Stoichiometric Relationship Research Articles

Iron redox shuttling and uptake by silicate minerals on the Namibian mud belt

Anoxic marine sediments represent an important source of bioavailable iron (Fe) to the ocean. The highest sedimentary Fe fluxes are observed in open-marine oxygen minimum zones where anoxic bottom waters are in contact with ferruginous surface sediments. Here, sedimentary Fe release, transport and re-deposition (i.e., Fe shuttling) may generate a lateral pattern of sedimentary Fe enrichment and depletion, which can be used to trace redox-related Fe mobility in the paleo-record. However, depending on the balance between terrigenous and authigenic (i.e., shuttle-related) Fe flux, the stability of bottom water redox conditions as well as post-depositional processes of mineral alteration, the sedimentary fingerprint of an Fe redox shuttle may be obscured and difficult to identify.We investigated sedimentary Fe cycling along two transects across the Namibian mud belt with variable terrigenous sedimentation (23°S < 25°S) and during two seasons with opposing bottom water redox conditions (oxic in austral winter versus anoxic to sulfidic in austral summer). On both transects, substantial benthic Fe fluxes up to −50 µmol m−2 d−1 were inferred based on pore water profiles. The magnitude of these fluxes is comparable to those reported for other open-marine oxygen minimum zones. On the transect at 23°S, Fe source areas with ferruginous surface sediments were clearly separated from Fe sink areas with highly sulfidic surface sediments. Therefore, Fe redox shuttling was reflected by a lateral pattern of reactive Fe depletion and enrichment relative to the terrigenous background sedimentation. By contrast, on the transect at 25°S, benthic Fe fluxes were temporally and spatially more variable and surface sediments were ferruginous or only weakly sulfidic. Therefore, sedimentary Fe depletion and enrichment was less pronounced at 25°S. In the Fe sink area at 23°S, hydrogen sulfide was present at the sediment surface during both sampling campaigns and solid phase data suggest that Fe sulfide minerals represented the main burial phase of reactive Fe. By contrast, at 25°S excess Fe was associated with potassium (K) rather than reduced sulfur. While a differing sediment provenance cannot be ruled out entirely, combined evidence from pore water silica profiles, K to Fe stoichiometric relationships and electron microprobe images suggest that laterally derived excess Fe was incorporated into pre-existing and/or authigenic clay minerals during early diagenesis. Iron uptake by clay minerals may be supported by frequent redox oscillations and sediment mixing preventing preservation of Fe sulfide minerals and promoting Fe and K fixation in clay minerals. The burial fluxes of excess Fe associated with sulfide minerals at 23°S and silicate minerals at 25°S were similar. Our findings thus underscore that neoformation or alteration of silicate minerals can be important processes within the low-temperature marine Fe cycle.

Patterns of Soil Stoichiometry Driven by Mixed Tree Species Proportions in Boreal Forest

Soil stoichiometry is essential for determining the ecological functioning of terrestrial ecosystems. Understanding the stoichiometric relationships in mixed forests could enhance our knowledge of nutrient cycling. In a mixed forest zone of Larix principis-rupprechtii (LP) and Betula Platyphylla (BP) in Hebei China, we conducted a study at six different sites with varying levels of tree species mixing. The proportion of L. principis-rupprechtii ranged from 0% to 100%, with intermediate values of 8.58%, 10.44%, 18.62%, and 38.32%. We compared soil stoichiometry, including carbon (C), nitrogen (N), and phosphorus (P), as well as chemical and physical properties across these sites. Piecewise structural equation modeling (piecewiseSEM) was used to assess the direct and indirect links between key ecosystem factors and their effects on soil stoichiometry. In mixed forests, the soil exhibited higher contents of soil organic matter (SOM), total nitrogen (TN), and total phosphorus (TP) compared to those in pure LP forests. Additionally, the soil C: N ratio in the 8.58% and 18.62% mixed forests as well as pure BP forests was significantly higher than that in LP forests. Structural equation modeling (SEM) revealed that the contents and ratios of soil C, N, and P exhibited different responses to mixed species proportions. The effect of mixed species proportions on soil nutrients was predominantly indirect, mediated primarily by variations in soil-available nutrients and, to a lesser extent, by physical properties and pH. Specifically, an increase in the proportion of LP in mixed forests had a direct negative effect on soil-available nutrients, which in turn had a positive effect on the content of SOM, TN, and TP and their respective ratios. Based on these findings, we can predict that soil nutrient limitation becomes more pronounced with increasing proportions of Larix principis-rupprechtii in the mixed forest. Our results emphasized the significance of changes in mixed species proportions on soil stoichiometry, providing valuable references for the sustainable development of forests.

