Naturally reductive pseudo-Riemannian spaces

A family of naturally reductive pseudo-Riemannian spaces is constructed out of the representations of Lie algebras with ad-invariant metrics. We exhibit peculiar examples, study their geometry and characterize the corresponding naturally reductive homogeneous structure.     

Recoverable silica-gel supported binam-prolinamides as organocatalysts for the enantioselective solvent-free intra- and intermolecular aldol reaction

Silica-gel supported binam-derived prolinamides are efficient organocatalysts for the direct intramolecular and intermolecular aldol reaction under solvent-free conditions using conventional magnetic stirring. These organocatalysts in combination with benzoic acid showed similar results to those obtained under similar homogeneous reaction conditions using an organocatalyst of related structure. For the intermolecular process, the aldol products were obtained at room temperature and using only 2 equiv of the ketone with high yields, regio-, diastereo- and enantioselectivities. Under these reaction conditions, also the cross aldol reaction between aldehydes is possible. The recovered catalyst can be reused up to nine times providing similar results. More interestingly, these heterogeneous organocatalysts can be used in the intramolecular aldol reaction allowing the synthesis of the Wieland–Miescher and ketone analogues with up to 92% ee, with its reused being possible up to five times without detrimental on the obtained results.     

Clearance of host cell impurities from plasmid-containing lysates by boronate adsorption

The ability of boronate adsorption to clear Escherichia coli impurities directly from plasmid-containing lysates (∼pH 5.2) was evaluated. Results show that 3-aminophenyl boronate (PB) controlled pore glass (CPG) is able to adsorb not only those species that bear cis-diol groups (RNA, lipopolysaccharides-LPS), and are thus able to form covalent bonds with boronate, but also cis-diol-free proteins and genomic DNA (gDNA) fragments, while leaving most plasmid DNA in solution. Control runs performed with phenyl Sepharose and with PB-free CPG beads ruled out hydrophobic interactions with the phenyl ring and non-specific interactions with the glass matrix, respectively, as being responsible for RNA and gDNA adsorption. In batch mode, up to 97.6 ± 3.1% of RNA, 94.6 ± 0.8% of proteins and 96.7 ± 11.7% of gDNA were cleared after 30 min, with a plasmid yield of 64%. In fixed-bed mode, most of the plasmid was recovered in the flowthrough (96.2 ± 4.0%), even though the RNA (65.5 ± 2.8%), protein (84.4 ± 1.3%) and gDNA clearance (44.7 ± 14.1%) were not as effective. In both cases, the LPS content was removed to a residual value of less than 0.005 EU/ml. The method is fast and straightforward, circumvents the need for pre-treatment of the feed and may contribute to shorten plasmid purification processes, as the treated streams can proceed directly to the final polishing steps.     

Determination of progesterone (P4) from bovine serum samples using a microfluidic immunosensor system

Progesterone (P4) is a steroidal hormone with a vital role in the maintenance of human and animal health. This paper describes the development of an immunosensor coupled to glassy carbon (GC) electrode and integrated to a microfluidic system to quantify P4 from bovine serum samples in a fast and sensitive way. The serum samples spiked with a given P4 concentration and a given P4 concentration bound to horseradish peroxide (HPR) were simultaneously added and, therefore, they competed immunologically with sheep monoclonal anti-P4 antibodies that were immobilized at a rotating disk. HRP in the presence of hydrogen peroxide (H₂O₂) catalyzes the chatecol (H₂Q) oxidation to benzoquinone (Q). Its reverse electrochemical reduction to H₂Q can be detected at a GC electrode surface at −0.15 V by chronoamperometric measurements. These current responses are proportional to the enzyme activity and inversely proportional to the P4 amount present in bovine serum samples. This P4 immunosensor showed a linear working range from 0.5 to 12.5 ng mL⁻¹. The detection (DL) and quantification (QL) limits were 0.2 and 0.5 ng mL⁻¹, respectively. The electrochemical immunosensor had a higher sensitivity than the ELISA method using conventional spectrophotometric detections. However, both methods allowed us to obtain similar detection limits. The immunosensor allowed us to make up to 100 determinations on different samples without any previous pre-treatment. This behavior proved to be suitable to detect P4 in routine veterinary, clinical, biological, physiological, and analytical assays.     

Enhanced Direct Electron Transfer of a Multihemic Nitrite Reductase on Single‐walled Carbon Nanotube Modified Electrodes

Single‐walled carbon nanotubes (SWCNTs) deposits on glassy carbon and pyrolytic graphite electrodes have dramatically enhanced the direct electron transfer of the multihemic nitrite reductase from Desulfovibrio desulfuricans ATCC 27774, enabling a 10‐fold increase in catalytic currents. At optimal conditions, the sensitivity to nitrite and the maximum current density were 2.4±0.1 A L mol^?1 cm^?2 and 1500 µA cm^?2, respectively. Since the biosensor performance decreased over time, laponite clay and electropolymerized amphiphilic pyrrole were tested as protecting layers. Both coating materials increased substantially the bioelectrode stability, which kept about 90 % and 60 % of its initial sensitivity to nitrite after 20 and 248 days, respectively.     

