Chromium Environment within Cr-Doped Silico-Aluminophosphate Molecular Sieves from Spin Density Studies
Ontology highlight
ABSTRACT:
SUBMITTER: Liao Y
PROVIDER: S-EPMC8162410 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:One of the most fundamental but yet unanswered questions in the synthesis of zeolites and zeolite-like materials is whether or not any parameter controlling the microporosity of the crystallized product from synthesis mixtures with feasible chemical compositions exists. Here we report that an experimentally optimized parameter (ca. 3.3 ≤ MOH/P2O5 ≤ 5.3, where M is alkali metal ions) is the criterion bringing about the successful formation of various high-charge-density silicoaluminophosphate (SAPO) and zincoaluminophosphate (ZnAPO) molecular sieves, without the aid of organic structure-directing agents. The materials obtained using this empirical concept include SAPO molecular sieves with CHA and LTA topologies, as well as a SAPO FAU/EMT intergrowth, and ZnAPO ones with CZP and SOD topologies. This study demonstrates the existence of an essential factor determining not only phase selectivity but also microporosity (0.3-2 nm) in the synthesis of zeotypes with charged frameworks which may offer interesting opportunities for more efficiently producing novel zeolite structures and/or compositions.
| S-EPMC8336471 | biostudies-literature
Project description:Zeolites have unique pore structures of molecular dimensions and tunable compositions, making them ideal for shape selective catalysis and separation. However, targeted synthesis of zeolites with new pore structures and compositions remains a key challenge. Here, we propose an approach based on a unique 3D-3D topotactic transformation, which takes advantage of weak bonding in zeolites. This is inspired by the structure transformation of PST-5, a new aluminophosphate molecular sieve, to PST-6 by calcination. The structure of nano-sized PST-5 crystals is determined by 3D electron diffraction. We find that the 3D-3D topotactic transformation involves two types of building units where penta- or hexa-coordinated Al is present. We apply this approach to several other zeolite systems and predict a series of new zeolite structures that would be synthetically feasible. This method provides a concept for the synthesis of targeted zeolites, especially those which may not be feasible by conventional methods.
| S-EPMC7387333 | biostudies-literature
Project description:Molecular sieve 5A was modified with (3-aminopropyl) triethoxysilane (APTES) as the support matrix, on which 4-VP was used as the ionic imprinting group. The as-prepared IIZMS-APTES was applied as the adsorbent for the recovery of chromium(vi) from aqueous solutions. The adsorbent was characterized via Fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), and X-ray diffraction (XRD). The influences of adsorption time, concentration of the ions, initial pH, and temperature on the adsorption performance to Cr(vi) were investigated. The selectivity and reusability of IIZMS-APTES are also evaluated. The results showed that the maximum adsorption capacity reached 56.46 mg g-1 when the initial concentration of metal ions was at 100 mg L-1 at pH 2 and 30 °C. The adsorption process followed the pseudo-second-order kinetic model and Langmuir adsorption isotherm model. The IIZMS-APTES exhibits an efficient selective adsorption of Cr(vi) from aqueous solutions.
| S-EPMC9058396 | biostudies-literature
Project description:Alternative UO2 nuclear fuels, incorporating Cr as a dopant, are currently in use in light–water reactors. Dissolution experiments using Cr-doped UO2, performed as a function of Cr content in a simplified groundwater solution and under oxic conditions, established that the addition of Cr to the UO2 matrix systematically reduced the normalised dissolution rate of U at 25 and 40 °C. This effect was most notable under dilute solution conditions, and is the result of galvanic coupling between Cr and U, resulting from the presence of Cr2+ in the UO2 matrix, as corroborated by activation energy determination. Under conditions of solution saturation, where schoepite ((UO2)8O2(OH)12·(H2O)12) and Na2U2O7·6H2O were identified as secondary phases, the rate of U dissolution was invariant with Cr content. Moreover, at 60 °C, the trend was reversed and the rate of U dissolution increased with increasing Cr content. Under these conditions, other factors, including U solubility or bicarbonate-surface interactions, exert a stronger influence on the U dissolution kinetics than Cr. Increased grain size, a feature of Cr-doped UO2 fuel, was also found to reduce the normalised dissolution rate of U. In establishing the mechanisms by which Cr dopants influence UO2 fuel dissolution, it can be concluded that, overall, Cr-doped UO2 nuclear fuel possesses similar dissolution kinetics to undoped UO2 fuel, giving confidence for its eventual disposal in a geological facility.
