Now showing items 21-40 of 51880

    • Defect Engineering in Metal-Organic Frameworks Towards Advanced Mixed Matrix Membranes for Efficient Propylene/Propane Separation

      Lee, Tae Hoon; Jung, Jae Gu; Kim, Yu Jin; Roh, Ji Soo; Yoon, Hee Wook; Ghanem, Bader; Kim, Hyo Won; Cho, Young Hoon; Pinnau, Ingo; Park, Ho Bum (Angewandte Chemie, Wiley, 2021-03-02) [Article]
      Highly permselective and durable membrane materials have been sought for energy-efficient C3H6/C3H8 separation. Mixed-matrix membranes (MMMs) comprising a polymer matrix and metal-organic frameworks (MOFs) are promising candidates for this application; however, rational matching of filler-matrix is challenging and their separation performances need to be further improved. Here, we propose a novel strategy of “defect engineering” in MOFs as an additional degree of freedom to design advanced MMMs. MMMs incorporated with defect-engineered MOFs exhibit exceptionally high C3H6 permeability and maintained C3H6/C3H8 selectivity, especially with enhanced stability under industrial mixed-gas conditions. The gas transport, sorption, and material characterizations reveal that the defect sites in MOFs provide the resulting MMMs with not only ultrafast diffusion pathways but also favorable C3H6 sorption by forming π-complexation with unsaturated open metal sites, confirmed by in-situ FT-IR studies. Most importantly, the concept is also valid for different polymer matrices and gas pairs, demonstrating its versatile potential in other fields.
    • Dark Self-Healing-Mediated Negative Photoconductivity of a Lead-Free Cs3Bi2Cl9 Perovskite Single Crystal.

      Tailor, Naveen Kumar; Maity, Partha; Saidaminov, Makhsud I.; Pradhan, Narayan; Satapathi, Soumitra (The journal of physical chemistry letters, arXiv, 2021-03-01) [Article]
      Recently, halide perovskites have emerged as a promising material for device applications. Lead-based perovskites have been widely explored, while investigation of the optical properties of lead-free perovskites remains limited. Lead-halide perovskite single crystals have shown light-induced positive photoconductivity, and as lead-free perovskites are optically active, they are expected to demonstrate similar properties. However, we report here light-induced negative photoconductivity with slow recovery in lead-free Cs3Bi2Cl9 perovskite. Femtosecond transient reflectance (fs-TR) spectroscopy studies further reveal that these electronic transport properties are due to the formation of light-activated metastable trap states within the perovskite crystal. The figure of merits were calculated for Cs3Bi2Cl9 single-crystal detectors, including responsivity (17 mA/W), detectivity (6.23 × 1011 Jones), and the ratio of current in dark to light (∼7160). These observations for Cs3Bi2Cl9 single crystals, which were optically active but showed retroactive photocurrent on irradiation, remain unique for such materials.
    • Bioprospecting of Novel Extremozymes From Prokaryotes-The Advent of Culture-Independent Methods.

      Sysoev, Maksim; Grötzinger, Stefan W.; Renn, Dominik; Eppinger, Jörg; Rueping, Magnus; Karan, Ram (Frontiers in microbiology, Frontiers Media SA, 2021-03-01) [Article]
      Extremophiles are remarkable organisms that thrive in the harshest environments on Earth, such as hydrothermal vents, hypersaline lakes and pools, alkaline soda lakes, deserts, cold oceans, and volcanic areas. These organisms have developed several strategies to overcome environmental stress and nutrient limitations. Thus, they are among the best model organisms to study adaptive mechanisms that lead to stress tolerance. Genetic and structural information derived from extremophiles and extremozymes can be used for bioengineering other nontolerant enzymes. Furthermore, extremophiles can be a valuable resource for novel biotechnological and biomedical products due to their biosynthetic properties. However, understanding life under extreme conditions is challenging due to the difficulties of in vitro cultivation and observation since > 99% of organisms cannot be cultivated. Consequently, only a minor percentage of the potential extremophiles on Earth have been discovered and characterized. Herein, we present a review of culture-independent methods, sequence-based metagenomics (SBM), and single amplified genomes (SAGs) for studying enzymes from extremophiles, with a focus on prokaryotic (archaea and bacteria) microorganisms. Additionally, we provide a comprehensive list of extremozymes discovered via metagenomics and SAGs.
    • Parallel Hierarchical Matrix Technique to Approximate Large Covariance Matrices, Likelihood Functions and Parameter Identi fication

