Efficient dechlorination of carbon tetrachloride by hydrophobic green rust intercalated with dodecanoate anions

The reductive dechlorination of carbon tetrachloride (CT) by Fe(II)-Fe(III) hydroxide (green rust) intercalated with dodecanoate, Fe(II)(4)Fe(III)(2)(OH)(12)(C(12)H(23)O(2))(2) · yH(2)O (designated GR(C12)), at pH ~ 8 and at room temperature was investigated. CT at concentration levels similar to those found in heavily contaminated groundwater close to polluted industrial sites (14-988 μM) was reduced mainly to the fully dechlorinated products carbon monoxide (CO, yields >54%) and formic acid (HCOOH, yields >6%). Minor formation of chloroform (CF), the only chlorinated degradation product, was also detected (yields <6.3%). Reactions carried out with excess GR followed pseudo first-order kinetics with respect to CT with rate constants ranging from 6.5 × 10(-2) to 0.47 h(-1). These rate constants are comparable to those measured for CT dechlorinations mediated by zerovalent iron. Reduction of the highest concentration of CT (1.4 mM) proceeds until 56% of the Fe(II) sites of GR(C12) was consumed. This reaction ceased after 10 h due to surface passivation of GR(C12).     

The influence of light/dark cycle at low light frequency on the desulfurization by a photosynthetic microorganism

H2S dissolved in water can be converted to elementary sulfur or sulfate by the photosynthetic bacterium Chlorobium thiosulfatophilum. The effects of the light/dark cycle on cell growth and the rate of sulfide removal were investigated to develop an appropriate fermentation strategy. Dark fermentation was also studied without addition of H2S and CO2 as electron and carbon sources. Average specific growth rates of bacterial cultures with a continuous supply of H2S and CO2 both in light and dark conditions were occurred in the range of 0.008 to 0.009 h(-1), indicating little dependence on the light/dark cycle, but about 25% of the growth rate that was occurred only in the presence of light. Average H2S removal capacities for cultures grown under the light/dark cycles of 14/10 , 12/12 , and 9/15 h, respectively, with a continuous supply of feed gases, were 0.08, 0.07, and 0.04 micromol H2S.min(-1)/mg protein.l(-1) in the dark, and was slightly less than those in the light. H2S removal capacity with variation of the light/dark cycle was about 30-60% of that obtained in the continuously illuminated cultures. ATP concentration in the dark decreased from 0.43 to 0.37 mg ATP.mg protein(-1) as the daily dark duration decreased from 15 to 10 h. The production rate for lactic acid from a culture grown without a supply of mixtures of H2S and CO2 gases was 0.218 g lactic acid.l(-1).h(-1), much more than that grown with a supply of feed gas mixtures. Time-averaged concentrations of lactic acid produced overall during the light and dark periods were 13.7 g lactic acid.l(-1) during the light/dark cycle of 14/10 h without a supply of feed gas, and 3.1 and 2.4 g lactic acid.l(-1) during the cycles of 9/15 and 14/10 h, respectively, with a supply of feed gas.     

The degradation of folic acid in a model food system and in beer

The rate of degradation of folic acid in the light and in the dark is investigated in a model buffer solution and in beer, with and without the addition of sulphur dioxide.In the model solution, held in the light, sulphur dioxide markedly accelerates the rate of degradation of folic acid whereas, in the dark, it exhibits a protective effect. In beer, the presence of sulphur dioxide has no effect on the degradation of folic acid, whether in the light or the dark. In the model solution, in the presence of sulphur dioxide, only the degradation product p-aminobenzoyl glutamic acid was identified. In the absence of sulphur dioxide and in the beer samples, pterin-6-carboxylic acid was additionally identified as a degradation product.     

