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1.
Neuroimage Clin ; 37: 103295, 2023.
Article in English | MEDLINE | ID: mdl-36549233

ABSTRACT

Major depressive disorder (MDD) is the leading mental disorder and afflicts more than 350 million people worldwide. The underlying neural mechanisms of MDD remain unclear, hindering the accurate treatment. Recent brain imaging studies have observed functional abnormalities in multiple brain regions in patients with MDD, identifying core brain regions is the key to locating potential therapeutic targets for MDD. The Granger causality analysis (GCA) measures directional effects between brain regions and, therefore, can track causal hubs as potential intervention targets for MDD. We reviewed literature employing GCA to investigate abnormal brain connections in patients with MDD. The total degree of effective connections in the thalamus (THA) is more than twice that in traditional targets such as the superior frontal gyrus and anterior cingulate cortex. Altered causal connections in patients with MDD mainly included enhanced bottom-up connections from the thalamus to various cortical and subcortical regions and reduced top-down connections from these regions to the THA, indicating excessive uplink sensory information and insufficient downlink suppression information for negative emotions. We suggest that the thalamus is the most crucial causal hub for MDD, which may serve as the downstream target for non-invasive brain stimulation and medication approaches in MDD treatment.


Subject(s)
Depressive Disorder, Major , Humans , Depressive Disorder, Major/diagnostic imaging , Depressive Disorder, Major/therapy , Brain Mapping , Brain/diagnostic imaging , Thalamus/diagnostic imaging , Gyrus Cinguli , Magnetic Resonance Imaging/methods
2.
Nano Res ; 16(1): 715-734, 2023.
Article in English | MEDLINE | ID: mdl-36156906

ABSTRACT

Nanoparticles-based drug delivery systems have attracted significant attention in biomedical fields because they can deliver loaded cargoes to the target site in a controlled manner. However, tremendous challenges must still be overcome to reach the expected targeting and therapeutic efficacy in vivo. These challenges mainly arise because the interaction between nanoparticles and biological systems is complex and dynamic and is influenced by the physicochemical properties of the nanoparticles and the heterogeneity of biological systems. Importantly, once the nanoparticles are injected into the blood, a protein corona will inevitably form on the surface. The protein corona creates a new biological identity which plays a vital role in mediating the bio-nano interaction and determining the ultimate results. Thus, it is essential to understand how the protein corona affects the delivery journey of nanoparticles in vivo and what we can do to exploit the protein corona for better delivery efficiency. In this review, we first summarize the fundamental impact of the protein corona on the delivery journey of nanoparticles. Next, we emphasize the strategies that have been developed for tailoring and exploiting the protein corona to improve the transportation behavior of nanoparticles in vivo. Finally, we highlight what we need to do as a next step towards better understanding and exploitation of the protein corona. We hope these insights into the "Yin and Yang" effect of the protein corona will have profound implications for understanding the role of the protein corona in a wide range of nanoparticles.

3.
Medicine (Baltimore) ; 101(48): e31827, 2022 Dec 02.
Article in English | MEDLINE | ID: mdl-36482602

ABSTRACT

BACKGROUND: Coronavirus disease 2019 (COVID-19) is an acute respiratory infectious disease that makes breathing difficult and is often accompanied by olfactory disorders and distension. Chinese herbal tonics, a special external treatment of traditional Chinese medicine, has shown beneficial effects in the treatment of olfactory disorders. Currently, there is a lack of systematic reviews on Chinese herbal tonics for the treatment of olfactory disorders. We conduct this study to evaluate the efficacy and safety of Chinese herbal tonics in the treatment of olfactory disorders. This study is designed to evaluate the effectiveness and safety of Chinese herbal tonics for olfactory disorders in COVID-19. METHODS: Randomized controlled trials from December 2019 to September 2022. will be included, without restrictions on language or publication date. PubMed, EMBASE, Cochrane Library, Web of Science, Chinese Biomedical Databases, China National Knowledge Infrastructure, Wanfang Database, and VIP Database were searched. Two researchers will independently select studies, extract data, and evaluate study quality. The Cochrane risk of bias tool for randomized trials will be used to assess the risk of bias in the included studies. Statistical analyses will be conducted using the Review Manager (RevMan 5.3, Cochrane Collaboration, Nordic Cochrane Center, Copenhagen, Denmark). RESULTS: This study aimed to prove the efficacy and safety of Chinese herbal tonics for olfactory disorders in patients with COVID-19. Our study provides a more accurate treatment method for olfactory disorders during COVID-19.We will publish our results in a peer-reviewed journal.


