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1.
medRxiv ; 2024 Apr 22.
Artículo en Inglés | MEDLINE | ID: mdl-38712274

RESUMEN

Introduction: Racial/ethnic disparities in maternal mortality rates represent one of the most significant areas of disparities amongst all conventional population perinatal health measures in the U.S. The alarming trends and persistent disparities of outcomes by race/ethnicity and geographic location reinforce the need to focus on ensuring quality and safety of maternity care for all women. Despite complex multilevel factors impacting maternal mortality and morbidity, there are evidence-based interventions that, when facilitated consistently and properly, are known to improve the health of mothers before, during and after pregnancy. The objective of this project is to test implementation of pre-conception counseling with father involvement in community-based settings to improve cardiovascular health outcomes before and during pregnancy in southeastern United States. Methods and Analysis: This study has two components: a comprehensive needs and assets assessment and a small-scale pilot study. We will conduct a community informed needs and assets assessment with our diverse stakeholders to identify opportunities and barriers to preconception counseling as well as develop a stakeholder-informed implementation plan. Next, we will use the implementation plan to pilot preconception counseling with father involvement in community-based settings. Finally, we will critically assess the context, identify potential barriers and facilitators, and iteratively adapt the way preconception counseling can be implemented in diverse settings. Results of this research will support future research focused on identifying barriers and opportunities for scalable and sustainable public health approaches to implementing evidence-based strategies that reduce maternal morbidity and mortality in the southeastern United States' vulnerable communities. Discussion: Findings will demonstrate that preconception counseling can be implemented in community health settings in the southeastern United States. Furthermore, this study will build the capacity of community-based organizations in addressing the preconception health of their clients. We plan for this pilot to inform a larger scaled-up clinical trial across community health settings in multiple southeastern states.

4.
Clin Oncol (R Coll Radiol) ; 36(4): 254-264, 2024 04.
Artículo en Inglés | MEDLINE | ID: mdl-38350785

RESUMEN

AIMS: Prehabilitation is a process of identifying and assessing factors that could compromise the physical and psychological health of patients undergoing cancer treatment and implementing an intervention to combat such concerns. The use of prehabilitation in cancer surgery has yielded positive outcomes in rectal, lung and abdominal cancers. Prehabilitation strategies have potential to improve the management of patients receiving radiation therapy or chemoradiation. The aim of the present study was to map the evidence of the assessment and evaluation of prehabilitation for radiation therapy patients. MATERIALS AND METHODS: A database search using EMBASE and PubMed was conducted. The PRISMA guidelines were adhered to. Keywords included prehabilitation, radiation therapy/radiotherapy, chemoradiotherapy/chemoradiation, intervention and exercise. Types of prehabilitation strategy, their purposes and impact, according to cancer site, were analysed. RESULTS: Prehabilitation is most commonly evaluated in head and neck cancer, whereby unimodal, physical interventions manage dysphagia. Prehabilitation for lung cancer demonstrated its ability to widen treatment options for patients. Physical prehabilitation is administered to combat adverse effects of neoadjuvant chemoradiation therapy in patients with rectal cancer. CONCLUSION: Prehabilitation is adaptive and tailored to specific patient and site needs; thus it is applied across a wide range of cancer sites. More interventions by which radiation therapy is the definitive treatment modality and larger sample sizes within these studies are warranted to increase prehabilitation utilisation for patients undergoing radiation therapy.


