Breaking space-time symmetries in two-dimensional crystals can markedly influence their macroscopic electronic properties. Monolayer transition metal dichalcogenides (TMDs) are prime examples where ...the intrinsically broken crystal inversion symmetry permits the generation of valley-selective electron populations, even though the two valleys are energetically degenerate, locked by time-reversal symmetry. Lifting the valley degeneracy in these materials is of great interest because it would allow for valley-specific band engineering and offer additional control in valleytronic applications. Although applying a magnetic field should, in principle, accomplish this task, experiments so far have not shown valley-selective energy level shifts in fields accessible in the laboratory. Here, we show the first direct evidence of lifted valley degeneracy in the monolayer TMD WS2. By applying intense circularly polarized light, which breaks time-reversal symmetry, we demonstrate that the exciton level in each valley can be selectively tuned by as much as 18 meV through the optical Stark effect. These results offer a new way to control the valley degree of freedom, and may provide a means to realize new Floquet topological phases in two-dimensional TMDs.
Polyrotaxanes and the pump paradigm Seale, James S. W; Feng, Yuanning; Feng, Liang ...
Chemical Society reviews,
10/2022, Letnik:
51, Številka:
2
Journal Article
Recenzirano
The year 2022 marks the 30th anniversary of the first reports of polyrotaxanes in the scientific literature. During the past three decades, many combinations of molecular rings and polymer chains ...have been synthesised and characterised. Until recently, however, the permutations of polyrotaxanes available to researchers were limited by synthetic methods which typically relied on an innate affinity between the molecular rings and polymer chains. With the advent of oligorotaxane-forming molecular pumps in 2015, it has now become possible to pump multiple rings against their will onto oligomer and polymer chains which have little or no affinity for the rings. These molecular pumps, which can recruit rings actively from solution to form precise polyrotaxanes, represent a major breakthrough in the field. This Tutorial Review highlights key milestones in the synthesis and investigation of polyrotaxanes along with recent developments in the synthesis and theory relating to molecular pumps. Polyrotaxane properties, arising from their topologies, have allowed them to steal a march on traditional polymers in a wide range of applications in materials, electronic and biological science, from slide-ring gels to robust coatings on cell phones, from molecular wires to flexible binders for battery anodes, from efficient multivalent protein binders to bio-cleavable polyplexes for cellular DNA delivery. Molecular pumps have the potential to blaze a contemporary trail for the synthesis of precise mechanically interlocked materials, especially those dependent on non-equilibrium chemistry and those related to energy storage and nanomedicine.
The year 2022 marks the 30th anniversary of the first reports of polyrotaxanes in the scientific literature.
Active mechanisorption driven by pumping cassettes Feng, Liang; Qiu, Yunyan; Guo, Qing-Hui ...
Science (American Association for the Advancement of Science),
2021-Dec-03, 2021-12-03, 20211203, Letnik:
374, Številka:
6572
Journal Article
Recenzirano
Over the past century, adsorption has been investigated extensively in equilibrium systems, with a focus on the van der Waals interactions associated with physisorption and electronic interactions in ...the case of chemisorption. In this study, we demonstrate mechanisorption, which results from nonequilibrium pumping to form mechanical bonds between the adsorbent and the adsorbate. This active mode of adsorption has been realized on surfaces of metal-organic frameworks grafted with arrays of molecular pumps. Adsorbates are transported from one well-defined compartment, the bulk, to another well-defined compartment, the interface, thereby creating large potential gradients in the form of chemical capacitors wherein energy is stored in metastable states. Mechanisorption extends, in a fundamental manner, the scope and potential of adsorption phenomena and offers a transformative approach to control chemistry at surfaces and interfaces.