Subject(s)
COVID-19 , Drugs, Chinese Herbal , Humans , Language , Meta-Analysis as Topic , Systematic Reviews as Topic
4.
Nat Commun ; 13(1): 5696, 2022 09 28.
Article in English | MEDLINE | ID: mdl-36171419

ABSTRACT

Fatty liver is a highly heterogenous condition driven by various pathogenic factors in addition to the severity of steatosis. Protein insufficiency has been causally linked to fatty liver with incompletely defined mechanisms. Here we report that fatty liver is a sulfur amino acid insufficient state that promotes metabolic inflexibility via limiting coenzyme A availability. We demonstrate that the nutrient-sensing transcriptional factor EB synergistically stimulates lysosome proteolysis and methionine adenosyltransferase to increase cysteine pool that drives the production of coenzyme A and glutathione, which support metabolic adaptation and antioxidant defense during increased lipid influx. Intriguingly, mice consuming an isocaloric protein-deficient Western diet exhibit selective hepatic cysteine, coenzyme A and glutathione deficiency and acylcarnitine accumulation, which are reversed by cystine supplementation without normalizing dietary protein intake. These findings support a pathogenic link of dysregulated sulfur amino acid metabolism to metabolic inflexibility that underlies both overnutrition and protein malnutrition-associated fatty liver development.


Subject(s)
Amino Acids, Sulfur , Fatty Liver , Amino Acids, Sulfur/metabolism , Animals , Antioxidants/metabolism , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors , Coenzyme A/metabolism , Cysteine/metabolism , Cystine/metabolism , Dietary Proteins/metabolism , Fatty Liver/metabolism , Glutathione/metabolism , Homeostasis , Lipids , Liver/metabolism , Methionine/metabolism , Methionine Adenosyltransferase/metabolism , Mice , Oxidation-Reduction
5.
Drug Des Devel Ther ; 16: 1697-1711, 2022.
Article in English | MEDLINE | ID: mdl-35693534

ABSTRACT

Intestinal barrier injury and hyperglycemia are common in patients with sepsis. Bacteria translocation and systemic inflammatory response caused by intestinal barrier injury play a significant role in sepsis occurrence and deterioration, while hyperglycemia is linked to adverse outcomes in sepsis. Previous studies have shown that hyperglycemia is an independent risk factor for intestinal barrier injury. Concurrently, increasing evidence has indicated that some anti-hyperglycemic agents not only improve intestinal barrier function but are also beneficial in managing sepsis-induced organ dysfunction. Therefore, we assume that these agents can block or reduce the severity of sepsis by improving intestinal barrier function. Accordingly, we explicated the connection between sepsis, intestinal barrier, and hyperglycemia, overviewed the evidence on improving intestinal barrier function and alleviating sepsis-induced organ dysfunction by anti-hyperglycemic agents (eg, metformin, peroxisome proliferators activated receptor-γ agonists, berberine, and curcumin), and summarized some common characteristics of these agents to provide a new perspective in the adjuvant treatment of sepsis.


