Evaluation of density functional theory methods for studying chemisorption of arsenite on ferric hydroxides

Understanding adsorption of arsenic on ferric hydroxide surfaces is important for predicting the fate of arsenic in the environment and in designing treatment systems for removing arsenic from potable water. This research investigated the binding of arsenite to ferric hydroxide clusters using several density functional theory methods. Comparison of calculated and experimentally measured As-O and As-Fe bond distances indicated that As(III) forms both bidentate and monodentante corner-sharing complexes with Fe(III) octahedra. Edge-sharing As(III) complexes were less energetically favorable and had As-O and As-Fe distances that deviated more from experimentally measured values than corner-sharing complexes. The hydrated bidentate complex was the most energetically favorable in the vacuum phase, while the monodentate complex was most favored in the aqueous phase. Structures optimized using the Harris and Perdew-Wang local functionals were close to both experimental data and structures optimized using the nonlocal Becke-Lee-Yang-Parr (BLYP) functional. Binding energies calculated with the gradient-corrected BLYP functional were only weakly dependent on the method used for geometry optimization. The approach of using low-level structures coupled with higher level single-point energies was found to reduce computational time by 75% with no loss in accuracy of the computed binding energies.     

Electrochemical investigation of the rate-limiting mechanisms for trichloroethylene and carbon tetrachloride reduction at iron surfaces

The mechanisms involved in reductive dechlorination of carbon tetrachloride (CT) and trichloroethylene (TCE) at iron surfaces were studied to determine if their reaction rates were limited by rates of electron transfer. Chronoamperometry and chronopotentiometry analyses were used to determine the kinetics of CT and TCE reduction by a rotating disk electrode in solutions of constant halocarbon concentration. Rate constants for CT and TCE dechlorination were measured as a function of the electrode potential over a temperature range from 2 to 42 degrees C. Changes in dechlorination rate constants with electrode potential were used to determine the apparent electron-transfer coefficients at each temperature. The transfer coefficient for CT dechlorination was 0.22 +/- 0.02 and was independent of temperature. The temperature independence of the CT transfer coefficient is consistent with a rate-limiting mechanism involving an outer-sphere electron-transfer step. Conversely, the transfer coefficient for TCE was temperature dependent and ranged from 0.06 +/- 0.01 at 2 degrees C to 0.21 +/- 0.02 at 42 degrees C. The temperature-dependent TCE transfer coefficient indicated that its reduction rate was limited by chemical dependent factors and not exclusively by the rate of electron transfer. In accord with a rate-limiting mechanism involving an electron-transfer step, the apparent activation energy (Ea) for CT reduction decreased with decreasing electrode potential and ranged from 33.0 +/- 1.6 to 47.8 +/- 2.0 kJ/mol. In contrast, the Ea for TCE reduction did not decline with decreasing electrode potential and ranged from 29.4 +/- 3.4 to 40.3 +/- 3.9. The absence of a potential dependence for the TCE Ea supports the conclusion that its reaction rate was not limited by an electron-transfer step. The small potential dependence of TCE reaction rates can be explained by a reaction mechanism in which TCE reacts with atomic hydrogen produced from reduction of water.     

Understanding the drying kinetics of phenolic compounds in strawberries: An experimental and density functional theory study

The deterioration of food quality during food processing has been the subject of intense research. Changes in the secondary metabolites present in foodstuff have been identified during drying (phenolic and anthocyanin compounds). To explain the effect of temperature on the phenolic and anthocyanin content in strawberries during drying, a molecular dynamics simulation study at the Density Functional Theory (DFT) level was performed and validated with experimental data. Solar drying and tray drying at different temperatures were investigated. The total phenolic compounds (TPC), anthocyanins, and antioxidant activity were measured. Aromaticity indexes were obtained to rank the stability during the simulated drying process. The changes observed in the aromatic behavior were related to destabilization of the compounds, which leads to the degradation process observed experimentally. These results are of utility in the selection of the operating conditions to prevent TPC deterioration and to understand the role played by the electronic structure properties of anthocyanin molecules on their degradation.     

