A non-linear (2,2,2) alkoxo-bridging in a Fe4O6 core potentially relevant to iron-tunicates

The tridentate unsymmetrical ligand N-(2-hydroxymethylphenyl)salicylideneimine H₂L, derived from salicylaldehyde and 2-aminobenzylalcohol, with [ONO] donor atoms yields [L₂Fe^III₂Cl₂] (1) and [L₆Fe^III₄] (2) complexes containing alkoxide bridges, which have been structurally characterized by X-ray diffraction. In complex 1, each ferric ion is five-coordinated with a distorted square-pyramidal geometry, the basal planes of which are symmetrically bridged by two alkoxide oxygen atoms. Analysis of the susceptibility data reveals antiferromagnetic interactions with an exchange parameter J = −15.8 cm⁻¹ between the high-spin d⁵ ferric centers. The structure of 2 can be considered as “linear (2,2,2)” to specify the number of enolate oxygen atoms between four iron atoms. Variable-temperature magnetic susceptibility data are fitted to a “three-J” model, yielding pairwise antiferromagnetic exchange interactions, J₁₂ = J₃₄ = −13.4 cm⁻¹, J₁₃ = J₂₄ = −7.1 cm⁻¹, J₂₃ = −14.9 cm⁻¹, between the neighboring ferric centers; J₁₄ is assumed to be negligible. Complex 2 has a complicated low-lying magnetic structure with a non-diamagnetic ground state. In addition, the Fe-O-Fe angles at the bridging ligands seem to be determinant for the strength of the antiferromagnetic interactions.     

Structure and magnetic properties of polynuclear copper(II) compounds with syn-anti carboxylato- and bromo-bridges

Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) polymers Cu(2-qic)Br (2-qic = quinoline-2-carboxylate) (1) and Cu(2-pic)Br (2-pic = pyridine-2-carboxylate) (2) are described. These compounds are isostructural with Cu(2-qic)Cl and Cu(2-pic)Cl, respectively, the X-ray crystal structures of which were reported recently. Both complexes are polynuclear copper(II) compounds (1D and 2D, respectively) based on syn-anti carboxylate bridges and additionally on linear monobromo- (in 1) and dibromo-bridging (in 2) motifs. The magnetic properties were investigated in the temperature range 1.8-300 K. They reveal the occurrence of strong antiferromagnetic coupling (J₁ = −102.5 cm⁻¹) through the single bromo-bridge in 1, which is much stronger than that transmitted by the single chloro-bridge (J = −57.0 cm⁻¹). Very weak ferromagnetic interaction through the syn-anti carboxylate bridge J₂ is expected as it was observed in isomorphous Cu(2-qic)Cl (J = 0.37 cm⁻¹). For 2 a weak ferromagnetic couplings through the syn-anti carboxylate (zJ′ = 1.35 cm⁻¹) and dibromo-bridges (J = 8.31 cm⁻¹) were found. The experimental results indicate that the observed ferromagnetic exchange through dibromo-bridge is weaker than that in the chloride analog (J = 15.0 cm⁻¹). The magnitude of magnetic interactions is discussed on the basis of structural data of compounds 1 and 2 and their halide analogues.     

Design,synthesis and in vitro anti-tuberculosis activity of benzo[6,7]cyclohepta[1,2-b]pyridine-1,2,3-triazole derivatives

A series of novel benzo[6,7]cyclohepta[1,2-b]pyridine-1,2,3-triazole hybrids (7a–j & 8a–j) have been designed and synthesized in excellent yields by Huisgen’s [3+2] cyclo addition reaction of 3-(azidomethyl)-2-methyl-6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine (5) with various alkynes 6 in presence of copper sulphate and sodium ascorbate and their structures were confirmed by IR, ¹H NMR, ¹³C NMR and HRMS. The newly synthesized compounds 7a–j & 8a–j were evaluated for their in vitro anti-mycobacterial activity against Mycobacterium tuberculosis H37Rv (ATCC 27294). Among the compounds tested, the compounds 7i and 8g displayed most potent activity with MIC value of 1.56?µg/mL with low cytotoxicity.     