Subject(s)
Hyperglycemia , Sepsis , Humans , Hypoglycemic Agents/pharmacology , Hypoglycemic Agents/therapeutic use , Intestinal Mucosa , Multiple Organ Failure , Sepsis/drug therapy
6.
Nat Commun ; 13(1): 426, 2022 01 20.
Article in English | MEDLINE | ID: mdl-35058459

ABSTRACT

Radical cascade reactions are powerful tools to construct structurally complex molecules. However, the stereochemical control of acyclic radical intermediates remains a persistent challenge, due to the low differentiation between the two faces of these species. This hurdle further makes stereodivergent synthesis rather more difficult to be accomplished, in particular for intermediates resulted from complex cascades. Here we report an efficient strategy for stereoselective hydrogen atom transfer (HAT) to acyclic carbon radicals, which are generated via N-heterocyclic carbene (NHC)-boryl radicals triggered addition-translocation-cyclization cascades. A synergistic control by the NHC subunit and a thiol catalyst has proved effective for one facial HAT, while a ZnI2-chelation protocol allows for the preferential reaction to the opposite face. Such a stereoselectivity switch enables diastereodivergent construction of heterocycles tethering a boron-substituted stereocenter. Mechanistic studies suggest two complementary ways to tune HAT diastereoselectivity. The stereospecific conversions of the resulting boron-handled products to diverse functionalized molecules are demonstrated.

7.
Sheng Li Xue Bao ; 73(6): 973-979, 2021 Dec 25.
Article in Chinese | MEDLINE | ID: mdl-34961872

ABSTRACT

Infra-slow oscillation (ISO) is a kind of brain rhythm between 0.01 and 0.5 Hz. ISO is widely distributed in multiple brain regions. As an important psychophysiological activity, the ISO interacts with high-frequency neural rhythm via cross-frequency coupling, but has different activity patterns from high-frequency neural activity. Physiologically, the ISO may be generated by the dynamic activity of thalamus, glia, and ions. Psychologically, the frequency, amplitude, and phase of ISO could all regulate cognitive activities, but in different ways. Investigations on the ISO expands the neural rhythm research to lower frequency range, further promoting the construction of rhythmic theory of brain function.


Subject(s)
Brain , Thalamus
8.
Sci Rep ; 11(1): 16945, 2021 08 20.
Article in English | MEDLINE | ID: mdl-34417513

ABSTRACT

The patterns of respiratory virus illness are expressed differently between temperate and tropical climates. Tropical outbreaks often peak in wet seasons. Temperate outbreaks typically peak during the winter. The prevailing causal hypotheses focus on sunlight, temperature and humidity variations. Yet no consistent factors have been identified to sufficiently explain seasonal virus emergence and decline at any latitude. Here we demonstrate close connections among global-scale atmospheric circulations, IgE antibody enhancement through seasonal pollen inhalation, and respiratory virus patterns at any populated latitude, with a focus on the US. Pollens emerge each Spring, and the renewed IgE titers in the population are argued to terminate each winter peak of respiratory illness. Globally circulated airborne viruses are postulated to subsequently deposit across the Southern US during lower zonal geostrophic winds each late Summer. This seasonally refreshed viral load is postulated to trigger a new influenza outbreak, once the existing IgE antibodies diminish to a critical value each Fall. Our study offers a new and consistent explanation for the seasonal diminishment of respiratory viral illnesses in temperate climates, the subdued seasonal signature in the tropics, the annually circulated virus phenotypes, and the northerly migration of influenza across the US every year. Our integrated geospatial and IgE hypothesis provides a new perspective for prediction, mitigation and prevention of the outbreak and spread of seasonal respiratory viruses including Covid-19 pandemic.


Subject(s)
COVID-19/epidemiology , Disease Outbreaks/statistics & numerical data , Influenza, Human/epidemiology , Respiratory Syncytial Virus Infections/epidemiology , Respiratory Tract Diseases/epidemiology , SARS-CoV-2/physiology , Antigens, Plant , Atmosphere , Humans , Immunoglobulin E/metabolism , Pandemics , Pollen , Seasons , United States/epidemiology
9.
Article in English | MEDLINE | ID: mdl-34007288

