Progress on Single-Atom Photocatalysts for H2 Generation: Material Design, Catalytic Mechanism, and Perspectives.

Solar energy utilization is of great significance to current challenges of the energy crisis and environmental pollution, which benefit the development of the global community to achieve carbon neutrality goals. Hydrogen energy is also treated as a good candidate for future energy supply since its combustion not only supplies high-density energy but also shows no pollution gas. In particular, photocatalytic water splitting has attracted increasing research as a promising method for H2 production. Recently, single-atom (SA) photocatalysts have been proposed as a potential solution to improve catalytic efficiency and lower the costs of photocatalytic water splitting for H2 generation. Owing to the maximized atom utilization rate, abundant surface active sites, and tunable coordination environment, SA photocatalysts have achieved significant progress. This review reviews developments of advanced SA photocatalysts for H2 generation regarding the different support materials. The recent progress of titanium dioxide, metal-organic frameworks, two-dimensional carbon materials, and red phosphorus supported SA photocatalysts are carefully discussed. In particular, the material designs, reaction mechanisms, modulation strategies, and perspectives are highlighted for realizing improved solar-to-energy efficiency and H2 generation rate. This work will supply significant references for future design and synthesis of advanced SA photocatalysts.

Transition metal anchored on red phosphorus to enable efficient photocatalytic H2 generation.

Transition metal (TM) single atom catalysts (SACs) are of great potential for photocatalytic H2 production because of their abundant catalytic active sites and cost-effectiveness. As a promising support material, red phosphorus (RP) based SACs are still rarely investigated. In this work, we have carried out systematic theoretical investigations by anchoring TM atoms (Fe, Co, Ni, Cu) on RP for efficient photocatalytic H2 generation. Our density functional theory (DFT) calculations have revealed that 3d orbitals of TM locate close to the Fermi level to guarantee efficient electron transfer for photocatalytic performances. Compared with pristine RP, the introduction of single atom TM on the surface exhibit narrowed bandgaps, resulting in easier spatial separation for photon-generated charge carriers and an extended photocatalytic absorption window to the NIR range. Meanwhile, the H2O adsorptions are also highly preferred on the TM single atoms with strong electron exchange, which benefits the subsequent water-dissociation process. Due to the optimized electronic structure, the activation energy barrier of water-splitting has been remarkably reduced in RP-based SACs, revealing their promising potential for high-efficiency H2 production. Our comprehensive explorations and screening of novel RP-based SACs will offer a good reference for further designing novel photocatalysts for high-efficiency H2 generation.

Synthesis and Preclinical Evaluation of 2-(4-[18F]Fluorophenyl)imidazo[1,2-h][1,7]naphthyridine ([18F]FPND-4): An Aza-Fused Tricyclic Derivative as Positron Emission Tomography Tracer for Neurofibrillary Tangle Imaging.

Tau accumulation is one of the predominant neuropathological biomarkers for in vivo diagnosis of Alzheimer's disease due to its high correlation with disease progression. In this study, we focused on the structure-activity relationship study of the substituent effect on the aza-fused tricyclic core imidazo[1,2-h][1,7]naphthyridine to screen 18F-labeled Tau tracers. Through a series of autoradiographic studies and biological evaluations, 4-[18F]fluorophenyl-substituted tracer [18F]13 ([18F]FPND-4) was identified as a promising candidate with high affinity to native Tau tangles (IC50 = 2.80 nM), few appreciable binding to Aß plaques and MAO-A/B. Validated by dynamic positron emission tomography (PET) imaging in rodents and rhesus monkey, [18F]13 displayed desirable brain uptake (SUV = 1.75 at 2 min), fast clearance (brain2min/60min = 5.9), minimal defluorination, and few off-target binding, which met the requirements of a Tau-specific PET radiotracer.

Fluorine-18-Labeled Diaryl-azines as Improved ß-Amyloid Imaging Tracers: From Bench to First-in-Human Studies.