Molecular-Scale Interactions in the Choline Chloride-Ethylene Glycol Deep Eutectic Solvent System: The Importance of Chromophore Charge in Mediating Rotational Dynamics.

We report on the rotational diffusion dynamics of three chromophores (disodium fluorescein, oxazine 725, and perylene) in a series of choline chloride-ethylene glycol (ChCl:EG) deep eutectic solvent (DES) systems. We observe behavior independent of DES bulk viscosity for the cationic and neutral probes and behavior that is consistent with stick-limit interactions for the modified Debye-Stokes-Einstein model for the anionic probe. This finding indicates that the anionic species is integral to the interactions between DES constituent species that are responsible for local organization, consistent with previous MD simulations that showed higher interaction energies associated with both the hydrogen bond donor (EG) and hydrogen bond acceptor (Ch+) interactions with Cl- in ChCl:EG mixtures. The reorientation data reported here also indicate a region around 15 mol % ChCl where the stoichiometric relationship between the species gives rise to changes in the details of intermolecular interactions.

Predicting Peptide Ionization Efficiencies for Electrospray Ionization Mass Spectrometry Using Machine Learning.

Mass spectrometry (MS) is inherently an information-rich technique. In this era of big data, label-free MS quantification for nontargeted studies has gained increasing popularity, especially for complex systems. One of the cornerstones of successful label-free quantification is the predictive modeling of ionization efficiency (IE) based on solutes' physicochemical properties. While many have studied IE modeling for small molecules, there are limited reports on peptide IEs. In this study, we leverage the stoichiometric relationship in trypsin digests of well-characterized monoclonal antibodies (mAbs) to compile a data set of relative ionization efficiencies (RIEs) for 241 peptides. From each peptide's sequence, we computed a set of physiochemical descriptors, which were then used to train machine learning regression models to predict RIEs. Peptides shorter than 20 amino acids had RIEs that were highly correlated to their molecular weight. A random forest (RF) model was able to best predict the RIEs of a test data set with a mean relative error of 23.9%. For larger peptides, a multilayer perceptron (MLP) model improved RIE prediction compared to current best practices, reducing mean relative error from 60.5% to 32.0%. Finally, we also show the application of the RF model in label-free relative protein quantification and improving the quantification of peptide post-translational modifications (PTMs). This approach to predicting peptide IEs from their sequences enables the development of accurate label-free quantification workflows for peptide and protein analysis.

The spontaneous passivation of (CoFeNi)(1-x)/3Crx alloys in sulfuric acid

The influence of at% Cr on the spontaneous passivation of (CoFeNi)(1-x)/3Crx alloys in 0.1 M H2SO4 was investigated. During spontaneous passivation, Cr enrichment occurs due to the selective dissolution of the matrix elements. The quantity of Cr enrichment is relatively constant with at% Cr while the total quantity of alloy dissolved decreases with increasing at% Cr. Element resolved polarization curves predict spontaneous passivation by comparing the critical dissolution rate with the cathodic kinetics near the corrosion potential. The stoichiometric relationships between the spontaneous dissolution rate, Cr enrichment, and the open circuit potential were determined and discussed.

Abstract Mo116: Evaluating MYBPC3 and MYBPHL missense mutations on sarcomere incorporation