ABSTRACT

BACKGROUND: This study conducted exploratory research using artificial intelligence methods. The main purpose of this study is to establish an association model between metabolic syndrome and the TCM (traditional Chinese medicine) constitution using the characteristics of individual physical examination data and to provide guidance for medicated diet care. METHODS: Basic demographic and laboratory data were collected from a regional hospital health examination database in northern Taiwan, and artificial intelligence algorithms, such as logistic regression, Bayesian network, and decision tree, were used to analyze and construct the association model between metabolic syndrome and the TCM constitution. Findings. It was found that the phlegm-dampness constitution (90.6%) accounts for the majority of TCM constitution classifications with a high risk of metabolic syndrome, and high cholesterol, blood glucose, and waist circumference were statistically significantly correlated with the phlegm-dampness constitution. This study also found that the age of patients with metabolic syndrome has been advanced, and shift work is one of the risk indicators. Therefore, based on the association model between metabolic syndrome and TCM constitution, in the future, metabolic syndrome can be predicted through the syndrome differentiation of the TCM constitution, and relevant medicated diet care schemes can be recommended for improvement. CONCLUSION: In order to increase the public's knowledge and methods for mitigating metabolic syndrome, in the future, nursing staff can provide nonprescription medicated diet-related nursing guidance information via the prediction and assessment of the TCM constitution.

10.
ACS Nano ; 15(4): 6517-6529, 2021 04 27.
Article in English | MEDLINE | ID: mdl-33749240

ABSTRACT

The combination of photothermal therapy (PTT) and gene therapy (GT) shows great potential to achieve synergistic anti-tumor activity. However, the lack of a controlled release of genes from carriers remains a severe hindrance. Herein, peptide lipid (PL) and sucrose laurate (SL) were used to coat single-walled carbon nanotubes (SCNTs) and multi-walled carbon nanotubes (MCNTs) to form bifunctional delivery systems (denoted SCNT-PS and MCNT-PS, respectively) with excellent temperature-sensitivity and photothermal performance. CNT/siRNA suppressed tumor growth by silencing survivin expression while exhibiting photothermal effects under near-infrared (NIR) light. SCNT-PS/siRNA showed very high anti-tumor activity, resulting in the complete inhibition of some tumors. It was highly efficient for systemic delivery to tumor sites and to facilitate siRNA release owing to the phase transition of the temperature-sensitive lipids, due to PL and SL coating. Thus, SCNT-PS/siRNA is a promising anti-tumor nanocarrier for combined PTT and GT.


Subject(s)
Nanotubes, Carbon , Cell Line, Tumor , Genetic Therapy , Lipids , Phototherapy , Photothermal Therapy , Temperature
11.
Environ Sci Process Impacts ; 23(1): 28-47, 2021 Feb 04.
Article in English | MEDLINE | ID: mdl-33404564

ABSTRACT

The most massive waste stream generated by conventional and unconventional hydrocarbon exploration is the produced water (PW). The costs and environmental issues associated with the management and disposal of PW, which contains high concentrations of inorganic and organic pollutants, is one of the most challenging problems faced by the oil and gas industry. Many of the current strategies for the reuse and recycling of PW are inefficient because of varying water demand and the spatial and temporal variations in the chemical composition of PW. The chemical composition of PW is controlled by a multitude of factors and can vary significantly over time. This study aims to understand different parameters and processes that control the quality of PW generated from hydrocarbon-bearing formations by analyzing relationships between their major ion concentrations, O, H, and Sr isotopic composition. We selected PW data sets from three conventional (Trenton, Edwards, and Wilcox Formations) and four unconventional (Lance, Marcellus, Bakken, and Mesaverde Formations) oil and gas formations with varying lithology and depositional environment. Using comparative geochemical data analysis, we determined that the geochemical signature of PW is controlled by a complex interplay of several factors, including the original source of water (connate marine vs. non-marine), migration of the basinal fluids, the nature and degree of water-mineral-hydrocarbon interactions, water recharge, processes such as evaporation and ultrafiltration, and production techniques (conventional vs. unconventional). The development of efficient PW recycle and reuse strategies requires a holistic understanding of the geological and hydrological history of each formation to account for the temporal and spatial heterogeneities.


