Magnetic coupling in EE and EO azido-bridged binuclear copper complexes: Synthesis,structure and magnetic studies

Four azide bridged dinuclear copper(II) complexes, [Cu₂(L^X)₂(N₃)₂](ClO₄)₂, with L^X = substituted N,N-bis[(3,5-dimethylpyrazole-1-yl)-methyl]benzylamine, [X = H (1), OMe (2), Me (3) and Cl (4)] have been synthesized, out of which complexes 1 and 2 have been characterized structurally. In Complex 1 the two bridging azide ligands have connected the two metal centers in an end-on (EO) fashion with aSP (asymmetric Square Pyramidal) geometry and showed an weak antiferromagnetic interaction (J = −3.34 cm⁻¹). On the contrary, in complex 2, the two metal centers have been connected in end-to-end (EE) fashion exhibiting moderately strong ferromagnetic interaction (J = +19.7 cm⁻¹). Cyclic voltammetric studies performed on all the four complexes show a reasonably good correlations when E_1/2 for Cu^IICu^II → Cu^IICu^III and Cu^IICu^III → Cu^IIICu^III oxidations are plotted against σ (substituent constants) with ρ = −0.182 (R² = 0.92) and −0.684 (R² = 0.99) respectively.     

Synthesis, crystal structure and biological activities of two novel organotin(IV) complexes constructed from 12-(4-methylbenzoyl)-9,10-dihydro-9,l0-ethanoanthracene-11-carboxylic acid

Two complexes: [(n-Bu₂Sn)₄(L)₂O₂(OC₂H₅)₂] (1) and [(C₆H₅)₃Sn(L)] (2) (where, HL is 12-(4-methylbenzoyl)-9,10-dihydro-9,10-ethanoanthracene-11-carboxylic acid) have been prepared and structurally characterized by means of elemental analysis and vibrational, ¹H NMR and FT-IR spectroscopies. The crystal structures of 1 and 2 have been determined by X-ray crystallography. Three distannoxane rings are present to the centrosymmetric dimeric tetraorganodistannoxane by virtue of μ₃-oxo form the central R₄Sn₂O₂ core with a planar Sn₂O₂ ring, resulting in a ladder type structural motif in the molecular structure of 1, and five-coordinated tin atoms are present in the distannoxane dimer. While the molecular of 2 adopts a monomeric distorted tetrahedral configuration with the carboxylate ligand coordinating in a monodentate mode. Both 1 and 2 exhibited good antibacterial and antitumour activities and have a potential to be used as drugs.     

Poly(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide), N,N,N′,N′-tetrabromobenzene-1,3-disulfonamide and novel poly(N,N′-dibromo-N-phenylbenzene-1,3-disulfonamide) as powerful reagents for benzylic bromination

N,N,N′,N′-Tetrabromobenzene-1,3-disulfonamide [TBBDA], poly(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) [PBBS], and novel poly(N,N′-dibromo-N-phenylbenzene-1,3-disulfonamide) [PBPS] can be used for bromination of benzylic positions in solvent.     

Structural characterization of triorganotin(IV) complexes with sodium fusidate and DFT calculations

Three new complexes of the steroid sodium fusidate (sodium 2-[(1S,2S,5R,6S,7S,10S,11S,13S, 14Z,15R,17R)-13-(acetyloxy)-5,17-dihydroxy-2,6,10,11-tetramethyl tetracyclo[8.7.0.0^2,7.0^11,15] heptadecan-14-ylidene]-6-methylhept-5-enoate = (NaFusidate, NaFA)]), with triorganotin(IV) moieties have been prepared and investigated by conventional techniques as FTIR, Mössbauer, ESI-MS and NMR spectroscopy. The isolated compounds showed stoichiometries organotin(IV)/fusidate 1/1, R₃Sn(IV)FA (R = Me, FA1; Bu, FA2; Ph, FA3). The ligand coordination sites were determined by FTIR spectroscopic measurements. In the complexes, the carboxylate group of the fusidate ligand behaves as monodentate monoanionic donor, binding the Sn(IV) through one oxygen atom.On the basis of C-Sn-O_COO angles, calculated through the rationalization of the ¹¹⁹Sn Mössbauer parameter nuclear quadrupole splitting, it has been confirmed that, in all the solid state complexes, the Sn(IV) was tetracoordinated in a distorted tetrahedral structure.Further data from ¹¹⁹Sn CP-MAS spectra confirmed the distorted tetrahedral arrangement.In MeOH solution, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy showed monomeric complexes, where the carboxylate group mainly acts as monodentate ester-type ligand, and the occurrence of a coordinated solvent molecule to the tin center, as validated by non-relativistic NMR DFT study.     

