Effects of the Intramolecular Group and Solvent on Vibrational Coupling Modes and Strengths of Fermi Resonances in Aryl Azides: A DFT Study of 4-Azidotoluene and 4-Azido-N-phenylmaleimide.

The high transition dipole strength of the azide asymmetric stretch makes aryl azides good candidates as vibrational probes (VPs). However, aryl azides have complex absorption profiles due to Fermi resonances (FRs). Understanding the origin and the vibrational modes involved in FRs of aryl azides is critically important toward developing them as VPs for studies of protein structures and structural changes in response to their surroundings. As such, we studied vibrational couplings in 4-azidotoluene and 4-azido-N-phenylmaleimide in two solvents, N,N-dimethylacetamide and tetrahydrofuran, to explore the origin and the effects of intramolecular group and solvent on the FRs of aryl azides using density functional theory (DFT) calculations with the B3LYP functional and seven basis sets, 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p), and 6-311++G(df,pd). Two combination bands consisting of the azide symmetric stretch and another mode form strong FRs with the azide asymmetric stretch for both molecules. The FR profile was altered by replacing the methyl group with maleimide. Solvents change the relative peak position and intensity more significantly for 4-azido-N-phenylmaleimide, which makes it a more sensitive VP. Furthermore, the DFT results indicate that a comparison among the results from different basis sets can be used as a means to predict more reliable vibrational spectra.

Theoretical investigation on the functional group modulation of UV-Vis absorption profiles of triphenylamine derivatives.

Understanding the functional group modulation of electronic structure and excitation is pivotal to the design of organic small molecules (OSMs) for photoelectric applications. In this study, we employed density functional theory (DFT) and time-dependent DFT (TDDFT) calculations to explore the unique absorption character of four triphenylamine photosensitizers. The various conformations were investigated given the multiple single bonds in the compounds, and the resemblance in the electronic structure of different conformations is affirmed because the coplanarity and consequent long-range conjugation is maintained regardless of the orientation of the flexible blocks. Six functionals were evaluated, and MN15 was found to successfully reproduce the intense secondary absorption peak for the double 3,4-ethylenedioxythiophene (EDOT) modified sensitizer over B3LYP, PBE0, M062X, CAM-B3LYP, and ωB97XD. The introduction of EDOT gives rise to a new excited state S4, which is a local excitation constrained in the EDOT substituent triphenylamine block. This new excited state S4, in combination with inherent S2 and S3 derived from prototype molecule TPA-Pyc, jointly contributes to the hump of the secondary absorption peak of ETE-Pyc and finally affects the light-harvesting ability of the dye-sensitized TiO2 photoanode. The current findings provide guidance toward the rational design of OSMs with good light-harvest ability.

UV-Curing-Enhanced Organic Long-Persistent Luminescence Materials.

Amorphous organic long-persistent luminescence materials (OLPLMs) can realize simpler solution processing and large-area uniform luminescence, where the luminescent properties are significantly influenced by the rigid environment. However, research on utilizing the rigidity to promote long-persistent luminescence (LPL) properties of amorphous OLPLMs is still relatively rare due to the lack of an unambiguous and effective strategy to construct the rigid environment. Here, a universal strategy is proposed to enhance the LPL performance of organic host-guest doping systems by UV curing, which utilizes the rigid environment constructed by UV curing to promote the interaction between host and guest, thus inducing a generation of materials with highly efficient LPL performance. This solution-processable, large-area, and "easy-to-realize" material fabrication strategy can make amorphous OLPLMs show broader application prospects in some fields, such as anti-counterfeiting, nondestructive detection, and pattern marking or indication.

Measurement and Classification Criteria of Strength Decrease Rate and Brittleness Indicator Index for Rockburst Proneness Evaluation of Hard Rocks.

