New Barrier Role of Iron Plaque: Producing Interfacial Hydroxyl Radicals to Degrade Rhizosphere Pollutants.

Iron plaque, as a natural barrier between rice and soil, can reduce the accumulation of pollutants in rice by adsorption, contributing to the safe production of rice in contaminated soil. In this study, we unveiled a new role of iron plaque, i.e., producing hydroxyl radicals (·OH) by activating root-secreted oxygen to degrade pollutants. The ·OH was produced on the iron plaque surface and then diffused to the interfacial layer between the surface and the rhizosphere environment. The iron plaque activated oxygen via a successive three-electron transfer to produce ·OH, involving superoxide and hydrogen peroxide as the intermediates. The structural Fe(II) in iron plaque played a dominant role in activating oxygen rather than the adsorbed Fe(II), since the structural Fe(II) was thermodynamically more favorable for oxygen activation. The oxygen vacancies accompanied by the structural Fe(II) played an important role in oxygen activation to produce ·OH. The interfacial ·OH selectively degraded rhizosphere pollutants that could be adsorbed onto the iron plaque and was less affected by the rhizosphere environments than the free ·OH. This study uncovered the oxidative role of iron plaque mediated by its produced ·OH, reshaping our understanding of the role of iron plaque as a barrier for rice.

The divergent fates of primitive hydrospheric water on Earth and Mars.

Despite active transport into Earth's mantle, water has been present on our planet's surface for most of geological time. Yet water disappeared from the Martian surface soon after its formation. Although some of the water on Mars was lost to space via photolysis following the collapse of the planet's magnetic field, the widespread serpentinization of Martian crust suggests that metamorphic hydration reactions played a critical part in the sequestration of the crust. Here we quantify the relative volumes of water that could be removed from each planet's surface via the burial and metamorphism of hydrated mafic crusts, and calculate mineral transition-induced bulk-density changes at conditions of elevated pressure and temperature for each. The metamorphic mineral assemblages in relatively FeO-rich Martian lavas can hold about 25 per cent more structurally bound water than those in metamorphosed terrestrial basalts, and can retain it at greater depths within Mars. Our calculations suggest that in excess of 9 per cent by volume of the Martian mantle may contain hydrous mineral species as a consequence of surface reactions, compared to about 4 per cent by volume of Earth's mantle. Furthermore, neither primitive nor evolved hydrated Martian crust show noticeably different bulk densities compared to their anhydrous equivalents, in contrast to hydrous mafic terrestrial crust, which transforms to denser eclogite upon dehydration. This would have allowed efficient overplating and burial of early Martian crust in a stagnant-lid tectonic regime, in which the lithosphere comprised a single tectonic plate, with only the warmer, lower crust involved in mantle convection. This provided an important sink for hydrospheric water and a mechanism for oxidizing the Martian mantle. Conversely, relatively buoyant mafic crust and hotter geothermal gradients on Earth reduced the potential for upper-mantle hydration early in its geological history, leading to water being retained close to its surface, and thus creating conditions conducive for the evolution of complex multicellular life.

Effect of Ferrous Ion on Heat-Induced Aroma Deterioration of Green Tea Infusion.

Aroma deterioration is one of the biggest problems in processing tea beverages. The aroma of tea infusion deteriorates fast during heat sterilization and the presence of ferrous ion (Fe2+) aggravates it. The underlying mechanism remains unveiled. In this study, Fe2+ was verified to deteriorate the aroma quality of green tea infusion with heat treatment. Catechins were necessary for Fe2+-mediated aroma deterioration. By enhancing the degradation of catechins, Fe2+ dramatically increased the production of hydrogen peroxide (H2O2). Fe2+ and H2O2 together exacerbated the aroma of green tea infusion with heat treatment. GC-MS analysis revealed that the presence of Fe2+ enhanced the loss of green/grassy volatiles and promoted the formation of new volatiles with diversified aroma characteristics, resulting in a dull scent of green tea infusion. Our results revealed how Fe2+ induced aroma deterioration of green tea infusion with heat treatment and could help guide tea producers in attenuating the aroma deterioration of tea infusion during processing.

