Search

The fabrication of high-quality epitaxial BiFeO3 (BFO) thin films is critical for their integrated device applications. This work demonstrates a modification of two cooling atmospheres, i.e., pure O2 and mixed Ar/O2, on the crystalline phase and electrical properties of BFO thin films prepared by radio-frequency magnetron sputtering. A good epitaxial growth of BFO thin films with a coexistence of dominant rhombohedral (R) and partial tetragonal (T) phases is identified by XRD analyses. Compared to an extremely small amount of (100)-oriented T phase detected in the BFO thin film cooled in mixed Ar/O2, an increased amount of T phase with (001) orientation is observed in the film cooled in pure O2. In addition, compared with the poor electrical properties, including leakage, dielectric behavior, and ferroelectric polarization, of the BFO film cooled in mixed Ar/O2, the film cooled in pure O2 exhibits the improved electrical properties, e.g., a low leakage current (J

The expressway is necessary for the development of the modern transportation industry, and the level of expressway construction reflects the overall grade of national or regional economic development. In order to process the expressway road property data information, based on the current mainstream Windows operating system, this study utilizes Geographic Information System (GIS) development technology, road video processing technology, and spatial data mining method to design and develop an expressway video and road infostructure GIS data production system. The system designs a multi-layer distributed application model in accordance with the ideas and methods of GIS engineering and the characteristics of road production data. In addition, according to the characteristics and specification requirements of basic geographic data, the road production database of spatial data and attribute data integrated storage is constructed by combining database and spatial data engine. Through the development of the GIS data production system for expressway video and road infostructure, various functions such as generation of road property data, dynamic management of road infostructure, and visualization of spatial information have been realized. The system focuses on improving the production efficiency and automation level of expressway production data and meets the construction requirements for modernization, informatization, and intelligence of expressways.

Amid the ongoing rapid digitalization, consistent advancements in technologies such as 5G have become crucial. The demand for 5G technologies is expected to surge owing to the continued hybrid work culture, and 5G stock will emerge from the stocks of older tech and telecom companies. However, the COVID-19 epidemic continues to spread globally, causing a major impact on China’s macroeconomy and the stock market. It has a significant impact on the trading behavior of investors in 5G stock. Based on the framework of information economics and 5G Networks, we use the TVP-VAR model to empirically analyze the time-varying effects of rational and irrational market sentiment on investor herd behavior and overconfidence. The results show that rational market sentiment can always suppress herding behavior and overconfidence, while irrational market sentiment intensifies investors’ herd behavior most of the time, suppressing overconfidence in the short term and turning it into a positive effect in the medium term, and its long-term effects have almost disappeared. Compared with rational market sentiment, irrational market sentiment has a more direct and significant impact on herd behavior. The absolute values of the impulse responses of both market sentiments to the impact of overconfidence are relatively close. In addition, both market sentiments have typical characteristics of vulnerability to investor psychology. After the epidemic spread, both market sentiments accelerate the generation of overconfidence, while the positive impact on herd behavior gradually decreases. Our research shows that in the environment of information asymmetry, although investors will restrain their irrational conformity psychology, they still have not demonstrated their reasonable investment capabilities. Our conclusions will provide some references for government regulatory agencies and market investors under the background of the epidemic.

由于温和的口服性能和良好的生物兼容性, 配位聚合物基膳 食补充剂一直在市场上广受欢迎. 这类膳食补充剂通常都是以片 剂的形式销售, 其片剂的加工和制造过程与其力学性质密切相关. 本文系统总结了配位聚合物膳食补充剂的晶体结构与力学性质之 间的内在关系, 并与小分子药物晶体和无机膳食补充剂进行比较, 为其片剂加工制造过程提供参考.