环木菠萝烯醇阿魏酸酯分子结构性质的密度泛函理论研究

该文基于密度泛函理论对环木菠萝烯醇阿魏酸酯分子结构、反应活性位点(分子表面静电势、原子电荷、前线分子轨道、概念密度泛函活性指数)、分子内弱作用力、芳香性以及红外光谱进行分析.结果表明,环木菠萝烯醇阿魏酸酯酚羟基氢原子(H99)附近具有分子表面静电势极大点(53.580 kcal/mol),且H99带有较高正电荷(0.3...     

Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy

This study investigated the reaction mechanisms of nitrate (NO3-) with zerovalent iron (ZVI) media under conditions relevantto groundwatertreatment using permeable reactive barriers (PRB). Reaction rates of NO3- with freely corroding and with cathodically or anodically polarized iron wires were measured in batch reactors. Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the reactions occurring on the iron surfaces. Reduction of NO3- by corroding iron resulted in near stoichiometric production of NO2-, which did not measurably react in the absence of added Fe(II). Increasing NO3- concentrations resulted in increasing corrosion currents. However, EIS and Tafel analyses indicated that there was little direct reduction of NO3- at the ZVI surface, despite the presence of water reduction. This behavior can be attributed to formation of a microporous oxide on the iron surfaces that blocked reduction of NO3- and NO2- but did not block water reduction. This finding is consistent with previous observations that NO3- impedes reduction of organic compounds by ZVI. Nitrite concentrations greater than 4 mM resulted in anodic passivation of the iron, but passivation was not observed with NO3- concentrations as high as 96 mM. This indicates that the passivating oxide preventing NO3- reduction was permeable toward cation migration. Since reaction with Fe(0) can be excluded asthe mechanism for NO3- and NO2- reduction, reaction with Fe(II)-containing oxides coating the iron surface is the most likely reaction mechanism. This suggests that short-term batch tests requiring little turnover of reactive sites on the iron surface may overestimate long-term rates of NO3- removal because the effects of passivation are not apparent in batch tests conducted with high initial Fe(II) to NO3- ratios.     

UV/Visible spectra of natural polyphenols: A time-dependent density functional theory study

In addition to their numerous biological activities, natural and hemisynthetic polyphenols contribute to the large variety of colours (from red to violet) in nature (e.g., fruit, vegetables, leaves and petals). In order to understand the colour variation attributed to the multitude of chemical structures of this wide class of compounds, time-dependent density functional quantum-chemical calculations at the B3P86/6-311+G(d,p) level of theory appears as a relevant and efficient tool. The UV/Vis properties of 33 polyphenols were systematically investigated, including mainly flavonoids, isoflavonoids and flavonolignans. On the basis of molecular orbital analysis we established the structure-property relationship, inter alia showing the role of π orbital (de-)localisation, mesomeric (+M) effects of hydroxyl groups and structural modification of the molecular backbone. The results might help in the future, for example, for the prediction of novel hemisynthetic compounds.     

Fortification of vegetarian diets for increasing bioavailable iron density using green leafy vegetables

There is a high prevalence of iron deficiency anaemia in many developing countries today; especially in vegetarian women. The major cause of this state is low bioavailability of nonheme iron from vegetarian diets. An investigation was undertaken to improve bioavailable contents of nonheme iron from vegetarian meals. Forty-eight meals with combinations of roti (unleavened whole cereal pancake) of one of the six cereals and one of the four commonly consumed green leafy vegetables (GLV) along with 35 meals with cereal roti and fruit vegetable/legume were tested for their in vitro dialysability of iron using simulated gastrointestinal conditions and standardised protocol with ⁵⁹Fe as a tracer. Average bioavailable iron density of GLV-based meals was significantly higher (1.2±0.7 mg /1000 kcal) as against the value in prevailing dietary patterns having cereal-legume or cereal-fruit vegetable combinations (0.36±0.17 mg/1000 kcal, p⩽0.001). Around 31 GLV-based meals were identified as having higher amounts of bioavailable iron density than 0.75 mg/1000 kcal. Thus, one such GLV-based meal per day will increase gross as well as bioavailable iron intake which will help in meeting daily requirements of iron especially for vegetarian women of reproductive age.     