Methylene blue (MB), the first lead chemical structure of phenothiazine and other derivatives, is commonly used in diagnostic procedures and as a treatment for methemoglobinemia. We have previously ...demonstrated that MB could function as an alternative mitochondrial electron transfer carrier, enhance cellular oxygen consumption, and provide protection in vitro and in rodent models of Parkinson's disease and stroke. In the present study, we investigated the structure-activity relationships of MB in vitro using MB and six structurally related compounds. MB reduces mitochondrial superoxide production via alternative electron transfer that bypasses mitochondrial complexes I-III. MB mitigates reactive free radical production and provides neuroprotection in HT-22 cells against glutamate, IAA and rotenone toxicity. Distinctly, MB provides no protection against direct oxidative stress induced by glucose oxidase. Substitution of a side chain at MB's 10-nitrogen rendered a 1000-fold reduction of the protective potency against glutamate neurototoxicity. Compounds without side chains at positions 3 and 7, chlorophenothiazine and phenothiazine, have distinct redox potentials compared to MB and are incapable of enhancing mitochondrial electron transfer, while obtaining direct antioxidant actions against glutamate, IAA, and rotenone insults. Chlorophenothiazine exhibited direct antioxidant actions in mitochondria lysate assay compared to MB, which required reduction by NADH and mitochondria. MB increased complex IV expression and activity, while 2-chlorphenothiazine had no effect. Our study indicated that MB could attenuate superoxide production by functioning as an alternative mitochondrial electron transfer carrier and as a regenerable anti-oxidant in mitochondria.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Linear ubiquitination is a newly discovered posttranslational modification that is currently restricted to a small number of known protein substrates. The linear ubiquitination assembly complex ...(LUBAC), consisting of HOIL-1L, HOIP, and Sharpin, has been reported to activate NF-κB-mediated transcription in response to receptor signaling by ligating linear ubiquitin chains to Nemo and Rip1. Despite recent advances, the detailed roles of LUBAC in immune cells remain elusive. We demonstrate a novel HOIL-1L function as an essential regulator of the activation of the NLRP3/ASC inflammasome in primary bone marrow-derived macrophages (BMDMs) independently of NF-κB activation. Mechanistically, HOIL-1L is required for assembly of the NLRP3/ASC inflammasome and the linear ubiquitination of ASC, which we identify as a novel LUBAC substrate. Consequently, we find that HOIL-1L(-/-) mice have reduced IL-1β secretion in response to in vivo NLRP3 stimulation and survive lethal challenge with LPS. Together, these data demonstrate that linear ubiquitination is required for NLRP3 inflammasome activation, defining the molecular events of NLRP3 inflammasome activation and expanding the role of LUBAC as an innate immune regulator. Furthermore, our observation is clinically relevant because patients lacking HOIL-1L expression suffer from pyogenic bacterial immunodeficiency, providing a potential new therapeutic target for enhancing inflammation in immunodeficient patients.
This study aimed to develop a quantitative PCR assay to simultaneously quantify human and dog DNA in a multispecies mixture to inform downstream analyses in routine forensic casework and scientific ...research. The human target is the
Yb8 element, which has approximately 2000 copies per cell, and the canine target is the SINEC_Cf element, which has approximately 200,000 copies per cell. The internal positive control is a universal exogenous assay consisting of forward and reverse primers, a NED-labeled probe with an MGBNFQ quencher and a 65-bp synthetic template. Results suggest a potentially robust assay with a fast run time and a high degree of sensitivity, precision and species specificity, with direct application to domestic pet samples in veterinary genetics and forensics.
The authors developed a fast, sensitive and precise TaqMan™ probe-based quantitative PCR assay targeting species-specific short interspersed nuclear elements for simultaneous absolute quantification of human and dog DNA via a standard curve for use in forensic investigation. An assessment of the assay's performance was conducted using single-source samples, mixtures and various domestic pet samples.
Inhibitory extracellular matrices form around mature neurons as perineuronal nets containing chondroitin sulfate proteoglycans that limit axonal sprouting after CNS injury. The enzyme chondroitinase ...(Chase) degrades inhibitory chondroitin sulfate proteoglycans and improves axonal sprouting and functional recovery after spinal cord injury in rodents. We evaluated the effects of Chase in rhesus monkeys that had undergone C7 spinal cord hemisection. Four weeks after hemisection, we administered multiple intraparenchymal Chase injections below the lesion, targeting spinal cord circuits that control hand function. Hand function improved significantly in Chase-treated monkeys relative to vehicle-injected controls. Moreover, Chase significantly increased corticospinal axon growth and the number of synapses formed by corticospinal terminals in gray matter caudal to the lesion. No detrimental effects were detected. This approach appears to merit clinical translation in spinal cord injury.
Abstract
Copper (Cu) is an important micronutrient for marine organisms, which can also be toxic at elevated concentrations. Here, we present a new model of global ocean Cu biogeochemical cycling, ...constrained by GEOTRACES observations, with key processes including sources from rivers, dust, and sediments, biological uptake and remineralization of Cu, reversible scavenging of Cu onto sinking particles, conversion of Cu between labile and inert species, and ocean circulation. In order for the model to match observations, in particular the relatively small increase in Cu concentrations along the global “conveyor belt,” we find it is necessary to include significant external sources of Cu with a magnitude of roughly 1.3 Gmol yr
−1
, having a relatively stronger impact on the Atlantic Ocean, though the relative contributions of river, dust, and sediment sources are poorly constrained. The observed nearly linear increase in Cu concentrations with depth requires a strong benthic source of Cu, which includes the sedimentary release of Cu that was reversibly scavenged from the water column. The processes controlling Cu cycling in the Arctic Ocean appear to be unique, requiring both relatively high Cu concentrations in Arctic rivers and reduced scavenging in the Arctic. Observed partitioning of Cu between labile and inert phases is reproduced in the model by the slow conversion of labile Cu to inert in the whole water column with a half‐life of ∼250 years, and the photodegradation of inert Cu to labile in the surface ocean with a minimum half‐life of ∼2 years at the equator.