Rapid determination of phenoxy acid residues in rice by modified QuEChERS extraction and liquid chromatography-tandem mass spectrometry

A new method for the analysis of phenoxy acid herbicide residues in rice, based on the use of liquid extraction/partition and dispersive solid phase extraction (dispersive-SPE) followed by ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS), is reported. 5% (v/v) formic acid in acetonitrile as the extraction solvent and inclusion of citrate buffer helped partitioning of all the analytes into the acetonitrile phase. The extract was then cleaned up by dispersive-SPE using C18 and alumina neutral as selective sorbents. Further optimization of sample preparation and determination allowed recoveries of between 45 and 104% for all 13 phenoxy acid herbicides with RSD values lower than 13.3% at 5.0 μg kg⁻¹ concentration level. Limit of detections (LODs) of 0.5 μg kg⁻¹ or below were attained for all 13 phenoxy acids. Quantitative analysis was done in the multiple-reaction monitoring (MRM) mode using two combinations of selected precursor ion and product ion transition for each compound. This developed method produced relatively higher recoveries of the acid herbicides with a smaller range of variation and less susceptibility to matrix effects, than the original QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method.     

Discontinuous crack growth in poly (vinyl fluoride) by mechanochemical ageing in sodium hydroxide

The mechanochemical degradation of poly (vinyl fluoride) (PVDF) was studied in sodium hydroxide solution (soda) in the presence of various gradients of imposed mechanical deformation. Compact tension (CT) and low-necked tensile specimens were used to study ageing in soda (pH 14) at 90 °C during up to 35 days. This made it possible to impose various strain fields during ageing. An image correlation method was used to estimate the displacement fields at the surface of the specimen during the mechanical tests. PVDF degradation in soda usually results in a reddish brown colouring and is essentially localised in the “fairly deformed zones” (30% < ?₁ < 70%). For more important strains (?₁ > 70%), no colouration is observed and the degradation is stopped by limitation of the soda diffusion in the material [1] and [2]. In the presence of an imposed strain field, there is a level of mechanochemical degradation “Stress Corrosion Cracking” (SCC) in soda for which the formation of microcracks is observed within a layer of exposed surface of degraded polymer. Cracking always starts at the border of the zone coloured by chemical degradation. The mechanical deformation in this bordering zone is approximately ?₁ ≈ 30%. The cracking continues via a discontinuous propagation of propagations and crack arrests usually called “stick-slip”. The fracture surfaces are marked by a succession of distinct coloured striations representing a temporary crack arrests characteristic of discontinuous crack growth. Cracking can stop with the elimination of one of the two combined causes of SCC, mechanical or chemical.     

A Baylis-Hillman/ozonolysis route towards (±) 4,5-dihydroxy-2,3-pentanedione (DPD) and analogues

The Baylis-Hillman reaction between 2-(tert-butyldimethylsilyloxy)ethanal and 3-buten-2-one followed by desilylation gave rise to the corresponding α-methylene-β,γ-dihydroxy ketone further converted by reductive ozonolysis of the carbon-carbon double bond into racemic 4,5-dihydroxy-2,3-pentanedione (DPD), a significant molecule in bacterial cell-cell communication systems. The same sequence applied to other substrates allowed the preparation of chain elongated analogues and 5-O-acylated derivatives of DPD.     

Eunicellin-based diterpenoids from the cultured soft coral Klyxum simplex

Eight new eunicellin-base diterpenoids, klysimplexins A-H (1-8), were isolated from a cultured soft coral Klyxum simplex. Their structures were elucidated by spectroscopic methods, particularly in 1D and 2D NMR experiments. The structure of 1 was further confirmed by a single-crystal X-ray diffraction analysis and the application of modified Mosher's method. Metabolites 2 and 8 were found to be cytotoxic toward a limited panel of cancer cell lines.     

Tonkinensines A and B, two novel alkaloids from Sophora tonkinensis

Tonkinensines A (1) and B (2), two novel cytisine-type alkaloids that feature the skeleton with a linkage to pterocarpan, were isolated from the roots of Sophora tonkinensis. Their structures and absolute configurations were elucidated by spectroscopic methods, especially X-ray crystal diffraction and CD spectral analysis. The proposed biosynthetic pathway was also discussed. Both 1 and 2 were tested in HeLa and MDA-MB-231 tumor cell lines, and compound 2 showed moderate cytotoxic activity.     