Identification of Cell Status via Simultaneous Multitarget Imaging Using Programmable Scanning Electrochemical Microscopy.

A programmable multitarget-response electrochemical imaging technique was presented using scanning electrochemical microscopy (SECM) combined with a self-designed waveform. The potential waveform applied to the tip decreased the charging current caused by the potential switch, enhancing the signal-to-noise ratio. This programmable SECM (P-SECM) method was used to scan a metal strip for verifying its feasibility in feedback mode. Since it could achieve simultaneous multitarget imaging during one single imaging process, PC12 cells status was imaged and identified through three different molecules (FcMeOH, Ru(NH3)63+, and oxygen). The FcMeOH image eliminated the error from cell height, and the Ru(NH3)63+ image verified the change of membrane permeability. Moreover, the oxygen image demonstrated the bioactivity of the cell via its intensity of respiration. Combining information from these three molecules, the cell status could be determined accurately and also the error caused by time consumption with multiple scans in traditional SECM was eliminated.

Application of capillary electrophoresis technique for the enantioseparation of bioactive ferrocene-based compounds versus DFT calculated data.

Herein, a series of bioactive ferrocene-modified N-heterocycles with alkyl linkers was prepared in good to quantitative yields starting from easy accessible ferrocene alcohols and heterocycles under acidic or neutral (for imidazole) conditions in racemic forms. The analytical resolution of a number of bioactive racemic ferrocene azoles 1-6 (where azole = imidazole, pyrazole, and benzotriazole derivatives) into enantiomers was first carried out by CE using sulfobuthylether-ß-CD (captisol) as a chiral selector. The analytical approaches to highly enantiomeric-enriched ferrocene derivatives are based on the formation of their inclusion complexes. The best chiral separation was achieved using zone CE in a quartz capillary. The ACE was used to evaluate the stability constants of captisol complexes with enantiomeric forms of two ferrocene derivatives 1, FcCHMe-imidazole, and 6, FcCHMe-benzotriazole. The optimal conditions for the resolution of the studied (R, S)-ferrocene compounds 1, 2, and 6 were predicted on the basis of the performed quantum chemical calculations and then implemented by the electrophoretic method. A high correlation between density functional theory calculation results and experimental electrophoresis data were obtained. Successful enantioseparation of racemic mixtures is of great importance for the characterization and further applications of drug candidates in enantiopure forms and in the development of clinical treatment. The advantages of the CE procedure make it possible to have important practical value and significance for determining the purity and enantiomeric excess of other ferrocene-containing compounds.

Microcystis aeruginosa inactivation and microcystin-LR degradation by the photo-Fenton process at the initial near-neutral pH.

Of all cyanobacteria, Microcystis aeruginosa is the most commonly found species in bloom episodes all over the world. This species is known to produce cyanopeptides with hepatotoxic effects, namely microcystins (MCs). In this regard, Advanced Oxidation Processes (AOPs) have been widely studied for cyanotoxin degradation, but very few studies focused on cyanobacteria inactivation combined with toxin removal. To our knowledge, this is the first report of the photo-Fenton process application focusing on M. aeruginosa inactivation and microcystin-LR (MC-LR) degradation. This research work aimed to evaluate the photo-Fenton process under three different conditions with regard to Fe2+/H2O2 ratios (0.6/10, 5/50, and 20/100 mg L-1) at the initial near-neutral pH. Process efficiency was measured by immediate cell density reduction, growth inhibition, effect on MC-LR concentrations, and scanning electron microscopy (SEM) to analyze any alterations in cell morphology. Growth inhibition test (GIT) results pointed to cell inactivation under all conditions tested, and MC-LR concentrations were reduced below WHO's maximum limit at medium and higher concentrations of reagents. The possible mechanisms of cell inactivation by oxidative species are discussed.

