Oxygen Transfer Mechanism Research Articles

Effects of dissolved oxygen tension and mechanical forces on fungal morphology in submerged fermentation

The effects of dissolved oxygen tension and mechanical forces on fungal morphology were both studied in the submerged fermentation of Aspergillus awamori. Pellet size, the hairy length of pellets, and the free filamentous mycelial fraction in the total biomass were found to be a function of the mechanical force intensity and to be independent of the dissolved oxygen tension provided that the dissolved oxygen tension was neither too low (5%) nor too high (330%). When the dissolved oxygen concentration was close to the saturation concentration corresponding to pure oxygen gas, A. awamori formed denser pellets and the free filamentous mycelial fraction was almost zero for a power input of about 1 W/kg. In the case of very low dissolved oxygen tension, the pellets were rather weak and fluffy so that they showed a very different appearance. The amount of biomass per pellet surface area appeared to be affected only by the dissolved oxygen tension and was proportional to the average dissolved oxygen tension to the power of 0.33. From this it was concluded that molecular diffusion was the dominant mechanism for oxygen transfer in the pellets and that convection and turbulent flow in the pellets were negligible in submerged fermentations. The biomass per wet pellet volume increased with the dissolved oxygen tension and decreased with the size of the pellets. This means that the smaller pellets formed under a higher dissolved oxygen tension had a higher intrinsic strength. Correspondingly, the porosity of the pellets was a function of the dissolved oxygen tension and the size of pellets. Within the studied range, the void fraction in the pellets was high and always much more than 50%. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 409-419, 1998.

Effects of dissolved oxygen tension and mechanical forces on fungal morphology in submerged fermentation

The effects of dissolved oxygen tension and mechanical forces on fungal morphology were both studied in the submerged fermentation of Aspergillus awamori. Pellet size, the hairy length of pellets, and the free filamentous mycelial fraction in the total biomass were found to be a function of the mechanical force intensity and to be independent of the dissolved oxygen tension provided that the dissolved oxygen tension was neither too low (5%) nor too high (330%). When the dissolved oxygen concentration was close to the saturation concentration corresponding to pure oxygen gas, A. awamori formed denser pellets and the free filamentous mycelial fraction was almost zero for a power input of about 1 W/kg. In the case of very low dissolved oxygen tension, the pellets were rather weak and fluffy so that they showed a very different appearance. The amount of biomass per pellet surface area appeared to be affected only by the dissolved oxygen tension and was proportional to the average dissolved oxygen tension to the power of 0.33. From this it was concluded that molecular diffusion was the dominant mechanism for oxygen transfer in the pellets and that convection and turbulent flow in the pellets were negligible in submerged fermentations. The biomass per wet pellet volume increased with the dissolved oxygen tension and decreased with the size of the pellets. This means that the smaller pellets formed under a higher dissolved oxygen tension had a higher intrinsic strength. Correspondingly, the porosity of the pellets was a function of the dissolved oxygen tension and the size of pellets. Within the studied range, the void fraction in the pellets was high and always much more than 50%.

Effect of oxygen-containing species on the impedance of the Pt/ YSZ interface

The modifications induced by oxygen on the impedance spectra of Pt/YSZ (platinum/yttria-stabilized zirconia) interfaces at 900 °C have been studied. Oxygen atmosphere and oxygen transfer utilizing both positive and negative direct currents influenced the concentration of oxygen-containing species (OCS) at the interface and that is shown to affect the shape of the impedance response. Two main types of OCS have been identified. The effect of chemical stripping of the OCS by utilizing a reducing COCO 2 atmosphere was also investigated. A mechanism for oxygen transfer across the Pt/YSZ interface is suggested. It involves two parallel paths: direct, fast interfacial transfer of the O 2− and a slow path, wherein the OCS participate.

Improvements to a stoat model of a full scale wastewater treatment works through the use of detailed mechanistic studies

The performance of a wastewater treatment works has been simulated using a dynamic modelling package from WRc, STOAT. The estimation of appropriate parameter values has been performed both prior to and after detailed investigations of the mechanisms of oxygen transfer and mixing within the aeration lanes of the activated sludge plant. Interpretation of reactor mixing characteristics in the light of dissolved oxygen data is considered. The need for accurate information concerning solids retention times is exemplified by the model's sensitivity to sludge wastage rates.