Stability of the Stevia‐Derived Sweetener Rebaudioside A in Solution as Affected by Ultraviolet Light Exposure

Rebaudioside A is a natural noncaloric high‐potency sweetener extracted from the leaves of Stevia rebaudiana. With rebaudioside A use increasing in foods, understanding the factors affecting its stability is necessary. This project evaluated the degradation rate constants of rebaudioside A in water, 0.1 M phosphate buffer, and 0.1 M citrate buffer at pH 3 and 7 as a function of ultraviolet (UV) light intensity (365 nm, 0 μW/cm² for dark conditions, 27 μW/cm² for low intensity, and 190 μW/cm² for high intensity) at 32.5 °C. Rebaudioside A stability was adversely affected by light exposure. The pseudo‐1st‐order degradation rate constants increased significantly (P < 0.05) with increasing light intensity in all solutions. Under dark conditions, rebaudioside A in phosphate buffers was more susceptible to breakdown than in water and citrate buffers at both pH levels. However, exposure to UV light resulted in rebaudioside A degradation occurring approximately 10 times faster in citrate than in phosphate buffers at both pH levels. The sensitivity of rebaudioside A to UV light was greater in citrate buffers than in water or phosphate buffers. The use of light‐protective packaging for beverages containing rebaudioside A will improve its stability.     

Predicting the migration rate of dialkyl organotins from PVC pipe into water

Organotins (OTs) are additives widely used as thermal and light stabilizers in polyvinyl chloride (PVC) plastics. OTs can leach into water flowing through PVC pipes. This work examines the leaching rates of two potentially neurotoxic OTs, dimethyl tin (DMT) and dibutyl tin (DBT), from PVC pipe. Water was circulated in a closed loop laboratory PVC pipe system. Using a gas chromatograph-pulsed flame photometric detector (GC-PFPD), the change in concentrations of DMT and DBT in the water in the system was monitored over time and allowed to reach equilibrium. OT concentration as a function of time was analyzed using a mechanistic leaching rate model. The diffusion coefficient for OT in the PVC pipe material, the only unknown model parameter, was found to be 9 × 10(-18) m(2)/s. This value falls within with the range of values estimated from the literature (2 × 10(-18) to 2 × 10(-17) m(2)/s) thus increasing confidence in the leaching rate model.     

Photochemical interaction of ascorbic acid with riboflavin, nicotinamide and alpha-tocopherol in cream formulations

The present work is based on a study of the effect of some vitamins such as riboflavin (RF), nicotinamide (NA) and alpha‐tocopherol (TP) on the photodegradation of ascorbic acid (vitamin C) (AH₂) in oil‐in‐water cream formulations using a UV irradiation source. A UV spectrophotometric and the official iodimetric methods have been used for the assay of AH₂ in cream formulations. These methods have been validated in the presence of RF, NA and TP before their application to the creams. The recoveries of AH₂ in the creams are in the range of 90–95% and the reproducibility of the method is within ±5%. The apparent first‐order rate constants (k_obs) for the photodegradation of AH₂ in the presence of RF, NA and TP, individually, in the creams have been obtained. The second‐order rate constants for the photochemical interaction of AH₂ and the vitamins RF, NA and TP have been determined from the plots of k_obs for AH₂ photolysis versus the individual vitamin concentration along with the values of k₀ from the intercept on the vertical axis. The values of k₀ in the presence of RF and NA are lower than those of the k_obs, indicating that these vitamins act as photosensitizers for the degradation of AH₂ in creams. On the contrary, the value of k₀ in the presence of TP is higher than that of the k_obs, suggesting a stabilizing effect of this vitamin on the degradation of AH₂ in creams. The mode of interaction of the individual vitamins with AH₂ on photolysis has been discussed.     

Degradation of 5-hydroxymethylfurfural during yeast fermentation

5-Hydroxymethyl furfural (HMF) may occur in malt in high quantities depending on roasting conditions. However, the HMF content of different types of beers is relatively low, indicating its potential for degradation during fermentation. This study investigates the degradation kinetics of HMF in wort during fermentation by Saccharomyces cerevisiae. The results indicated that HMF decreased exponentially as fermentation progressed. The first-order degradation rate of HMF was 0.693 × 10(-2) and 1.397 × 10(-2)min(-1) for wort and sweet wort, respectively, indicating that sugar enhances the activity of yeasts. In wort, HMF was converted into hydroxymethyl furfuryl alcohol by yeasts with a high yield (79-84% conversion). Glucose and fructose were utilised more rapidly by the yeasts in dark roasted malt than in pale malt (p<0.05). The conversion of HMF into hydroxymethyl furfuryl alcohol seems to be a primary activity of yeast cells, and presence of sugars in the fermentation medium increases this activity.     