The deposition of ß-amyloid (Aß) in the brain is a pathologic hallmark of Alzheimer's disease (AD), appearing years before the onset of symptoms, and its detection is incorporated into clinical diagnosis. Here, we have discovered and developed a class of diaryl-azine derivatives for detecting Aß plaques in the AD brain using PET imaging. After a set of comprehensive preclinical assessments, we screened out a promising Aß-PET tracer, [18F]92, with a high binding affinity to the Aß aggregates, significant binding ability with the AD brain sections, and optimal brain pharmacokinetic properties in rodents and non-human primates. The first-in-human PET study declared that [18F]92 displayed low white matter uptake and could bind to Aß pathology for distinguishing AD from healthy control subjects. All these results support that [18F]92 might become a promising PET tracer for visualizing Aß pathology in AD patients.

Probing the affinity of noble metal nanoparticles to the segments of the SARS-CoV-2 spike protein.

Currently, scientists have devoted great efforts to finding effective treatments to combat COVID-19 infections. Although noble metal nanoparticles are able to realize protein modifications, their interactions with the protein are still unclear from the atomic perspective. To supply a general understanding, in this work, we have carried out theoretical calculations to investigate the interaction between protein segments (RBD1, RBD2, RBD3) of SARS-Cov-2 spike protein and a series of noble metal (Au, Ag, Cu, Pd, Pt) surfaces regarding the binding strength, protein orientations, and electronic modulations. In particular, the Au surface has shown the strongest binding preferences for the protein segments, which induces electron transfer between the Au and receptor-binding domain (RBD) segments. This further leads to the polarization of segments for virus denaturation. This work has offered a direct visualization of protein interactions with noble metal surfaces from the atomic level, which will benefit anti-virus material developments in the future.

Fused Cycloheptatriene-BODIPY Is a High-Performance Near-Infrared Probe to Image Tau Tangles.

Neurofibrillary tangles (NFTs), which are composed of abnormally hyperphosphorylated Tau, are one of the main pathologic hallmarks of Alzheimer's disease and other tauopathies. The fluorescent imaging probes currently used to target NFTs cannot distinguish them well from ß-amyloid plaques, thus limiting their utility to diagnose diseases. Here, we developed a fused cycloheptatriene-BODIPY derivative (TNIR7-1A) that displays properties favorable for near-infrared (NIR) imaging with high affinity and specificity to NFTs in vitro. In addition, TNIR7-1A effectively penetrated the blood-brain barrier and clearly distinguished tauopathy in transgenic mice (rTg4510) from control mice using NIR fluorescence imaging in vivo. The sensitivity and specificity of TNIR7-1A for NFTs were confirmed ex vivo by fluorescence staining of the tauopathy mouse model, while molecular docking studies indicated that TNIR7-1A bound to NFTs through hydrophobic interactions. These results suggest that TNIR7-1A can act as a high-performance probe to detect NFTs in vitro and in vivo selectively.

All-inorganic perovskite nanocrystals: next-generation scintillation materials for high-resolution X-ray imaging.

With super strong penetrability, high-energy X-rays can be applied to probe the inner structure of target objects under nondestructive situations. Scintillation materials can down-convert X-rays into visible light, enabling the reception of photon signals and photoelectric conversion by common sensing arrays such as photomultiplier tubes and amorphous-Si photodiode matrixes. All-inorganic perovskite nanocrystals are emerging photovoltaic and scintillation materials, with tremendous light-conversion efficiency and tunable luminous properties, exhibiting great potential for high-quality X-ray imaging. Recent advancements in nanotechnology further accelerate the performance improvement of scintillation materials. In this review, we will provide a comprehensive overview of novel all-inorganic perovskite nano-scintillators in terms of potential applications in low-dose X-ray medical radiography. Compared with conventional scintillators, the merits/drawbacks, challenges, and scintillation performance control will be the focus of this article.

Proteomic characteristics of plasma and blood cells in natural aging rhesus monkeys.

