Structural Rearrangement Followed by Entrapment of Subnanometer Building Blocks of Iron Oxyhydroxide in Aqueous Iron Chloride Solutions.

Iron oxyhydroxide, a natural nanophase of iron found in the environment, plays a crucial role in regulating surface and groundwater composition. Recent research proposes that within the nonclassical prenucleation cluster growth model, subnanometer-sized clusters (olation clusters/Fe13 δ-Keggin oxolation clusters) might act as the prenucleation clusters (PNCs) of ferrihydrite or iron oxyhydroxide solid phase. However, these clusters are difficult to characterize as they are only observable momentarily in low-pH, high-Fe concentration solutions before agglomerating into extended solids, keeping the controversy over the true nature of the PNCs alive. In this study, we introduce large quantities of zinc acetate salt (ZA) into iron chloride solutions at the olation-oxolation boundary (3.6 mM Fe3+ at pH ∼2.6). Remarkably, this manipulation is found to alter the structural arrangement of these subnanometer clusters before blocking them in isolation for hours, even at pH 6, where extended iron oxyhydroxide phases typically precipitate. On the other hand, controlled addition of ZA allows partial unblocking, leading to anisotropic agglomeration into cylindrical rod-like structures. Experimental techniques such as synchrotron-based small-angle X-ray scattering, X-ray absorption spectroscopy, high-resolution transmission electron microscopy (TEM), and cryo-TEM, along with density functional theory (DFT) calculations, reveal the nature of the structural rearrangement and the crucial role of Zn2+ ions in cluster stabilization.

Probing the Magnetic Ground State of Ba2YIrO6: Impact of Nonmagnetic Dopants and Spin-Orbit Coupling.

Strong spin-orbit coupling (SOC) in iridates has long been predicted to lead to exotic electronic and magnetic ground states. Ba2YIrO6 (BYIO) has attracted particular attention due to the expectation of a Jeff = 0 state for Ir5+ ions under the jj-coupling scheme. However, controversies surround the actual realization of this state, as finite magnetic moments are consistently observed experimentally. We present a multi-physics study of this system by progressively introducing nonmagnetic Sb5+ ions in place of Ir5+ (Ba2YIr​1-ySb​yO​6, BYISO). Despite similar charge and ionic radii, Sb​5+ doping appears highly inhomogeneous, coexisting with a fraction of nearly pure BYIO regions, as confirmed by X-ray diffraction (XRD). This aligns with observations in related compounds. While inhomogeneity creates uncertainty, the doped majority phases offer valuable insights. It is relevant that the inclusion of even small amounts of Sb​5+ (10-20%) leads to a rise in magnetization. This strengthens our previous suggestion that magnetic Ir ions form dynamic singlets in BYIO, resulting in a near-nonmagnetic background. The observed moment enhancement with nonmagnetic doping supports the breakdown of these singlets. Furthermore, the magnetization steadily increases with an increasing Sb​5+ content, contradicting the anticipated approach towards the Jeff = 0 state with increased SOC due to reduced hopping between Ir​5+ ions. This reinforces the presence of individual Ir​5+ moments. Overall, our findings suggest that Ba​2YIrO​6 might not possess sufficiently strong SOC to be solely described within the jj-coupling picture, paving the way for further investigation.

Curious Behavior of Fe3+-As3+ Chemical Interactions and Nucleation of Clusters in Aqueous Medium.

The simultaneous presence of Fe3+ and As3+ ions in groundwater (higher ppb or lower ppm level concentrations at circumneutral pH) as well as in acid mine drainages (AMDs)/industrial wastewater (up to few thousand ppm concentration at strongly acidic pH) are quite common. Therefore, understanding the chemical interactions prevalent between Fe3+ and As3+ ions in aqueous medium leading to nucleation of ionic clusters/solids, followed by aggregation and growth, is of great environmental significance. In the present work, we attempt to probe the nucleation process of Fe3+-As3+ clusters in solutions of various concentrations and pHs (from AMD to groundwater-like) using a combination of experimental and theoretical techniques. Interestingly, our study reveals nucleation of primary FeAs clusters in nearly all of them independent of concentration or pH. Theoretical studies employed density functional theory (DFT) to predict the primary clusters as stable Fe4As4 units. The surprising resemblance of these clusters with known Fe3+-As3+ minerals at the local level was observed experimentally, which provides an important clue about solid-phase growth from a range of Fe3+-As3+ solutions. Our experimental findings are further supported by a stepwise reaction mechanism established from detailed DFT studies.