High spatial resolution remote sensing image (HSRRSI) data provide rich texture, geometric structure, and spatial distribution information for surface water bodies. The rich detail information provides better representation of the internal components of each object category and better reflects the relationships between adjacent objects. In this context, recognition methods such as geographic object-based image analysis (GEOBIA) have improved significantly. However, these methods focus mainly on bottom-up classifications from visual features to semantic categories, but ignore top-down feedback which can optimize recognition results. In recent years, deep learning has been applied in the field of remote sensing measurements because of its powerful feature extraction ability. A special convolutional neural network (CNN) based region proposal generation and object detection integrated framework has greatly improved the performance of object detection for HSRRSI, which provides a new method for water body recognition based on remote sensing data. This study uses the excellent &ldquo, self-learning ability&rdquo, of deep learning to construct a modified structure of the Mask R-CNN method which integrates bottom-up and top-down processes for water recognition. Compared with traditional methods, our method is completely data-driven without prior knowledge, and it can be regarded as a novel technical procedure for water body recognition in practical engineering application. Experimental results indicate that the method produces accurate recognition results for multi-source and multi-temporal water bodies, and can effectively avoid confusion with shadows and other ground features.

The driving forces for the phase transitions of ABX3 hybrid organic-inorganic perovskites have been limited to the octahedral tilting, order-disorder, and displacement. Now, a complex structural phase transition has been explored in a HOIP, [CH3 NH3 ][Mn(N3 )3 ], based on structural characterizations and ab initio lattice dynamics calculations. This unusual first-order phase transition between two ordered phases at about 265 K is primarily driven by changes in the collective atomic vibrations of the whole lattice, along with concurrent molecular displacements and an unusual octahedral tilting. A significant entropy difference (4.35 J K-1 mol-1 ) is observed between the low- and high-temperature structures induced by such atomic vibrations, which plays a main role in driving the transition. This finding offers an alternative pathway for designing new ferroic phase transitions and related physical properties in HOIPs and other hybrid crystals.

In view of the current situation of the development of residential accommodation in rural areas in China, this paper starts from the spatial distribution and structural characteristics of residential accommodation with national characteristics, taking the national rural characteristic hostels as the research object, analyzes the spatial distribution characteristics of the characteristic hostels in the whole country by using the inverse distance weight method and Kriging spatial interpolation method, and visually expresses the development status of the characteristic hostels in the whole country by using the spatial thermal diagram.The experimental results show that the distribution of residential accommodation with rural characteristics in China has strong spatial agglomeration characteristics. Residential accommodation with rural characteristics in China is generally positively correlated with population density, occupied area and GDP in various regions. Relying on the beautiful natural environment and simple human resources, the development of the rural residents’ lodging has made the rural residents’ lodging itself a tourism attraction, transforming the disadvantages into advantages, driving the development of rural tourism and related industries, stimulating the employment of farmers and promoting cultural revival and the prosperity of the common people.

The fundamental mechanical properties of a dense metal–organic framework material, [NH2CHNH2][Er(HCOO)4] (1), have been studied using nanoindentation technique. The results demonstrate that the elastic moduli, hardnesses, and yield stresses on the (021)/(02−1) facets are 29.8/30.2, 1.80/1.83 and 0.93/1.01 GPa, respectively. Moreover, variable-temperature powder and single-crystal X-ray diffraction experiments reveal that framework 1 shows significant negative thermal expansion along its b axis, which can be explained by using a hinge–strut structural motif.

Very few materials expand two-dimensionally under pressure, and this extremely rare phenomenon, namely negative area compressibility (NAC), is highly desirable for technological applications in pressure sensors and actuators., Very few materials expand two-dimensionally under pressure, and this extremely rare phenomenon, namely negative area compressibility (NAC), is highly desirable for technological applications in pressure sensors and actuators. Hitherto, the few known NAC materials have dominantly been limited to 2D crystals bonded via coordination interactions while other 2D systems have not been explored yet. Here, we report the large NAC of a hydrogen-bonded 2D supramolecular coordination complex, Zn(CH3COO)2·2H2O, with a synergistic microscopic mechanism. Our findings reveal that such an unusual phenomenon, over a wide pressure range of 0.15–4.44 GPa without the occurrence of any phase transitions, arises from the complex cooperation of intra-layer coordination and hydrogen-bonding interactions, and inter-layer van der Waals forces. In addition, we propose that these NAC crystals could have important applications as pressure-converting materials in ultrasensitive pressure sensing devices.