Oxidations of benzyl and phenethyl phenyl sulfides. Implications for the mechanism of the microsomal and biomimetic oxidation of sulfides

The study of the oxidation of 4-methoxyphenethyl phenyl sulfide and 3,4-dimethoxy-phenethyl phenyl sulfide with potassium 12-tungstocobalt(III)ate [Co(III)W] suggests that in the radical cations of 3,4,5-(MeO) 3PhCH 2SPh ( 4) and 2,4,6(MeO) 3PhCH 2SPh ( 5) the positive charge is not localized on the sulfur atom, but in the benzylic aromatic ring. Nevertheless, in the biomimetic and microsomal oxidation of 4 and 5 the products observed are exclusively sulfoxides and sulfones, which appears in contrast with a mechanism involving the formation of an intermediate sulfide radical cation followed by a fast oxygen rebound. A direct oxygen transfer mechanism seems most likely.

Improvements to a stoat model of a full scale wastewater treatment works through the use of detailed mechanistic studies

The performance of a wastewater treatment works has been simulated using a dynamic modelling package from WRc, STOAT. The estimation of appropriate parameter values has been performed both prior to and after detailed investigations of the mechanisms of oxygen transfer and mixing within the aeration lanes of the activated sludge plant. Interpretation of reactor mixing characteristics in the light of dissolved oxygen data is considered. The need for accurate information concerning solids retention times is exemplified by the model's sensitivity to sludge wastage rates.

Multiplicity of Reaction Pathways in the Processes of Oxygen Transfer to Secondary Amines by Mo(VI) and W(VI) Peroxo Complexes.

Oxidation of N,N-benzylmethylamine, N,N-benzylisopropylamine, and N,N-benzyl-tert-butylamine by both anionic and neutral Mo(VI) and W(VI) oxodiperoxo complexes yields the corresponding nitrones quantitatively. The oxidation reactions employing anionic oxidants were performed in CHCl(3) and follow second-order kinetics, first order with respect to the amine and to the oxidant. The data were rationalized on the basis of a rate-determining nucleophilic attack of the amine onto the peroxide oxygen of the oxidant, with a transition state in which N-O bond formation and O-O bond cleavage occur in a concerted way (electrophilic oxygen transfer mechanism). This attack yields the corresponding hydroxylamine, which then is furtherly oxidized to nitrone in a fast step. On the other hand, in the case of neutral oxidants (1)H-NMR data as well as kinetic data indicate that amine coordinates the metal center replacing the original ligand HMPA and yields a new peroxo complex. For N,N-benzyl-tert-butylamine such a complex was isolated and characterized. These new peroxo complexes can themselves behave as electrophilic oxidants, transferring oxygen to external amine molecules through the same pathway followed by anionic oxidants, or can yield the reaction product by intramolecular oxidation of the coordinate amine. Measurements of added HMPA effects on oxidation rate would seem more consistent with the electrophilic oxygen transfer mechanism.

Oxygen Mass Transfer Fundamentals of Surface Aerators

The use of surface aerators as oxygen transfer devices in biological wastewater treatment systems has been commonplace for at least several decades. The current state-of-the-art oxygen mass transfer analysis for surface aerators is essentially limited to the first-order, exponential model employed in the ASCE Standard for the Measurement of Oxygen Transfer in Clean Water. This simple model has been used for several decades to characterize the oxygen mass transfer performance of surface aerators as well as many other types of aerators. This study develops a more fundamentally rigorous oxygen mass transfer model for surface aerators which provides a more physically realistic description of the actual oxygen transfer mechanisms. This new oxygen mass transfer model separates the oxygen transfer process into a liquid spray mass transfer zone and a surface reaeration mass transfer zone. The model independently analyzes the oxygen transfer process within these two distinctively separate zones and provides the methodology and techniques for quantitatively determining the oxygen transfer rate within each of these important, but fundamentally different, oxygen mass transfer zones.