Understanding chromate reaction kinetics with corroding iron media using Tafel analysis and electrochemical impedance spectroscopy

The kinetics of chromate removal from contaminated water by zerovalent iron media are not well understood. This study investigated the reactions occurring on iron surfaces in chromate solutions in order to understand the removal kinetics and to assess the long-term ability of zerovalent iron for removing Cr(VI) from contaminated water. Tafel polarization analysis and electrochemical impedance spectroscopy were used to determine the corrosion rates and charge-transfer resistances associated with Cr(VI) removal by iron wires suspended in electrolyte solutions with initial Cr(VI) concentrations of 10,000 microg/L. The condition of the iron surfaces at the time of their exposure to chromate determined the effectiveness of the iron for chromate removal. Both iron coated with a water-formed oxide and initially oxide-free iron were effective for chromate removal. However, iron coated with an air-formed oxide was an order of magnitude less effective for removing soluble chromium. Although iron with the air-formed oxide was largely passivated with respect to chromate removal, its overall rate of corrosion was similar to that for iron with the other initial surface conditions. This indicates that water, but not chromate, was able to penetrate the air-formed oxide coating and access cathodic sites. For all initial surface conditions, addition of chromate decreased the corrosion rate by increasing the corrosion potential and the anodic charge transfer resistance. Although Cr(VI) is a strong oxidant rates of iron corrosion were not proportional to the aqueous Cr(VI) concentrations due to anodic control of iron corrosion. Under anodically controlled conditions, the rate of corrosion was limited by the rate at which Fe2+ could be released at anodic sites and not by the rate at which oxidants were able to accept electrons. This study shows that the zero order removal kinetics of Cr(VI) by iron media can be explained by anodic control of iron corrosion and the concomitant anodic control of Cr(VI) reduction.     

Characterization and density functional theory study of the antioxidant activity of quercetin and its sugar-containing analogues

Inhibition of free radicals using quercetin, hyperin and rutin is examined to determine their antioxidant effects and the structure–activity relationships of flavonoids. Two species of the free radicals are used, including hydroxyl radical (·OH) and superoxide anion radical (O₂ ^?·). Density functional theory calculations under the level of B3LYP/6-311G (d) have been utilized to explore the structure, molecular properties and antioxidant abilities of the three flavonoids. Bond dissociation enthalpy (BDE) and frontier molecular orbital energy gap are investigated. They are compared with the experiment results assayed by the spectrophotometric. All of the flavonoids show a high activity on inhibiting ·OH and O₂ ^?· radicals. Scavenging activity determined by half maximal inhibitory concentration (IC₅₀) values of the three flavonoids decreases in the order: quercetin > hyperin > rutin. The calculations show that quercetin owns the lowest BDE values, which agree well with the experimental results of antioxidant activity determined by IC₅₀ values.     