A new ratiometric fluorescent probe for the detection of highly toxic thiophenols was reported. To produce ratiometric fluorescence signal changes for thiophenols, this probe was designed to use a coumarin–naphthalimide dyad as the fluorescence resonance energy transfer (FRET) platform and dinitrophenyl ether as the recognition unit. This probe features high selectivity and sensitivity for thiophenols with a rapid detection process under mild conditions and remarkable fluorescence emission ratio changes (up to 340-fold). The application of this probe for thiophenol detection in real water samples was successfully applied.

In this paper, a new low dose fluorescent probe with excellent sensing properties for detection of biothiols (GSH, Cys and Hcy) was developed. This probe shows rapid response, high selectivity and sensitivity for biothiols with dual colorimetric and fluorescent turn-on signal changes. The detection limit of this probe for biothiols was found to be

Streptonigrin methylesterase A (StnA) is one of the tailoring enzymes that modify the aminoquinone skeleton in the biosynthesis pathway of Streptomyces species. Although StnA has no significant sequence homology with the reported α/β-fold hydrolases, it shows typical hydrolytic activity in vivo and in vitro. In order to reveal its functional characteristics, the crystal structures of the selenomethionine substituted StnA (SeMet-StnA) and the complex (S185A mutant) with its substrate were resolved to the resolution of 2.71 Å and 2.90 Å, respectively. The overall structure of StnA can be described as an α-helix cap domain on top of a common α/β hydrolase domain. The substrate methyl ester of 10′-demethoxystreptonigrin binds in a hydrophobic pocket that mainly consists of cap domain residues and is close to the catalytic triad Ser185-His349-Asp308. The transition state is stabilized by an oxyanion hole formed by the backbone amides of Ala102 and Leu186. The substrate binding appears to be dominated by interactions with several specific hydrophobic contacts and hydrogen bonds in the cap domain. The molecular dynamics simulation and site-directed mutagenesis confirmed the important roles of the key interacting residues in the cap domain. Structural alignment and phylogenetic tree analysis indicate that StnA represents a new subfamily of lipolytic enzymes with the specific binding pocket located at the cap domain instead of the interface between the two domains.

In this paper, a new dual colorimetric and fluorescent probe for cyanide anions was developed. This probe contains an electron-donating phenanthroimidazole moiety and a strong electron-withdrawing indolium derivative. The detection of cyanide was performed via the fast nucleophilic attack of cyanide on the indolium group of the probe, resulting in a rapid sensing process for cyanide with obvious color and fluorescence (at two different emission channels, one in the visible region and one in the near infrared region) signal changes, and with high selectivity and sensitivity. The detection limit was found to be 26 nM in aqueous solution, and the application of this probe for cyanide detection in simulated wastewater samples was investigated.

A new near-infrared (NIR) fluorescent probe, which contains a conjugated dicyanomethylene-benzopyran structure as the NIR fluorophore and an acrylate moiety as the reaction site, was found to be a promising NIR probe for biothiols (Cys, Hcy and GSH). This probe shows rapid response, high selectivity and sensitivity for biothiols (particularly for Cys and Hcy), accompanied by distinct color changes and significant NIR fluorescence turn on responses. The detection limit for Cys was found to be 81 nM. In addition, the imaging of biothiols by this probe was also successfully applied in living cells, indicating that this probe holds promise for applications in biological samples.

Introducing four –CH2OH groups to an anthracene bridged Zn–DPA complex was found to result in a new highly selective and controllable excimer-based fluorescent sensor for pyrophosphate in water.

