Fe OH Research Articles

Miocene weathering environments in Western Australia—Inferences from the abundance and 13C/12C of Fe(CO3)OH in CID goethite

The channel iron deposits (CID) of the Hamersley Province in Western Australia are dominated by pedogenic goethite/hematite-rich ooids and pisoids that were transported to, and deposited in, the meandering channels of Miocene rivers. Information about the Miocene weathering environments that produced the Fe(III) oxides is archived in the mole fraction (X) and δ13C of the Fe(CO3)OH component in solid solution in oolitic CID goethite (α-FeOOH).Values of X and δ13C were measured for 12 oolitic goethite samples from different depths in two cores drilled in CID of the Robe Formation of Mesa J. The weighted-average plateau values of X ranged from 0.0098 to 0.0334, which suggest ambient CO2 concentrations that ranged from ∼50,000 ppm V to perhaps as much as ∼200,000 ppm V at the time of goethite crystallization. In a vadose zone characterized by in situ production of CO2 with steady-state Fickian diffusive transport of the gas, such concentrations would correspond to modeled soil respiration rates (Q) ranging from about 10 to 30 mmol/m2/h. Values for Q of about 10 mmol/m2/h are reported for soils in modern tropical forests with MAP ≥ ∼2000 mm. However, model-derived values of Q that exceed 15 mmol/m2/h are larger than observed in modern systems. This could indicate that some of the CID goethites crystallized in conditions that were phreatic or near phreatic rather than vadose.The δ13C values of the Fe(CO3)OH component in these 12 CID samples ranged from −24.0‰ to −22.3‰, which are among the most negative measured to date. If they reflect steady-state diffusive transport of CO2 in vadose environments, the soil CO2 would have been derived from a source with δ13C values that ranged from ∼−31‰ to −29‰. If, on the other hand, the goethites crystallized in a nearly phreatic environment that was moderately acidic, the inferred δ13C of the ancient CO2 source would have been about −27.6‰ to −25.8‰. In either case, the δ13C values point to in situ oxidation of C3 organic matter as the predominant source of the ambient CO2.The Fe(III) oxides in the CID ooids suggest crystallization in aerobic environments. However, even in aerobic environments, many microbial species can reduce the Fe3+ in oxides to relatively soluble Fe2+ and may have facilitated progressive Fe enrichment during multiple cycles of Fe(III) oxide dissolution and recrystallization. At the same time, microbially mediated oxidation of organic matter could have produced the high concentrations of soil CO2 with the very negative δ13C values recorded in the Fe(CO3)OH component in oolitic goethite.More frequent summer storms in the Miocene, may have been a significant factor in forming and eroding these soil systems and in concentrating large volumes of oolitic Fe(III) oxides in the local river systems to form channel iron deposits. However, published (U-Th)/He ages indicate that the oolitic CID goethites of Mesa J became closed systems after ∼7 Ma, which suggests a change in local climate and/or conditions of burial at about that time in the Miocene.

Transfer of electrons on scratched iron surfaces: Photoelectron emission and X-ray photoelectron spectroscopy studies

We report the activation energy, ΔEa, for the quantum yield in thermally assisted photoelectron emission (TAPE) under 210-nm-wavelength light irradiation, and the associated X-ray photoelectron spectroscopy (XPS) results. Samples were cleaned only in acetone and scratched in air, water, methanol, ethanol, acetone, benzene, and cyclohexane. Glow curves, describing the temperature dependence of photoelectron emission (PE) quantum yield (emitted electrons/photon), Y, were obtained. A simple method of determining ΔEa using Y, called YGC, at seven temperatures up to 353 °C, for the same Y glow curve, was proposed. The ΔEa obtained using this method was almost the same as that obtained from Y for seven stationary temperatures (YST). For scratched samples, the TAPE was measured over two cycles of temperature increase and subsequent decrease (Up1, Down1 and Up2, Down2 scans) in the 25–339 °C range, and ΔEa was obtained from YGC. The Arrhenius plot was approximated by a straight line, although a convex swelling peak appeared in the Up1 scan. ΔEaUp1 was in the 0.212–0.035 eV range, depending on the environment in which scratching was performed; ΔEaUp1 for water was much higher than that for acetone. This was explained in terms of the mode of the acid–base interaction between the liquid molecules and the hydroxyl group of Fe–OH. The values of ΔEaDown1, ΔEaUp1, and ΔEaDown2 were in the 0.038–0.012 eV range. The total count of electrons emitted during the Up1 and Up2 scans was found to decrease with increasing ΔEaDown1 and ΔEaDown2, respectively. ΔEaUp2 was found to increase with increasing presence of the FeO component in the analyzed Fe oxides. The convex swelling peak was attributed to the removal of carbon materials from the scratched surface and the effect of the increased electron density of the surface hydroxyl group of FeOH under the light irradiation.

