Theoretical understanding of the effect of specifically adsorbed halide anions on Cu-catalyzed CO2 electroreduction activity and product selectivity.

Initial CO2 electroreduction into CO and its subsequent electroreduction pathways were selected to study the effect of specifically adsorbed halide anions X- (X = F, Cl, Br, I) on CO2 electroreduction activity and product selectivity at Cu(111)/H2O interfaces via DFT calculations. The calculated results show that the presence of halide anions can exert a notable effect on the CO2 adsorption characteristics and that chemically adsorbed CO2 molecules can be formed. Furthermore, the halide-anion-modified Cu(111)/H2O interfaces could significantly enhance the initial CO2 electroreduction into CO activity, which is regarded as the rate-determining step during CO2 electroreduction at clean Cu(111)/H2O interfaces. Analysis of the initial CO2 electroreduction and Volmer reaction pathways showed that the halide-anion-modified Cu(111)/H2O interfaces could suppress the HER and thus improve the CO2 electroreduction activity and product selectivity. It is speculated that the enhanced initial CO2 electroreduction activity at the F--, Cl--, Br--, and I--modified Cu(111)/H2O interfaces may originate from the decreased work functions and anion radical ·CO2- formations. Simultaneously, we concluded that dimer OCCO formations in the presence of halide anions were more favorable than CHO during CO electroreduction according to the order of I- > Br- > Cl- > F- and could result in the production of C2 product, suggesting an improved CO2 electroreduction product selectivity. The present analyses of electronic structure may explain the more favorable OCCO formations in the order of I- > Br- > Cl- > F-. The present understanding of this effect will provide an improved scientific guideline for the control of CO2 electroreduction pathways and design of more efficient electrocatalysts.

Exploring the inhibition mechanism of SARS-CoV-2 main protease by ebselen: A molecular docking, molecular dynamics simulation and DFT approach.

The main protease (Mpro) of SARS-CoV-2 plays an essential role in the virus life cycle and is considered a key target for therapeutic development. This study explores the inhibition mechanism of SARS-CoV-2 Mpro by ebselen, an organoselenium drug that shows potent inhibitory activity. By using a combination of multiple computational methods including molecular docking, molecular dynamics simulations, and density functional theory calculations, the complete covalent inhibition process of ebselen is simulated for the first time. Two possible pathways with different bound conformations of ebselen are identified. The hydrolysis of the enzyme-ebselen adduct is found to be the rate-determining step. The simulation results show that the behavior of water molecules at the hydrolysis site is crucial to distinguish the two paths energetically. Our simulations, which are in agreement with existing experimental results, provide a theoretical basis for the rational design and mechanism exploration of ebselen-based inhibitors.

Theoretical Insights into Potential-Dependent C-C Bond Formation Mechanisms during CO2 Electroreduction into C2 Products on Cu(100) at Simulated Electrochemical Interfaces.

An improved CO coverage-dependent electrochemical interface model with an explicit solvent effect on Cu(100) is presented in this paper, by which theoretical insights into the potential-dependent C-C bond formation pathways occurring in CO2 electrochemical reduction to C2 products can be obtained. Our present studies indicate that CHO is a crucial intermediate toward C1 products on Cu(111), and dimer OCCO is found to not be a viable species for the production of C2 products on Cu(100). The reaction pathway of CHO with CO and CHO dimerization into dimers COCHO and CHOCHO may be C-C bond formation mechanisms at low overpotential. However, at medium overpotential, C-C bond coupling takes place preferentially through the reaction of COH with CO species and COH dimerization into dimers COCOH and COHCOH. The formed dimers COCHO, CHOCOH, and CHOCHO via reactions of CHO with CO, COH, and CHO species may lead to C2 products, which are regarded as C-C bond formation mechanisms at high overpotential. The difference of obtained adsorption isotherms of CO on Cu(100) with that of Cu(111) may be able to explain the effect of the crystal face of Cu on product selectivity. The excellent consistencies between our present obtained conclusions and the available experimental reports and partial theoretical studies validate the reasonability of the present employed methodology, which can be also used to systematically study potential-dependent CO2 electroreduction pathways toward C2 products on Cu(100) or other metal catalysts.

