A four-electron O(2)-electroreduction biocatalyst superior to platinum and a biofuel cell operating at 0.88 V

O2 was electroreduced to water, at a true-surface-area-based current density of 0.5 mA cm-2, at 37 degrees C and at pH 5 on a "wired" laccase bioelectrocatalyst-coated carbon fiber cathode. The polarization (potential vs the reversible potential of the O2 /H2O half-cell in the same electrolyte) of the cathode was only -0.07 V, approximately one-fifth of the -0.37 V polarization of a smooth platinum fiber cathode, operating in its optimal electrolyte, 0.5 M H2SO4. The bioelectrocatalyst was formed by "wiring" laccase to carbon through an electron conducting redox hydrogel, its redox functions tethered through long and flexible spacers to its cross-linked and hydrated polymer. Incorporation of the tethers increased the apparent electron diffusion coefficient 100-fold to (7.6 +/- 0.3) x 10-7 cm 2 s-1. A miniature single-compartment glucose-O2 biofuel cell made with the novel cathode operated optimally at 0.88 V, the highest operating voltage for a compartmentless miniature fuel cell.     

Organic matter transformation in the environment investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy: studies on lignins

The lignins separated from angiosperm and gymnosperm trees, peat and xylitic brown coal were investigated by quantitative EPR. Observed free radicals in lignins are sensitive to alkaline environment. Gaseous ammonia interacting with solid lignins in resonance cavity shifts quinone-hydroquinone equilibria towards formation of semiquinone anions. Complexation of copper(II) by lignins causes drastic decrease of the semiquinones in the matrices. Formation of lignin-Pb(II) complexes yielded radicals characterised by unusually low g-value (1.9999-2.0003). Monomeric structural units of the investigated lignins were recognised by pyrolysis with in situ methylation by tetramethylammonium hydroxide. Although for the natural lignins the mixture of normal semiquinone signals at g about 2.0034 and signals at g 1.9999 were observed, some monomeric components of lignins (e.g., caffeic acid, pyrogallol) gave pure lines at g = 1.9999. The bacterial oxidative biodegradation of lignin monomeric components and their Pb(II) complexes resulted in increase of the radical signals.     

Automated high-capacity sorption probe for extraction of organic compounds in aqueous samples followed by gas chromatographic analysis

An automated high-capacity sorption device for GC analysis of ultra trace components has been developed. The scope of the presented technique was to combine the simplicity of solid-phase microextraction (SPME) with the high extraction efficiency of the stir bar sorptive extraction technology. Sorptive extractions of water samples were performed using polydimethylsiloxane (PDMS) rubber tubing (120 microl) mounted onto a glass rod. The sampling procedure was carried out by a robotic autoinjector. Since the setup is fully automated, unattended and precise time-controlled extraction of samples is possible and makes quantitation with non-equilibrium extractions feasible. The sorption probes are easy to exchange, which facilitates off-line/in-field sampling. The system was evaluated with a test mixture of 44 environmentally hazardous compounds. Detection limits were found to be in the sub-ppt region. The performance of the system was demonstrated with the analysis of polycyclic aromatic hydrocarbons in urban snow.     

Molybdenum triamidoamine complexes that contain hexa-tert-butylterphenyl, hexamethylterphenyl, or p-bromohexaisopropylterphenyl substituents. An examination of some catalyst variations for the catalytic reduction of dinitrogen

Three new tetramines, (ArNHCH(2)CH(2))(3)N, have been synthesized in which Ar = 3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3) (H(3)[HTBTN(3)N]), 3,5-(2,4,6-Me(3)C(6)H(2))(2)C(6)H(3) (H(3)[HMTN(3)N]), or 4-Br-3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(2) (H(3)[pBrHIPTN(3)N]). The diarylated tetramine, [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(2), has also been isolated, and the "hybrid" tetramine [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(4-t-BuC(6)H(4)) has been prepared from it. Monochloride complexes, [(TerNCH(2)CH(2))(3)N]MoCl, have been prepared, as well as a selection of intermediates that would be expected in a catalytic dinitrogen reduction such as [(TerNCH(2)CH(2))(3)N]Mo[triple bond]N and [[(TerNCH(2)CH(2))(3)N]Mo(NH(3))][BAr'(4)] (Ter = HTBT, HMT, or pBrHIPT and Ar' = 3,5-(CF(3))(2)C(6)H(3))). Intermediates that contain the new terphenyl-substituted ligands are then evaluated for their efficiency for the catalytic reduction of dinitrogen under conditions where analogous [HIPTN(3)N]Mo species give four turnovers to ammonia under "standard" conditions with an efficiency of approximately 65%. Only [pBrHIPTN(3)N]Mo compounds are efficient catalysts for dinitrogen reduction. The reasons are explored and discussed.     