Radical reaction caught on the rebound

For more than 40 years, chemists and biologists have used the radical rebound mechanism to describe what happens when enzymes with transition metals, such as cytochrome P450, hydroxylate C–H bonds. Such enzymes first remove a hydrogen atom from a C–H bond using a high-valent metal-oxo species. This produces a carbon radical and a metal-OH intermediate that then rebounds—the hydroxyl group moves onto the carbon radical and the metal is reduced by one electron. Although plenty of circumstantial evidence suggests this is what happens, observing the rebound step in this reaction has been impossible because it is fast compared with the hydrogen atom removal step. Now, chemists led by David P. Goldberg of Johns Hopkins University have created the first model system in which the rebound reaction can be observed (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.7b07979). The system features Fe–OH ensconced in a tris(triphenyl)phenyl corrole ligand, which stabilizes the high

Coexistence of localized and itinerant magnetism in intercalated iron-selenide (Li,Fe)OHFeSe

The electronic structure and magnetism of a new magnetic intercalation compound (Li0.8Fe0.2)OHFeSe are investigated theoretically. The electronic structure calculations predict that the Fe in the (Li,Fe)OH intercalated layer is in a +2 valence state, i.e. there is electron doping to the FeSe layer, resulting in the shrinking of the Fermi surface (FS) pocket around Γ and a strong suppression of dynamical spin susceptibility at M in comparison with the bulk FeSe compound. The ground state of the FeSe layer is a striped antiferromagnetic (SAFM) metal, while the (Li,Fe)OH layer displays a very weak localized magnetism, with an interlayer ferromagnetic (FM) coupling between the FeSe and intercalated (Li,Fe)OH layers. Moreover, the (Li,Fe)OH is more than a block layer; it is responsible for enhancing the antiferromagnetic (AFM) correlation in the FeSe layer through interlayer magnetic coupling. We propose that the magnetic spacer layer introduces a tuning mechanism for spin fluctuations associated with superconductivity in iron-based superconductors.

Characteristics of Iron Sand Magnetic Material from Bugel Beach, Kulon Progo, Yogyakarta

Magnetic material (MM) of iron sands from Bugel Beach, Kulon Progo, Yogyakarta has been prepared and characterized. Magnetic material was separated from iron sands using a permanent magnet followed by treating with sodium hydroxide (NaOH) solution. The magnetic material product was characterized with X-ray Fluorescence, X-ray Diffraction, Fourrier Transform Infrared spectrophotometry, and Vibrating Sample Magnetometer to determine the chemical composition, crystallinity, presence of functional groups and the magnetization, respectively. Results showed that the investigated iron sand contained magnetic materials up to 89.47% (w/w). The main composition of MM included Fe2O3, TiO2, and SiO2, with percentages of 72.6, 7.0, and 10.0%, respectively, and the functional groups of material was dominated with Fe–OH and Fe–O. Treatment with NaOH 4M and NaOH 8M increased the content of Fe2O3 and TiO2, otherwise reduced the concentration of SiO2 and contributed to the improvement of the magnetization from 42.1 to 44.3 emu/g (with 4 M NaOH) and 64.0 emu/g (with 8 M NaOH). Additionally, MM was dominated with mineral of magnetite and contained functional groups of Fe–OH and Fe–O.