Immunomodulatory therapy with glatiramer acetate reduces endoplasmic reticulum stress and mitochondrial dysfunction in experimental autoimmune encephalomyelitis.

Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are found in lesions of multiple sclerosis (MS) and animal models of MS such as experimental autoimmune encephalomyelitis (EAE), and may contribute to the neuronal loss that underlies permanent impairment. We investigated whether glatiramer acetate (GA) can reduce these changes in the spinal cords of chronic EAE mice by using routine histology, immunostaining, and electron microscopy. EAE spinal cord tissue exhibited increased inflammation, demyelination, mitochondrial dysfunction, ER stress, downregulation of NAD+ dependent pathways, and increased neuronal death. GA reversed these pathological changes, suggesting that immunomodulating therapy can indirectly induce neuroprotective effects in the CNS by mediating ER stress.

The Critical Role of Stereochemically Active Lone Pair in Introducing High Temperature Ferroelectricity.

In this paper, a comparative structural, dielectric, and magnetic study of two langasite compounds Ba3TeCo3P2O14 (absence of lone pair) and Pb3TeCo3P2O14 (Pb2+ 6s2 lone pair) have been carried out to precisely explore the development of room temperature spontaneous polarization in the presence of a stereochemically active lone pair. In the case of Pb3TeCo3P2O14, mixing of both Pb 6s with Pb 6p and O 2p helps the lone pair to be stereochemically active. This stereochemically active lone pair brings a large structural distortion within the unit cell and creates a polar geometry, while the Ba3TeCo3P2O14 compound remains in a nonpolar structure due to the absence of any such effect. Consequently, polarization measurement under varying electric fields confirms room temperature ferroelectricity for Pb3TeCo3P2O14, which was not the case for Ba3TeCo3P2O14. A detailed study was carried out to understand the microscopic mechanism of ferroelectricity, which revealed the exciting underlying activity of a polar TeO6 octahedral unit as well as Pb-hexagon.

Revisiting Goodenough-Kanamori rules in a new series of double perovskites LaSr1-xCaxNiReO6.

The magnetic ground states in highly ordered double perovskites LaSr1-xCaxNiReO6 (x = 0.0, 0.5, 1.0) are studied in view of the Goodenough-Kanamori rules of superexchange interactions in this paper. In LaSrNiReO6, Ni and Re sublattices are found to exhibit curious magnetic states separately, but no long range magnetic ordering is achieved. The magnetic transition at ~255 K is identified with the independent Re sublattice magnetic ordering. Interestingly, the sublattice interactions are tuned by modifying the Ni-O-Re bond angles through Ca doping. Upon Ca doping, the Ni and Re sublattices start to display a ferrimagnetically ordered state at low temperature. The neutron powder diffraction data reveals long range ferrimagnetic ordering of the Ni and Re magnetic sublattices along the crystallographic b-axis. The transition temperature of the ferrimagnetic phase increases monotonically with increasing Ca concentration.

Hopping-Induced Ground-State Magnetism in 6H Perovskite Iridates.