Asunto(s)
Neoplasias de Cabeza y Cuello , Neoplasias Pulmonares , Ejercicio Preoperatorio , Neoplasias del Recto , Humanos , Neoplasias de Cabeza y Cuello/terapia , Cuidados Preoperatorios , Neoplasias del Recto/terapia , Neoplasias Pulmonares/terapia
5.
Sci Adv ; 10(1): eadj8765, 2024 Jan 05.
Artículo en Inglés | MEDLINE | ID: mdl-38181087

RESUMEN

Numerous technologies-with catalytic, therapeutic, and diagnostic applications-would benefit from improved chelation strategies for heavy alkaline earth elements: Ra2+, Ba2+, and Sr2+. Unfortunately, chelating these metals is challenging because of their large size and weak polarizing power. We found 18-crown-6-tetracarboxylic acid (H4COCO) bound Ra2+, Ba2+, and Sr2+ to form M(HxCOCO)x-2. Upon isolating radioactive 223Ra from its parent radionuclides (227Ac and 227Th), 223Ra2+ reacted with the fully deprotonated COCO4- chelator to generate Ra(COCO)2-(aq) (log KRa(COCO)2- = 5.97 ± 0.01), a rare example of a molecular radium complex. Comparative analyses with Sr2+ and Ba2+ congeners informed on what attributes engendered success in heavy alkaline earth complexation. Chelators with high negative charge [-4 for Ra(COCO)2-(aq)] and many donor atoms [≥11 in Ra(COCO)2-(aq)] provided a framework for stable complex formation. These conditions achieved steric saturation and overcame the weak polarization powers associated with these large dicationic metals.

6.
Water Res ; 250: 120901, 2024 Feb 15.
Artículo en Inglés | MEDLINE | ID: mdl-38118255

RESUMEN

Current circularity assessment terminology restricts application to wastewater processes due to the focus on technical systems. Waste stream and wastewater discharge circularity definitions lead to paradoxical assessments that generate results of little value for evidence-based decision making. Therefore, a classification approach was developed to measure inflow and outflow circularity of the main wastewater resource flows using the principle of traceability, adopting the attitude that not all waste is created equally. Applying it to a wastewater treatment plant (12,000 m3/d load) showed how upstream agricultural, industrial, and human practices impact downstream treatment, and the effectiveness of resource cycling within the natural environment. Industrial actions increasing fossil carbon concentration (400 m3/d effluent at 1000 mgC/l) reduced inflow and outflow circularity by 16 % and 10.6 % respectively, as secondary and sludge treatment fossil emissions increase significantly. Alternatively, changes to human and agricultural practices (50 % reduction of detergent and synthetic fertiliser usage) improved phosphorus inflow and nitrogen outflow circularity by 5.2 % and 20.1 % respectively. This approach can educate and assign responsibility to water users for developing robust circular economy policy, shifting the pattern from promoting circularity to discouraging linear actions, overcoming the shared economic and environmental burden of linear water use.


Asunto(s)
Eliminación de Residuos Líquidos , Aguas Residuales , Humanos , Eliminación de Residuos Líquidos/métodos , Aguas del Alcantarillado , Nitrógeno , Agua
7.
bioRxiv ; 2023 Nov 17.
Artículo en Inglés | MEDLINE | ID: mdl-38014232

RESUMEN

Alzheimer's disease (AD) patients exhibit neuropsychiatric symptoms that extend beyond classical cognitive deficits, suggesting involvement of subcortical areas. Here, we investigated the role of midbrain dopamine (DA) neurons in AD using the amyloid + tau-driven 3xTg-AD mouse model. We found deficits in reward-based operant learning in AD mice, suggesting possible VTA DA neuron dysregulation. Physiological assessment revealed hyperexcitability and disrupted firing in DA neurons caused by reduced activity of small-conductance calcium-activated potassium (SK) channels. RNA sequencing from contents of single patch-clamped DA neurons (Patch-seq) identified up-regulation of the SK channel modulator casein kinase 2 (CK2). Pharmacological inhibition of CK2 restored SK channel activity and normal firing patterns in 3xTg-AD mice. These findings shed light on a complex interplay between neuropsychiatric symptoms and subcortical circuits in AD, paving the way for novel treatment strategies.