The atmospheric photolysis of o-tolualdehyde

The photolysis of o-tolualdehyde by natural sunlight has been investigated at the large outdoor European Photoreactor (EUPHORE) in Valencia, Spain. The photolysis rate coefficient was measured directly under different solar flux levels, with values in the range j(o-tolualdehyde) = (1.62-2.15) × 10(-4) s(-1) observed, yielding an average value of j(o-tolualdehyde)/j(NO(2)) = (2.53 ± 0.25) × 10(-2). The estimated photolysis lifetime is 1-2 h, confirming that direct photolysis by sunlight is the major atmospheric degradation pathway for o-tolualdehyde. Published UV absorption cross-section data were used to derive an effective quantum yield (290-400 nm) close to unity, within experimental error. Possible reaction pathways for the formation of the major photolysis products, benzocyclobutenol (tentatively identified) and o-phthalaldehyde, are proposed. Appreciable yields (5-13%) of secondary organic aerosol (SOA) were observed at EUPHORE and also during supplementary experiments performed in an indoor chamber using an artificial light source. Off-line analysis by gas chromatography-mass spectrometry allowed identification of o-phthalaldehyde, phthalide, phthalic anhydride, o-toluic acid, and phthalaldehydic acid in the particle phase.     

Kinetic studies of heterogeneous reactions of polycyclic aromatic hydrocarbon aerosols with NO₃ radicals

Polycyclic aromatic hydrocarbons (PAHs) and their derivates are mutagenic and carcinogenic substances widely distributed in the atmospheric environment. In this study, effective rate constants for heterogeneous reactions of NO(3) radicals with five 4-ring PAHs [benzo[a]anthracene (BaA), chrysene (Ch), pyrene (Py), 1-nitropyrene (1-NP), and 1-hydroxypyrene (1-OHP)] adsorbed on suspended azelaic acid particles are investigated by a mixed-phase relative rate method with gas-phase isoprene as the reference substance. The concentrations of suspended PAH particles and gas-phase isoprene are monitored concurrently by a real-time vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an online atmospheric gas analysis mass spectrometer, respectively. The obtained effective rate constants for the reactions of BaA, Ch, Py, 1-NP, and 1-OHP particles with NO(3) radicals are 4.3 × 10(-12), 4.0 × 10(-12), 6.4 × 10(-12), 1.3 × 10(-12), and 1.0 × 10(-11) cm(3)·molecule(-1)·s(-1), respectively, and their corresponding atmospheric lifetimes range from several minutes to half an hour at the NO(3) radical concentration of 5 × 10(8) molecules·cm(-3). In addition, the NO(3) uptake coefficients on particulate PAHs are estimated according to the consumption of PAHs under the exposure of NO(3) radicals. The experimental results of these heterogeneous reactions in the aerosol state provide supplementary knowledge for kinetic behaviors of airborne PAHs particles.     

Production of biomass and extracellular 5-aminolevulinic acid by Rhodopseudomonas palustris KG31 under light and dark conditions using volatile fatty acid