Aging has become a serious social issue that places a heavy burden on society. However, the underlying mechanisms of aging remain unclear. This study sought to understand the aging process as it may be affected by proteins in the blood, the most important functional system for material transportation in the body. We analyzed and compared the protein expression spectrums in the blood of old and young rhesus monkeys and found 257 proteins expressed differentially in plasma and 1183 proteins expressed differentially in blood cells. Through bioinformatics analysis, we found that the differentially-expressed proteins in plasma were involved in signal pathways related to complement and coagulation cascades, pertussis, malaria, phagosome, and cholesterol metabolism, while the differentially-expressed proteins in blood cells were involved in endocytosis, proteasome, ribosome, protein processing in the endoplasmic reticulum, and Parkinson's disease. We confirmed that the protein levels of complement C2 in plasma and actin-related protein 2/3 complex subunit 2 (ARPC2) in blood cells obviously decreased, whereas the complement C3 and complement component 4 binding protein beta (C4BPB) significantly increased in plasma of old rhesus monkeys and C57BL/6 mice. Our results suggest that C2, C3, C4BPB, and ARPC2 can be used as target proteins for anti-aging research.

Detection of plasma Aß seeding activity by a newly developed analyzer for diagnosis of Alzheimer's disease.

OBJECTIVE: To evaluate the diagnostic value of plasma ß-amyloid (Aß) seeding activity measured using a newly developed instrument to distinguish Alzheimer's disease (AD) from other forms of dementia. METHODS: Seventy-nine AD patients, 64 non-AD dementia (NADD) patients, and 75 cognitively normal (NC) subjects were recruited in the study. To measure the levels of Aß seeding activity in the plasma samples, we have developed an AD-seeds protein analyzer. We used receiver operating characteristic (ROC) curves to quantify the ability of plasma Aß seeding activity to distinguish between AD and NADD or NC individuals. Spearman's correlation was used to examine the associations between plasma Aß seeding activity and global cognitive function or conventional AD biomarkers. RESULTS: The Aß seeding activities were 0.83 (0.58-1.16) A.U. in AD, 0.42 (0.04-0.74) A.U. in NADD and 0.42 (0.09-0.69) A.U. in NC, respectively. The Aß seeding activity was able to identify AD patients and distinguish them from NC or NADD with high accuracy (AUC = 0.85-0.86). In addition, the plasma Aß seeding activity showed a strong correlation with cognitive performance (mini-mental state examination, r = - 0.188; Montreal cognitive assessment, r = - 0.189; clinical dementia rating, r = 0.205) and conventional biomarkers (cerebrospinal fluid [CSF] Aß42/40, r = -0.227; CSF T-tau/Aß42, r = 0.239; CSF P-tau/Aß42, r = 0.259). CONCLUSION: Our results confirmed that plasma Aß seeding activity is an antibody-free and low-cost biomarker for the diagnosis of AD. TRIAL REGISTRATION: Trial registration number NCT04850053.

Evaluation of N, O-Benzamide difluoroboron derivatives as near-infrared fluorescent probes to detect ß-amyloid and tau tangles.

ß-Amyloid (Aß) plaques and Tau tangles are cognitive impairment markers vital for diagnosing and preventing Alzheimer's disease (AD). To systematically explore the relationship between the number or position of nitrogen atoms and their optical properties and biological properties, five series of new N, O-coordinated organo-difluoroboron probes were introduced as binding scaffolds for Aß plaques and Tau tangles. These probes exhibited suitable optical properties for near-infrared (NIR) imaging. Probe 4PmNO-2 (4-((1E,3E)-4-(1,1-difluoro-1H-1λ4,9λ4-pyrimido[1,6-c][1,3,5,2]oxadiazaborinin-3-yl)buta-1,3-dien-1-yl)-N,N-dimethylaniline) displayed the excellent emission maximum (716 nm in PBS), a high quantum yield (61.4% in CH2Cl2), and a high affinity for synthetic Aß1-42 (Kd = 23.64 ± 1.08 nM) and Tau (K18) aggregates (Kd = 26.38 ± 1.29 nM), as well as for native Aß plaques and NFTs in the brain tissue from AD patients. 4PmNO-2, with significantly enhanced fluorescence (Aß1-42, 136 fold; Tau (K18), 96 fold) and the highest initial brain uptake (11.57% ID/g at 2 min) in normal ICR mice, was evaluated further. In vivo NIR fluorescent imaging studies in living Aß and Tau transgenic mice revealed that it could differentiate healthy and diseased animals. Further ex vivo fluorescent staining studies showed that 4PmNO-2 specifically bound to Aß plaques and Tau tangles in transgenic mice. In summary, the probe 4PmNO-2 may be a useful near-infrared fluorescence (NIRF) probe for AD biomarkers.

