Near-neutral pH Values Research Articles

Serpentine Geoecology of Eastern North America: A Review

Abstract Serpentine outcrops are model habitats for geoecological studies. While much attention has been paid to serpentine outcrops worldwide, the literature on eastern North American serpentine and associated biota is scant. This review examines the available literature, published and unpublished, on geoecological studies conducted on serpentine in eastern North America, from Newfoundland through Quebec and New England south to Alabama. Most serpentine outcrops in the region have been mapped, but there have been few intensive mineralogical and pedological investigations. The limited soil analyses available suggest elevated levels of heavy metals such as Ni, near-neutral pH values, and Ca∶Mg ratios < 1, characteristic of serpentine soils worldwide. Botanical studies to date have largely focused on floristic surveys and the influence of fire exclusion and grazing on indigenous vegetation. To date, 751 taxa of vascular plants belonging to 92 families have been reported from serpentine outcrops in the regio...

Oligopeptide-porphyrin interactions studied by circular dichroism spectroscopy: the effect of metalloporphyrin axial ligands on peptide matrix conformation

Vibrational (VCD) and electronic circular dichroism (ECD) spectroscopies were used to investigate non-covalent interactions between the cationic tripeptide L-lysyl-L-alanyl-L-alanine (KAA) and the anionic porphyrin meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) in aqueous solution. Also studied were the interactions between KAA and the three metal derivatives of TPPS (copper(II), iron(III), and manganese(III)), each of which has a different number of axial ligands. VCD spectra in the amide I' ( C = O stretching vibration) region are extremely sensitive to peptide conformation, and, consequently, provide direct information about the conformational changes of host oligopeptide matrices caused by electrostatic interaction with guest porphyrin molecules. We found that pure KAA adopts a left-handed polyproline II (PPII) helical conformation when dissolved in aqueous solution at near-neutral pH values. When mixed with metal-free TPPS under the same conditions, VCD intensities were markedly reduced in the amide I' region and a new negative band was observed at 1634 cm−1; both findings indicating the transition of the PPII conformation into a less compact structure having similarities to β-sheet, herein termed a β-sheet-like conformation. In the case of the metal derivatives of TPPS studied, only variations in the VCD intensities in the amide I' region were observed. Compared to the results for pure KAA, the binding of Cu (II) TPPS , which has no axial ligand, resulted in the greatest decrease in amide I' VCD intensity. Nevertheless, the shape of a VCD spectrum characteristic for a PPII conformation was maintained, thereby indicating the presence of an “extended” PPII conformation in the Cu (II) TPPS -KAA complex. Conversely, Mn (III) TPPS , which has two axial ligands, did not significantly affect the PPII conformation of KAA in the Mn (III) TPPS -KAA complex. The effects of the metalation and axial ligation of TPPS on the conformation of KAA in peptide-porphyrin complexes are discussed, together with the results of our ECD study.

Water chemistry of lakes related to active and inactive Mexican volcanoes

Water chemistry of crater lakes, maars and water reservoirs linked to some Mexican volcanoes within and outside the Mexican Volcanic Belt has been determined for several years and examined regarding environmental and volcanic factors. All the analyzed lakes are relatively small with a maximum depth of 65 m, and are located in regions with different climates, from semi-arid to very humid, with altitudes ranging from 100 to more than 4000 m a.s.l. Crater lakes in active volcanoes (El Chichón, Popocatépetl) have very low pH, moderate to high temperatures and major ion concentrations varying with the level of volcanic unrest. Lakes in sub-arid and temperate-arid regions (like maars in Puebla and Guanajuato states) show high alkalinity and pH, with bicarbonate/carbonate, chloride, sodium and magnesium as predominant ions. Lakes located in humid climates (Central Michoacán and Veracruz state) have low mineralization and near-neutral pH values. In general, conservative dissolved ions and conductivity appear to be mostly controlled by precipitation/evaporation and by the ionic concentration of groundwater inputs. Calcium, magnesium, sulfate concentrations and pH are strongly influenced by volcanic-rock or volcanic gas interactions with water. The influence of low-level volcanic activity on crater lakes may be obscured by water–rock interactions, and climatic factors. One of the aims of this paper is to define the relative influence of these factors searching for a reference frame to recognize the early volcanic precursors in volcano-related lakes.