8.
Proc Natl Acad Sci U S A ; 120(49): e2305763120, 2023 Dec 05.
Artículo en Inglés | MEDLINE | ID: mdl-38015845

RESUMEN

Marine dissolved organic nitrogen (DON) is one of the planet's largest reservoirs of fixed N, which persists even in the N-limited oligotrophic surface ocean. The vast majority of the ocean's total DON reservoir is refractory (RDON), primarily composed of low molecular weight (LMW) compounds in the subsurface and deep sea. However, the composition of this major N pool, as well as the reasons for its accumulation and persistence, are not understood. Past characterization of the analytically more tractable, but quantitatively minor, high molecular weight (HMW) DON fraction revealed a functionally simple amide-dominated composition. While extensive work in the past two decades has revealed enormous complexity and structural diversity in LMW dissolved organic carbon, no efforts have specifically targeted LMW nitrogenous molecules. Here, we report the first coupled isotopic and solid-state NMR structural analysis of LMW DON isolated throughout the water column in two ocean basins. Together these results provide a first view into the composition, potential sources, and cycling of this dominant portion of marine DON. Our data indicate that RDON is dominated by 15N-depleted heterocyclic-N structures, entirely distinct from previously characterized HMW material. This fundamentally new view of marine DON composition suggests an important structural control for RDON accumulation and persistence in the ocean. The mechanisms of production, cycling, and removal of these heterocyclic-N-containing compounds now represents a central challenge in our understanding of the ocean's DON reservoir.

9.
Inorg Chem ; 2023 Oct 18.
Artículo en Inglés | MEDLINE | ID: mdl-37851526

RESUMEN

Gallium trichloride (GaCl3) was used as a solvent for the oxidative dissolution of the lanthanide (Ln) metals cerium (Ce) and holmium (Ho). Reactions were performed at temperatures above 100 °C in sealed vessels to maintain the liquid phase for GaCl3 during the oxidizing reactions. The best results were obtained from reactions using 8 equiv of GaCl3 to metal where the inorganic complexes [Ga][Ln(GaCl4)4] [Ln = Ce (1), Ho (2)] could be isolated. Recrystallization of 1 and 2 employing fluorobenzene (C6H5F) produced [Ga(η6-C6H5F)2][Ln(GaCl4)4] [Ln = Ce (3), Ho (4)] where reversible η6 coordination of C6H5F to [Ga]+ was observed. All complexes were characterized through elemental analysis (F and Cl), IR and UV-vis-near-IR spectroscopies, and both solution and solid-state NMR techniques.

10.
J Magn Reson ; 355: 107540, 2023 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-37722217

RESUMEN

There is growing interest in using low-field magnetic resonance experiments for routine chemical characterization. Earth's field NMR is one such technique that can garner structural information and enable sample differentiation with low cost and highly portable designs. The resulting NMR spectra are primarily influenced by J-couplings, resulting in so-called J-coupled spectra (JCS). Many small molecules include atoms with NMR-active nuclei that are quadrupolar either at natural abundance or are often isotopically enriched (e.g.,2H, 6Li, 11B, 14N, 17O, etc.) where the effects of quadrupolar J-couplings and relaxation on JCS of strongly- and weakly-coupled spin systems have not been explored to date. Herein, using a set of seven fluoropyridine samples with unique substitution and J-couplings, we demonstrate that the 14N relaxation rates can induce drastic line-broadening in the JCS. This includes a previously unexplored unique line broadening mechanism enabled by strongly coupled spins at low-field. Numerical simulations are used to model and refine the magnitudes and signs of J-couplings, as well as indirectly determine the 14N relaxation rates in a single 1D experiment that has a higher fidelity than observed in high-field NMR experiments.