Quasi-Type II Core-Shell Perovskite Nanocrystals for Improved Structural Stability and Optical Gain.

In recent years, core-shell lead halide perovskite nanocrystals (PeNCs) and their devices have attracted intensive attention owing to nearly perfect optoelectronic properties. However, the complex photophysical mechanism among them is still unclear. Herein, monodispersed core-shell PeNCs coated with an all-inorganic cesium lead bromide (CsPbBr3) shell epitaxially grown on the surface of formamidinium lead bromide (FAPbBr3) PeNCs were synthesized. Through power- and temperature-dependent photoluminescence (PL) measurements, it is found that the electronic structure of the core-shell FAPbBr3/CsPbBr3 PeNCs has a quasi-type II band alignment. The presence of Cs+ in the shell limits ion migration and helps to stabilize structural and optical properties. On this basis, after being exposed to pulsed nanosecond laser for a period, an amplified spontaneous emission (ASE) can be observed, which is attributed to the effective passivation induced by laser irradiation on defects at the interface. The ASE threshold of the core-shell PeNCs showing high structural and optical stability is 447 nJ/cm2 under pulsed nanosecond optical pumping. The results that are demonstrated here provide a new idea and perspective for improving the stability of perovskite and can be of practical interest for the utilization of the core-shell PeNCs in optoelectronic devices.

Neuronal loss and microgliosis are restricted to the core of Aß deposits in mouse models of Alzheimer's disease.

Amyloid-ß (Aß) deposits, pathologic tau, and neurodegeneration are major pathological hallmarks of Alzheimer's disease (AD). The relationship between neuronal loss and Aß deposits is one of the fundamental questions in the pathogenesis of AD. However, this relationship is controversial. One main reason for the conflicting results may be the confounding effects of pathologic tau, which often coexists with Aß deposits in the brains of AD patients. To clarify the relationship between neuronal loss and Aß deposits, mouse models of AD, which develop abundant Aß deposits in the aged brain without pathologic tau, were used to examine the co-localization of NeuN-positive neurons, NF-H-positive axons, MBP-positive myelin sheaths, and Aß deposits. Neuronal loss, as measured by decreased staining of the neuronal cell body, axon, and myelin sheath, as well as the IBA-1-positive microglia, was significantly increased in the core area of cerebral Aß deposits, but not in adjacent areas. Furthermore, neuronal loss in the core area of cerebral Aß deposits was correlated with Aß deposit size. These results clearly indicate that neuronal loss is restricted to the core of Aß deposits, and this restricted loss probably occurs because the Aß deposit attracts microglia, which cluster in the core area where Aß toxicity and neuroinflammation toxicity are restrained. These findings may contribute to our understanding of the relationship between neuronal loss and Aß deposits in the absence of pathologic tau.

Brains of rhesus monkeys display Aß deposits and glial pathology while lacking Aß dimers and other Alzheimer's pathologies.

Cerebral amyloid beta (Aß) deposits are the main early pathology of Alzheimer's disease (AD). However, abundant Aß deposits also occur spontaneously in the brains of many healthy people who are free of AD with advancing aging. A crucial unanswered question in AD prevention is why AD does not develop in some elderly people, despite the presence of Aß deposits. The answer may lie in the composition of Aß oligomer isoforms in the Aß deposits of healthy brains, which are different from AD brains. However, which Aß oligomer triggers the transformation from aging to AD pathogenesis is still under debate. Some researchers insist that the Aß 12-mer causes AD pathology, while others suggest that the Aß dimer is the crucial molecule in AD pathology. Aged rhesus monkeys spontaneously develop Aß deposits in the brain with striking similarities to those of aged humans. Thus, rhesus monkeys are an ideal natural model to study the composition of Aß oligomer isoforms and their downstream effects on AD pathology. In this study, we found that Aß deposits in aged monkey brains included 3-mer, 5-mer, 9-mer, 10-mer, and 12-mer oligomers, but not 2-mer oligomers. The Aß deposits, which were devoid of Aß dimers, induced glial pathology (microgliosis, abnormal microglia morphology, and astrocytosis), but not the subsequent downstream pathologies of AD, including Tau pathology, neurodegeneration, and synapse loss. Our results indicate that the Aß dimer plays an important role in AD pathogenesis. Thus, targeting the Aß dimer is a promising strategy for preventing AD.