Smart Design of Self-Assembled Mesoporous α-FeOOH Nanoparticles: High-Surface-Area Sorbent for Hg2+ from Wastewater

Self-assembled mesoporous α-FeOOH nanoparticles with high surface area and controlled structure have been synthesized through a simple and environmentally friendly method. The formation mechanism of self-assembled mesoporous structures, as well as the effect of pH on the structure of the materials, is carefully discussed. The self-assembled mesoporous α-FeOOH nanoparticles have been characterized by small-angle X-ray scattering (SAXS) analysis, powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), N2 sorption, and X-ray photoelectron spectroscopic (XPS) studies. N2 sorption analysis revealed high surface areas (74–152 m2 g–1) and narrow pore size distributions (2.5 nm) for different samples. The XPS analysis revealed that the materials contain a large amount of surface Fe–OH groups which are the active suite for Hg2+ adsorption. The adsorption process has been discussed using Langmuir and Freundlich models. These self...

Polyelectrolyte coating on superparamagnetic iron oxide nanoparticles as interface between magnetic core and biorelevant media

Nanoparticles do not exist in thermodynamical equilibrium because of high surface free energy, thus they have only kinetic stability. Spontaneous changes can be delayed by designed surface coating. In biomedical applications, superparamagnetic iron oxide nanoparticles (SPIONs) require an optimized coating in order to fulfil the expectation of medicine regulatory agencies and ultimately that of biocompatibility. In this work, we show the high surface reactivity of naked SPIONs due to ≡Fe-OH sites, which can react with H+/OH- to form pH- and ionic strength-dependent charges. We explain the post-coating of naked SPIONs with organic polyacids via multi-site complex bonds formed spontaneously. The excess polyacids can be removed from the medium. The free COOH groups in coating are prone to react with active biomolecules like proteins. Charging and pH- and salt-dependent behaviour of carboxylated SPIONs were characterized quantitatively. The interrelation between the coating quality and colloidal stability measured under biorelevant conditions is discussed. Our coagulation kinetics results allow us to predict colloidal stability both on storage and in use; however, a simpler method would be required to test SPION preparations. Haemocompatibility tests (smears) support our qualification for good and bad SPION manufacturing; the latter 'promises' fatal outcome in vivo.

Enhanced phosphate and fluoride removal from aqueous solution by ferric-modified chromium (Ⅲ)-fibrous protein

Ferric modified chromium (III)-fibrous protein (Fe–CrFP) sorbent for phosphate and fluoride removal was prepared through crosslinking reaction. This adsorbent was characterized by elemental analysis, X-ray diffraction (XRD), Scanning electron microscope (SEM), Fourier Transform infrared spectroscopy (FTIR) and zeta potential. Results indicated that Fe–CrFP possessed good adsorption ability for both phosphate and fluoride due to its higher isoelectric point (pH=9.2). Phosphate and fluoride had different pH dependence on solution pH: phosphate removal decreased rapidly beyond pH=6.0, while a higher fluoride sorption amount was obtained in a pH range of 3.0–9.0. Adsorption isotherms for PO43− and F− were well described by the Langmuir equation. XRD analysis illustrated that Fe(III) on Fe–CrFP was amorphous, and hydrous ferric oxide formed on Fe–CrFP played an important role in adsorption. The main adsorption mechanisms of phosphate and fluoride were attributed to electrostatic attraction, additionally Fe–CrFP could also capture phosphate and fluoride through specific adsorption with formation of inner-sphere complex by surface hydroxyl groups (Fe–OH). Fluoride was easier to be influenced by coexisting anions in comparison to PO43−, and competitive sorption occurred in F− in presence of PO43−. Phosphate and fluoride adsorbed on Fe–CrFP could be totally desorbed by alkali solution, recycling experiment suggested that Fe–CrFP had a good utilization in treatment of phosphate and fluoride and provided a possibly valuable application for tanning leather waste.

