Atomistic simulations of calcium uranyl(VI) carbonate adsorption on calcite and stepped-calcite surfaces

Adsorption of actinyl ions onto mineral surfaces is one of the main mechanisms that control the migration of these ions in environmental systems. Here, we present computational classical molecular dynamics (MD) simulations to investigate the behavior of U(VI) in contact with different calcite surfaces. The calcium-uranyl-carbonate [Ca(2)UO(2)(CO(3))(3)] species is shown to display both inner- and outer-sphere adsorption to the flat {101?4} and the stepped {314?8} and {31?2?16} planes of calcite. Free energy calculations, using the umbrella sampling method, are employed to simulate adsorption paths of the same uranyl species on the different calcite surfaces under aqueous condition. Outer-sphere adsorption is found to dominate over inner-sphere adsorption because of the high free energy barrier of removing a uranyl-carbonate interaction and replacing it with a new uranyl-surface interaction. An important binding mode is proposed involving a single vicinal water monolayer between the surface and the sorbed complex. From the free energy profiles of the different calcite surfaces, the uranyl complex was also found to adsorb preferentially on the acute-stepped {314?8} face of calcite, in agreement with experiment.     

Characterization of Hydroxyethyl Starch by Polymer Analysis for Use as a Plasma Volume Expander

Hydroxyethyl starch is currently finding increasing use as a basis material for plasma volume expanders. In clinical applications it is desirable to have a precise knowledge of the steric and chemical structure, as these affect the pharmacokinetics and pharmacology. Characterization involved the determination of the mean molar masses and distribution functions of various hydroxyethyl starches, with molar masses ranging from 40,000 g/mol to 200,000 g/mol and degrees of substitution from 0.38 to 0.64, by means of size exclusion chromatography followed by double detection (MALLS/RI). Hydrodynamic data (Staudinger indices, Huggins constants and equivalent diameters) were determined by viscometric means. The chemical structure of the hydroxyethyl starches were clarified by {¹H}-¹³C NMR spectroscopy. Signal assignment for the {¹H}-¹³C NMR spectra made it possible to carry out an absolute determination of the molar, mean and partial degrees of substitution and the degree of branching. The partial degrees of substitution of the carbon atom C-2 was found to constitute between 60 and 80% of the total degree of substitution. This value is significantly larger than the partial degrees of substitution at the atoms C-3 and C-6, which were found to contribute up to approximately 10% and 20% respectively of the total degree of substitution. Degrees of branching ranging from 3.1% to 5.5% were detected.     

Inhibition of calcite precipitation by natural organic material: kinetics, mechanism, and thermodynamics

The inhibition of calcite precipitation by natural organic material (NOM) in solutions seeded with calcite was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25 degrees C and 1 atm suggest that the interaction between NOM molecules and the calcite surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of calcite precipitation was dictated bythe balance between the enthalpy change and the entropy change of the adsorption reaction.     

Use of organic acids for the control of Clostridium perfringens in cooked vacuum-packaged restructured roast beef during an alternative cooling procedure

This study was conducted to determine how well Clostridium perfringens spores germinate and grow in restructured roast beef treated with different commercial organic salts during an alternative chilling procedure. The meat was prepared according to an industrial recipe (10% water, 1.5% sodium chloride, and 0.5% sodium triphosphate). The base meat was treated with sodium citrate at 2 or 4.8% (wt/wt), buffered to a pH of 5.6, 5.0, or 4.4 (six treatments); a 60% (wt/wt) solution of sodium lactate at 2 or 4.8% (wt/wt); sodium acetate at 0.25% (wt/wt); or sodium diacetate at 0.25% (wt/wt). Untreated meat was used as a control. Meat samples were inoculated with a three-strain cocktail of C. perfringens spores (strains ATCC 10388, NCTC 8238, and NCTC 8239). Meat was vacuum packaged in bags and cooked in a stirred water bath to an internal temperature of 75 degrees C for 20 min, and then the bags were cooled from 54.4 to 4.4 degrees C within 18 h. Samples were taken after inoculation, after cooking, and after chilling. Spore and vegetative cell counts were obtained after incubation at 37 degrees C for 8 to 10 h in Fung's Double Tubes containing tryptose sulfite agar without egg yolk enrichment. Cooking was not sufficient to eliminate C. perfringens spores. Over the 18-h cooling period, sodium citrate, sodium lactate, and sodium diacetate reduced the growth of C. perfringens to < 1 log unit, a growth level that meets U.S. Department of Agriculture performance standards. The use of sodium citrate or sodium lactate at a concentration of > or = 2% (wt/wt) inhibited C. perfringens growth over the 18-h cooling period.     