      Litvinenko, Alexander; Berikov, V.; Genton, Marc G.; Keyes, David E.; Kriemann, R.; Sun, Ying (2021-03-01) [Presentation]
      We develop the HLIBCov package, which is using parallel hierarchical (H-) matrices to: 1) Approximate large dense inhomogeneous covariance matrices with a log-linear computational cost and storage requirement. 2) Compute matrix-vector product, Cholesky factorization and inverse with a log-linear complexity. 3) Identify unknown parameters of the covariance function (variance, smoothness, and covariance length). These unknown parameters are estimated by maximizing the joint Gaussian log-likelihood function. To demonstrate the numerical performance, we identify three unknown parameters in an example with 2,000,000 locations on a PC-desktop.
    • Fine-scale metabolic discontinuity in a stratified prokaryote microbiome of a Red Sea deep halocline

      Michoud, Gregoire; Ngugi, David; Barozzi, Alan; Merlino, Giuseppe; Calleja Cortes, Maria de Lluch; Delgado-Huertas, Antonio; Moran, Xose Anxelu G.; Daffonchio, Daniele (The ISME Journal, Springer Science and Business Media LLC, 2021-03-01) [Article]
      AbstractDeep-sea hypersaline anoxic basins are polyextreme environments in the ocean’s interior characterized by the high density of brines that prevents mixing with the overlaying seawater, generating sharp chemoclines and redoxclines up to tens of meters thick that host a high concentration of microbial communities. Yet, a fundamental understanding of how such pycnoclines shape microbial life and the associated biogeochemical processes at a fine scale, remains elusive. Here, we applied high-precision sampling of the brine–seawater transition interface in the Suakin Deep, located at 2770 m in the central Red Sea, to reveal previously undocumented fine-scale community structuring and succession of metabolic groups along a salinity gradient only 1 m thick. Metagenomic profiling at a 10-cm-scale resolution highlighted spatial organization of key metabolic pathways and corresponding microbial functional units, emphasizing the prominent role and significance of salinity and oxygen in shaping their ecology. Nitrogen cycling processes are especially affected by the redoxcline with ammonia oxidation processes being taxa and layers specific, highlighting also the presence of novel microorganisms, such as novel Thaumarchaeota and anammox, adapted to the changing conditions of the chemocline. The findings render the transition zone as a critical niche for nitrogen cycling, with complementary metabolic networks, in turn underscoring the biogeochemical complexity of deep-sea brines.
    • Dissipation and dilatation rates in premixed turbulent flames

      Sabelnikov, V. A.; Lipatnikov, A. N.; Nishiki, S.; Dave, H. L.; Hernández Pérez, F. E.; Song, W.; Im, Hong G. (Physics of Fluids, AIP Publishing, 2021-03-01) [Article]
      Velocity dilatation and total, solenoidal, and dilatational dissipation rates of the total flow kinetic energy are extracted from three different direct numerical simulation databases obtained by three independent research groups using different numerical codes and methods (e.g., single-step chemistry and complex chemistry flames) from six different premixed turbulent flames associated with flamelet, thin reaction zone, and broken reaction zone regimes of turbulent burning. The results show that dilatational dissipation can be larger than solenoidal dissipation in the flamelet regime and is substantial in the thin reaction zone regime. Accordingly, the influence of combustion-induced thermal expansion on the dissipation rate is not reduced to an increase in the mixture viscosity by the temperature. A simple criterion for identifying conditions associated with significant dilatational dissipation is discussed, and dilatational dissipation due to the influence of turbulence on mixing in preheat zones is argued to play a role even at high Karlovitz numbers Ka. In particular, the magnitude of dilatation fluctuations and probability of finding negative local dilatation are increased by Ka, thus implying that the impact of molecular transport of species and heat on the dilatation increases with increasing Karlovitz number.
    • Energy Efficiency and Sustainability Assessment for Methane Harvesting from Lake Kivu

      Favero Bolson, Natanael; Yutkin, Maxim; Patzek, Tadeusz (Energy, Elsevier BV, 2021-03) [Article]
      Lake Kivu is a great environmental and economic resource in Rwanda. Its deep-water methane reservoir can help the country to narrow its energy supply gap. However, mishandling of the lake could lead to devastating consequences, from potable water contamination to limnic eruption. To evaluate the lake’s potential for energy harvesting, we have developed a numerical model and validated it experimentally. Based on this model, we propose an optimal methane harvesting strategy. The harvesting efficiency improvement is from 4 to 6% relative to the alternatives. While seemingly insignificant, a 1% improvement of harvesting efficiency extends the operational time of a gas power plant by 5%. With these improvements, the lake will sustainably supply 100 MW of electricity for up to 100 years. Potential CO2 emissions are negligible in comparison with the low-emitting developed countries. We conclude that forestry and agroforestry can mitigate CO2 emissions and reduce currently widespread deforestation. The degassed water after methane extraction poses another environmental concern. It must be reinjected at the depth of 190 – 250 m to minimize the environmental impacts on the lake and allow for continuous methane harvesting.
    • On some singular mean-field games

      Cirant, Marco; Gomes, Diogo A.; Pimentel, Edgard A.; Sánchez-Morgado, Héctor (Journal of Dynamics & Games, American Institute of Mathematical Sciences (AIMS), 2021-03) [Article]
      Here, we prove the existence of smooth solutions for mean-field games with a singular mean-field coupling; that is, a coupling in the Hamilton-Jacobi equation of the form g(m)=−m−α with α>0. We consider stationary and time-dependent settings. The function g is monotone, but it is not bounded from below. With the exception of the logarithmic coupling, this is the first time that MFGs whose coupling is not bounded from below is examined in the literature. This coupling arises in models where agents have a strong preference for low-density regions. Paradoxically, this causes the agents move towards low-density regions and, thus, prevents the creation of those regions. To prove the existence of solutions, we consider an approximate problem for which the existence of smooth solutions is known. Then, we prove new a priori bounds for the solutions that show that 1m is bounded. Finally, using a limiting argument, we obtain the existence of solutions. The proof in the stationary case relies on a blow-up argument and in the time-dependent case on new bounds for m−1.
    • Seaweed farms provide refugia from ocean acidification.

      Xiao, Xi; Agusti, Susana; Yu, Yan; Huang, Yuzhou; Chen, Weizhou; Hu, Jing; Li, Chao; Li, Ke; Wei, Fangyi; Lu, Yitian; Xu, Caicai; Chen, Zepan; Liu, Shengping; Zeng, Jiangning; Wu, Jiaping; Duarte, Carlos M. (The Science of the total environment, Elsevier BV, 2021-02-28) [Article]
      Seaweed farming has been proposed as a strategy for adaptation to ocean acidification, but evidence is largely lacking. Changes of pH and carbon system parameters in surface waters of three seaweed farms along a latitudinal range in China were compared, on the weeks preceding harvesting, with those of the surrounding seawaters. Results confirmed that seaweed farming is efficient in buffering acidification, with Saccharina japonica showing the highest capacity of 0.10 pH increase within the aquaculture area, followed by Gracilariopsis lemaneiformis (ΔpH = 0.04) and Porphyra haitanensis (ΔpH = 0.03). The ranges of pH variability within seaweed farms spanned 0.14-0.30 unit during the monitoring, showing intense fluctuations which may also help marine organisms adapt to enhanced pH temporal variations in the future ocean. Deficit in pCO2 in waters in seaweed farms relative to control waters averaged 58.7 ± 15.9 μatm, ranging from 27.3 to 113.9 μatm across farms. However, ΔpH did not significantly differ between day and night. Dissolved oxygen and Ωarag were also elevated in surface waters at all seaweed farms, which are benefit for the survival of calcifying organisms. Seaweed farming, which unlike natural seaweed forests, is scalable and is not dependent on suitable substrate or light availability, could serve as a low-cost adaptation strategy to ocean acidification and deoxygenation and provide important refugia from ocean acidification.
    • Controlling wave fronts with tunable disordered non-Hermitian multilayers.

      Novitsky, Denis V; Lyakhov, Dmitry; Michels, Dominik L.; Redka, Dmitrii; Pavlov, Alexander A; Shalin, Alexander S (Scientific reports, Springer Science and Business Media LLC, 2021-02-27) [Article]
      Unique and flexible properties of non-Hermitian photonic systems attract ever-increasing attention via delivering a whole bunch of novel optical effects and allowing for efficient tuning light-matter interactions on nano- and microscales. Together with an increasing demand for the fast and spatially compact methods of light governing, this peculiar approach paves a broad avenue to novel optical applications. Here, unifying the approaches of disordered metamaterials and non-Hermitian photonics, we propose a conceptually new and simple architecture driven by disordered loss-gain multilayers and, therefore, providing a powerful tool to control both the passage time and the wave-front shape of incident light with different switching times. For the first time we show the possibility to switch on and off kink formation by changing the level of disorder in the case of adiabatically raising wave fronts. At the same time, we deliver flexible tuning of the output intensity by using the nonlinear effect of loss and gain saturation. Since the disorder strength in our system can be conveniently controlled with the power of the external pump, our approach can be considered as a basis for different active photonic devices.
    • Metadata standards and practical guidelines for specimen and DNA curation when building barcode reference libraries for aquatic life

      Rimet, Frédéric; Aylagas, Eva; Borja, Ángel; Bouchez, Agnès; Canino, Alexis; Chauvin, Christian; Chonova, Teofana; Ciampor Jr, Fedor; Costa, Filipe O.; Ferrari, Benoit J. D.; Gastineau, Romain; Goulon, Chloé; Gugger, Muriel; Holzmann, Maria; Jahn, Regine; Kahlert, Maria; Kusber, Wolf-Henning; Laplace-Treyture, Christophe; Leese, Florian; Leliaert, Frederik; Mann, David G.; Marchand, Frédéric; Méléder, Vona; Pawlowski, Jan; Rasconi, Serena; Rivera, Sinziana; Rougerie, Rodolphe; Schweizer, Magali; Trobajo, Rosa; Vasselon, Valentin; Vivien, Régis; Weigand, Alexander; Witkowski, Andrzej; Zimmermann, Jonas; Ekrem, Torbjørn (Metabarcoding and Metagenomics, Pensoft Publishers, 2021-02-26) [Article]
      DNA barcoding and metabarcoding is increasingly used to effectively and precisely assess and monitor biodiversity in aquatic ecosystems. As these methods rely on data availability and quality of barcode reference libraries, it is important to develop and follow best practices to ensure optimal quality and traceability of the metadata associated with the reference barcodes used for identification. Sufficient metadata, as well as vouchers, corresponding to each reference barcode must be available to ensure reliable barcode library curation and, thereby, provide trustworthy baselines for downstream molecular species identification. This document (1) specifies the data and metadata required to ensure the relevance, the accessibility and traceability of DNA barcodes and (2) specifies the recommendations for DNA harvesting and for the storage of both voucher specimens/samples and barcode data.
    • Theoretical Insights into the Limitation of Photocatalytic Overall Water Splitting Performance of VIA Group Elements Doped Polymeric Carbon Nitride: A DFT Calculation Predicting Solar-to-Hydrogen Efficiency

      Wang, Yiqing; Zhao, Daming; Deng, Hao; Li, Mingtao; Chen, Jie; Shen, Shaohua (Solar RRL, Wiley, 2021-02-26) [Article]
      Polymeric carbon nitride (p-C3N4) is thermodynamically feasible for photocatalytic overall water splitting. Element doping has been proved effective in enhancing the photocatalytic performance of p-C3N4. The effect of doping is usually interpreted from the angle of electronic structures by first-principles density functional theory (DFT) calculations. However, the information on electronic structures is insufficient for understanding and predicting the ultimate criterion of solar-to-hydrogen (STH) efficiency. Herein, we provided a DFT calculation method to investigate and predict the STH of VIA group elements doped p-C3N4 by calculating the efficiencies of both light absorption and carrier utilization. Particularly, significant efforts were made to calculating the energy barriers for surface hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) to determine the carrier utilization efficiency. Moreover, the chemisorption energies of the reactant intermediates were calculated to quantify the intermediates affinity for HER and OER on the surface. Among the VIA elements, oxygen was discovered as the most effective dopant in promoting the STH because that oxygen-doped p-C3N4 has the lowest energy barriers for OER and the largest chemisorption energy for intermediates absorption. The calculation results highlight the importance of the surface reaction properties for efficient photocatalytic overall water splitting.
    • All-Solution-Processed Quantum Dot Electrical Double-Layer Transistors Enhanced by Surface Charges of Ti3C2Tx MXene Contacts