Common and rare iron, sulfur, and zinc minerals in technogenically contaminated hydromorphic soil from Southern Russia.

Soils formed after the desiccation of Lake Atamanskoe, which has served as a reservoir for liquid industrial waste from the city of Kamensk-Shakhtinsky during a long time, were studied. These soils differ from zonal soils by a strong contamination with zinc and sulfur. Preliminary studies showed that Fe compounds fix a significant part of zinc. This requires to study S, Zn, and Fe minerals. In this work, Mössbauer spectroscopy was used for the identification of iron compounds and scanning electron microscopy was used for the microanalysis of these and other minerals. To facilitate the identification of Fe minerals, brown iron ocher was removed from a contaminated soil sample and analyzed. From electron microscopy and Mössbauer spectroscopy data, ocher contained hydrogoethite with a high content of sorption water and schwertmannite (a rare mineral, probably found in Russia for the first time). The chemical composition of this schwertmannite better corresponds to the Cashion-Murad model than to the Bigham model. Particles of partially oxidized magnetite and wustite enriched with zinc were revealed under electron microscope. Siderite with partial substitution of Fe2+ by Zn2+ was detected. Thus, contaminated hydromorphic soil contains both common minerals (illite, goethite, hematite, gypsum) and rare minerals (schwertmannite, Zn siderite, partially oxidized magnetite and wustite enriched with zinc).

Bioimaging and Biosensing of Ferrous Ion in Neurons and HepG2 Cells upon Oxidative Stress.

Iron ions, as a main component of intracellular labile iron, not only play an important function in oxygen transport, enzymatic reactions, and electron transport but also are vitally important in oxidative stress. In this work, we developed a ratiometric fluorescent biosensor for ferrous ion (Fe2+), in which gold nanoclusters (AuNCs) were synthesized as a stable fluorescent probe and a ligand (FeL) was designed for specific recognition of Fe2+ and conjugated onto AuNCs (AuNC@FeL). Meanwhile, water-soluble sulfocyanine 7 N-hydroxysuccinimide ester (Cy7 NHS ester) was immobilized onto AuNC@FeL as a reference element. The developed ratiometric fluorescent nansosensor displayed good linearity with the concentration of Fe2+ in the range of 1-105 µM, and detection limit was achieved down to 210 nM. In addition, this nanosensor responded to Fe2+ in less than 1.23 s and showed high selectivity against other metal ions, amino acids, and reactive oxygen species. With the advantages of high selectivity and accuracy, as well as quick response and long-term stability, this organic-inorganic ratiometric fluorescent probe was successfully applied in real-time biosensing and bioimaging of Fe2+ in neurons and HepG2 cells. By use of this tool, it was found that the increasing concentration of Fe2+ in live cells was closely related to oxidative stress.

A reactivity-based probe of the intracellular labile ferrous iron pool.

Improved methods for studying intracellular reactive Fe(II) are of significant interest for studies of iron metabolism and disease-relevant changes in iron homeostasis. Here we describe a highly selective reactivity-based probe in which a Fenton-type reaction with intracellular labile Fe(II) leads to unmasking of the aminonucleoside puromycin. Puromycin leaves a permanent and dose-dependent mark on treated cells that can be detected with high sensitivity and precision using a high-content, plate-based immunofluorescence assay. Using this new probe and screening approach, we detected alteration of cellular labile Fe(II) in response extracellular iron conditioning, overexpression of iron storage and/or export proteins, and post-translational regulation of iron export. We also used this new tool to demonstrate that labile Fe(II) pools are larger in cancer cells than in nontumorigenic cells.

Optimization of kinetics and operating parameters for the bioleaching of heavy metals from sewage sludge, using co-inoculation of two Acidithiobacillus species.