Neptunium(V) coprecipitation with calcite

Coprecipitation experiments of Np(V) and U(VI) with calcite were performed in mixed-flow reactors under steady state conditions at room temperature for up to 400 h at precipitation rates of 1.0 x 10(-8) to 6.8 x 10(-8) mol/(m2 s). The saturation index with respect to calcite varied between 0.04 and 0.95. Initial Np(V) or U(VI) concentrations were 1 micromol/L, 0.01 mol/L NaCl was used as background electrolyte, and pH ranged from 7.8 to 12.8. Partition coefficients for Np(V) were in the range of 0.5-10.3, compared to 0.02 for U(VI). Np L(III) and U L(III) EXAFS were used to characterize the local structural environment of the incorporated actinides. In the case of U(VI), the structural environment is not unambiguously characterized. Our data suggest that Np(V) ions occupy calcium lattice sites. The two axial oxygen atoms of the linear neptunyl moiety substitute two calcite carbonate groups in the first coordination sphere. Thus, four carbonate groups coordinate the neptunyl-ion in a monodentate fashion with four equatorial oxygen atoms (Oeq) at 2.4 A and associated carbon atoms (C) at 3.2 A. The interatomic distances indicate slight structural relaxation of the carbonate groups from their ideal sites. A similar structural model has been reported for U(VI) incorporated into natural calcite.     

Evidence of a stable uranyl site in ancient organic-rich calcite

The mechanism of uranium (U) incorporation into calcite (calcium carbonate) is of fundamental importance to the fate and transport of U at the surface and in the shallow subsurface and has implications for (a) the accuracy of U-Pb and U-series isotope ratio methods used to determine the ages of ancient deposits and (b) potential remediation strategies based on sequestration of U in the subsurface. Extended X-ray absorption fine structure (EXAFS) spectroscopy is uniquely suited to the study of U-calcite systems. The sensitivity of the EXAFS spectrum to the local atomic Ca coordination about U(VI) in the calcite structure results in an increase in the number and amplitude of Ca signals as the U(VI) becomes more ordered within the crystal structure. Our X-ray microprobe (10-microm) measurements of an ancient 298 million-year-old organic-rich calcite (calcrete) clearly revealed three coordination shells of Ca atoms, defining a well-ordered calcite structure about uranyl to a distance of approximately 6.5 angstroms. These results indicate that uranyl is incorporated at the Ca2+ site in calcite and that the uranyl environment may evolve over long time scales, becoming more calcite-like and more stable for long-term sequestration of uranium. These results therefore validate U-related dating methods and show that calcite can be effective at sequestering U in vadose zone sediments.     

