable stripping and separation conditions were obtained. The enthalpy changes ΔH_Np, ΔH_Pu, ΔH_Am associated with their extraction process were estimated individually. The composition of extracted complex of Np(IV), Pu(IV) and Am(III) was determined.     

Physicochemical and biological properties of 6(1),6(3),6(5)-tri-O-alpha-maltosyl-cyclomaltoheptaose (6(1),6(3),6(5)-tri-O-alpha-maltosyl-beta-cyclodextrin)

A unique multibranched cyclomaltooligosaccharide (cyclodextrin, CD) of 6(1),6(3),6(5)-tri-O-alpha-maltosyl-cyclomaltoheptaose [6(1),6(3),6(5)-tri-O-alpha-maltosyl-beta-cyclodextrin, (G(2))(3)-betaCD] was prepared. The physicochemical and biological properties of (G(2))(3)-betaCD were determined together with those of monobranched CDs (6-O-alpha-D-glucopyranosyl-alpha-cyclodextrin (G(1)-alphaCD), 6-O-alpha-D-glucopyranosyl-beta-cyclodextrin (G(1)-betaCD), and 6-O-alpha-maltosyl-beta-cyclodextrin (G(2)-betaCD)). NMR spectra of (G(2))(3)-betaCD were measured using various 2D NMR techniques. The solubility of (G(2))(3)-betaCD in water and MeOH-water solutions was extremely high in comparison with nonbranched betaCD and was about the same as that of the other monobranched betaCDs. The formation of an inclusion complex of (G(2))(3)-betaCD with stereoisomers (estradiol, retinoic acid, quinine, citral, and glycyrrhetinic acid) depends on the cis-trans isomers of guest compounds. The cis isomers of estradiol, retinoic acid, and glycyrrhetinic acid were included more than their trans isomers, while the trans isomers of citral and quinine fit more tightly than their cis isomers. (G(2))(3)-betaCD was the most effective host compound in the cis-trans resolution of glycyrrhetinic acid. Among the branched betaCDs, (G(2))(3)-betaCD exhibited the weakest hemolytic activity in human erythrocytes and showed negligible cytotoxicity in Caco-2 cells up to 200 microM. These results indicate unique characteristics of (G(2))(3)-betaCD in some biological responses of cultured cells.     

Semi-synthetic antibiotics: Titanium(IV), zirconium(IV) and mercury(II) complexes of 6-amino penicillinic acid

A number of organometallic derivatives involving 6-amino penicillinic acid (I), of the types η⁵-R)₂M- (Cl)L^?Et₃NH⁺ (II), (η⁵-R)₂M(Cl)L (III) and R′HgL [R = cyclopentadienyl (C₅H₅), indenyl (C₉H₇), R′ = phenyl (C₆H₅), p-acetoxyphenyl (p-CH₃COOC₆H₄), o-hydroxyphenyl (o-HOC₆H₄), p-hydroxyphenyl (p-HOC₆H₄); M = Ti(IV), Zr(IV); LH = 6-amino penicillinic acid] have been synthesized and characterized. Conductance measurements indicate that while the (η⁵-R)₂M(Cl)L^?Et₃NH⁺ complexes are 1:1 electrolytes, the remaining compounds are non-electrolytes. From IR and UV spectral studies it is concluded that the penicillin moiety is bidentate. PMR and CMR studies support the stoichiometry of the complexes. Fluorescence studies have been carried out for o- and p-HOC₆H₄HgL complexes and relevant photochemical parameters have been elucidated. X-ray diffraction studies have been made for the o-HOC₆H₄HgL complex. For the C₆H₅HgL, p-CH₃COOC₆H₄HgL and p-HOC₆H₄HgL complexes, thermal studies (TG and DTA) have been carried out and kinetic parameters for thermal degradation have been enumerated. In addition, the fragmentation pattern of these complexes has been analysed on the basis of mass spectra. The C₆H₅HgL and p-CH₃COOC₆H₄HgL complexes show positive bactericidal activities.     