Selenocysteine (Sec) has emerged as an important sensing target in recent years. In this paper, a colorimetric and near-infrared fluorescent turn-on probe for Sec was developed. This probe features a remarkable large Stokes shift (146nm) and shows a rapid, highly selective detection process for Sec with obvious colorimetric and near-infrared fluorescent (Em 706nm with Ex 560nm) turn-on responses. In addition, this probe can be used to quantitatively detect Sec with high sensitivity with a detection limit of 62nM over a wide linear range (0.2-80μM). Moreover, it was further demonstrated that this NIR fluorescent probe can be employed to image both exogenous and endogenous Sec in living cells, indicating that this probe has great potential for biological applications.

High pressure behavior of a 2D hybrid perovskite semiconductor, (BA)2PbBr4 (BA = benzylammonium), has been systematically studied via synchrotron powder X-ray diffraction over the range of 0-14.22 GPa. (BA)2PbBr4 shows a soft nature with a bulk modulus of 10(1) GPa and anisotropic linear compressibility with βa = 25(6), βb = 5.3(4), and βc = 15.1(8) TPa−1. Experiment-aided density functional theory calculations reveal that the structural changes of (BA)2PbBr4 under compression are attributed to the configurational alterations of BA+ organic cations and synergistic distortion of the (PbBr4)2− inorganic layer. Further extensive theoretical calculations of elastic tensors give full mapping of Young’s moduli, shear moduli, and Poisson’s ratios of (BA)2PbBr4, which confirm its anisotropic nature in elasticity. In addition, the photoluminescence of (BA)2PbBr4 exhibits a significant red-shift and an intensity decrease in response to hydrostatic stress which respectively arise from the contractions of Pb–Br bonds and distortions of PbBr6 octahedra in the inorganic layer mediated by the configurational alterations of BA+ cations upon compression.

The reaction catalyzed by the protein phosphatase-1 (PP1) has been examined by linear free energy relationships and kinetic isotope effects. With the substrate 4-nitrophenyl phosphate (4NPP), the reaction exhibits a bell-shaped pH-rate profile for kcat/KM indicative of catalysis by both acidic and basic residues, with kinetic pKa values of 6.0 and 7.2. The enzymatic hydrolysis of a series of aryl monoester substrates yields a Brønsted beta(lg) of -0.32, considerably less negative than that of the uncatalyzed hydrolysis of monoester dianions (-1.23). Kinetic isotope effects in the leaving group with the substrate 4NPP are (18)(V/K) bridge = 1.0170 and (15)(V/K) = 1.0010, which, compared against other enzymatic KIEs with and without general acid catalysis, are consistent with a loose transition state with partial neutralization of the leaving group. PP1 also efficiently catalyzes the hydrolysis of 4-nitrophenyl methylphosphonate (4NPMP). The enzymatic hydrolysis of a series of aryl methylphosphonate substrates yields a Brønsted beta(lg) of -0.30, smaller than the alkaline hydrolysis (-0.69) and similar to the beta(lg) measured for monoester substrates, indicative of similar transition states. The KIEs and the beta(lg) data point to a transition state for the alkaline hydrolysis of 4NPMP that is similar to that of diesters with the same leaving group. For the enzymatic reaction of 4NPMP, the KIEs are indicative of a transition state that is somewhat looser than the alkaline hydrolysis reaction and similar to the PP1-catalyzed monoester reaction. The data cumulatively point to enzymatic transition states for aryl phosphate monoester and aryl methylphosphonate hydrolysis reactions that are much more similar to one another than the nonenzymatic hydrolysis reactions of the two substrates.