Subject(s)
Oil and Gas Fields , Water Pollutants, Chemical , Hydrocarbons , Minerals , Wastewater , Water Pollutants, Chemical/analysis
12.
Phytomedicine ; 77: 153272, 2020 Oct.
Article in English | MEDLINE | ID: mdl-32702592

ABSTRACT

BACKGROUND: Alstonia scholaris is a folk medicine used to treat cough, asthma and chronic obstructive pulmonary disease in China. Total alkaloids (TA) from A. scholaris exhibit anti-inflammatory properties in acute respiratory disease, which suggests their possible anti-inflammatory effect on influenza virus infection. PURPOSE: To assess the clinical use of TA by demonstrating their anti-influenza and anti-inflammatory effects and the possible mechanism underlying the effect of TA on influenza A virus (IAV) infection in vitro and to reveal the inhibitory effect of TA on lung immunopathology caused by IAV infection. METHODS: Antiviral and anti-inflammatory activities were assessed in Madin-Darby canine kidney (MDCK) and A549 cells and U937-derived macrophages infected with influenza A/PR/8/34 (H1N1) virus. Proinflammatory cytokine levels were measured by real-time quantitative PCR and Bio-Plex assays. The activation of innate immune signaling induced by H1N1 virus in the absence or presence of TA was detected in A549 cells by Western blot. Furthermore, mice were infected intranasally with H1N1 virus and treated with TA (50, 25 and 12.5 mg/kg/d) or oseltamivir (60 mg/kg/d) for 5 days in vivo. The survival rates and body weight were recorded, and the viral titer, proinflammatory cytokine levels, innate immune cell populations and histopathological changes in the lungs were analyzed. RESULTS: TA significantly inhibited viral replication in A549 cells and U937-derived macrophages and markedly reduced cytokine and chemokine production at the mRNA and protein levels. Furthermore, TA blocked the activation of pattern recognition receptor (PRR)- and IFN-activated signal transduction in A549 cells. Critically, TA also increased the survival rate, reduced the viral titer, suppressed proinflammatory cytokine production and innate immune cell infiltration and improved lung histopathology in a lethal PR8 mouse model. CONCLUSION: TA exhibits anti-viral and anti-inflammatory effects against IAV infection by interfering with PRR- and IFN-activated signal transduction.


Subject(s)
Alkaloids/pharmacology , Alstonia/chemistry , Antiviral Agents/pharmacology , Influenza A Virus, H1N1 Subtype/drug effects , Lung/drug effects , A549 Cells , Alkaloids/chemistry , Animals , Anti-Inflammatory Agents, Non-Steroidal/chemistry , Anti-Inflammatory Agents, Non-Steroidal/pharmacology , Antiviral Agents/chemistry , Cytokines/metabolism , Dogs , Female , Humans , Immunity, Innate/drug effects , Influenza A Virus, H1N1 Subtype/physiology , Influenza, Human/drug therapy , Lung/immunology , Lung/pathology , Lung/virology , Madin Darby Canine Kidney Cells , Mice, Inbred C57BL , Orthomyxoviridae Infections/drug therapy , Orthomyxoviridae Infections/immunology , Orthomyxoviridae Infections/pathology , Virus Replication/drug effects
13.
Schizophr Res ; 189: 175-180, 2017 11.
Article in English | MEDLINE | ID: mdl-28236519

ABSTRACT

Schizophrenia is a prototypical disorder of brain connectivity with altered neural activity in regions extending throughout the brain. Regions, including the subcortex and cortex, present activity mainly within a specific frequency band in resting-state. Whether these altered resting-state functional connections also present frequency specificity is unknown. In the present study, empirical mode decomposition, which is a pure data-driven method suitable for nonlinear and nonstationary signals, was used to decompose blood-oxygen-level-dependent (BOLD) signals into different intrinsic frequency bands. Our study included 42 first-episode drug-naive patients with schizophrenia and 38 controls. Significant aberration in functional connectivity was observed only at a higher frequency range (the peak spectral density power was 0.06Hz). In this frequency band, patients with schizophrenia showed significantly increased functional connections between the bilateral cuneus and right supplementary motor area, reduced connections within the basal ganglia, and reduced connections between the dorsal striatum and left supplementary motor area. The dysfunction of the frontal gyrus significantly correlated with the dysfunction of the basal ganglia. Notably, these altered connections were significantly correlated with symptom severity. Our results demonstrate that frequency-selective altered corticostriatal-thalamo-cortical circuits in patients with schizophrenia are associated with symptoms severity.