Spectral and thermodynamic properties of Ag(I), Au(III), Cd(II), Co(II), Fe(III), Hg(II), Mn(II), Ni(II), Pb(II), U(IV), and Zn(II) binding by methanobactin from Methylosinus trichosporium OB3b

Methanobactin (mb) is a novel chromopeptide that appears to function as the extracellular component of a copper acquisition system in methanotrophic bacteria. To examine this potential physiological role, and to distinguish it from iron binding siderophores, the spectral (UV–visible absorption, circular dichroism, fluorescence, and X-ray photoelectron) and thermodynamic properties of metal binding by mb were examined. In the absence of Cu(II) or Cu(I), mb will bind Ag(I), Au(III), Co(II), Cd(II), Fe(III), Hg(II), Mn(II), Ni(II), Pb(II), U(VI), or Zn(II), but not Ba(II), Ca(II), La(II), Mg(II), and Sr(II). The results suggest metals such as Ag(I), Au(III), Hg(II), Pb(II) and possibly U(VI) are bound by a mechanism similar to Cu, whereas the coordination of Co(II), Cd(II), Fe(III), Mn(II), Ni(II) and Zn(II) by mb differs from Cu(II). Consistent with its role as a copper-binding compound or chalkophore, the binding constants of all the metals examined were less than those observed with Cu(II) and copper displaced other metals except Ag(I) and Au(III) bound to mb. However, the binding of different metals by mb suggests that methanotrophic activity also may play a role in either the solubilization or immobilization of many metals in situ.     

Oxydiacetato complexes of thorium(IV), the crystal structures of tetra-aquo bis(oxydiacetato)thorium(IV) hexahydrate and di(sodium nitrate) disodium tris(oxydiacetato)thorium(IV)

The crystal and molecular structures of Th(oda)₂(H₂O)₄·6H₂O (1) and Na₂[Th(oda)₃]·2NaNO₃ (2) (oda = oxydiacetate) have been determined from three-dimensional X-ray diffraction data and refined by least squares to R = 0.049 and Rw = 0.049 for 2265 independent reflections for (1) and to R = 0.024 and Rw = 0.023 for 2196 independent reflections for (2).Crystal parameters are as follows: (1), tetragonal, space group P4₁2₁2, a = 10.335(2), c = 20.709(5) Å and Z = 4; (2), monoclinic, space group C2/c, a = 17.096(5), b = 9.451(2), c = 16.245(4) Å, β = 107.8(1) and Z = 4.In both compounds the thorium atom lies on a crystallographic two-fold axis. The co-ordination number for thorium in (1) is 10 (bicapped square antiprism geometry), the compound is monomeric, the two oda ligands are tridentate to the metal, and four water molecules complete the coordination sphere; in thorium (2) the coordination number is 9 (tricapped trigonal prism geometry) with three oda ligands tridentate to the metal, the [Th(oda)₃]^2? and NO₃^? anions are held together through the sodium ions which are coordinated both to the oda carboxylic oxygens and to the nitrate oxygens.The ThO coordination distances are: in (1) 2.411(8), 2.414(9) for the carboxylic oxygens, 2.479(10) and 2.486(8) for water molecules and 2.697(9) for the etheric oxygen and in (2) 2.384(3), 2.402(4) and 2.402(4) for the carboxylic oxygens, 2.559(5) and 2.562(4) Å for the etheric oxygens.     

Heterobimetallic chloro bridgedcomplexes of (η:η−C10H16)-ruthenium(IV) with palladium(II), platinum(II), rhodium(III), iridium(III), copper(I) and rhodium(I)

Metathesis of [(η³:η³−C₁₀H₁₆)Ru(Cl) (μ−Cl)]₂ (1) with [R₃P) (Cl)M(μ-Cl)]₂ (M = Pd, Pt), [Me₂NCH₂C₆H₄Pd(μ-Cl)]₂ and [(OC)₂Rh(μ-Cl)]₂ affords the heterobimetallic chloro bridged complexes (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂M(PR₃)(Cl) (M = Pd, Pt), (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂PdC₆H₄CH₂NMe₂ and (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂Rh(CO)₂, respectively. Complex 1 reacts with [Cp^*M(Cl) (μ-Cl)]₂ (M = Rh, Ir), [p-cymene Ru(Cl) (μ-Cl]₂ and [(Cy₃P)Cu(μ-Cl)]₂ to give an equilibrium of the heterobimetallic complexes and of educts. The structures of (η³:η³-C₁₀H₁₆)Ru(μ-Cl)₂Pd(PR₃) (Cl) (R = Et, Bu) and of one diastereoisomer of (η³:η³-C₁₀H₁₆)Ru(μ-Cl)₂IrCp^*(Cl) were determined by X-ray diffraction.     

