Relative Stability Research Articles

Intrasubject and intersubject variability of stabilography parameters in normal conditions and simulated space mission isolation

The state of isolation and confinement causes several symptoms as a psycho-physiological stressor. The crew’s health and condition may play a crucial role in prolonged space sojourns success. However, it’s important to distinguish the role of microgravity from the distress aspect to better understand human physiology in training during space missions. Although stabilography is a commonly used biomechanical technique, there is not enough data on the measurement repeatability. It has already been proven that the stabilograms differ between subjects due to multiple anatomical and physiological characteristics but the intersubject variability remains unclear. The study provides statistical data on 10 different stabilography measurements of 18 participants performed on different days during an analog space mission (5 females and 4 males) and in normal conditions (5 females and 4 males). Descriptive statistics and interclass correlation were used to determine intra- and intersubject variability. Mann-Whitney test was used for group comparison. Isolation was found to significantly impact symmetry and forefoot/backfoot index in trials with eyes open and ellipse area and forefoot/backfoot index in trials with eyes closed. The results show a diverse level of stabilography parameters measurement repeatability. The least stable parameter was the ellipse area (%SD = 45.79 %) and the most stable stance symmetry (%SD = 4.60 %). The results confirm ellipse area and center of pressure path poor repeatability and relative stability of parameters describing load distribution. It also proves the importance of performing multiple trials in stabilography studies to reduce the risk of erroneous results caused by intersubject variability.

Surface and bulk viscoelastic stability of solvent-stored bulk-fill resin-based composite

ObjectiveInvestigate the effect of solvent-storage on surface hardness and bulk creep of fast photo-cured bulk-fill resin-based composite (RBC) compared to conventionally irradiated bulk-fill RBCs. MethodsThree bulk-fill RBCs were studied: Tetric® PowerFill (fast photo-cured bulk-fill RBC) (TPF), Tetric EvoCeram® (EVO), and GrandioSO® x-tra (GSOx) (conventional). Disk-shaped specimens of clinically realistic thickness (4 mm) were prepared from each material for: Group A: surface measurements (18 mm diameter) and Group B: 4 mm diameter for bulk compressive creep measurements. Group A disks were light-cured from the upper ‘occlusal’ surface for either 3 s or 20 s according to the manufacturer’s recommendation. Martens hardness (HM) of both top and bottom surfaces of each specimen were measured. Group B: 4 × 4 mm cylindrical specimens were fully cured to measure bulk creep (CB). A 20 MPa static compressive stress was applied for 2 h, followed by 2 h of unloading. Strain deformation was recorded continuously for 4 h. Both Martens and bulk creep studies were performed under the following storage conditions at 37 °C: (i) dry at 24 h post curing (baseline), and (ii) after 7 and 30 d of storage in two different media: distilled water (DW) and 75 % ethanol/water (75 % E/W). ResultsAt baseline, HM for all materials ranged from 587 to 439 N/mm2 (top) and 398 to 342 N/mm2 (bottom). After 30 d of solvent-storage, more pronounced HM changes were observed, with the bottom surface being more affected. Normalised HM for TPF decreased by 44 % after 30 d in 75 % E/W. Maximum creep strain ranged from 1.1 % to 2.1 % at baseline, and after 30 d in 75 % E/W this increased from 1.9 % to 2.9 %. Depending on the material and storage condition, the percentage creep strain recovery after 30 d ranged between 65.2 % and 80 %. Increased filler loading in the bulk-fill RBCs decreased the creep strain magnitude and increased the surface hardness. SignificanceSolvent storage decreased the Martens hardness of both upper and lower surfaces and increased the bulk creep characteristics of bulk-fill RBCs. Nevertheless, there was a similar relative stability in surface hardness and viscoelastic stability of fast-cured PowerFill compared to conventionally irradiated RBCs.

