A Modular Approach for Interlocking Enzymes in Whatman Paper

A potentially universal approach is presented for enzyme attachment to cellulose that significantly enhances enzyme stability while retaining high activity, and involves no chemical functionalization of cellulose. Bovine serum albumin (BSA) was interlocked in cellulose to form a protein‐friendly surface (named BSA‐Paper), while also providing COOH and NH₂ groups for subsequent attachment of enzymes. The desired enzyme is then mixed with additional BSA and interlocked on BSA‐Paper. The second BSA layer dilutes and crosslinks the enzyme for improved stability. Laccase was tested as a model enzyme for interlocking on BSA‐Paper, and was found to retain over 100 % activity and was 240 times more stable at 25 °C (half life=180 d) than laccase. This new approach was also tested with a few other enzymes with encouraging results, thus providing a potentially universal method for stabilization of enzymes on cellulose with retention of high activities.     

Room temperature LPG resistive sensor based on the use of a few-layer graphene/SnO<Subscript>2</Subscript> nanocomposite

A nanocomposite consisting of a few layers of graphene (FLG) and tin dioxide (SnO₂) was prepared by ultrasound-assisted synthesis. The uniform SnO₂ nanoparticles (NPs) on the FLG were characterized by X-ray diffraction in terms of lattice and phase structure. The functional groups present in the composite were analyzed by FTIR. Electron microscopy (HR-TEM and FE-SEM) was used to study the morphology. The effect of the fraction of FLG present in the nanocomposite was investigated. Sensitivity, selectivity and reproducibility towards resistive sensing of liquid propane gas (LPG) was characterized by the I-V method. The sensor with 1% of FLG on SnO₂ operated at a typical voltage of 1 V performs best in giving a rapid and sensitive response even at 27 °C. This proves that the operating temperature of such sensors can be drastically decreased which is in contrast to conventional metal oxide LPG sensors.

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Graphical abstract Schematic of a room temperature gas sensor for liquefied petroleum gas (LPG). It is based on the use of a few-layered graphene (1 wt%)/SnO₂ nanocomposite that was deposited on an interdigitated electrode (IDEs). A sensing mechanism for LPG detection has been established.

     

Organic amines reduce trans-dichlorotetrakis(pyridine)cobalt(III) chloride to cobalt(II)

Summary The reaction of dichlorotetrakis(pyridine)cobalt(III) chloride. [CoCl₂(Py)₄]Cl, with alkyl- or arylamines in EtOH or i-PrOH yielded [CoCl₂(Py)₂] in all cases. This reduction of Co^III to Co^II takes place only in the presence of the amines. [CoCl₂(Py)₂] in EtOH is oxidized by Cl₂ gas and in the presence of pyridine gives [CoCl₂(Py)₄] ⁺, while in pyridine alone [CoCl₂(Py)₄] is formed.     

Ultrathin layered myoglobin-polyion films functional and stable at acidic pH values

Cross-linking of myoglobin (Mb) promoted by 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide within films of polystyrene sulfonate after layer-by-layer self-assembly provided remarkable stabilization. Cross-linking greatly improved adhesion of the films to fused silica slides and allowed extensive optical studies over a wide pH range. Circular dichroism and visible absorbance spectra showed that Mb retained its native conformation when films were placed in solutions of pH as low as 2 and up to pH 11. Linear dichroism revealed an average orientation of the Mb iron heme cofactors of 58 degrees to the film normal. High concentrations of urea did denature the protein in the films, however. At pH 1, Mb in solution is fully unfolded but retained considerable alpha-helical content in the cross-linked films. Both the polyion film environment and cross-linking seem to play roles in stabilizing protein secondary structure and function at low pH. Cross-linked myoglobin-polyion films on pyrolytic graphite electrodes were used in strongly acidic solutions for the electrochemical catalytic reduction of trichloracetic acid, hydrogen peroxide, and oxygen. The pH-dependent catalytic reduction of trichloracetic acid was faster in 0.1 M HCl than in the medium pH range.     