      Kim, Hyunho; Nugraha, Mohamad Insan; Guan, Xinwei; Wang,Zhenwei; Hota, Mrinal Kanti; Xu, Xiangming; Wu, Tao; Baran, Derya; Anthopoulos, Thomas D.; Alshareef, Husam N. (ACS Nano, American Chemical Society (ACS), 2021-02-26) [Article]
      Fully solution-processed, large-area, electrical double-layer transistors (EDLTs) are presented by employing lead sulfide (PbS) colloidal quantum dots (CQDs) as active channels and Ti3C2Tx MXene as electrical contacts (including gate, source, and drain). The MXene contacts are successfully patterned by standard photolithography and plasma-etch techniques and integrated with CQD films. The large surface area of CQD film channels is effectively gated by ionic gel, resulting in high performance EDLT devices. A large electron saturation mobility of 3.32 cm2 V-1 s-1 and current modulation of 1.87 × 104 operating at low driving gate voltage range of 1.25 V with negligible hysteresis are achieved. The relatively low work function of Ti3C2Tx MXene (4.42 eV) compared to vacuum-evaporated noble metals such as Au and Pt makes them a suitable contact material for n-type transport in iodide-capped PbS CQD films with a LUMO level of ∼4.14 eV. Moreover, we demonstrate that the negative surface charges of MXene enhance the accumulation of cations at lower gate bias, achieving a threshold voltage as low as 0.36 V. The current results suggest a promising potential of MXene electrical contacts by exploiting their negative surface charges.
    • Surrogate formulation and molecular characterization of sulfur species in vacuum residues using APPI and ESI FT-ICR mass spectrometry

      Abdul Jameel, Abdul Gani; Alquaity, Awad B.S.; Campuzano, Felipe; Emwas, Abdul-Hamid M.; Saxena, Saumitra; Sarathy, Mani; Roberts, William L. (Fuel, Elsevier BV, 2021-02-26) [Article]
      Vacuum residues (VR) are the bottom of the barrel products left after vacuum distillation of crude oils. VR are primarily used as feedstock for production of syn-gas and hydrogen via gasification; and heavy fuel oil (HFO) for use as fuel in power generation and shipping. However, VR contain relatively large amounts of sulfur (upto 8% by mass) and require the removal of varying amounts depending on the emission norms (eg. International Maritime Organization 2020 sulfur regulations). Understanding the fuel molecular structure and, in particular, the structure of sulfur species enables the adoption and optimization of suitable desulfurization strategies. In the present work, detailed molecular characterization of the sulfur species in VR was performed using positive ion atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS). Ions possessing mass to charge (m/z) in the range of 100 to 1200 were detected using the ultra-high resolution instrument and were resolved into unique chemical formulas (CcHhSsNnOo). The assigned masses were then divided into molecular classes based on the presence of heteroatoms, and plots of carbon number versus double bond equivalency (DBE) were made for each molecular class. The molecular classes were further sub-divided based on the presence of sulfur families like sulfides (Su), thiophenes (Th), benzothiophenes (BT), dibenzothiophenes (DBT) and benzonaphthothiophene (BNT) and their derivatives. A single surrogate molecule that represents the average structure of the VR sample was then designed based on the average molecular parameters (AMP) obtained from APPI and ESI FT-ICR MS. Plausible core skeletal structures of VR were drawn from the average DBE value, and then a symmetrical, alkylated, polyaromatic sulfur heterocycles (PASH) molecule was formulated as the VR surrogate. A number of physical and thermo-chemical properties of the VR surrogate were then predicted using quantitative structure property relationships (QSPR). The VR surrogate proposed here will enable high-fidelity computational studies, including chemical kinetic modeling, property estimation, and emissions modeling.
    • Vector Autoregressive Models with Spatially Structured Coefficients for Time Series on a Spatial Grid