Electronic absorption and MCD spectra for octacyanometallate complexes M(CN)8, M=Mo(IV), W(IV), n=4 and Mo(V), W(V), n=3

Electronic absorption and 8.0 T magnetic circular dichroism (MCD) spectra are reported for M(CN)₈ ⁴⁻, M=Mo(IV) and W(IV), in aqueous solution and M(CN)₈ ³⁻, M=Mo(V) and W(V), in acetonitrile solutions. In addition some absorption and MCD spectra are reported for the M(CN)₈ ³⁻ ions embedded in thin poly methyl methacrylate (PMMA) plastic films at temperatures from 295 to 10 K. The temperature dependence of the MCD spectra confirms the presence of C terms. The solution and PMMA spectra for the both Mo and W complexes in either the IV or V oxidation states are remarkably similar to each other for the same oxidation state and are interpreted within a D_2d structural framework for the isotropic environment. The weak bands below 3.0 μm⁻¹ (1 μm⁻¹=10⁴ cm⁻¹) for the M(IV) complexes are assigned as metal-localized ligand field (LF) transitions. LF transitions are also suggested for weaker unresolved absorption between 3.0 and 3.6 μm⁻¹ for the M(V) ions. The intense bands above 3.6 μm⁻¹ for M(IV) and 4.6 μm⁻¹ for M(V) complexes are interpreted as metal to ligand charge transfer (MLCT) from the metal b₁(x²−y²) HOMO to CN⁻-based π * orbitals. The prominent intense bands observed below 4.5 μm⁻¹for the M(V) complexes are assigned as ligand to metal charge transfer (LMCT) from occupied non-bonding or weakly π bonding CN⁻ orbitals to the half-filled b₁(x²−y²) HOMO.     

Spectral and thermodynamic properties of Ag(I), Au(III), Cd(II), Co(II), Fe(III), Hg(II), Mn(II), Ni(II), Pb(II), U(IV), and Zn(II) binding by methanobactin from Methylosinus trichosporium OB3b

Methanobactin (mb) is a novel chromopeptide that appears to function as the extracellular component of a copper acquisition system in methanotrophic bacteria. To examine this potential physiological role, and to distinguish it from iron binding siderophores, the spectral (UV–visible absorption, circular dichroism, fluorescence, and X-ray photoelectron) and thermodynamic properties of metal binding by mb were examined. In the absence of Cu(II) or Cu(I), mb will bind Ag(I), Au(III), Co(II), Cd(II), Fe(III), Hg(II), Mn(II), Ni(II), Pb(II), U(VI), or Zn(II), but not Ba(II), Ca(II), La(II), Mg(II), and Sr(II). The results suggest metals such as Ag(I), Au(III), Hg(II), Pb(II) and possibly U(VI) are bound by a mechanism similar to Cu, whereas the coordination of Co(II), Cd(II), Fe(III), Mn(II), Ni(II) and Zn(II) by mb differs from Cu(II). Consistent with its role as a copper-binding compound or chalkophore, the binding constants of all the metals examined were less than those observed with Cu(II) and copper displaced other metals except Ag(I) and Au(III) bound to mb. However, the binding of different metals by mb suggests that methanotrophic activity also may play a role in either the solubilization or immobilization of many metals in situ.     

Adducts of guanine with chromium(III), iron(III) and oxovanadium(IV) chlorides

The preparation of well-defined adducts of the M(guH)(₂Cl₃ (M = Cr, Fe) and VO(guH)Cl₂ types (guH = neutral guanine), by refluxing ligand and metal chloride mixtures in ethanol-triethyl orthoformate, is reported. Characterization studies suggest that the new complexes are probably linear chain-like polymeric species, involving single bridges of bidentate guH ligands between adjacent metal ions. Bidentate bridging guH is most probably coordinated through the N(7) and N(9) imidazole nitrogens. The chloro ligands present in the adducts are exclusively terminal. Infrared evidence rules out the possibility of coordination of guanine through either of its exocyclic potential binding sites (i.e., CO oxygen and NH₂ nitrogen) [1].     

Organic Constituents and Complexation of Nickel(II), Iron(III), Cadmium(II), and plutonium(IV) in Soybean Xylem Exudates

The xylem exudates of soybean (Glycine max cv Williams), provided with fixed N, were characterized as to their organic constituents and in vivo and in vitro complexation of plutonium, iron, cadmium, and nickel. Ion exchange fractionation of whole exudates into their compound classes (organic acid, neutral, amino acid, and polyphosphate), followed by thinlayer electrophoresis, permitted evaluation of the types of ligands which stabilize each element. The polyvalent elements plutonium(IV) and iron(III) are found primarily as organic acid complexes, while the divalent elements nickel(II) and cadmium(II) are associated primarily with components of the amino acid/peptide fraction. For plutonium and cadmium, it was not possible to fully duplicate complexes formed in vivo by back reaction with whole exudates or individual class fractions, indicating the possible importance of plant induction processes, reaction kinetics, and/or the formation of mixed ligand complexes. The number and distribution of specific iron- and nickel-containing complexes varies with plant age and appears to be related to the relative concentration of organic acids and amino acids/peptides being produced and transported in the xylem as the plant matures.     