Computational Analysis of Dinucleoside Monophosphates: Comparing Structural Properties of Analogous Strands of Deoxyribonucleic Acids and Ribonucleic Acids Using Quantum Density Functional Calculations

The objective of this experiment was to determine the relative stabilities of dinucleoside monophosphates using density functional theory calculations. The calculations performed used Gaussian16 density functionals (Frisch et al., 2014) and Schrödinger’s equation to determine the optimal structure of single strands of two-base long deoxyribonucleic acids and their analogous ribonucleic acids. The strands looked at were composed of, respectively, deoxyadenosine-deoxycytidine, and deoxyguanosine-deoxythymidine for the DNA strands. The RNA strands were composed of, respectively, adenosine-cytosine, guanine-uracil, and guanine-thymine. The Hartree-Fock energies of the DNA AC and GT strands as well as those of the RNA AC, GT, and GU strands respectively were of -9.5672 x10-15 J, -1.0153 x10-14 J, -1.0223 x10-14 J, -1.0809 x10-14 J, and -1.0638 x10-14 J. Each of these were determined using Gaussian16 with the wB97X-D/6-31+G(d,p) model and tabulated using AIMAll (AIMSum, 2019). These values show that the RNA strands are more stable than the DNA strands with the adenosine-containing strands being the least stable in both the DNA and RNA forms respectively.

Isolation and evaluation of bacteriophage cocktail for the control of colistin-resistant Escherichia coli

The frequent emergence of colistin-resistant E. coli worldwide drives the exploration of alternative therapies, and bacteriophages (phages) have emerged as promising candidates to tackle this challenge. In this study, three E. coli phages were isolated, screened, and evaluated against 96 colistin-resistant strains obtained from diverse sources. The combined recognition rate for these strains was 43.6%, while individually it ranged from 17.0% to 24.5%. Notably, among the tested phages (FJ3-79, SD1-92L, and FJ4-63), FJ4-63 demonstrated exceptional characteristics in regulating host population dynamics upon infection by exhibiting a shorter latent period (20 min) and a larger burst size (95.99 ± 3.61 PFU/cell). Furthermore, it exhibited relative stability at pH 3-11 and below 60°C. Transmission electron microscopy and genomic analysis classified phage FJ4-63 belongs to the Dhakavirus genus within the Straboviridae family. Its genome comprised a linear double-stranded DNA measuring 169,669 bp (containing 272 coding sequences) with a GC content of 39.76%, of which 93 (34.2%) had known functions, and the remaining 177 were annotated as hypothetical proteins. Additionally, two tRNAs were recognized, possess the “holin-endolysin” lytic system, and no resistance or virulence genes were detected. The phylogenetic tree and average nucleotide identity (ANI) analysis revealed that phage FJ4-63 exhibited the highest similarity to Escherichia phage C6 (679410.1), indicating a consistent close relationship within the same branch. The cocktail comprising three phages exhibits enhanced in vitro bactericidal efficacy compared to a single phage. At high doses with MOI = 100, it rapidly and completely eradicates bacteria within 1 h while significantly reducing bacterial biofilms. All this evidence suggests that lytic phages offer an effective solution for clinical treatment, with a phage cocktail demonstrating greater potential in the alternative management of colistin-resistant E. coli infections.

Recognition of inheritance as escheated

The features of recognition of inheritance as escheated are determined. The author analyses the peculiarities of interest construction in the system of legal relations of inheritance escheat. It is determined that the institution of inheritance escheat is aimed at satisfying the public interest in maintaining the stability of property relations in society. The property (economic) interest in acquiring ownership of inherited property is derived from the main public interest. By its legal nature, an escheated inheritance is a legal succession. The author emphasises that the procedure for transferring escheated property to municipal ownership is established in local acts of local self-government bodies which have a procedural nature regarding the acquisition of municipal ownership of escheated property. It is argued that depending on the type of real estate object, it is advisable to determine the legal regime of escheated property, in particular, land and residential real estate. It is proved that the construction of interest in the system of legal relations of escheatment of inheritance is complex and combines public (social) and economic (property) interest. The public (social) interest is to preserve the stability of property relations in society. The economic (property) interest has a public and private orientation, in particular, it satisfies the interest of the territorial community as both the acquirer of the property right and the creditor to satisfy the testator’s obligations at the expense of the deceased property. At the same time, a public entity assumes the burden of the testator’s obligations sometimes not in its own interests, but in order to ensure the stability of property relations in society. The improvement of civil legislation on the possibility of a territorial community to waive the obligation to file an application to the court for recognition of inheritance as escheated in case of destruction of real estate or its significant damage in view of martial law is proposed.