Anticancer activity, topoisomerase I inhibition, DNA 'light switch' behavior and molecular docking of two ruthenium complexes containing phenazine ring.

Ruthenium(II) complexes containing phenazine ring have attracted attention to design as 'molecular light switches'. In this study, we synthesized two ruthenium complexes containing phenazine ring and studied their abilities to function as DNA intercalators, DNA 'light switches', DNA topo I inhibitors, DNA photocleavers and potential antitumor reagents. [Ru(bpy)2(mbipz)](PF6)2 (1) (bpy = 2,2'-bipyridine, mbipz = 2-(4'-methyl-bipyridine-4-yl)-1H-imidazo[4,5-b]phenazine) exhibited off-on type DNA 'light swtich' behavior. DNA binding modes of the two complexes were determined as intercalation by using UV-vis spectra, emission spectra, viscosity and molecular docking experiments. DNA photocleavage experimental results showed that the two ruthenium complexes effectively cleave plasmid DNA by producing singlet oxygen. Furthermore, they displayed good topo I inhibition activities. We further found that the two complexes displayed good antitumor activities against Eca-109 cells and A549 cells. The results demonstrated that introduction of phenazine ring will be helpful to design DNA 'light switch' based on ruthenium complex.Communicated by Ramaswamy H. Sarma.

Theoretical insights into the electroreduction mechanism of N2 to NH3 from an improved Au(111)/H2O interface model.

An improved H coverage-dependent Au(111)/H2O electrochemical interface model is proposed in this paper, which is firstly used to study electroreduction mechanisms of N2 into NH3 at the thermodynamical equilibrium potential in cooperation with electronic structure analysis. The results show that the associative mechanism is more favorable on Au(111) and therein alternating and distal pathways may be able to parallelly occur in gas phase and the present simulated electrochemical interface. The initial N2 reduction into the N2H intermediate is the rate determining step, which may be able to be regarded as the origin of the observed experimentally high overpotential during N2 electroreduction. The presence of an electrochemical environment can significantly change the N2 reduction pathway and decrease the barrier of the rate determining step, which can be ascribed to the significant electron accumulation and interaction between N2 molecules and H2O clusters. The theoretical results display excellent consistency with the available experimental data, confirming the rationality of the present proposed electrochemical model. The comparison of the barrier between the hydrogen evolution reaction and rate determining step well explains why the activity of Au electrodes is usually unsatisfactory. Accordingly, a single descriptor can be proposed, in which an ideal electrocatalyst should be able to reduce the barrier for initial N2 electroreduction into N2H. In this way, N2 electroreduction pathways can be facilitated and the yield of NH3 can be enhanced. We believe that the present study can represent progress to study N2 electroreduction mechanisms from an improved electrochemical model.

Density Functional Studies on Photophysical Properties of Boron-Pyridyl-Imino-Isoindoline Dyes: Effect of the Fusion.

In this work, to make out the aryl-fusion effect on the photophysical properties of boron-pyridyl-imino-isoindoline dyes, compounds 1-5 were theoretically studied through analyses of their geometric and electronic structures, optical properties, transport abilities, and radiative (k r) and non-radiative decay rate (k nr) constants. The highest occupied molecular orbitals of aryl-fused compounds 2-5 are higher owing to the extended conjugation. Interestingly, aryl fusion in pyridyl increases the lowest unoccupied molecular orbital (LUMO) level, while isoindoline decreases the LUMO level; thus, 4 and 5 with aryl fusion both in pyridyl and isoindoline exhibit a similar LUMO to 1. Compounds 4 and 5 show relatively low ionization potentials and high electron affinities, suggesting a better ability to inject holes and electrons. Importantly, the aryl fusion is conducive to the decrease of k IC. The designed compound 5 exhibits a red-shifted emission maximum, low λh, and low k IC, which endow it with great potential for applications in organic electronics. Our investigation provides an in-depth understanding of the aryl-fusion effect on boron-pyridyl-imino-isoindoline dyes at molecular levels and demonstrates that it is achievable.