Subject(s)
Cerebral Cortex/diagnostic imaging , Corpus Striatum/diagnostic imaging , Neural Pathways/diagnostic imaging , Rest , Schizophrenia/diagnostic imaging , Thalamus/diagnostic imaging , Adult , Brain Mapping , Female , Humans , Image Processing, Computer-Assisted , Magnetic Resonance Imaging , Male , Neural Pathways/physiology , Oxygen/blood , Schizophrenia/pathology , Young Adult
14.
J Am Chem Soc ; 136(16): 6011-20, 2014 Apr 23.
Article in English | MEDLINE | ID: mdl-24730391

ABSTRACT

A method for synthesis of 3-azabicyclo[3.1.0]hex-2-enes has been developed by intramolecular cyclopropanation of readily available N-allyl enamine carboxylates. Two complementary reaction conditions, CuBr-mediated aerobic and CuBr2-catalyzed-PhIO2-mediated systems effectively induced stepwise cyclopropanation via carbocupration of alkenes. Oxidative cyclopropane ring-opening of 5-substituted 3-azabicyclo[3.1.0]hex-2-enes was also developed for synthesis of highly substituted pyridines. In addition, diastereoselective reduction of 3-azabicyclo[3.1.0]hex-2-enes to 3-azabicyclo[3.1.0]hexanes was achieved using NaBH3CN in the presence of acetic acid.


Subject(s)
Alkenes/chemistry , Carboxylic Acids/chemistry , Copper/chemistry , Heterocyclic Compounds/chemistry , Heterocyclic Compounds/chemical synthesis , Amines/chemistry , Catalysis , Chemistry Techniques, Synthetic , Oxidation-Reduction , Pyridines/chemistry , Stereoisomerism , Substrate Specificity
15.
J Am Chem Soc ; 133(35): 13942-5, 2011 Sep 07.
Article in English | MEDLINE | ID: mdl-21823614

ABSTRACT

Synthetic methods for 3-azabicyclo[3.1.0]hex-2-enes and 4-carbonylpyrroles have been developed that use copper-mediated/catalyzed reactions of N-allyl/propargyl enamine carboxylates under an O(2) atmosphere and involve intramolecular cyclopropanation and carbooxygenation, respectively. These methodologies take advantage of orthogonal modes of chemical reactivity of readily available N-allyl/propargyl enamine carboxylates; the complementary pathways can be accessed by slight modification of the reaction conditions.


Subject(s)
Bridged Bicyclo Compounds/chemistry , Carboxylic Acids/chemistry , Copper/chemistry , Pargyline/analogs & derivatives , Pargyline/chemistry , Pyrroles/chemical synthesis , Catalysis , Chemistry Techniques, Synthetic/methods , Oxygen/chemistry , Pyrroles/chemistry
16.
Endocrinology ; 152(6): 2311-20, 2011 Jun.
Article in English | MEDLINE | ID: mdl-21447634

ABSTRACT

The hypothalamic-pituitary-gonadal (HPG) axis exerts a profound effect on animal development, reproduction, and response to stress, and new insights into its complicated functional activities are continuously being made. In the present study, by using immunohistochemical studies and different mouse models (ovariectomy and ob/ob mice), we systemically analyzed the expression of a novel mitochondria-localized glutamic acid-rich protein (MGARP)/ovary-specific acid protein and demonstrated that MGARP is under the regulation of the HPG axis. MGARP is highly enriched in steroidogenic tissues and the visual system. Interestingly, its expression increases as mice develop. Early in development, MGARP is mainly detected in the retina and adrenal gland. At this early developmental stage, its expression is not detectable in the gonads, but its expression in the gonads dramatically increases during the first 2-4 wk after birth. Importantly, MGARP levels correlate with estrogen levels in the ovaries during the estrous cycle, and estrogen regulates the expression of MGARP in a tissue-specific manner and through a feedback regulatory mechanism. Functional inhibition of GnRH with an antagonist strongly reduces MGARP levels, and knockout of leptin (ob/ob) significantly reduces the MGARP expression in follicular granular cells. We proposed a model that elucidates the role MGARP plays in the HPG axis. Within the HPG axis loop, MGARP participates in hormone biosynthesis while being under the regulation of the hormones derived from the HPG axis.


