等浓度的氯化铵和硫酸铵溶液哪个pH高

有中学化学参考资料题:0.10 mol/L的NH4Cl和(NH4)2SO4溶液哪个pH值高?这似乎是个中学生可做的简单题目,仔细考虑不是如此.如果简单地认为盐酸和硫酸都是强酸,而硫酸是二元酸,硫酸铵溶液中铵盐浓度为0.20 mol/L,那么NH4Cl溶液pH高,那是不妥的.硫酸是二元酸,第一个氢离子能完全电离,第二个氢离子部分电离,如此考虑情况怎么样呢?是不是答案发生变化?这要通过计算来说明.     

Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

The conversion efficiencies reported for Tin(Sn)halide-based perovskite solar cells(PSCs)fall a large gap behind those of lead halide-based PSCs,mainly because of poor film quality of the former.Here we report an efficient strategy based on a simple secondary crystallization growth(SCG)technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface.They were discovered to enhance the film crystallinity and suppress the oxidation of Sn²⁺remarkably,hence reduce trap state density and non-irradiative recombination in the absorber films.Furthermore,the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces.Consequently,a champion device efficiency of 8.07% was achieved alo ng with significant enhancements in VOC and JSC,in contrast to 5.35% of the control device value.Moreover,the SCG film-based devices also exhibit superior stability comparing with the control one.This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.     

Energy level engineering of charge selective contact and halide perovskite by modulating band offset:Mechanistic insights

Mixed cation and anion based perovskites solar cells exhibited enhanced stability under outdoor conditions,however,it yielded limited power conversion efficiency when TiO₂ and Spiro-OMeTAD were employed as electron and hole transport layer(ETL/HTL)respectively.The inevitable interfacial recombination of charge carriers at ETL/perovskite and perovskite/HTL interface diminished the efficiency in planar(n-i-p)perovskite solar cells.By employing computational approach for uni-dimensional device simulator,the effect of band offset on charge recombination at both interfaces was investigated.We noted that it acquired cliff structure when the conduction band minimum of the ETL was lower than that of the perovskite,and thus maximized interfacial recombination.However,if the conduction band minimum of ETL is higher than perovskite,a spike structure is formed,which improve the performance of solar cell.An optimum value of conduction band offset allows to reach performance of 25.21%,with an open circuit voltage(VOC)of 1231 mV,a current density JSC of 24.57 mA/cm² and a fill factor of 83.28%.Additionally,we found that beyond the optimum offset value,large spike structure could decrease the performance.With an optimized energy level of Spiro-OMeTAD and the thickness of mixed-perovskite layer performance of 26.56% can be attained.Our results demonstrate a detailed understanding about the energy level tuning between the charge selective layers and perovskite and how the improvement in PV performance can be achieved by adjusting the energy level offset.     

Recent Advances of Pure Organic Room Temperature Phosphorescence Materials for Bioimaging Applications

Bioimaging,as a powerful and helpful tool,which allows people to investigate deeply within living organisms,has contributed a lot for both clinical theranostics and scientific research.Pure organic room temperature phosphorescence(RTP)materials with the unique features of ultralong luminescence lifetime and large Stokes shift,can efficiently avoid biological autofluorescence and scattered light through a time-resolved imaging modality,and thus are attracting increasing attention.This review classifies pure organic RTP materials into three categories,including small molecule RTP materials,polymer RTP materials and supramolecular RTP materials,and summarizes the recent advances of pure organic RTP materials for bioimaging applications.     

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes(CNTs),as one-dimensional nanomaterials,show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer.However,the security risks,time-consuming and high cost of the preparation process hinder its further application.Here,we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs(Co/N-CNTs) by using cobalt zeolitic imidazolate framework(ZIF-67) as a precursor,in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs.Importantly,the obtained Co/N-CNTs,with high content of pyridinic nitrogen and abundant graphitized structure,exhibit superior catalytic activity for oxygen reduction reaction(ORR) with half-wave potential(E_1/2) of 0.85 V and durability in terms of the minimum current loss(2%) after the 30,000 s test.Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.     

Stabilizing High-voltage Cathode Materials for Next-generation Li-ion Batteries

The pressing demand for high-energy/power lithium-ion batteries requires the deployment of cathode materials with higher capacity and output voltage.Despite more than ten years of research,high-voltage cathode mate-rials,such as high-voltage layered oxides,spinel LiNi0.5Mn1.5O4,and high-voltage polyanionic compounds still cannot be commercially viable due to the instabilities of standard electrolytes,cathode materials,and cathode electrolyte interphases under high-voltage operation.This paper summarizes the recent advances in addressing the surface and interface issues haunting the application of high-voltage cathode materials.The understanding of the limitations and advantages of different modification protocols will direct the future endeavours on advancing high-energy/power lithium-ion batteries.     