| S-EPMC10079487 | biostudies-literature
Project description:Despite its role in spin density functional theory and it being the basic observable for describing and understanding magnetic phenomena, few studies have appeared on the electron spin density subtleties thus far. A systematic full topological analysis of this function is lacking, seemingly in contrast to the blossoming in the last 20 years of many studies on the topological features of other scalar fields of chemical interest. We aim to fill this gap by unveiling the kind of information hidden in the spin density distribution that only its topology can disclose. The significance of the spin density critical points, the 18 different ways in which they can be realized and the peculiar topological constraints on their number and kind, arising from the presence of positive and negative spin density regions, is addressed. The notion of molecular spin graphs, spin maxima (minima) joining paths, spin basins and of their valence is introduced. We show that two kinds of structures are associated with a spin-polarized molecule: the usual one, defined through the electron density gradient, and the magnetic structure, defined through the spin density gradient and composed in general by at least two independent spin graphs, related to spin density maxima and minima. Several descriptors, such as the spin polarization index, are introduced to characterize the properties of spin density critical points and basins. The study on the general features of the spin density topology is followed by the specific example of the water molecule in the 3B1 triplet state, using spin density distributions of increasing accuracy.
| S-EPMC7436107 | biostudies-literature
Project description:Pyrolysis in an inert atmosphere is a widely applied route to convert tannery wastes into reusable materials. In the present study, the Cr(III) conversion into the toxic hexavalent form in the pyrolyzed tannery waste referred to as KEU was investigated. Ageing experiments and leaching tests demonstrated that the Cr(III)-Cr(VI) inter-conversion occurs in the presence of air at ambient temperature, enhanced by wet environmental conditions. Microstructural analysis revealed that the Cr-primary mineral assemblage formed during pyrolysis (Cr-bearing srebrodolskite and Cr-magnetite spinel) destabilized upon spray water cooling in the last stage of the process. In the evolution from the higher to the lower temperature mineralogy, Cr is incorporated into newly formed CrOOH flakes which likely react in air forming extractable Cr(VI) species. This property transforms KEU from an inert waste to a hazardous material when exposed to ordinary ambient conditions.
| S-EPMC10539330 | biostudies-literature
Project description:Novel Cr(III)-imprinted poly(vinyl alcohol)/sodium alginate/AuNPs hydrogel membranes (Cr(III)-IIMs) were obtained and characterized and further applied as a sorbent for chromium speciation in waters. Cr(III)-IIMs were prepared via solution blending method using blends of poly(vinyl alcohol) and sodium alginate as film-forming materials, poly(ethylene glycol) as a porogen agent, sodium alginate stabilized gold nanoparticles (SA-AuNPs) as a crosslinking and mechanically stabilizing component, and Cr(III) ions as a template species. The physicochemical characteristics of pre-synthesized AuNPs and obtained hydrogel membranes Cr(III)-IIM were studied by UV-vis and FTIR spectroscopy, TEM and SEM observations, N2 adsorption-desorption measurements, and XRD analysis. The mechanism of the adsorption process toward Cr(III) was best described by pseudo-first-order kinetic and Langmuir models. Experiments performed showed that quantitative retention of Cr(III) is attained in 20 h at pH 6 and temperature 40 °C. Under the same conditions, the adsorption of Cr(VI) is below 5%. A simple and sensitive analytical procedure was developed for the speciation of Cr in an aquatic environment using dispersive solid phase extraction of Cr(III) by Cr(III)-IIM prior to selective Cr(VI) measurement by ETAAS in the supernatants. The detection limits and reproducibility achieved for the Cr speciation analysis fulfill the requirements for their monitoring in waters under the demand of the Water Framework Directive.