Enhanced adsorption of zinc is associated with aging and lysis of bacterial cells in batch incubations

Bacteria can immobilize significant quantities of trace metals through surface complexation reactions. However, bacterial cell lysis is an integral part of the development process, and the extent to which this process affects adsorbed metals has not been properly investigated. In order to evaluate the effects of cell lysis on metal fixation, bacterial suspensions containing approximately 10 ppm Zn in 0.01 M NaNO(3) were monitored over an one-month period for adsorbed Zn, pH, cell concentration, dissolved organic carbon, NH(3) and dissolved amino acids. Cell concentration decreased with time, in parallel with an increase in dissolved organic carbon. Zn adsorption decreased with time for suspensions with near-neutral (5.5-7.0) initial pH values, consistent with the reduction in cell concentration and/or formation of metal-ligand complexes in solution, with lysis products acting as ligands. However, Zn adsorption increased with time for suspensions with initially low pH (<or=5), and was accompanied by an upward shift in suspension pH. Surface complexation modelling suggests that enhanced adsorption of Zn is predominantly due to the increase in pH, with ternary surface complexation at pH values below the pK(a) of the carboxyl surface sites. The increase in pH is due to production of ammonia, and/or proton buffering by the amphoteric cytoplasmic compounds. The observed changes may have implications for understanding metal sequestration during remineralisation of organic matter in nature.

Solubility products of amorphous ferric arsenate and crystalline scorodite (FeAsO 4 · 2H 2O) and their application to arsenic behavior in buried mine tailings

Published solubility data for amorphous ferric arsenate and scorodite have been reevaluated using the geochemical code PHREEQC with a modified thermodynamic database for the arsenic species. Solubility product calculations have emphasized measurements obtained under conditions of congruent dissolution of ferric arsenate (pH < 3), and have taken into account ion activity coefficients, and ferric hydroxide, ferric sulfate, and ferric arsenate complexes which have association constants of 10 4.04 (FeH 2AsO 4 2+), 10 9.86 (FeHAsO 4 +), and 10 18.9 (FeAsO 4). Derived solubility products of amorphous ferric arsenate and crystalline scorodite (as log K sp) are −23.0 ± 0.3 and −25.83 ± 0.07, respectively, at 25 °C and 1 bar pressure. In an application of the solubility results, acid raffinate solutions (molar Fe/As = 3.6) from the JEB uranium mill at McClean Lake in northern Saskatchewan were neutralized with lime to pH 2–8. Poorly crystalline scorodite precipitated below pH 3, removing perhaps 98% of the As(V) from solution, with ferric oxyhydroxide (FO) phases precipitated starting between pH 2 and 3. Between pH 2.18 and 7.37, the apparent log K sp of ferric arsenate decreased from −22.80 to −24.67, while that of FO (as Fe(OH) 3) increased from −39.49 to −33.5. Adsorption of As(V) by FO can also explain the decrease in the small amounts of As(V)(aq) that remain in solution above pH 2–3. The same general As(V) behavior is observed in the pore waters of neutralized tailings buried for 5 yr at depths of up to 32 m in the JEB tailings management facility (TMF), where arsenic in the pore water decreases to 1–2 mg/L with increasing age and depth. In the TMF, average apparent log K sp values for ferric arsenate and ferric hydroxide are −25.74 ± 0.88 and −37.03 ± 0.58, respectively. In the laboratory tests and in the TMF, the increasing crystallinity of scorodite and the amorphous character of the coexisting FO phase increases the stability field of scorodite relative to that of the FO to near-neutral pH values. The kinetic inability of amorphous FO to crystallize probably results from the presence of high concentrations of sulfate and arsenate.

Abiotic degradation of pentachloronitrobenzene by Fe(III): reactions on goethite and iron oxide nanoparticles.