      Yan, Yuan; Huang, Hsin-Cheng; Genton, Marc G. (Journal of Agricultural, Biological and Environmental Statistics, Springer Science and Business Media LLC, 2021-02-26) [Article]
      Motivated by the need to analyze readily available data collected in space and time, especially in environmental sciences, we propose a parsimonious spatiotemporal model for time series data on a spatial grid. In essence, our model is a vector autoregressive model that utilizes the spatial structure to achieve parsimony of autoregressive matrices at two levels. The first level ensures the sparsity of the autoregressive matrices using a lagged-neighborhood scheme. The second level performs a spatial clustering of the nonzero autoregressive coefficients such that within some subregions, nearby locations share the same autoregressive coefficients while across different subregions the coefficients may have distinct values. The model parameters are estimated using the penalized maximum likelihood with an adaptive fused Lasso penalty. The estimation procedure can be tailored to accommodate the need and prior knowledge of a modeler. Performance of the proposed estimation algorithm is examined in a simulation study. Our method gives reliable estimation results that are interpretable and especially useful to identify geographical subregions, within each of which, the time series have similar dynamical behavior with homogeneous autoregressive coefficients. We apply our model to a wind speed time series dataset generated from a climate model over Saudi Arabia to illustrate its power in explaining the dynamics by the spatially structured coefficients. Moreover, the estimated model can be useful for building stochastic weather generators as an approximation of the computationally expensive climate model.
    • The Importance of Thermal Treatment on Wet-Kneaded Silica–Magnesia Catalyst and Lebedev Ethanol-to-Butadiene Process

      Chung, Sang-Ho; Galilea, Adrian; Shoinkhorova, Tuiana; Mukhambetov, Ildar; Abou-Hamad, Edy; Telalovic, Selevedin; Gascon, Jorge; Ruiz-Martinez, Javier (Nanomaterials, MDPI AG, 2021-02-26) [Article]
      The Lebedev process, in which ethanol is catalytically converted into 1,3-butadiene, is an alternative process for the production of this commodity chemical. Silica–magnesia (SiO2–MgO) is a benchmark catalyst for the Lebedev process. Among the different preparation methods, the SiO2–MgO catalysts prepared by wet-kneading typically perform best owing to the surface magnesium silicates formed during wet-kneading. Although the thermal treatment is of pivotal importance as a last step in the catalyst preparation, the effect of the calcination temperature of the wet-kneaded SiO2–MgO on the Lebedev process has not been clarified yet. Here, we prepared and characterized in detail a series of wet-kneaded SiO2–MgO catalysts using varying calcination temperatures. We find that the thermal treatment largely influences the type of magnesium silicates, which have different catalytic properties. Our results suggest that the structurally ill-defined amorphous magnesium silicates and lizardite are responsible for the production of ethylene. Further, we argue that forsterite, which has been conventionally considered detrimental for the formation of ethylene, favors the formation of butadiene, especially when combined with stevensite.
    • The global network of ports supporting high seas fishing

      Rodríguez, J. P.; Fernández-Gracia, Juan; Duarte, Carlos M.; Irigoien, Xabier; Eguíluz, V. M. (Science Advances, American Association for the Advancement of Science (AAAS), 2021-02-26) [Article]
      Fisheries in waters beyond national jurisdiction (“high seas”) are difficult to monitor and manage. Their regulation for sustainability requires critical information on how fishing effort is distributed across fishing and landing areas, including possible border effects at the exclusive economic zone (EEZ) limits. We infer the global network linking harbors supporting fishing vessels to fishing areas in high seas from automatic identification system tracking data in 2014, observing a modular structure, with vessels departing from a given harbor fishing mostly in a single province. The top 16% of these harbors support 84% of fishing effort in high seas, with harbors in low- and middle-income countries ranked among the top supporters. Fishing effort concentrates along narrow strips attached to the boundaries of EEZs with productive fisheries, identifying a free-riding behavior that jeopardizes efforts by nations to sustainably manage their fisheries, perpetuating the tragedy of the commons affecting global fishery resources.
    • Superconductivity and High-Pressure Performance of 2D Mo2C Crystals