Structure and magnetic properties of a tetranuclear Cu4O4 open-cubane in [Cu(L)]4·4H2O with L = (E)-N′-(2-oxy-3-methoxybenzylidene)benzohydrazide

The in-situ formed hydrazone Schiff base ligand (E)-N′-(2-oxy-3-methoxybenzylidene)benzohydrazide (L²⁻) reacts with copper(II) acetate to a tetranuclear open cubane [Cu(L)]₄ complex which crystallizes as two symmetry-independent (Z′ = 2) S₄-symmetrical molecules in different twofold special positions with a homodromic water tetramer. The two independent (A and B) open- or pseudo-cubanes with Cu₄O₄ cores of 4 + 2 class (Ruiz classification) each have three different magnetic exchange pathways leading to an overall antiferromagnetic coupling with J_1B = J_2B = −17.2 cm⁻¹, J_1A = −36.7 cm⁻¹, J_2A = −159 cm⁻¹, J_3A = J_3B = 33.5 cm⁻¹, g = 2.40 and ρ = 0.0687. The magnetic properties have been analysed using the H = −Σ_i,jJ_ij(S_iS_j) spin Hamiltonian.     

Synthesis, structure and magnetic studies of two-dimensional network of Cu(II) polymer using malonate and 4,4′-azobispyridine ligands

The malonato-bridged copper(II) complex [Cu(mal)(H₂O)(azpy)_1/2] · H₂O (1) (mal = malonate, azpy = 4,4′-azobispyridine) has been synthesized and characterized by X-ray diffraction. The structure of 1 consists of malonato-bridged uniform copper(II) chains which are covalent connected through azpy to form two-dimensional wavelike network. The magnetic pathway of complex 1 is through a single syn-anti carboxylate bridge connecting equatorial and equatorial positions of adjacent copper(II) atoms, and have the value of the intrachain ferromagnetic coupling (J = 8.73(3) cm⁻¹) and interchain antiferromagnetic coupling (zJ′ = − 1.31(1) cm⁻¹) through a numerical expression for a ferromagnetic uniform chain.     

Proton magnetic resonance studies of 9-(β-d-xylofuranosyl)adenine 3′,5′-cyclic monophosphate and 9-(β-d-arabinofuranosyl)adenine 2′,5′-cyclic monophosphate

A detailed ¹H 220-MHz n.m.r. study of 9-(β-d-xylofuranosyl)adenine 3′,5′-cyclic monophosphate (3′,5′-xylo-cAMP, 1) and 9-(?-d-arabinofuranosyl)adenine 2′,5′-cyclic monophosphate (2′,5′-ara-cAMP, 2) in D₂O solution is described. The sugar-ring conformations in 1 and 2 are shown to be ³E and ²E, respectively, and the phosphate rings are in a chair form. An unusual ⁴J_P,H coupling of 2.4 Hz is observed between H-4′ and phosphorus in 1 and a vicinal J_P,H of 30.8 Hz between H-5′ and phosphorus in 2. This latter coupling verifies a similar value found previously in the ara-cytidine analog of 2. A comparison of the conformational properties of cyclic nucleotides having fused phosphate and sugar rings has been made, together with an assessment of the use of the Karplus constants in such ring-systems.     

Molecular structure and intra- and intermolecular magnetic interactions in chloro-bridged copper(II) dimers