Pentachloronitrobenzene is a fungicide that is degraded in anoxic soils and sediments through unknown processes that are often thought to be biologically mediated. The present research describes the kinetics for the abiotic reduction of this compound in aqueous Fe(II)/goethite systems at near-neutral pH values. The results provide evidence for a rate-affecting surface-association process rather than a direct (i.e., kinetically second-order) reaction with an adsorbed Fe(II) species. It is therefore likely that the iron oxide surface participates directly in the reaction. Furthermore, reduction is observed in the apparent presence of trace amounts of suspended iron oxide nanoparticles, formed in situ by the oxidation of Fe(II). Given that Fe(III) colloids and other nanoscale phases may occur in natural sediments, such abiotic reactions could significantly influence the environmental fate of nitroaromatic compounds.

Demonstration of simultaneous anion-exchange and reversed-phase behavior on a strong anion-exchange column

We demonstrate in this report that a conventional silica-based strong anion-exchange column can exhibit reversed-phase chromatographic behavior simultaneously with ion-exchange in a methanol–aqueous phthalate mobile phase. Reversed-phase behavior is shown for PAHs in relatively high methanol-content mobile phases, while polar organics exhibit reversed-phase behavior in 0–10% (v/v) methanol–water eluents. At low concentrations (0–10% v/v) methanol has little or no effect on anion retention, while the anions exhibit only slight increases in retention in 60–80% (v/v) methanol at near-neutral pH values. Likewise, pH changes used to manipulate anion retention have essentially no effect on PAH retention, and cause only small decreases in retention for most of the polar organics studied. Little or no pH-effect was seen on a phenyl column (no exchange group) or with acetate mobile phase. It is shown that manipulation of pH and methanol content allows the grouping of neutral organic analytes early in a chromatogram, followed by the anions, with no class overlap. Several example chromatograms are given, including that of a red wine sample. Column efficiency was good for anions but only modest for organics.

Rate and extent of aqueous perchlorate removal by iron surfaces.

The rate and extent of perchlorate reduction on several types of iron metal was studied in batch and column reactors. Mass balances performed on the batch experiments indicate that perchlorate is initially sorbed to the iron surface, followed by a reduction to chloride. Perchlorate removal was proportional to the iron dosage in the batch reactors, with up to 66% removal in 336 h in the highest dosage system (1.25 g mL(-1)). Surface-normalized reaction rates among three commercial sources of iron filings were similar for acid-washed samples. The most significant perchlorate removal occurred in solutions with slightly acidic or near-neutral initial pH values. Surface mediation of the reaction is supported by the absence of reduction in batch experiments with soluble Fe2+ and also by the similarity in specific reaction rate constants (kSA) determined for three different iron types. Elevated soluble chloride concentrations significantly inhibited perchlorate reduction, and lower removal rates were observed for iron samples with higher amounts of background chloride contamination. Perchlorate reduction was not observed on electrolytic sources of iron or on a mixed-phase oxide (Fe3O4), suggesting that the reactive iron phase is neither pure zerovalent iron nor the mixed oxide alone. A mixed valence iron hydr(oxide) coating or a sorbed Fe2+ surface complex represent the most likely sites for the reaction. The observed reaction rates are too slow for immediate use in remediation system design, but the findings may provide a basis for future development of cost-effective abiotic perchlorate removal techniques.

Synthesis of cytidine ribonucleotides by stepwise assembly of the heterocycle on a sugar phosphate.

Although various syntheses of the nucleic acid bases exist and ribose is a product of the formose reaction, no prebiotically plausible methods for attaching pyrimidine bases to ribose to give nucleosides have been described. Kinetic and thermodynamic factors are thought to mitigate against such condensation reactions in aqueous solution. This inability to produce pyrimidine nucleosides and hence nucleotides is a major stumbling block of the "RNA World" hypothesis and has led to suggestions of alternative nucleic acids as evolutionary precursors to RNA. Here, we show that a process in which the base is assembled in stages on a sugar phosphate can produce cytidine nucleotides. The sequential action of cyanamide and cyanoacetylene on arabinose-3-phosphate produces cytidine-2',3'-cyclophosphate and arabinocytidine-3'-phosphate.

