Luminescent complexes of silver(I) with pyridylbis(3-hexamethyleneiminyl thiosemicarbazone): effect of the counterion on the nuclearity

The reaction of pyridylbis(3-hexamethyleneiminyl thiosemicarbazone) (H(2)Plhexim) with various silver(I) salts and metal-ligand ratios led to the isolation of different complexes of the formulae [Ag(NO(3))(H(2)Plhexim)]·H(2)O (1), [Ag(2)(NO(3))(H(2)Plhexim)(CH(3)OH)](NO(3)) (2), [Ag(2)(ClO(4))(2)(H(2)Plhexim)] (3), [Ag(HPlhexim)]·xH(2)O (4), [Ag(HPlhexim)] (4a), [Ag(2)(Plhexim)(PPh(3))(4)]·2MeOH (5) and [Ag(4)(Plhexim)(2)]·DMF (6). The complexes were fully characterized by elemental analysis, ESI mass spectrometry, IR and NMR ((1)H, (31)P) spectroscopy. The structures of 4a, 5 and 6 were also identified by single crystal X-ray structure determination. The concentration dependence on the absorption spectra of the methanolic solutions indicates polymerization equilibria in the ground state in both the ligand and the complexes. While H(2)Plhexim is essentially non-fluorescent, complexes 1-5 fluoresce more strongly by comparison. This fluorescent behavior is consistent with the monomeric or dimeric nature of the complexes.     

Synthesis of an enantiopure 2-arylcyclohexanols from prochiral enol acetates by an enantioselective protonation/diastereoselective reduction sequence

The enantioselective protonation with 2-sulfinyl alcohols of lithium enolates of 2-arylcyclohexanones with different substituents on the phenyl group takes place with excellent enantioselectivities (89–99%). Chiral 2-phenylcyclohexanone and 2-arylcyclohexanones carrying electron donor substituents on the aromatic ring are converted into the corresponding trans-2-arylcyclohexanols by diastereoselective reduction with sodium naphthalenide in the presence of acetamide. The stereochemical integrity of the tertiary stereocenter is fully preserved using this reduction procedure. Interestingly, the chiral proton source is not consumed in the synthesis.     

Ex vivo assessment of polyol coated-iron oxide nanoparticles for MRI diagnosis applications: toxicological and MRI contrast enhancement effects

Polyol synthesis is a promising method to obtain directly pharmaceutical grade colloidal dispersion of superparamagnetic iron oxide nanoparticles (SPIONs). Here, we study the biocompatibility and performance as T2-MRI contrast agents (CAs) of high quality magnetic colloidal dispersions (average hydrodynamic aggregate diameter of 16-27 nm) consisting of polyol-synthesized SPIONs (5 nm in mean particle size) coated with triethylene glycol (TEG) chains (TEG-SPIONs), which were subsequently functionalized to carboxyl-terminated meso-2-3-dimercaptosuccinic acid (DMSA) coated-iron oxide nanoparticles (DMSA-SPIONs). Standard MTT assays on HeLa, U87MG, and HepG2 cells revealed that colloidal dispersions of TEG-coated iron oxide nanoparticles did not induce any loss of cell viability after 3 days incubation with dose concentrations below 50 μg Fe/ml. However, after these nanoparticles were functionalized with DMSA molecules, an increase on their cytotoxicity was observed, so that particles bearing free terminal carboxyl groups on their surface were not cytotoxic only at low concentrations (<10 μg Fe/ml). Moreover, cell uptake assays on HeLa and U87MG and hemolysis tests have demonstrated that TEG-SPIONs and DMSA-SPIONs were well internalized by the cells and did not induce any adverse effect on the red blood cells at the tested concentrations. Finally, in vitro relaxivity measurements and post mortem MRI studies in mice indicated that both types of coated-iron oxide nanoparticles produced higher negative T2-MRI contrast enhancement than that measured for a similar commercial T2-MRI CAs consisting in dextran-coated ultra-small iron oxide nanoparticles (Ferumoxtran-10). In conclusion, the above attributes make both types of as synthesized coated-iron oxide nanoparticles, but especially DMSA-SPIONs, promising candidates as T2-MRI CAs for nanoparticle-enhanced MRI diagnosis applications.     