Identifying how enzymes stabilize high-energy species along the reaction pathway is central to explaining their enormous rate acceleration. β-Phosphoglucomutase catalyses the isomerization of β-glucose-1-phosphate to β-glucose-6-phosphate and appeared to be unique in its ability to stabilize a high-energy pentacoordinate phosphorane intermediate sufficiently to be directly observable in the enzyme active site. Using 19 F-NMR and kinetic analysis, we report that the complex that forms is not the postulated high-energy reaction intermediate, but a deceptively similar transition state analogue in which MgF 3 − mimics the transferring PO 3 − moiety. Here we present a detailed characterization of the metal ion–fluoride complex bound to the enzyme active site in solution, which reveals the molecular mechanism for fluoride inhibition of β-phosphoglucomutase. This NMR methodology has a general application in identifying specific interactions between fluoride complexes and proteins and resolving structural assignments that are indistinguishable by x-ray crystallography.

The thermal expansion behavior of a metal-formate framework, Zn(HCOO)2·2(H2O) (1), has been systematically studied via variable temperature single-crystal X-ray diffraction. Our results demonstrate that this formate exhibits significant negative thermal expansion (NTE, −26(2) MK−1) along its c-axis. Detailed structural analyses reveal that the large NTE response is attributed to the ‘hinge-strut’ like framework motion. In addition, the fundamental mechanical properties of framework 1 have been explored via nanoindentation experiments. The measured elastic modulus and hardness properties on the (00-2)/(100)/(110) facets are 35.5/35.0/27.1 and 2.04/1.83/0.47 GPa, respectively. The stiffness and hardness anisotropy can be correlated well with the underlying framework structure, like its thermoelastic behavior.

A readily available naphthofluorescein-based near-infrared (NIR) fluorescent probe was reported for rapid, colorimetric and NIR fluorescent turn-on detection of cysteine (Cys) with high selectivity and sensitivity over various analytes including the similar structured homocysteine (Hcy) and glutathione (GSH). This probe was successfully applied to bioimage intracellular Cys in living cells with low cytotoxicity.

Introducing hydrogen bond donors to a receptor was found to be an effective approach to improve both its selectivity and binding affinity for pyrophosphate in water. The crystal structure of Zn3–ADP complex showed the improvements come from the combination of H-bonding and metal coordination in a manner similar to many metalloenzymes.

Reversible addition fragmentation chain transfer (RAFT) synthesis and self-assembly of free-base porphyrin cored star polymers are reported. The polymerization, in the presence of a free-base porphyrin cored chain transfer agent (CTA-FBP), produced porphyrin star polymers with controlled molecular weights and narrow polydispersities for a number of monomers includingN,N-dimethylacrylamide (DMA) and styrene (St). Well-defined amphiphilic star block copolymers, P-(PS-PDMA)4and P-(PDMA-PS)4(P: porphyrin), were also prepared and used for self-assembly studies. In methanol, a selective solvent for PDMA, spherical micelles were observed for both block copolymers as characterized by TEM. UV-vis studies suggested star-like micelles were formed from P-(PS-PDMA)4, while P-(PDMA-PS)4aggregated into flower-like micelles. Spectrophotometric titrations indicated that the optical response of these two micelles to external ions was a function of micellar structures. These structure-related properties will be used for micelle studies and functional material development in the future.

Reactivities of five phosphonate esters each coordinated to a dinuclear Co(III) complex were investigated ([Co(2)(tacn)(2)(OH)(2){O(2)P(Me)OAr}](3+); tacn = 1,4,7-triazacyclononane; substituent = m-F, p-NO(2) (1a); p-NO(2) (1b); m-NO(2) (1c); p-Cl (1d); unsubstituted (1e)). Hydrolysis of the phosphonate esters in 1a to 1e is specific base catalyzed and takes place by intramolecular oxide attack on the bridging phosphonate. These data define a Brønsted beta(lg) of -1.12, considerably more negative than that of the hydrolysis of the uncomplexed phosphonates (-0.69). For 1b, the kinetic isotope effects in the leaving group are (18)k(lg) = 1.0228 and (15)k = 1.0014, at the nonbridging phosphoryl oxygens (18)k(nonbridge) = 0.9954, and at the nucleophilic oxygen(18)k(nuc) = 1.0105. The KIEs and the beta(lg) data point to a transition state for the alkaline hydrolysis of 1b that is similar to that of a phosphate monoester complex with the same leaving group, rather than the isoelectronic diester complex. The data from these model systems parallel the observation that in protein phosphatase-1, which has an active site that resembles the structures of these complexes, the catalyzed hydrolysis of aryl methylphosphonates and aryl phosphates are much more similar to one another than the uncomplexed hydrolysis reactions of the two substrates.