Abiotic Degradation of Trifluralin by Fe(II): Kinetics and Transformation Pathways

The herbicide trifluralin (2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine) is widely used in agriculture and may pose toxic risks to some aquatic organisms. While its degradation has been investigated in field studies, this research is the first to elucidate the specific abiotic transformations that trifluralin may undergo in reducing environments such as flooded soils and wetland sediments. Kinetic data and product identities were determined for the degradation of trifluralin in Fe(II)/goethite suspensions at near-neutral pH values. Under these conditions, trifluralin is consumed rapidly through a surface-mediated process that includes three distinct reactions: reduction of nitro groups, dealkylation of propylamines, and cyclization to form benzimidazoles. All detected products are among those that have been reported in natural soils and sediments. Therefore, these transformation pathways may play a significant role in affecting the fate of trifluralin in the environment.

Effects of Iron and pH on Glass Dissolution Rate

ABSTRACTShort-term static tests were conducted with a surrogate high-level waste glass to measure the effects of pH and dissolved iron on the glass dissolution rate. The tests were conducted to determine if a term to account for the effects of dissolved iron is needed in the glass degradation model developed for Total System Performance Assessment (TSPA) calculations for the Yucca Mountain disposal system license application. The glass degradation model includes terms for dependencies on temperature, pH, and chemical affinity. A series of tests was conducted at 90 °C in various pH solutions without iron and with added FeCl3, Fe2O3, Fe3O4, and FeOOH. Tests were conducted at glass surface area/solution volume (S/V) ratios about 2 and 10 m-1for between 2 and 21 days. Solution concentrations of boron were used to measure the extent of reaction and calculate the glass dissolution rates. Similar rates were measured in tests conducted with and without iron at each pH. Both the results of the tests with and without iron showed V-shaped pH dependence curves with minima at near-neutral pH values. The pH dependencies (η) are about 0.44 in basic solutions and –0.49 in acidic solutions, based on the combined results of tests with and without iron. These are within the range of values for the pH dependence in the TSPA model for site recommendation.

An on-line protein digestion device for rapid peptide mapping by electrospray mass spectrometry.

A simple laboratory-constructed device has been developed for fast on-line protein digestion followed by peptide mapping by use of electrospray mass spectrometry. Taking advantage of its nonsolubility properties at near-neutral pH values, pepsin could be nonpermanently attached to the PEEK tube commonly employed as transfer capillary between the syringe and the electrospray ion source. After optimization of experimental conditions such as pH, solvent, and exposure time, efficient digestion of several model proteins of molecular weights between 14,000 and 66,000, some having disulfide bridges, was successfully carried out. This technique provided reliable and reproducible sequence information by means of C-terminal-specific cleavages of aromatic and hydrophobic residues. As an application, protein identification could be achieved using a protein database search software.

The interaction of hydrophilic thiols with cadmium: investigation with a simple model, 3-mercaptopropionic acid

Environmental contamination by cadmium is widely recognized as a serious problem. All cadmium compounds are considered toxic and are regulated by the US Environmental Protection Agency. In organisms, thiols or organic sulfhydryl compounds are primarily involved in mobilizing and detoxifying cadmium through the formation of cadmium–thiol complexes inside the cell. This complexation is also of environmental importance because a variety of thiols are generated by biotic and abiotic processes in anaerobic environments, such as estuarine wetlands and coastal sediments, which have increasingly become the targets of metal pollution. We investigated the complexation of cadmium by 3-mercaptopropionic acid (MPA), using it as a simple model to better understand the potential pathways of cadmium transformations by hydrophilic thiols. Our results show that cadmium forms primarily 1:1 and 1:2 complexes with MPA in aqueous solutions at near-neutral pH values. While the dithio complex was highly soluble in water, the monothio complex rapidly precipitated from solution. Based on mass spectrometric and X-ray absorption spectroscopic data, we propose a cyclic, charge-neutralized structure for the monothio complex, and a linear ionic structure for the dithio complex. These results suggest that the type of complex formed is an important determinant of the mobility of cadmium.

Alkaliphiles: some applications of their products for biotechnology.

