Separation and purification of aflatoxins B1, B2, G1 and G2, and comparison of semi-synthetic aflatoxins B2 and G2 with naturally-occurring aflatoxins B2 and G2

A method is described for the isolation of highly purified aflatoxins B₁, B₂, G₁ and G₂ from extracts ofAspergillus flavus. The four aflatoxins, isolated from background impurities by rapid passage of the extracts through an acid alumina column, are separated from each other by chromatography on a silica gel column. Aflatoxins B₂ and G₂ are prepared by hydrogenation of the mixture of aflatoxins B₁, B₂, G₁ and G₂ and then separated by elution from a silica gel column with chloroform containing 0.7% ethanol. A comparison of semi-synthetic aflatoxins B₂ and G₂ with naturally-occurring aflatoxins B₂ and G₂ shows no significant difference in physical properties. Presented at the AOCS-AACC Meeting, Washington, D.C. April, 1968.     

Aflatoxins B1, B2, G1, and G2: Separation and purification

Aflatoxins B₁, B₂, G₁, and G₂ have been separated on a series of chromatographic columns. Chromatography of crude products isolated from molded wheat and rice on silicic acid with washed chloroform:ethanol (99:1) gave relatively pure B₁. The rest of the column fractions containing predominantly G₁, along with B₁, B₂, and G₂, were pooled and fractionated on a Silica Gel G column. The mobile phase was washed chloroform:acetone:ethanol (97.3:2.0:0.75). Thin-layer chromatography was used to follow column development. Each of the aflatoxins was treated with either decolorizing carbon or copper carbonate to remove colored pigments, and rechromatographed on Silica Gel G. Crystalline aflatoxins were prepared from chloroform solutions by addition ofn-hexane, methanol, or ethanol. Presented at the AOCS Meeting, New Orleans, May 1967. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Kinetics of the vapour-phase hydrogenation of benzene over a supported nickel catalyst in a stirred-vessel reactor

The catalytic hydrogenation of benzene was investigated over a supported nickel catalyst in a continuous stirred-vessel reactor between 260° and 450°F at atmospheric pressure. The effects of temperature, ratio of hydrogen to benzene and total feed rate (or contact time) on the conversion of benzene and yield of cyclohexane were determined. The use of the stirred reactor helped to eliminate mass transfer limitations. The investigation was carried out using surface-coated catalysts in order to eliminate pore diffusion which might otherwise mask the actual kinetics. Studies of the mixing characteristics of the reactor were carried out under both reacting and non-reacting conditions, by following conversion as a function of stirrer speed and by a tracer (pulse) technique, respectively. The kinetic data were analysed to determine the most probable model to represent the reaction. The Houghen–Watson type analysis was carried out using non-linear least squares instead of the usual linear one. The model that satisfactorily correlated the data over the entire temperature range describes the rate-controlling step as the surface reaction between adsorbed hydrogen and adsorbed benzene, the hydrogen addition being simultaneous. The following Hougen–Watson type equation was proposed: r = k_e K_H ³K_B P_H ³P_B/(1+K_HP_H+K_BP_B+K_CP_C)⁴. The constants in this rate equation were expressed as a function of temperature.     

Effect of potassium ion on the stability and release rate of hydrogen peroxide encapsulated in silica hydrogels

Hydrogen peroxide (H₂O₂) is encapsulated in silica hydrogels using sol‐gel method and the effects of the K⁺ : Na⁺ ion ratio on gelation time, hydrogel structure, stability, and release rate of H₂O₂ were investigated. As the amount of K⁺ ions increased relative to the amount of Na⁺ ions at the same pH, the gel structure became less compact and the pore diameter increased. Hydrogen peroxide retention values up to 90 and 80% were observed at the end of 7 and 20 days, respectively, in the presence of K⁺ ions at low pH values when the initial H₂O₂ concentration was 19.9 wt %. Release rate of hydrogen peroxide decreased with decreasing pH for the two K⁺ : Na⁺ ion ratios studied. This work presents an environmentally friendly, low cost, and easy to scale up method to increase the stability of high initial concentrations of H₂O₂ at room temperature and customize the release rate. © 2016 American Institute of Chemical Engineers AIChE J, 63: 409–417, 2017     