Synthesis of non-THF analogs of acetogenin toward simplified mimics

Acetogenin analogs in which the bis-adjacent THF ring was replaced with an enantioselectively synthesized 1,2-cyclopentanediol bis-ether skeleton were synthesized to obtain simplified mimics, and their inhibitory effect on mitochondrial NADH-ubiquinone oxidoreductase (complex I) was examined. The results clearly demonstrate that the 1,2-cyclopentanediol bis-ether motif can substitute for the bis-THF ring while maintaining very potent inhibitory activity at the nanomolar level.     

Disparate orientation of [1]rotaxanes

A novel [1]rotaxane 2 has been synthesized employing a 4-methyl-benzenesulfonyl and an azobenzene modified β-cyclodextrin (β-CyD) at the 2 position, through self-inclusion complexation and Suzuki-coupling capping in aqueous solution. Disparate absorption, induced circular dichroism (ICD) properties from its isomer [1]rotaxane 1, prepared from the isomeric β-CyD modifier at the 6 position, and the photoisomerization of [1]rotaxane 2 were thoroughly investigated.     

PS-SNAP, a practical polymer-supported nitrosation reagent in organic synthesis

PS-SNAP was designed and evaluated as a practical nitrosating polymer-supported reagent for the nitrosation of sec-amines. Nitrosated dialkyl amines, alkyl anilines, and bis-anilines were obtained in good yields and high purities after shaking the corresponding amines in the presence of an excess of the newly described reagent followed by simple filtration and removal of solvents.     

First stereoselective synthesis of synargentolide A and revision of absolute stereochemistry

The first stereoselective total synthesis of synargentolide A isolated from Syncolostemon argenteus has been achieved from commercially available (R)-benzyl glycidyl ether using Sharpless asymmetric epoxidation and cross-metathesis reactions as the key steps. Comparing the spectral data of the synthesized and naturally occurring synargentolide A, the C4′ and C6′- stereogenic centers of the natural synargentolide A were assigned a corrected anti relationship.     

Synthesis of stereodefined fused δ-hydroxy-γ-lactones from dealkylative cyclization of epoxy-diesters

A dealkylative lactonization of stereodefined aryl-substituted epoxides allows the preparation of densely functionalized fused δ-hydroxy-γ-lactones having three consecutive stereochemically defined stereocenters.     

Characterization of the structure and reactivity of monocopper-oxygen complexes supported by beta-diketiminate and anilido-imine ligands

Copper-oxygen complexes supported by beta-diketiminate and anilido-imine ligands have recently been reported (Aboelella et al., J Am Chem Soc 2004, 126, 16896; Reynolds et al., Inorg Chem 2005, 44, 6989) as potential biomimetic models for dopamine beta-monooxygenase (DbetaM) and peptidylglycine alpha-hydroxylating monooxygenase (PHM). However, in contrast to the enzymatic systems, these complexes fail to exhibit C--H hydroxylation activity (Reynolds et al., Chem Commun 2005, 2014). Quantum chemical characterization of the 1:1 Cu-O(2) model adducts and related species (Cu(III)-hydroperoxide, Cu(III)-oxo, and Cu(III)-hydroxide) indicates that the 1:1 Cu-O(2) adducts are unreactive toward substrates because of the weakness of the O--H bond that would be formed upon hydrogen-atom abstraction. This in turn is ascribed to the 1:1 adducts having both low reduction potentials and basicities. Cu(III)-oxo species on the other hand, determined to be intermediate between Cu(III)-oxo and Cu(II)-oxyl in character, are shown to be far more reactive toward substrates. Based on these results, design strategies for new DbetaM and PHM biomimetic ligands are proposed: new ligands should be made less electron rich so as to favor end-on dioxygen coordination in the 1:1 Cu-O(2) adducts. Comparison of the relative reactivities of the various copper-oxygen complexes as hydroxylating agents provides support for a Cu(II)-superoxide species as the intermediate responsible for substrate hydroxylation in DbetaM and PHM, and suggests that a Cu(III)-oxo intermediate would be competent in this process as well.     

The perturbing effect of cholesterol on the interaction between labdanes and DPPC bilayers