A importância do aprofundamento teórico-metodológico na formação docente e nas produções de materiais didáticos dialógicos no curso de Letras

The Bakhtinian approach has been present in Brazilian official curricular documents since the 1990s. However, its pedagogical appropriation has been guided by the linguistic structure to the detriment of social interaction (Faraco, 2009), demanding efforts in Portuguese school subject teacher training. In this article, the objective is to show how the dialogic discourse theory deepening can contribute to teaching materials production, based on Portuguese language major training experience at the University of São Paulo in 2020. In this experience, the theoretical-methodological approach includes the concepts of speech genres (Bakhtin, 2016 [1952-1953]) and theme (Volóchinov, 2018 [1929]) and on the production of didactic proposals aligned with the Base Nacional Comum Curricular (BNCC) (Brasil, 2018) and with the Sustainable Development Goals (SDGs) (Unesco, 2017). In this work, we analyze the proposal “Gênero do discurso e produção de texto: editorial” [“Speech genres and text production: editorial”], identifying the authors' observance of Bakhtinian discursive referents: i) sphere/field of human activity; ii) speech genre; iii) its relative stability; iv) multiple voices in statements; v) thematic totality. The results indicate dialogical quality in the material with the presence of elements that express social dynamics, confirming the relevance of theoretical deepening and its practical application in undergraduate teacher training.

Structural geology and tectonic influence on lineament density and slope variation in Southern Ebonyi, Nigeria: An ArcGIS Approach

This study investigates the structural geology and tectonic influences on lineament density and slope variation in Southern Ebonyi, Nigeria, using ArcGIS. The research aims to analyze the spatial distribution and density of lineaments and their correlation with slope variations to understand the region's geomorphology. Slope data was categorized into five classes, revealing that the majority of the area exhibits gentle slopes, indicative of tectonic stability. Conversely, regions with steeper slopes suggest localized tectonic activity. The analysis of lineament density identified areas with varying tectonic influences, with most of the study area showing low-density lineaments, suggesting relative tectonic stability. High-density lineament zones correspond to regions of significant tectonic deformation, often aligning with steeper slopes. The study concludes that the geomorphology of Southern Ebonyi is predominantly shaped by long-term erosional processes and localized tectonic activities. The novelty of this research lies in its comprehensive spatial analysis of both slope variation and lineament density, providing new insights into the tectonic and structural dynamics of the region.

Controlled Synthesis and Phase Transition Mechanisms of Palladium Selenide: A First-Principles Study.

Using density functional theory, we carefully calculated the relative stability of monolayer, few-layer, and cluster structures with Penta PdSe2, T-phase PdSe2, and Pd2Se3-phase. We found that the stability of Penta PdSe2 increases with the number of layers. The Penta PdSe2, T-phase PdSe2, and Pd2Se3 monolayers are all semiconducting, with band gaps of 1.77, 0.81, and 0.65 eV, respectively. The formation energy of palladium selenide clusters with different phase structures is calculated, considering the cluster size, stoichiometry, and chemical environment. Under typical experimental conditions, Pd2Se3 phase clusters are found to be dominant, having the lowest formation energy among all of the phases considered, with this dominance increasing as cluster size grows. Adjusting the Pd-Se ratio in the environment allows for controlled synthesis of specific palladium selenide phases, providing theoretical insights into the nucleation mechanisms of PdSe2 and other transition metal chalcogenides.