Assets of imputation to ultra-high density for productive and functional traits

The aim of this study was to evaluate different-density genotyping panels for genotype imputation and genomic prediction. Genotypes from customized Golden Gate Bovine3K BeadChip [LD3K; low-density (LD) 3,000-marker (3K); Illumina Inc., San Diego, CA] and BovineLD BeadChip [LD6K; 6,000-marker (6K); Illumina Inc.] panels were imputed to the BovineSNP50v2 BeadChip [50K; 50,000-marker; Illumina Inc.]. In addition, LD3K, LD6K, and 50K genotypes were imputed to a BovineHD BeadChip [HD; high-density 800,000-marker (800K) panel], and with predictive ability evaluated and compared subsequently. Comparisons of prediction accuracy were carried out using Random boosting and genomic BLUP. Four traits under selection in the Spanish Holstein population were used: milk yield, fat percentage (FP), somatic cell count, and days open (DO). Training sets at 50K density for imputation and prediction included 1,632 genotypes. Testing sets for imputation from LD to 50K contained 834 genotypes and testing sets for genomic evaluation included 383 bulls. The reference population genotyped at HD included 192 bulls. Imputation using BEAGLE software (http://faculty.washington.edu/browning/beagle/beagle.html) was effective for reconstruction of dense 50K and HD genotypes, even when a small reference population was used, with 98.3% of SNP correctly imputed. Random boosting outperformed genomic BLUP in terms of prediction reliability, mean squared error, and selection effectiveness of top animals in the case of FP. For other traits, however, no clear differences existed between methods. No differences were found between imputed LD and 50K genotypes, whereas evaluation of genotypes imputed to HD was on average across data set, method, and trait, 4% more accurate than 50K prediction, and showed smaller (2%) mean squared error of predictions. Similar bias in regression coefficients was found across data sets but regressions were 0.32 units closer to unity for DO when genotypes were imputed to HD density. Imputation to HD genotypes might produce higher stability in the genomic proofs of young candidates. Regarding selection effectiveness of top animals, more (2%) top bulls were classified correctly with imputed LD6K genotypes than with LD3K. When the original 50K genotypes were used, correct classification of top bulls increased by 1%, and when those genotypes were imputed to HD, 3% more top bulls were detected. Selection effectiveness could be slightly enhanced for certain traits such as FP, somatic cell count, or DO when genotypes are imputed to HD. Genetic evaluation units may consider a trait-dependent strategy in terms of method and genotype density for use in the genome-enhanced evaluations.     

Electronic polarizability as a predictor of biodegradation rates of dimethylnaphthalenes. an ab initio and density functional theory study

Geometries, relative stabilities, electronic excited states, atomic charges, and electronic dipole polarizabilities of dimethylnaphthalene (DMN) isomers have been calculated in gas and aqueous phases by ab initio and DFT methods. At the highest levels of calculation, alpha,alpha-DMN (2,6-DMN, 2,7-DMN, and 2,3-DMN) are the lowest energy isomers, while 1,8-DMN is the less stable by 7-8 kcal mol(-1). The averaged electronic polarizability, , is dependent on the position of the methyl substituents, increasing in the order alpha, alpha-DMN < (a, beta-DMN < beta, beta-DMN, with the largest values being obtained for 2,6-DMN and 2,7-DMN, while the lowest value is calculated for 1,8-DMN isomer. Polarizability differences among the isomers have been related to their spectroscopic properties. The computed value of DMN isomers, with the notable exception of 2,7-DMN, is in excellent linear relationship with the observed first-order biomass-normalized rate coefficient, a parameter related to the rate of biodegradation of polycyclic aromatic hydrocarbons (PAHs). This result suggests that electronic polarizability may be a useful tool for prediction of biodegradation trends of series of compounds, and inductive and dispersive interactions play a fundamental role in the biodegradation process of DMNs. The present approach is potentially suitable for applications on PAHs with higher molecular weight.     

Iron-fortified parboiled rice – A novel solution to high iron density in rice-based diets