Magnetic interactions in binuclear copper(II) complexes, [Cu₂(apyhist)₂Cl₂](ClO₄)₂ (1) and [Cu₂(2-pyhist)₂Cl₂](ClO₄)₂ (2) with tridentate diimine ligands and chloro-bridged groups (where apyhist=(4-imidazolyl)ethylene-2-amino-1-ethylpyridine and 2-pyhist=(4-imidazolyl)ethylene-2-aminomethylpyridine) were studied with the aim of better elucidating magneto-structural correlations in such species, both in solution and in solid state. X-ray analyses revealed that chloro-bridged ligands keep the copper(II) ion coordinated to adjacent unit, at Cu-Cl distances of 2.271 and 2.737 Å, and a Cu-Cl-Cu angle of 87.46° in compound 1. Each Cu^II atom is also coordinated to three N atoms from the imine ligand, in a distorted tetragonal pyramidal environment. Magnetic measurements carried out in temperatures from 0.8 to 290 K and in magnetic field up to 170 kOe indicated that besides the intramolecular magnetic coupling between the copper centers [J/k=−(1.93±0.05) K] further interactions between adjacent dimers [J^′z/k=−(1.3±0.1) K] should be taken into account. Similar results were observed for compound 2, for which [J/k=−(4.27±0.05) K] and [J^′z/k=−(3.7±0.1) K]. In solution, the interconversion of the dimer 1 and the related monomer species [Cu(apyhist)(H₂O)₂] (ClO₄)₂ (3) monitored by EPR spectra, was verified to be very dependent on the solvent.     

Synthesis and an angiolytic role of novel piperazine–benzothiazole analogues on neovascularization,a chief tumoral parameter in neoplastic development

A novel series of benzoic acid N′-[2-(4-benzothiazol-2-yl-piperazin-1-yl)-acetyl]-hydrazides 6a–j were synthesized and characterized by IR, ¹H, ¹³C NMR, elemental and mass spectral analyses. The in-vitro cytotoxicity and cell viability assay of the synthesized compounds 6a–j were evaluated against Dalton’s lymphoma ascites (DLA) cells. Our results showed that compound 6c with a bromo group on phenyl ring has showed promising antiproliferative efficacy. Further investigation of compound 6c on in-vivo treatment model depicts the increased tumor suppression through inhibition of angiogenesis.     

1-D coordination chains of Cu(hfac)2 and Mn(hfac)2 bridged by phenyl-nitronylnitroxide derivatives

Two alternating 1-D metal-radical linear [L:Cu(hfac)₂]_n and zig-zag [L:Mn(hfac)₂]_n chains (where L = 4-trimethylsilylethynyl-1-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)benzene) and hfac = hexafluoroacetylacetonate) are described and characterized by X-ray diffraction of their crystals. Bulk magnetic measurements of L:Cu(hfac)₂ indicated a ferromagnetic interaction with J = 6 cm⁻¹ and L:Mn(hfac)₂ yielded ferrimagnetic interactions with J = −95 cm⁻¹. For the latter, a strong increase of their magnetic moment at lowest temperatures was observed only at very low static magnetic field, while for H_dc > 0.05 T saturation effect led to a downward slope after reaching a maximum.     

Synthesis, crystal structure and magnetic properties of quasi-linear tetranuclear copper(II) Schiff base complexes formed by covalent linkage of asymmetrically dibridged dicopper(II) units

Alkoxo-phenoxo bridged tetranuclear copper(II) complexes [Cu₄L₂(O₂CC₆H₄-p-OH)₂] (1) and [Cu₄L₂(O₂CC₆H₄-o-OH)₂] (2) containing pentadentate Schiff base ligand N,N^′-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) (H₃L) are prepared and structurally characterized. Crystal structures of the complexes show the covalent linkage between two {Cu₂L(O₂CR)}(R = C₆H₄-p-OH, C₆H₄-o-OH) units through the phenoxo atoms of the Schiff base ligand showing axial/equatorial bonding modes. The Cu(1)-O(2)-Cu(2) alkoxo bridge angle is 131° in 1 and 2. The pendant ortho- and para- OH groups of the three-atom bridging carboxylate ligands show no apparent bonding interactions with the metal or other group(s). The complexes show a d-d band near 635 nm in CH₂Cl₂. Variable temperature magnetic susceptibility measurements in the temperature range 300-18 K show antiferromagnetically coupled spin system. A theoretical fit of the magnetic data using exchange parameters J₁ and J₂ for the intradimer and interdimer units of the quasi-linear tetrameric core gave values as: J₁=−132,J₂=−72 cm⁻¹ for 1 and J₁=−167,J₂=−67 cm⁻¹ for 2.     