Subject(s)
Gene Expression Regulation , Gonads/metabolism , Hypothalamus/metabolism , Membrane Proteins/genetics , Mice/metabolism , Pituitary Gland/metabolism , Animals , Eye Proteins , Female , Gene Expression Regulation, Developmental , Gonads/growth & development , Hormones/metabolism , Male , Membrane Proteins/metabolism , Mice/genetics , Mice/growth & development , Mice, Inbred ICR , Mitochondrial Proteins
17.
Environ Sci Technol ; 38(5): 1480-6, 2004 Mar 01.
Article in English | MEDLINE | ID: mdl-15046350

ABSTRACT

A durable titanate ceramic waste form (Synroc) with pyrochlore (Ca(U,Pu)Ti2O7) and zirconolite (CaZrTi2O7) as major crystalline phases has been considered to be a candidate for immobilizing various high-level wastes containing fissile elements (239Pu and 235U). Transmission electron microscopy study of a sintered ceramic with stoichiometry of Ca(U(0.5)Ce(0.25)Hf(0.25))Ti2O7 shows the material contains both pyrochlore and zirconolite phases and structural intergrowth of zirconolite lamellae within pyrochlore. The (001) plane of zirconolite is parallel to the (111) plane of pyrochlore because of their structural similarities. The pyrochlore is relatively rich in U, Ce, and Ca with respect to the coexisting zirconolite. Average compositions for the coexisting pyrochlore and zirconolite at 1350 degrees C are Ca(1.01)(Ce3+(0.13)Ce4+(0.19)U(0.52)Hf(0.18))(Ti(1.95)Hf(0.05))O7 (with U/(U + Hf) = 0.72) and (Ca(0.91)Ce(0.09))(Ce3+(0.08)U(0.26)Hf(0.66)Ti(0.01))Ti(2.00)O7 (with U/(U + Hf) = 0.28), respectively. A single pyrochlore (Ca(U,Hf)Ti2O7) phase may be synthesized at 1350 degrees C if the ratio of U/(U + Hf) is greater than 0.72, and a single zirconolite (Ca(Hf,U)Ti2O7) phase may be synthesized at 1350 degrees C if the ratio of U/(U + Hf) is less than 0.28. The synthesized products were used for dissolution tests. The single-pass flow-through dissolution tests show that the dissolution of the U-bearing pyrochlore is incongruent. All the elements are released at differing rates. The dissolution data also show a decrease in rate with run time. The results indicate that a diffusion-controlled process may play a key role during the release of U. TEM observation of the leached pyrochlore directly proves that an amorphous leached layer that is rich in Ti and Hf formed on the surface after the ceramic was leached in pH 4 buffered solution for 835 days. The thickness of the layer ranges from 6 to 10 nm. A nanocrystalline TiO2 phase also forms in the leached layer. The U leaching rate (g/(m2 day)) in acidic solutions can be expressed as log(NR) = -5.36-0.20 pH, where NR is the normalized rate. Conservative leaching rates of uranium [log(NR)] for the U-bearing ceramic at pH 2 and pH 4 solutions are -5.76 and -6.16 g/(m2 day), respectively. The results show that the U release rate of the ceramic waste is 10 times slower than that of defense high-level waste glass and about 1000 times slower than that of spent fuel. The pyrochlore-based ceramic is an ideal waste form for immobilizing long-lived radionuclides of 239Pu and 235U due to the Ti- and Hf-rich leached layer that forms on the ceramic surface. The leached layer functions as a protective layer and therefore reduces the leaching rate as thickness of the leached layer increases.


Subject(s)
Environmental Pollution/prevention & control , Niobium/chemistry , Radioactive Waste , Uranium/analysis , Ceramics , Coloring Agents/chemistry , Environmental Monitoring , Microscopy, Electron , Radioactive Pollutants , Titanium/chemistry
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