The present study pioneered an investigation of a novel and cost-effective approach to fortify Fe in rice and to greatly improve Fe nutrition in rice-based diets through parboiling, though it remains at its preliminary phase. Rice grains of seven cultivars were parboiled in deionised water containing different levels of Fe chelate made by mixing different proportions of Fe sulfate (FeSO₄) with ethylenediaminetetra-acetic acid disodium salt (Na₂EDTA). Adding Fe to the parboiling water resulted in an increased Fe concentration in the most grain, effectively where FeSO₄ and Na₂EDTA were mixed at 2:1 molar ratio (11.16 g Fe per 100 g raw paddy grain). This treatment resulted in Fe concentrations in white rice milled for 60 s and 120 s, which were 20–50 times higher than those in the unfortified milled raw rice grains. The Fe concentrations in milled rice grains were 50–150 mg Fe kg⁻¹ in 60 s milled grains with a slight reduction in 120 s milled grains. Perls Prussian blue staining of the cross section of Fe-fortified parboiled rice grains suggested inward movement of added Fe into the endosperm through the apoplastic pathway in the dorsal region of the rice grain. The retention rates of fortified Fe varied among the different cultivars, possibly due to different physical–chemical properties of the grains. The percentages of soluble fraction of the total Fe were higher than 50% in all cultivars tested, indicating its high bioavailability potential, though it remains to be evaluated. The present findings provided a preliminary basis for further investigation of this innovative technique, before its adoption by parboiled rice industry, such as optimising the levels of Fe addition and industrial process and Fe bioavailability in Fe-fortified-parboiled rice.     

Influence of ferric iron on complete dechlorination of trichloroethylene (TCE) to ethene: Fe(III) reduction does not always inhibit complete dechlorination

The effects of Fe(III) reduction on TCE, cis-DCE, and VC dechlorination were studied in both contaminated aquifer material and enrichment cultures. The results from sediment batch experiments demonstrated that Fe(III) reduction did not inhibit complete dechlorination. TCE was reduced concurrently with Fe(III) in the first 40 days of the incubations. While all incubations (plus and minus Fe(III)) generated approximately the same mass of ethene within the experimental time frame, Fe(III) speciation (ferrihydrite versus Fe(III)-NTA) had an impact on daughter product distribution and dechlorination kinetics. 16S rRNA gene clone library sequencing identified Dehalococcoides and Geobacteraceae as dominant populations, which included G. lovleyi like organisms. Quantitative PCR targeting 16S rRNA genes and Reductive Dehalogenase genes (tceA, bvcA, vcrA) indicated that Dehalococcoides and Geobacteraceae were enriched concurrently in the TCE-degrading, Fe(III)-reducing sediments. Enrichment cultures demonstrated that soluble Fe(III) had a greater impact on cis-DCE and VC reduction than solid-phase Fe(III). Geobacteraceae and Dehalococcoides were also coenriched in the liquid cultures, and the Dehalococcoides abundance in the presence of Fe(III) was not significantly different from those in the cultures without Fe(III). Hydrogen reached steady-state concentrations most amenable to complete dechlorination very quickly when Fe(III) was present in the culture, suggesting that Fe(III) reduction may actually help dechlorination. This was contrasted to hydrogen levels in nitrate-amended enrichments, in which hydrogen concentration was too low for any chlororespiration.     

利用铁、铜间相互作用减轻烤烟铜毒害的研究

采用温室溶液培养方法,研究利用铁、铜间相互作用减轻烤烟铜毒害。试验结果显示,K326品种Cu2 毒害临界值在1.0-1.2mg/L之间。在低浓度Cu2 (0.1-1.2mg/L)时,烟株吸铁总量增加;高浓度Cu2 (≥1.4mg/L)时,吸铁总量降低。溶液中添加过量的Fe3 (5.61mg/L和11.23mg/L)后,烟株的吸铁量显著增加,而吸铜量明显减少,铁和铜元素由根系向地上部的转运增加,生物量增加4-7倍,可以明显减轻Cu2 的毒害。因此,利用铁、铜间相互作用减轻烤烟铜毒害是可行的。     

CO2-filling capacity and selectivity of carbon nanopores: synthesis, texture, and pore-size distribution from quenched-solid density functional theory (QSDFT)

Porous carbons synthesized by KOH activation of petroleum coke can have high surface areas, over 3000 m(2)/g, and high CO(2) sorption capacity, over 15 wt % at 1 bar. This makes them attractive sorbents for carbon capture from combustion flue gas. Quenched solid density functional theory (QSDFT) analysis of high-resolution nitrogen-sorption data for such materials leads to the conclusion that it is the pores smaller than 1 nm in diameter that fill with high-density CO(2) at atmospheric pressure. Upon increasing pressure, larger and larger pores are filled, up to about 4 nm at 10 bar. An ideal CO(2)/N(2) selectivity of such carbon materials tends to decrease substantially upon increasing pressure, for example, from about 8-10 at 1 bar to about 4-5 at 10 bar. All in all, this work confirms the robust CO(2)-filling properties of porous carbon sorbents, their low-pressure selectivity advantages, and points to the critical role of <1 nm pores that can be controlled with activation conditions.     