Hypertrophic cardiomyopathy (HCM) is one of the common genetic heart diseases and causes hypercontractility and pathological thickening of the myocardium. Cardiac myosin binding protein-C (cMyBP-C) is an important regulator of cardiac contractility and MYBPC3 mutations accounts for 40% of HCM cases, resulting in the truncation and loss of cMyBP-C. While cMyBP-C is expressed in both atria and ventricle, its recently identified homologous partner, myosin binding protein-HL (MyBP-HL) is solely expressed in the atria. Loss of function mutations in MYBPHL cause dilated cardiomyopathy in humans and mice. MyBP-HL and cMyBP-C bind to specific positions on the thick filament within the C-zone of sarcomere. In the atria, there is a 1:1 ratio between MyBP-HL and cMyBP-C, whereas cMyBP-C is solely expressed in the ventricle at double the cMyBP-C content of the the atria, establishing a stoichiometric relationship between these two proteins in their ability to bind to the thick filament within the sarcomere. Within the ventricle, heterozygous missense mutations within the necessary myosin binding domains of cMyBP-C may prevent proper myosin binding and sarcomere incorporation, but function may still be preserved due to the other unaffected allele. Since the atria expresses MyBP-HL and cMyBP-C, we hypothesize that MYBPC3 and MYBPHL missense mutations are more severe due to the competition for binding sites within the sarcomere between these proteins. We have identified MYBPC3 and MYBPHL missense mutations and variants to evaluate their pathogenicity and sarcomere incorporation via immunofluorescence microscopy within neonatal rat ventricular cardiomyocytes. To test these mutations, we created a “Mini-C” construct consisting of the thick filament binding domains of cMyBP-C. We validated our Mini-C construct via transfection and co-localization with endogenous cMyBP-C in neonatal rat ventricular cardiomyocytes (NRVMs). Our data demonstrate that known pathogenic MYBPC3 missense mutations have improper sarcomere incorporation within NRVMs. Disease associated MYBPHL missense mutations also show improper sarcomere incorporation. To test the effects of missense mutations on myosin binding protein stoichiometry within the sarcomere, we have created and validated a T2A/P2A construct, expressing our Mini-C construct, a fluorescent reporter, Td-Tomato, and our hMyBP-HL construct at consistent and reproducible expression levels via western blot and mass spectrometry.

Simultaneous determination of peroxydisulfate and bisulfite concentrations with quenching-agent-assisted iodometry

Fenton/Fenton-like reactions have gained popularity for their remarkable proficiency in decomposing organic pollutants, especially when enhanced by reductants addition for accelerating the Fe2+ regeneration. Nevertheless, these works predominantly centered on the formation and utilization of hydroxyl radicals (•OH) in the process, neglecting the evolution of oxidant and reductant due to the difficulty in the simultaneous determination of these two components. By employing the quenching-iodometric method, we could simultaneously determine the concentrations of HSO3- and peroxydisulfate (PDS). This method first employed an excess of peroxymonosulfate (PMS) to effectively quench HSO3-, and then used the iodometric spectrophotometry to simultaneously determine the concentrations of PMS and PDS in the reaction system. Finally, through precise stoichiometric relationships, we could accurately calculate the concentration of HSO3-. Based on this method, we achieved concentration measurements that, upon linear fitting, yielded a correlation coefficient (R2) surpassing 0.99, unequivocally affirming the method's accuracy and trustworthiness. In this work, an innovation approach for determining the concentrations of HSO3- (reductant) and PDS(oxidant) was explored.Additionally, the resilience of the method was verified across different pH levels and in the presence of diverse impurity ions. The results ensured precise concentration measurements in the real wastewater. This method was characterized by its simplicity, rapid analysis, and environmental friendliness, offering a new analytical strategy for the determination of PDS and HSO3- in environmental samples. The method enables more meticulous monitoring of chemical usage in water treatment, facilitating optimized dosing strategies and assessments of reductant-enhanced Fenton or Fenton-like system in water purification.

Surface modification of carbon dots with cyclodextrins as potential biocompatible photoluminescent delivery/bioimaging nanoplatform

BackgroundCyclodextrins are a well-established system which form inclusion complexes with many guest molecules. This property can be easily exploited to develop drug delivery systems. Additionally, carbon dots (CD) are a low-toxic photoluminescent product which have been used as luminescent tags. The combination of cyclodextrins and carbon dots allows obtaining a new nanoplatform, a biocompatible material, with both capabilities, increasing as well the internalization by the cells of the CD, induced by the cyclodextrins. ResultsIn the present work, we have modified the surface of carbon dots obtained from citric acid and glutathione with β and γ cyclodextrins. After a morphological and spectroscopic characterization, we concluded that the luminescence quantum yield and absorption molar coefficient of the derivatized and unmodified carbon dots was the same. These findings, together with the spectroscopic detection of active cyclodextrins, those bond to the CD able to interact with a guest molecule, allowed determination of the ratios: cyclodextrins/CD, active cyclodextrins/CD and an estimation of the CD molecular mass. Furthermore, the biocompatibility of the new materials was evaluated through cytotoxicity and cell-penetrance assays revealing that the materials were non cytotoxic up to 0.1 mg/mL. Moreover, the biocompatible developed nanoplatform penetrates in the cells maintaining the material's intrinsic fluorescence, thus constituting an adequate photoluminescent-tag with high-contrast for in vitro cell imaging. SignificanceThis work provides a new and easy method to combine cyclodextrins and carbon dots into a biocompatible material which can be used as nanoplatform both as drug delivery system and as photoluminescent tag in cell imaging. Likewise, this paper shows how to characterize the number of cyclodextrins and active cyclodextrins per CD, having an average stoichiometric relation of 1:1 for guest molecule – CD. Additionally, the minimum molecular mass of the unmodified CD was indirectly obtained, yielding about 1.6–1.9 kDa.