This study explores the potential for synchronous extraction of Cu, Cr, Ni and Zn during sewage sludge bioleaching processes, using three types of bacterial cultures: a pure culture of Acidithiobacillus ferrooxidans (A. ferrooxidans); a pure culture of Acidithiobacillus thiooxidans (A. thiooxidans); and a mixed culture of A. ferrooxidans and A. thiooxidans. Variable operating parameters included initial pH, solids concentration, sulfur concentration and ferrous iron concentration, with optimization via Box-Behnken design of response surface methodology. Results indicate that the mixed culture of A. ferrooxidans and A. thiooxidans, was the most effective at bioleaching heavy metals from sewage sludge. The optimal operating conditions were as follows: an initial pH of 2.0, with concentrations of 3% solids, 6.14 g L-1 sulfur and 4.55 g L-1 ferrous iron. Maximum extraction efficiencies obtained after 14 days of bioleaching under optimal conditions, were 98.54% Cu, 57.99% Cr, 60.06% Ni and 95.60% Zn. Bioleaching kinetics were effectively simulated using a shrinking core model to explain the leaching reaction, with modelling results suggesting that the rate was determined by the diffusion step.

Photo-Fenton degradation of ethyl xanthate catalyzed by bentonite-supported Fe(II)/phosphotungstic acid under visible light irradiation.

In this study, using bentonite-supported Fe(II)/phosphotungstic acid composite (HPW-Fe-Organicbent) prepared by mechanochemical synthesis as heterogeneous catalyst, the photo-Fenton degradation of ethyl xanthate under visible light irradiation was studied in detail. The results showed that the degradation of ethyl xanthate was mainly impacted by H2O2 dosage, catalyst dosage and reaction time. HPW-Fe-Organicbent catalyst had a wide applicable range of pH and kept a high catalytic activity even at high pH in the photo-Fenton degradation of ethyl xanthate. It was found that the degradation of ethyl xanthate in the photo-Fenton process catalyzed by HPW-Fe-Organicbent mainly resulted from the hydroxyl radicals. HPW-Fe-Organicbent had an excellent stability in use, and retained almost all of its catalytic activity for four recycling times. Moreover, the kinetics study showed the degradation of ethyl xanthate, with the initial concentration below 50 mg/L, was well fitted by the pseudo-first-order rate model.

Calibrant-Free Analyte Quantitation via a Variable Velocity Flow Cell.

In this paper, we describe a novel method for analyte quantitation that does not rely on calibrants, internal standards, or calibration curves but, rather, leverages the relationship between disparate and predictable surface-directed analyte flux to an array of sensing addresses and a measured resultant signal. To reduce this concept to practice, we fabricated two flow cells such that the mean linear fluid velocity, U, was varied systematically over an array of electrodes positioned along the flow axis. This resulted in a predictable variation of the address-directed flux of a redox analyte, ferrocenedimethanol (FDM). The resultant limiting currents measured at a series of these electrodes, and accurately described by a convective-diffusive transport model, provided a means to calculate an "unknown" concentration without the use of calibrants, internal standards, or a calibration curve. Furthermore, the experiment and concentration calculation only takes minutes to perform. Deviation in calculated FDM concentrations from true values was minimized to less than 0.5% when empirically derived values of U were employed.

Chiral analysis of α-diimine Ru(II) and Fe(II) complexes by capillary electrophoresis using sulfated cyclodextrins as stereoselectors.