Iron-Catalyzed Gasification of Coal Char under Composition Modulation

Experiments are described which attempt to exploit the redox or oxygen transfer mechanism of iron-catalyzed coal gasification by periodically alternating between an oxidizing and a reducing gas environment. A low-rank, Canadian coal was used and carbon dioxide was the oxidizing gas. A 15% increase in the yield of CO based on CO 2 supplied compared to the steady-state operation of the gasifier was observed at 800°C for a coal loaded with 3 wt % Fe using a cycle period of 60 s. The advantage for the modulation operation decreased with increasing temperature and became negligible at 900°C

Interaction between Oxygen Transfer Mechanisms in Lake Models

Dissolved oxygen (DO) distributions in stratified lakes can be simulated by a one-dimensional (vertical), deterministic, unsteady (time-variant) diffusion equation with surface gas transfer as a boundary condition and photosynthetic oxygen production as an internal source. Both surface gas transfer and vertical diffusion depend on turbulence near the water surface. The interaction between these two mechanisms, and photosynthetic productivity of dissolved oxygen in lake models is therefore studied analytically and numerically. The analytical solution of the DO transport equation in a semiinfinite medium is developed. Predicted DO concentrations at depth z are shown to depend on three dimensionless parameters, and the strength of net photosynthetic oxygen production is an important parameter in this analysis. The increases of DO concentrations due to photosynthesis are modulated by surface aeration and vertical diffusion in the lake. A numerical solution of the dissolved oxygen transport equation is also obtained and used to illustrate simulated DO profiles over an entire open water season in two Minnesota lakes. The analytical solution is used to explain certain features of the numerical results.

Fragmentation reactions of aromatic cation radicals: a tool for the detection of electron transfer mechanisms in biomimetic and enzymatic oxidations.

1. Mechanistic criteria, based on the side-chain fragmentation reactions of aromatic cation radicals, involving the cleavage of a beta bond (i.e. C-H, C-Si and C-S) have been developed for the detection of electron transfer mechanisms in oxidative processes of alkylbenzenes and aromatic sulphides. 2. For benzylic oxidations, the distinction between electron transfer (ET) and hydrogen atom transfer mechanism (HAT) has been based: (a) on studies of intramolecular selectivity, which, with appropriate substrates (5-Z-1,2,3,-trimethylbenzenes and 4-Z-1,2-dimethylbenzenes, where Z = OMe, alkyl), turns out to be much higher in ET than in HAT processes; and (b) on products studies concerning the reactions of bicumyl and benzyltrimethylsilanes since in these systems, the nature of products can be significantly different for ET and HAT mechanisms. 3. These criteria have been applied to the reactions of alkylbenzenes with an NO3 radical (shown to be an ET process) as well as to the microsomal and biomimetic (by iron porphyrins in the presence of PhIO) side-chain oxidation of the same compounds, where the mechanistic probes have suggested a HAT mechanism, with the exception of the biomimetic oxidation of 4-methoxybenzyltrimethylsilane in CH2Cl2-H2O-MeOH, which probably occurs by an ET mechanism. 4. For the enzymatic and biomimetic oxidation of aromatic sulphides an oxygen transfer is suggested, since, with cumyl phenyl sulphide and 4-methoxybenzyl phenyl sulphide, these reactions lead exclusively to the corresponding sulphoxides and sulphones, whereas the same substrates, in genuine ET reactions, form cation radicals which undergo C-H and C-S bond cleavage. 5. An oxygen transfer mechanism is also likely in the biomimetic and enzymatic oxidations of sulphoxides since in these reactions 4-methoxybenzyl phenyl sulphoxide is exclusively converted to sulphone, whereas in ET reactions it forms only C-S bond cleavage products.

Central role of radical cations in metabolic activation of polycyclic aromatic hydrocarbons

1. Development of the chemistry of polycyclic aromatic hydrocarbon (PAH) radical cations has provided evidence that these intermediates play a major role in the metabolism of PAHs by P450 and in their binding to DNA. 2. Fluoro substitution of benzo[a]pyrene (BP) represents a suitable probe for studying mechanisms of oxygen transfer in the P450-catalysed formation of quinones and phenols from BP. Formation of BP-1,6-, -3,6- and -6,12-dione from the metabolism of 6-fluoroBP (6-FBP) is mediated by the intermediate 6-FBP+. Similarly, metabolism of 1-FBP and 3-FBP by rat liver microsomes produces BP-1,6-dione and BP-3,6-dione respectively. These results demonstrate that formation of quinones and phenols occurs via an initial electron transfer from BP to P450 and subsequent transfer of oxygen from the iron-oxo complex of P450 to BP. 3. Radical cations also play a major role in the formation of DNA adducts by the potent carcinogens 7,12-dimethylbenz[a]anthracene (DMBA), BP and dibenzo[a,l]pyrene (DB[a,l]P). In the binding of BP both in vitro and in vivo, 80% of the adducts are formed by one-electron oxidation, namely, 8-(BP-6-yl)guanine (BP-6-C8Gua), BP-6-N7Gua and BP-6-N7adenine (Ade), and are lost from the DNA by depurination. For DB[a,l]P, depurinating adducts formed from the radical cation, DB[a,l]P-10-C8Gua, DB[a,l]P-10-N7Gua, DB[a,l]P-10-N7Ade, and DB[a,l]P-10-N3Ade comprise 50% of the total DNA adducts. For DMBA, 99% of the adducts are depurinating adducts formed from the radical cation, 7-CH3BA-12-CH2-N7Gua and 7-CH3BA-12-CH2-N7Ade. 4. In summary, radical cations of PAHs play a major role in both the metabolism and metabolic activation leading to formation of DNA adducts that are critical in the mechanism of tumour initiation.