| S-EPMC9689422 | biostudies-literature
Project description:Fanconi anemia (FA) is a rare autosomal recessive disorder characterized by congenital abnormalities, progressive bone marrow failure, and cancer susceptibility. FA cells are hypersensitive to DNA crosslinking agents. FA is a genetically heterogeneous disease with at least 11 complementation groups. The eight cloned FA proteins interact in a common pathway with established DNA-damage-response proteins, including BRCA1 and ATM. Six FA proteins (A, C, E, F, G, and L) regulate the monoubiquitination of FANCD2 after DNA damage by crosslinking agents, which targets FANCD2 to BRCA1 nuclear foci containing BRCA2 (FANCD1) and RAD51. Some forms of hexavalent chromium [Cr(VI)] are implicated as respiratory carcinogens and induce several types of DNA lesions, including DNA interstrand crosslinks. We have shown that FA-A fibroblasts are hypersensitive to both Cr(VI)-induced apoptosis and clonogenic lethality. Here we show that Cr(VI) treatment induced monoubiquitination of FANCD2 in normal human fibroblasts, providing the first molecular evidence of Cr(VI)-induced activation of the FA pathway. FA-A fibroblasts demonstrated no FANCD2 monoubiquitination, in keeping with the requirement of FA-A for this modification. We also found that Cr(VI) treatment induced significantly more S-phase-dependent DNA double strand breaks (DSBs), as measured by gamma-H2AX expression, in FA-A fibroblasts compared to normal cells. However, and notably, DSBs were repaired equally in both normal and FA-A fibroblasts during recovery from Cr(VI) treatment. While previous research on FA has defined the genetic causes of this disease, it is critical in terms of individual risk assessment to address how cells from FA patients respond to genotoxic insult.
| S-EPMC2080350 | biostudies-literature
Project description:The present work demonstrates the heavy metal resistance and detoxification of Cr(VI) by the probiotic actinobacterial cultures isolated from chicken and goat feces. The actinobacterial isolates were screened for heavy metal resistance by qualitative, semiquantitative assays and Cr(VI) biosorption was determined by analytical techniques such as atomic absorption spectrophotometry and Fourier transform infrared spectrometry (FT-IR). All the tested actinobacterial isolates (n = 20) showed resistance toward K2Cr2O7, NiCl2, ZnCl2, CuSO4 and PbNO3 at 20 mg L-1 concentration. The maximum tolerance concentration values were found to be 200-250 mg L-1 for K2Cr2O7, 100-250 mg L-1 for PbNO3 and <50-250 mg L-1 for NiCl2, ZnCl2 and CuSO4. Among the five tested heavy metals, Cr(VI) was resisted by 95 % of the tested actinobacterial cultures up to 250 mg L-1 concentration; particularly, the isolate LD22 exhibited a high degree of tolerance to all the tested heavy metals. Thus, the isolate was justifiably chosen for Cr(VI) biosorption study and the biosorption efficacy was found maximum at 100 mg L-1 of metal ion concentration (3 g L-1 of biomass dosage and pH 7.0). FT-IR spectrum revealed the chemical interactions between the hydroxyl, amine and carboxyl groups of the biomass and the metal ions. On the basis of phenotypic, physiological, biochemical and molecular characteristics the isolate LD22 was identified as Streptomyces werraensis LD22 (JX524481) which could be used to develop a biosorbent for adsorbing Cr(VI) metal ions.
| S-EPMC4522735 | biostudies-literature
Project description:Electron paramagnetic resonance (EPR) oximetry is a powerful technique capable of providing accurate, reliable, and repeated measurements of tissue oxygenation, which is crucial to the diagnosis and treatment of several pathophysiological conditions. Measurement of tissue pO(2) by EPR involves the use of paramagnetic, oxygen-sensitive probes, which can be either soluble (molecular) in nature or insoluble paramagnetic materials. Development of innovative strategies to enhance the biocompatibility and in vivo application of these oxygen-sensing probes is crucial to the growth and clinical applicability of EPR oximetry. Recent research efforts have aimed at encapsulating particulate probes in bioinert polymers for the development of biocompatible EPR probes. In this study, we have developed novel EPR oximetry probes, called perchlorotriphenylmethyl triester (PTM-TE):polydimethyl siloxane (PDMS) chips, by dissolving and incorporating the soluble (molecular) EPR probe, PTM-TE, in an oxygen-permeable polymer matrix, PDMS. We demonstrate that such incorporation (doping) of PTM-TE in PDMS enhanced its oxygen sensitivity several fold. The cast-molding method of fabricating chips enabled them to be made with increasing amounts of PTM-TE (spin density). Characterization of the spin distribution within the PDMS matrix, using EPR micro-imaging, revealed potential inhomogeneties, albeit with no adverse effect on the oxygen-sensing characteristics of PTM-TE:PDMS. The chips were resistant to autoclaving or in vitro oxidoreductant treatment, thus exhibiting excellent in vitro biostability. Our results establish PTM-TE:PDMS as a viable probe for biological oxygen-sensing, and also validate the incorporation of soluble probes in polymer matrices as an innovative approach to the development of novel probes for EPR oximetry.
| S-EPMC2866758 | biostudies-literature