Novel bioactive Fe-based metallic glasses with excellent apatite-forming ability

We demonstrate, for the first time, that the (Fe0.75B0.15Si0.1)100−xNbx (x=0, 1 and 3at.%) metallic glasses without toxic and allergic elements exhibit excellent apatite-forming ability in simulated body fluids (SBF), which is expected to be a new generation of biomaterials in stents and orthopedic implants. For the alloys without any surface treatment, spherical particles corresponding to octacalcium phosphate are spontaneously nucleated and precipitated throughout the alloy surface after immersion only for 1day, indicating that the present alloys possess an unusual high bioactivity. During the subsequent in-vitro immersion for 3days, SEM image reveals the typical ‘cauliflower’ morphology of bone-like hydroxyapatite (HA) with Ca/P ratio of 1.65. In addition, it is surprising to find that the in-vitro SBF immersion not only leads to the formation and growth of the apatite layer but also causes the progressive development of the underlying alloy substrate. Moreover, for the alloys immersed for 3 or 9days, the substrate alloy just beneath the apatite layer consists of a hierarchical nano/macro-porous structure through selective dissolution of the active components Fe and B in the surface. XPS analysis indicates that the apatite nucleation on the present alloys in SBF is attributed to the specific dissolution properties of the present alloys and the fast formation of Si-OH and Fe–OH or Nb-OH functional groups, followed by combination of these groups with Ca2+ and phosphate ions.

All-Soluble All-Iron Aqueous Redox-Flow Battery

The rapid growth of intermittent renewable energy (e.g., wind and solar) demands low-cost and large-scale energy storage systems for smooth and reliable power output, where redox-flow batteries (RFBs) could find their niche. In this work, we introduce the first all-soluble all-iron RFB based on iron as the same redox-active element but with different coordination chemistries in alkaline aqueous system. The adoption of the same redox-active element largely alleviates the challenging problem of cross-contamination of metal ions in RFBs that use two redox-active elements. An all-soluble all-iron RFB is constructed by combining an iron–triethanolamine redox pair (i.e., [Fe(TEOA)OH]−/[Fe(TEOA)(OH)]2–) and an iron–cyanide redox pair (i.e., Fe(CN)63–/Fe(CN)64–), creating 1.34 V of formal cell voltage. Good performance and stability have been demonstrated, after addressing some challenges, including the crossover of the ligand agent. As exemplified by the all-soluble all-iron flow battery, combining redox pairs o...

Iron Loading Effects in Fe/SSZ-13 NH3-SCR Catalysts: Nature of the Fe Ions and Structure–Function Relationships

Using a traditional aqueous solution ion exchange method under a protecting atmosphere of N2, a series of Fe/SSZ-13 catalysts with various Fe loadings were synthesized. UV–vis, EPR, and Mossbauer spectroscopic methods, coupled with temperature-programmed reduction and desorption techniques, were used to probe the nature of the Fe sites. The major Fe species are extraframework Fe(III) species: [Fe(OH)2]+ (monomeric) and [HO–Fe–O–Fe–OH]2+ (dimeric). Larger oligomers with unknown nuclearity, poorly crystallized Fe oxide particles, together with isolated Fe2+ ions, are minor Fe-containing moieties. Reaction rate and Fe loading correlations, and temperature and Fe loading effects on SCR selectivities, suggest that isolated Fe3+ ions are the active sites for low-temperature standard SCR, and dimeric sites provide the majority of reactivity at higher temperatures. For NO oxidation, dimeric sites are the active centers. NH3 oxidation, on the other hand, is catalyzed by sites with higher nuclearity.