Growth of submerged mycelia of Aspergillus kawachii in solid-state culture

Submerged mycelial growth of Aspergillus kawachii IFO4308 in solid-state culture (SSC) was studied. From the result of Northern blot analysis, acid-stable α-amylase was found to be produced mainly by the submerged mycelia rather than the aerial mycelia. The submerged mycelia showed better growth in SSC using rice as the solid substrate ( koji) than in agar plate culture in spite of low concentrations of dissolved oxygen in koji. Good growth in SSC suggested the existence of an effective oxygen transfer mechanism in koji which governed the mycelial growth. When koji was submerged in water, small bubbles were generated. This phenomenon indicated the formation of vacant spaces in koji during SSC. The submerged mycelia showed better growth in the koji having a larger number of vacant spaces. Considering these facts it was concluded that the vacant spaces participate in effecting an oxygen transfer mechanism in koji as air vents because the diffusivity of oxygen in an air is larger than in koji itself.

The mechanism of enzymatic and biomimetic oxidations of aromatic sulfides and sulfoxides

Biomimetic and enzymatic oxidations of benzyl sulfides and sulfoxides lead to products (sulfoxides or sulfones) different from those obtained with bona fide electron transfer oxidations (products of CH and/or CS bond cleavage), which suggests the operation of an oxygen transfer mechanism.

Oxygen transfer reactions. 2. A comparison of the reactions of ruthenium tetroxide, chromyl chloride, and permanganate with thianthrene 5-oxide

Products obtained from the oxidation of thianthrene 5-oxide, SSO, have been used to compare oxygen transfer mechanisms for three high-valent transition metals. Oxidation of SSO by benzyltriethylammonium permanganate in methylene chloride gives the corresponding sulfone, thianthrene 5,5-dioxide (SSO2), as the exclusive product. Oxidation of SSO by ruthenium tetroxide also gives SSO2 as the predominant product along with minor amounts of the disulfoxide, thianthrene 5,10-dioxide (SOSO). However, the converse is observed when chromyl chloride is used as the oxidant; SOSO is the major product. It is suggested that oxygen transfers from permanganate and ruthenium tetroxide are initiated by complexation between the central metal atom and the oxygen end of the S=O dipole, while oxidation by chromyl chloride is likely initiated by an alternative mechanism, possibly a single electron transfer.

Photosensitization by hypericin: Electron spin resonance (ESR) evidence for the formation of singlet oxygen and superoxide anion radicals in an in vitro model

The ability of hypericin (HYP) to photoreact by type I and type II mechanisms was investigated in egg yolk lecithin (EYL) liposomes as a model membrane system. On visible irradiation in aerobic conditions at pH 7, the formation of singlet oxygen and superoxide anion radicals was demonstrated unequivocally using electron spin resonance (ESR) spectrometry with the spin traps 2,2,6,6-tetramethyl-4-piperidone (TEMP) and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). We conclude from our results that HYP in EYL liposome membranes appears to act through both singlet oxygen and electron transfer mechanisms.