Plain Language Summary
Living organisms in the ocean need a small amount of copper (Cu) as a nutrient. Therefore, it is important to investigate the abundance of Cu in different regions of the ocean and the processes that influence the marine Cu cycle. We have developed a 3‐dimensional model to study the distribution of Cu constrained by ocean Cu observations while simulating the processes that bring Cu into the ocean and redistribute Cu within the ocean interior. We find that Cu distributions are largely controlled by ocean circulation and the external Cu sources into each ocean basin. Cu concentrations increase gradually from the surface to the deep ocean, and based on the model outputs, we interpret this feature as a combination of Cu‐particle interactions and Cu inputs from the seafloor. Cu cycling in the Arctic Ocean appears to be very different from other parts of the ocean, with large amounts of Cu in Arctic rivers and weak particle adsorption in the Arctic. These model results have important implications for understanding why Cu distributions in the ocean are different from other metals, and how Cu interacts with marine organisms, organic matter, and particles.
Key Points
Large Cu inputs to the Atlantic Ocean lead to a small Atlantic‐Pacific concentration gradient along the conveyor belt
Labile Cu is actively involved in ocean biogeochemical processes, while inert Cu builds up as water masses age
Arctic Ocean Cu is impacted by large riverine inputs, and possibly weaker scavenging in the water column
Significance One of the hallmarks of Alzheimer’s disease (AD) is cerebral amyloid angiopathy (CAA), which is a strong and independent risk factor for cerebral hemorrhage, ischemic stroke, and ...dementia. However, the mechanisms by which CAA contributes to these conditions are poorly understood. Results from the present study provide strong evidence that vascular oxidative stress plays a causal role in CAA-induced cerebrovascular dysfunction, CAA-induced cerebral hemorrhage, and CAA formation, itself. They also suggest that NADPH oxidase is the source of this oxidative stress and that strategies to inhibit NADPH oxidase may have therapeutic potential in patients with AD and CAA.
Cerebral amyloid angiopathy (CAA) is characterized by deposition of amyloid β peptide (Aβ) within walls of cerebral arteries and is an important cause of intracerebral hemorrhage, ischemic stroke, and cognitive dysfunction in elderly patients with and without Alzheimer’s Disease (AD). NADPH oxidase-derived oxidative stress plays a key role in soluble Aβ-induced vessel dysfunction, but the mechanisms by which insoluble Aβ in the form of CAA causes cerebrovascular (CV) dysfunction are not clear. Here, we demonstrate evidence that reactive oxygen species (ROS) and, in particular, NADPH oxidase-derived ROS are a key mediator of CAA-induced CV deficits. First, the NADPH oxidase inhibitor, apocynin, and the nonspecific ROS scavenger, tempol, are shown to reduce oxidative stress and improve CV reactivity in aged Tg2576 mice. Second, the observed improvement in CV function is attributed both to a reduction in CAA formation and a decrease in CAA-induced vasomotor impairment. Third, anti-ROS therapy attenuates CAA-related microhemorrhage. A potential mechanism by which ROS contribute to CAA pathogenesis is also identified because apocynin substantially reduces expression levels of ApoE—a factor known to promote CAA formation. In total, these data indicate that ROS are a key contributor to CAA formation, CAA-induced vessel dysfunction, and CAA-related microhemorrhage. Thus, ROS and, in particular, NADPH oxidase-derived ROS are a promising therapeutic target for patients with CAA and AD.
Cryptococcus curvatus, an oleaginous yeast was observed to grow on crude glycerol derived from yellow grease. When cultured in a one-stage fed-batch process wherein crude glycerol and nitrogen source ...were fed intermittently for 12
days, the final biomass density and lipid content were 31.2
g/l and 44.2%, respectively. When cultured in a two-stage fed-batch operation wherein crude glycerol was supplemented at different time points while nitrogen source addition was discontinued at the middle of the experiment, the biomass density was 32.9
g/l and the lipid content was 52% at the end of 12
days. Compared with other oil feedstocks for biodiesel production, lipid accumulated by
C. curvatus grown on glycerol has high concentration of monounsaturated fatty acid, which makes it an excellent source for biodiesel use.
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