Nano/microscale order affects the early stages of biofilm formation on metal surfaces

The adhesion of Pseudomonas fluorescens was studied on nano/microengineered surfaces. Results show that these bacteria formed well-defined aggregates on randomly oriented nanosized granular gold substrates. These aggregates consist of aligned ensembles of bacteria, with some of them strongly elongated. This kind of biological structure was not found on ordered engineered surfaces because bacterial alignment and cell-to-cell sticking were hindered. Importantly, differences in cell morphology, length, orientation, and flagellation were observed between bacteria attached on the ordered nano/microstructures and the randomly ordered surfaces. The implications of the results are related to the design of engineered surfaces to enhance (nanostructured filters) or inhibit (medical implants and industrial biofouling) bacterial colonization on the surfaces and to the biocontrol of soil ecosystems.     

Insights into the photocatalytic mechanism of the C4N/MoS2 heterostructure: A first-principle study

Constructing heterostructures by combining COFs and TMD is a new strategy to design efficient photocatalysts for CO₂ reduction reaction (CO₂RR) due to their good stability, tunable band gaps and efficient charge separation. Based on the synthesis of completely novel C₄N−COF in our previous reported work, a new C₄N/MoS₂ heterostructure was constructed and then the related structural, electronic and optical properties were also studied using first principle calculations. The interlayer coupling effect and charge transfer between the C₄N and MoS₂ layer are systematically illuminated. The reduced band gap of the C₄N/MoS₂ heterostructure is beneficial to absorb more visible light. For the formation of type-II band alignment, a built-in electric field appears which separates the photogenerated electrons and holes into different layers efficiently and produces redox active sites. The band alignment of the heterostructure ensures its photocatalytic activities of the whole CO₂ reduction reaction. Furthermore, the charge density difference and charge carrier mobility confirm the existence of the built-in electric field at the interface of the C₄N/MoS₂ heterostructure directly. Finally, the high optical absorption indicates it is an efficient visible light harvesting photocatalyst. Therefore, this work could provide strong insights into the internal mechanism and high photocatalytic activity of the C₄N/MoS₂ heterostructure and offer guiding of designing and synthesizing COF/TMD heterostructure photocatalysts.     

Kinetics of the formation of silver dimers: early stages in the formation of silver nanoparticles

Silver clusters too small to support a plasmon band possess interesting fluorescence properties as well as being a convenient route to studying the early stages of nanoparticle formation. Fluorescent silver clusters are synthesized in toluene solution, and the formation is monitored herein by laser flash photolysis (LFP). Kinetic analysis of the formation of the Ag clusters is consistent with the formation of the smallest possible clusters, silver dimers (Ag(2)), whereby a mechanism for the formation of these clusters is provided as well as the first reported extinction coefficient and association constant for Ag(0) to form Ag(2). The formation of Ag(2) clusters is contrasted with the formation of Ag nanoparticles in aqueous media, and the particular stability and selectivity toward Ag(2) in this system is also studied using LFP.     

Initial stages of the formation of the structure of metal hydroxides

Based on the data for the initial stage of aging of metal hydroxides that exhibit nitrogen fixation properties and the exact solution of the model kinetic problem for the association of aqua and hydroxo complexes, the regularities of the formation of the structure of primary amorphous particles of metal hydroxides have been revealed. The primary particles consist of chain hydroxo polymers that containca. 10 units and are chemically bound to each other by ₃-OH bridging groups in sites at chaotically arranged intersections.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 12, pp. 2852–2857, December, 1996. 1996.     

Insights into photodissociation dynamics of benzamide and formanilide from ab initio calculations

In the present study, the five lowest electronic states that control the UV photodissociation of formanilide and benzamide have been characterized using the complete active space self-consistent field theory. The mechanisms for the initial relaxation and subsequent dissociation processes have been determined on the basis of the calculated potential energy surfaces and their intersections. It was found that the S(1)/T(1)/T(2) three-surface intersection plays an important role in the photodissociation processes of benzamide. However, the dissociation behavior of formanilide and benzamide was found to be quite different from that for aliphatic amides. The present study provides several insights into the photodissociation dynamics of formanilide and benzamide.     