Biotransformations of differently configured 2,2-dimethyl-3-substitued-cyclopropanecarbonitriles were studied using a nitrile hydratase/amidase-containing Rhodococcus sp. AJ270 whole-cell catalyst under very mild conditions. Although all of the cis-3-aryl-2,2-dimethylcyclopropanecarbonitriles appeared inert toward the biocatalyst, a number of racemic trans-isomers efficiently underwent a highly enantioselective hydrolysis to produce (+)-(1R,3R)-3-aryl-2,2-dimethylcyclopropanecarboxylic acids and (-)-(1S,3S)-3-aryl-2,2-dimethylcyclopropanecarboxamides in high yields with excellent enantiomeric excesses in most cases. The overall enantioselectivity of the biotransformations of nitriles originated from the combined effects of 1R-enantioselective nitrile hydratase and amidase, with the later being a dominant factor. The influence of the substrates on both reaction efficiency and enantioselectivity was discussed in terms of steric and electronic effects. Coupled with chemical transformations, biotransformations of nitriles provided convenient syntheses of optically pure geminally dimethyl-substituted cyclopropanecarboxylic acids and amides, including chrysanthemic acids, in both enantiomeric forms.

The activity of a Zn(II) complex of a tetradentate, tripodal ligand for catalyzing phosphodiester cleavage is enhanced 750-fold by introducing three hydrogen bond donors to the ligand. Inhibition studies show that the Zn-aqua complex is the kinetically active form and that it binds the transition state with a formal dissociation constant of 3 x 108 M-1. The effect of these ligand modifications on the transition-state affinity is comparable to the rate acceleration provided by the metal ion itself. Overall, this mononuclear complex is more active than the most reactive dinuclear Zn(II) complexes reported to date.

A robust and copper-free clicked quantum dot–DNA sensor for sensitive and ratiometric detection of specific DNA and protein targets at the pM level is reported., We report herein the successful preparation of a compact and functional CdSe–ZnS core–shell quantum dot (QD)–DNA conjugate via highly efficient copper-free “click chemistry” (CFCC) between a dihydro-lipoic acid–polyethylene glycol–azide (DHLA–PEG–N3) capped QD and a cyclooctyne modified DNA. This represents an excellent balance between the requirements of high sensitivity, robustness and specificity for the QD-FRET (Förster resonance energy transfer) based sensor as confirmed by a detailed FRET analysis on the QD–DNA conjugate, yielding a relatively short donor–acceptor distance of ∼5.8 nm. We show that this CFCC clicked QD–DNA conjugate is not only able to retain the native fluorescence quantum yield (QY) of the parent DHLA–PEG–N3 capped QD, but also well-suited for robust and specific biosensing; it can directly quantitate, at the pM level, both labelled and unlabelled complementary DNA probes with a good SNP (single-nucleotide polymorphism) discrimination ability in complex media, e.g. 10% human serum via target-binding induced FRET changes between the QD donor and the dye acceptor. Furthermore, this sensor has also been successfully exploited for the detection, at the pM level, of a specific protein target (thrombin) via the encoded anti-thrombin aptamer sequence in the QD–DNA conjugate.

A novel merocyanine-based chemodosimeter was developed to detect fluoride ions in aqueous solution. This chemodosimeter was found to be a highly selective and sensitive colorimetric and fluorescent sensor for fluoride, and moreover, it shows a fast response within a few minutes to fluoride, thus providing a new and very promising sensor for rapid detection of fluoride in aqueous solution.