有机溶剂中脂肪酶催化辛酸辛酯的合成

以猪胰腺脂肪酶为催化剂合成辛酸辛酯。研究有机溶剂、反应温度、加水量、加酶量、反应时间、底物浓度及底物物质的量比7 个因素对酶促酯化反应的影响,优化得到最佳合成条件。结果表明：最佳反应温度45℃、正己烷有机溶剂、加水量29μL、酶质量浓度2.314g/L、反应时间24h、辛酸与辛醇物质的量比为1:1.2～1:1.5、辛酸浓度为0.23～0.33mol/L。在优化条件下,辛酸的转化率达到98.12% 以上,并通过IR、1H NMR、13CNMR 谱表征了产物结构。酶催化法能在温和的反应条件下合成高产率的酯。     

Optimizing Conditions for TEMPO/NaOCl-Mediated Chemoselective Oxidation of Primary Alcohols in Sweet Potato Residue

Sweet potato residue (SPR), a by-product of the sweet potato-based beverage industry, contains health-beneficial dietary fiber, but it has been limited to secondary-use applications due to poor water solubility. The water solubility of polysaccharides in SPR increases following chemoselective oxidation of the primary alcohol group through 2,2,6,6-tetramethyl-1-piperidinyl oxoammonium ion (TEMPO)/sodium hypochlorite (NaOCl)-mediated oxidation. In the present study, a central composite experimental design was used to optimize conditions for chemoselective oxidation of SPR with three variables, including TEMPO concentration (0.05–0.25 mmol, X ₁), NaOCl concentration (4.0–12.0 mmol, X ₂), and pH of the reactants (9.5–11.5, X ₃). The quadratic polynomial model equation describing this relationship was as follows: $ {\text{degree of oxidation}}\left( \% \right) = - {871}.{929} + {975}.{4}0{5}{X_{{1}}} + {2}0.{7181}{X_{{2}}} + {143}.{358}{X_{{3}}}-{12}0.{682}X_1^2-0.{59}0{426}X_2^2-{5}.{78182}X_3^2-{7}.{725}00{X_{{1}}}{X_{{2}}}-{76}.{4}000{X_{{1}}}{X_{{3}}}-0.{55}0000{X_{{2}}}{X_{{3}}}\left( {{R^{{2}}} = 0.{9633}} \right) $ . The maximum degree of oxidation (98.3%) was consistent with the expected value (100%) and was obtained from a TEMPO concentration, NaOCl concentration, and reactant pH of 0.1980 mmol, 9.6236 mmol, and 10.6271, respectively. The introduction of a C6 carboxyl group without oxidation of the secondary alcohols was confirmed by ¹³C nuclear magnetic resonance and Fourier transform infrared spectroscopy. The water solubility of the oxidized products was 99.95%, whereas that of native SPR was <26.45%. The initial velocity of the oxidation showed a strong linear relationship (R ²?=?0.9239) with the degree of oxidation, indicating that initial velocity could be another quantitative index for determining the degree of oxidation and productivity of oxidized SPR. These results suggest that oxidized SPR could be used as a new water-soluble dietary fiber in the food industry.     

Effect of spices and organic acids on the growth of Clostridium perfringens during cooling of cooked ground beef

This study evaluated the effect of organic acids and spices, alone or combined, on Clostridium perfringens growth in cooked ground beef during alternative cooling procedures. Ground beef was inoculated with a three-strain cocktail of C. perfringens (ATCC 10388, NCTC 8238, and NCTC 8239) at 2 log spores per g and prepared following an industrial recipe (10% water, 1.5% sodium chloride, and 0.5% sodium triphosphate [wt/wt]). Treatments consisted of the base meat plus combinations of commercial solutions of sodium lactate or sodium citrate (0 or 2%, wt/wt) with chili, garlic and herbs, curry, oregano, or clove in commercial powder form (0 or 1%, wt/wt). Untreated meat was used as a control. Vacuum-packaged samples of each treatment were cooked (75 degrees C for 20 min) and cooled from 54.4 to 7.2 degrees C in 15, 18, or 21 h. Spore counts were estimated after inoculation, cooking, and cooling. All treatments containing sodium citrate reduced the population of C. perfringens about 0.38 to 1.14 log units during each of the three cooling procedures. No sodium citrate and spice treatment combinations showed antagonisms or synergisms. Regardless of the cooling time, the control ground beef or treatments with any of the five spices alone supported C. perfringens growth above the U.S. Department of Agriculture stabilization guidelines of 1 log unit. Except for the 21-h cooling period, addition of sodium lactate prevented C. perfringens growth over 1 log unit. Depending on the cooling time and spice, some combinations of sodium lactate and spice kept C. perfringens growth below 1 log unit.     