Changes in plant-soil-microbe C-N-P contents and stoichiometry during poplar shelterbelt degradation

Extensive poplar shelterbelts are experiencing degradation, yet the consequences of this deterioration on plant-soil-microbe stoichiometry remain poorly understood. In this study, we selected three distinct types of pure poplar shelterbelts and examined the dynamics of tree leaf, soil, and microbial biomass carbon (C), nitrogen (N), and phosphorus (P) contents, as well as their stoichiometric relationships, at different stages of shelterbelt degradation, in order to explore the balance and limitation of nutrients in these rapidly degrading ecosystems. Our results show a consistent reduction in foliar N:P ratio throughout the degradation process for all shelterbelts, indicating an amplified N limitation on tree growth as degradation ensued. However, the underlying mechanisms varied among tree species. For Populus alba shelterbelts, the diminished soil organic carbon and total nitrogen (TN) contents during degradation suggest a reduction in the availability of substrates and energy sources for N mineralization, which combines with higher microbial N assimilation reflected by elevated soil microbial biomass carbon (SMBC) content, contributing to lower N absorption by trees. In Lombardy poplar shelterbelts, the inconsistent trends among reduced foliar N, stable soil TN, and unaltered SMBC and SMBC: SMBN ratio suggest either a decrease in microbial activity as degradation advanced or a reallocation of N by trees into tissues like roots, leaving the leaves N-deficient. Within Populus popular’s shelterbelts, the diminished foliar N content, accompanied by an augmented foliar C:N ratio and reduced soil N:P ratio, indicates potentially deteriorated litter quality. This deterioration contributes to knock-on effects involving N-deficit soil organic matter, limited soil N availability, decreased N absorption by trees, and subsequently reduced foliar N content. Our study highlights the distinctive responses of plant-soil-microbe C-N-P stoichiometry to shelterbelt degradation, contingent on tree species, underscoring the diverse strategies that poplar shelterbelts employ when confronted with harsh internal and external conditions.

Mathematical Modeling of the Process of Acid Rain Formation in Case of Emissions from Thermal Power Plants

Purpose. It is known that acid rain has a negative impact on the environment. The formation of acid precipitation in the atmosphere occurs as a result of the chemical interaction of fuel combustion products and atmospheric humidity. Acid rain leads to crop losses, deterioration of soil fertility, and acidification of water in reservoirs. The development of scientifically based methods for studying the intensity of such acidic pollution of the air and soil surface in regions with significant emissions from thermal power plants remains an urgent problem. To solve this problem, it is important to use mathematical modeling, since it is impossible to determine the impact of emissions from thermal power plants on the formation of acid rain experimentally. Therefore, the main goal of the work is to create a mathematical model for predicting the formation of acid rain in the event of emissions from thermal power plants. Methodology. To predict the process of acid rain formation, a three-dimensional equation of convective diffusion transport of a pollutant is used, which takes into account the wind speed profile, atmospheric stratification, emission intensity of an impurity, and wind direction. This equation is also used to describe the process of water vapor transport in atmospheric air. To describe the process of acid formation in atmospheric air, a stoichiometric relationship is used. The numerical integration of the modeling equation of transfer was carried out using the splitting method. Findings. A multifactorial numerical model was built that allows determining the zones where acid rain is formed. The problem of predicting the formation of acid rain in the case of emissions from thermal power plants on the basis of the constructed numerical model is considered. Originality. A numerical model is proposed to predict the occurrence of acid rain due to emissions from thermal power plants. The model is multifactorial and takes into account convection, atmospheric diffusion, and an uneven wind profile. A computer code has been created that allows for rapid assessment of acid pollution zones. Practical value. The developed computer code for analyzing the zones of acidic pollution of the environment in the case of industrial emissions makes it possible to predict the intensity of such pollution in various meteorological conditions.