Suppressing trap states and energy loss by optimizing vertical phase distribution through ternary strategy in organic solar cells

Suppressing the trap-state density and the energy loss via ternary strategy was demonstrated.Favorable vertical phase distribution with donors(acceptors)accumulated(depleted)at the interface of active layer and charge extraction layer can be obtained by introducing appropriate amount of polymer acceptor N2200 into the systems of PBDB-T:IT-M and PBDB-TF:Y6.In addition,N2200 is gradiently distributed in the vertical direction in the ternary blend film.Various measurements were carried out to study the effects of N2200 on the binary systems.It was found that the optimized morphology especially in vertical direction can significantly decrease the trap state density of the binary blend films,which is beneficial for the charge transport and collection.All these features enable an obvious decrease in charge recombination in both PBDB-T:IT-M and PBDB-TF:Y6 based organic solar cells(OSCs),and power conversion efficiencies(PCEs)of 12.5%and 16.42%were obtained for the ternary OSCs,respectively.This work indicates that it is an effective method to suppress the trap state density and thus improve the device performance through ternary strategy.     

Conformational Properties of Comb-shaped Polyelectrolytes with Negatively Charged Backbone and Neutral Side Chains Studied by a Generic Coarse-grained Bead-and-Spring Model

A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.     

Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating conditions

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_0.5Co_0.2Mn_0.3O₂ cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.     

Mesh-like vertical structures enable both high areal capacity and excellent rate capability

In order to balance electrochemical kinetics with loading level for achieving efficient energy storage with high areal capacity and good rate capability simultaneously for wearable electronics,herein,2 D meshlike vertical structures(NiCo_2 S_4@Ni(OH)_2) with a high mass loading of 2.17 mg cm^-2 and combined merits of both 1 D nanowires and 2 D nanosheets are designed for fabricating flexible hybrid supercapacitors.Particularly,the seamlessly interconnected NiCo_2 S_4 core not only provides high capacity of 287.5 μAh cm^-2 but also functions as conductive skeleton for fast electron transport;Ni(OH)_2 sheath occupying the voids in NiCo_2 S_4 meshes contributes extra capacity of 248.4 μAh cm^-2;the holey features guarantee rapid ion diffusion along and across NiCO_2 S_4@Ni(OH)_2 meshes.The resultant flexible electrode exhibits a high areal capacity of 535.9 μAh cm^-2(246.9 mAh g^-1) at 3 mA cm^-2 and outstanding rate performance with 84.7% retention at 30 mA cm^-2,suggesting efficient utilization of both NiCo_2 S_4 and Ni(OH)_2 with specific capacities approaching to their theoretical values.The flexible solid-state hybrid device based on NiCo_2 S_4@Ni(OH)_2 cathode and Fe_2 O_3 anode delivers a high energy density of 315 μWh cm^-2 at the power density of 2.14 mW cm^-2 with excellent electrochemical cycling stability.     

Combining Cryo-EM Density Map and Residue Contact for Protein Secondary Structure Topologies

Although atomic structures have been determined directly from cryo-EM density maps with high resolutions, current structure determination methods for medium resolution (5 to 10 Å) cryo-EM maps are limited by the availability of structure templates. Secondary structure traces are lines detected from a cryo-EM density map for α-helices and β-strands of a protein. A topology of secondary structures defines the mapping between a set of sequence segments and a set of traces of secondary structures in three-dimensional space. In order to enhance accuracy in ranking secondary structure topologies, we explored a method that combines three sources of information: a set of sequence segments in 1D, a set of amino acid contact pairs in 2D, and a set of traces in 3D at the secondary structure level. A test of fourteen cases shows that the accuracy of predicted secondary structures is critical for deriving topologies. The use of significant long-range contact pairs is most effective at enriching the rank of the maximum-match topology for proteins with a large number of secondary structures, if the secondary structure prediction is fairly accurate. It was observed that the enrichment depends on the quality of initial topology candidates in this approach. We provide detailed analysis in various cases to show the potential and challenge when combining three sources of information.     

