Deglycosylation of glucose oxidase to improve biosensors and biofuel cells

We demonstrate that a more efficient redox hydrogel structure can be achieved by engineering the size and the surface charge of the bioelectrocatalyst. Deglycosylated glucose oxidase (GOx) modified electrode exhibits higher current density than native GOx, for the same molar composition of the hydrogel. This improvement is very likely due to a more efficient hydrogel structure rather than a better intrinsic electron transfer between the FAD/FADH₂ redox center and the redox mediator.     

A Combined Solid‐State NMR and X‐ray Crystallography Study of the Bromide Ion Environments in Triphenylphosphonium Bromides

Multinuclear (³¹P and ^79/81Br), multifield (9.4, 11.75, and 21.1 T) solid‐state nuclear magnetic resonance experiments are performed for seven phosphonium bromides bearing the triphenylphosphonium cation, a molecular scaffold found in many applications in chemistry. This is undertaken to fully characterise their bromine electric field gradient (EFG) tensors, as well as the chemical shift (CS) tensors of both the halogen and the phosphorus nuclei, providing a rare and novel insight into the local electronic environments surrounding them. New crystal structures, obtained from single‐crystal X‐ray diffraction, are reported for six compounds to aid in the interpretation of the NMR data. Among them is a new structure of BrPPh₄, because the previously reported one was inconsistent with our magnetic resonance data, thereby demonstrating how NMR data of non‐standard nuclei can correct or improve X‐ray diffraction data. Our results indicate that, despite sizable quadrupolar interactions, ^79/81Br magnetic resonance spectroscopy is a powerful characterisation tool that allows for the differentiation between chemically similar bromine sites, as shown through the range in the characteristic NMR parameters. ^35/37Cl solid‐state NMR data, obtained for an analogous phosphonium chloride sample, provide insight into the relationship between unit cell volume, nuclear quadrupolar coupling constants, and Sternheimer antishielding factors. The experimental findings are complemented by gauge‐including projector‐augmented wave (GIPAW) DFT calculations, which substantiate our experimentally determined strong dependence of the largest component of the bromine CS tensor, δ₁₁, on the shortest Br? P distance in the crystal structure, a finding that has possible application in the field of NMR crystallography. This trend is explained in terms of Ramsey’s theory on paramagnetic shielding. Overall, this work demonstrates how careful NMR studies of underexploited exotic nuclides, such as ^79/81Br, can afford insights into structure and bonding environments in the solid state.     

Synthesis of pyrrolo[3,2-b]benzofurans and pyrrolo[3,2-b]naphthofurans via addition of a silyloxypyrrole to activated quinones

The uncatalyzed reaction of N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole 3 with 1,4-quinones bearing an electron withdrawing group at C-2 has been studied. Use of 1,4-quinones 4, 5 bearing an ester group at C-2 provided an efficient synthesis of the respective pyrrolidinobenzofuran adduct 9 or pyrrolidinonaphthofuran adduct 10 whereas use of 1,4-quinones 6, 7 and 8 bearing an acetyl group at C-2 afforded silyloxypyrroles 11, 12 and 13 resulting from direct electrophilic substitution of the silyloxypyrrole by the electrophilic quinone. Addition of Eu(fod)₃ to the reaction of 2-acetyl-1,4-naphthoquinone 7 and 3-acetyl-5-methoxy-1,4-naphthoquinone 8 with N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole 3 provided a method for obtaining the pyrrolidinonaphthofuran adducts 14 and 15 together with silyloxypyrroles 12 and 13. Oxidative rearrangement of pyrrolidinonaphthofuran adduct 15 to pyrrolidino pyranonaphthoquinone 16 using ceric ammonium nitrate in acetonitrile provided a novel approach for the synthesis of an aza-analogue of the pyranonaphthoquinone antibiotic kalafungin.     

