Efficient emission of Zn(II) and Cd(II) complexes with nopinane-annelated 4,5-diazafluorene and 4,5-diazafluoren-9-one ligands: how slight structural modification alters fluorescence mechanism.

Zinc(II) and cadmium(II) chlorido complexes with an N,N-chelating nopinane-annelated 4,5-diazafluoren-9-one ligand (LO) were synthesized. While the zinc(II) complex is mononuclear and adopts a tetrahedral ZnN2Cl2 coordination geometry, its cadmium(II) analogue features a 1D polymeric structure due to the bridging coordination of chlorido ligands with Cd2+ ions having an octahedral CdN2Cl4 coordination geometry. The photophysical properties of the oxygen-containing LO ligand and its zinc(II) and cadmium(II) complexes were studied in solution and in the solid state and matched against the properties of its oxygen-free 4,5-diazafluorene congener L and its complexes of the same metal ions. Comprehensive experimental and theoretical studies revealed the impact of the oxygen atom in the ligand core on the luminescence of the ligands and the complexes. For the oxygen-free L ligand and L-based complexes, the structural differences between the S0 and S1 geometries are small, which leads to fluorescence with extraordinarily small Stokes shifts. The emission of these compounds is of locally excited character for L and of mixed locally excited + ligand-to-halide charge transfer character for the L-based complexes. The introduction of the oxygen atom in the ligand core results in a drastic red-shift of the emission band due to short-range charge transfer. The differences between the S0 and S1 geometries are much more pronounced for LO and LO-based compounds than those of their oxygen-free analogues, leading to an order of magnitude larger Stokes shifts. On going from solution to the solid state, LO and its complexes exhibit aggregation-induced emission (AIE) behaviour with photoluminescence quantum yields (PLQYs) reaching tens of percent.

Novel Copper(II) Complexes with Dipinodiazafluorene Ligands: Synthesis, Structure, Magnetic and Catalytic Properties.

The reactions of CuX2 (X = Cl, Br) with dipinodiazafluorenes yielded four new complexes [CuX2L1]2 (X = Cl (1), Br (2), L1 = (1R,3R,8R,10R)-2,2,9,9-Tetramethyl-3,4,7,8,9,10-hexahydro-1H-1,3:8,10-dimethanocyclopenta [1,2-b:5,4-b']diquinolin-12(2H)-one) and [(CuX2)2L2]n (X = Cl (3), Br (4), L2 = (1R,3R,8R,10R,1'R,3'R,8'R,10'R)-2,2,2',2',9,9,9',9'-Octamethyl-1,1',2,2',3,3',4,4',7,7',8,8',9,9',10,10'-hexadecahydro-1,3:1',3':8,10:8',10'-tetramethano-12,12'-bi(cyclopenta [1,2-b:5,4-b']diquinolinylidene). The complexes were characterized by IR and EPR spectroscopy, HR-ESI-MS and elemental analysis. The crystal structures of compounds 1, 2 and 4 were determined by X-ray diffraction (XRD) analysis. Complexes 1-2 have a monomeric structure, while complex 4 has a polymeric structure due to additional coordinating N,N sites in L2. All complexes contain a binuclear fragment {Cu2(µ-X)2×2} (X = Cl, Br) in their structures. Each copper atom has a distorted square-pyramidal coordination environment formed by two nitrogen atoms and three halogen atoms. The Cu-Nax distance is elongated compared to Cu-Neq. The EPR spectra of compounds 1-4 in CH3CN confirm their paramagnetic nature due to the d9 electronic configuration of the copper(II) ion. The magnetic properties of all compounds were studied by the method of static magnetic susceptibility. For complexes 1 and 2, the effective magnetic moments are µeff ≈ 1.87 and 1.83 µB (per each Cu2+ ion), respectively, in the temperature range 50-300 K, which are close to the theoretical spin value (1.73 µB). Ferromagnetic exchange interactions between Cu(II) ions inside {Cu2(µ-X)2X2} (X = Cl, Br) dimers (J/kB ≈ 25 and 31 K for 1 and 2, respectively) or between dimers (θ' ≈ 0.30 and 0.47 K for 1 and 2, respectively) were found at low temperatures. For compounds 3 and 4, the magnetic susceptibility is well described by the Curie-Weiss law in the temperature range 1.77-300 K with µeff ≈ 1.72 and 1.70 µB for 3 and 4, respectively, and weak antiferromagnetic interactions (θ ≈ -0.4 K for 3 and -0.65 K for 4). Complexes 1-4 exhibit high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The maximum yield of cyclohexane oxidation products reached 50% (complex 3). Based on the data on the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play a decisive role in the oxidation reaction. The initial products in reactions with alkanes are alkyl hydroperoxides.

Variations in Essential Oils from South Siberian Conifers of the Pinaceae Family: New Data towards Identification and Quality Control.