Mechanistic insights into potential dependence of CO electrochemical reduction into C1 products based on a H coverage-dependent Cu(111)/H2O interface model.

A H coverage-dependent Cu(111)/H2O interface model incorporated with electronic structure analysis is employed to investigate the potential dependence of CO electroreduction into C1 products with the aim of solving the long dispute over CO2 electrocatalytic reduction mechanisms. The results indicate that CH4 formation mainly proceeds through CO, CHO, CH2O, CH2OH and CHx (x = 2 and 3) species at various applied potentials. CH3OH may be formed via a CH3O intermediate at high overpotential and the present study can confirm that CH3OH is only produced in a trace amount as detected in experiments. The high overpotential results in the formation of CH4, explaining the experimentally required high overpotential on Cu. The calculated energetics concludes that CO electroreduction into CHO may be a potential-limiting step, being regarded as the origin of the required high overpotentials for CO2 electroreduction in this paper. The electronic structure calculations show that more electronic transfer to the adsorbed H atoms occurs with increasing H coverage, which can be considered as the origin of the more negative electrode potentials. Interestingly, it is observed that the s orbital of the C atom in the valence shell of the adsorbed CO molecule gains more and more electrons, whereas the s orbital of the O atom gains less and less electrons, and even loses electrons with increasing H coverage, implying easier and easier proton transfer towards the C-center site. Thus, the easier occurrence of CO electroreduction may be ascribed to the more electron transfer into the s orbital of the C atom at high overpotential. We believe that the present study represents theoretical progress to systematically study potential-dependent CO2 electroreduction mechanisms on Cu electrodes.

Effect of Multidonor and Insertion Position of a Chromophore on the Photovoltaic Properties of Phenoxazine Dyes.

Research and development of new organic semiconductor materials can never be terminated because any structural fine-tuning may result in an important impact on its application performance, although the effect may be negative in many cases. Herein, we designed and synthesized a series of phenoxazine-based dyes, YH1, YH2, YH3, and YH4, whose absorption spectrum, electrochemical cyclic voltammetry, theoretical calculation, dye-sensitized solar cell photovoltaic characteristics, and electrochemical AC impedance are used to analyze the photophysical, electrochemical, and photovoltaic performance of the materials, aiming to study the effect of multidonor and adjustment of the chromophore insertion position on their photovoltaic performance. When donor triphenylamine is added at the end of YH1 and YH3, the absorption spectrum and photovoltaic performance of dyes YH2 and YH4 improved a little. The improvement is much greater when the chromophore (ethylenedioxy)thiophene in YH1 and YH2 is adjusted and inserted on the other side of phenoxazine and the energy conversion efficiencies (photon-to-current conversion efficiency) of the resulting dyes YH3 and YH4 reach 8.02 and 8.97%, respectively, which are 23 and 25% higher than those of YH1 and YH2, respectively. Although the improvement may be because of factors such as the dihedral angle, the result will undoubtedly provide some reference for the future study of the relationship between the structure and performance of organic dyes.

Photovoltaic Performance of 4,8-Bis(2'-ethylhexylthiophene)thieno[2,3-f]benzofuran-Based Dyes Fabricated with Different Donors in Dye-Sensitized Solar Cells.