Experimental synthesis of ThSiO4 by fluid-induced alteration of chevkinite-(Ce): Evidence for element mobility and variable crystal structure

During a series of high P-T experiments aimed at understanding the hydrothermal alteration of the REE,Ti silicate chevkinite-(Ce), three ThSiO4 phases (thorite, huttonite, and an amorphous ThSiO4 variety) were formed, showing a wide range of textures from small discrete grains to large-scale replacement of the chevkinite-(Ce). All three phases have compositions close to ThSiO4, except that the amorphous type contains small amounts of LREE (≤ 0.025 apfu) and inferred H2O. The three different forms have been confirmed by electron backscatter diffraction, which has also provided information on the microstructure of the crystals. The earliest phase to form was huttonite, composed of many randomly oriented microcrystals. This was later replaced by thorite via fluid-aided coupled dissolution-reprecipitation. The amorphous type formed both by apparent hydrous alteration of the original crystalline thorite and huttonite. The inferred sequence of events is compatible with thermodynamic constraints on the relative stability of thorite and huttonite.

High-ranking officials of the plenipotentiary representative offices of the President of the Russian Federation in the federal districts: recruitment channels and careers

The article covers the analysis of the main recruitment channels for high-ranking officials of the plenipotentiary representative offices of the President of the Russian Federation in the federal districts. As the empirical basis of the study serves the biographical database, that includes information on 154 presidential bureaucrats as of April 2023. Recruitment of people from various socio-professional groups to the apparatus of the plenipotentiary representative offices reveals a number of trends caused by interacting push (specific features of the candidate's position and associated resources and interests) and pull (place in the power system and functional specialisation of the plenipotentiary representative offices, specifics of leadership positions in them, as elements of the opportunity structure, as well as personal connections) factors. One of the most important trends is militarisation: most officials of the plenipotentiary representative offices have work experience in law enforcement agencies and even spent there most of their previous careers. Recruiting security officials who are, in terms of career, “ideal-typical” federal officials and professionally socialised within the framework of rigid, centralised hierarchies probably strengthens the autonomy of the plenipotentiary representations from actors and interests external to federal power, including regional administrations, that these bodies are called upon to control. The logic of autonomisation is also in line with the fact that one of the main suppliers (especially direct) of key officials of the plenipotentiary representations is the Presidential Administration, first of all, the apparatus of the representations themselves. However, a significant minority of presidential officials have experience working in regional administrations (especially among deputies and assistants to plenipotentiaries), as well as in business, both public and private (especially among plenipotentiaries and their deputies). At the same time positions in these structures rarely serve as a direct springboard to a key position in the plenipotentiary representations. Finally, the role of legislative bodies as a channel for recruiting presidential officials is insignificant. In general, the author's findings are consistent with the results of previous studies, indicating the relative stability of recruitment trends.

Transition-Metal-Mediated Radiohalogenation using Aryl Boron Reagents

AbstractBiomolecules labeled with radioisotopes of iodine and fluorine play a major role in science and medicine, with a range of applications including molecular imaging of disease, as radiopharmaceuticals for therapy and as tools for drug discovery. Due to the relative stability of Csp2–halogen bonds, radioiodine and radiofluorine labels are commonly incorporated into tracers via arene substitution. The wide availability of aryl boron reagents has led to their use for the development of radioiodination and radiofluorination methods, particularly using transition-metal complexes for accelerated reactions. Here, we review the range of transition-metal-mediated methods that have been developed for radiohalogenation of aryl boron compounds. Applications of these transformations for the preparation of molecular imaging agents and the use of new technologies to advance automated synthesis or high-throughput discovery are also described.1 Introduction2 Radioiodination Using Aryl Boron Reagents2.1 Applications of Copper-Mediated Radioiodination Reactions3 Radiofluorination Using Aryl Boron Reagents3.1 Radiofluorination Using Palladium, Nickel and Silver Complexes3.2 Radiofluorination Using Copper Complexes3.3 Applications of Copper-Mediated Radiofluorination Reactions3.4 New Technology for Copper-Mediated Radiofluorination Reactions4 Conclusions

Modelling the Non-linear Associations between Age and Health: Implications for Care