Design,synthesis and biological evaluation of artemisinin derivatives containing fluorine atoms as anticancer agents

Ten novel artemisinin derivatives containing fluorine atoms were synthesized and their structures were confirmed by ¹H NMR, ¹³C NMR and HRMS technologies in this study. The in vitro cytotoxicity against U87MG, SH-SY5Y, MCF-7, MDA-MB-231, A549 and A375 cancer cell lines was evaluated by MTT assay. Compound 9j was the most potent anti-proliferative agent against the human breast cancer MCF-7 cells (IC₅₀?=?2.1?μM). The mechanism of action of compound 9j was further investigated by analysis of cell apoptosis and cell cycle. Compound 9j induced cell apoptosis and arrested cell cycle at G1 phase in MCF-7 cells. Our promising findings indicated that the compound 9j could stand as potential lead compound for further investigation.     

Structure and magnetism of two new linear trinuclear copper(II) clusters obtained from the tetradentate N2O2 ligand bis(2-hydroxybenzyl)-1,3-diaminopropane

Reaction of bis(2-hydroxybenzyl)-1,3-diaminopropane (H₂bhbd) with copper(II) perchlorate and copper(II) chloride in methanol, respectively, leads to linear trinuclear clusters, namely [Cu₃(bhbd)₂(CH₃OH)₂(ClO₄)₂] (1) and [Cu₃(bhbd)₂Cl₂](CH₃OH)₄ (2). These coordination compounds were characterized by X-ray crystallography, UV-Vis, IR and EPR spectroscopy, and magnetic susceptibility measurements. Both complexes have a linear trinuclear array of copper ions bridged by means of phenolato O atoms and separated by a distance of 2.985(4) Å (1) and 2.937(4) Å (2). Strong antiferromagnetic interactions between these adjacent Cu^II ions govern the magnetochemistry of 1 (J = −303(1) cm⁻¹) and 2 (J = −482(3) cm⁻¹) resulting in S = 1/2 ground states fully populated below 150 K. A correlation between the interaction parameter J and the angles within the trinuclear clusters is proposed.     

Experimental and theoretical investigations of magnetic properties for two low-dimensional spin systems based on bis(2-thioxo-1,3-dithiole-4,5-dithiolato)nickelate monoanion building blocks

Two complexes of [Ni(dmit)₂]⁻ (dmit²⁻ = 2-thioxo-1,3-dithiole-4,5-dithiolate) with nonmagnetic Schiff base cations, 1-(4-bromobenzylideneamino)pyridinium (4-BrBz-1-APy⁺; 1) and 1-(3-nitrobenzylideneamino)pyridinium (3-NO₂Bz-1-APy⁺; 2), have been characterized structurally. Their striking structural feature is the deviation of the [Ni(dmit)₂]⁻ anion from the square-planar environment around the Ni atom with 11.42° and 6.57° dihedral angles (between the mean molecular planes of two dmit²⁻ ligands) in 1 and 2, respectively. These twists arise from the molecular packing interactions between the superimposed anion and cation. In 1, the magnetic [Ni(dmit)₂]⁻ anions are arranged into a wave-shaped regular spin chain, whose magnetism was well fitted by one-dimensional (1D) Heisenberg uniform linear antiferromagnetic chain with |J/k_B| = 66 K. In 2, 1D ladder-shape [Ni(dmit)₂]⁻ chains are formed through lateral-to-lateral S?S contacts between the adjacent anions, which are further aligned into a two-dimensional (2D) anion layer via van der Waals forces. Complex 2 shows Curie-Weiss-type paramagnetic behavior with Curie constant C = 0.421 emu K mol⁻¹ and Weiss constant θ = −1.279 K. The broken-symmetry DFT approach was utilized to evaluate the magnetic coupling nature for 1 and 2, the theoretical analyses performed at ubpw91/lanl2dz level and concerned the so-called “weak bonding” regime approaches qualitatively explained the magnetic behaviors of 1 and 2.     