Process parameter optimization and enhancement of photo-biohydrogen production by mixed culture of Rhodobacter sphaeroides NMBL-02 and Escherichia coli NMBL-04 using Fe-nanoparticle

In this study, comparative enhancement effect of nanoparticle form and bulk form of Fe(SO4)OH(H2O)2 on hydrogen production by mixed culture of Rhodobacter sphaeroides NMBL-02 and Escherichia coli NMBL-04 was investigated in batch process. The maximum cumulative hydrogen production and % substrate conversion efficiencies were observed at 300 mg/L Fe(SO4)OH(H2O)2 concentration (Fe-concentration) with nano as well as bulk form. But the results obtained with nano form of Fe(SO4)OH(H2O)2 were 1.2 fold higher in contrast to bulk form. Further optimization studies were also performed with two more factors namely pH and malate concentration. Response surface methodology (RSM) in accordance with Box-Behnken Design was employed to evaluate the interactive effects of these factors. From RSM the optimum values of pH and, malate concentration and Fe-concentration were obtained as 5.603, 3.948 g/L and 312.168 mg/L respectively.Response surface methodology analysis showed best fitting of experimental data with statistical model. At the optimal conditions, the cumulative hydrogen production was reported as 2046 mL H2/L of medium which was in vicinity of predicted value (2029.405 mL H2/L).

Arsenate and arsenite adsorption onto Al-containing ferrihydrites. Implications for arsenic immobilization after neutralization of acid mine drainage

Natural ferrihydrites (Fh) often contain impurities such as aluminum, especially in acid mine drainage, and these impurities can potentially impact the chemical reactivity of Fh with respect to metal (loid) adsorption. In the present study, we have investigated the influence of aluminum on the sorption properties of ferrihydrite with respect to environmentally relevant aqueous arsenic species, arsenite and arsenate. We have conducted sorption experiments by reacting aqueous As(III) and As(V) with synthetic Al-free and Al-bearing ferrihydrite at pH 6.5. Our results reveal that, when increasing the Al:Fe molar ratio in Fh, the sorption density dramatically decreased for As(III), whereas it increased for As(V). Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy analysis at the As K-edge indicated that the AsIIIO3 pyramid binds to FeO6 octahedra on both Al-free Fh and Al-bearing Fh, by forming bidentate mononuclear edge-sharing (2E) and bidentate binuclear corner-sharing (2C) surface complexes characterized by As–Fe distances of 2.9 Å and 3.4 Å, respectively. The decrease in As(III) sorption density with increasing Al:Fe ratio in Fh could thus be explained by a low affinity of the As(OH)3 molecule for Al surface sites compared to Fe ones. In contrast, on the basis of available literature on As(V) adsorption mechanisms, we suggest that, in addition to inner-sphere 2C arsenate surface complexes, outer-sphere arsenate surface complexes forming hydrogen bonds with both Al–OH and Fe–OH surface sites could explain the enhancement of As(V) sorption onto aluminous Fh relative to Al-free Fh, as observed in the present study. The presence of aluminum in Fh may thus enhance the mobility of arsenite with respect to arsenate in Acid Mine Drainage impacted systems, while mixed Al:Fe systems could present an alternative for arsenic removal from impacted waters, provided that As(III) would be oxidized to As(V).

Theoretical Investigation of the Methanol Decomposition by Fe+)and Fe(C2H4)+: A π-Type Ligand Effect.

Density functional theory has been used to probe the mechanism of gas-phase methanol decomposition by bare Fe(+) and ligated Fe(C(2)H(4))(+) in both quartet and sextet states. For the Fe(+)/methanol system, Fe(+) could directly attach to the O and methyl-H atoms of methanol, respectively, forming two encounter isomers. The methanol reaction with Fe(+) prefers initial C-O bond activation to yield methyl with slight endothermicity, whereas CH(4) elimination is hindered by the strong endothermicity and high-energy barrier of hydroxyl-H shift. For the Fe(C(2)H(4))(+)/methanol system, the major product of H(2)O is formed through six elementary steps: encounter complexation, C-O bond activation, C-C coupling, β-H shift, hydride H shift, and nonreactive dissociation. Both ligand exchange and initial C-O bond activation mechanisms could account for ethylene elimination with the ion products Fe(CH(3)OH)(+) and (CH(3))Fe(OH)(+), respectively. With the assistance of a π-type C(2)H(4) ligand, the metal center in the Fe(C(2)H(4))(+)/CH(3)OH system avoids formation of unfavorable multi-σ-type bonding and thus greatly enhances the reactivity compared to that of bare Fe(+).