12.
Nat Commun ; 14(1): 4782, 2023 Aug 08.
Artículo en Inglés | MEDLINE | ID: mdl-37553366

RESUMEN

Element isotopes are characterized by distinct atomic masses and nuclear spins, which can significantly influence material properties. Notably, however, isotopes in natural materials are homogenously distributed in space. Here, we propose a method to configure material properties by repositioning isotopes in engineered van der Waals (vdW) isotopic heterostructures. We showcase the properties of hexagonal boron nitride (hBN) isotopic heterostructures in engineering confined photon-lattice waves-hyperbolic phonon polaritons. By varying the composition, stacking order, and thicknesses of h10BN and h11BN building blocks, hyperbolic phonon polaritons can be engineered into a variety of energy-momentum dispersions. These confined and tailored polaritons are promising for various nanophotonic and thermal functionalities. Due to the universality and importance of isotopes, our vdW isotope heterostructuring method can be applied to engineer the properties of a broad range of materials.

13.
Geroscience ; 45(5): 3019-3043, 2023 10.
Artículo en Inglés | MEDLINE | ID: mdl-37393197

RESUMEN

Major histocompatibility complex I (MHC-I) CNS cellular localization and function is still being determined after previously being thought to be absent from the brain. MHC-I expression has been reported to increase with brain aging in mouse, rat, and human whole tissue analyses, but the cellular localization was undetermined. Neuronal MHC-I is proposed to regulate developmental synapse elimination and tau pathology in Alzheimer's disease (AD). Here, we report that across newly generated and publicly available ribosomal profiling, cell sorting, and single-cell data, microglia are the primary source of classical and non-classical MHC-I in mice and humans. Translating ribosome affinity purification-qPCR analysis of 3-6- and 18-22-month-old (m.o.) mice revealed significant age-related microglial induction of MHC-I pathway genes B2m, H2-D1, H2-K1, H2-M3, H2-Q6, and Tap1 but not in astrocytes and neurons. Across a timecourse (12-23 m.o.), microglial MHC-I gradually increased until 21 m.o. and then accelerated. MHC-I protein was enriched in microglia and increased with aging. Microglial expression, and absence in astrocytes and neurons, of MHC-I-binding leukocyte immunoglobulin-like (Lilrs) and paired immunoglobin-like type 2 (Pilrs) receptor families could enable cell -autonomous MHC-I signaling and increased with aging in mice and humans. Increased microglial MHC-I, Lilrs, and Pilrs were observed in multiple AD mouse models and human AD data across methods and studies. MHC-I expression correlated with p16INK4A, suggesting an association with cellular senescence. Conserved induction of MHC-I, Lilrs, and Pilrs with aging and AD opens the possibility of cell-autonomous MHC-I signaling to regulate microglial reactivation with aging and neurodegeneration.


Asunto(s)
Enfermedad de Alzheimer , Microglía , Humanos , Ratones , Ratas , Animales , Microglía/patología , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/metabolismo , Complejo Mayor de Histocompatibilidad , Envejecimiento/fisiología , Encéfalo/metabolismo
14.
Phys Rev Lett ; 130(22): 222501, 2023 Jun 02.
Artículo en Inglés | MEDLINE | ID: mdl-37327448

RESUMEN

The ß-delayed proton decay of ^{13}O has previously been studied, but the direct observation of ß-delayed 3αp decay has not been reported. Rare 3αp events from the decay of excited states in ^{13}N^{⋆} provide a sensitive probe of cluster configurations in ^{13}N. To measure the low-energy products following ß-delayed 3αp decay, the Texas Active Target (TexAT) time projection chamber was employed using the one-at-a-time ß-delayed charged-particle spectroscopy technique at the Cyclotron Institute, Texas A&M University. A total of 1.9×10^{5} ^{13}O implantations were made inside the TexAT time projection chamber. A total of 149 3αp events were observed, yielding a ß-delayed 3αp branching ratio of 0.078(6)%. Four previously unknown α-decaying excited states were observed in ^{13}N at 11.3, 12.4, 13.1, and 13.7 MeV decaying via the 3α+p channel.