Structural and magnetic properties of O-bridged tetranuclear and binuclear Cu(II) complexes

Two copper(II) complexes [Cu₄(L¹)₄] (1) and [Cu₂(phen)₂(HL²)₂] (ClO₄)₂ (2) have been synthesized from two potentially tridentate ligands N-(2-hydroxybenzyl) propanolamine (H₂L¹) and N-(2-hydroxybenzyl) ethanolamine (H₂L²). X-ray analyses revealed that 1 contains a Cu₄O₄ cubane core, with each two Cu(II) atoms bridged by a pair of alkoxides; 2 has a bis(μ₂-phenoxo)-bridged dicopper(II) structure. Variable temperature magnetic measurements of 1 have revealed that the correlation between 2J and the bridge angles φ for 1 shows a very strong antiferromagnetic tendency, i.e. the ferromagnetic and antiferromagnetic interactions cross at the φ of 94.5°. The relatively weak antiferromagnetic interactions (2J=−226.8 cm⁻¹) with respect to the bridge angles (φ=100.4°) for 2 have been ascribed to the pyramidal distortions at the phenoxide oxygen atoms in addition to the unfavorable overlaps of the magnetic orbitals for the highly distorted copper coordination polyhedra.     

Synthesis,structures and magnetic properties of pentanuclear and trinuclear heterometallic complexes with bended and linear cyano-bridges (tren = tris(2-aminoethyl)amine)

The reaction of [Cu(tren)(OH₂)](ClO₄)₂ with KCN gave a mononuclear complex [Cu(tren)(CN)](ClO₄) (1) (tren = tris(2-aminoethyl)amine). Using 1 as a building block, one pentanuclear compound, [{Cu(tren)(NC)}₄Ni](ClO₄)₆ (2) and two trinuclear complexes, [{Cu(tren)NC}₂Co(tren)](ClO₄)₅ · 2H₂O (3), [{Cu(tren)CN}₂NiL](ClO₄)₄ (4) (L = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) were prepared and characterized by single crystal X-ray analysis. In 1, Cu(II) atom adopts a distorted trigonal bipyramidal (TBP) geometry. In 2, the Ni(II) atom occupies the center of the pentanuclear compound with a square-planar coordination geometry. In 3, the six-coordinated Co(III) atom presents a distorted octahedral geometry with four nitrogen atoms from tren and two carbon atoms of bridged cyano groups in cis-positions. In 4, the nickel atom is located in an inversion center and coordinated with two [(tren)CuCN]⁺ moieties through cyano-bridging ligands. Magnetic susceptibility measurements of 2–4 show that the magnetic interactions between the heterometallic ions are antiferromagnetical coupling through the cyano bridges with g = 2.25, J = −0.142 cm⁻¹ and J′ = −0.167 cm⁻¹ for 2, g = 2.06, J = −0.094 cm⁻¹ for 3, and g = 2.20, J = −33.133 cm⁻¹ for 4. The correlations between the structures and the J values are discussed.     

Synthesis and bioactivities evaluation of l-pyroglutamic acid analogues from natural product lead

A series of l-pyroglutamic acid analogues from natural product lead were designed and synthesized, as well as their antifungal activities against Phytophthora infestans, neuritogenic activities, antibacterial activities and anti-inflammatory activities are described. The bioassays and SAR study showed that the majority of l-pyroglutamic acid esters have a significant antifungal activity against P. infestans, especially 2d and 2j demonstrated the best activities with EC₅₀ values of 1.44 and 1.21?μg?mL^?1, which were about seven times that of commercial azoxystrobin (7.85?μg?mL^?1). Moreover, compounds 2e, 2g and 4d displayed anti-inflammatory activity against LPS-induced NO production in BV-2 microglial cells; neuritogenic activity in NGF-induced PC-12 cells is the same activity. This study demonstrates that compounds 2d and 2j are potential drugs to control P. infestans.     