The term "alkaliphile" is used for microorganisms that grow optimally or very well at pH values above 9 but cannot grow or grow only slowly at the near-neutral pH value of 6.5. Alkaliphiles include prokaryotes, eukaryotes, and archaea. Many different taxa are represented among the alkaliphiles, and some of these have been proposed as new taxa. Alkaliphiles can be isolated from normal environments such as garden soil, although viable counts of alkaliphiles are higher in samples from alkaline environments. The cell surface may play a key role in keeping the intracellular pH value in the range between 7 and 8.5, allowing alkaliphiles to thrive in alkaline environments, although adaptation mechanisms have not yet been clarified. Alkaliphiles have made a great impact in industrial applications. Biological detergents contain alkaline enzymes, such as alkaline cellulases and/or alkaline proteases, that have been produced from alkaliphiles. The current proportion of total world enzyme production destined for the laundry detergent market exceeds 60%. Another important application is the industrial production of cyclodextrin by alkaline cyclomaltodextrin glucanotransferase. This enzyme has reduced the production cost and paved the way for cyclodextrin use in large quantities in foodstuffs, chemicals, and pharmaceuticals. It has also been reported that alkali-treated wood pulp could be biologically bleached by xylanases produced by alkaliphiles. Other applications of various aspects of alkaliphiles are also discussed.

Environmental geochemistry of shale-hosted Ag [sbnd]Pb [sbnd]Zn massive sulfide deposits in northwest Alaska: natural background concentrations of metals in water from mineralized areas

Red Dog, Lik and Drenchwater are shale-hosted stratiform Ag Pb Zn massive sulfide deposits in the northwestern Brooks Range. Natural background concentrations of metals in waters from the undisturbed (unmined) Drenchwater prospect and Lik deposit were compared to pre-mining baseline studies conducted at Red Dog. The primary factors affecting water chemistry are the extent of exposure of the deposits, the grade of mineralization, the presence of carbonate rocks in the section, and the proportion of Fe-sulfide in the ore. Surface water samples from the Drenchwater prospect, which has pyrite-dominant mineralization exposed in outcrop, have pH values as low as 2.8 and high dissolved concentrations of metals including as much as 95 mg l −1 Al, 270 mg l −1 Fe, 8 μl −1 Cd, 10 μl −1 Pb, and 2600 μl −1 Zn, with As up to 26 μgl −1. Surface waters from the Red Dog deposit prior to mining were also acidic and metal-rich, however, dissolved metal concentrations in Red Dog waters were many times greater. The higher metal concentrations in Red Dog waters reflect the high Zn grades and the abundant sphalerite, pyrite, and galena that were present in outcrop prior to mining. In contrast,l despite significant mineralization at the Lik deposit, carbonate rocks in the section buffer the system, resulting in less acidic, mostly near-neutral pH values with low concentrations of most metals except Zn.

P-17-5 - Regional cerebral perfusion by Tc-99m HMPAO SPECT before and after tacrine in alzheimer's disease

Microvillus membrane vesicles isolated from renal cortex have subsequently served as a useful model system for characterizing the kinetic and biochemical features of a Na+–H+ exchanger whose properties are largely representative of plasma membrane Na+–H+ exchangers in general. This chapter reviews studies on the molecular properties of the renal microvillus membrane Na+–H+ exchanger. Additional transport systems for the transfer of acids or bases exist in parallel with the Na+–H+ exchanger on the luminal membrane of proximal tubule cells. The chapter describes the kinetics of the renal Na+–H+ exchanger. As the imidazolium ring of histidine is the principal ionic group in proteins that is titratable at near-neutral pH values, in the study described in the chapter, this helped to evaluate the effect of histidine-specific reagents on the activity of the renal microvillus membrane Na+–H+ exchanger. The carboxyl-activating reagent N-ethoxycarbonyl-2-ethoxy- 1,2-dihydroquinoline (EEDQ) inhibits Na+–H + exchange in renal microvillus vesicles. Also, The observations that N,N'-dicyclohexyl-carbodiimide (DCCD) inactivates the renal Na+–H+ exchanger irreversibly and that amiloride protects against this inactivation suggested a strategy for covalently labeling the transport protein or one of its subunits. The renal Na+–H+ exchanger helps in facilitating anion transport by HCO−3 reabsorption, organic anion reabsorption, Cl− reabsorption, and anion transport and maintaining intracellular pH.