Gas-phase formaldehyde adsorption isotherm studies on activated carbon: correlations of adsorption capacity to surface functional group density

Formaldehyde (HCHO) adsorption isotherms were developed for the first time on three activated carbons representing one activated carbon fiber (ACF) cloth, one all-purpose granular activated carbon (GAC), and one GAC commercially promoted for gas-phase HCHO removal. The three activated carbons were evaluated for HCHO removal in the low-ppm(v) range and for water vapor adsorption from relative pressures of 0.1-0.9 at 26 °C where, according to the IUPAC isotherm classification system, the adsorption isotherms observed exhibited Type V behavior. A Type V adsorption isotherm model recently proposed by Qi and LeVan (Q-L) was selected to model the observed adsorption behavior because it reduces to a finite, nonzero limit at low partial pressures and it describes the entire range of adsorption considered in this study. The Q-L model was applied to a polar organic adsorbate to fit HCHO adsorption isotherms for the three activated carbons. The physical and chemical characteristics of the activated carbon surfaces were characterized using nitrogen adsorption isotherms, X-ray photoelectron spectroscopy (XPS), and Boehm titrations. At low concentrations, HCHO adsorption capacity was most strongly related to the density of basic surface functional groups (SFGs), while water vapor adsorption was most strongly influenced by the density of acidic SFGs.     

Utilisation of beef lung protein powder as a functional ingredient to enhance protein and iron content of fresh pasta

Beef lungs are an underutilised co-product of the meat industry that could be used as an ingredient to supplement the protein content of cereal foods. Beef lung powder (BLP) had a protein content of 87% (dry weight basis), an amino acid score of 1, and contained 1 mg g⁻¹ iron. Fresh semolina pasta was used as a model food, and BLP was incorporated up to 20%. Incorporation of 10% BLP improved the indispensable amino acid score of the pasta from 0.48 to 0.91. At that level of incorporation, higher cooking loss and redder (increased ‘a’ value) and darker (decreased ‘L’ value) colour resulted. The fresh pasta with BLP had a lower glycaemic response compared to control samples. BLP improved the functional value of the fresh pasta and is a potential ingredient in the development of new food products.     

利用红曲菌及植物乳酸杆菌生产功能性镇江香醋工艺的研究

在基本不改变原有镇江香醋生产工艺和控制参数的条件下,添加安卡红曲菌和植物乳酸杆菌,从而保持镇江香醋的原有风味,同时提高莫纳考林K和γ-氨基丁酸的含量,增强镇江香醋的功能性。     

Use of iron oxides to influence the weathering characteristics of wood surfaces: a systematic survey of particle size,crystal shape and concentration

Iron oxide pigments may be an alternative treatment for limiting weathering of wood surfaces instead of stains or clear coatings. An earlier study suggested the ability of iron oxides to protect against discoloration varied with particle size. In this study, iron oxides with different crystal shapes and particle sizes were investigated along with a carbon black pigment. Loblolly pine (Pinus taeda L.) samples were impregnated with water borne iron oxide dispersions, exposed to predetermined amounts of solar radiation in the high desert of Eastern Oregon, and then evaluated for discoloration, checking and changes in chemical composition. The results from this observational study suggest that much higher levels of iron oxide are required than previously thought to prevent discoloration and limit lignin degradation. Large particle sizes led to greater opacity and provided greater protection, but no iron oxide protected as well as carbon black. The findings also suggested that iron oxides had no effect on checking, indicating that the mechanisms of discoloration and checking were not directly related.