Abstract Background Ageing is a complex biological process that weakens the body's defences against various health problems and diseases. This decline is not uniform or linear; rather, it varies significantly among individuals. Understanding the non-linear progression of ageing is crucial for identifying critical periods where intervention might be most beneficial. This study aimed to explore nonlinearities in the association between age and health outcomes. Methods Using generalised additive models, we analysed data from the 2020 wave of the United States Health and Retirement Study. This modelling approach allows for the detailed examination of nonlinearities in health outcomes across different ages. Our sample consisted of adults aged over 50 (n = 1338; mean = 68; range = 50 – 95). We assessed seven health outcomes (heart conditions, diabetes, cholesterol, blood pressure, fatigue, back pain, and headaches) and seven protective behaviours (prostate exams, mammograms, cholesterol screenings, pap smears, flu vaccinations, dental check-ups, and smoking patterns) reflecting various aspects of health status and behaviour. Results The analysis indicated a significant and pronounced non-linear relationship between age and certain health outcomes, namely headaches, blood pressure, diabetes, and heart conditions. Additionally, ageing was non-linearly associated with specific health behaviours, including the uptake of prostate exams, mammograms, flu vaccinations, and smoking prevalence. Notably, distinct patterns emerged concerning health behaviours in relation to age-specific screening policies. Conclusion The findings of this study reveal that the probability of developing health problems or engaging in health protective behaviours do not increase/decrease linearly in direct proportion to age. Rather, the probability curve exhibits fluctuations, presenting periods of heightened odds interspersed with phases of relative stability. Such non-linearity may be partially attributed to policy decisions but could also reflect a complex interplay of factors such as weakened immune systems, access to healthcare, personal health beliefs, and the evolving perception of risk as one grows older.

Hydride and halide abstraction reactions behind the enhanced basicity of Be and Mg clusters with nitrogen bases.

In this study, we investigate the protonation effects on the structure, relative stability and basicity of complexes formed by the interaction of monomers and dimers of BeX2 and MgX2 (X = H, F) with NH3, CH2NH, HCN, and NC5H5 bases. Calculations were performed using the M06-2X/aug-cc-pVTZ formalism, along with QTAIM, ELF and NCI methods for electron density analysis and MBIE and LMO-EDA energy decomposition analyses for interaction enthalpies. The protonation of the MH2- and M2H4-Base complexes occurs at the negatively charged hydrogen atoms of the MH2 and M2H4 moieties through typical hydride abstraction reactions, while protonation at the N atom of the base is systematically less exothermic. The preference for the hydride transfer mechanism is directly associated with the significant exothermicity of H2 formation through the interaction between H- and H+, and the high hydride donor ability of these complexes. The basicity of both, MH2 and M2H4 compounds increases enormously upon association with the corresponding bases, with the increase exceeding 40 orders of magnitude in terms of ionization constants. Due to the smaller exothermicity of HF formation, the basicity of fluorides is lower than that of hydrides. In Be complexes, the protonation at the N atom of the base dominates over the fluoride abstraction mechanism. However, for the Mg complexes the fluoride abstraction mechanism is energetically the most favorable process, reflecting the greater facility of Mg complexes to lose F-.

Explainable machine learning model of disorganisation in swarms of drones.

The main challenges when managing a fleet of unmanned aerial vehicles are to ensure the relative stability of its formation and to minimise disorganisation, specifically when undergoing an intrusion. When planning the mission it is beneficial for the operator to set the parameters of the formation to balance the needs of the mission with the disorganisation that an intruder may cause. The model developed in this research predicts the anticipated disturbance as a function of the parameters of the formation. The effectiveness of six machine learning methods are compared with a previously established baseline, using data obtained from simulations. CatBoost (categorical boosting) delivered the best results, with an (coefficient of determination) value of 83.3%, representing an improvement of 80% over the baseline. The SHAP (Shapley Additive Explanations) method was used to extend the model beyond predictability for particular combinations of values of parameters, towards generalised recommendations for the operator of the formation.

Housing Insecurity and Older Adults' Health and Well-Being in a Gentrifying City: Results from the EPIPorto Cohort Study.