Assessing the Corrosion Resistance of Nonequilibrium Magnesium-Yttrium Alloys

Abstract Magnesium-yttrium (Mg-Y) alloys containing 7 at% to 26 at% solute were fabricated using magnetron cosputter deposition. X-ray diffraction (XRD) revealed that no second phases were present in any of the alloys and that all but two of the alloys (Mg-7% Y and Mg-14% Y) were nanocrystalline and/or amorphous. Anodic potentiodynamic polarization performed in 0.1 M sodium chloride (NaCl) at both near-neutral and high pH values showed improved anodic polarization behavior for most of the alloys when compared to either pure Mg or one of the most corrosion-resistant commercial Mg alloys (alloy WE43 [UNS M18430]). In the high-pH solution, it was not uncommon for breakdown potentials (Eb) of the Mg-Y alloys to be 2,000 mV higher than values for alloy WE43. Long-term galvanic and potentiostatic testing was performed on selected alloys to verify anodic polarization behavior. Potentiostatic testing also was performed in a pH 12 buffer solution. When defects did not affect corrosion behavior, low current density...

Rare earth geochemistry in sediments of the Upper Manso River Basin, Río Negro, Argentina

The abundance, distribution and fractionation of rare earth elements was studied in solid material transported by the Upper Manso River and in the sediments deposited in Lake Mascardi, Argentina. The pristine condition of the area offers an ideal environment for assessing geochemical processes, and the seasonal cycles to which the basin is subjected permit us to study seasonal variations that are mainly influenced by glacial pulses. The most remarkable characteristics observed in the REE-normalized patterns are a strong HREE enrichment and a positive Eu anomaly. These normalized patterns are atypical as compared to those considered representative of the world's major rivers and are caused by drainage basin geology. Due to the dissected topography and the small size of the basin, intense mixing phenomena are not favoured and the weathering reactions are inhibited by the fast-flowing river. These physicochemical conditions and near-neutral pH values have an important influence on the REE patterns of the sediments, which mainly originated by glacial erosion, that are transported by the river. The feldspars and their secondary products, which are both enriched in Eu, might be the cause of the Eu anomaly. HREE enrichment, which is mainly associated with high-pH systems or with the presence of accessory phases, shows a clear dependence on source rocks. The calculated(La/Yb) N ratios oscillate between 0.5 and 0.6, contrasting with the values reported in the literature as average values for suspended load material. Nevertheless, these values are consistent with the dependence of(La/Yb) N values on the age of drainage area rocks as was observed by Goldstein and Jacobsen [3]. Seasonal variations are not manifested in REE concentrations, and additional elemental determinations showed coherent behaviour during weathering for all elements except Sr and Ba, which exhibited selective elemental mobilization during periods of minimum discharge.

LED-compatible fluorosensor for measurement of near-neutral pH values

We report on an optical sensor material suitable for fluorimetric measurement of pH in the 6–9 range using a new, fully LED-compatible fluorescent dye. Its base form has a strong absorption between 580 and 630 nm that matches the emission band of conventional yellow or orange light-emitting diodes. Two kinds of dye immobilization are reported. The first is based on covalent binding to a cellulosic matrix and the resulting material is intended for use in sensing membranes. The second involves physical entrapment of the dye in a sol-gel matrix which can be used for optical fiber tip coating as well as in evanescent wave type sensors. Both kinds of sensor materials are studied with respect to dynamic pH ranges, response times, sensitivity toward ion strength, and stability.

Production of β-galactosidase by Aspergillus oryzae in submerged bioreactor cultivation

Eleven strains of Aspergillus oryzae were screened for production of β-galactosidase on media based on lactose and wheat bran. All the strains produced highest levels of activity on the wheat bran medium. Production by the best strain, A. oryzae VTT-D-88353 (ATCC 20423) was considerably better than that obtained with A. niger VTT-D-80144, previously reported as an efficient producer of β-galactosidase, in both shake flask and laboratory bioreactor cultivations. Production on a lactose-based medium in the bioreactor was better in fed-batch than in simple batch cultivation, but considerably poorer than on wheat bran. The role of the organic nitrogen source was also of major importance for β-galactosidase production by the A. oryzae strain. The cultivation time required for maximal production by A. oryzae was longer than that required by A. niger and could not be reduced by the use of surface active agents. In lactose hydrolysis experiments the enzyme of A. oryzae was somewhat more efficient that that of A. niger at near-neutral pH values at 30°C, but at 50°C the A. niger enzyme was more effective at all pH values between 5.0 and 7.0.