高速逆流色谱分离制备胡椒中的胡椒碱

采用高速逆流色谱(high-speed countercurrent chromatography,HSCCC)法从胡椒中分离制备胡椒碱。HSCCC的溶剂系统条件为正己烷-乙酸乙酯-甲醇-水(1:1:1:1,V/V)。从5g粗提物中可一次分离得到纯度为98.72%的胡椒碱单体1.58g,分离得到的胡椒碱结构经电喷雾质谱以及核磁共振氢谱(1H NMR)和碳谱(13C NMR)进行鉴定。该法制备量大、分离效率高,对胡椒碱在食品医药领域的应用具有重要意义。     

Impact of source and level of calcium fortification on the heat stability of reconstituted skim milk powder

Calcium enrichment of food and dairy products has gained interest with the increased awareness about the importance of higher calcium intake. Calcium plays many important roles in the human body. Dairy products are an excellent source of dietary calcium, which can be further fortified with calcium salts to achieve higher calcium intake per serving. However, the addition of calcium salts can destabilize food systems unless conditions are carefully controlled. The effect of calcium fortification on the heat stability of reconstituted skim milk was evaluated, using reconstituted skim milks with 2 protein levels: 1.75 and 3.5% (wt/wt) prepared using low and high heat powders. Calcium carbonate, phosphate, lactate, and citrate were used for fortification at 0.15, 0.18, and 0.24% (wt/wt). Each sample was analyzed for solubility, heat stability, and pH. The addition of phosphate and lactate salts lowered the pH of milk, citrate did not have any major effect, and carbonate for the 1.75% protein samples increased the pH. In general, changes in solubility and heat stability were associated with changes in pH. Calcium addition decreased the solubility and heat stability. However, interestingly, the presence of carbonate salt greatly increased the heat stability for 1.75% protein samples. This is due to the neutralizing effect of calcium carbonate when it goes into solution. The results suggested that the heat stability of milk can be affected by the type of calcium salt used. This may be applied to the development of milk-based calcium enriched beverages.     

Effects of the biologically produced polymer alginic acid on macroscopic and microscopic calcite dissolution rates

Dissolution of carbonate minerals has significant environmental effects. Microorganisms affect carbonate dissolution rates by producing extracellular metabolites, including complex polysaccharides such as alginic acid. Using a combined atomic force microscopy (AFM)/flowthrough reactor apparatus, we investigated the effects of alginic acid on calcite dissolution. Macroscopic dissolution rates, derived from the aqueous metal ion concentrations, are 10(-5.5) mol m(-2) s(-1) for 5 < pH < 12 in the absence of alginic acid compared to 10(-4.8) mol m(-2) s(-1) in its presence. The AFM images demonstrate that alginic acid preferentially attacks the obtuse steps of dissolution pits on the calcite surface. In pure water, the obtuse and acute steps retreat at similar rates, and the pits are nearly isotropic except under highly acidic conditions. In alginic acid, the acute step retreat rate is nearly unchanged in comparison to water, whereas the obtuse step retreat rate increases with decreasing pH values. As a result, the pits remain rhombohedral but propagate faster in the obtuse direction. To explain these observations, we propose that alginic acid preferentially forms dissolution active surface complexes with calcium atoms on the obtuse step, which results in anisotropic ligand-promoted dissolution.     