Rockburst is one of the common geological hazards. It is of great significance to study the evaluation indexes and classification criteria of the bursting liability of hard rocks, which is important for the prediction and prevention of rockbursts in hard rocks. In this study, the evaluation of the rockburst tendency was conducted using two indoor non-energy indexes, namely the brittleness indicator (B2) and the strength decrease rate (SDR). The measuring methods of B and SDR as well as the classification criteria were analyzed. Firstly, the most rational calculation formulas for B and SDR were selected based on previous studies. The B2 equaled to the ratio between the difference and sum of uniaxial compressive strength and Brazilian tensile strength of rocks. The SDR was the average stress decrease rate of the post-peak stage in uniaxial compression tests and equaled the uniaxial compressive strength dividing the duration time of post-peak rock failure in uniaxial compression tests. Secondly, the uniaxial compression tests of different rock types were designed and carried out, and the change trend of B and SDR with the increase of loading rate in uniaxial compression tests were studied in detail. The results showed that after the loading rate was greater than 5 mm/min or 100 kN/min, the B value was affected, limited by the loading rate, while the SDR value was more affected by the strain rate. The displacement control, with a loading rate of 0.1-0.7 mm/min, was recommended for the measurement of B and SDR. The classification criteria of B2 and SDR were proposed, and four grades of rockburst tendency were defined for SDR and B2 according to the test results.

Insight into the solvent effects on ethanol oxidation on Ir(100).

Solvent effects have always been a non-negligible factor for aqueous catalytic reactions, though few studies have been devoted towards the molecular understanding and impact of solvent effects on catalysis. In this work, we investigated ethanol dehydrogenation and C-C bond cleavage over Ir(100) in an aqueous solution using density functional theory calculations with both the implicit and explicit solvent models and transition state theory-based kinetics simulations. The results show that solvent polarization assists the α- and ß-dehydrogenation of ethanol on Ir(100) in the aqueous solution and hydrogen bonding also assists the ethanol ß-dehydrogenation and C-C bond cleavage in CH2CO. The hydrogen bond between the ethanol and water molecule hinders ethanol hydroxyl dehydrogenation while the CHCO⋯H2O hydrogen bond radically alters the adsorption configuration of CHCO, which leads to an increase in the C-C cleavage barrier by 2.5 fold. Furthermore, the solvent changes the reaction pathways significantly. In an aqueous solution, ethanol ß-dehydrogenation on Ir(100) is the dominant ethanol dehydrogenation pathway and C-C bond cleavage occurs predominantly via CH2CO species.

Density functional theory based computational investigations on the stability of highly active trimetallic PtPdCu nanoalloys for electrochemical oxygen reduction.

Activity, cost, and durability are the trinity of catalysis research for the electrochemical oxygen reduction reaction (ORR). While studies towards increasing activity and reducing cost of ORR catalysts have been carried out extensively, much effort is needed in durability investigation of highly active ORR catalysts. In this work, we examined the stability of a trimetallic PtPdCu catalyst that has demonstrated high activity and incredible durability during ORR using density functional theory (DFT) based computations. Specifically, we studied the processes of dissolution/deposition and diffusion between the surface and inner layer of Cu species of Pt20Pd20Cu60 catalysts at electrode potentials up to 1.2 V to understand their role towards stabilizing Pt20Pd20Cu60 catalysts. The results show there is a dynamic Cu surface composition range that is dictated by the interplay of the four processes, dissolution, deposition, diffusion from the surface to inner layer, and diffusion from the inner layer to the surface of Cu species, in the stability and observed oscillation of lattice constants of Cu-rich PtPdCu nanoalloys.

Genomic and transcriptomic analyses provide insights into valuable fatty acid biosynthesis and environmental adaptation of yellowhorn.