Interaction of hydantoins with transition metal ions: synthesis,structural, spectroscopic,thermal and magnetic properties of [M(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>(phenytoinate)<Subscript>2</Subscript>] M = Ni(II), Co(II)

Complexes of Ni(II) and Co(II) of the formulae [Ni(H₂O)₄(pht)₂] (1) and [Co(H₂O)₄(pht)₂]·1,5NH₃·H₂O (2) (where pht = phenotoinate anion) were obtained and characterized physicochemically. [Ni(H₂O)₄(pht)₂] (1) crystallizes in a monoclinic space group P2₁/c; a = 11.7358(8), b = 11,1250(8), 11.4182(7) Å; β = 97.076(5)°; V = 1479.41 Å³; Z = 2. The environment around the nickel and cobalt ions can be described as a distorted octahedron. The metal ion was found to bind to four water molecules and two nitrogen atoms derived from two anions of the monodentate phenytoinate. Four intramolecular hydrogen bonds designated as S(6) graph set are found in one [Ni(H₂O)₄(pht)₂] (1) molecule. Two chain HB patterns, constructed by the [Ni(H₂O)₄(pht)₂] molecules extending along the c and b axes, respectively, have been observed. The cobalt complex precipitates with the additional solvent molecules: one and a half of ammonia and one water. The results document the preferential binding of hydantoins to the metal ions through N(3) atom.     

Electronic spectra and crystal structure of dinuclear Cu(II) ‘paddle wheel’ acetate complex containing axially coordinated 3-methyl-4-nitropyridine-<Emphasis Type="Italic">N</Emphasis>-oxide

This article presents the electronic spectral characteristics enhanced with the structural, IR and magnetic data of the copper(II) acetate complex with 3-methyl-4-nitropyridine-N-oxide. The complex of the formula, [Cu₂(OAc)₄(3-mnpn)₂], belongs to the group of the ‘paddle wheel’ type species with a very short (2.58 Å) metal–metal distance. In the electronic spectra, new bands were found at 16,000 and 24,000 cm^?1, which have been tentatively assigned to the metal–metal interactions and solid state effects, respectively. The complex show fast kinetic exchange of the apical ligand, i.e. 3-methyl-4-nitropyridine-N-oxide.     

Transition metal ion-modified polyurethanes: Spectroscopic and thermal studies on polyesterurethane/chromium metallopolymers

Polyesterurethane/chromium(III) metallopolymers (PUCr) having chromium contents below 1% were prepared by using different initial molar ratios urethane groups/chromium ions. PUCr were characterized in comparison with the parent polyurethane (PU) by AAS, UV-Vis absorption spectroscopy, FTIR spectroscopy, DSC, DMA and TGA. Chromium ions form coordination complexes with the urethane nitrogen atoms, the intermolecular complexation bringing about the crosslinking of the hard segments. As a result, disturbance of the hydrogen bonding and modifications in the crystallinity of the hard-segment domains take place. PUCr exhibit higher values of soft-segment glass transition and storage modulus than PU, revealing the reinforcing effect of chromium ions on the polyurethane matrix. As compared with PU, PUCr present lower initial thermal stability, a strongly catalyzed final stage of the thermal decomposition process and more thermally stable intermediate decomposition products.     

On the index and the order of quasi-regular implicit systems of differential equations

This paper is mainly devoted to the study of the differentiation index and the order for quasi-regular implicit ordinary differential algebraic equation (DAE) systems. We give an algebraic definition of the differentiation index and prove a Jacobi-type upper bound for the sum of the order and the differentiation index. Our techniques also enable us to obtain an alternative proof of a combinatorial bound proposed by Jacobi for the order.As a consequence of our approach we deduce an upper bound for the Hilbert–Kolchin regularity and an effective ideal membership test for quasi-regular implicit systems. Finally, we prove a theorem of existence and uniqueness of solutions for implicit differential systems.     

A cationic mononuclear and a neutral trinuclear boron compound derived from boric acid and N2O2-type ligands of the Salan class

Four different ligands of the Salan class have been prepared and reacted with boric acid. Reaction of saleanH₄ (saleanH₄ = N,N′-bis(o-hydroxybenzyl)-1,2-diaminoethane) with three equivalents of boric acid gave a neutral trinuclear boron complex containing two four-coordinate and one three-coordinate boron atom involved in a system of four heterocyclic rings of the composition {C₃BNO}, {C₂B₂N₂O} and {B₃O₃}. The salceanH₄ ligand (salceanH₄ = N,N′-bis(o-hydroxybenzyl)-trans-1,2-diaminocyclohexane) gave a so far unknown mononuclear boronium complex of the general formula [(RO)₂B(NR′R′′)₂]⁺. Both compounds might have applications, the trinuclear species as Lewis acid catalyst and the borocation as positively charged counterion for voluminous anions. With salpanH₄ (salpanH₄ = N,N′-bis(o-hydroxybenzyl)-1,3-diaminopropane) and salophanH₄ (salophanH₄ = N,N′-bis(o-hydroxybenzyl)-1,2-diaminobenzene) only unseparable product mixtures of oligo- and/or polymeric boron complexes could be obtained.