The carboxylate type siderophore rhizoferrin and its analogs produced by directed fermentation

Summary Rhizoferrin is a novel carboxylate-type siderophore which has recently been isolated fromRhizopus microsporus and other fungi of the Mucorales (Zygomycetes). The present investigation shows that a variety of rhizoferrin analogs can be produced by directed fermentation. Thus both the diaminobutane backbone and the citric acid side chains of rhizoferrin have been substituted by diamine and citric acid analogs added to the culture medium. The new ligands as well as their iron complexes have been characterized by physicochemical methods. Conditions of precursor incorporation and implications for the biosynthesis of the new siderophores are discussed.     

Synthesis, spectral and magnetical characterization of monomeric [Cu(2-NO2bz)2(nia)2(H2O)2] and structural analysis of similar [Cu(RCOO)2(L-N)2(H2O)2] complexes

A new complex of composition [Cu(2-NO₂bz)₂(nia)₂(H₂O)₂] (1) (nia = nicotinamide, 2-NO₂bz = 2-nitrobenzoate) has been prepared and its composition and stereochemistry as well as coordination mode have been determined by elemental analysis, electronic, infrared and EPR spectroscopy, magnetization measurements over the temperature range 1.8-300 K, and its structure has been solved, as well. The complex structure consists of the centrosymmetric molecules with Cu(II) atom monodentately coordinated by the pair of 2-nitrobenzoato anions and by the pair of nicotinamide molecules, forming nearly tetragonal basal plane, and by a pair of water molecules that complete tetragonal-bipyramidal coordination polyhedron about the copper atom. The complex 1 exhibits magnetic moment μ_eff = 1.86 B.M. at 300 K which decreases to μ_eff = 1.83 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie-Weiss law with Curie constant of 0.442 cm³ K mol⁻¹ and with Weiss constant of −1.0 K. EPR spectra at room temperature as well as at 77 K are of axial type with g_⊥ = 2.065 and g_∥ = 2.280 and exhibit clearly, but partially resolved parallel hyperfine splitting with A_II = 160 G, that is consistent with the determined molecular structure of 1. In order to analyze the factors influencing the degree of tetragonal distortion of coordination polyhedron, the dataset of 72 structures similar to that of 1 was extracted from CCD and analyzed. A significant correlation between the average Cu-O_ax bond length and tetragonality parameter τ which was found as a consequence of the Jahn-Teller effect.     

Synthesis, structure and magnetic properties of a new family of chiral metal(II) citramalates

A new series of chiral carboxylate-bridged complexes of Mn(II), Co(II), and Ni(II) has been synthesized by reaction of M(II) salts with (S)-2-hydroxy-2-methyl-butanedioic acid ((S)-citramalic acid) under solvothermal conditions. The Mn(II) compound 1 is obtained as a crystalline powder, whereas the Co(II) and Ni(II) compounds (2 and 3 respectively) are obtained as single crystals. All the compounds crystallize in orthorhombic chiral space group P2₁2₁2₁. Compounds 2 and 3 are isostructural, and their structure consists in helicoïdal chains of M(II) centres linked by carboxylate bridges. The magnetic data indicate a rather weak coupling interaction between paramagnetic centres. The Mn(II) compound 1 exhibits antiferromagnetic ordering at T_N = 2.64 K. The Co(II) and Ni(II) compounds show ferromagnetic interactions within the chains. For 3, the chains couple antiferromagnetically, which leads to a metamagnetic behaviour with T_N = 1.69 K.     

Carboxylate and dicarboxylate derivatives of [Et4N][Re2(CO)6(OR)3] (R = H or Me)

The ligand exchange reaction of the anionic binuclear rhenium complexes (R = H (1) or Me (2)) has been studied with the carboxylic acids; benzoic acid (3, 4, and 5), fumaric acid (6), and terephthalic acid (7). The exchange with benzoic acid can be controlled by stoichiometry to one, two, or three substitutions. The doubly (4) and triply (5) substituted complexes represent new structural motifs for the triply bridged Re₂(CO)₆ unit. The dicarboxylic acids fumaric and terephthalic bridge two dirhenium centers. Crystal structure determinations have been carried out for the new complexes synthesized.     