Generating viable mice with heritable embryonically lethal mutations using the CRISPR-Cas9 system in two-cell embryos.

A substantial number of mouse genes, about 25%, are embryonically lethal when knocked out. Using current genetic tools, such as the CRISPR-Cas9 system, it is difficult-or even impossible-to produce viable mice with heritable embryonically lethal mutations. Here, we establish a one-step method for microinjection of CRISPR reagents into one blastomere of two-cell embryos to generate viable chimeric founder mice with a heritable embryonically lethal mutation, of either Virma or Dpm1. By examining founder mice, we identify a phenotype and role of Virma in regulating kidney metabolism in adult mice. Additionally, we generate knockout mice with a heritable postnatally lethal mutation, of either Slc17a5 or Ctla-4, and study its function in vivo. This one-step method provides a convenient system that rapidly generates knockout mice possessing lethal phenotypes. This allows relatively easy in vivo study of the associated genes' functions.

Oligoethyleneoxy-Modified 99mTc-Labeled ß-Amyloid Imaging Probes with Improved Brain Pharmacokinetics for Single-Photon Emission Computed Tomography.

An oligoethyleneoxy linker was introduced for conjugation between 99mTc/Re-bis(aminoethanethiol) (BAT) and ß-amyloid (Aß) binding scaffolds. Rhenium complexes exhibited high to moderate binding affinity to Aß1-42 aggregates and efficient fluorescent staining to Aß plaques in brain tissue. After radiolabeling, the 99mTc-labeled probes revealed improved brain pharmacokinetics in normal ICR mice. Probe [99mTc]15 with potent binding affinity (Ki = 13.4 nM) and the highest initial brain uptake (2.10% ID/g at 2 min) in normal ICR mice was evaluated further. In vitro autoradiography showed specific labeling of Aß plaques by [99mTc]15 in transgenic (Tg) mouse brain tissue. Ex vivo autoradiography further demonstrated its efficient labeling of Aß plaques in a living Tg mouse. In vivo single photon emission computed tomography (SPECT)/CT imaging in six rhesus monkeys revealed remarkably improved brain uptakes (1.94-2.63% ID within 20 min) of [99mTc]15, making it highly potential to be used in humans for Aß plaques imaging in the brain.

Amyloid-ß Derived from the Brain of the Alzheimer's Disease Transgenic Mouse Is Resistant to Proteolytic Digestion Due to Its Conformation.

The main pathological feature of Alzheimer's disease (AD) is the formation of abundant amyloid-ß (Aß) plaques in the human brain. Studies have reported that Aß from the AD brain is resistant to proteolytic digestion, which may explain why Aß cannot be readily eliminated from this organ. However, there are only a few studies that address this important question. We used the AD transgenic mouse (APP/PS1) model to show that Aß derived from the brain of the old mouse is resistant to proteolytic digestion. This was in contrast to the proteinase K-sensitive human Aß peptide, whose amino acid sequence was identical to that of AD mouse-derived Aß but whose conformation was different (i.e., the native protein, but not the peptide, folded into a three-dimensional conformation). To address this question, we denatured AD mouse-derived Aß with urea and found that Aß became proteinase K-sensitive. This phenomenon was concentration-dependent, and these results were confirmed by another protein denaturant, guanidinium hydrochloride. We recovered the conformation of the denatured AD mouse-derived Aß by eliminating urea and adding the human Aß peptide, and we found that human Aß was converted to the proteinase K-resistant form in the presence of partially undenatured AD mouse-derived Aß. However, upon the addition of the rat Aß peptide, there were no Aß proteinase K-resistant fragments. Our results show that the resistance of AD mouse-derived Aß to proteolytic digestion is dependent on the three-dimensional conformation of Aß. In summary, this study provides new insights on why Aß plaques fail to be degraded in the human brain.

Upregulation of Aß42 in the Brain and Bodily Fluids of Rhesus Monkeys with Aging.