Yellowhorn (Xanthoceras sorbifolium) is an oil-bearing tree species growing naturally in poor soil. The kernel of yellowhorn contains valuable fatty acids like nervonic acid. However, the genetic basis underlying the biosynthesis of valued fatty acids and adaptation to harsh environments is mainly unexplored in yellowhorn. Here, we presented a haplotype-resolved chromosome-scale genome assembly of yellowhorn with the size of 490.44 Mb containing scaffold N50 of 34.27 Mb. Comparative genomics, in combination with transcriptome profiling analyses, showed that expansion of gene families like long-chain acyl-CoA synthetase and ankyrins contribute to yellowhorn fatty acid biosynthesis and defense against abiotic stresses, respectively. By integrating genomic and transcriptomic data of yellowhorn, we found that the transcription of 3-ketoacyl-CoA synthase gene XS04G00959 was consistent with the accumulation of nervonic and erucic acid biosynthesis, suggesting its critical regulatory roles in their biosynthesis. Collectively, these results enhance our understanding of the genetic basis underlying the biosynthesis of valuable fatty acids and adaptation to harsh environments in yellowhorn and provide foundations for its genetic improvement.

MicroRNA and Degradome Profiling Uncover Defense Response of Fraxinus velutina Torr. to Salt Stress.

Soil salinization is a major environmental problem that seriously threatens the sustainable development of regional ecosystems and local economies. Fraxinus velutina Torr. is an excellent salt-tolerant tree species, which is widely planted in the saline-alkaline soils in China. A growing body of evidence shows that microRNAs (miRNAs) play important roles in the defense response of plants to salt stress; however, how miRNAs in F. velutina exert anti-salt stress remains unclear. We previously identified two contrasting F. velutina cuttings clones, salt-tolerant (R7) and salt-sensitive (S4) and found that R7 exhibits higher salt tolerance than S4. To identify salt-responsive miRNAs and their target genes, the leaves and roots of R7 and S4 exposed to salt stress were subjected to miRNA and degradome sequencing analysis. The results showed that compared with S4, R7 showed 89 and 138 differentially expressed miRNAs in leaves and roots, respectively. Specifically, in R7 leaves, miR164d, miR171b/c, miR396a, and miR160g targeting NAC1, SCL22, GRF1, and ARF18, respectively, were involved in salt tolerance. In R7 roots, miR396a, miR156a/b, miR8175, miR319a/d, and miR393a targeting TGA2.3, SBP14, GR-RBP, TCP2/4, and TIR1, respectively, participated in salt stress responses. Taken together, the findings presented here revealed the key regulatory network of miRNAs in R7 responding to salt stress, thereby providing new insights into improving salt tolerance of F. velutina through miRNA manipulation.

Insights and Activation Energy Surface of the Dehydrogenation of C2 Hx O Species in Ethanol Oxidation Reaction on Ir(100).

Dehydrogenation of an organic compound is the first and the most fundamental elementary reaction in many organic reactions. In ethanol oxidation reaction (EOR) to form CO2 , there are a total of 46 pathways in C2 Hx O (x=1-6) species leading to the removal of all six hydrogen atoms in five C-H bonds and one O-H bond. To investigate the degree of dehydrogenation in EOR under operando conditions, we performed density function theory (DFT) calculations to study 28 dehydrogenation steps of C2 Hx O on Ir(100). An activation energy surface was then constructed and compared with that of the C-C bond cleavages to understand the importance of the degree of dehydrogenation in EOR. The results show that there are likely 28 dehydrogenations in EOR under fuel cell temperatures and the last two hydrogens in C2 H2 O are less likely cleaved. On the other hand, deep dehydrogenation including 45 dehydrogenations can occur under ethanol steam reforming conditions.

Genomic analyses provide insights into the evolution and salinity adaptation of halophyte Tamarix chinensis.

BACKGROUND: The woody halophyte Tamarix chinensis is a pioneer tree species in the coastal wetland ecosystem of northern China, exhibiting high resistance to salt stress. However, the genetic information underlying salt tolerance in T. chinensis remains to be seen. Here we present a genomic investigation of T. chinensis to elucidate the underlying mechanism of its high resistance to salinity. RESULTS: Using a combination of PacBio and high-throughput chromosome conformation capture data, a chromosome-level T. chinensis genome was assembled with a size of 1.32 Gb and scaffold N50 of 110.03 Mb. Genome evolution analyses revealed that T. chinensis significantly expanded families of HAT and LIMYB genes. Whole-genome and tandem duplications contributed to the expansion of genes associated with the salinity adaptation of T. chinensis. Transcriptome analyses were performed on root and shoot tissues during salt stress and recovery, and several hub genes responding to salt stress were identified. WRKY33/40, MPK3/4, and XBAT31 were critical in responding to salt stress during early exposure, while WRKY40, ZAT10, AHK4, IRX9, and CESA4/8 were involved in responding to salt stress during late stress and recovery. In addition, PER7/27/57/73 encoding class III peroxidase and MCM3/4/5/7 encoding DNA replication licensing factor maintained up/downregulation during salt stress and recovery stages. CONCLUSIONS: The results presented here reveal the genetic mechanisms underlying salt adaptation in T. chinensis, thus providing important genomic resources for evolutionary studies on tamarisk and plant salt tolerance genetic improvement.