A regenerable immobilized nadh model IV: Reduction of pyridine-2-carbaldehyde by immobilized 1,4-dihydronicotinamide in the presence of Mg2+ ions

Dihydronicotinamide, anchored to a macroreticular polystyrene resin, reduces pyridine-2-carbaldehyde (PCA) in the presence of Mg²⁺ ions in acetonitrile. The reactions are clean at room temperature, the high rate precluding complications arising from slow side reactions. The influence of Mg²⁺ concentration on the rate of reduction of PCA by polymer-bound reagent and BNAH (1-benzyl-1,4-dihydronicotinamide; low-molar-mass analog) has been studied. Analysis of the kinetic data showed that of the processes contributing to the overall reduction, the reaction between the reductant and the complexed substrate proceeded at the highest rate. In the polymer-bound reagent, “site isolation” on the rigid matrix was observed to prevent bimolecular disproportionation of the neighboring dihydronicotinamides. Regeneration of the polymeric reagent was achieved with an efficiency of 98% per cycle.     

Coprecipitation as a means of separation in substoichiometric isotope dilution analysis

Chromium has been determined by isotope dilution in artificial standards and in standard alloys using the substoichiometric principle. As a substoichiometric reaction the reduction of Cr(VI) to Cr(III) was used, followed by separation of these species by coprecipitation of the trivalent chromium on a Ti(OH)₄ precipitate. For amounts smaller than 1 μg the standard method had to be modified owing to spontaneous reduction of hexavalent chromium in the solution. Interferences from other metals, if they occur, can be easily overcome. The method is simple and inexpensive.     

Electrostatic potential and electric field mapping of some sweeteners of the suosan series: A search for the structure–activity relationship

Electrostatic potential and electric field maps of some suosan series of sweeteners have been studied. Geometries optimized using the MNDO molecular orbital method and charge distributions obtained by the Mulliken population analysis were employed in the calculations. Sweetness potencies of the molecules were compared with electrostatic potentials and electric field strengths near the terminal COOH group. The observed sweetness potencies of the compounds and calculated electric fields near the carbonyl oxygen of the COOH group are found to be strongly correlated. © 1994 John Wiley & Sons, Inc.     

Synthesis and kinetic analysis of isothermal and non-isothermal decomposition of ammonium dinitramide prills

Ammonium dinitramide (ADN) prills were prepared by emulsion crystallization and characterized by optical microscopic, thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques. The isothermal and non-isothermal decomposition kinetics of ADN prills were studied by TG. The differential isoconversional method of Friedman (FR) and integral isoconversional method of Vyazovkin were used to investigate the dependence of activation energy (E _a) with conversion (α) and the results were compared with literature data. The dependence of activation energy was also derived from isothermal data. A strong dependence of E _a with α is observed for the ADN prills. All the methods showed an initial increase in E _a up to α=∼0.2 and later decreases over the rest of conversion. The apparent E _a values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean E _a values by FR, Vyazovkin and standard isoconversional method for α between 0.05 and 0.95 were 211.0, 203.9 and 156.9 kJ mol⁻¹, respectively.     

Radical Polymerization of Vinyl Acetate with Bis(tetramethylheptadionato)cobalt(II): Coexistence of Three Different Mechanisms

Poly(vinyl acetate) by OMRP : Increasing the steric encumbrance of the β‐diketonate R substituents in vinyl acetate (VAc) polymerization mediator [Co{OC(R)CHC(R)O}₂] from Me to tBu sufficiently weakens the Co^III? PVAc bond of the polymer chain to allow it to operate by both associative (degenerative transfer) and dissociative (organometallic radical polymerization, OMRP) mechanisms (see scheme). The Co^III? PVAc species also acts as a transfer agent in the absence of Lewis bases, whereas the Co^II complex shows catalytic chain transfer (CCT) activity.