The cerebral accumulation of amyloid beta (Aß) is one of the key pathological hallmarks of Alzheimer's disease (AD). Aß is also found in bodily fluids such as the cerebrospinal fluid (CSF) and plasma. However, the significance of Aß accumulation in the brain and different bodily pools, as well as its correlation with aging and cerebral amyloid pathology, is not completely understood. To better understand this question, we selected the rhesus monkey, which is phylogenetically and physiologically highly similar to the human, as a model to study. We quantified the levels of the two main Aß isoforms (Aß42 and Aß40) in different sections of the brain (frontal cortex, temporal cortex, and hippocampus) and bodily fluids (CSF and plasma) of rhesus monkeys at different developmental phases (young, 5-9 years of age; mature, 10-19 years of age; and old, 21-24 years of age). We found that the levels of neuronal and insoluble Aß42 increased significantly in the brain with aging, suggesting that this specific isoform might be directly involved in aging and AD-like pathophysiology. There was no significant change in the Aß40 level in the brain with aging. In addition, the Aß42 level, but not the Aß40 level, in both the CSF and plasma increased with aging. We also identified a positive correlation between Aß42 in the CSF and plasma and Aß42 in the brain. Taken collectively, our results indicate that there is an association between Aß accumulation and age. These results support the increased incidence of AD with aging.

99mTc-Labeled 2-Arylbenzothiazoles: Aß Imaging Probes with Favorable Brain Pharmacokinetics for Single-Photon Emission Computed Tomography.

A series of 2-arylbenzothiazole derivatives conjugated with bis(aminoethanethiol) (BAT) chelating groups were designed and synthesized. A competitive binding assay-based screening was used to select seven rhenium complexes with potent binding affinity toward Aß1-42 aggregates (Ki < 50 nM) for 99mTc labeling and further evaluation. The 99mTc-labeled probes showed good affinity and specificity to Aß plaques in Tg mouse brain tissue in in vitro autoradiography studies. Moreover, [99mTc]14b exhibited favorable brain pharmacokinetics in normal mice (2.11% ID/g at 2 min and 0.62% ID/g at 60 min). Ex vivo autoradiography revealed extensive labeling of Aß plaques by [99mTc]14b in the brain of Tg mice. Furthermore, we performed the first single-photon emission computed tomography (SPECT) imaging study in nonhuman primates with 99mTc-labeled Aß probes. The semiquantitative data showed that [99mTc]14b penetrated the brains of rhesus monkeys. These results indicate that [99mTc]14b could be utilized as a SPECT imaging probe for Aß plaques.

Chronic restraint stress reduces carbon tetrachloride-induced liver fibrosis.

Stress as a cofactor has been reported to affect the progression and severity of liver diseases. The present study investigated the effect of chronic restraint stress on carbon tetrachloride (CCl4)-induced liver fibrosis. A total of 30 male BALB/c mice were randomly divided into three groups: Oil-treated control group; CCl4-treated group; and CCl4 + restraint-treated group. CCl4 was administrated via intraperitoneal injection once every 3 days over a period of 42 days. In the CCl4 + restraint-treated group, mice were immobilized using 50 ml centrifuge tubes for 0.5 h to inflict chronic restraint stress immediately after the injection of CCl4. On day 42, blood and liver tissue samples were collected for analysis. The effect of restraint on CCl4-induced liver fibrosis in mice was evaluated by analyzing the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Histopathological examination of liver samples was performed using hematoxylin and eosin (HE), Masson's trichrome, 5-hydroxytryptamine 2B (5-HT2B) receptor and α-smooth muscle actin (α-SMA) immumohistochemical staining. ALT, AST, 5-HT2B receptor and α-SMA expression levels were significantly increased in mice exposed to CCl4 in comparison with those in the oil-treated control mice (P<0.01). However, these increases were significantly reduced by exposure to restraint (P<0.05). HE and Masson's trichrome staining revealed that restraint can alleviate CCl4-induced liver fibrosis. These results suggest that chronic restraint stress reduces the development of liver fibrosis by inhibiting the activation of hepatic stellate cells via 5-HT2B receptor. Therefore, restraint may be a useful therapeutic approach in the management of liver fibrosis.