Study on structural, optical, and electrical properties of yttrium doped molybdenum oxide thin film and its MIS diode performance

In this study, Orthorhombic pure MoO3 and various weight percentages of Y-doped MoO3 nanostructure arrays were successfully deposited using the simple jet nebulizer spray pyrolysis process at an ideal substrate temperature of 500 °C. In order to create metal-insulator-semiconductor-based Schottky barrier diodes, Y-doped MoO3 nanostructure arrays were employed as an insulating layer. The influence of Y-doped MoO3 concentration during the deposition process was carefully analyzed in relation to the structural, morphological, optical, and electrical characteristics of Y-doped MoO3 nanostructure array films. The produced films' crystalline nature with an orthorhombic phase was shown by the XRD pattern. An FE-SEM was used to analyse the solidly linked plate-like structure of Y-doped MoO3 at higher concentrations of 6 wt%. The EDAX spectrum was used to confirm the stoichiometric relationship between the elements O, Mo, and Y. The band gap values of the Y-doped MoO3 were determined using UV–Vis spectroscopy to range from 3.3 to 3.18 eV with doped concentrations. The film made with 6 wt% Y doped MoO3 showed a sharp improvement in electrical conductivity according to a DC electrical analysis. Notably, MIS diode made with 6 wt% Y-doped MoO3 in particular showed a low ideality factor (n = 2.63), strong photosensitivity (PS = 17,509.62%), responsivity of 738 mA/W, and a maximum QE of 97.49% under illumination (130 mW/cm2). Additionally, a 6 wt percent Y-based diode obtained a greater detectivity of D* = 7.16 1009 jones in a dark environment condition.

Corymbia citriodora Girdling Aiming Forest Restoration Intensifies the Production of Labile C, N and P in the Soil

ABSTRACT Understanding the effect of different C. citriodora removal management in a Conservation Unit (CU) aimed at forest restoration on the dynamics of the labile and stable fractions of the SOM and to quantify the stoichiometric relationships of these fractions. Soil samples were collected in four areas in the União Biological Reserve (REBIO), Rio de Janeiro, Brazil, namely: forest (FF); C. citriodora trees submitted to girdling (GR); C. citriodora trees submitted to the practice of clear cutting and subsequent planting of native species (PL); abandoned C. citriodora trees without management practice (EU). In these samples, the total content of carbon (C), nitrogen (N) and phosphorus (P) in the air-dried fine earth (ADFE) were determined; in light-fraction organic matter (LFOM) and in the particle size fractions of SOM. It was observed that the C:N and C:P ratios were higher in the EU area and lower in PL in both ADFE and LFOM samples. In EU, lower levels of C, N and P were observed in the SOM particulate fraction. GR favors the production of less recalcitrant and more labile material when compared to EU. The short time (4 years) of implementation of the system in PL directly affects the low production of LFOM; however, this material has high levels of N and P, favoring the low C:N and C:P ratio. EU intensifies the concentration of nutrients in stable fractions in the soil, which can favor the preservation of the soil structure, mitigating its losses.

Solubilization mechanism of α-glycosylated naringin based on self-assembled nanostructures and its application to skin formulation

We previously reported that α-glycosylated naringin (naringin-G), synthesized by enzyme-catalyzed transglycosylation, can enhance the solubility of poorly water-soluble compounds without surface-active property. However, the solubilization mechanism has not been fully elucidated. In this study, the solubilization mechanism of naringin-G was investigated using nuclear magnetic resonance (NMR) spectroscopy, and its application in skin formulations was further investigated. 1H NMR and dynamic light scattering measurements at various concentrations confirmed the self-assembled nanostructures of naringin-G above a critical aggregation concentration of approximately 2.2 mg/mL. Two-dimensional 1H–1H nuclear Overhauser effect spectroscopy and solubility tests revealed that flavone with poor water solubility, could be solubilized in its self-assembled structure with a stoichiometric relationship with naringin-G. When naringin-G was included in the skin formulation, the permeated amount and permeability coefficient (Papp) of flavones improved up to four times with increasing amounts of naringin-G. However, flavone solubilization by adding an excessive amount of naringin-G resulted in a decreased permeated amount and Papp of flavones, indicating the interplay between the apparent solubility and skin permeability of flavones. Naringin-G, which forms a nanoaggregate structure without exhibiting surface-active properties, has the potential to enhance the solubility and skin permeation of poorly water-soluble compounds.

The Antitumoral Effect In Ovo of a New Inclusion Complex from Dimethoxycurcumin with Magnesium and Beta-Cyclodextrin.