Graft copolymerization of 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid onto carboxymethylcellulose (sodium salt) by H2O2/Fe+2 redox pair

The effect of the reaction conditions on the grafting parameters during grafting of 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid onto sodium carboxymethylcellulose using H₂O₂/Fe⁺² redox pair are studied at 30°C. The grafting ratio, add on, and conversion initially increase with the H₂O₂ concentration in the range of (10.0–15.0) × 10^?2 mol dm^?3. Thereafter, these parameters decrease with the H₂O₂ concentration. The grafting ratio, add on, and conversion increase when increasing the ferrous ion concentration from (0.5 to 4.0) × 10^?2 mol dm^?3 and decrease with a further increase in the concentration. It is observed that the grafting ratio and add on increase with the monomer concentration, whereas the conversion decrease. The hydrogen ions seem to be facilitating the grafting reaction up to a certain concentration and after this concentration seem to be retarding the process. The grafting ratio, add on, and conversion decrease with the sodium carboxymethylcellulose concentration. When increasing the time period from 60 to 90 min, the grafting parameters increase but decrease thereafter. Similarly, when increasing the temperature from 25 to 30°C, the grafting parameters increase and decrease thereafter. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4819–4825, 2006     

Acid dissociation constants of anilinium and mono-nitro anilinium ions in formamide

The acid dissociation constant of anilinium ion and those of o-, m- and p-nitro anilinium ions have been determined accurately in formamide over the temperature range 10–50°C (283.15–323.15 K) from the measurement of the emf of the cells, Pt, H₂/B(m₁), BHCl(m₂)/AgClAg.The dissociation constants at 25°C (298.15 K) have been checked by determining the same with the help of the cells, Pt, Q-QH₂/B(m₁), BHCl(m₂/AgClAg.Thermodynamical changes ΔG⁰, ΔH⁰ and ΔS⁰ for the dissociation processes have been evaluated. The results show that the dissociation constants of these conjugate acids are in general lower (pK_a's higher) in formamide than their corresponding values in water.     

Kinetics and mechanism of the reaction between ammonium and nitrite ions: experimental and theoretical studies

The kinetics of the reaction between ammonium ion (NH₄⁺) and nitrite ion (NO₂⁻) in aqueous solutions was studied as a function of pH, temperature, and activities of the reactants. This reaction belongs to a class of fused chemical reactions that can be used to remediate paraffin and asphaltene deposition problems in oil pipelines. The reaction rate was found to be first-order with respect to the total concentration of ammonium species and second-order with respect to the total concentration of nitrite species. The reaction is strongly dependent on the pH of the solution, increasing the rate by a factor of 4000 as pH decreased from 7 to 3. The activity of hydrogen ion catalyzes the reaction by changing the concentrations of the two true reactants (ammonia (NH₃) and nitrogen trioxide (N₂O₃)), not by changing the reaction pathway. Reaction mechanisms were developed. A mechanism involving the S_N2 reaction in which the nucleophile NH₃ reacts with the electrophile N₂O₃ in the rate-limiting step was found to fit all experimental observations. This reaction mechanism releases the nitrite ion (NO₂⁻) to produce an intermediate (nitrosamine (H₂NNO)) which dissociates very rapidly to form the final products (nitrogen (N₂) and water (H₂O)).     

Homogeneous liquid–liquid extraction using perfluorooctanesulfonic acid and calcium and its application to the separation and recovery of vitamin B12

A new phase separation phenomenon was observed in which the perfluorooctanesulfonate ion (PFOS⁻) and calcium ion form an ion‐pair associator and the sedimented liquid phase occurs from the homogeneous aqueous solution. This phenomenon was observed in the neutral pH region at room temperature (25 °C). The optimum concentration conditions for the reagents were [PFOS⁻]_T = 7 × 10⁻³ mol dm^‐3 and [Ca²⁺]_T = 1.1 mol dm^‐3. When these findings were applied to the homogeneous liquid–liquid extraction of vitamin B₁₂, the extraction percentage (E) was 83% and the concentration ratio (ie V_a/V_s, where V_a is the volume of the aqueous phase and V_s is the volume of the sedimented liquid phase) was a maximum of 149. The recovery of vitamin B₁₂ was achieved by adding the propanol–acetone (20 : 80 v/v%) mixed solvent to the sedimented liquid phase; the vitamin B₁₂ precipitated and was filtered. Both the PFOS⁻ and Ca²⁺ were removed by dissolution in the mixed solvent. The recovery percentage of vitamin B₁₂ was 78%. © 1999 Society of Chemical Industry     

Study of the Water Molecule in the Gaseous Phase Excited States of H2O,H2O+ and H2O−

A short account of the electron configuration of water, including symmetry properties, is given. These simple considerations permit the explanation of the results of photoelectron spectroscopy experiments and photoionization experiments; the ²B₂ state of H₂O⁺ is predissociated. Excited states of water are all repulsive or predissociated, the more important fragments being OH²τ, OH²Σ⁺ and O. Some repulsive states of H₂O^? are known, but the important low-lying ²A′ state is unknown.     

Studies of latex paint films exposed to aqueous SO2: pH effects

Latex paint films containing the acid-soluble extender calcium carbonate have been exposed to aqueous SO₂ and other acidic solutions to evaluate the effects of acidic deposition at different pH values on the coatings. CaCO₃ is completely removed from these films upon immersion in acidic solutions. The leaching process was monitored with weight loss and infrared measurements. The removal rate was found to be strongly dependent on pH, decreasing with increasing pH. Removal of CaCO₃ occurs even for distilled water which has been allowed to equilibrate with atmospheric CO₂ (pH 5.6). The removal rate seems to depend only on [H⁺]; the identity of the acidic anion is apparently insignificant. An empirical relation between the rate of removal and pH was formulated from the weight loss data. The analyses of the results from both weight loss and infrared methods suggested that the mechanism of removal at pH 2.0 is diffusion controlled, whereas a chemical reaction involving H⁺ becomes more important at higher pH values.     

Kinetics of sulfur transfer from H2S to Fe1-xS

The rate of sulfur transfer across the gas/solid interface involving H₂S(g) and Fe_1-xS surface has been investigated using resistance relaxation measurements at 600°C. The rate of the oxidation reaction incorporating sulfur into Fe_1-xS has been found to decrease with sulfur activity (a_S) in the sample as (a_S)^-2/3, while the rate of the reduction reaction corresponding to sulfur loss is found to increase with the sulfur activity as (a_S)^1/3. The kinetic finding has been combined with the appropriate defect models for FeS to identify the rate limiting step for the sulfur transfer reaction from H₂S to FeS. Accordingly, the rate limiting step has been identified to be: H₂S(g) + 2e^-\rightleftharpoons S^2-(ad) + H₂(g). This revised version was published online in July 2006 with corrections to the Cover Date.     

硼酸盐热力学基元贡献模型及在MgBO2(OH)纳米晶须水热合成过程分析中应用

以MgCl₂·6H₂O、H₃BO₃、NaOH为原料,控制摩尔比Mg:B:Na=2:3:4,经室温共沉淀及水热转化(220～240℃,6.0～30.0 h)制得了单斜相MgBO₂(OH)纳米晶须。借鉴机械混合模型、基团贡献法思想,根据质量守恒原则将硼酸镁盐按照复盐分子式进行基元拆分,通过引入校正因子k,利用复盐基元的基础热力学数据拟合建立了Δ_fH_m及Δ_fG_m等硼酸盐热力学基础数据估算的基元贡献模型,估算了共沉淀产物Mg₇B₄O₁₃·7H₂O及水热产物MgBO₂(OH)不同温度下的Δ_fH_m、Δ_fG_m热力学数据,得到了25～100℃下共沉淀反应及25～250℃下水热转化的Δ_rH_m、Δ_rG_m。结果显示,共沉淀反应在室温条件下可自发进行,水热转化须借助一定温度条件方能自发实现,且反应趋势随水热温度升高时间延长而增大。该热力学基元贡献模型有望为其他结构复杂复盐化合物纳米结构的湿化学法控制合成分析及预测提供借鉴。     

Poly(oligo-oxyethylene methacrylate-co-alkali metal acrylamidocaproate) as a single ion conductor

Summary The new single ion conductors, poly(oligo-oxyethylene methacrylate-co-alkali metal acrylamidocaproic acid) ((CH₂CCH₃COO(CH₂CH₂O)₉H)_x–(CH₂CHCONH(CH₂)₅ COO-M⁺)_1-x), M⁺=Li⁺, Na⁺, K⁺, were synthesized and the effects of the cation and the temperature on ionic conductivity were investigated. The alkyl spacer in the alkali metal acrylamidocaproate was introduced to increase the flexibility of the side chain for the complex formation between the ionic groups and the oxygens in PEO unit. The room temperature(30°C) conductivity of the K single ion conductor was found to be 5x10^-7 S/cm which is the highest value reported for the single ion conductors having carboxylate groups without any additives. The pseudo-activation energy in the VTF equation was not dependent on the type of the cation, which indicates that the ion hopping rate is higher than the string renewal rate in these single ion conductors.     

Graft polymerization of 2-methyl-5-vinyl pyridine on poly(ethylene terephthalate) fibres using H2O2 as initiator

Graft polymerization of 2-methyl-5-vinyl pyridine (MVP) on unstretched poly(ethylene terephthalate) fibers (PET) using H₂O₂ as initiator was investigated under different conditions. The extents and rates of grafting, homopolymer and total conversion depended upon concentration of the initiator and the monomer as well as on the polymerization temparature. The extent and rate of grafting decreased as the H₂O₂ concentration increased from 6.82x10^?2 to 27.29x10^?2 mol · 1^?1. The same holds for the extents and rates of homopolymerization and total conversion. Whereas the extents and rates of grafting and total conversion increased significantly by increasing the MVP concentration from 0.162 to 0.648 mol.1^?1. Raising the polymerization temperature from 65 to 95°C was also accompanied by a significant enhancement in the extents and rates of grafting and total conversion. Stretching the PET fibres prior to grafting reduced appreciably the susceptibility of the fibres towards grafting, being dependent on the magnitude of stretching.     

Increased thromboxane B2 biosynthesis in platelets

The synthesis of thromboxane B₂ is increased in platelets from rabbits with experimental hypercholesterolemia, but the increase is not due to increased phospholipids hydrolysis. We have clarified the mechanism for the increased thromboxane synthesis. The biosyntheses of prostaglandin H₂ and thromboxane B₂ were unaffected by supperoxide dismutase, xanthine oxidase, mannitol, or benzoate in other experiments designed to study the possible involvement of reactive oxygen species. These results suggest that O₂ ^.− and OH^. were not likely to be involved as intermediates in the synthesis of prostaglandin H₂ and thromboxane B₂ in platelets. The rate of prostaglandin H₂ biosynthesis was promoted in deuterium oxide, and this deuterium oxide enhancement effect was reversed by 2,5-diphenylfuran, suggesting that singlet oxygen may be involved in prostaglandin H₂ biosynthesis. The biosynthesis of prostaglandin H₂ was promoted by ADP-Fe³⁺ but inhibited by EDTA and EDTA-Fe³⁺. The effect of ADP-Fe³⁺ could not be replaced by EDTA-Fe³⁺. The effects of glutathione, glutathione peroxidase and H₂O₂ on cyclooxygenase and thromboxane synthetase were studied by using partially purified enzymes and platelet microsomes. Glutathione and glutathione peroxidase inhibited the activity of cyclooxygenase but did not inhibit that of thromboxane synthetase. H₂O₂ caused the inactivation of cyclooxygenase, but the addition of H₂O₂ did not inhibit the formation of thromboxane B₂ from prostaglandin H₂. An examination of glutathione concentration and glutathione peroxidase activity in platelets from normal and experimentally hypercholesterolemic rabbits demonstrated that both were decreased in platelets from later group. The observed alterations in glutathione levels and glutathione peroxidase activity are large enough to cause increased thromboxane B₂ synthesis in platelets but the possibility that other unidentified factors may also contribute cannot be excluded.     

Studies in mineralization of aqueous aniline using Fenton and wet oxidation (FENTWO) as a hybrid process

A hybrid process for mineralization of aqueous aniline using Fenton and wet oxidation (FENTWO) is studied. It is important to have maximum conversion of ‘N’ atoms from the waste to N₂. The conversion of input ‘N’ atoms in aniline to N₂ was 15% during wet oxidation without the Fenton process and was improved to 50% with the Fenton process. Therefore, a hybrid process of Fenton followed by wet oxidation was studied for mineralization of the aqueous aniline stream. The parameters for the Fenton process were optimized (pH, catalyst, H₂O₂ to catalyst (FeSO₄) ratio, quantity of H₂O₂). The waste obtained after the Fenton process was then treated by wet oxidation for mineralization by having homogeneous CuSO₄ as the catalyst by keeping FeSO₄ therein. This combined catalyst was found to be more effective for the degradation of the intermediates formed in the Fenton process. Wet oxidation (WO) was studied in the temperature range 473–513 K and the oxygen partial pressure range 0.345–1.38 MPa at pH 6.5. The kinetic data was modeled using a power law rate expression in terms of chemical oxygen demand (COD). The optimum temperature for formation of more N₂ gas was found to be 493 K. The treated waste stream was found to contain oxalic acid using HPLC, and NH₄⁺, NO₃^? and NO₂^? ions using ion chromatography analysis. Copyright © 2007 Society of Chemical Industry     

The Softness Parameters of Ions. Prediction of the Occurrence of Miscibility Gaps in Molten Salt Mixtures

Softness parameters σ_M for cations and σ_X for anions, have been calculated as dimensionless quantities for approx. 90 cations and 18 anions. They are given by σ_M = [σ_A (M^m+) - σ_A(H⁺)]/σ_A(H⁺) and σ_X = [σ_B(X^a?) - σ_B(OH^?)]/σ_A(H⁺) where σ_A = [σI_i(M) + ΔH⁰_h(M^m+)]/m and σ_B = [-E_a(X) + ΔH⁰_h(X^a?)]/a are Ahrland's parameters. The new normalized and comparative (to the test ions H⁺ and OH^?) softness parameters are positive for soft ions and negative for hard ones. These parameters, obtained independently, are used with a four-coefficient equation to calculate coordinate bond energies for metal halides with acceptable accuracy. Considerations of the average coordination in reciprocal molten salt mixture lead to an expression for the metathesis energy change as proportional to the product of the differences in softness parameters of the two cations and the two anions. An empirical one-coefficient equation involving the softness parameters is proposed to deal with next-nearest-neighbor interactions in binary common-ion molten salt mixtures. These relationships are then used with Blander and Topol's equation to predict the occurrence of irascibility gaps in uni-univalent reciprocal salt mixtures. The gaps found in other systems are also discussed in terms of the softness of the constituent ions.     

The C-substituted charge-compensated dicarbollide [7-SMe2-7,8-C2B9H10]−: Synthesis and room-temperature rearrangement of the iridium complex

The reaction of [7-SMe₂-7,8-C₂B₉H₁₀]⁻ with [(cod)IrCl]₂ at room temperature affords iridacarborane 1-cod-8-SMe₂-1,2,8-IrC₂B₉H₁₀. The metal insertion is accompanied by polyhedral rearrangement of the carborane ligand with migration of the substituted carbon atom from the metal bonded pentagonal face. The electronic factors rather than steric ones play the main role in the ligand rearrangement. According to DFT calculations the final iridacarborane is more stable by 6–7 kcal mol^− 1 than the transient pseudocloso-1-cod-2-SMe₂-1,2,3-IrC₂B₉H₁₀ complex. Structures of 7-SMe₂-7,8-C₂B₉H₁₁ and 2 were determined by X-ray diffraction.     

The cationic oligomerization of p-aminostyrene 2. Dimerization in the intial stage

Summary It was found that p-aminostyrene (PAS) could be oligomerized by using several aminium perchlorates as catalysts in acetonitrile to give a dimer D in the initial stage of the reaction and finally the isomerization oligomer 1 at the end, in quite similar manner to the preceding paper (1), where dimerization (hydroamination) is the main reaction in the initial stage. The pK_a values for the amines were evaluated by the indicator method, and the [H⁺]₀ and [MH⁺]₀ values were calculated from equilibrium equations. As a result, the rate increased with decreasing pK_a of the catalytic amine used and reached an overall constant value. From the relationships between the rate of the reaction and the [H⁺]₀ or [MH⁺]₀ values calculated numerically, however, it was determined that the rate was more affected by the [H⁺]₀ or [M⁺]₀ values rather than the pK_a of the catalyst. It was assumed that the reaction would be initiated by the electrophilic attack of MH⁺ on the double bond of the monomer. Three successive reactions were proposed for the dimerization step: slow protonation followed by subsequent fast reactions; amine addition to the resultant styryl cation and proton elimination. It was assumed that oligomerization might proceed via the same three successive reactions as proposed for the dimerization step. Received: 24 July 2000/Revised version: 8 September 2000/Accepted: 18 September 2000     

Expanding the chemistry of single‐ion conducting poly(ionic liquid)s with polyhedral boron anions

The synthesis of a new family of single‐ion conducting random copolymers bearing polyhedral boron anions is reported. For this purpose two novel ionic monomers, namely [B₁₂H₁₁(OCH₂CH₂)₂OC(?O)C(CH₃)?CH₂]^2?[(C₄H₉)₄N⁺]₂ and [8‐(OCH₂CH₂)₂OC(?O)C(CH₃)?CH₂‐3,3′‐Co(1,2‐C₂B₉H₁₀)(1′,2′‐C₂B₉H₁₁)]^?K⁺, having methacrylate function, diethylene glycol bridge and closo‐dodecaborate or cobalt bis(1,2‐dicarbollide) anions were designed. Such monomers differ from previously reported ones by (i) chemically attached highly delocalized boron anions, by (ii) valency of the anion (divalent anion and monovalent one) and by (iii) the presence of oxyethylene flexible spacer between the methacrylate group and bonded anion. Their free radical copolymerization with poly(ethylene glycol) methyl ether methacrylate and subsequent ion exchange provided lithium‐ion conducting polyelectrolytes showing low glass transition temperature (?53 to ?49 °C), ionic conductivity up to 9.1 × 10^?7 S cm^?1, lithium transference number up to 0.61 (70 °C) and electrochemical stability up to 4.1 V versus Li⁺/Li (70 °C). The incorporation of propylene carbonate (20–40 wt%) into the copolymers resulted in the enhancement of their ionic conductivity by one order of magnitude and significantly increased their electrochemical stability up to 4.7 V versus Li⁺/Li (70 °C). © 2019 Society of Chemical Industry