CE using randomly highly sulfated α-, ß-, and γ-CDs (S-α-CD, S-ß-CD, S-γ-CD), sulfobutylether-ß-CD (SBE-ß-CD), single isomer (6-O-sulfo) α-, ß-, and γ-CDs, and their derivatives as stereoselectors was applied to chiral analysis of polypyridyl complexes of [Ru(bpy)3 ]2+ , [Ru(phen)3 ]2+ , and [Fe(phen)3 ]2+ (bpy = 2,2'-bipyridine; phen = 1,10 phenanthroline). The best separations of Δ- and Λ-enantiomers of the these complexes with high resolution (up to R1,2  = 7.0) and short analysis times (10-20 min) were achieved in the BGE composed of 22 mM NaOH/35 mM H3 PO4 , pH 2.4, containing 1.5-6.0 mM S-α-CD or S-ß-CD, or SBE-ß-CD as chiral selectors. The developed method was applied to the assessment of enantiomeric purity of several samples of [Ru(bpy)3 ]2+ catalyst. CE experiments were performed in a homemade analyzer equipped with bare or hydroxypropylcellulose-coated fused-silica capillaries (total/effective length 40/29 cm, id/od 50/375 µm) and an UV absorption detector operating at 206 nm. In addition to chiral analysis, apparent binding constants of the complexes of [Ru(bpy)3 ]2+ , [Ru(phen)3 ]2+ , and [Fe(phen)3 ]2+ enantiomers with five sulfated CDs (S-α-CD, S-ß-CD, S-γ-CD, SBE-ß-CD, and 16Me-8S-γ-CD) were determined from the dependence of their effective electrophoretic mobilities on the concentration of the CDs in the BGE by nonlinear regression analysis. Calculated apparent binding constants of these complexes were found to be in the (1.10-4.66) × 103  L/mol range. Moreover, it was shown that at selected concentrations of some S-CDs and suppressed or very low electroosmotic flow, the exceptional enantioseparations with infinite resolution could be achieved.

Thiolate-based dinitrosyl iron complexes: Decomposition and detection and differentiation from S-nitrosothiols.

Dinitrosyl iron complexes (DNIC) spontaneously form in aqueous solutions of Fe(II), nitric oxide (NO), and various anions. They exist as an equilibrium between diamagnetic, dimeric (bi-DNIC) and paramagnetic, monomeric (mono-DNIC) forms. Thiolate groups (e.g., on glutathione or protein cysteine residues) are the most biologically relevant anions to coordinate to Fe(II). Low molecular weight DNIC have previously been suggested to be important mediators of NO biology in cells, and emerging literature supports their role in the control of iron-dependent cellular processes. Recently, it was shown that DNIC may be one of the most abundant NO-derived products in cells and may serve as intermediates in the cellular formation of S-nitrosothiols. In this work, we examined the stability of low molecular weight DNIC and investigated issues with their detection in the presence of other NO-dependent metabolites such as S-nitrosothiols. By using spectrophotometric, Electron Paramagnetic Resonance, ozone-based chemiluminesence, and HPLC techniques we established that at neutral pH, bi-DNIC remain stable for hours, whereas excess thiol results in decomposition to form nitrite. NO was also detected during the decomposition, but no S-nitrosothiol formation was observed. Importantly, mercury chloride accelerated the degradation of DNIC; thus, the implications of this finding for the diagnostic use of mercury chloride in the detection of S-nitrosothiols were determined in simple and complex biological systems. We conclude S-nitrosothiol levels may have been substantially overestimated in all methods where mercury chloride has been used.

Ferrous iron content of intravenous iron formulations.

The observed biological differences in safety and efficacy of intravenous (IV) iron formulations are attributable to physicochemical differences. In addition to differences in carbohydrate shell, polarographic signatures due to ferric iron [Fe(III)] and ferrous iron [Fe(II)] differ among IV iron formulations. Intravenous iron contains Fe(II) and releases labile iron in the circulation. Fe(II) generates toxic free radicals and reactive oxygen species and binds to bacterial siderophores and other in vivo sequestering agents. To evaluate whether differences in Fe(II) content may account for some observed biological differences between IV iron formulations, samples from multiple lots of various IV iron formulations were dissolved in 12 M concentrated HCl to dissociate and release all iron and then diluted with water to achieve 0.1 M HCl concentration. Fe(II) was then directly measured using ferrozine reagent and ultraviolet spectroscopy at 562 nm. Total iron content was measured by adding an excess of ascorbic acid to reduce Fe(III) to Fe(II), and Fe(II) was then measured by ferrozine assay. The Fe(II) concentration as a proportion of total iron content [Fe(III) + Fe(II)] in different lots of IV iron formulations was as follows: iron gluconate, 1.4 and 1.8 %; ferumoxytol, 0.26 %; ferric carboxymaltose, 1.4 %; iron dextran, 0.8 %; and iron sucrose, 10.2, 15.5, and 11.0 % (average, 12.2 %). The average Fe(II) content in iron sucrose was, therefore, ≥7.5-fold higher than in the other IV iron formulations. Further studies are needed to investigate the relationship between Fe(II) content and increased risk of oxidative stress and infections with iron sucrose.