Kinetic parameters for growth and extracellular 5-aminolevulinic acid (ALA) production of Rhodopseudomonas palustris KG31 under light and dark conditions in a medium containing volatile fatty acids (VFA) as the carbon sources were estimated using a Gompertz model. The lag phase for growth and the maximum specific growth rate under microaerobic-light cultivations were 7.29-12.49 h and 0.038-0.094 h(-1), respectively, whereas under aerobic-dark cultivations, they were 2.03-14.25 h and 0.016-0.022 h(-1), respectively. The lag phase for extracellular ALA production and the maximum specific extracellular ALA production rate under microaerobic-light cultivations (15.72-24.74 h and 0.222-0.299 h(-1), respectively) were better than those obtained under aerobic-dark cultivations (24.57-44.84 h and 0.103-0.215 h(-1), respectively). The biomass and the extracellular ALA yields of 39.66-56.25 gDCW/l/mol C, and 148.47-245.75 μM/mol C, respectively, under microaerobic-light cultivations were higher than of those obtained under aerobic-dark conditions. An enhancement of extracellular ALA production under aerobic-dark conditions revealed that the ALA yield was markedly increased 8-fold (48.36 μM) by the addition of 10mM succinate, 4.5mM glycine, and 15 mM levulinic acid (LA). By controlling dissolved oxygen (DO) and pH values, a maximum extracellular ALA yield of 66.38 μM was found. The degradation rate of ALA in the culture broth was closely related to the pH value.     

Mass transfer kinetics during osmotic dehydration of pomegranate arils

The mass transfer kinetics during osmotic dehydration of pomegranate arils in osmotic solution of sucrose was studied to increase palatability and shelf life of arils. The freezing of the whole pomegranate at -18 °C was carried out prior to osmotic dehydration to increase the permeability of the outer cellular layer of the arils. The osmotic solution concentrations used were 40, 50, 60°Bx, osmotic solution temperatures were 35, 45, 55 °C. The fruit to solution ratio was kept 1:4 (w/w) during all the experiments and the process duration varied from 0 to 240 min. Azuara model and Peleg model were the best fitted as compared to other models for water loss and solute gain of pomegranate arils, respectively. Generalized Exponential Model had an excellent fit for water loss ratio and solute gain ratio of pomegranate arils. Effective moisture diffusivity of water as well as solute was estimated using the analytical solution of Fick's law of diffusion. For above conditions of osmotic dehydration, average effective diffusivity of water loss and solute gain varied from 2.718 × 10(-10) to 5.124 × 10(-10) m(2)/s and 1.471 × 10(-10) to 5.147 × 10(-10) m(2)/s, respectively. The final product was successfully utilized in some nutritional formulations such as ice cream and bakery products.     

提高彩色小麦中天然色素稳定性的方法

以彩色小麦为试验材料,通过超声波辅助提取、柱层析纯化得到彩色小麦色素,研究绿小麦天然色素在稳定剂存在条件下的稳定性。结果表明:最佳稳定剂组合为抗坏血酸钠+VB1+柠檬酸组合,在此条件下温度改变,在60℃以下绿小麦色素有较好的热稳定性,温度在80℃绿小麦色素热稳定性差;绿小麦色素对光很敏感,在光照的条件下容易分解,产生褪色现象,避光条件下稳定性最好;绿小麦色素色调在酸性和碱性范围内变化均呈现一定的规律性,在酸性条件下比较稳定,碱性条件下不稳定;绿小麦色素对H2O2稳定较差。     

碱减量废水对苯二甲酸回收工艺的影响因素

针对酸析法回收对苯二甲酸(TA)中存在沉淀分离较困难、脱水性能差的问题,对碱减量废水中TA回收工艺影响因素进行了分析探讨,获得的优化回收工艺参数是:酸析pH值3.5～4.0;滴定过程中搅拌速度300 r/min,时间1～2 min;凝过程中搅拌速度60～100 r/min,时间5～10 min;沉降时间10～12 h。在该工艺条件下,粗TA酸析回收率为77%,酸析TA絮体平均粒径11.56μm,碱减量工艺废水COD_(Cr)去除率50.5%。     

油酸和亚油酸在聚吡咯修饰铂电极上的电化学反应

基于醌的电化学还原原理,利用1,4-萘醌对游离脂肪酸的还原峰电流的测定,检测植物油中油酸和亚油酸的浓度,从而求出所测植物油的酸价。采用循环伏安法在乙腈溶液中聚合吡咯单体于铂电极表面制备化学修饰电极Ppy/ClO4-/Pt,用线性伏安法检测油酸和亚油酸浓度。结果表明:在浓度分别为5.3×10-3～7.9×10-2mol/L和9.6×10-6～1.28×10-3mol/L之间,还原峰电流与油酸和亚油酸浓度呈现良好的线性关系,相关系数(R2)分别是0.9948和0.9922,亚油酸和油酸的检出限为3.0×10-6mol/L和1.6×10-3mol/L(S/N=3)。并且将该化学修饰电极用于植物油橄榄油、玉米油、花生油、大豆油和芝麻油中酸价的检测,结果表明,化学修饰电极法是一种简便、快速实用的酸价滴定方法,可以作为碱滴定法的替代方法。     

Analysis of volatile compounds from chlorophyll photosensitized linoleic acid by headspace solid-phase microextraction (HS-SPME)

Volatile compounds from linoleic acid with or without added 5 ppm chlorophyll under light and in the dark were studied by headspace-solid phase microextraction (HS-SPME)-gas chromatography (GC)-mass spectrometry (MS). Coefficient of variation (R²) for the total peak areas by HS-SPME was 1.8%. Total volatiles (TI) in linoleic acid without added chlorophyll under light and in the dark were not significantly different for 48 hr at 4°C (p>0.05). TI in linoleic acid with 5 ppm chlorophyll under light at 4°C for 0, 6, 12, 24, and 48 hr increased from 8.9 to 11.6, 21.7, 26.1, and 29.3 (1×10⁴) in electronic counts, respectively. 2-Pentylfuran, an undesirable reversion flavor compound in soybean oil, trans-2-heptenal, and 1-octen-3-ol were formed and increased only in chlorophyll photosensitized samples. Chlorophyll can generate singlet oxygen from triplet oxygen upon the exposure of fluorescent light, which plays important roles in the formation of 2-pentylfuran, trans-2-heptenal, and 1-octen-3-ol in linoleic acid.     

磁性MOF制备及对阳离子翠蓝X-GB的吸附和光催化降解

选用Cu(NO3)2·3H2O、双(3,5-二羧基苯基)对苯二甲酰胺(H4L1)以及纳米Fe3O4,采用混合法制备了一种磁性有机骨架材料Fe3O4/Cu-H4L1,并将其用于阳离子翠蓝X-GB的吸附和可见光催化降解.结果表明:30 mg的吸附材料在180 min内对10 mL质量浓度为15 mg/L的阳离子翠蓝X-GB...     

In vitro interactions of biological nucleophiles with fluorotelomer unsaturated acids and aldehydes: fate and consequences

Fluorotelomer unsaturated aldehydes and acids (FTUALs and FTUCAs) are intermediate metabolites that form from the biotransformation of fluorotelomer-based chemicals. FTUALs and FTUCAs have been previously suggested to contribute to the toxicity associated with human exposure to fluorotelomer compounds by covalently binding to biological nucleophiles. However, the extent of their reactivity has only been assessed with glutathione. The purpose of the present study was to assess the reactivity of these intermediate metabolites with a series of nucleophilic amino acids and model proteins. In vitro experiments were carried out in an aqueous buffer system to determine the reactivity of nucleophilic amino acids with FTUCAs and FTUALs having varying fluorinated chain lengths. Using (19)F NMR spectroscopy to monitor the disappearance of the FTUCAs and FTUAL signals and the production of a fluoride signal, reaction rate constants were determined under pseudo-first-order conditions. The FTUCAs reacted only with cysteine with the following second order rate constants: 3.63 (± 1.37) × 10(-5) min(-1) mM(-1) (4:2 FTUCA), 1.19 (± 0.91) × 10(-5) min(-1) mM(-1) (6:2 FTUCA), and 4.56 (± 0.94) × 10(-5) min(-1) mM(-1) (8:2 FTUCA). The FTUALs were significantly more reactive than any of the FTUCAs with reactivity decreasing in the following order: cysteine > histidine > lysine > arginine. The following second-order rate constants were obtained: 5.7 (± 4.2) × 10(-4) min(-1) mM(-1) (histidine), 4.3 (± 1.4) × 10(-4) min(-1) mM(-1) (lysine), and 1.4 (± 0.73) × 10(-4) min(-1) mM(-1) (arginine). FTUCAs and FTUALs were also reacted with model proteins to assess their potential for forming covalent adducts. Electrospray ionization mass spectrometry (ESI-MS) was used to investigate the stoichiometry of FTUCAs and FTUALs covalently bound to apomyoglobin (ApoMg) and human serum albumin (HSA). FTUCAs were not reactive, whereas two measurable FTUAL adducts were formed with both ApoMg and HSA at each of the FTUAL chain lengths (6:2, 8:2, and 10:2). This is the first study to probe the reactivity of FTUALs and FTUCAs with nucleophiles other than glutathione, further elucidating possible FTUAL and FTUCA fate within biological systems.     