Two cyano-bridged heterotrinuclear complexes built from [(Tp)Fe(CN)3] (Tp = hydrotris(pyrazolyl)borate): synthesis, crystal structures and magnetic properties

Using an anionic precursor [(Tp)Fe^III(CN)₃]⁻ (1) as a building block, two cyano-bridged centrosymmetric heterotrinuclear complexes, (2) and (3) (en = ethylenediamine), have been synthesized and structurally characterized. In each complex, [TpFe(CN)₃]⁻ acts as a monodentate ligand toward a central [Mn(C₂H₅OH)₄]²⁺ or [Ni(en)₂]²⁺ core through one of its three cyanide groups, the other two cyanides remaining terminal. The intramolecular Fe-Mn and Fe-Ni distances are 5.2354(4) and 5.0669(11) Å, respectively. The magnetic properties of complexes 2 and 3 have been investigated in the temperature range of 2.0-300 K. A weak antiferromagnetic interaction between the Mn(II) and Fe(III) ions has been found in complex 2. The magnetic data of 2 can be fitted with the isotropic Hamiltonian: where J and J′ are the intramolecular exchange coupling parameters between adjacent and peripheral spin carriers, respectively. This leads to values of J = −1.37 cm⁻¹ and g = 2.05. The same fitting method is applied to complex 3 to give values of J = 1.2 cm⁻¹ and g = 2.25, showing that there is a ferromagnetic interaction between the Fe(III) and Ni(II) ions.     

On the calculation of magnetic fields based on multipole modeling of focal biological current sources.

Spatially restricted biological current distributions, like the primary neuronal response in the human somatosensory cortex evoked by electric nerve stimulation, can be described adequately by a current multipole expansion. Here analytic formulas are derived for computing magnetic fields induced by current multipoles in terms of an nth-order derivative of the dipole field. The required differential operators are given in closed form for arbitrary order. The concept is realized in different forms for an expansion of the scalar as well as the dyadic Green's function, the latter allowing for separation of those multipolar source components that are electrically silent but magnetically detectable. The resulting formulas are generally applicable for current sources embedded in arbitrarily shaped volume conductors. By using neurophysiologically relevant source parameters, examples are provided for a spherical volume conductor with an analytically given dipole field. An analysis of the signal-to-noise ratio for multipole coefficients up to the octapolar term indicates that the lateral extent of cortical current sources can be detected by magnetoencephalographic recordings.     

Synthesis, characterization, and magnetic study of pyrazine bridged polymeric complexes of copper(II)

The synthesis, structural characterization and magnetic property of two new coordination polymers [Cu(pyz)(μ-CH₃CO₂)₄]_n (1) and [Cu(pyz)(μ-CCl₃CO₂)₄]_n (2) (pyz = pyrazine) are reported. Here, the carboxylato bridged two dinuclear copper(II) complexes are linked through pyrazine giving a 1-D alternating chain. The magnetic property of the complexes indicates a significant difference originated from the introduction of electron withdrawing substituent on the bridging dicarboxylate. Complex 1 exhibits strong antiferromagnetic interactions with J = −344.61 cm⁻¹, whereas 2 exhibits comparatively less strong antiferromagnetic coupling with J = −238.53 cm⁻¹.     

Syntheses, crystal structures, and magnetic properties of two cyclic dimer M2L2 complexes constructed from a new nitronyl nitroxide ligand and M(hfac)2 (M = Cu, Mn)

Two new binuclear radical complexes derived from a new long nitronyl nitroxide ligand, 2-[4-(5-pyrimidyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (4-NITPhPyrim), and M(hfac)₂ (M²⁺ = Cu²⁺, Mn²⁺; hfac⁻ = hexafluoroacetylacetonato), [Cu(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (1) and [Mn(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (2), were synthesized as well as characterized structurally and magnetically. X-ray analysis indicates that 1 and 2 are rectangle-like centrosymmetric dimer M₂L₂ complexes. Magnetic measurements indicate that there are two types of magnetic exchanges in 1: the ferromagnetic (FM) exchange between the Cu(II) ion and the directly bonded nitroxide unit (J₁ = 24.20 cm⁻¹) and the weak FM exchange of Cu-NIT through the pyrimidine and phenyl rings (J₂ = 0.62 cm⁻¹). Besides the strong antiferromagnetic (AFM) coupling between the Mn(II) ion and the directly bonded nitroxide unit (J = −87.61 cm⁻¹), there is a weak FM interaction between the two Mn-NIT pairs (θ = 0.39 K) in 2.