Photoinduced charge-separated molecular probe for ultrasensitive spectrum analysis and rapid colorimetric detection of platinum ions.

Increased utilization of platinum ions in chemicals and drugs escalates environmental pollution and toxicity associated with Pt ions. However, current analysis and detection strategies of Pt ions display limited sensitivity due to the similar inert metal nature of platinum to gold. Herein, a photoinduced charge-separated molecule (MTPA)2Ab was synthesized as a probe for enhanced sensitive selection of Pt ions. Long-lived charge-separated states generated upon exposure to 365 nm light lead to a stable complex between (MTPA)2Ab and PtCl2/PtCl4 with highly-selectivity via sequential photoinduced electron transfers. Owing to the linear relationship of complex characteristic absorption and fluorescence emission intensities to Pt2+/Pt4+ concentrations, ultrasensitive spectrum analysis of Pt ions is achieved with a detection limit of 14.2 nM (2.8 ppb) for Pt2+ and 12.6 nM (2.5 ppb) for Pt4+ by an absorption spectrometer and 9.8 nM (1.9 ppb) for Pt ions (Pt2+/Pt4+) by a fluorescence spectrometer, far less than the reported values. Furthermore, a portable test box is developed based on (MTPA)2Ab test strips due to distinguishable color change with Pt2+/Pt4+ concentrations for rapid colorimetric detection of Pt ions. The results highlight the promise of photoinduced charge-separated molecular probe in ultrasensitive and rapid detection of Pt ions to overcome current limitations of detection strategies.

Impact of the degree of dehydrogenation in ethanol C-C bond cleavage on Ir(100).

A lack of comprehensive studies of the C-C bond cleavage in organic molecules hampers the rational design of catalysts for many applications, such as in fuel cells and steam reforming technologies. Employing ethanol on Ir(100) as an example, we studied 14 C-C bond cleavages of various species involved in the ethanol oxidation reaction using density functional theory calculations and used the degree of dehydrogenation (DoDH) of the reactant species as a variable to correlate the C-C bond cleavage barrier and reaction energy. This correlation method was also applied to the dehydrogenation reactions of ethanol on various catalysts, and great insight was obtained. The results show that the C-C cleavage barrier generally decreases with DoDH, with a local minimum around 33.3% DoDH. For reactants having more than 50% DoDH, the C-C cleavage is more ready to take place than the dehydrogenation and can occur at room temperature. Furthermore, the O atom in the reactive species plays a critical role in lowering the C-C bond cleavage barrier. The results provide necessary inputs for kinetic studies of ethanol reactions under operando conditions, where a reaction network beyond the minimum energy pathway is needed. The results will also serve as a benchmark for future studies of the ethanol C-C cleavage on other facets of Ir catalysts or on different catalysts. Furthermore, this work demonstrates that the proposed method opens up a new and effective way of correlating catalytic activities for the C-C bond cleavage involving long-chain alkanes and alcohols.

Systematically Deciphering the Pharmacological Mechanism of Fructus Aurantii via Network Pharmacology.