O掺杂MgF2电子结构和光学性质的第一性原理研究

基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了O原子不同比例(12.5％,8.33％和6.25％)掺杂MgF2晶体的几何结构、电子结构和光学性质.通过对比发现,由于O原子的掺入,体系的禁带宽度减小,材料呈现半金属性.计算也表明,O掺杂对静态介电常数和光吸收系数有重要调制作用,同时也给出了体系性质变化的...     

Investigations into sulfobetaine-stabilized Cu nanoparticle formation: toward development of a microfluidic synthesis

The mechanistic aspects of the formation of sulfobetaine-stabilized copper nanoparticles were investigated by using in situ XANES (X-ray absorption near edge structure), UV-vis spectroscopy, and reaction calorimetry. The tetracoordinated sulfobetaine-Cu(II) complex was reduced to a stable sulfobetaine-Cu(I) complex prior to the formation of sulfobetaine-stabilized copper nanoparticles. The stability of the Cu(I) complex was found to be sensitive to the concentration of the sulfobetaine stabilizer and the addition rate of the reducing agent. It appears to exist primarily as a linear complex. A tetracoordinated Cu(I) complex as an intermediate has also been postulated. Based on the understanding from these investigations, a microfluidic process for copper nanoparticle synthesis was designed by using sulfobetaine-Cu(I) complex as the starting material. When compared with the copper nanoparticles synthesized by a conventional batch process, the microfluidic reactor process provided particles with a smaller size and narrower size distribution. The copper nanoparticles from the microreactor process could also be more easily purified and the particles were relatively stable in air. Both XRD and SAED indicated that the Cu nanoparticles synthesized have fcc structure.     

Insights into dynamics of the S2 state of thiophosgene from ab initio calculations

The S2 potential energy surface for Cl2CS dissociation has been characterized with a combined complete active space self-consistent field and multireference configuration interaction method. The S3/S2 minimum-energy intersection has been determined with the state-averaged complete active space self-consistent field method. The S2 direct dissociation was found to have a barrier of 6.0 kcal/mol, leading to formation of Cl(X2P)+ClCS(A2A") in the excited electronic state. Dynamics of the S2 state of Cl2CS can be summarized as follows: (1) The S2-S0 fluorescence occurs with high quantum yield at low excess energies; (2) Both the S(2) dissociation and the S2-->S3 internal conversion cause the loss of the S2-S0 fluorescence upon photoexcitation at 235-253 nm; (3) The S2-->S3 internal conversion (IC) followed by the direct IC to the ground electronic state results in the fragments produced in the ground state, while the S2 dissociation leads to formation of the fragments in excited electronic states.     

Insights into the Mechanism of BN Generation via Boron Triazide Precursor: Theoretical Study

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Insights into the mechanism of BN generation via boron triazide precursor: theoretical study

Potential-energy surfaces for unimolecular decomposition of B(N3)(3) have been studied to understand the possible mechanism for BN generation. The decomposition of B(N3)(3) takes place on either the singlet and triplet surface, and both processes are high exothermic and obey sequential mechanisms. For the singlet reaction, the rate-determining step corresponds to cleavage of the first azide bond and linear (1)NBNN instead of (1)BN was suggested as the dominant product at room temperature. For the triplet surface, a fragment process from (3)BN(7) to (3)BN(5) is predicted to be the rate-determining step; once this barrier is counteracted, the subsequent decomposition processes could easily occur to form final product (3)BN. In addition, the possible mechanism for generating BN film via B(N3)(3) was discussed based on MC-SCF calculation results. These findings might be helpful in understanding the controllable decomposition of B(N3)(3) as well as its application in generating BN films.     

Growth versus cyclization in the early stages of the polycondensation of metal alkoxides

The early steps of the polycondensation of transition metal alkoxide have been studied from the chemical and structural points of view. Polyoxoalkoxides are described like macromolecules by the composition of the repeating unit, the degree of polymerization (N), and the radius of gyration (R). The fraction p of binding sites of the coordination sphere of the metal centers occupied by terminal ligands determines N as follows: N proportional, variant pdf (dA-df), where df is the fractal dimension and dA is defined by Np proportional, variant RdA. This approach addresses difficulties raised by both coordinative unsaturation and cyclization in the modelization of the polycondensation of metal alkoxides. The coordinative unsaturation is accounted for by a particularly small value of dA= 1 in the very early steps, while the cyclization frequency is measured by the difference dA-df. This difference is not constant along the polycondensation process, and its dependence on the extent of reaction provides clues for understanding the high apparent kinetics order of gelation often reported in the literature.     