Conifer essential oils have been used for centuries in traditional medicine, and nowadays they are of special interest for official medicine, aromatherapy and perfumery. In the present work, comprehensive information is given on the composition of essential oils prepared from the twigs of the conifer trees of the pine family (Pinaceae): Abies sibirica Ledeb., Larix sibirica Ledeb., Picea obovata Ledeb., Pinus sibirica Du Tour, Pinus sylvestris L. A total of 50 samples of essential oils have been studied. The samples were prepared during vegetation stage in the time period 1998-2012 from the growing wild trees in the South part of the Western Siberia (Russian Federation) and neighboring territories of Republic of Kazakhstan within the area with geographical coordinates LAT 49.180012-57.908583 and LON 83.213217-91.258717 at elevation of 82-2070 m above sea level. All the essential oil samples were obtained from freshly collected plant raw material by steam distillation at atmospheric pressure in stainless steel apparatus, which had been specially designed for field research. All the chromatographic profiles were prepared from authentic samples whose voucher specimens are deposited at the Central Siberian Botanical Garden of the Siberian Branch of the Russian Academy of Sciences (NS). The following information for each sample is provided: (1) date and location of the plant raw material collecting, indicating administrative areas and the exact geographic coordinates; (2) yield of essential oil, (3) chemical composition of the essential oil sample based on GC/MS experiments using full mass-spectra (EI, 70 eV) and linear retention indices of the components, (4) results of GC-FID quantification based on internal standards and response factors, (5) enantiomeric composition of the main components based on GC×GC experiments using the 2nd column with cyclodextrin-based chiral selector, (6) GC profile of the high-boiling fractions indicating the characteristic sesquiterpenoids. Therefore, this study provides reliable information about the variability and true composition of the Siberian conifer oils, and the experimental data given can serve as reference chromatographic profiles of volatile substances to solve the problems of quality, authenticity and safety.

Electron-Precise Semiconducting ReGa2Ge: Extending the IrIn3 Structure Type to Group 7 of the Periodic Table.

Intermetallic compounds with semiconducting properties are rare, but they give rise to advanced materials for energy conversion and saving applications. Here, we present ReGa2Ge, a new electron-precise narrow-gap intermetallic semiconductor. The compound crystallizes in the IrIn3 structure type (space group P42/mnm, a = 6.5734(3) Å, c = 6.7450(8) Å, and Z = 4), where Re atoms occupy the Ir site, while Ga and Ge jointly populate the In sites. 69,71Ga nuclear quadrupole resonance spectroscopy indicates nonstatistical partially ordered distribution of Ga and Ge over two available crystallographic sites; however, the Ga:Ge ratio is exactly 2:1 without noticeable homogeneity range. The stoichiometry of ReGa2Ge ensures its precise valence electron count, which is 17 e- per formula unit. Accordingly, a narrow energy gap opens up at the Fermi energy in the electronic structure. Electrical resistivity, Seebeck coefficient, and thermal conductivity are in agreement with the semiconducting behavior deduced from the electronic structure calculations and point to prospective thermoelectric properties at high temperatures. Bonding analysis reveals dominant covalency in Re-E (E = Ga, Ge) and Re-Re interactions.

Luminescent Zn(ii) and Cd(ii) complexes with chiral 2,2'-bipyridine ligands bearing natural monoterpene groups: synthesis, speciation in solution and photophysics.

Mononuclear zinc(ii) and cadmium(ii) complexes, ZnLCl2 (1), CdLCl2 (2), ZnL1Cl2·2H2O (3), and CdL1Cl2·2H2O (4), with chiral ligands containing a 2,2'-bipyridine moiety and natural terpene (+)-limonene (L) or (+)-3-carene (L1) moieties were synthesized. In these complexes the L and L1 ligands are shown to coordinate Zn2+ and Cd2+ ions through the 2,2'-bipyridine moiety. The acetamide group of the ligands interacts with M2+ ions by forming NM2+ and C[double bond, length as m-dash]OM2+ contacts and N-HCl hydrogen bonds with coordinated Cl- ions. In solutions the complexes have several conformers differing by the degree of the turn of the acetamide moiety relative to the ligand core and the type of its interaction with the coordination core. The ligands and complexes exhibit luminescence with the quantum yield increasing in the order: ligand < cadmium(ii) complex < zinc(ii) complex. The complexes 3 and 4 demostrate excitation wavelength independent single-channel fluorescence. As opposed to 3 and 4, the complexes 1 and 2 demonstrate excitation wavelength dependent emission with nanosecond and microsecond lifetimes of the excited states. According to our TD-DFT calculations, an interplay of ligand centered and halide to ligand transitions facilitates two deactivation channels in 1 and 2: S1-S0 and T1-S0.

Magnetic properties of biofunctionalized iron oxide nanoparticles as magnetic resonance imaging contrast agents.

