Masayuki Itagaki

Microbial Production of Glyceric Acid, an Organic Acid That Can Be Mass Produced from Glycerol

ABSTRACT Glyceric acid (GA), an unfamiliar biotechnological product, is currently produced as a small by-product of dihydroxyacetone production from glycerol by Gluconobacter oxydans. We developed a method for the efficient biotechnological production of GA as a target compound for new surplus glycerol applications in the biodiesel and oleochemical industries. We investigated the ability of 162 acetic acid bacterial strains to produce GA from glycerol and found that the patterns of productivity and enantiomeric GA compositions obtained from several strains differed significantly. The growth parameters of two different strain types, Gluconobacter frateurii NBRC103465 and Acetobacter tropicalis NBRC16470, were optimized using a jar fermentor. G. frateurii accumulated 136.5 g/liter of GA with a 72% d-GA enantiomeric excess (ee) in the culture broth, whereas A. tropicalis produced 101.8 g/liter of d-GA with a 99% ee. The 136.5 g/liter of glycerate in the culture broth was concentrated to 236.5 g/liter by desalting electrodialysis during the 140-min operating time, and then, from 50 ml of the concentrated solution, 9.35 g of GA calcium salt was obtained by crystallization. Gene disruption analysis using G. oxydans IFO12528 revealed that the membrane-bound alcohol dehydrogenase (mADH)-encoding gene (adhA) is required for GA production, and purified mADH from G. oxydans IFO12528 catalyzed the oxidation of glycerol. These results strongly suggest that mADH is involved in GA production by acetic acid bacteria. We propose that GA is potentially mass producible from glycerol feedstock by a biotechnological process.

Production of Glyceric Acid by Gluconobacter sp. NBRC3259 Using Raw Glycerol

Gluconobacter sp. NBRC3259 converted glycerol to glyceric acid (GA). The enantiomeric composition of the GA produced was a mixture of DL-forms with a 77% enantiomeric excess of D-GA. After culture conditions, such as initial glycerol concentration, types and amounts of nitrogen sources, and initial pH, were optimized, Gluconobacter sp. NBRC3259 produced 54.7 g/l of GA as well as 33.7 g/l of dihydroxyacetone (DHA) from 167 g/l of glycerol during 4 d of incubation in a jar fermentor with pH control. GA production from raw glycerol samples, the main by-product of the transesterification process in the biodiesel production and oleochemical industries, was also evaluated after proper pretreatment of the samples. Using a raw glycerol sample with activated charcoal pretreatment, 45.9 g/l of GA and 28.2 g/l of DHA were produced from 174 g/l of glycerol.

Study of dissolution mechanisms of copper in perchloric acid solution containing NaCl by channel flow double electrode and electrochemical quartz crystal microbalance

Active dissolution of Cu in perchloric acid solution containing NaCl is divided into three distinct potential regions, namely, a Tafel region, a limiting current region and an aggressive dissolution region. Cuprous and cupric ions dissolved from copper electrode were detected using a channel flow double electrode (CFDE) system. The dependence of the working electrode current and formation rates of cuprous and cupric ions on chloride concentration and electrolyte flow rate was determined. Dissolution mechanisms for three potential regions were proposed on the basis of the steady-state measurement. The proposed dissolution mechanisms were examined by an electrochemical impedance spectroscopy (EIS) and an electrochemical quartz crystal microbalance (EQCM). Dissolution efficiency of cuprous ions described a loop in the forth quadrant on the Nyquist plane suggesting the existence of adsorbed intermediate in the Tafel region. EQCM measurements indicated that the final products in the Tafel region were cuprous ions.

Study of dissolution mechanisms of nickel in sulfuric acid solution by electrochemical quartz crystal microbalance

Abstract Investigations of nickel dissolution in sulfuric acid solution have been performed by using an electrochemical quartz crystal microbalance (EQCM). The anodic polarization curve of electrodeposited nickel shows distinct three dissolution regions, i.e. two active dissolution regions at low anodic overvoltages and the transpassive dissolution region at high anodic overvoltages. The comparison of EQCM response with transient current indicates that the final products in the two active dissolution regions are almost Ni(II) and that the Ni(ll) dissolution ratio to the total anodic charge in the transpassive dissolution region is smaller than that in the two active dissolution regions. On the basis of reaction parameters obtained experimentally, the active dissolution mechanism of nickel can be explained by the Bockris mechanism.