Asunto(s)
Protones , Humanos , Análisis Espectral
15.
bioRxiv ; 2023 Jun 02.
Artículo en Inglés | MEDLINE | ID: mdl-36945372

RESUMEN

Major Histocompatibility Complex I (MHC-I) CNS cellular localization and function is still being determined after previously being thought to be absent from the brain. MHC-I expression has been reported to increase with brain aging in mouse, rat, and human whole tissue analyses but the cellular localization was undetermined. Neuronal MHC-I is proposed to regulate developmental synapse elimination and tau pathology in Alzheimer's disease (AD). Here we report that across newly generated and publicly available ribosomal profiling, cell sorting, and single-cell data, microglia are the primary source of classical and non-classical MHC-I in mice and humans. Translating Ribosome Affinity Purification-qPCR analysis of 3-6 and 18-22 month old (m.o.) mice revealed significant age-related microglial induction of MHC-I pathway genes B2m , H2-D1 , H2-K1 , H2-M3 , H2-Q6 , and Tap1 but not in astrocytes and neurons. Across a timecourse (12-23 m.o.), microglial MHC-I gradually increased until 21 m.o. and then accelerated. MHC-I protein was enriched in microglia and increased with aging. Microglial expression, and absence in astrocytes and neurons, of MHC-I binding Leukocyte Immunoglobulin-like (Lilrs) and Paired immunoglobin-like type 2 (Pilrs) receptor families could enable cell-autonomous MHC-I signaling and increased with aging in mice and humans. Increased microglial MHC-I, Lilrs, and Pilrs were observed in multiple AD mouse models and human AD data across methods and studies. MHC-I expression correlated with p16INK4A , suggesting an association with cellular senescence. Conserved induction of MHC-I, Lilrs, and Pilrs with aging and AD opens the possibility of cell-autonomous MHC-I signaling to regulate microglial reactivation with aging and neurodegeneration.

16.
Sci Rep ; 13(1): 1025, 2023 01 19.
Artículo en Inglés | MEDLINE | ID: mdl-36658269

RESUMEN

Substantia nigra pars compacta (SNc) dopamine neurons are required for voluntary movement and reward learning, and advanced age is associated with motor and cognitive decline. In the midbrain, D2-type dopamine receptors located at dendrodendritic synapses between dopamine neurons control cell firing through G protein-activated potassium (GIRK) channels. We previously showed that aging disrupts dopamine neuron pacemaker firing in mice, but only in males. Here we show that the amplitude of D2-receptor inhibitory postsynaptic currents (D2-IPSCs) are moderately reduced in aged male mice. Local application of dopamine revealed a reduction in the amplitude of the D2-receptor currents in old males compared to young, pointing to a postsynaptic mechanism. Further experiments indicated that reduced D2 receptor signaling was not due to a general reduction in GIRK channel currents or degeneration of the dendritic arbor. Kinetic analysis showed no differences in D2-IPSC shape in old versus young mice or between sexes. Potentiation of D2-IPSCs by corticotropin releasing factor (CRF) was also not affected by age, indicating preservation of one mechanism of plasticity. These findings have implications for understanding dopamine transmission in aging, and reduced D2 receptor inhibition could contribute to increased susceptibility of males to SNc dopamine neuron degeneration in Parkinson's disease.


Asunto(s)
Dopamina , Neuronas Dopaminérgicas , Ratones , Masculino , Animales , Neuronas Dopaminérgicas/metabolismo , Cinética , Sustancia Negra/metabolismo , Porción Compacta de la Sustancia Negra/metabolismo , Receptores de Dopamina D2/metabolismo
17.
Epidemiol Psychiatr Sci ; 32: e1, 2023 Jan 10.
Artículo en Inglés | MEDLINE | ID: mdl-36624694