Fructus Aurantii (FA) is a traditional herbal medicine that has been widely used for thousands of years in China and possesses a variety of pharmacological effects. However, the active ingredients in FA and the potential mechanisms of its therapeutic effects have not been fully explored. Here, we applied a network pharmacology approach to explore the potential mechanisms of FA. We identified 5 active compounds from FA and a total of 209 potential targets to construct a protein-protein interaction (PPI) network. Prostaglandin G/H synthase 2 (PTGS2), heat shock protein 90 (HSP90), cell division protein kinase 6 (CDK6), caspase 3 (CASP3), apoptosis regulator Bcl-2 (Bcl-2), and matrix metalloproteinase-9 (MMP9) were identified as key targets of FA in the treatment of multiple diseases. Gene ontology (GO) enrichment demonstrated that FA was highly related to transcription initiation from RNA polymerase II promoter, DNA-templated transcription, positive regulation of transcription, regulation of apoptosis process, and regulation of cell proliferation. Various signaling pathways involved in the treatment of FA were identified, including pathways in cancer and pathways specifically related to prostate cancer, colorectal cancer, PI3K-Akt, apoptosis, and non-small-cell lung cancer. TP53, AKT1, caspase 3, MAPK3, PTGS2, and BAX/BCL2 were related key targets in the identified enriched pathways and the PPI network. In addition, our molecular docking results showed that the bioactive compounds in FA can tightly bind to most target proteins. This article reveals via network pharmacology research the possible mechanism(s) by which FA exerts its activities in the treatment of various diseases and lays a foundation for further experiments and the development of a rational clinical application of FA.

Alloying-realloying enabled high durability for Pt-Pd-3d-transition metal nanoparticle fuel cell catalysts.

Alloying noble metals with non-noble metals enables high activity while reducing the cost of electrocatalysts in fuel cells. However, under fuel cell operating conditions, state-of-the-art oxygen reduction reaction alloy catalysts either feature high atomic percentages of noble metals (>70%) with limited durability or show poor durability when lower percentages of noble metals (<50%) are used. Here, we demonstrate a highly-durable alloy catalyst derived by alloying PtPd (<50%) with 3d-transition metals (Cu, Ni or Co) in ternary compositions. The origin of the high durability is probed by in-situ/operando high-energy synchrotron X-ray diffraction coupled with pair distribution function analysis of atomic phase structures and strains, revealing an important role of realloying in the compressively-strained single-phase alloy state despite the occurrence of dealloying. The implication of the finding, a striking departure from previous perceptions of phase-segregated noble metal skin or complete dealloying of non-noble metals, is the fulfilling of the promise of alloy catalysts for mass commercialization of fuel cells.

Cause, Regulation and Utilization of Dye Aggregation in Dye-Sensitized Solar Cells.

As an important member of third generation solar cell, dye-sensitized solar cells (DSSCs) have the advantages of being low cost, having an easy fabrication process, utilizing rich raw materials and a high-power conversion efficiency (PCE), prompting nearly three decades as a research hotspot. Recently, increasing the photoelectric conversion efficiency of DSSCs has proven troublesome. Sensitizers, as the most important part, are no longer limited to molecular engineering, and the regulation of dye aggregation has become a widely held concern, especially in liquid DSSCs. This review first presents the operational mechanism of liquid and solid-state dye-sensitized solar cells, including the influencing factors of various parameters on device efficiency. Secondly, the mechanism of dye aggregation was explained by molecular exciton theory, and the influence of various factors on dye aggregation was summarized. We focused on a review of several methods for regulating dye aggregation in liquid and solid-state dye-sensitized solar cells, and the advantages and disadvantages of these methods were analyzed. In addition, the important application of quantum computational chemistry in the study of dye aggregation was introduced. Finally, an outlook was proposed that utilizing the advantages of dye aggregation by combining molecular engineering with dye aggregation regulation is a research direction to improve the performance of liquid DSSCs in the future. For solid-state dye-sensitized solar cells (ssDSSCs), the effects of solid electrolytes also need to be taken into account.

Surface-Mediated Interconnections of Nanoparticles in Cellulosic Fibrous Materials toward 3D Sensors.