Investigation of elementary excitations has advanced our understanding of many-body physics governing most physical properties of matter. Recently spin-orbit excitons have drawn much attention, whose condensates near phase transitions exhibit Higgs mode oscillations, a long-sought-after physical phenomenon [A. Jain, et al., Nat. Phys. 13, 633 (2017)NPAHAX1745-247310.1038/nphys4077]. These critical transition points, resulting from competing spin-orbit coupling (SOC), local crystalline symmetry, and exchange interactions, are not obvious in iridium-based materials, where SOC prevails in general. Here, we present results of resonant inelastic x-ray scattering on a spin-orbital liquid Ba_{3}ZnIr_{2}O_{9} and three other 6H-hexagonal perovskite iridates that show magnetism, contrary to the nonmagnetic singlet ground state expected due to strong SOC. Our results show that substantial hopping between closely placed Ir^{5+} ions within Ir_{2}O_{9} dimers in these 6H iridates modifies spin-orbit coupled states and reduces spin-orbit excitation energies. Here, we are forced to use at least a two-site model to match the excitation spectrum going in-line with the strong intradimer hopping. Apart from SOC, low-energy physics of iridates is thus critically dependent on hopping and may not be ignored even for systems having moderate hopping, where the excitation spectra can be explained using an atomic model. SOC, which is generally found to be 0.4-0.5 eV in iridates, is scaled in effect down to ∼0.26 eV for the 6H systems, sustaining the hope of achieving quantum criticality by tuning Ir-Ir separation.

Development of half metallicity within mixed magnetic phase of Cu1-x Co x MnSb alloy.

Cubic half-Heusler Cu1-x Co x MnSb ([Formula: see text]) compounds have been investigated both experimentally and theoretically for their magnetic, transport and electronic properties in search of possible half metallic antiferromagnetism. The systems (Cu,Co)MnSb are of particular interest as the end member alloys CuMnSb and CoMnSb are semi metallic (SM) antiferromagnetic (AFM) and half metallic (HM) ferromagnetic (FM), respectively. Clearly, Co-doping at the Cu-site of CuMnSb introduces changes in the carrier concentration at the Fermi level that may lead to half metallic ground state but there remains a persistent controversy whether the AFM to FM transition occurs simultaneously. Our experimental results reveal that the AFM to FM magnetic transition occurs through a percolation mechanism where Co-substitution gradually suppresses the AFM phase and forces FM polarization around every dopant cobalt. As a result a mixed magnetic phase is realized within this composition range while a nearly HM band structure is developed already at the 10% Co-doping. Absence of T 2 dependence in the resistivity variation at low T-region serves as an indirect proof of opening up an energy gap at the Fermi surface in one of the spin channels. This is further corroborated by the ab initio electronic structure calculations that suggests that a nearly ferromagnetic half-metallic ground state is stabilized by Sb-p holes produced upon Co doping.

Renal aquaporin-4 associated pathology in TG-26 mice.

Human immunodeficiency virus-associated nephropathy (HIVAN) is a leading cause of end-stage renal disease in HIV patients, which is characterized by glomerulosclerosis and renal tubular dysfunction. Aquaporin-4 (AQP-4) is a membrane bound water channel protein that plays a distinct role in water reabsorption from renal tubular fluid. It has been proven that failure of AQP-4 insertion into the renal tubular membrane leads to renal dysfunction. However, the role of AQP-4 in HIVAN is unclear. We hypothesize that impaired water reabsorption leads to renal injury in HIVAN, where AQP-4 plays a crucial role. Renal function is assessed by urinary protein and serum blood urea nitrogen (BUN). Kidneys from HIV Transgenic (TG26) mice (HIVAN animal model) were compared to wild type mice by immunostaining, immunoblotting and quantitative RT-PCR. TG26 mice had increased proteinuria and BUN. We found decreased AQP-4 levels in the renal medulla, increased endothelin-1, endothelin receptor A and reduced Sirtuin1 (SIRT-1) levels in TG26 mice. Also, oxidative and endoplasmic reticulum stress was enhanced in kidneys of TG26 mice. We provide the first evidence that AQP-4 is inhibited due to induction of HIV associated stress in the kidneys of TG26 mice which limits water reabsorption in the kidney which may be one of the cause associated with HIVAN, impairing kidney physiology. AQP-4 dysregulation in TG26 mice suggests that similar changes may occur in HIVAN patients. This work may identify new therapeutic targets to be evaluated in HIVAN.