Metabolism of 1- and 3-Fluorobenzo[a]pyrene by Cytochrome p450 and Horseradish Peroxidase

Abstract Benzo[a]pyrene (BP) is a good model for elucidating the mechanism of oxygen transfer for substrates that are considered good electron donors. Fluoro substitution of BP represents a suitable probe for studying mechanisms of oxygen transfer in the metabolic formation of BP quinones and BP phenols. By using this strategy with 6-fluoroBP (6-FBP), we have previously demonstrated that the BP quinones are formed metabolically via an initial one-electron oxidation of BP catalyzed by cytochrome P450. Now we have synthesized 1-FBP and 3-FBP with the purpose of elucidating the mechanism of phenol formation. If formation of 3-hydroxyBP (3-OHBP) (major metabolite of BP) and 1-OHBP (minor metabolite of BP) occurs via an initial electron transfer from BP to cytochrome P450, when we use 3-FBP and 1-FBP as substrates, one of the metabolites formed should be BP-3,6-dione and BP-1,6-dione, respectively, with displacement of fluorine. Metabolism of 1-FBP and 3-FBP by rat liver microsomes and by horseradish peroxidas...

Ruthenium (II) - catalysed oxidation of alcohols by persulfate

Alcohols are oxidized to carbonylic compounds by aqueous persulfate in the presence of catalytic amounts (0.2%) of ruthenium trichloride and of a choice of ruthenium(II) complexes. Secondary alcohols are quantitatively converted to ketones, whereas primary alcohols can be converted to aldehydes with good selectivities. A kinetic investigation suggests a concerted mechanism for the bi-electronic oxygen transfer.

Kinetics and Equilibrium of Reaction between Octakis (dimethyl sulfoxide) uranium(IV) and Nitrite Ion in Dimethyl Sulfoxide

The kinetics and equilibrium of the reaction between octakis (dimethyl sulfoxide) uranium (IV), U(dmso)8 4+, and nitrite ion N02 − were studied in dmso solutions by using stopped-flow, diode-array and UV-visible spectrophotometers. Three different reactions were observed under the condition of an excess NaNO2, and U(IV) was finally oxidized to U(VI) by N02 −. The first reaction is the formation of 1: 2 adduct complex [U (dmso8)(NO2)2 2+), the rate of which was so fast that the rate constant kl obs was not determined accurately even by the stopped-flow method. If the concentration of N02 − was as low as that of U(IV), 1:1 adduct complex was formed. However, 1:1 complex was inert for further redox process, i.e. U(IV) was not oxidized by N02 − under this condition. The second reaction represents the substitution of coordinated dmso with N02 − forming mixed ligand complex [U(dmso) 8-x(N02 −)x+2(2-x +) The rate constant k 20bs for the second reaction was measured by the conventional method using a diode-array spectrophotometer and k 20bs increased linearly with the concentration of free N02 −. The third reaction coincides with the intra-molecular oxygen transfer from coordinated N02 − to U(IV) and this process is accompanied by the oxidation of U(IV) to U(VI). The oxygen transfer mechanism was confirmed by 17O labeled experiments using 17O-NMR. It was found from acid dependence experiments that only nitrite ion oxidized U(IV) and that nitrous acid was inert as an oxidant for U(IV).

Disproportionation of sulfur dioxide to octasulfur and sulfur trioxide on Cp*2Cr2S5. Crystallographic and sulfur-34-labeling evidence for an oxygen-transfer mechanism and observation of facile exchange of Cr2S5 core sulfurs with 34S. Structures of Cp*2Cr2(.mu.-S)(.mu.-.eta.2-S2)(.mu.-.eta.1-SS.cntdot.SO2).cntdot.SO2 and Cp*2Cr2(.mu.-S)(.mu.-.eta.2-S2)(.mu.-SSO3)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDisproportionation of sulfur dioxide to octasulfur and sulfur trioxide on Cp*2Cr2S5. Crystallographic and sulfur-34-labeling evidence for an oxygen-transfer mechanism and observation of facile exchange of Cr2S5 core sulfurs with 34S. Structures of Cp*2Cr2(.mu.-S)(.mu.-.eta.2-S2)(.mu.-.eta.1-SS.cntdot.SO2).cntdot.SO2 and Cp*2Cr2(.mu.-S)(.mu.-.eta.2-S2)(.mu.-SSO3)Andreas Toupadakis, Gregory J. Kubas, and Carol J. BurnsCite this: Inorg. Chem. 1992, 31, 18, 3810–3817Publication Date (Print):September 1, 1992Publication History Published online1 May 2002Published inissue 1 September 1992https://doi.org/10.1021/ic00044a025RIGHTS & PERMISSIONSArticle Views140Altmetric-Citations14LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (994 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts