In DNA, thymine typically forms hydrogen bonds with adenine to hold two complementary strands together and to preserve the genetic code. While thymine is typically absent in RNA, a thymine–thymine ...hydrogen bonding structure is reminiscent of the wobble region in tRNA recognition, where noncanonical base pairing can occur. This noncanonical base pairing can be applied to synthetic polymer systems, where thymine is free to hydrogen bond with itself. In this work, the natural hydrogen bonding capacity of thymine was used to produce silicone polymer systems designed to be cross-linked by hydrogen bonds. Backbone and end-group-modified silicones were synthesized with differing concentrations of thymine, which facilitated the cross-linking of the polymeric strands. Removing the hydrogen on N3which is typically involved in hydrogen bondingresulted in systems with similar viscosities to the starting material and that were devoid of any apparent cross-links. Differential scanning calorimetry (DSC) studies of the thymine-modified polymers displayed thermal absorptions and releases, indicative of bond breaking and reformation, around 100 and 60 °C, respectively. The cycle of bond breaking and formation could be repeated without any noticeable degradation of the chemical structure of the polymers. These polymeric materials could be readily recycled and remolded by heating them at 110 °C for 5 min, followed by cooling to room temperature, confirming their thermoplastic nature.
Abstract
Tessellation of self-assembling molecular building blocks is a promising strategy to design metal-organic materials exhibiting geometrical frustration and ensuing frustrated physical ...properties. Appearing in two-dimensional quasiperiodic phases, tilings consisting of five-vertex nodes are regarded as approximants for quasicrystals. Unfortunately, these structural motifs are exceedingly rare due to the complications of acquiring five-fold coordination confined to the plane. Lanthanide ions display the sufficient coordinative plasticity, and large ionic radii, to allow their incorporation into irregular molecule-based arrays. We herein present the use of ytterbium(II) as a five-vertex node in a two-dimensional coordination solid, YbI
2
(4,4′-bipyridine)
2.5
. The semi-regular Archimedean tessellation structure verges on quasicrystallinity and paves the way for lanthanide-based metal-organic materials with interesting photonic and magnetic properties.
The unique properties of graphene, transition-metal dichalcogenides and other two-dimensional (2D) materials have boosted interest in layered coordination solids. In particular, 2D materials that ...behave as both conductors and magnets could find applications in quantum magnetoelectronics and spintronics. Here, we report the synthesis of CrCl2(pyrazine)2, an air-stable layered solid, by reaction of CrCl2 with pyrazine (pyz). This compound displays a ferrimagnetic order below ∼55 K, reflecting the presence of strong magnetic interactions. Electrical conductivity measurements demonstrate that CrCl2(pyz)2 reaches a conductivity of 32 mS cm–1 at room temperature, which operates through a 2D hopping-based transport mechanism. These properties are induced by the redox-activity of the pyrazine ligand, which leads to a smearing of the Cr 3d and pyrazine π states. We suggest that the combination of redox-active ligands and reducing paramagnetic metal ions represents a general approach towards tuneable 2D materials that consist of charge-neutral layers and exhibit both long-range magnetic order and high electronic conductivity.
The COVID-19 pandemic has exerted great pressure on national health systems, which have aimed to ensure comprehensive healthcare at all times. Healthcare professionals working with COVID-19 patients ...are on the frontline and thereby confronted with enormous demands. Although early reports exist on the psychological impact of the pandemic on frontline medical staff working in Asia, little is known about its impact on healthcare professionals in other countries and across various work sectors. The present cross-sectional, online survey sought to investigate common work stressors among healthcare professionals, their psychological stress as well as coping resources during the pandemic.
A sample of 575 healthcare professionals (57% male) in three different sectors (hospital, prehospital emergency care, and outpatient service) reported their experiences concerning work and private stressors, psychological stress, and coping strategies between April 17, 2020 and June 5, 2020. To capture pandemic-specific answers, most of the items were adapted or newly developed. Exploratory factor analyses (EFA) were conducted to detect underlying latent factors relating to COVID-specific work stressors. In a next step, the effects of these latent stressors across various work sectors on psychological stress (perceived stress, fatigue, and mood) were examined by means of structural equation models (SEM). To add lived experience to the findings, responses to open-ended questions about healthcare professionals' stressors, effective crisis measures and prevention, and individual coping strategies were coded inductively, and emergent themes were identified.
The EFA revealed that the examined work stressors can be grouped into four latent factors: "fear of transmission", "interference of workload with private life", "uncertainty/lack of knowledge", and "concerns about the team". The SEM results showed that "interference of workload with private life" represented the pivotal predictor of psychological stress. "Concerns about the team" had stress-reducing effects. The latent stressors had an equal effect on psychological stress across work sectors. On average, psychological stress levels were moderate, yet differed significantly between sectors (all p < .001); the outpatient group experienced reduced calmness and more stress than the other two sectors, while the prehospital group reported lower fatigue than the other two sectors. The prehospital group reported significantly higher concerns about the team than the hospital group (p < .001). In their reports, healthcare professionals highlighted regulations such as social distancing and the use of compulsory masks, training, experience and knowledge exchange, and social support as effective coping strategies during the pandemic. The hospital group mainly mentioned organizational measures such as visiting bans as effective crisis measures, whereas the prehospital sector most frequently named governmental measures such as contact restrictions.
The study demonstrated the need for sector-specific crisis measures to effectively address the specific work stressors faced by the outpatient sector in particular. The results on pandemic-specific work stressors reveal that healthcare professionals might benefit from coping strategies that facilitate the utilization of social support. At the workplace, team commitment and knowledge exchange might buffer against adverse psychological stress responses. Schedules during pandemics should give healthcare workers the opportunity to interact with families and friends in ways that facilitate social support outside work. Future studies should investigate cross-sector stressors using a longitudinal design to identify both sector- and time-specific measures. Ultimately, an international comparison of stressors and measures in different sectors of healthcare systems is desirable.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
General interest in the deployment of molten salt reactors (MSRs) is growing, while the available data on uranium-containing fuel salt candidates remains scarce. Thermophysical data are one of the ...key parameters for reactor design and understanding reactor operability. Hence, filling in the gap of the missing data is crucial to allow for the advancement of MSRs. This study provides novel data for two eutectic compositions within the NaF-KF-UFsub.4 ternary system which serve as potential fuel candidates for MSRs. Experimental measurements include their melting point, density, fusion enthalpy, and vapor pressure. Additionally, their boiling point was extrapolated from the vapor pressure data, which were, at the same time, used to determine the enthalpy of vaporization. The obtained thermodynamic values were compared with available data from the literature but also with results from thermochemical equilibrium calculations using the JRCMSD database, finding a good correlation, which thus contributed to database validation. Preliminary thoughts on fluoride salt reactor operability based on the obtained results are discussed in this study.
Abstract
Electronic synergy between metal ions and organic linkers is a key to engineering molecule-based materials with a high electrical conductivity and, ultimately, metallicity. To enhance ...conductivity in metal-organic solids, chemists aim to bring the electrochemical potentials of the constituent metal ions and bridging organic ligands closer in a quest to obtain metal-
d
and ligand-
π
admixed frontier bands. Herein, we demonstrate the critical role of the metal ion in tuning the electronic ground state of such materials. While VCl
2
(pyrazine)
2
is an electrical insulator, TiCl
2
(pyrazine)
2
displays the highest room-temperature electronic conductivity (5.3 S cm
–1
) for any metal-organic solid involving octahedrally coordinated metal ions. Notably, TiCl
2
(pyrazine)
2
exhibits Pauli paramagnetism consistent with the specific heat, supporting the existence of a Fermi liquid state (i.e., a correlated metal). This result widens perspectives for designing molecule-based systems with strong metal-ligand covalency and electronic correlations.
Spermatogonial stem cells (SSCs) provide the basis for lifelong male fertility through self-renewal and differentiation. Prepubertal male cancer patients may be rendered infertile by gonadotoxic ...chemotherapy and, unlike sexually mature men, cannot store sperm. Alternatively, testicular biopsies taken prior to treatment may be used to restore fertility in adulthood. Testicular SSC populations are limited, and in vitro culture systems are required to increase numbers of SSCs for treatment, demanding culture systems for SSC propagation. Using the pig as a non-rodent model, we developed culture systems to expand spermatogonia from immature testis tissue, comparing different feeders (Sertoli cells, peritubular myoid cells (PMCs) and pig fetal fibroblasts (PFFs)). Spermatogonia co-cultured with Sertoli cells, PMCs and PFFs had comparable rates of proliferation and apoptosis. To elucidate the mechanism behind the beneficial nature of feeder layers, we investigated the role of extracellular vesicles in crosstalk between spermatogonia and feeder cells. Sertoli cell-released exosomes are incorporated by spermatogonia, and inhibition of exosomal release reduces spermatogonial proliferation. Together, these results show that PMCs, PFFs and Sertoli cells promote spermatogonial proliferation in co-culture, with exosomal exchange representing one possible mechanism. Further characterization of exosomal cargo may ultimately allow the development of feeder-free culture systems for clinical use.
Successful sports performance often requires choosing what to do and how to do it in dynamic, complex, and uncertain environments. Thus, an understanding of the processes underpinning judgment and ...decision making in sports (JDMS) is crucial for both researchers and applied practitioners. Despite the research developments, examining JDMS from several perspectives, there are still significant gaps in the knowledge of the processes involved. In this article we explore how the theoretical understanding of JDMS can be extended by acknowledging that cognition and action dynamics are intertwined, deploy in parallel, and influence each other bidirectionally. We present a holistic approach that integrates simple heuristics and embodied cognition to explain JDMS. Importantly, our aim is not to devalue previous JDMS theories but rather to exemplify how embodied choices can redirect the current interpretation of judgment and decision-making processes in sports. Taking this embodied choice perspective, we reinterpret the findings of four prototypical research papers on JDMS, each representing one of the most influential perspectives in JDMS (i.e., the economic, social cognition, cognitive, and ecological dynamics approaches). Last, we discuss future directions for JDMS research from an embodied choice perspective.
The spermatogonial stem cell (SSC) is a unique adult stem cell that requires tight physiological regulation during development and adulthood. As the foundation of spermatogenesis, SSCs are a ...potential tool for the treatment of infertility. Understanding the factors that are necessary for lifelong maintenance of a SSC pool in vivo is essential for successful in vitro expansion and safe downstream clinical usage. This review focused on the current knowledge of prepubertal testicular development and germ cell metabolism in different species, and implications for translational medicine. The significance of metabolism for cell biology, stem cell integrity, and fate decisions is discussed in general and in the context of SSC in vivo maintenance, differentiation, and in vitro expansion.
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