Absence of mobile carbohydrate domains in dry humic substances proven by NMR, and implications for organic-contaminant sorption models

The mobility and domain structure of various standard humic substances have been investigated by 1H and 1H-13C solid-state nuclear magnetic resonance (NMR) experiments. In four dry humic acids, a fulvic acid, a natural organic matter sample, and a whole peat sample, segments that undergo fast, large-amplitude motions account for <9% of the sample. This disproves a previous suggestion, based on 1H NMR data, that flexible domains, presumably carbohydrates, make up >40% of various humic acids; these putative mobile domains were also linked to dual-mode sorption. In particular, neither the polar alkyl (carbohydrate) nor the aromatic components show any fast, large-amplitude mobility. A small fraction of mobile nonpolar alkyl segments identified by us before is the only component undergoing large-amplitude motions, apart from absorbed water that we observe in humic acids exposed to ambient air. 1H-13C wide-line separation NMR shows that, contrary to previous suggestions, the dipolar couplings in the aromatic regions are smaller than in the polar alkyl segments, most likely due to differences in local 1H densities. Series of 1H-13C heteronuclear correlation experiments with 1H spin diffusion reveal close proximity of aromatic and polar alkyl segments in several humic acids, precluding carbohydrate domains on a scale of > 1-nm diameter. In the standard peat humic acid, nonpolar aromatic segments also do not form sorption domains of significant size, while nonpolar aliphatic domains, which we had previously shown to correlate with sorption capacity, have been confirmed.     

柠檬酸钠协同碳酸氢钠替代磷酸盐对法兰克福香肠品质的影响

为减少磷酸盐在肉类加工中的使用,降低乳化肉糜制品中磷酸盐的含量,开发高效的无磷保水剂正逐步成为肉品行业的研究热点.本研究在添加0.2％(w/w)碳酸氢钠的基础上,将柠檬酸钠分别以0.1％、0.15％、0.2％、0.25％和0.3％(w/w)的添加量与碳酸氢钠进行复配,利用其替代传统的磷酸盐,探究其对乳化肉糜制品(以法兰...     

Efficient recovery of CO2 from flue gas by clathrate hydrate formation in porous silica gels

Thermodynamic measurements and NMR spectroscopic analysis were used to show that it is possible to recover CO2 from flue gas by forming a mixed hydrate that removes CO2 preferentially from CO2/N2 gas mixtures using water dispersed in the pores of silica gel. Kinetic studies with 1H NMR microimaging showed that the dispersed water in the silica gel pore system reacts readily with the gas, thus obviating the need for a stirred reactor and excess water. Hydrate phase equilibria for the ternary CO2-N2-water system in silica gel pores were measured, which show that the three-phase hydrate-water-rich liquid-vapor equilibrium curves were shifted to higher pressures at a specific temperature when the concentration of CO2 in the vapor phase decreased. 13C cross-polarization NMR spectral analysis and direct measurement of the CO2 content in the hydrate phase suggested that the mixed hydrate is structure I at gas compositions of more than 10 mol % CO2, and that the CO2 molecules occupy mainly the more abundant 5(12)6(2) cages. This makes it possible to achieve concentrations of more than 96 mol % CO2 gas in the product after three cycles of hydrate formation and dissociation. 1H NMR microimaging showed that hydrate yields of better than 85%, based on the amount of water, could be obtained in 1 h when a steady state was reached, although approximately 90% of this yield was achieved after approximately 20 min of reaction time.     

山东金刚石晶体中氮片晶的分布特征及其表面微形貌

为研究山东蒙阴金伯利岩型金刚石晶体中氮片晶的分布特征,采用红外光谱仪对116粒宝石级金刚石晶体样品中的氮片晶进行分析,并采用微分干涉显微镜观察氮片晶在金刚石表面所具有的物理化学性质及其表面微细结构。结果表明,80.2%的金刚石样品中具有氮片晶;在个别浅褐色、八面体金刚石样品{111}面上观察到平行于[100]晶带方向的长条状蚀像,这些蚀像相互平行,大小不等。显微红外光谱对具长条状蚀像的金刚石样品{111}面的测试结果表明,该类晶体均具有较强的氮片晶的吸收峰(1359~1375cm-1)。综合浅褐色、八面体金刚石样品的红外光谱及其表面微形貌特征,推测长条状蚀像是由氮片晶的出露点受优先选择性腐蚀而致。     