      Zhang, Junli; Cao, Zhen; He, Xin; Liu, Wenhao; Wen, Yan; Cavallo, Luigi; Ren, Wencai; Cheng, Huiming; Zhang, Xixiang (The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2021-02-26) [Article]
      Two-dimensional (2D) materials have attracted significant attention for their ability to support novel magneto-electrical transport and their optical and magnetic properties, of which their superconductivity is particularly of interest. Here we report on the behavior of superconductivity in 2D Mo2C crystals when hydrostatic pressure is applied, which has not yet been described in the literature. We found that the localization of boundary atoms disorder-induced Cooper pairs can suppress the superconducting transition temperature (Tc) as effectively as a magnetic field and current. We observed that the Tc initially decreased as the pressure increased to 1.75 GPa but then began to increase as the pressure increased further to 2.5 GPa. Our density functional theory calculations revealed that this behavior was linked to the modulation of the strength of the electron-phonon coupling and the electron property, which was triggered by compression of the lattice under high pressure. We attributed the inflection point in the hydrostatic pressure-dependent Tc curve to the structural phase transition of Mo2C from a hexagonal to an orthorhombic structure. This work presents a new avenue for the study of the superconductivity of Mo2C, which can be extended to apply to other 2D superconductors to modulate their electronic states.
    • Layer number dependent ferroelasticity in 2D Ruddlesden–Popper organic-inorganic hybrid perovskites

      Xiao, Xun; Zhou, Jian; Song, Kepeng; Zhao, Jingjing; Zhou, Yu; Rudd, Peter Neil; Han, Yu; Li, Ju; Huang, Jinsong (Nature Communications, Springer Science and Business Media LLC, 2021-02-26) [Article]
      AbstractFerroelasticity represents material domains possessing spontaneous strain that can be switched by external stress. Three-dimensional perovskites like methylammonium lead iodide are determined to be ferroelastic. Layered perovskites have been applied in optoelectronic devices with outstanding performance. However, the understanding of lattice strain and ferroelasticity in layered perovskites is still lacking. Here, using the in-situ observation of switching domains in layered perovskite single crystals under external strain, we discover the evidence of ferroelasticity in layered perovskites with layer number more than one, while the perovskites with single octahedra layer do not show ferroelasticity. Density functional theory calculation shows that ferroelasticity in layered perovskites originates from the distortion of inorganic octahedra resulting from the rotation of aspherical methylammonium cations. The absence of methylammonium cations in single layer perovskite accounts for the lack of ferroelasticity. These ferroelastic domains do not induce non-radiative recombination or reduce the photoluminescence quantum yield.
    • A Novel One-Pot Enzyme Cascade for the Biosynthesis of Cladribine Triphosphate

      Frisch, Julia; Maršić, Tin; Loderer, Christoph (Biomolecules, MDPI AG, 2021-02-25) [Article]
      Cladribine triphosphate is the active compound of the anti-cancer and multiple sclerosis drug Mavenclad (cladribine). Biosynthesis of such non-natural deoxyribonucleotides is challenging but important in order to study the pharmaceutical modes of action. In this study, we developed a novel one-pot enzyme cascade for the biosynthesis of cladribine triphosphate, starting with the nucleobase 2Cl-adenine and the generic co-substrate phosphoribosyl pyrophosphate. The cascade is comprised of the three enzymes, namely, adenine phosphoribosyltransferase (APT), polyphosphate kinase (PPK), and ribonucleotide reductase (RNR). APT catalyzes the binding of the nucleobase to the ribose moiety, followed by two consecutive phosphorylation reactions by PPK. The formed nucleoside triphosphate is reduced to the final product 2Cl-deoxyadenonsine triphosphate (cladribine triphosphate) by the RNR. The cascade is feasible, showing comparative product concentrations and yields to existing enzyme cascades for nucleotide biosynthesis. While this study is limited to the biosynthesis of cladribine triphosphate, the design of the cascade offers the potential to extend its application to other important deoxyribonucleotides.