The first direct evaluation of the two-active site mechanism for chitin synthase

Chitin synthase polymerizes UDP-GlcNAc to form chitin (poly-beta(1,4)-GlcNAc) and is essential for fungal cell wall biosynthesis. The alternating orientation of the GlcNAc residues within the chitin chain has led to the proposal that chitin synthase possesses two active sites. We report the results of the first direct test of this possibility. Two simple uridine-derived dimeric inhibitors are shown to exhibit 10-fold greater inhibition than a monomeric control, consistent with the presence of two active sites. This observation has important implications for the development of antifungal agents, as well as the understanding of polymerizing glycosyltransferases.     

Synthesis and evaluation of the catalytic properties of semicarbazides derived from N-triphenylmethyl-aziridine-2-carbohydrazides

A straightforward synthesis of a series of new catalysts derived from N-triphenylmethyl-aziridine-2-carbohydrazides is described. The new compounds have been tested for the enantioselective addition of diethyl- and phenylethynylzinc to aryl and alkyl aldehydes, which afforded the corresponding chiral alcohols in high chemical yields (up to 92%) and with excellent ee’s of approximately 90%.     

Reliable determination of amidicity in acyclic amides and lactams

Two independent computational methods have been used for determination of amide resonance stabilization and amidicities relative to N,N-dimethylacetamide for a wide range of acyclic and cyclic amides. The first method utilizes carbonyl substitution nitrogen atom replacement (COSNAR). The second, new approach involves determination of the difference in amide resonance between N,N-dimethylacetamide and the target amide using an isodesmic trans-amidation process and is calibrated relative to 1-aza-2-adamantanone with zero amidicity and N,N-dimethylacetamide with 100% amidicity. Results indicate excellent coherence between the methods, which must be regarded as more reliable than a recently reported approach to amidicities based upon enthalpies of hydrogenation. Data for acyclic planar and twisted amides are predictable on the basis of the degrees of pyramidalization at nitrogen and twisting about the C-N bonds. Monocyclic lactams are predicted to have amidicities at least as high as N,N-dimethylacetamide, and the β-lactam system is planar with greater amide resonance than that of N,N-dimethylacetamide. Bicyclic penam/em and cepham/em scaffolds lose some amidicity in line with the degree of strain-induced pyramidalization at the bridgehead nitrogen and twist about the amide bond, but the most puckered penem system still retains substantial amidicity equivalent to 73% that of N,N-dimethylacetamide.     

Boroalkyl group migration provides a versatile entry into α-aminoboronic acid derivatives

A reaction exemplifying migration of boron-substituted carbon is described. We show that α-boroalkyl groups of transient boroalkyl acyl azide intermediates readily migrate from carbon to nitrogen. This process allows access to a new class of stable molecules, α-boryl isocyanates, from α-borylcarboxylic acid precursors. The methodology facilitates synthesis of a wide range of α-aminoboronic acid derivatives, including α,α-disubstituted analogues.     

Hematite nanoparticle monolayers on mica preparation by controlled self-assembly

In this research, a simple, green and effective strategy was developed to produce long-term stable oil in water emulsion from soy protein and soy polysaccharide. Soy protein and soy polysaccharide formed dispersible complexes at pH around 3.25 aqueous solution through electrostatic and hydrophobic interactions. A high pressure homogenization produced the protein/polysaccharide complex emulsion having a droplet size about 250 nm. A heat treatment of the emulsion resulted in the protein denaturation, forming irreversible oil-water interfacial films composed of soy protein/soy polysaccharide complexes. The droplets of the emulsion were characterized by dynamic light scattering, ζ-potential, transmission electron microscopy, polysaccharide digestion via pectinase, and confocal laser scanning microscopy observation via dual fluorescence probes. As a result of the polysaccharide being fixed on the droplet surface, the emulsions exhibited long-term stability in the media containing pH values of 2-8 and 0.2 mol/L NaCl. The stable soy protein/soy polysaccharide complex emulsion is a suitable food-grade delivery system in which lipophilic bioactive compounds can be encapsulated.