Experimental probes of silver metal nanoparticle formation kinetics: Comparing indirect versus more direct methods

The kinetics of noble metal nanoparticle formation in bottom-up syntheses are important for controlling and optimizing these methods. Hence, experimental probes that are easily accessible to most laboratories are also of interest. We collected kinetic curves for the formation of silver nanoparticles in a modified Turkevich method with citrate acting as the reducing and stabilizing agent by (i) measuring the change in silver nanoparticle surface plasmon resonance by UV-visible spectroscopy, a somewhat indirect method, and then also by (ii) measuring the change in silver ion concentration by ion-selective electrode potentiometry and/or atomic absorption spectroscopy, two more direct methods. The resulting sigmoidal kinetic curves were curvefitted with the Finke-Watzky two-step kinetic model of slow, continuous nucleation and fast autocatalytic growth to extract average rate constants. We found that the kinetic curves obtained by following the change in silver ion concentration were apparent mirror images of those constructed by following the change in nanoparticle surface plasmon resonance, and that their respective curvefits displayed the same sigmoidal characteristics. The resultant values of the rate constants for nucleation and growth overlapped within experimental error between the methods and showed similar trends over the range of citrate concentrations studied. The use of multiple probes in this work to follow the kinetics of nanoparticle formation helps fill a need for the comparison and evaluation of different methods available to scientists, particularly those considered easily accessible.     

Two-dimensional polymer formation on surfaces: insight into the roles of precursor mobility and reactivity

We report on a combined scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) study on the surface-assisted assembly of the hexaiodo-substituted macrocycle cyclohexa-m-phenylene (CHP) toward covalently bonded polyphenylene networks on Cu(111), Au(111), and Ag(111) surfaces. STM and XPS indicate room temperature dehalogenation of CHP on either surface, leading to surface-stabilized CHP radicals (CHPRs) and coadsorbed iodine. Subsequent covalent intermolecular bond formation between CHPRs is thermally activated and is found to proceed at different temperatures on the three coinage metals. The resulting polyphenylene networks differ significantly in morphology on the three substrates: On Cu, the networks are dominated by "open" branched structures, on the Au surface a mixture of branched and small domains of compact network clusters are observed, and highly ordered and dense polyphenylene networks form on the Ag surface. Ab initio DFT calculations allow one to elucidate the diffusion and coupling mechanisms of CHPRs on the Cu(111) and Ag(111) surfaces. On Cu, the energy barrier for diffusion is significantly higher than the one for covalent intermolecular bond formation, whereas on Ag the reverse relation holds. By using a Monte Carlo simulation, we show that different balances between diffusion and intermolecular coupling determine the observed branched and compact polyphenylene networks on the Cu and Ag surface, respectively, demonstrating that the choice of the substrate plays a crucial role in the formation of two-dimensional polymers.     

Insights into the structure of cyclohexane from femtosecond degenerate four-wave mixing spectroscopy and ab initio calculations

In this paper, we report the use of femtosecond time-resolved degenerate four-wave mixing rotationally resolved spectroscopy to obtain very accurate structural information on the symmetric top cyclohexane. Apart from highlighting the versatility of this method in determining accurate structures of large and complex molecules without dipole moment, the present study also details the comparison of the experimentally determined rotational constant B(0) with that obtained from high-level ab initio calculations. The theoretical calculations, which were carried out at both the second-order M?ller-Plesset (MP2) and coupled-cluster with single, double, and perturbative triple substitutions [CCSD(T)] levels of theory, also take into account vibrational averaging effects. A detailed investigation of the vibrational averaging effects reveals that the corrections emerge from only the six highly symmetric A(1g) modes, a justification of which is provided by an analysis of these modes.     

Effect of metal complex formation on the antibacterial activity of nitazoxanide: Spectroscopic and density functional theory calculations

In the present work, experimental and theoretical structural studies of two new nitazoxanide (NTZ) complexes, [Co(NTZ)(NO₃)₂(OH₂)] ( 1 ) and [Ni(NTZ)(CH₃COO)(OH₂)]·CH₃COO ( 2 ) were reported. The susceptibility of Staphylococcus aureus and Escherichia coli towards NTZ and its complexes was assessed. NTZ behaves as a monodentate ligand via the thiazole N atom forming distorted octahedral and tetrahedral complexes with Co(II) and Ni(II) ions, respectively. The d‐d transitions were assigned by the aid of time‐dependent density functional theory calculations. The magnetic susceptibility value of 1 remains unchanged in the temperature range of 298–77K, while that of 2 decreases linearly with the temperature to attain 2.79 μ_B at 77K. Coordination of NTZ (0.084 μmol ml^?1) to Co(II) ( 1 ) (0.028 μmol ml^?1) and Ni(II) ions ( 2 ) (0.079 μmol ml^?1) leads to an improvement in the toxicity against S. aureus.     