Background: One of the future applications of magnetic nanoparticles is the development of new iron-oxide-based magnetic resonance imaging (MRI) negative contrast agents, which are intended to improve the results of diagnostics and complement existing Gd-based contrast media. Results: Iron oxide nanoparticles designed for use as MRI contrast media are precisely examined by a variety of methods: powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, Mössbauer spectroscopy and zero-field nuclear magnetic resonance (ZF-NMR) spectroscopy. TEM and XRD measurements reveal a spherical shape of the nanoparticles with an average diameter of 5-8 nm and a cubic spinel-type crystal structure of space group Fd-3m. Raman, Mössbauer and NMR spectroscopy clearly indicate the presence of the maghemite γ-Fe2O3 phase. Moreover, a difference in the magnetic behavior of uncoated and human serum albumin coated iron oxide nanoparticles was observed by Mössbauer spectroscopy. Conclusion: This difference in magnetic behavior is explained by the influence of biofunctionalization on the magnetic and electronic properties of the iron oxide nanoparticles. The ZF-NMR spectra analysis allowed us to determine the relative amount of iron located in the core and the surface layer of the nanoparticles. The obtained results are important for understanding the structural and magnetic properties of iron oxide nanoparticles used as T 2 contrast agents for MRI.

Chiral C2-Symmetric Diimines with 4,5-Diazafluorene Units.

A synthetic approach to a new group of stable chiral C2-symmetric diimines with the 4,5-diazafluorene core has been developed based on condensation of dipinodiazafluorene with aromatic diamines. The chemical structures of new compounds were proven by spectroscopic methods and X-ray crystallography. All the compounds form solvates with organic solvents (chloroform, benzene, 1,4-dioxane) and water. Specific spectral data of the new compounds are explained using calculated data (DFT). Diimines of the pinodiazafluorene series give colored reactions with transition metal ions and can be regarded as prospective polydentate ligands with interesting luminescent and chiroptical properties.

ReGaGe2: an intermetallic compound with semiconducting properties and localized bonding.

ReGaGe2 is a new member of the family of intermetallic compounds with non-metallic properties. It displays highly localized covalent bonding patterns. Its electronic structure is governed by mixing of Re d orbitals with the s and p orbitals of Ga and Ge and features the Fermi level falling into the opened band gap, ensuring experimentally confirmed semiconducting properties.

Ln(iii) complexes (Ln = Eu, Gd, Tb, Dy) with a chiral ligand containing 1,10-phenanthroline and (-)-menthol fragments: synthesis, structure, magnetic properties and photoluminescence.

A series of lanthanide(iii) complexes based on the new chiral ligand L, which contains 1,10-phenanthroline and (-)-menthol fragments, namely [LnL2(NO3)3] (Ln = Eu (1), Gd (2), Tb (3), Dy (4)), have been synthesized and structurally characterized. Complexes 1-4 are isostructural and crystallize in the non-centrosymmetric space group P41212. The mononuclear complexes comprise a 10-coordinate Ln3+ ion with two bidentate N,N-donor ligands (L) and three bidentate chelating nitrate groups. The magnetic properties of complexes 1-4 are determined mainly by the Ln3+ ions. In the case of complexes 3 and 4, significant anisotropy results in nonlinear field dependences of magnetization at low temperature. Complexes 1, 3 and 4 exhibit metal-centered red (Eu3+), green (Tb3+) and yellow (Dy3+) luminescence, respectively, whereas complex 2 displays blue ligand-based luminescence in the solid state at room temperature. The luminescence quantum yield for the solid samples increases in the order 4 < 2 ≈ 3 < 1. The europium(iii) complex shows long luminescence lifetimes (up to 1750 µs) and a very high quantum yield (φf = 0.87); these make this compound promising for application in sensing and optoelectronics.

CIDNP and EPR study of phototransformation of lappaconitine derivatives in solution.

Chemically induced dynamic nuclear polarization (CIDNP) and electron paramagnetic resonance (EPR) techniques have been used to study the paramagnetic species formed during the photolysis of the alkaloid lappaconitine and its synthetic analogues in solution. Lappaconitine is a photosensitive antiarrhythmic and hypertension drug, whose major photoproduct (N-acetyl anthranilic acid) is also a potent photosensitizer. Both these compounds are lipophilic and might bind efficiently to cell membranes thereby causing phototoxic damage. Photolysis of natural lappaconitine (I) as well as its N(20) des-ethyl derivatives (N-Bz (II), N-Me (III), N-H (IV), and N(O)-Et (V)) results in cleavage of the ester bond with the formation of N-acetyl anthranilic acid (VIII) and corresponding enamine. The lappaconitine derivative V shows maximum photostability which correlates with reference data about its low toxicity. It was shown that the primary reaction step is electron transfer from the amino group to the anthranilic fragment of lappaconitine resulting in an intermediate biradical. The final products are formed via fragmentation of the neutral lappaconitine radicals.

De novo production of (+)-aristolochene by sporulated surface cultures of Penicillium roqueforti.

The de novo production of the fungal metabolite, (+)-aristolochene by sporulated surface cultures of Penicillium roqueforti is reported for the first time. The biosynthesis of fungal volatiles by various sporulated surface cultures was monitored by solid phase micro-extraction (SPME). When comparing malt extract agar with sabouraud dextrose agar, the highest yield of the fungal metabolite (0.04 mg/ml of culture) was obtained with the latter medium. The biosynthesis of (+)-aristolochene showed a maximum during the fourth day after inoculation.