Photomechanical control of the electronic properties of linear pi-conjugated systems

Photodynamic molecular architectures have been synthesized by covalent fixation of a photoisomerizable dimethylazobenzene group at two fixed points of conformationally flexible pi-conjugated quater- and sexithiophene chains. Theoretical geometry optimization shows, in excellent agreement with crystallographic structures, that the mode of fixation of the azo group plays a determining role in the geometry of the final molecular architecture and on its ability to perform the expected photoinduced molecular motion. Thus, covalent fixation of meta-dimethylazobenzene on a quaterthiophene chain results in a conformationally locked system in which photoisomerization of the azo group is hindered. However, the experimental results of optical, (1)H NMR spectroscopic, and electrochemical investigations show that when an azobenzene group is connected at the para positions of the phenyl rings, trans-to-cis photoisomerization of the azo group induces a conformational transition and dimensional changes in the underlying pi-conjugated oligothiophene chain. These experimental results unequivocally show that the photochemically induced geometrical changes produce in turn an increase in the HOMO level and a narrowing of the HOMO-LUMO gap. This therefore provides the first evidence of photomechanical control of the electronic properties of linear pi-conjugated systems.     

Formation of unusual iridabenzene and metallanaphthalene containing electron-withdrawing substituents

A new route to irida-aromatic derivatives which consists of the oxidation of bicyclic compounds has been disclosed. The iridanaphthalene 3 experiences hydrolytic cleavage of the Ir-carboxylate moiety regenerating the bicyclic structure 5, whereas treatment of 5 with ClC(O)CO2Me yields back the metalla-aromatic 3.     

Identification of platelet activating factor by tandem mass spectrometry

Platelet activating factor, a phospholipid (1-O-alkyl-2-O-acetyl-sn-glycerophosphocholine), is a potent mediator of inflammation and acute hypersensitivity reactions. Chemical ionization mass spectra provide useful information for confirmation of structure. However at low levels the confirmation of structure in biological samples is difficult because the chemical noise level is too great. Collisionally activated decomposition daughter spectra of the protonated molecule and major fragment ions of authentic standards were recorded and are discussed. Selected tandem mass spectral scans provided the improvement in signal-to-noise to allow positive confirmation of structure at nanogram levels in partially purified extracts from a biological source, the epidermal cell secretions of the saltwater catfish Arius thalassinus.     

Die Kristallstruktur der Verbindung Li2ZnGeO4

The crystal structure of dilithiumzine orthogermanate, Li₂ZnGeO₄, has been determined and refined byFourier syntheses and least-squares, using three dimensional single-crystal data. A finalR-value of 5.7% was obtained. The monoclinic unit cell (Pn–C_s ²) with the dimensionsa=6.40,b=5.45,c=5.04 Å and =90.2° contains two formula units Li₂ZnGeO₄. The crystal structure is built up by [GeO₄] tetrahedra, which are linked together by [LiO₄] and [ZnO₄] tetrahedra. The average interatomic distances are found to be: Ge–O=1.77, Li–O=2.01 and Zn–O=1.93 Å.     

Elasticp+12C scattering between 0.3 and 2 MeV

Absolute differential cross-sections ofp+¹²C elastic scattering have been measured atθ _cm=89.1°, 118.7°, 146.9° for bombarding energies between 0.3 and 2.0 MeV. Revised level parameters of the first three excited states in¹³N have been extracted with aR-matrix analysis. It is shown that the influence of the bound ground-state of¹³N has an appreciable effect on low-energy scattering. Recent predictions concerning Mott-Schwinger polarization are also discussed.     

Defect-induced acceleration of a solid-state chemical reaction in zinc alkoxide single crystals

A family of dinuclear (salicylaldimato)zinc(micro(2)-alkoxide) complexes show unusual behavior, decomposing to olefins and the corresponding micro(2)-hydroxide complexes under very mild conditions in the solid state. The reaction in homogeneous solution is, on the other hand, not observable, even at elevated temperatures over extended periods of time. The reaction in the solid state occurs preferentially on one crystallographic face and displays kinetics characteristic of polymorphic transformations in single crystals.     

A mild and efficient protocol for the conversion of carboxylic acids to olefins by a catalytic decarbonylative elimination reaction

A new method for the conversion of aliphatic carboxylic acids to olefins under unprecedented mild conditions is disclosed, wherein the carboxylic acids are converted in situ with pivalic anhydride to the mixed anhydrides, which regioselectively add to a PdCl(2)-DPE-Phos catalyst. At a temperature of only 110 degrees C, smooth decarbonylation and beta-hydride elimination occur, and the corresponding olefins along with CO, CO(2) and pivalic acid are liberated.