Planar tetracoordinate carbons in cyclic semisaturated hydrocarbons

A series of planar tetracoordinate carbon molecules in cyclic semisaturated hydrocarbons resulting from the combination of the C5(2-) skeleton with saturated hydrocarbon fragments is reported. The electronic stabilization and the bonding situation are studied through the analyses of molecular orbitals and the electron localization function. The magnetic properties are also revised, giving particular attention to the induced magnetic field. These systems are the first semisaturated cycles containing a planar tetracoordinate carbon stabilized only by electronic factors.     

Identification and characterization of isomeric N-glycans of human alfa-acid-glycoprotein by stable isotope labelling and ZIC-HILIC-MS in combination with exoglycosidase digestion

In this study, a ZIC-HILIC-MS methodology for the analysis of N-glycan isomers was optimized to obtain greater detection sensitivity and thus identify more glycan structures in hAGP. In a second step, this method was combined with glycan reductive isotope labelling (GRIL) through [¹²C₆]/[¹³C₆]-aniline and exoglycosidase digestion to characterize the different glycan isomers. The GRIL method allows the peak areas resulting from two different labelled samples to be compared, since neither retention time shifts nor variations in the ionization of glycans between these samples are obtained. First, sialic acid linkage assignations were performed for most hAGP glycan isomers with α2-3 sialidase digestion. Bi-, tri- and tetraantennary glycan isomers with different terminal sialic acid linkages to galactose (α2-3 or α2-6) were assigned, and the potential of this technique for the structural characterization of isobaric isomers was therefore demonstrated. Furthermore, fucose linkage isomers of hAGP glycans were also characterized using this isotope-labelling approach in combination with α1-3,4 fucosidase and β1-4 galactosidase digestion. α1-3 antennary fucoses and α1-6 core fucosylation were detected in hAGP fucosylated glycans. These established methodologies can be extremely useful for patho-glycomic studies to characterize glycoproteins of biomedical interest and find novel glycan isomers that could be used as biomarkers in cancer research.     

Scopine Isolated in the Gas Phase

The rotational spectrum of the tropane alkaloid scopine is detected by Fourier transform microwave spectroscopy in a pulsed supersonic jet. A nonconventional method for bringing the molecules intact into the gas phase is used in which scopine syrup is mixed with glycine powder and the solid mixture is vaporized with an ultrafast UV laser beam. Laser vaporization prevents the easy isomerization to scopoline previously observed with conventional heating methods. A single conformer is unambiguously observed in the supersonic jet and corresponds to the energetically most stable species according to quantum chemical calculations. Rotational and centrifugal distortion constants are accurately determined. The spectrum shows fine and hyperfine structure due to the hindered rotation of the methyl group and the presence of a quadrupolar nucleus (¹⁴N), respectively. This additional information allows the angle of N‐methyl inversion between the N?CH₃ bond and the bicyclic C‐N‐C plane to be determined (131.8–137.8°), as well as the internal rotation barrier of the methyl group (6.235(1) kJ mol^?1).     

Characterization of an ion-selective polypyrrole coating and application to the joint determination of potassium, sodium and ammonium by electrochemical impedance spectroscopy and partial least squares method

A stable immobilization of ionophores (INPHs) was achieved by selectively electropolymerizing overoxidized pyrrol on the working electrode surface. The optimal conditions found allowed the immobilization of a huge amount of INPH which remained its recognition properties. A single sensing chip, containing a generic INPH or an INPH mixture, was employed to the joint quantification of potassium, ammonium and sodium in fertilizer samples. Electrochemical impedance spectroscopy (EIS) and partial least square (PLS) regression were used to obtain and process the data, respectively. The sensing element (INPH) and the exposure time were optimized. The best results were obtained by using the dibenzo-18-crown-6 INPH after waiting for 60 s, the time required to stabilize the impedimetric measurement. Taking into account that a single chip was employed, acceptable relative errors were obtained in the determination of potassium and ammonium (17% and 9%, respectively) in real fertilizer samples, also containing sodium. Although sodium concentration could not be estimated with precision, it had to be introduced into the calibration set data in order to model its interference with the other two ions.     