Spectral properties and bio-activity of copper(II) clofibriates, part III: crystal structure of Cu(clofibriate)2(2-pyridylmethanol)2, Cu(clofibriate)2(4-pyridylmethanol)2(H2O) dihydrate, and Cu2(clofibriate)4(N,N-diethylnicotinamide)2

New copper(II) clofibriates (clof, {2-(4-chlorophenoxy)-2-methylpropionic or 2-(4-chlorophenoxy)isobutyric acid}) of composition Cu(clof)₂L₂ (where L=2-pyridylmethanol (2-pymeth) (1), N-methylnicotinamide (Menia) (4), N,N-diethylnicotinamide (Et₂nia) (5), isonicotinamide (isonia) (7) or methyl-3-pyridylcarbamate (mpc) (8)), [Cu(clof)₂(4-pymeth)₂(H₂O)] · 2H₂O (4-pymeth=4-pyridylmethanol) (2 · 2H₂O) and Cu(clof)₂L (where L=4-pymeth (3) or Et₂nia (6)) have been prepared and spectroscopically characterized. All the Cu(clof)₂L₂ compounds seem to possess distorted octahedral copper(II) stereochemistry with differing tetragonal distortions. An X-ray analysis of 1 was carried out and it featured a tetragonal-bipyramidal geometry around the copper(II) atom. X-ray analysis of 2 · 2H₂O featured a square-pyramidal geometry around copper(II) atom. Both the Cu(clof)₂L compounds seem to consist of a binuclear unit of tetracarboxylate type bridging. An X-ray analysis of 6 revealed typical binuclear paddle-wheel type structure, consisting of two copper(II) atoms in square-pyramidal geometry bridged by four carboxylate anions in the xy-plane. All complexes under study were characterized by EPR and electronic spectroscopy. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi.     

Synthesis, structural characterization and redox properties of copper(II) and manganese(II) complexes containing tridentate (N-(2-methylpyridine)-2-aminomethyl benzoate) ligand

Two new complexes, [Cu(mamba)₂] and [Mn(mamba)₂] (mamba⁻, N-(2-methylpyridine)-2-aminomethyl benzoate) were synthesized and characterized by X-ray crystallography. Whereas the [Cu(mamba)₂] complex crystallizes in a monoclinic P2₁/c space group, the [Mn(mamba)₂] complex crystallizes in a triclinic space group. The nature of the metal ion greatly influences the lattices and the molecular structures of the compounds. In the crystal lattice of the copper complex are four cocrystallized methanol solvent, which are all involved in building six strong H-bonds with the complex. However, the lattice for the manganese complex contain only one cocrystallized methanol, along with one NaClO₄, that is also involved in making one H-bond with the [Mn(mamba)₂] unit. Nevertheless, the sodium ion is coordinated to the ClO₄⁻, the methanol and two [Mn(mamba)₂] to form a stable extended chain metal complex. Electrochemical studies indicated that both complexes undergo quasi reversible one electron reduction in acetonitrile.     

Syntheses, structures and magnetic properties of Mn(II), Co(II) and Ni(II) metal-organic frameworks constructed from 1,3,5-benzenetricarboxylate and formate ligands

Three compounds, [(CH₃)₂NH₂][M₃(BTC)(HCOO)₄(H₂O)]·H₂O (M = Mn (1), Co (2), Ni (3), H₃BTC = 1,3,5-benzenetricarboxylic acid), were synthesized under hydrothermal conditions and were characterized by single crystal and powder X-ray diffraction, IR spectra, elemental analysis, coupled TG-MS and magnetic measurements. Compounds 1-3 are isostructural analogues and crystallize in monoclinic space group P2₁/c. Each metal ion in these compounds connects to six oxygen atoms to form a MO₆ octahedron. Six MO₆ octahedra link to each other to form a corner-shared hexameric M₆ cluster, which is linked by BTC ligands to form two-dimensional layers. The two-dimensional layers are further connected by formic ions to form a three-dimensional network with channels, where (CH₃)₂NH₂⁺ ions and water molecular are located. Magnetic measurements indicate that anti-ferromagnetic ordering occurs at low temperature for these compounds.     