RESUMEN

AIMS: Childhood adversities (CAs) predict heightened risks of posttraumatic stress disorder (PTSD) and major depressive episode (MDE) among people exposed to adult traumatic events. Identifying which CAs put individuals at greatest risk for these adverse posttraumatic neuropsychiatric sequelae (APNS) is important for targeting prevention interventions. METHODS: Data came from n = 999 patients ages 18-75 presenting to 29 U.S. emergency departments after a motor vehicle collision (MVC) and followed for 3 months, the amount of time traditionally used to define chronic PTSD, in the Advancing Understanding of Recovery After Trauma (AURORA) study. Six CA types were self-reported at baseline: physical abuse, sexual abuse, emotional abuse, physical neglect, emotional neglect and bullying. Both dichotomous measures of ever experiencing each CA type and numeric measures of exposure frequency were included in the analysis. Risk ratios (RRs) of these CA measures as well as complex interactions among these measures were examined as predictors of APNS 3 months post-MVC. APNS was defined as meeting self-reported criteria for either PTSD based on the PTSD Checklist for DSM-5 and/or MDE based on the PROMIS Depression Short-Form 8b. We controlled for pre-MVC lifetime histories of PTSD and MDE. We also examined mediating effects through peritraumatic symptoms assessed in the emergency department and PTSD and MDE assessed in 2-week and 8-week follow-up surveys. Analyses were carried out with robust Poisson regression models. RESULTS: Most participants (90.9%) reported at least rarely having experienced some CA. Ever experiencing each CA other than emotional neglect was univariably associated with 3-month APNS (RRs = 1.31-1.60). Each CA frequency was also univariably associated with 3-month APNS (RRs = 1.65-2.45). In multivariable models, joint associations of CAs with 3-month APNS were additive, with frequency of emotional abuse (RR = 2.03; 95% CI = 1.43-2.87) and bullying (RR = 1.44; 95% CI = 0.99-2.10) being the strongest predictors. Control variable analyses found that these associations were largely explained by pre-MVC histories of PTSD and MDE. CONCLUSIONS: Although individuals who experience frequent emotional abuse and bullying in childhood have a heightened risk of experiencing APNS after an adult MVC, these associations are largely mediated by prior histories of PTSD and MDE.


Asunto(s)
Trastorno Depresivo Mayor , Trastornos por Estrés Postraumático , Adulto , Humanos , Adolescente , Adulto Joven , Persona de Mediana Edad , Anciano , Trastornos por Estrés Postraumático/epidemiología , Trastornos por Estrés Postraumático/etiología , Trastornos por Estrés Postraumático/diagnóstico , Trastorno Depresivo Mayor/psicología , Depresión/psicología , Encuestas y Cuestionarios , Vehículos a Motor
18.
Knee ; 40: 245-255, 2023 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-36521417

RESUMEN

BACKGROUND: Little is known about ability to work after unicompartmental knee replacement (UKR) and total knee replacement (TKR), especially in physically-demanding occupations. This study described rates of return-to-work (RTW) and ability to sustain work by job after arthroplasty. METHOD: Participants from The Clinical Outcomes in Arthroplasty Study (COASt) aged 18-65 were eligible if they underwent UKR or TKR and had at least 5 years' follow-up post-operation. We posted a survey asking about pre-operative occupation, post-operative occupations and associated physical demands, and whether they had quit a job post-surgery due to difficulties with the operated knee (knee-related job loss (KRJL)). We fitted Cox Proportional Hazard Models to investigate the role of demanding physical activities on KRJL. RESULTS: 251 people (143 UKR, 108 TKR) returned a questionnaire, of whom 101 UKR and 57 TKR worked post-operatively. Rates of RTW were highest amongst those in managerial and professional or technical roles, whichever operation they received. RTW was poorest amongst those in elementary occupations. In associate professional/technical occupations, RTW rates were better amongst UKR recipients. Amongst participants who returned to work, 17 reported KRJL (8.5% UKR and 16.7% TKR). Respondents were more likely to have KRJL if their job involved carrying/lifting ≥10 kg (HR:4.81, 95%CI 1.55-14.93) or climbing >30 flights of stairs (HR:4.03, 95%CI 1.36-11.98). CONCLUSIONS: Knee arthroplasty recipients working pre-operatively mostly RTW. RTW may be more difficult after TKR than UKR. Jobs which involve lifting and climbing stairs may be particularly challenging. Surgeons offering knee arthroplasty should counsel patients about workability as well as risk of revision.