Insights into the photochemical processes of ClC(O)SCl from ab initio calculations

All possible unimolecular processes upon photolysis of ClC(O)SCl in the UV-visible region have been characterized in the present paper through the optimized stationary structures and computed potential-energy profiles of the S0, S1, T2, and S2 states with the MP2, B3LYP, CASSCF, and MR-CI methods in conjugation with the cc-pVDZ basis set. Upon photoexcitation in the range of 300-400 nm, the ClC(O)SCl molecules are excited to the S1 state. From this state, the dissociation into ClC(O)S + Cl takes place immediately and subsequently Cl2 and SCO are formed. The C-Cl and C-S bond fissions that start from the S2 state are the dominant channels upon photodecomposition of ClC(O)SCl in the gas and condensed phases in the wavelength range of 200-248 nm. The formed Cl, C(O)SCl, ClCO, and SCl radicals are very reactive, and the Cl2, SCO, CO, and SCl2 molecules are subsequently produced as stable products in the condensed phase.     

New insights into the formation of silicon-oxygen layer on lithium metal anode via in situ reaction with tetraethoxysilane

Lithium metal-based secondary batteries are very promising for next generation power battery due to their high energy density.However,lithium anodes suffer from poor electrochemical reversibility in organic electrolytes due to Li dendrites and instability of the solid electrolyte interphase.Recent research demonstrated that the problem can be alleviated via tetraethoxysilane(TEOS)treated lithium metal to form a silicon oxide layer on the lithium surface,however,its reaction mechanism is controversial.Herein,we deeply explore the reaction mechanism between TEOS and Li and propose:Fresh Li can directly react with TEOS even though no lithium hydroxide exists on the lithium surface,and the participation of water will accelerate the reaction process.Moreover,it was found that the silicon oxide layer can promote the uniform deposition of lithium ions by providing lithiophilic nucleation sites,thereby achieving a long cycle life of Li metal batteries.     

Insights into the metabolite profiles of Rubus chingii Hu at different developmental stages of fruit

The fruits of Rubus chingii Hu have high medicinal and nutritional values. However, the metabolite profiles of R. chingii, especially the alterations during different development stages of fruit, have not been comprehensively analyzed, hindering the effective utilization of the unique species. In this study, we comprehensively analyzed the metabolites of R. chingii fruit at four developmental stages using systematic untargeted and targeted liquid chromatography-mass spectrometry metabolomics analysis and identified 682 metabolites. Significant changes were observed in metabolite accumulation and composition in fruits during the different developmental stages. The contents of the index components, kaempferol-3-O-rutinoside and ellagic acid, were the highest in immature fruit. The analysis identified 64 differentially expressed flavonoids and 39 differentially expressed phenolic acids; the accumulation of most of these differentially expressed metabolites decreased with the developmental stages of fruit from immaturity to maturity. These results confirmed that the developmental stages of fruit are a critical factor in determining its secondary metabolite compositions. This study elucidated the metabolic profile of R. chingii fruit at different stages of development to understand the dynamic changes in metabolites.     

Early stages of ZnS growth studied by stopped-flow UV absorption spectroscopy: effects of educt concentrations on the nanoparticle formation

The growth of ZnS nanoparticles by precipitation from supersaturated aqueous solution is studied by stopped-flow UV absorption spectroscopy. The average size, size distribution, and concentration of the particles are monitored within the sub-second time regime with a resolution of 1.28 ms. Particle growth at these early stages is governed by pronounced ripening. The UV absorption data strongly suggest that growth occurs by preferential adsorption of HS- anions relative to Zn(2+) or ZnOH(+) cations. Correspondingly, the initial sulfide concentration has a much more pronounced influence on the growth kinetics than the initial zinc concentration. These findings are verified by zeta-potential measurements which confirm that the particle surfaces are negatively charged under near-neutral pH conditions.