DEVELOPMENT OF A NEW IMMUNOMODULATING DRUG TIMOFER

Results of the development of an immunomodulating drug timofer based on coordination compounds isoleucyl-tryptophan dipeptide with iron (II), including the study of coordinate isoleucyl-tryptophan dipeptide with iron (II), the study of the immunostimulatory activity of the coordination compounds, the results of the preclinical and clinical studies of timotsin are presented. Method of pH titration showed that the interaction of zinc and dipeptide isoleucyltryptophan formed in solution following complex forms: [Fe (HL±)]2+ (β = 1,00×1034), [Fe(HL±)2]2+ (β = 6,25×1011), [Fe (HL±)OH]+ (β = 4,01×1026), [Fe (L)]+ (β = 8,10×1018), [Fe (L)2]+ (β = 7,50×1028), [Fe (L)OH]+ (β = 1,03×1029). It was shown that the immunostimulatory activity of the coordination compounds is 2 times higher than that starting dipeptide. The substance sample and standard formulation of timofer were developed and standardized. The developed immunomodulatory drug timofer showed a high therapeutic efficacy in the treatment of iron deficiency anemia patients with inflammatory processes and traumatic injuries of the maxillofacial region, with chronic inflammatory diseases of the the genitals (CMV, HSV, chlamydia, chronic endometritis, chronic salpingoopharitis, ureaplasmosis) with chronic bronchitis, chronic obstructive bronchitis, bronchial asthma, pneumonia, chronic glomerulonephritis, and chronic renal failure complicated by anemia Bright, withrheumatic diseases, gynecological patients with anemia of moderate and severe degrees of severity, at surgical treatment of patients with suppurative lung disease, heart disease and chronic pericarditis operated with cardiopulmonary bypass. Timofer is registered in Tajikistan (registration number of medical drug №002866).

Chemical, structural and hyperfine characterization of goethites with simultaneous incorporation of manganese, cobalt and aluminum ions

To elucidate the influence of bi-substitution on the structural and hyperfine properties of goetites, two series of (Al,Co)- and (Mn,Co)-substituted goethites were synthesized in alkaline media by aging several ferrihydrites with different Al/Co and Mn/Co ratios. The samples were fully characterized by chemical analyses, X-ray diffraction (XRD) and Mössbauer spectroscopy; scanning electron microscopy (SEM), zeta potential and BET surface area measurements were also performed. All the solids presented only an α-FeOOH-like structure, with the exception of two preparations with high Co concentrations that developed two phases, goethite and small amounts of the Co-ferrite (CoFe2O4). The cell parameters in the Co-substituted goethites were markedly smaller than that of the pure sample indicating a oxidation of Co(II) to Co(III) before the incorporation step. In the Co+Mn series the metal substitution followed the trend Co~Mn, and in the Co+Al series the trend was Al>Co, and in both cases the incorporation of Co decreased the crystallite size of the samples. The metal-for-Fe incorporation changed the specific surface areas and the morphology of the acicular formed particles. Cobalt containing samples had the highest SSA, while Mn-containing samples had the lowest SSA. The IEP values of the bi-substituted samples were similar to that of pure α-FeOOH, but mono-substitution by Mn and Al diminished the isoelectric points. The low IEP values detected in Mn-goethite (5.8) and Al-goethite (5.2) could be respectively ascribed to an inhomogeneous distribution of Mn(III), and to the different basicity properties of the surface Fe–OH and Al–OH groups. The hyperfine magnetic field Bhf, increased quasi linearly with the incorporation of Co in both series. In the Co–Mn series the effect was attributed to variations in particle size distribution, in contrast the marked increase observed in the Co–Al series can be attributed to the decrease in the content of diamagnetic ion Al(III). The results indicate that simultaneous substitutions produce substantial changes in the structural, surface and hyperfine properties of goethites. As the characteristics of the dissolution and adsorption processes of the goethites greatly depend on particle size, BET areas and surface charge of the solids, the reported results will allow us to predict changes in the chemical reactivity and adsorption of the multi-substituted goethites. Also the data on hyperfine properties will help to elucidate the probable substitution in natural samples. The fact that Co-incorporation in bi-substituted samples greatly decreased the particle size increasing the specific surface area is an important parameter for technological applications in adsorption removal processes.