Glomerular mitochondrial changes in HIV associated renal injury.

HIV-associated nephropathy (HIVAN) is an AIDs-related disease of the kidney. HIVAN is characterized by severe proteinuria, podocyte hyperplasia, collapse, glomerular, and tubulointerstitial damage. HIV-1 transgenic (Tg26) mouse is the most popular model to study the HIV manifestations that develop similar renal presentations as HIVAN. Viral proteins, including Tat, Nef, and Vpr play a significant role in renal cell damage. It has been shown that mitochondrial changes are involved in several kidney diseases, and therefore, mitochondrial dysfunction may be implicated in the pathology of HIVAN. In the present study, we investigated the changes of mitochondrial homeostasis, biogenesis, dynamics, mitophagy, and examined the role of reactive oxygen species (ROS) generation and apoptosis in the Tg26 mouse model. The Tg26 mice showed significant impairment of kidney function, which was accompanied by increased blood urea nitrogen (BUN), creatinine and protein urea level. In addition, histological, western blot and PCR analysis of the Tg26 mice kidneys showed a downregulation of NAMPT, SIRT1, and SIRT3 expressions levels. Furthermore, the kidney of the Tg26 mice showed a downregulation of PGC1α, MFN2, and PARKIN, which are coupled with decrease of mitochondrial biogenesis, imbalance of mitochondrial dynamics, and downregulation of mitophagy, respectively. Furthermore, our results indicate that mitochondrial dysfunction were associated with ER stress, ROS generation and apoptosis. These results strongly suggest that the impaired mitochondrial morphology, homeostasis, and function associated with HIVAN. These findings indicated that a new insight on pathological mechanism associated with mitochondrial changes in HIVAN and a potential therapeutic target.

Rapid decadal evolution in the groundwater arsenic content of Kolkata, India and its correlation with the practices of her dwellers.

Increasing arsenic contamination in the groundwater is one of the biggest environmental challenges that the Bengal delta is facing today. Groundwater is still the main source of water for a large number of population in this region and therefore, significant presence of toxic arsenic has a direct consequence on human lives here. Moreover, arsenic also enters into the food chain through the consumed agricultural products grown in this area. Therefore, acquiring knowledge about the ever-changing map of arsenic contamination and employing adequate protective measures are of utmost importance. Here, we present a comprehensive municipal ward-wise map of the arsenic content of the shallow groundwater table of Kolkata-the most important and highly population dense city of the delta. Comparison with previously available data reveals a rapid change and the grim situation for the city. Our study suggests that it should be an immediate task of the administration to extend treated water service to the whole population of the city for direct consumption, and artificial recharge and maximum rainwater replenishment need to be taken up with utmost urgency to avoid intrusion of toxicity in biological food chains via agricultural products. We hope our study would drive the city planners to reconsider the existing urbanization and development plans of all the cities, placed over arsenic-contaminated groundwater aquifers.

Efficient artificial mineralization route to decontaminate Arsenic(III) polluted water - the Tooeleite Way.

Increasing exposure to arsenic (As) contaminated ground water is a great threat to humanity. Suitable technology for As immobilization and removal from water, especially for As(III) than As(V), is not available yet. However, it is known that As(III) is more toxic than As(V) and most groundwater aquifers, particularly the Gangetic basin in India, is alarmingly contaminated with it. In search of a viable solution here, we took a cue from the natural mineralization of Tooeleite, a mineral containing Fe(III) and As(III)ions, grown under acidic condition, in presence of SO4(2-) ions. Complying to this natural process, we could grow and separate Tooeleite-like templates from Fe(III) and As(III) containing water at overall circumneutral pH and in absence of SO4(2-) ions by using highly polar Zn-only ends of wurtzite ZnS nanorods as insoluble nano-acidic-surfaces. The central idea here is to exploit these insoluble nano-acidic-surfaces (called as INAS in the manuscript) as nucleation centres for Tooeleite growth while keeping the overall pH of the aqueous media neutral. Therefore, we propose a novel method of artificial mineralization of As(III) by mimicking a natural process at nanoscale.

Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba_{3}ZnIr_{2}O_{9}.

We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba_{3}ZnIr_{2}O_{9} is a realization of a novel spin-orbital liquid state. Our results reveal that Ba_{3}ZnIr_{2}O_{9} with Ir^{5+} (5d^{4}) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J=0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir_{2}O_{9} dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.

Investigating the development of spurious magnetism in single crystalline BaTi0.95Fe0.05O3-δ with high δ by local structural probes.

BaTi0.95Fe0.05O3-δ has been suggested to be an intrinsic dilute magnetic oxide with a clear dependence of magnetism on oxygen vacancy concentration. However, it has also been shown that the dopant Fe ions distribute themselves rather inhomogeneously within the lattice, though without disrupting the crystal phase of the parent BaTiO3. With the help of x-ray absorption spectroscopy (XAS), here we find that the incorporation of a larger amount of anion vacancy pushes this inhomogeneity to the extreme, leading to the precipitation of Fe metal clusters. It is also observed that the residual solid, without the Fe-metal cluster, undergoes massive structural and compositional reorganization.

Microscopic distribution of metal dopants and anion vacancies in Fe-doped BaTiO(3-δ) single crystals.

A detailed microscopic structural study on two single crystalline dilute magnetic oxides, BaTi0.95Fe0.05O(3-δ) with and without perceptible δ, has been carried out. Although it has been reported earlier that varying δ significantly affects high temperature ferromagnetism, the real distribution/redistribution of vacancies and dopant Fe ions inside the 6H hexagonal structure was never probed. This study reveals that oxygen vacancies reduce the dopant Fe(3+) ions to Fe(2+) and mostly accumulate around these Fe(2+) ions. Another distinct trend is the tendency of the dopant Fe ions to get closer instead of being distributed randomly, thereby creating Fe2(2+)O(9-δ') like dimers within the 6H hexagonal unit cell. This experimental observation definitively confirms previous hypotheses based on theoretical models.

Mobilization of progenitor cells into peripheral blood by gamma-tocotrienol: a promising radiation countermeasure.

Gamma-tocotrienol (GT3), a vitamin E isoform, is shown to induce high levels of granulocyte colony stimulating factor (G-CSF) in mice. G-CSF is a key cytokine used for stimulation of hematopoiesis, and mobilization of hematopoietic stem and progenitor cells into peripheral blood. GT3 is also shown to induce vascular endothelial growth factor (VEGF), another important cytokine necessary for vasculogenesis and endothelial progenitor mobilization. Since GT3 induces both these cytokines, we tested whether GT3 mobilizes hematopoietic and endothelial progenitors in mice. GT3 (200mg/kg) was injected in 10-week-old CD2F1 mice and mobilization of progenitors in peripheral blood was analyzed at 24, 48, and 72 h post-administration. Circulating hematopoietic progenitor cells (HPCs, Lin(-), cKit(+)), endothelial progenitor cells (EPCs, Lin(-), CD34(+), Flk(+)), and stromal progenitor cells (SPCs, Lin(-), CD29(+), CD105(+)) in peripheral blood mononuclear cells (PBMCs) were analyzed simultaneously by flow cytometry. Mobilized HPCs, EPCs and SPCs in PBMC were also measured by colony-forming unit (CFU) assay in progenitor-specific media. Three groups of mice received vehicle, GT3 and GT3 plus AMD3100, a receptor antagonist used to enhance mobilization. GT3 induced significant mobilization of all three progenitor cell types compared to vehicle in peripheral blood; AMD3100 enhanced GT3-induced mobilization even further. Mobilization of progenitor cells in peripheral blood by GT3 indicates that GT3 can be used as an alternative to G-CSF and VGEF to mobilize HPCs and EPCs.