Mechanistic insights into the chemistry of RuII complexes containing Cl and DMSO ligands

Two new isomers trans,mer-[RuIICl2(bpea)(DMSO)], 2a, and cis,fac-[RuIICl2(bpea)(DMSO)], 2b, (bpea = N,N-bis(2-pyridylmethyl)ethylamine), as well as the bis-DMSO complex trans,fac-[RuIICl(bpea)(DMSO)2]Cl, 3, have been synthesized and characterized by cyclic voltammetry and UV-vis and 1D and 2D NMR spectroscopy in solution. Their solid-state structure has also been solved by means of single-crystal X-ray diffraction analysis. All the three complexes display a ruthenium metal center possessing a distorted-octahedral type of coordination, where the bpea ligand is coordinated in a meridional fashion in 2a and in a facial fashion in 2b and 3. The isomer 2a is the kinetically favored and thus can be thermally converted into 2b, that is the thermodynamically favored one. A thorough kinetic analysis strongly points toward a dissociative mechanism, where in the first step a chloro ligand is removed from the metal coordination sphere, followed by a geometric rearrangement before the chloro ligand coordinates again, generating the final complex. DFT calculations agree with the experimental data for the proposed mechanism and allow us to further characterize the mechanism of the 2a --> 2b rearrangement by obtaining the intermediates and transition state.     

Structural and kinetic study of reversible CO2 fixation by dicopper macrocyclic complexes. From intramolecular binding to self-assembly of molecular boxes

A study of the reversible CO2 fixation by a series of macrocyclic dicopper complexes is described. The dicopper macrocyclic complexes [Cu2(OH)2(Me2p)](CF3SO3)2, 1(CF3SO3)2, and [Cu2(mu-OH)2(Me2m)](CF3SO3)2, 2(CF3SO3)2, (Scheme 1) containing terminally bound and bridging hydroxide ligands, respectively, promote reversible inter- and intramolecular CO2 fixation that results in the formation of the carbonate complexes [{Cu2(Me2p)}2(mu-CO3)2](CF3SO3)4, 4(CF3SO3)4, and [Cu2(mu-CO3)(Me2m)](CF3SO3)2, 5(CF3SO3)2. Under a N2 atmosphere the complexes evolve CO2 and revert to the starting hydroxo complexes 1(CF3SO3)2 and 2(CF3SO3)2, a reaction the rate of which linearly depends on [H2O]. In the presence of water, attempts to crystallize 5(CF3SO3)2 afford [{Cu2(Me2m)(H2O)}2(mu-CO3)2](CF3SO3)4, 6(CF3SO3)4, which appears to rapidly convert to 5(CF3SO3)2 in acetonitrile solution. [Cu2(OH)2(H3m)]2+, 7, which contains a larger macrocyclic ligand, irreversibly reacts with atmospheric CO2 to generate cagelike [{Cu2(H3m)}2(mu-CO3)2](ClO4)4, 8(ClO4)4. However, addition of 1 equiv of HClO4 per Cu generates [Cu2(H3m)(CH3CN)4]4+ (3), and subsequent addition of Et3N under air reassembles 8. The carbonate complexes 4(CF3SO3)4, 5(CF3SO3)2, 6(CF3SO3)4, and 8(ClO4)4 have been characterized in the solid state by X-ray crystallography. This analysis reveals that 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 consist of self-assembled molecular boxes containing two macrocyclic dicopper complexes, bridged by CO32- ligands. The bridging mode of the carbonate ligand is anti-anti-mu-eta1:eta1 in 4(CF3SO3)4, anti-anti-mu-eta2:eta1 in 6(CF3SO3)4 and anti-anti-mu-eta2:eta2 in 5(CF3SO3)2 and 8(ClO4)4. Magnetic susceptibility measurements on 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 indicate that the carbonate ligands mediate antiferromagnetic coupling between each pair of bridged CuII ions (J = -23.1, -108.3, and -163.4 cm-1, respectively, H = -JS1S2). Detailed kinetic analyses of the reaction between carbon dioxide and the macrocyclic complexes 1(CF3SO3)2 and 2(CF3SO3)2 suggest that it is actually hydrogen carbonate formed in aqueous solution on dissolving CO2 that is responsible for the observed formation of the different carbonate complexes controlled by the binding mode of the hydroxy ligands. This study shows that CO2 fixation can be used as an on/off switch for the reversible self-assembly of supramolecular structures based on macrocyclic dicopper complexes.     