Active dissolution mechanisms of iron using EIS with channel flow double electrode. Influences of chloride and fluoride ions

The active dissolution mechanism of iron in acidic solutions containing halide ions was investigated by electrochemical impedance spectroscopy (EIS) with channel flow double electrode (CFDE). CFDE is a hydrodynamic technique similar in principle to the rotating ring disc electrode (RRDE). A dissolution efficiency Φdiss of the iron electrode in the frequency domain was obtained using the dynamic collection efficiency N(ω). By the addition of NaCl and NaF in sulfuric acid solution (pH 1), Nyquist plot of the electrochemical impedance Z showed a capacitive semicircle and apparently two inductive semicircles, and that of Φdiss showed two semicircles. These experimental results indicate that ferrous ions dissolve through two dissolution paths in the presence of chloride ions, ie, reaction paths through a FeOH adsorbed intermediate and through a FeCl adsorbed intermediate. In order to investigate the role of chloride ions, numerical simulations for EIS responses and polarization curves were performed on the basis of the above reaction model, assuming the two dissolution paths, and simulated results were in good agreement with the experimental results.

Electroreduction mechanism of oxygen investigated by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy yields significant information concerning oxygen reduction because the time constants in the reduction process can be discriminated. In the present paper, the theoretical equations of the electrochemical impedance for the various oxygen reduction pathways are derived. In the cases of the two-electron and direct four-electron reductions, the electrochemical impedance simply shows one capacitive semicircle on the complex plane. When the oxygen is reduced by an indirect four-electron reaction or a two-electron reduction followed by a disproportionation reaction, the complex plane plot of the electrochemical impedance shows two semicircles. In this case, the semicircle in the low frequency range is related to the time constant of adsorption and desorption of the reaction intermediate involved in the consecutive reactions. The conditions that the electrochemical impedance shows an inductive semicircle in the low frequency range are discussed on the basis of numerical simulations. The channel flow double electrode was used to measure the j–E curve and electrochemical impedance of glassy carbon, Pt and Ag electrodes at oxygen reduction potentials in alkaline solution. The complex plane plots of the electrochemical impedance of Ag and Pt electrodes show an apparent inductive semicircle, indicating the presence of the reaction intermediate HO2−.

Channel flow double electrode study on anodic dissolution of molybdenum in sulfuric acid solution

Abstract The in situ detection method of dissolved molybdenum ions has been established by a channel flow double electrode. Mo(V) sol and Mo(VI) sol were detected on the collecting electrode, which was located at the downstream of the Mo working electrode, at 1.0 V and −0.4 V, respectively. Anodic dissolution of Mo in sulfuric acid solution was investigated by using the developed analytical method. Dissolved Mo(V) sol was detected in the passive region. In the transpassive region, both Mo(V) sol and Mo(VI) sol were detected, and these dissolutions were explained by chemical dissolutions from complicated oxides. The above-mentioned results were compared with the experimental results obtained by spectrophotometric determination.

Active dissolution mechanisms of copper in acidic solutions containing sodium fluoride

The dissolution of copper in acidic solution containing fluoride ions has been investigated by channel flow double electrode (CFDE) and steady-state electrochemical measurements. Polarization curves of copper in the presence of fluoride ions apparently show the Tafel region, whose slope is 0.06 V/dec. The pH of the solution affects the dissolution rate at low fluoride concentrations. On the other hand, fluoride ions influence the dissolution rate at high fluoride concentrations. Using the CFDE system, cuprous and cupric ions were detected during polarization curve measurements. Both cuprous and cupric ions are found in a wide potential range, and the presence of cupric ion is explained by the disproportionation reaction which follows the surface dissolution process, forming cuprous ion. On the basis of experimental results, the active dissolution mechanisms of copper in acidic solution containing fluoride ions were proposed.

Use of a Gluconobacter frateurii Mutant to Prevent Dihydroxyacetone Accumulation during Glyceric Acid Production from Glycerol

To prevent dihydroxyacetone (DHA) by-production during glyceric acid (GA) production from glycerol using Gluconobacter frateurii, we used a G. frateurii THD32 mutant, ΔsldA, in which the glycerol dehydrogenase subunit-encoding gene (sldA) was disrupted, but ΔsldA grew much more slowly than the wild type, growth starting after a lag of 3 d under the same culture conditions. The addition of 1% w/v D-sorbitol to the medium improved both the growth and the GA productivity of the mutant, and ΔsldA produced 89.1 g/l GA during 4 d of incubation without DHA accumulation.

The electrochemical impedance response of transpassive dissolution of chromium in neutral solutions containing sodium chloride and sodium fluoride

Abstract The kinetics of transpassive dissolution of chromium have been investigated using electro-chemical impedance spectroscopy (EIS). Nyquist plots of electrochemical impedance responses corresponding to transpassive dissolution of chromium in neutral solutions containing chloride and fluoride ions show capacitive and inductive behaviour at around 0.7 V (SSE) and an apparent Warburg impedance at noble potentials. A theoretical model which takes into account the electrochemical processes at the electrode surface and the diffusion process of generated chromate ion is proposed. Experimental results of electrochemical impedances and polarization curves were simulated on the basis of the proposed model. They are in good agreement with the simulated results. Transpassive dissolution rate of chromium in the presence of fluoride ion is larger than in chloride ion. This discrepancy was explained using the reaction rate constants obtained by the simulation.