The effect of biotin on the production of succinic acid byAnaerobiospirillum succiniciproducens

Applied Biochemistry and Biotechnology - The effect of biotin at 50 mg/L on the production of succinic acid byA. succiniciproducens has been studied. Biotin improved glucose consumption, cell...     

Modulated polarographic and voltammetric techniques in the study of natural water chemistry

Modulated polarographic and voltammetric techniques are of particular importance in natural water chemistry because of their sensitivity not only to very low concentrations of electroactive components but also to their chemical form. Direct polarographic techniques are most useful for the analysis of non-metallic components at low concentrations since metal levels are only rarely high enough for the analysis of untreated samples. Preconcentration by chemical or electrochemical techniques have both been employed. Potentially the most productive field of application of polarographic and voltammetric methods is in determining the chemical speciation of electroactive components in natural waters. Some clarification is required of the chemical and biological significance of operational classifications currently employed. Intermetallic interferences and the influence of surface films on electrode behaviour need to be more thoroughly investigated before analyses or speciation studies on untreated samples can be routinely undertaken. Chemical and electrochemical understanding rather than increased sophistication in the instrumentation is required at this stage if full advantage is to be taken of the capabilities of modulated polarographic and voltammetric methods in natural water chemistry.     

Design and demonstration of an immobilized-cell fluidized-bed reactor for the efficient production of ethanol

Applied Biochemistry and Biotechnology - Initial studies have been carried out on the scale-up of a medium-scale (2–5 m tall with a 10.2-cm id), fluidized-bed reactor (FBR) designed for fuel...     

Screening of resins for use in a biparticle fluidized-bed bioreactor for the continuous fermentation and separation of lactic acid

Applied Biochemistry and Biotechnology - A continuous particle fluidized-bed reactor is being developed for the simultaneous fermentation and purification of lactic acid. Unlike conventional...     

The synthesis of μ-(η5-η5-4,5-dihydro-as-indecenyl)bis(η5-cyclopentadienyliron)

μ-(η⁵,η⁵-4,5-Dihydro-as-indecenyl)bis(η⁵-cyclopentadienyliron) (I) was synthesized from 2-[(dimethylamino)methyl]biferrocene via 2-[(dimethylamino)methyl]biferrocene methiodide. The latter was converted to 2-(cyanomethyl)biferrocene, which was subjected to base hydrolysis to give (2-biferrocenyl)acetic acid. The acid was cyclized with trifluoroacetic anhydride to [4-μ-(η⁵,η⁵-as-indecenyl)bis(η⁵-cyclopentadienyliron)]trifluoroacetate ester. Hydrolysis of the latter followed by reduction gave compound I.     

Spectroscopic studies of the intermolecular interactions of Congo red and tinopal CBS with modified cellulose fibers

The adsorption of Congo red and tinopal CBS dyes on cellulose fibers was investigated using electronic absorption and fluorescence spectroscopies. Hydrogen bonds appear to be relevant for the dye-fiber interactions as indicated by the solvatochromism of Congo red in water, methanol, and dimethyl sulfoxide solutions, and when adsorbed on cellulose fibers. We also demonstrate that electrostatic interactions play an important role in the dye-medium interaction, through the analysis of absorption spectra of Congo red and fluorescence spectra of tinopal in aqueous solutions containing salt and in layer-by-layer nanostructured films with poly(allylamine hydrochloride). For instance, dye adsorption was enhanced when salt was added to the dipping solution, which was explained by the synergistic effect between the conformational changes of the cellulose and changes in the solvation layer around the cellulose chains and around dye molecules. On the basis of the fluorescence results for tinopal CBS, we inferred that dye aggregation is not relevant for adsorption on the fibers. In addition, fluorescence spectroscopy is proven very sensitive for studying the organization of dye molecules in layer-by-layer films, particularly those undergoing irreversible structural changes.     

Determination of chromium speciation in natural systems using DGT

The techniques of diffusive gradients (DGT) and equilibration (DET) in thin-films have been combined in a single probe that can determine Cr(III) and Cr(VI) simultaneously in solution. The assembly has a layer of polyacrylamide hydrogel overlying a separate layer of resin embedded in gel. Cr(III) species accumulate exclusively and quantitatively in the resin layer, while Cr(VI) species equilibrate with both hydrogel and resin layers. The species are separated by peeling the two layers apart. Chromium is then eluted from each of the two layers. Cr(III) and Cr(VI) were determined quantitatively in standard, mixed solutions by in situ separation with DGT and detection by GF-AAS. With this method, Cr(III) is typically preconcentrated by a factor of 10 over a 24 h deployment, and limits of detection of 8 ng/L Cr(III) and 0.3 micro g/L Cr(VI) were achieved. Due to the inbuilt preconcentration of Cr(III), the technique is particularly good at measuring low concentrations of Cr(III) in the presence of an excess of Cr(VI). Measurements were performed in three soils with various levels of chromium contamination. A concentration of 3 micro g/L of labile Cr(III) was measured reproducibly in the presence of 290 micro g/L of unreactive Cr species and 0.2 micro g/L of labile Cr(III) was measured in the presence of 24 micro g/L of unreactive Cr. The unique feature of the method is that the separation of Cr(III) from Cr(VI) occurs in situ. The Cr species are then stable in the resin and gel prior to analysis, eliminating the artefacts associated with sampling and storage, which are particularly prevalent for redox-sensitive elements. Therefore, it has great potential for assessing Cr(III) and Cr(VI) concentrations in situ in environments near redox boundaries where possible dynamic changes in Cr(III) and Cr(VI) concentrations are occurring.     

Surface states in electrochemisorption

The recursive Green function (RGF) method is used to obtain the surface and adatom RGFs for an electrified substate. The electrochemisorption (ECS) process is described, by invoking the Anderson–Newns (AN) model, whereby a self-consistent treatment of the ECS energy and charge transfer is provided. The role of the electric field, and the presence of surface states (SS), in governing magnetic and non-magnetic ECS is discussed in the case of H–Cr.     

Boundary effects on the electrophoretic motion of cylindrical particles: concentrically and eccentrically-positioned particles in a capillary

The bounded electrophoretic motion of a cylindrical particle in a circular cylindrical microchannel is explored for two cases: (1) the particle is located on the centerline of a channel (concentrically), with a symmetric wall boundary condition since gap width is constant throughout; and (2) the particle is at an eccentric location in the channel, with an asymmetric boundary condition set by the walls. The objective is to determine the effect of different boundary conditions, geometries, and physical properties on the velocity and orientation of the cylinder with respect to the boundary. A theoretical model for the motion of the cylinder is presented and the problem is solved numerically. The steady-state simulations show that the velocity of the cylinder is reduced at small gap widths for the concentric case, but the velocity is increased at small gap widths for the eccentric case. When the cylinder is angled with respect to the horizontal in the symmetric case or is near the boundary in the asymmetric case, vertical and rotational components of velocity are predicted. In such cases, transient simulations are appropriate for most accurately representing particle motion. Two such simulations are included herein and show both horizontal and vertical translation plus rotation of the particle as a function of time.