Adsorption of<Emphasis Type="Italic"> N</Emphasis>-dodecyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl-3-ammonio-1-propanesulfonate (DDAPS), a model zwitterionic surfactant,on the Au(111) electrode surface

Electrochemical measurements including cyclic voltammetry, differential capacity, and chronocoulometry have been used to characterize the adsorption behaviors of the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) on the Au(111) electrode surface. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DDAPS has a multistate character. The first two states are observed at potentials close to zero charge. At low bulk DDAPS concentrations, it corresponds to the formation of a film of nearly flat adsorbed molecules. At higher concentrations it is converted into a hemimicellar state. The second state is formed at negative potentials and charge densities close to 0 C cm^–2. It corresponds to a film of tilted molecules oriented with the hydrocarbon tail towards the metal and the polar head toward the solution.Dedicated to Professor Zbigniew Galus on the occasion of his 70^th birthday and in recognition of his many contributions to electrochemistry.     

Syntheses and spectroscopic properties of energy transfer systems based on squaraines

The purpose of this project was to prepare fluorescent dyes that could absorb energy at relatively short wavelengths, and fluoresce in the near-IR region. To achieve this, copper- and palladium-mediated C-N couplings were used to prepare the ‘cassettes’, i.e the carbazole derivative 3b and the carbazole-, phenothiazine-, and phenoazine-squaraines 4b-d. These compounds have carbazole, phenothiazine, and phenoazine donor-components that absorb around about 300-320 nm, and squaraine acceptor-parts that fluoresce in the range 650-700 nm. The efficiencies of energy transfer from the donor to the acceptor, and the overall quantum yields of the cassettes were determined.     

Instantaneous, stoichiometric generation of powerfully reducing states of protein active sites using Eu(II) and polyaminocarboxylate ligands

Addition of an equivalent of a polyaminocarboxylate ligand (L) to a solution of a redox protein and the aqua Eu2+ ion results in the instantaneous in situ generation of a very powerful reductant Eu(II)-L that can rapidly drive an electron stoichiometrically onto a redox centre having an extremely negative reduction potential (lower than -1 V): this is exemplified by straightforward generation of the super-reduced state of the Fe-protein of nitrogenase.     

Physical aging in amorphous poly(ethylene furanoate): Enthalpic recovery,density, and oxygen transport considerations

The current work utilizes three separate techniques to study the physical aging process in amorphous poly(ethylene furanoate) (PEF), which is a recently introduced engineering thermoplastic with enhanced properties compared to petroleum‐sourced poly(ethylene terephthalate). Differential scanning calorimetry aging experiments were conducted at multiple aging temperatures and times, and the resultant enthalpic recovery values compared to the theoretical maximum enthalpy loss evaluated from calculations involving extrapolation of the equilibrium liquid line. Density measurements reveal densification of the matrix for the aged versus unaged samples, and provide an estimate for the reduction in free volume for the aged samples. Complementary oxygen permeation and pressure‐decay sorption experiments provide independent verification of the free volume reduction mechanism for physical aging in glassy polymers. The current work provides the first detailed aging study for PEF. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 389–399     

Development of a Henry’s constant correlation and solubility measurements of n-pentane,i-pentane,cyclopentane, n-hexane,and toluene in water

In this communication, we report new experimental data on n-pentane, i-pentane, cyclopentane, n-hexane, and toluene solubility in water at low temperature (below 298.15 K) and atmospheric pressure conditions. The new experimental data together with those reported in the literature have been used in developing a new equation for Henry’s constants of normal alkanes (methane to decane), BETEX compounds, and acid gases in aqueous phase over a wide range of temperature (typically from 273.15 K to 373.15 K). The new equation is based on a thermodynamic model, which uses the Peng–Robinson equation of state combined with the classical quadratic mixing rules for modelling non-aqueous phases, while the NRTL model is used to calculate the water activity.The predictions of the developed thermodynamic model are compared to the experimental data and the results of a thermodynamic approach, which uses the Valderrama modification of the Patel–Teja equation of state and non-density dependent mixing rules for modelling all fluid phases. Good agreement is observed between the experimental data and the model predictions.