Thieno[2,3-f]benzofuran (BDF) has the advantages of a highly planarized structure, strong electron-donating ability, high hole mobility, good conjugation, and a wide spectral response range. In recent years, BDF has been widely used in organic solar cells, especially in bulk-heterojunction (BHJ) organic solar cells. In this work, a model molecule PSB-1 was synthesized based on this highly planar fragment and used as a photosensitizer in dye-sensitized solar cells (DSCs), then different aromatic amine donors such as triphenylamine (TPA), carbazole (CZ), and phenothiazine (PTZ) were introduced to the end of PSB-1, and a series of dyes PSB-2, PSB-3, and PSB-4 were designed and synthesized. After that, the relationship among the molecular structure, energy level, and photovoltaic performance of the benzo-[1,2-b:4,5-b']dithiophene (BDT) dye was studied by theoretical calculations, photophysics, electrochemistry, and photovoltaic properties. The results show that the introduction of a strong donor can effectively improve the energy level, absorption spectrum, and photovoltaic performance of PSB-1. Through the preliminary test, we found that the energy conversion efficiency (photovoltaic conversion efficiency-PCE) of PSB-4 is up to 5.5%, which is nearly 90% higher than that of PSB-1 (PCE = 2.9%), while the introduction of a weak donor greatly weakens the effect, in which the PCE of PSB-3 is 3.5%, which is only 20% higher than that of the model molecule. By an analysis of the molecular frontier orbital distribution using theoretical calculations, we found that the electron cloud of the highest occupied orbital level (highest occupied molecular orbital-HOMO) of PSB-3 is mainly distributed on the BDF group so that the electron transfer of excited-state molecules mainly occurs from the BDF to the receptor (CA).

A novel pyridinium-based fluorescent probe for ratiometric detection of peroxynitrite in mitochondria.

Peroxynitrite (ONOO-) is a primary kind of reactive oxygen species. Excessive ONOO- can induce oxidative damage to biomolecules and further results in various diseases. So, quantitative monitoring ONOO- with excellent selectivity and sensitivity is imperative for elucidating its role in biological processes. In this study, a novel pyridinium fluorescent ONOO- probe (CPC) has been constructed base on ICT-modulated by combining coumarin fluorophore and diphenylphosphinate recognition group. The fluorescence response of CPC for ONOO- is realized via the removal of diphenylphosphinate group. The probe CPC shows prominent features for detection of ONOO- including fast response rate (within 3 min), excellent selectivity and sensitivity, distinct colorimetric (red to green), and a large emission wavelength shift (105 nm). The emission intensity ration (I538/I643) exhibits 153-fold enhancement along with the increasing ONOO- and the detection limit is as low as 1.60 × 10-8 M. These good response properties make CPC possible to quantitative detection of ONOO- concentration. By using the strategy, the ratiometric CPC has been employed to detection of mitochondrial ONOO- in live cell successfully.

Nitro-Substituted Ruthenium(II) Complex: A New Strategy for a G-Quadruplex DNA Fluorescent Probe.

A new strategy for a G-quadruplex fluorescent probe based on a nitro-substituted ruthenium complex is described. G-quadruplex DNA can be distinguished from double- or single-strand DNA by the naked eye. This ability originates from variation of the degree of protection of the nitro group on the complex from water by G-quadruplex and other structure DNAs.

An in Situ Template for the Synthesis of Tunable Hollow Carbon Particles for High-Performance Lithium-Sulfur Batteries.

Nanostructured materials with hollow interior voids are gaining great attention due to their fantastic geometries and unique physicochemical properties competent for many applications. However, the development of a fast approach to prepare the hollow structured particles remains challenging. Herein, a new and efficient in situ hard-template method was developed to synthesize hollow carbon nano- and microparticles using the as-prepared SiO2 particles as a hard template directly, without any separation, drying, or redispersion. In this way, the hollow carbon particles with tunable diameters and shell thickness can be synthesized readily, which is simpler and more efficient than the traditional ones. In addition, the universality of this strategy allows us to study the different behaviors of hollow carbon particles in lithium-sulfur batteries when the architectures of hollow particles (i.e., diameter, shell thickness, etc.) were changed. We believe that this in situ method is applicable for synthesizing other core-shell or hollow structured materials (e.g., metal oxide), and also, the high performance of hollow carbon particles in lithium-sulfur batteries and beyond can be further explored.

Electrochemical Polymerization-Fabricated Several Triphenylamine-Carbazolyl-Based Polymers with Improved Short-Circuit Current and High Adsorption Stability in Dye-Sensitized Solar Cells.