Spatial and temporal resolution in cryo-electron microscopy—A scope for nano-chemistry

Cryo-electron microscopy has evolved in an established approach to study the structure of bio-colloids. Recent developments in instrumentation and automation, often demanded by life sciences, made cryo-EM a general tool in colloid chemistry. Recently improved instrumentation for vitrification has resulted in reliable and reproducible preparation of specimen in water and other solvents. A dynamic approach, following processes in time is gaining importance and a time resolution up to 1 ms is expected to become general available. With improved instrumentation and automation 3D reconstructions by cryo-EM tomography are becoming routinely accessible. Tomography as such or in conjunction with time resolved microscopy is expected to give new insights in (macro)molecular assembly/disassembly mechanisms and thus become an essential tool in nano-chemistry.     

Haruspex: A Neural Network for the Automatic Identification of Oligonucleotides and Protein Secondary Structure in Cryo-Electron Microscopy Maps

In recent years, three-dimensional density maps reconstructed from single particle images obtained by electron cryo-microscopy (cryo-EM) have reached unprecedented resolution. However, map interpretation can be challenging, in particular if the constituting structures require de-novo model building or are very mobile. Herein, we demonstrate the potential of convolutional neural networks for the annotation of cryo-EM maps: our network Haruspex has been trained on a carefully curated set of 293 experimentally derived reconstruction maps to automatically annotate RNA/DNA as well as protein secondary structure elements. It can be straightforwardly applied to newly reconstructed maps in order to support domain placement or as a starting point for main-chain placement. Due to its high recall and precision rates of 95.1 % and 80.3 %, respectively, on an independent test set of 122 maps, it can also be used for validation during model building. The trained network will be available as part of the CCP-EM suite.     

Structural Modeling of TRPA1 Ion Channel—Determination of the Binding Site for Antagonists

TRPA1 is a transmembrane cation channel, one of the most promising targets in the context of respiratory diseases. Its general structure has already been experimentally resolved, but the binding site of TRPA1 antagonists such as HC-030031, a model methylxanthine derivative, remains unknown. The present study aimed to determine the potential binding site of xanthine antagonists and to describe their binding mode, using a molecular modeling approach. This study represents the first attempt to bring together site-directed mutagenesis reports and the latest cryo-EM structure of an antagonist bound to TRPA1. Our research suggests that the core moiety of HC-030031 binds to a pocket formed by the TRP-like domain and the pre-S1, S4, S5 helices of one subunit. The structure, determined by cryo-EM, shows interactions of a core hypoxanthine moiety in the same area of the binding site, sharing the interaction of xanthine/hypoxanthine with Trp-711. Moreover, the predicted binding mode of HC-030031 assumes interaction with Asn-855, a residue demonstrated to be important for HC-030031 recognition in site-directed mutagenesis studies. Our model proved to be advantageous in a retrospective virtual screening benchmark; therefore, it will be useful in research on new TRPA1 antagonists among xanthine derivatives and their bioisosteres.     

The Mutation of the “Nobel Prize in Chemistry” into the “Nobel Prize in Chemistry or Life Sciences”: Several Decades of Transparent and Opaque Evidence of Change within the Nobel Prize Program

Over the past several decades, the Nobel Prize program has slowly but steadily been modified in both transparent and opaque ways. A transparent change has been the creation of the Nobel Prize in Economic Sciences, officially known as the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel. An opaque change has been the mutation of the Nobel Prize in Chemistry into what is effectively the “Nobel Prize in Chemistry or Life Sciences.” This paper presents a detailed study of this opaque change, including evidence that the disciplines of chemistry and biochemistry cover, today, intellectually quite distinct and generally scientifically-unrelated intellectual territory. This paper supports the evolution of the Nobel Prizes, and encourages the Nobel Prize program to move from opaque to transparent change processes for the next generations of achievement in the sciences.     

The Mutation of the “Nobel Prize in Chemistry” into the “Nobel Prize in Chemistry or Life Sciences”: Several Decades of Transparent and Opaque Evidence of Change within the Nobel Prize Program

Over the past several decades, the Nobel Prize program has slowly but steadily been modified in both transparent and opaque ways. A transparent change has been the creation of the Nobel Prize in Economic Sciences, officially known as the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel. An opaque change has been the mutation of the Nobel Prize in Chemistry into what is effectively the “Nobel Prize in Chemistry or Life Sciences.” This paper presents a detailed study of this opaque change, including evidence that the disciplines of chemistry and biochemistry cover, today, intellectually quite distinct and generally scientifically‐unrelated intellectual territory. This paper supports the evolution of the Nobel Prizes, and encourages the Nobel Prize program to move from opaque to transparent change processes for the next generations of achievement in the sciences.     