Adsorption of ethylene glycol vapor on (alpha-AI2O3 (0001) and amorphous SiO2 surfaces: observation of molecular orientation and surface hydroxyl groups as sorption sites

Vapor adsorption is an important process influencing the migration and the fates of many organic pollutants in the environment. In this study, adsorption of ethylene glycol (EG) vapor onto single crystal alpha-Al2O3 (0001) and fused SiO2 (amorphous) surfaces was studied with sum frequency generation spectroscopy, a well-suited surface specific technique for probing interfacial phenomena atthe molecular scale. Air-aqueous EG solutions were also investigated to compare to the adsorption at the air-solid interface in the presence of water vapor. The gauche conformer of EG molecules dominates the air-aqueous EG solution interface, and EG molecules act as hydrogen acceptors at the air-liquid interface. Water and surface hydrophilic/ hydrophobic properties play important roles for the adsorption of EG onto silica and alumina surfaces. The adsorbed EG molecules interact in different ways at the two different oxide surfaces. EG molecules weakly physisorb onto the alpha-Al2O3 (0001) surface by forming relatively weak hydrogen bonds with surface water molecules. On the silica surface, the suppression of the silanol OH stretching peak indicates that EG molecules form hydrogen bonds with silanol OH groups.     

Sulfide species as a sink for mercury in lake sediments

The interaction between two contrasting examples of lake sediments and small concentrations of mercury added to the sediments in solution has been studied using X-ray absorption spectroscopy. Whereas one lake (Esthwaite Water) is biologically productive, with a seasonal cycle of phytoplankton activity, including stratification and Fe(III) reduction, and a mineralogy involving quartz, muscovite, and clinochlore, the other (Botany Pond) remains oxic throughout the year. In the latter case, the sediment is predominantly quartz and calcite. Chemical analyses of these two lake sediments reflectthe differences in mineralogy and showthat both contain significant organic carbon (approximately 10-12 wt %) and smaller amounts of S (approximately 0.2-1.7 wt %) and Cl (approximately 0.4-1.1 wt %). Despite the substantial amounts of organic matter in both sediments, the spectroscopic data show that the mercury occurs as a sulfide phase with a local structural environment akin to that in cinnabar. Parallel spectroscopic studies conducted on Hg either coprecipitated or sorbed onto FeS (mackinawite), and on oxidized mackinawite, provide supporting information; the possibility of Hg forming a chloride was eliminated by careful mapping of the relevant elements by an electron microprobe. It appears, therefore, that the high affinity of Hg for S predominates even in substantially oxic environments.     

Abundant and stable char residues in soils: implications for soil fertility and carbon sequestration

Large-scale soil application of biochar may enhance soil fertility, increasing crop production for the growing human population, while also sequestering atmospheric carbon. But reaching these beneficial outcomes requires an understanding of the relationships among biochar's structure, stability, and contribution to soil fertility. Using quantitative (13)C nuclear magnetic resonance (NMR) spectroscopy, we show that Terra Preta soils (fertile anthropogenic dark earths in Amazonia that were enriched with char >800 years ago) consist predominantly of char residues composed of ～6 fused aromatic rings substituted by COO(-) groups that significantly increase the soils' cation-exchange capacity and thus the retention of plant nutrients. We also show that highly productive, grassland-derived soils in the U.S. (Mollisols) contain char (generated by presettlement fires) that is structurally comparable to char in the Terra Preta soils and much more abundant than previously thought (～40-50% of organic C). Our findings indicate that these oxidized char residues represent a particularly stable, abundant, and fertility-enhancing form of soil organic matter.