Fibrous materials serve as an intriguing class of 3D materials to meet the growing demands for flexible, foldable, biocompatible, biodegradable, disposable, inexpensive, and wearable sensors and the rising desires for higher sensitivity, greater miniaturization, lower cost, and better wearability. The use of such materials for the creation of a fibrous sensor substrate that interfaces with a sensing film in 3D with the transducing electronics is however difficult by conventional photolithographic methods. Here, a highly effective pathway featuring surface-mediated interconnection (SMI) of metal nanoclusters (NCs) and nanoparticles (NPs) in fibrous materials at ambient conditions is demonstrated for fabricating fibrous sensor substrates or platforms. Bimodally distributed gold-copper alloy NCs and NPs are used as a model system to demonstrate the semiconductive-to-metallic conductivity transition, quantized capacitive charging, and anisotropic conductivity characteristics. Upon coupling SMI of NCs/NPs as electrically conductive microelectrodes and surface-mediated assembly (SMA) of the NCs/NPs as chemically sensitive interfaces, the resulting fibrous chemiresistors function as sensitive and selective sensors for gaseous and vaporous analytes. This new SMI-SMA strategy has significant implications for manufacturing high-performance fibrous platforms to meet the growing demands of the advanced multifunctional sensors and biosensors.

Exploiting singlet excited state conformation for rational design of highly efficient photoinduced electron transfer molecules.

In spite of the pivotal role of excited state electronic structures as regulation of photoinduced electron transfer (PET) process, the effect of excited state conformation on PET remains elusive. Here we exploit distinguishable emission characters of trans and cis singlet excited states of donor-acceptor-donor ensemble MTPAAZO to reveal that its PET efficiency and rate are closely depended on its singlet excited state conformation. The PET process occurs solely in cis conformation of MTPAAZO singlet excited states. Novel molecule (MTPA)2Ab as-designed with similar structure of MTPAAZO cis singlet excited states shows high PET efficacy and rate, leading to long-lived CS states. Our findings enable the rational design of the novel molecules with highly efficient PET process suitable for charge separation applications.

1,1'-Biaceanthrylene and 2,2'-Biaceanthrylene: Models for Linking Larger Polycyclic Aromatic Hydrocarbons via Five-Membered Rings.

We show that polycyclic aromatic hydrocarbon (PAH) chromophores that are linked between two five-membered rings can access planarized structures with reduced optical gaps and redox potentials. Two aceanthrylene chromophores were connected into dimer model systems with the chromophores either projected outward (2,2'-biaceanthrylene) or inward (1,1'-biaceanthrylene), and the optical and electronic properties were compared. Only the planar 2,2'-biaceanthrylene system showed significant reductions of the optical gaps (1 eV) and redox potentials in relation to the aceanthrylene monomer. Organic field effect transistors based on 2,2'-biaceanthrylene were prepared and were found to operate in the hole transport regime with an average charge carrier mobilities of 1.8 × 10-4 cm2 V-1 s-1.

Understanding deep dehydrogenation and cracking of n-butane on Ni(111) by a DFT study.

Steam reforming is a main industrial process for hydrogen production. In particular, with the carbon chain increasing to n-butane, a main component in liquefied petroleum gas (LPG) and shale oil gas, chemically different C-C bonds ((C-C)α,ß and (C-C)ß,ß') will be involved in cleavages. In addition, understanding the role of catalysis in these pathways is critical toward the advancement in technology, yet is largely lacking. As such, we have performed density functional theory (DFT) calculations to study the two possible C-C cleavage pathways of n-butane on Ni(111), i.e., the (C-C)α,ß cleavage from the n-butane deep dehydrogenation product of 1-butyne, and the (C-C)ß,ß' cleavage from 2-butyne. The results indicate that these two different pathways have distinct dehydrogenations to butyne, and that Ni is suitable for the deep dehydrogenation. The C-C cleavage in both pathways serves as the rate-determining step with a higher energy barrier than that for the preceding C-H bond cleavage. In addition, the 1-butyne pathway was found to be more favorable than that of 2-butyne in thermodynamics and kinetics. Our results provide insights into the alkane dehydrogenation and cracking of long-chain hydrocarbons on Ni-based catalysts.