Cryo-EM structure of acylpeptide hydrolase reveals substrate selection by multimerization and a multi-state serine-protease triad

The first structure of tetrameric mammalian acylaminoacyl peptidase, an enzyme that functions as an upstream regulator of the proteasome through the removal of terminal N-acetylated residues from its protein substrates, was determined by cryo-EM and further elucidated by MD simulations. Self-association results in a toroid-shaped quaternary structure, guided by an amyloidogenic β-edge and unique inserts. With a Pro introduced into its central β-sheet, sufficient conformational freedom is awarded to the segment containing the catalytic Ser587 that the serine protease catalytic triad alternates between active and latent states. Active site flexibility suggests that the dual function of catalysis and substrate selection are fulfilled by a novel mechanism: substrate entrance is regulated by flexible loops creating a double-gated channel system, while binding of the substrate to the active site is required for stabilization of the catalytic apparatus – as a second filter before hydrolysis. The structure not only underlines that within the family of S9 proteases homo-multimerization acts as a crucial tool for substrate selection, but it will also allow drug design targeting of the ubiquitin-proteasome system.

The structure of tetrameric mammalian acylaminoacyl peptidase – a key upstream regulator of the proteasome – was determined by cryo-EM (and elucidated by MD), showing a “shutters-and-channels” substrate selection apparatus created by oligomerization.     

Synthesis and characterization of Au102(p-MBA)44 nanoparticles

The synthesis of Au(102)(p-MBA)(44) nanoparticles on a preparative scale in high yield is described. Various analytical methods are shown to give results consistent with the composition and known structure of the particles, showing the preparation is essentially homogeneous, and attesting to the validity of the methods as well. Derivatization of the particles with proteins and DNA is demonstrated, and conditions are described for imaging individual particles by cryo-EM at low electron dose, close to focus, conditions optimal for recording high-resolution details.     

A carbapenem antibiotic inhibiting a mammalian serine protease: structure of the acylaminoacyl peptidase–meropenem complex

The structure of porcine AAP (pAAP) in a covalently bound complex with meropenem was determined by cryo-EM to 2.1 Å resolution, showing the mammalian serine-protease inhibited by a carbapenem antibiotic. AAP is a modulator of the ubiquitin-proteasome degradation system and the site of a drug–drug interaction between the widely used antipsychotic, valproate and carbapenems. The active form of pAAP – a toroidal tetramer – binds four meropenem molecules covalently linked to the catalytic Ser587 of the serine-protease triad, in an acyl–enzyme state. AAP is hindered from fully processing the antibiotic by the displacement and protonation of His707 of the catalytic triad. We show that AAP is made susceptible to the association by its unusually sheltered active pockets and flexible catalytic triads, while the carbapenems possess sufficiently small substituents on their β-lactam rings to fit into the shallow substrate-specificity pocket of the enzyme.

The structure of porcine AAP (pAAP) in a covalently bound complex with meropenem was determined by cryo-EM to 2.1 Å resolution, showing the mammalian serine-protease inhibited by a carbapenem antibiotic.     

Membrane protein selectively oriented on solid support and reconstituted into a lipid membrane

Mimetic functional membranes on solid support are now emerging for the development of membrane biosensor or for the study of membrane-mediated processes and should have an important impact on biodiagnostics. We established a method to reconstitute a membrane protein into a lipid membrane in a selective orientation on a solid support. Membrane protein OprM, a component of OprM-MexA-MexB multidrug efflux pump, solubilized in detergent was immobilized via its extracellular domain on aminosilane-modified silica surface. The oriented protein was reconstituted into a lipid membrane by detergent removal. The membrane protein reconstitution process carried out on silica nanoparticles and on planar silica surfaces was followed by cryo-electron microscopy (cryo-EM) and quartz crystal microbalance with dissipation monitoring (QCM-D) respectively. The selective protein orientation on aminosilane-modified silica surface was assessed by cryo-EM and was compared to the nonspecific protein deposition on silica surface. Finally, the binding of MexA, a periplasmic component of the tripartite efflux complex, was monitored with QCM-D on the oriented OprM protein monolayer. The large adsorbed mass gave a direct evidence of the high affinity of MexA with the periplasmic helical part of OprM.