18O/16O in CO2 evolved from goethite during some unusually rapid solid state α-FeOOH to α-Fe2O3 phase transitions: Test of an exchange model for possible use in oxygen isotope analyses of goethite

The initial ∼60% of an isothermal vacuum dehydration of goethite can commonly be approximated by first order kinetics. Also, natural goethites contain small amounts of an Fe(CO3)OH component in apparent solid solution. The 18O/16O of CO2 evolved from the Fe(CO3)OH during isothermal vacuum dehydrations is related to the 18O/16O of the goethite by an apparent fractionation factor (αapp) that is, in turn, correlated with a first order rate constant, |m|. A kinetic exchange model predicts that αapp should decrease as |m| increases for a range of |m| that corresponds to relatively slow rates of dehydration. This pattern has been observed in published results. In contrast, for rapid rates of dehydration, αapp is predicted to increase with increasing |m|. Isothermal vacuum dehydrations of two natural goethites had unusually large values of |m| and provided serendipitous tests of this rapid-rate prediction. For these experiments, the measured values of αapp were consistent with patterns of variation predicted by the model. This allowed an estimate of the activation energy (E2) of a model parameter, K2, which is the rate constant for oxygen isotope exchange between CO2 and H2O during the solid-state goethite to hematite phase transition. The estimated value of E2 is only ∼9kJ/mol. Heterogeneous catalysis tends to decrease the activation energies of gas reactions. Consequently, the inferred value of E2 suggests that goethite and/or hematite catalyze oxygen isotope exchange between CO2 and H2O during the solid-state phase change.Yield, δ13C, and δ18O values are routinely measured for increments of CO2 evolved from the Fe(CO3)OH component during isothermal vacuum dehydration of goethite. Model-predicted values of αapp can be combined with plateau δ18O values of the evolved CO2 to estimate the δ18O of the goethite with a less than optimal, but potentially useful, precision of about ±0.8‰. Therefore, a single analytical procedure (incremental dehydration) applied to one aliquot of a sample could provide not only δ13C and mole fractions (X) of the Fe(CO3)OH component, but also hydrogen yield, δD, and the approximate δ18O value of the goethite. Recovery of multiple types of geochemical data from a single aliquot would be particularly useful if the amount of sample available for analysis were limited. Also, the method could be used to estimate the δ18O value of goethite in mixtures of minerals not amenable to selective dissolution – e.g., goethite admixed with hematite.

Quantum mechanical/molecular mechanical calculated reactivity networks reveal how cytochrome P450cam and Its T252A mutant select their oxidation pathways.