Assimilatory sulfate reduction in C(3), C(3)-C(4), and C(4) species of Flaveria

The activity of the enzymes catalyzing the first two steps of sulfate assimilation, ATP sulfurylase and adenosine 5'-phosphosulfate reductase (APR), are confined to bundle sheath cells in several C(4) monocot species. With the aim to analyze the molecular basis of this distribution and to determine whether it was a prerequisite or a consequence of the C(4) photosynthetic mechanism, we compared the intercellular distribution of the activity and the mRNA of APR in C(3), C(3)-C(4), C(4)-like, and C(4) species of the dicot genus Flaveria. Measurements of APR activity, mRNA level, and protein accumulation in six Flaveria species revealed that APR activity, cysteine, and glutathione levels were significantly higher in C(4)-like and C(4) species than in C(3) and C(3)-C(4) species. ATP sulfurylase and APR mRNA were present at comparable levels in both mesophyll and bundle sheath cells of C(4) species Flaveria trinervia. Immunogold electron microscopy demonstrated the presence of APR protein in chloroplasts of both cell types. These findings, taken together with results from the literature, show that the localization of assimilatory sulfate reduction in the bundle sheath cells is not ubiquitous among C(4) plants and therefore is neither a prerequisite nor a consequence of C(4) photosynthesis.     

Relative steric size of SCH(3), OCH(3), and CH(3) groups from circular dichroism measurements

The relative steric size of methyl, methoxy, and methylthio groups was determined from circular dichroism (CD) spectroscopy using a sensitive system based on the bilirubin model. In the cyclohexane model, equatorial vs. axial orientation and conformational analysis led to quantitative measurements of orientation preference or steric demand: conformational A-values CH(3) > SCH(3) > OCH(3). A more sterically demanding model for assessing group size has been found in bilirubin analogs, which are yellow pigments that adopt a ridge-tile shape stabilized by a matrix of intramolecular hydrogen bonds. Optically active bilirubins have been shown to exhibit intense bisignate CD Cotton effects from exciton coupling of their two dipyrrinone chromophores held in either of two enantiomeric ridge-tile conformations. Interconversion of these M and P conformational enantiomers of helical chirality is rapid at room temperature but may be displaced toward either enantiomer by intramolecular nonbonded steric interactions that arise when substituents are introduced at equivalent sterically demanding sites, viz., the alpha or beta carbons of the pigment's propionic acid chains. Such substituents shift the conformational equilibrium toward the M or the P-chirality conformer, depending only on the S or R stereochemistry at the alpha and beta sites, and the resulting exciton CD for the approximately 430 nm transition(s) was used to evaluate the relative steric size, SCH(3) > CH(3) > OCH(3).     

Photophysical characterization and in vitro anti-leishmanial effect of 5,10,15,20-tetrakis(4-fluorophenyl) porphyrin and the metal (Zn(II), Sn(IV), Mn(III) and V(IV)) derivatives

BioMetals - In this report 5 compounds were synthesized and structural and their photophysical characterization was performed (ΦΔ and Φf). Furthermore, in this in vitro study, their...     

Synthesis,characterization and catalytic oxidations of oxovanadium(IV), oxotitanium(IV) and dioxomolybdenum(VI) complexes with chiral imines of L-amino acids

Representative oxovanadium(IV), oxotitanium(IV), and dioxomolybdenum(VI) complexes of N-salicylidene-L-amino acids (the amino acids are: valine, leucine, except for Mo(VI), and histidine) have been synthesized and characterized by various spectroscopic techniques. It has been found that while in the histidine complexes of titanium(IV) and vanadium(IV) the amino acid residue is bound in the expected glycine-like mode, in the molybdenum(VI) complex it is bound in the unusual histamine-like mode. Also, the structure of this molybdenum(VI) complex contains imidazolate-bridged polymeric units in the solid state, while the carboxyl group of the amino acid residue is protonated. In solution the polymeric structure is cleaved and the monomers contain carboxylate and protonated imidazole groups at the histidine residue. The histamine-like structure of the histidine complex was probcd by comparison with that of the chiral dioxomolybdenum(VI) complex of N-salicylidene-L-histidinol. While the structure of the metal centers is six-coordinate for the dioxomolybdenum(VI) complexes and the histidine complexes of oxotitanium(IV) and oxovanadium(IV), it is likely that the complexes of the latter metals derived from nonpolar amino acids do not achieve coordination numbers higher than five. The present oxometal complexes are catalytically active in the sulfoxidation of sulfides and in the epoxidations of activated olefins by tert-butyl hydroperoxide, but in general exhibit a low degree of asymmetric induction in these reactions.