Defect controlled room temperature ferromagnetism in Co-doped barium titanate nanocrystals.

Defect mediated high temperature ferromagnetism in oxide nanocrystallites is the central feature of this work. Here, we report the development of room temperature ferromagnetism in nanosized Co-doped barium titanate particles with a size of around 14 nm, synthesized by a solvothermal drying method. A combination of x-ray diffraction with state-of-the-art electron microscopy techniques confirms the intrinsic doping of Co into BaTiO3. The development of the room temperature ferromagnetism was tracked down to the different donor defects, namely hydroxyl groups at the oxygen site (OH·(O) and oxygen vacancies (V··(O), and their relative concentrations at the surface and the core of the nanocrystal, which could be controlled by post-synthesis drying and thermal treatments.

Spin-valve-type magnetoresistance: a generic feature of ferromagnetic double perovskites.

An unusual magnetoresistance (MR) behavior in Sr(2)FeMoO(6), recently termed as spin-valve-type MR (SVMR), presents several anomalies that are little understood so far. The formation of a magnetically distorted skin layer around every soft, ferromagnetic grain seems to be the reason behind such an unprecedented tunneling MR (TMR) response. However, initially it appeared that Sr(2)FeMoO(6) is an exclusive TMR material showing an unusual SVMR effect, while other well-known magnetoresistive compounds do not exhibit such behavior. Instead, in this present work, we show that SVMR is a generic feature of the extremely important class of the metallic, ferromagnetic double perovskite family as a whole. Our detailed magnetic study also offers a serious correction to our previous SVMR model, where the strong exchange coupling between the ferromagnetic core and the magnetically frustrated skin of each grain, generating the famous 'exchange bias' effect and consequently the 'valve' for SVMR, needs to be considered.

Nature of "disorder" in the ordered double perovskite Sr2FeMoO6.

The degree of B/B;{'} alternate cation order is known to heavily influence the magnetic properties of A_{2}BB;{'}O_{6} double perovskites although the nature of such disorder has never been critically studied. Our detailed x-ray absorption fine structure studies in conjunction with synchrotron radiation x-ray diffraction experiments on polycrystalline Sr_{2}FeMoO_{6} samples with various degrees of disorder reveal that a very high degree of short range order is preserved even in samples with highly reduced long range chemical order. Based on these experimental results and with the help of detailed structural simulations, we are able to model the nature of the disorder in this important class of materials and discuss the consequent implications on its physical properties.

Local structure of Sr(2)FeMo(x)W(1-x)O(6) double perovskites across the composition-driven metal to insulator transition.

Sr(2)FeMoO(6) oxides exhibit a half-metallic ferromagnetic (HM-FM) ground state and peculiar magnetic and magnetotransport properties, which are interesting for applications in the emerging field of spintronics and attractive for fundamental research in the field of heavily correlated electron systems. Sr(2)FeWO(6) is an insulator with an antiferromagnetic (I-AFM) ground state. The solid solutions Sr(2)FeMo(x)W(1-x)O(6) also have peculiar properties-W doping enhances chemical order which allows stabilization of the HM-FM state; as the W content exceeds a certain value a metal to insulator transition (MIT) occurs. The role of W in determining the physical properties of Sr(2)FeMo(x)W(1-x)O(6) systems has been a matter of intense investigation. This work deals with the problem of the structural and electronic changes related to the MIT from a local perspective by means of x-ray absorption spectroscopy (XAS). This technique allows one to probe in detail the local structure and electronic modifications around selected absorber ions (W, Mo, Fe and Sr in our case). The results of XAS analysis in the whole composition range (0≤x≤1), in the near edge (XANES) and extended (EXAFS) regions, demonstrate an abrupt change of the local structure around the Fe and Mo sites at the critical composition, x(c). This change represents the microstructural counterpart associated with the MIT. Conversely, the local structure and electronic configuration of W ions remain unaltered in the whole composition range, suggesting indirect participation of W in the MIT.