Breast cancer is one of the leading causes of death in the female population because of the resistance of cancer cells to many anticancer drugs used. Curcumin has cytotoxic activities against breast cancer cells, although it has limited use due to its poor bioavailability and rapid metabolic elimination. The synthesis of metal complexes of curcumin and curcuminoids is a relevant topic in the search for more active and selective derivatives of these molecular scaffolds. However, solubility and bioavailability are concomitant disadvantages of these types of molecules. To overcome such drawbacks, the preparation of inclusion complexes offers a chemical and pharmacologically safe option for improving the aqueous solubility of organic molecules. Herein, we describe the preparation of the inclusion complex of dimethoxycurcumin magnesium complex (DiMeOC-Mg, (4)) with beta-cyclodextrin (DiMeOC-Mg-BCD, (5)) in the stoichiometric relationship 1:1. This new inclusion complex's solubility in aqueous media phosphate buffer saline (PBS) was improved by a factor of 6x over the free metal complex (4). Furthermore, 5 affects cell metabolic rate, cell morphology, cell migration, induced apoptosis, and downregulation of the matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9), interleukin-6 (IL-6), and signal transducer and activator of transcription-3 (STAT3) expression levels on MD Anderson metastasis breast-231 cancer (MDA-MB-231) cell lines. Results of an antitumor assay in an in ovo model showed up to 30% inhibition of tumor growth for breast cancer (MDA-MB-231) when using (5) (0.650 mg/kg dose) and 17.29% inhibition with the free homoleptic metal complex (1.5 mg/kg dose, (4)). While the formulation of inclusion complexes from metal complexes of curcuminoids demonstrates its usefulness in improving the solubility and bioavailability of these metallodrugs, the new compound (5) exhibits excellent potential for use as a therapeutic agent in the battle against breast cancer.

Controls on distributions of aluminium, manganese and cobalt in the South Atlantic Ocean along GEOTRACES transect GA10

Trace metals (TMs) manganese (Mn), cobalt (Co), and aluminium (Al) have important geochemical and biological roles in the ocean. Here, we present full depth profiles of dissolved (d) and particulate Al, Mn, and Co along the latitude of 40 °S in the South Atlantic Ocean from the GEOTRACES GA10 cruises that operated in austral spring 2010 and summer 2011. The region is characterized by enhanced primary productivity and forms a key transition zone between the Southern Ocean and South Atlantic Subtropical Gyre. The mean concentrations of dAl, dCo, and dMn (±standard deviation) were 3.36 ± 2.65 nmol kg−1, 35.3 ± 17.6 pmol kg−1, and 0.624 ± 1.08 nmol kg−1, respectively. Their distributions in surface waters were determined by external sources and complex internal biogeochemical processes. Specifically, surface ocean dCo was controlled by the interplay between phytoplankton uptake, remineralization and external inputs; dMn was likely determined by the formation and photoreduction of Mn-oxides; and dAl was supplied by atmospheric deposition and removed by scavenging onto particles. Fluvial and sedimentary inputs near the Rio de La Plata estuary and benthic sources from the Agulhas Bank resulted in elevated dTM concentrations in near-shore surface waters. These externally sourced dTMs were effectively delivered to the open ocean by offshore diffusion and/or advection, and potentially facilitated enhanced primary productivity along the transect.The distributions of dTMs at depth were predominantly controlled by the mixing of North Atlantic Deep Water (NADW) and waters of Antarctic origin (e.g., Upper Circumpolar Water (UCDW) and Antarctic Bottom Water (AABW)). The calculated endmember concentrations of dAl and dCo in NADW showed minor decreases in the SASTG following north–south transport, suggesting removal rates of 0.064 nM/year and 0.035–0.075 pM/year, respectively. The endmember concentration of dCo in AABW was maintained at ∼30 pmol kg−1 without evidence for scavenging removal in the Southern Ocean and SASTG (time frame >400 years). The concentrations of dMn in NADW and AABW were between 0.1 and 0.16 nmol kg−1, and any elevated dMn concentrations were ascribed to local external inputs (e.g., from sediments in the Argentine Basin and hydrothermal activity near the Mid-Atlantic Ridge). Hence, four controlling factors (sources, internal cycling, water mass mixing and time) need to be considered when assessing TM distributions in the global ocean, even for TMs that are vulnerable to scavenging removal processes. Because the deep waters formed in high latitude oceans are crucial components of the global thermohaline overturning system, any processes (e.g., glacier melting, upwelling and sinking, and biological activity) that impact the preformed dTM concentrations in high latitude oceans will determine the downstream dTM distributions. Therefore, the sources and sinks of TMs and associated biological activity in high latitude oceans could engender basin to global scale impacts on seawater distributions of Al, Co, and Mn and their stoichiometric relationships with macronutrients, and the global biogeochemical cycles of these scavenged-type TMs.