Quantum mechanical/molecular mechanical calculations address the longstanding-question of a "second oxidant" in P450 enzymes wherein the proton-shuttle, which leads to formation of the "primary-oxidant" Compound I (Cpd I), was severed by mutating the crucial residue (in P450cam: Threonine-252-to-Alanine, hence T252A). Investigating the oxidant candidates Cpd I, ferric hydroperoxide, and ferric hydrogen peroxide (Fe(III)(O2H2)), and their reactions, generates reactivity networks which enable us to rule out a "second oxidant" and at the same time identify an additional coupling pathway that is responsible for the epoxidation of 5-methylenylcamphor by the T252A mutant. In this "second-coupling pathway", the reaction starts with the Fe(III)(O2H2) intermediate, which transforms to Cpd I via a O-O homolysis/H-abstraction mechanism. The persistence of Fe(III)(O2H2) and its oxidative reactivity are shown to be determined by interplay of substrate and protein. The substrate 5-methylenylcamphor prevents H2O2 release, while the protein controls the Fe(III)(O2H2) conversion to Cpd I by nailing-through hydrogen-bonding interactions-the conformation of the HO(•) radical produced during O-O homolysis. This conformation prevents HO(•) attack on the porphyrin's meso position, as in heme oxygenase, and prefers H-abstraction from Fe(IV)OH thereby generating H2O + Cpd I. Cpd I then performs substrate oxidations. Camphor cannot prevent H2O2 release and hence the T252A mutant does not oxidize camphor. This "second pathway" transpires also during H2O2 shunting of the cycle of wild-type P450cam, where the additional hydrogen-bonding with Thr252 prevents H2O2 release, and contributes to a successful Cpd I formation. The present results lead to a revised catalytic cycle of Cytochrome P450cam.

Characterizing clay mineralogy in Lake Towuti, Indonesia, with reflectance spectroscopy

We tested the use of visible to near-infrared (VNIR) reflectance spectroscopy to characterize the relative abundances of clay minerals in sediments from Lake Towuti, a large tectonic lake in Sulawesi, Indonesia. We measured VNIR spectra of lake and river sediments from Lake Towuti and its catchment to identify clay minerals, fit major VNIR absorption features with a modified Gaussian model to estimate relative abundances of these minerals, and compared these absorptions to the samples’ chemistry to test the utility of VNIR spectroscopy to characterize sediment compositional variations. We found that major absorptions are caused by vibrations of Al–OH in kaolinite (2.21 μm), Fe–OH in nontronite (2.29 μm), Mg–OH in saponite and serpentine (2.31 μm), and Mg–OH in serpentine (2.34 μm). This was confirmed with X-ray diffraction data. The correlations between absorption band areas for Fe–OH, Al–OH, and Mg–OH vibrations and Fe, Al and Mg concentrations, respectively, are statistically significant, varying between r = 0.51 and r = 0.90, and spatial variations in inferred clay mineralogy within the lake are consistent with variations in the geology of the catchment. We conclude that VNIR spectroscopy is an effective way to characterize the clay mineralogy of lake sediments, and can be used to investigate changes in mineral inputs to lake deposits.

Coverage Dependent Water Dissociative Adsorption on the Clean and O-Precovered Fe(111) Surfaces

Water dissociative adsorption on the clean and O-precovered Fe(111) surfaces at different coverage have been studied using the density functional theory method (GGA-PBE) and ab initio atomistic thermodynamics. On the clean p(3 × 3) Fe(111) surface, surface H, O, OH, and H2O species can migrate easily. Considering adsorption and H-bonding, the adsorbed H2O molecules can be dispersed or aggregated in close energies at low coverage, while in different aggregations at high coverage, indicating that the adsorbed H2O molecules might not have defined structures, as observed experimentally. On the O-precovered surface (nO = 1–8), the first dissociation step, nO + H2O = (n – 1)O + 2OH, has a very low barrier and is reversible; and the barriers of the sequential OH dissociation steps, (n – 1)O + 2OH = nO + H + OH and nO + H + OH = (n + 1)O + 2H, are close (0.9–1.2 eV). All of these barriers are coverage independent. For OH and H adsorption at 1/3 ML coverage, surface OH forms a trimer (OH)3 unit, and surface O forms a regular linear pattern. At one ML coverage, there are three dispersed (OH)3 units for OH adsorption and three well-ordered parallel lines for O adsorption. The average adsorption energies for OH and O adsorption are coverage independent. Desorption temperatures of H2O and H2 under ultrahigh vacuum conditions are computed. Systematic comparison among the Fe(110), Fe(100), and Fe(111) surfaces reveal their intrinsic differences in water dissociative adsorption and provide a basic understanding of water-involved reactions catalyzed by iron and interaction mechanisms of water interaction with metal surfaces.