Single (19)F probe for simultaneous detection of multiple metal ions using miCEST MRI.

The local presence and concentration of metal ions in biological systems has been extensively studied ex vivo using fluorescent dyes. However, the detection of multiple metal ions in vivo remains a major challenge. We present a magnetic resonance imaging (MRI)-based method for noninvasive detection of specific ions that may be coexisting, using the tetrafluorinated derivative of the BAPTA (TF-BAPTA) chelate as a (19)F chelate analogue of existing optical dyes. Taking advantage of the difference in the ion-specific (19)F nuclear magnetic resonance (NMR) chemical shift offset (Δω) values between the ion-bound and free TF-BAPTA, we exploited the dynamic exchange between ion-bound and free TF-BAPTA to obtain MRI contrast with multi-ion chemical exchange saturation transfer (miCEST). We demonstrate that TF-BAPTA as a prototype single (19)F probe can be used to separately visualize mixed Zn(2+) and Fe(2+) ions in a specific and simultaneous fashion, without interference from potential competitive ions.

Simultaneous detection of polar and nonpolar compounds by ambient mass spectrometry with a dual electrospray and atmospheric pressure chemical ionization source.

A dual ionization source combining electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) was developed to simultaneously ionize both polar and nonpolar compounds. The source was constructed by inserting a fused silica capillary into a stainless steel column enclosed in a glass tube. A high dc voltage was applied to a methanol solution flowing in the fused silica capillary to generate an ESI plume at the capillary tip. A high ac voltage was applied to a ring electrode attached to the glass tube to generate plasma from the nitrogen gas flowing between the glass tube and the stainless steel column. The concentric arrangement of the ESI plume and the APCI plasma in the source ensured that analytes entering the ionization region interacted with both ESI and APCI primary ion species generated in the source. Because the high voltages required for ESI and APCI were independently applied and controlled, the dual ion source could be operated in ESI-only, APCI-only, or ESI+APCI modes. Analytes were introduced into the ESI and/or APCI plumes by irradiating sample surfaces with a continuous-wavelength laser or a pulsed laser beam. Analyte ions could also be produced by directing the dual ESI+APCI source toward sample surfaces for desorption and ionization. The ionization mechanisms involved in the dual ion source include Penning ionization, ion molecule reactions, and fused-droplet electrospray ionization. Standards of polycyclic aromatic hydrocarbons, angiotensin I, lidocaine, ferrocene, diesel, and rosemary oils were used for testing. Protonated analyte ions were detected in ESI-only mode, radical cations were detected in APCI-only mode, and both types of ions were detected in ESI+APCI mode.

Chemically and biologically harmless versus harmful ferritin/copper-metallothionein couples.