Using 2022 data from 600 adults (≥ 60years) in Porto, Portugal, we explored the association between housing insecurity and various health outcomes. We examined housing conditions, affordability, and stability in relation to loneliness, quality of life, cognitive function, perception of healthy ageing, and sleep using regression models. Older adults without house heating (β = 2.293; 95%CI = 0.753, 3.833), with leaks/dampness/rot (β = 3.741; 1.818, 5.664), insufficient daylight (β = 2.787; 0.095, 5.479), living in neighborhoods with noise (β = 1.793, 0.280 to 3.305), pollution/grime (β = 2.580; 0.746, 4.414), and violence/crime/vandalism (β = 3.940; 1.723, 6.157), who faced housing cost overburden (β = 2.001; 0.426, 3.577), eviction (β = 12.651; 0.852, 24.450), and moved frequently (β = 4.129; 1.542, 6.716) exhibited higher levels of loneliness. Similarly, lack of house heating (β = - 1.942; - 3.438, - 0.445), leaks/dampness/rot (β = - 4.157; - 5.999, - 2.316), insufficient daylight (β = - 3.124; - 5.714, - 0.534), noise (β = - 2.143; - 3.600, - 0.686), pollution/grime (β= - 2.093; - 3.860, - 0.325), violence/crime/vandalism (β= - 2.819; - 4.948, - 0.691), and those with housing cost overburden (β= - 2.435; - 3.930, - 0.940) reported lower quality of life.Those with no toilet (β = - 1.891; - 3.760, - 0.021) or shower (β = - 1.891; - 3.760, - 0.021) and who faced forced displacement (β = - 2.179; - 3.516, - 0.842) presented lower cognitive function. Furthermore, those living in neighborhoods with pollution/grime (OR = 0.494; 0.322, 0.756) and violence/crime/vandalism (OR = 0.477; 0.284, 0.801), those in social housing (OR = 0.728; 0.575, 0.922), and those who moved frequently (OR = 0.475; 0.257, 0.879) reported lower levels of perceived healthy ageing. Insufficient sleep was more common among residents in social housing (OR = 2.155; 1.102, 4.213), while poor sleep quality was least likely both among those living in social housing (OR = 0.445; 0.220, 0.900) and affordable housing (OR = 0.381; 0.162, 0.896). Good quality, stable, and affordable housing seems crucial for healthy ageing.

Understand the Relative Stability of Single-Gyroid to Double-Gyroid in AB-Type Block Copolymer: Chain Packing and Geometric Analysis

Understand the Relative Stability of Single-Gyroid to Double-Gyroid in AB-Type Block Copolymer: Chain Packing and Geometric Analysis

Leveraging neural networks to correct FoldX free energy estimates.

Proteins play a pivotal role in many biological processes, and changes in their amino acid sequences can lead to dysfunction and disease. These changes can affect protein folding or interaction with other biomolecules, such as preventing antibodies from inhibiting a viral infection or causing proteins to misfold. The ability to predict the effects of mutations in proteins is crucial. Although experimental techniques can accurately quantify the effect of mutations on protein folding free energies and protein-protein binding free energies, they are often time-consuming and costly. By contrast, computational techniques offer fast and cost-effective alternatives for estimating free energies, but they typically suffer from lower accuracy. Enhancing the accuracy of computational predictions is therefore of high importance, with the potential to greatly impact fields ranging from drug design to understanding disease mechanisms. One such widely used computational method, FoldX, is capable of rapidly predicting the relative folding stability ( ) for a protein as well as the relative binding affinity ( ) between proteins using a single protein structure as input. However, it can suffer from low accuracy, especially for antibody-antigen systems. In this work, we trained a neural network on FoldX output to enhance its prediction accuracy. We first performed FoldX calculations on the largest datasets available for mutations that affect binding (SKEMPIv2) and folding (ProTherm4) with experimentally measured . Features were then extracted from the FoldX output files including its prediction for . We then developed and optimized a neural network framework to predict the difference between FoldX's estimated and the experimental data, creating a model capable of producing a correction factor. Our approach showed significant improvements in Pearson correlation performance. For single mutations affecting folding, the correlation improved from a baseline of 0.3 to 0.66. In terms of binding, performance increased from 0.37 to 0.61 for single mutations and from 0.52 to 0.81 for double mutations. For epistasis, the correlation for binding affinity (both singles and doubles) improved from 0.19 to 0.59. Our results also indicated that models trained on double mutations enhanced accuracy when predicting higher-order mutations (such as triple or quadruple mutations), whereas models trained on singles did not. This suggests that interaction energy and epistasis effects present in the FoldX output are not fully utilized by FoldX itself. Once trained, these models add minimal computational time but provide a substantial increase in performance, especially for higher-order mutations and epistasis. This makes them a valuable addition to any free energy prediction pipeline using FoldX. Furthermore, we believe this technique can be further optimized and tested for predicting antibody escape, aiding in the efficient development of watch lists.