The Extraction Mechanism of Zirconium and Hafnium in the MIBK-HSCN System

The extraction of zirconium (Zr) and hafnium (Hf) in methyl isobutyl ketone (MIBK)—thiocyanic acid (HSCN) system has been widely used in the production of nuclear-grade zirconium and hafnium in industry, while the extraction mechanism was not adequately studied. In this study, the extraction and stripping equilibrium of Zr and Hf in the MIBK-HSCN system was studied. The results showed that elevated HCl concentration can increase the distribution ratio of SCN− and decrease that of Zr/Hf in organic phase. In the stripping process, HCl concentration and the Organic/Aqueous (O/A) phase ratio played important roles. The mechanism of the extraction reaction was discussed by considering the stoichiometric relationship of possible reaction equations and corresponding equilibrium constants. The results indicated that SCN− could be extracted into MIBK as HSCN·MIBK. Meanwhile, SCN− could also be extracted into MIBK by complexing with metal (Zr or Hf). The molar ratios of MIBK to the complexes of Zr and Hf have been found to be 5.34 and 5.03, respectively. With the increase in the initial concentration of HCl in the aqueous phase, the complexation molar ratios of SCN− to Zr and Hf increased first and then decreased, and so do the extraction equilibrium constants, which might be due to the extraction competition of HSCN and metal complexes.

Speciation and Organic Phase Structure in Nitric Acid Extraction with Trioctylamine.

Understanding chemical speciation and intermolecular interactions in multicomponent liquids is essential to understanding their phase and chemical equilibria, which underpin chemical separation processes, including solvent extraction. Here we report on the extraction of nitric acid from its aqueous solutions into organic solutions of trioctylamine (TOA) in toluene, investigated with spectroscopic, X-ray scattering, and computational tools to understand molecular speciation in the organic phase and its relationship with the nanoscale structure of the organic phase. Trends in acid and water extraction clearly show two and three regimes, respectively, indicating different stoichiometric relationships, but speciation of HNO3, water, and amine in these regimes is not apparent. 1H NMR of the organic phase shows that there are at least two distinct acidic protons in the organic phase while ATR-FTIR results show that the organic phase with excess acid extraction is a mixture of trioctylammonium-nitrate ion pairs (TOAH·NO3), and undissociated HNO3 molecules. Comparison with DFT-computed IR spectra show that the chain-like configurations of TOAH·NO3·HNO3·H2O are favored over TOAH·NO3·H2O·HNO3, i.e., direct interaction between the nitrate and HNO3 molecules is more favored compared to a water-mediated interaction. SAXS of the organic phases were modeled as sums of Ornstein-Zernike (O-Z) scattering and a prepeak feature in the higher Q region that corresponds to extractant packing. The extraction of undissociated HNO3 by the ion pairs leads to an increased X-ray scattering contrast in the organic phase without any significant change in the correlation length. These results show that the organic phase nanostructure is more sensitive to the concentration of TOAH·NO3 and is relatively unaffected by excess acid extraction. These findings will enable a molecular understanding of the mechanisms behind metal extraction from acidic media with basic extractants.

S2P2-the chloroplast-located intramembrane protease and its impact on the stoichiometry and functioning of the photosynthetic apparatus of A. thaliana.