Differential scanning calorimetry (DSC) was used to study the effect of cholesterol on the perturbation of DPPC bilayers induced by eight bioactive structurally related labdanes isolated from the resin ‘ladano’ of Cistus creticus subsp. creticus (Cistaceae) or semisynthesized from the mother compounds. Labdanes themselves induced profound modifications in DPPC bilayer organization and thermotropic properties that were altered when cholesterol was incorporated in equimolar amounts to the labdanes. The present work shows that, up to 10 mol% of the equimolar mixture of cholesterol and the labdanes, the modifications evoked on DPPC bilayer organization are in accordance to these induced by the labdanes themselves. When the concentration exceeded 20 mol%, cholesterol influence dominated while the effect of the labdanes was suppressed and their interaction with the bilayer was probably prevented. The degree by which cholesterol modulated the labdane interaction with the bilayer depended on their structural characteristics that determine their localization in the bilayer interior. Polar groups that force the labdanes to localize themselves at the interfacial region broadened the concentration range by which labdanes interacted with the DPPC bilayer even in the presence of high concentration of cholesterol where cholesterol-rich domains are preferentially formed. On the other hand, labdanes possessing functional groups that promote their deeper penetration in the bilayer interior compete with cholesterol in a high extent for the same localization sites resulting in their possible elimination from the bilayer when the concentration of cholesterol present exceeds the 20 mol%.     

Influence of core materials on thermal properties of melamine-formaldehyde microcapsules

A series of melamine-formaldehyde microcapsules as an intrinsic intumescent system was prepared by an in situ polymerization. The structural and thermal properties of the resultant microcapsules were studied. The surface morphology and chemical structure of microcapsules were investigated using scanning electron microscope (SEM), and Fourier-transform infrared spectroscope (FT-IR), respectively. The thermal properties of samples were investigated by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC). The results showed that the thermo-physical properties are strongly dependant on the nature core content and the synthesis conditions. From the thermal analysis, it was concluded that microcapsules containing di-ammonium hydrogen phosphate exhibits characteristics of an intumescent system during their thermal degradation and could be interpreted due to the interaction between phosphate and melamine.     

Preparation and crystal structure of new samarium complexes with glutamic acid

Samarium complexes with glutamic acid containing cationic [Sm₂(Glu)₂(H₂O)₈]⁴⁺ units have been prepared and characterized by using elemental analysis, infrared absorption spectra and thermal analysis. In addition, the crystal and molecular structure of [Sm₂(Glu)₂(H₂O)₈](ClO₄)₄·3H₂O was determined by X-ray diffraction. The presence of glutamic acid in the Sm coordination sphere allows the formation of a singular extended 2D arrangement. Sm atoms are nine coordinated, in a monocapped square antiprism geometry. They are connected by means of different μ-COO⁻ bridges, involving - and γ-carboxylate groups of the amino acid.     

Synthesis and characterization of new cardo poly(bisbenzothiazole)s containing cyclohexylidene units

A new diaminobenzenethiol 1,1-bis(4-amino-3-mercaptophenyl) cyclohexane dihydrochloride (BAMPCH · 2HCl) containing the bulky pendant cyclohexylidene group was synthesized from cyclohexanone in three steps. Its chemical structure was characterized by ¹H NMR, ¹³C NMR, MS, FT-IR and EA. Aromatic poly(bisbenzothiazole)s (PBTs) were prepared from the new monomer and five aromatic dicarboxylic acids by direct polycondensation. The inherent viscosities were in the range of 0.78-2.04 dL/g. These polymers exhibited good solubility and thermal stability. Most of the prepared PBTs were soluble in various polar solvents. The decomposition temperatures at 10% weight loss were in the range of 482-518 °C in nitrogen. X-ray diffractograms of PBTs showed that all polymers were amorphous.     

Synthesis,crystal structures and properties of five-coordinate Schiff-base Zn(II) complexes

Five-coordinate Schiff-base Zn complexes (1,2-cyclohexanediamino-N,N′-bis(salicylidene)) zinc-pyridine 1 and (1,2-cyclohexanediamino-N,N′-bis(3,5-di-tert-butylsalicylidene)) zinc-pyridine 2 were synthesized and the structures of 1 and 2 have been determined by single-crystal X-ray analysis. All Zn atoms are five-coordinate in both structures. Both complexes exhibit interesting structures based on intermolecular π–π stacking and hydrogen bond interactions. Complex 1 has a one-dimensional molecular chain structure via π–π stacking interaction, while complex 2 has an interesting lattice structure (with cavities with dimensions 10.9?×?6.9?Å) formed through intermolecular π–π stacking and hydrogen bond interactions. 1 and 2 are compared and characterized by MS, elemental analysis, IR, UV-Vis and Photoluminescence (PL). Fluorescence spectra show that the maximal emission wavelength of 1 and 2 are 454?nm, and 480?nm, respectively, upon radiation by UV light. Cyclic voltammetry performed on 1 and 2 indicate a dependence of the cathodic potentials upon conformational and electronic effects. Electronic spectral properties of 1 and 2 were studied by TD-DFT methods. The fluorescent emission of these complexes originates from ligand-centred π–π? transitions. The Zn (II) centres play a key role in enhancing the fluorescent emission of the ligands.