Polymer dyes have many potential advantages, such as high molecular weight, better light capture ability, thermal stability, film-forming ability, light resistance, and electrochemical corrosion resistance. They are expected to provide opportunities for the development of high-stability dye-sensitized solar cells (DSCs). However, polymer DSCs (PDSCs) have poor short-circuit current and filling factor (FF) due to polymer aggregation and chain-winding effect. Therefore, the energy conversion efficiency is low. In this work, we are trying to find a way to solve this problem. Herein, three polymers, polyPAC-01, polyPAC-02, and polyPAC-03 with different π-bridge chains were prepared on a titanium dioxide electrode using an "adsorption first, then electropolymerization (EP)" process. Meanwhile, as a comparison, three oligomers, PAC-01, PAC-02, and PAC-03 with the same skeleton were synthesized by the Suzuki coupling reaction and fabricated on a titanium dioxide electrode with a "first polymerization, then adsorption" process. Then, the photoanode adsorbed by those polymers or oligomers were applied to DSCs. The results show that polymers prepared by the EP method obtained a higher short-circuit (J sc) increase, exceeding 30% and a FF increase of about 10%, and finally, the photo-to-electric conversion efficiency (PCE) increased exceeding 40%, compared to the oligomers. In addition, desorption experiments in a harsh environment show that the EP method-synthesized polymers (polyPAC-03 as a representative) have better solvent resistance and adsorption stability than the corresponding oligomers (PAC-03). The results show that the process of "adsorption first, then EP" may be an effective way to solve the bottlenecks of low energy conversion efficiency on PDSCs and provide a new way to develop stable and efficient DSCs.

Mechanistic study on Cu-catalyzed CO2 electroreduction into CH4 at simulated low overpotentials based on an improved electrochemical model.

An improved CO coverage-dependent electrochemical model with explicit relaxed H2O molecules used in CO2 electroreduction is presented, which is firstly applied to Cu-catalyzed CO2 electroreduction into CH4 production at low overpotentials in this paper. The results show that the present defined CH2O and CHOH pathways via common intermediates CHO and CH2 may be able to occur parallelly at the present simulated low overpotential. The potential-limiting steps may be the formation of CO and its further electroreduction into CHO, which are considered as the origin of the observed experimentally high overpotential. The present study also explains why at electrochemical interfaces, only CH4 is observed experimentally on the Cu surface rather than CH3OH. The present results are found to be in excellent agreement with the available experimental data and partial theoretical analysis, further validating the rationality of the present employed methodology.

A lysosome targetable fluorescent probe for palladium species detection base on an ESIPT phthalimide derivative.

A novel lysosome-targetable phthalimide fluorescent probe was designed for detecting palladium based on ESIPT for signal transduction. The fluorescent probe conjugating with allylcarbamate displayed weak fluorescent due to the ESIPT process hinder by allylcarbamate. But with the addition of palladium, the ESIPT emission was recovery though the palladium-catalyzed deallylation reaction and the fluorescence intensity exhibited 40-fold enhancement at 511 nm. In addition, the probe showed excellent selectivity, high sensitivity, fast responds and low limit detection for palladium with a larger Stoke-shift. Moreover, the targetable probe was also successfully applied for detecting palladium in lysosomes of living cells. Hence, the probe though ESIPT modulation is a promising for monitoring palladium in practical samples.

Study on DNA binding behavior and light switch effect of new coumarin-derived Ru(II) complexes.

A new ligand mhcip (mhcip=2-(4-methyl-7-hydroxyl-8-coumarinyl)imidazo[4,5-f]-[1,10]phenanthroline) and its ruthenium complexes, [Ru(L)2mhcip](2+) (L=bpy (2,2'-bipyridine), phen (1,10-phenanthroline)), have been synthesized and characterized. The introduction of coumarin ring may play an important role in the strong fluorescence of the complexes. Intercalative binding mode between both complexes and CT-DNA was determined by UV-visible spectroscopy, fluorescence spectroscopy and viscosity measurements. The two complexes show efficient DNA photocleavage under irradiation at 365 nm. The cycling of light switch off and on has been achieved for both complexes through the introduction of Cu(2+) and EDTA in the absence or presence of DNA.

Luminescence properties of Tb(3+)-doped borosilicate scintillating glass under UV excitation.