S2P2 is a nuclear-encoded protease, potentially located in chloroplasts, which belongs to the zinc-containing, intramembrane, site-2 protease (S2P) family. In A. thaliana cells, most of the S2P proteases are located within the chloroplasts, where they play an important role in the development of chloroplasts, maintaining proper stoichiometric relations between polypeptides building photosynthetic complexes and influencing the sensitivity of plants to photoinhibitory conditions. Among the known chloroplast S2P proteases, S2P2 protease is one of the least known. Its exact location within the chloroplast is not known, nor is anything known about its possible physiological functions. Therefore, we decided to investigate an intra-chloroplast localization and the possible physiological role of S2P2. To study the intra-chloroplast localization of S2P2, we used specific anti-S2P2 antibodies and highly purified chloroplast fractions containing envelope, stroma, and thylakoid proteins. To study the physiological role of the protease, we used two lines of insertion mutants lacking the S2P2 protease protein. Here, we present results demonstrating the thylakoid localization of S2P2. Moreover, we present experimental evidence indicating that the lack of S2P2 in A. thaliana chloroplasts leads to a significant decrease in the level of photosystem I and photosystem II core proteins: PsaB, PsbA, PsbD, and PsbC, as well as polypeptides building both the main light-harvesting antenna (LHC II), Lhcb1 and Lhcb2, as well as Lhcb4 and Lhcb5 polypeptides, constituting elements of the minor, peripheral antenna system. These changes are associated with a decrease in the number of PS II-LHC II supercomplexes. The consequence of these disorders is a greater sensitivity of s2p2 mutants to photoinhibition. The obtained results clearly indicate that the S2P2 protease is another thylakoid protein that plays an important role in the proper functioning of A. thaliana chloroplasts, especially in high-light-intensity conditions.

Interpreting biogeochemical processes through the relationship between total alkalinity and dissolved inorganic carbon: Theoretical basis and limitations

AbstractThe marine carbonate system is influenced by anthropogenic CO2 uptake, biogeochemical processes, and physical changes that involve freshwater input and removal. Two frequently used parameters to quantify seawater carbonate system are total alkalinity (TA) and total dissolved inorganic carbon (DIC). To account for the physical changes, both TA and DIC are usually normalized to a reference salinity (i.e., nTA and nDIC), and then the relationship between nTA and nDIC is used to identify major biogeochemical processes that regulate the carbonate system, based on process‐specific reaction stoichiometry. However, the theoretical basis of this interpretation has not been holistically examined. In this study, we validated this method under idealized conditions and discussed the associated assumptions and limitations. Furthermore, we applied this method to interpret field TA and DIC data from a lagoonal estuary in the northwestern Gulf of Mexico. Our results demonstrated that evaluating field data that encompass multiple stations and time periods could be problematic. In addition, various combinations of biogeochemical processes can lead to the same nTA–nDIC relationship, even though the relative importance of each individual process may vary significantly. Therefore, the stoichiometric relationship relying solely on TA and DIC data is not a definitive approach for uncovering dominant biogeochemical processes. Instead, measurements of process‐specific parameters are necessary.

Spatial Distribution Characteristics of Soil C:N:P:K Eco-Stoichiometry of Farmland and Grassland in the Agro-Pastoral Ecotone in Inner Mongolia, China

Ecological stoichiometry (ES) is an important index that reflects the balance of various elements in ecological processes. Therefore, it is of great significance to understand the soil nutrient cycle to clarify the environmental control of soil carbon (C), nitrogen (N), phosphorus (P), and potassium (K). In this study, we analyzed the spatial distribution of soil C, N, P, and K contents and the C:N:P:K stoichiometric characteristics of 0–20 cm and 20–40 cm of farmland and grassland in four agro-pastoral areas in Inner Mongolia. Spearman correlation was used to analyze the effects of environmental factors on the soil C:N:P:K stoichiometric relationship. The results showed that there was no fixed Redfield ratio for the soil stoichiometric relationship of farmland and grassland in Inner Mongolia, and the values were 15:2:1:9 to 145:10:1:26 and 25:1:1:29 to 228:15:1:65, respectively. The stoichiometric relationships between farmland and grassland were consistent with the law of geographical and spatial heterogeneity. The ratios of C:N, C:P, C:K, N:P, and N:K showed an N distribution from west to east, while the ratio of P:K showed a V distribution. The stoichiometric relationships in grassland soil were mainly affected by soil organic carbon and total nitrogen content, while those in farmland were mainly affected by total nitrogen and total phosphorus content. The annual mean precipitation has a significant effect on stoichiometric relationships in farmland, while the annual mean temperature has a more significant effect on grassland. In conclusion, the spatial distribution difference in the soil stoichiometric relationship in the agro-pastoral ecotone of Inner Mongolia was more significant than the difference in the land use pattern. The influences of annual mean temperature and annual mean precipitation on soil ecological stoichiometry were in accordance with the geographical spatial similarity law. Compared with grassland, the stoichiometric relationship of farmland soil was greatly affected by fertilization, and farmland in this region was mainly limited by carbon and nitrogen. Thus, field management should be carried out according to local conditions. This study is of great significance as it promotes the rational utilization of land resources and the sustainable development of agriculture.