Synthesis and use of deuterated palmitic acids to decipher the cryptoregiochemistry of a Delta13 desaturation

The synthesis of two hexadeuterated palmitic acids differing in the position of the diagnostic labels, and their use to decipher the cryptoregiochemistry of a Delta13 desaturation are described. A dithiane and a triple bond functionalities were used to introduce the diagnostic (C13 or C14) and tagging (C8 and C9) labels, respectively, in the palmitic acid skeleton. Using these probes, the cryptoregiochemistry of the Delta13 desaturation involved in the biosynthesis of Thaumetopoea pityocampa sex pheromone was studied by means of kinetic isotope effect determinations. Transformation of both (Z)-11-hexadecenoic and 11-hexadecynoic acids into (Z, Z)-11,13-hexadecadienoic and (Z)-13-hexadecen-11-ynoic acids, respectively, is initiated by abstraction of the hydrogen atom at the C13 position, followed by the fast elimination of the C14 hydrogen to give the double bond.     

Gas chromatographic determination of pesticide residues in malt, spent grains, wort, and beer with electron capture detection and mass spectrometry

A method for the simultaneous determination of 9 pesticides (dinitroanilines, organophosphorus, triazoles, and pyrimidines) in several products (malt, spent grains, wort, and beer) of the beer industry is reported. Solid samples (malt and spent grains) are extracted by homogenization with a water-hexane mixture, and the pesticides are partitioned with dichloromethane. Liquid samples (wort and beer) are extracted by sonication with a hexane-dichloromethane mixture. Determination of pesticide residues was made by capillary gas chromatography with an electron capture detector (ECD). Confirmation of the compounds was performed by gas chromatography/ion trap mass spectrometry in the selected ion monitoring mode. Detection limits for GC-ECD varied from 0.2 to 5.5 pg for trifluralin and malathion, respectively. Recoveries of the pesticides from spiked samples ranged from 81.2 to 113.7% with a relative standard deviation between 3.4-7.5%. The method presents good linearity over the studied range (0.005-2 microg/mL). The proposed method is rapid and reliable and can be useful for routine monitoring during brewing.     

Versatility of 2,6-diacetylpyridine (dap) hydrazones in generating varied molecular architectures: synthesis and structural characterization of a binuclear double helical Zn(II) complex and a Mn(II) coordination polymer

A binuclear complex of Zn(ii) with formula [Zn(dap(A)(2))](2).2.25DMF (.2.25DMF) and a Mn(ii) coordination polymer with formula [Mn(3)(dap(In)(2))(3)(H(2)O)(2).2DMSO](n) (.2DMSO)(n) have been prepared and structurally characterized [dap(A)(2) = dideprotonated form of 2,6-diacetylpyridine bis(anthraniloyl hydrazone); dap(In)(2) = doubly deprotonated form of 2,6-diacetylpyridine bis(isonicotinoyl hydrazone)]. In the Zn(ii) complex the molecular units are double helical, with the Zn(ii) ions in a square pyramidal environment. The Mn(ii) complex on the other hand is a coordination polymer containing two different types of hepta-coordinated Mn(ii) ions, which differ in their axial ligands. The magnetic properties of the Mn(ii) complex, along with those of a double helical pyridine bridged binuclear Ni(ii) complex, earlier synthesized by us, are also reported. The ability of the 2,6-diacetylpyridine bis(aroyl hydrazone) ligands to form double helical complexes is analyzed in terms of the conformational flexibility of the ligands. The differences in the magnetic properties of the micro-N bridged binuclear complexes formed by 1,1 azido N-bridging ligands, and pyridine N-bridging ligands, is analyzed with the help of EHMO calculations.     

The influence of sodium perfluorooctanoate on the conformational transitions of human immunoglobulin

In the field of bioscience, the study of the interactions between blood proteins and fluorinated materials is very important from both theoretical and applied points of view. Fluorinated materials have potential use in drug delivery, as blood substitutes, and in biotechnology. Using a combination of ultraviolet-visible (UV-vis) and ultraviolet-circular dichroism (UV-CD) spectroscopies and ion-selective electrodes, the complete interaction of sodium perfluorooctanoate (SPFO) and the most important immunoglobulin (on a quantitative basis) in human serum, immunoglobulin G (IgG), has been evaluated. The study has been focused on bulk solution. By the application of an SPFO selective electrode, it was determined that there were true specific unions between surfactant molecules and IgG structure. The experimental data were presented as Koltz and Scatchard plots and analyzed on the basis of an empirical Hill equation. The conformational changes at the bulk solution were well characterized by UV-vis and UV-CD spectroscopies. As a consequence of these changes, the protein structure was affected.