Transparent Li2O-BaO-La2O3-Al2O3-B2O3-SiO2 glasses doped with Tb(3+) ion were prepared by high temperature melting method. Luminescence properties of Tb(3+)-doped borosilicate glasses have been investigated by transmission, excitation, emission and luminescence decay measurements. The transmission spectrum shows the glass has good transmittance in the visible region. Under the 236 nm UV excitation the intense green emission from (5)D4 level is observed in Tb(3+)-doped borosilicate glass, comparable in intensity to the violet-blue emission starting from the (5)D3 level. The green emission intensity of Tb(3+) ion firstly increases and then decreases with the decreasing B2O3/SiO2 ratio in glass matrix. (5)D4→(7)FJ (J=6, 5, 4 and 3) transitions of Tb(3+) ion in borosilicate glass are greatly enhanced with increasing concentration of Tb(3+) through the cross relaxation [Tb(3+) ((5)D3)+Tb(3+) ((7)F6)→Tb(3+) ((5)D4)+Tb(3+) ((7)F0)] between two Tb(3+) ions. Luminescence decay time of 2.13 ms is obtained for the emission transitions starting from (5)D4 level in 2.5Li2O-20BaO-20La2O3-2.5Al2O3-20B2O3-35SiO2-0.5Tb4O7 glass. The results show that Tb(3+)-doped borosilicate glasses would be potential candidates for scintillating material for static X-ray imaging.

DNA-binding, photocleavage studies of ruthenium(II) complexes with 2-(2-quinolinyl) imidazo[4,5-f][1,10]phenanthroline.

Two new ruthenium complexes with [Ru(L)(2)(qip)](2+) (L=bpy (2,2'- bipyridine), phen (1,10-phenanthroline); qip=2-(2-quinolinyl)imidazo[4,5-f][1,10]phenanthroline), have been synthesized and characterized by elemental analysis, ES-MS, (1)H NMR. The binding properties of two complexes towards CT-DNA were investigated by various optical methods and viscosity measurements. The experiment results suggested that both Ru(II) complexes can intercalate into DNA base pairs. Strong quenching in emission intensity of two Ru(II) complexes were observed upon addition of Ag(+) in the absence and presence of CT-DNA. Furthermore, the two complexes can promote cleavage of pBR322 DNA under irradiation at 365 nm, and complex 2 exhibits a stronger DNA-photocleavage efficiency than complex 1. The mechanism of DNA cleavage suggests that singlet oxygen ((1)O(2)) is likely to be the cleaving agent.

DNA-binding and photocleavage studies of ruthenium(II) complexes containing asymmetric intercalative ligand.

A novel asymmetric ligand 2-(pyridine-2-yl)-1-H-imidazo[4,5-i]dibenzo[2,3-a:2',3'-c]phenazine (pidbp) and its ruthenium complexes [Ru(L)(2)(pidbp)](2+) (L=bpy (2, 2'- bipyridine), phen (1, 10 - phenanthroline)), have been synthesized and characterized by elemental analysis, ES-MS, (1)H NMR. Various methods support the conclusion that both Ru(II) complexes can intercalate into DNA base pairs. Complex [Ru(bpy)(2)(pidbp)](2+)4 exhibits its DNA "molecular light switch" properties. Furthermore, the two complexes are efficient DNA-photocleavers under irradiation at 365 nm, and complex 5 exhibits a stronger DNA-photocleavage efficiency than complex 4. The mechanism of DNA cleavage is an oxidative process by generating singlet oxygen.

N,N'-Bis(pyridin-3-yl)terephthalamide-terephthalic acid (1/1).

In the title compound, C(18)H(14)N(4)O(2)·C(8)H(6)O(4), both types of mol-ecule lie on inversion centers. In the N,N'-bis-(pyridin-3-yl)terephthalamide mol-ecule, the pyridine ring forms a dihedral angle of 11.33 (9)° with the central benzene ring. In the crystal, N-H⋯O and O-H⋯N hydrogen bonds connect the components into a three-dimensional network.