稳定剂对软冰淇淋品质的影响

对软冰淇淋浆料的粘度及软冰淇淋的硬度、膨胀率、抗融性等指标进行测试来观察黄原胶、刺槐豆胶和卡拉胶对软冰淇淋品质的影响.结果表明：在没有乳化剂存在的前提下,刺槐豆胶的抗融性最好,卡拉胶次之,黄原胶较差,但刺槐豆胶对软冰淇淋膨胀率的影响不稳定,当添加量为0.2%～0.4%时能显著提高软冰淇淋的膨胀率,其他用量时膨胀率则反而降低,黄原胶可提高产品的膨胀率,卡拉胶则降低膨胀率;在粘度方面,三者均有增稠作用,作用大小依次为黄原胶、刺槐豆胶和卡拉胶;三者均有降低产品硬度的趋势,刺槐豆胶的降低程度大于卡拉胶和黄原胶.     

铜基有机骨架Cu-H4L1的制备及对阳离子艳红5GN的光催化降解

制备了一种铜基有机骨架材料Cu-H4L1,并用其对水相中的阳离子艳红5GN进行吸附和可见光催化降解试验。结果表明:30 mg Cu-H4L1在180 min内对10 mL质量浓度为10 mg/L的阳离子艳红5GN吸附率高达88.42%,吸附速率为9.70×10^-2mg/(g·min);在可见光照射下,100 min内5 mg Cu-H_4L_1对40 mL质量浓度为10 mg/L的阳离子艳红5GN的光催化降解效率达到100%。采用傅里叶红外光谱、X射线衍射和热重分析等对Cu-H_4L_1进行测试表征,结果显示Cu-H_4L_1具有较好的晶形和较高的热稳定性。     

Influence of PET and PET/PEN Blend Packaging on Ascorbic Acid and Color in Juices Exposed to Fluorescent and UV Light

ABSTRACT: Apple and orange juices packed in polyester bottles were stored in dark, intense fluorescent (1500 lux), and UV light conditions in temperature-controlled (22 °C) chambers and monitored more than 7 mo for ascorbic acid content and color changes. Polyester beverage bottles were made of polyethylene terephthalate (PET), or PET blended with 0.25%, 1%, and 4% polyethylene naphthalate (PEN). The cut-off wavelength ranged from 322 nm for PET to 373 nm for the 4% PEN/PET blend. Spectral irradiance, visible light intensity, and light distribution were evaluated in the light chambers and compared with supermarket display lighting and outdoor daylight conditions. Only the UV chamber and sunlight showed significant irradiance at wavelengths below 400 nm. Ascorbic acid (AA) degradation and concurrent color changes occurred in both juices during storage in all 3 lighting conditions and in all 4 bottle types. Zero-order reaction kinetics described the AA degradation rate for all treatments. Apple juice stored in UV had a significantly higher ( P < 0.05) AA degradation rate than juice stored in the dark or in fluorescent light. Under UV conditions, apple juice in PET/ PEN bottles had a lower AA degradation rate than the juice in PET bottles. AA degradation in orange juice was less affected by UV exposure than in apple juice. Both juices darkened over time when stored in dark and fluorescent conditions, whereas UV exposure caused some initial bleaching of color before darkening. The bleaching effect was reduced in apple juice stored in the PET/PEN bottles.