Asunto(s)
Artroplastia de Reemplazo de Rodilla , Osteoartritis de la Rodilla , Humanos , Artroplastia de Reemplazo de Rodilla/efectos adversos , Reinserción al Trabajo , Articulación de la Rodilla/cirugía , Empleo , Reoperación , Osteoartritis de la Rodilla/cirugía , Osteoartritis de la Rodilla/etiología
19.
Inorg Chem ; 62(16): 6242-6254, 2023 Apr 24.
Artículo en Inglés | MEDLINE | ID: mdl-36580490

RESUMEN

Deciphering the solution chemistry and speciation of actinides is inherently difficult due to radioactivity, rarity, and cost constraints, especially for transplutonium elements. In this context, the development of new chelating platforms for actinides and associated spectroscopic techniques is particularly important. In this study, we investigate a relatively overlooked class of chelators for actinide binding, namely, polyoxometalates (POMs). We provide the first NMR measurements on americium-POM and curium-POM complexes, using one-dimensional (1D) 31P NMR, variable-temperature NMR, and spin-lattice relaxation time (T1) experiments. The proposed POM-NMR approach allows for the study of trivalent f-elements even when only microgram amounts are available and in phosphate-containing solutions where f-elements are typically insoluble. The solution-state speciation of trivalent americium, curium, plus multiple lanthanide ions (La3+, Nd3+, Sm3+, Eu3+, Yb3+, and Lu3+), in the presence of the model POM ligand PW11O397- was elucidated and revealed the concurrent formation of two stable complexes, [MIII(PW11O39)(H2O)x]4- and [MIII(PW11O39)2]11-. Interconversion reaction constants, reaction enthalpies, and reaction entropies were derived from the NMR data. The NMR results also provide experimental evidence of the weakly paramagnetic nature of the Am3+ and Cm3+ ions in solution. Furthermore, the study reveals a previously unnoticed periodicity break along the f-element series with the reversal of T1 relaxation times of the 1:1 and 1:2 complexes and the preferential formation of the long T1 species for the early lanthanides versus the short T1 species for the late lanthanides, americium, and curium. Given the broad variety of POM ligands that exist, with many of them containing NMR-active nuclei, the combined POM-NMR approach reported here opens a new avenue to investigate difficult-to-study elements such as heavy actinides and other radionuclides.

20.
Small ; 19(6): e2205487, 2023 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-36470595

RESUMEN

Metal boride nanostructures have shown significant promise for hydrogen storage applications. However, the synthesis of nanoscale metal boride particles is challenging because of their high surface energy, strong inter- and intraplanar bonding, and difficult-to-control surface termination. Here, it is demonstrated that mechanochemical exfoliation of magnesium diboride in zirconia produces 3-4 nm ultrathin MgB2 nanosheets (multilayers) in high yield. High-pressure hydrogenation of these multilayers at 70 MPa and 330 °C followed by dehydrogenation at 390 °C reveals a hydrogen capacity of 5.1 wt%, which is ≈50 times larger than the capacity of bulk MgB2 under the same conditions. This enhancement is attributed to the creation of defective sites by ball-milling and incomplete Mg surface coverage in MgB2 multilayers, which disrupts the stable boron-boron ring structure. The density functional theory calculations indicate that the balance of Mg on the MgB2 nanosheet surface changes as the material hydrogenates, as it is energetically favorable to trade a small number of Mg vacancies in Mg(BH4 )2 for greater Mg coverage on the MgB2 surface. The exfoliation and creation of ultrathin layers is a promising new direction for 2D metal boride/borohydride research with the potential to achieve high-capacity reversible hydrogen storage at more moderate pressures and temperatures.

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