Thermodynamic study on the relative stability of 2-amino-1,3,4-thiadiazole and two alkyl-substituted aminothiadiazoles

Thermodynamic study on the relative stability of 2-amino-1,3,4-thiadiazole and two alkyl-substituted aminothiadiazoles

Sedimentary Greigite Formation

Revised thermodynamic data for greigite (Fe3S4) indicate that it is a stable sedimentary Fe-S phase. Greigite was previously regarded as metastable. Equilibrium computations using revised data explain apparently contradictory observations regarding greigite occurrences in sediments and sedimentary rocks. Greigite has a large stability area in pe-pH space relative to pyrite. It dominates in low pe regimes especially near the lower water stability boundary, which is consistent with its widespread occurrence in methanic sediments. It also has a small but significant stability zone near the sulfate-sulfide stability boundary. Its significance increases in regimes with relatively high dissolved Fe:S ratios, which explains its occurrence in freshwater sediments and iron-enriched marine sediments. It is also a paleoenvironmental marker for transitional environments, especially between freshwater and marine systems. It is stable relative to pyrrhotite and smythite, although their formation together with greigite in low pe environments may be facilitated by catalytic processes. The greigite-smythite (pyrrhotite)-siderite association is a potential marker for ancient methanogenesis. Greigite is relatively sensitive to oxidation and its long-term geological preservation depends mostly on protection from oxidation by low sediment permeability or enclosure in other minerals or organic remains. Most sedimentary and biological greigite forms via equilibrium reactions involving mackinawite-like precursors, with no direct coupling of greigite with pyrite; these minerals form independently during sedimentary diagenesis. Magnetosomal greigite production by magnetotactic bacteria is a consequence of relative greigite stability, its decoupling from pyrite, and its protection from oxidation by cell membranes.

Mass spectrometry provides insights into the structures of polyoxovanadate alkoxide clusters substituted with Fe and W heterometals

Atom-by-atom substitution is a promising strategy for tailoring the electronic properties of transition metal oxide clusters. This approach typically generates a mixture of species that are difficult to separate using conventional methods. As a result, the characterization of their structures and electronic properties remains challenging. Herein, we use collision-induced dissociation (CID) to study the fragmentation of well-defined Fe- and W-doped Lindquist polyoxovanadate methoxides synthesized as a mixture of singly and doubly substituted species. Fragmentation reveals that Fe heteroatoms are efficiently retained within the metal oxide core. In contrast, one W atom is incorporated into the primary WO2(OCH3)2 neutral loss from both the singly and doubly substituted W-containing clusters. Collision energy-resolved CID provides insights into the fragmentation pathways, which are compared to those of the homometallic polyoxovanadate methoxide species. The incorporation of Fe into the cluster reduces its stability towards fragmentation, which could be attributed to the increase in the relative stability of Fe-containing fragment ions with four metal atoms in comparison with their homometallic analog. The observed fragmentation is rationalized by assuming that Fe atoms are incorporated within the low valent plane, while one W atom occupies the axial out-of-plane position in the cluster.