The simultaneous measurement of the decrease of available Fe(II) ions and the increase of available Fe(III) ions allowed the analysis of the ferroxidase activity of two distinct apoferritins. Although recombinant human apoferritin (HuFtH) rapidly oxidizes Fe(II) to Fe(III) , this iron is not properly stored in the ferritin cavity, as otherwise occurs in horse-spleen H/L-apoferritin (HsFt; H=heavy subunit, L=light subunit). Iron storage in these apoferritins was also studied in the presence of two copper-loaded mammalian metallothioneins (MT2 and MT3), a scenario that occurs in different brain-cell types. For HuFtH, unstored Fe(III) ions trigger the oxidation of Cu-MT2 with concomitant Cu(I) release. In contrast, there is no reaction with Cu-MT2 in the case of HsFt. Similarly, Cu-MT3 does not react during either HuFtH or HsFt iron reconstitution. Significantly, the combination of ferritin and metallothionein isoforms reported in glia and neuronal cells are precisely those combinations that avoid a harmful release of Fe(II) and Cu(I) ions.

Characterizing phosphorus speciation of Chesapeake Bay sediments using chemical extraction, 31P NMR, and X-ray absorption fine structure spectroscopy.

Nutrient contamination has been one of the lingering issues in the Chesapeake Bay because the bay restoration is complicated by temporally and seasonally variable nutrient sources and complex interaction between imported and regenerated nutrients. Differential reactivity of sedimentary phosphorus (P) pools in response to imposed biogeochemical conditions can record past sediment history and therefore a detailed sediment P speciation may provide information on P cycling particularly the stability of a P pool and the formation of one pool at the expense of another. This study examined sediment P speciation from three sites in the Chesapeake Bay: (i) a North site in the upstream bay, (ii) a middle site in the central bay dominated by seasonally hypoxic bottom water, and (iii) a South site at the bay-ocean boundary using a combination of sequential P extraction (SEDEX) and spectroscopic techniques, including (31)P NMR, P X-ray absorption near edge structure spectroscopy (XANES), and Fe extended X-ray absorption fine structure (EXAFS). Results from sequential P extraction reveal that sediment P is composed predominantly of ferric Fe-bound P and authigenic P, which was further confirmed by solid-state (31)P NMR, XANES, and EXAFS analyses. Additionally, solution (31)P NMR results show that the sediments from the middle site contain high amounts of organic P such as monoesters and diesters, compared to the other two sites, but that these compounds rapidly decrease with sediment depth indicating remineralized P could have precipitated as authigenic P. Fe EXAFS enabled to identify the changes in Fe mineral composition and P sinks in response to imposed redox condition in the middle site sediments. The presence of lepidocrocite, vermiculite, and Fe smectite in the middle site sediments indicates that some ferric Fe minerals can still be present along with pyrite and vivianite, and that ferric Fe-bound P pool can be a major P sink in anoxic sediments. These results provide improved insights into sediment P dynamics, particularly the rapid remineralization of organic P and the stability of Fe minerals and the ferric Fe-bound P pool in anoxic sediments in the Chesapeake Bay.

Ultrafast vibrational and structural dynamics of dimeric cyclopentadienyliron dicarbonyl examined by infrared spectroscopy.

In this work, we carry out steady-state, femtosecond pump-probe and two-dimensional (2D) infrared spectroscopic studies on dimeric π-cyclopentadienyliron dicarbonyl [CpFe(CO)2]2 in the C≡O stretching vibration frequency region in CCl4 and CH2Cl2. The cis and trans isomers, in terms of the position of two terminal C≡O groups, are found to coexist in the two solvents. A weak asymmetric stretching peak of the cis-isomer is revealed under that of the IR-active trans-isomer by analyzing the 2D infrared cross peak, which is supported by ab initio computations. Furthermore, vibrational population relaxation is found to be both solute and solvent dependent (ranging from 21 ps to 32 ps)--the fastest dynamics is found for the trans-isomer in the polar solvent environment, which is believed to be associated with the availability and the number of efficient energy accepting channels for solvent molecules. The spectral diffusion dynamics of the C≡O stretching vibrations, occurring on an even faster time scale (1 ps to 3 ps), mainly exhibits solvent dependence--faster dynamics is found in the polar solvent, involving weak and rapidly fluctuating hydrogen bonding interactions between CH2 groups of the solvent and the terminal carbonyls of solutes.