Cluster-root formation, carboxylate exudation and proton release of Lupinus pilosus Murr. as affected by medium pH and P deficiency

The study examined the interactive effect of pH and P supply on cluster-root formation, carboxylate exudation and proton release by an alkaline-tolerant lupin species (Lupinus pilosus Murr.) in nutrient solution. The plants were exposed to 1 (P₁, deficient) and 50 μM P (P₅₀, adequate) for 34 days in nutrient solution at either pH 5.6 or 7.8. Plant biomass was not influenced by pH at P₁, but at P₅₀ shoot and root dry weights were 23 and 18% higher, respectively, at pH 7.8 than at pH 5.6. There was no significant difference in plant biomass between two P treatments regardless of medium pH. Phosphorus deficiency increased significantly the number of the second-order lateral roots compared with the P₅₀ treatment. Both total root length and specific root length of plants grown at pH 5.6 were higher than those at pH 7.8 regardless of P supply. Cluster roots were formed at P₁, but cluster-root number was 2-fold higher at pH 7.8 than pH 5.6. Roots released 16 and 31% more protons at pH 5.6 and 7.8, respectively, in P₁ than in P₅₀ treatments, and the rate of proton release followed the similar pattern. At pH 5.6, citrate exudation rate was 0.39 μmol g⁻¹ root DW h⁻¹ at P₁, but was under the detection limit at P₅₀; at pH 7.8, it was 2.4-fold higher in P₁ than in P₅₀ plants. High pH significantly increased citrate exudation rate in comparison to pH 5.6. The uptake of anions P and S was inhibited at P₁ and high pH increased cations Na, Mg and Ca uptake. The results suggested that enhanced cluster-root formation, proton release and citrate exudation may account for the mechanism of efficient P acquisition by alkaline-tolerant L. pilosus well adapted to calcareous soils. Cluster-root formation and citrate exudation in L. pilosus can be altered by medium pH and P deficiency. Phosphorus deficiency-induced proton release may be associated with the reduced anion uptake, but high pH-induced proton release may be partly attributed to increased cation uptake.     

Synthesis, structures and thermal properties of three new two-dimensional coordination networks assembled by lanthanide salts and carboxylate ligand

Three new rare-earth coordination polymers, [La₂(PDC)₂(NO₃)₂(H₂O)₃] (1) and [Dy(PDC)(ox)_0.5(H₂O)₂] · H₂O (2), and [Sm(PDC)(ox)_0.5(H₂O)₂] · H₂O (3) (H₂PDC = pyridine-3,4-dicarboxylic acid, ox = oxalic acid), have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, TGA, and single-crystal X-ray diffraction. Of the three compounds, La-O-La and Dy(Sm)-O-C-O-Dy(Sm) chains are cross-linked by PDC ligands into interesting two-dimensional framework structures. They represent, to the best of our knowledge, the first examples of rare-earth complexes in the {M/PDC} (M = metal) system.     

Complexation of 2-hydroxynicotinic and 3-hydroxypicolinic acids with zinc(II). Solution state study and crystal structure of trans-diaqua-bis-(3-hydroxypicolinato)zinc(II)

The interactions between zinc(II) and the two ligands 2-hydroxynicotinic acid (HNic) and 3-hydroxypicolinic acid (HPic) have been investigated by means of potentiometric titrations in aqueous 0.6 m (Na)Cl at 25 °C. In both cases, only mononuclear complexes are formed. The qualitative and quantitative results obtained have been confirmed in part by UV-Vis spectrophotometry and ¹H NMR spectroscopy. The complex trans-diaqua-bis-(3-hydroxypicolinato)zinc(II) was obtained as a crystal and examined by X-ray crystallography. The thermodynamic results allow drawing some conclusions regarding the extent of Zn(II) interference in a hypothetical chelation therapy treatment of aluminium or iron overload with these two ligands.