Search

An aerobic oxidative method was developed for conversion of arylethenes to aromatic nitriles using (NH4)2CO3 as the nitrogen source and Cu(NO3)2 as the catalyst. The present method allowed a series of arylethenes to underwent oxidative cleavage of C=C bonds to give the targeted products in low to high yields. In addition, the present conditions are compatible with many groups such as alkyl, alkoxy, N,N-dimethylamino, chloro, bromo, iodo, ester, cyano group, and so on.

A strategy for using green water as a hydrogen source and electron donor to enable the hydrogenation of aryl bromides is reported.

Nitrogen transfer from cyanide anion to an aldehyde is emerging as a promising method for the synthesis of aromatic nitriles. However, this method still suffers from a disadvantage that a use of stoichiometric Cu(II) or Cu(I) salts is required to enable the reaction. As we report herein, we overcame this drawback and developed a catalytic method for nitrogen transfer from cyanide anion to an alcohol via the complete cleavage of the C≡N triple bond using phen/Cu2 O as the catalyst. The present condition allowed a series of benzyl alcohols to be smoothly converted into aromatic nitriles in moderate to high yields. In addition, the present method could be extended to the conversion of cinnamic alcohol to 3-phenylacrylonitrile.

Weak complementary interactions between proteins and nucleic acids are the main driving forces of intracellular liquid-liquid phase separation. The sticker-spacer model has emerged as a unifying principle for understanding the phase behavior of these multivalent molecules. It remains elusive how specific interactions mediated by stickers contribute to the rheological properties of the liquid condensates. Previous studies have revealed that for strong binding strength ɛ_{b}, the bulk diffusivity D depends on the effective bond lifetime τ, viz., D∝τ^{-1}. Consequently, equal concentrations of the complementary stickers induce a slow down in the dynamics of the condensates D∝e^{-1.5ɛ_{b}}. However, for weak-binding strength, it is expected that the resulting condensates are dynamic, loose network liquids rather than kinetically arrested, compact clusters. We develop a mean-field theory using the thermodynamics of the associative polymers and perform molecular-dynamics simulations based on the sticker-spacer model to study the controlling factors in the structure and dynamics of such condensates in the weak-binding regime. Through scaling analysis, we delineate how the free sticker fraction W_{f} and the bulk diffusivity D decrease with increasing binding energy and find that the internal dynamics of such network liquids are controlled by the free sticker fraction D∝W_{f}∝e^{-0.5ɛ_{b}} rather than the effective bond lifetime. Referred to as the free-sticker-dominated diffusivity, the microscopic slowdown due to a gradual loss of the free stickers affects the viscosity of the condensates as well, with the scaling of the zero-shear viscosity η∝e^{0.5ɛ_{b}}. Therefore, the way of controlling the structure, diffusivity, and viscosity of the condensates through the binding energy can be tested experimentally.

Recent studies reported that adenosine triphosphate (ATP) could inhibit as well as enhance the phase separation in prion-like proteins. The molecular mechanism underlying such a puzzling phenomenon remains elusive. Here, taking the fused in sarcoma (FUS) solution as an example, we comprehensively reveal the underlying mechanism by which ATP regulates phase separation by combining the semiempirical quantum mechanical method, mean-field theory, and molecular simulation. At the microscopic level, ATP acts as a bivalent or trivalent binder; at the macroscopic level, the reentrant phase separation indeed occurs in dilute FUS solutions, resulting from the ATP-concentration--dependent binding ability under different conditions. Importantly, the ATP concentration for dissolving the protein condensates is about 10 mM, agreeing with experimental results. Furthermore, from a dynamic point of view, the effect of ATP on phase separation is also non-monotonic. This work provides a clear physical description of the microscopic interaction and macroscopic phase diagram of the ATP-modulated phase separation., Comment: 24 pages, 5 figures

The pH-regulated charge inversions on polyethylenimine (PEI)-coated surfaces are indispensable to their applications in biomaterials and nanomaterials. Various PEI-coated surfaces, where single charge inversion happens, have been extensively investigated, while the surfaces where double charge inversion appears are less reported. Here, using a molecular theory, we systematically study the pH-regulated charge density of PEI-coated surfaces. The results suggest whether single or double charge inversion happens depends on PEI affinity to the surface and the bare surface charge density. The region of double charge inversion is much smaller than that of single charge inversion, revealing the reason why double charge inversion is less observed in experiments. Besides, the charge inversions are significantly influenced by the solution condition. The present work provides a useful guideline to the selection of the coated materials and the parameters of PEI solution in the design of PEI-coated surfaces aiming to promote their applications in multifunctional nanomaterials.

Noble metal-based high-entropy alloy nanoparticles (NM-HEA NPs) have exhibited brilliant catalytic performance toward electrocatalytic energy conversion and attracted increasing attention. The near-equimolar mixed elements of NM-HEA NPs may result in the unique properties including cocktail effect, high entropy effect and lattice distortion effect, which are beneficial for improving the catalytic performance and reducing the amount of noble metal. Herein, several advanced NM-HEA NPs as electrocatalysts for energy conversion are systematically summarized. The preparation methods of NM-HEA NPs are evaluated as well as the catalytic properties and mechanism are discussed classified by electrocatalytic reactions. Finally, the challenges and prospects in this field are carefully discussed. This review provides an overview on recent advances of NM-HEA electrocatalysts for energy conversion and draws more attention in this infant research field.

A new and effective method was developed for the synthesis of aromatic nitriles from arylacetic acids by using NaNO2 as the nitrogen source and Fe(OTf)3 as the promoter at 50 °C. A series of arylacetic acids underwent this transformation to give the targeted products in yields of 51–90%. Because of the mild conditions, the reaction is compatible with a broad range of functional groups, including ester, carboxy, hydroxy, acetamido, halo, nitro, cyano, methoxy, and even highly reactive formyl groups.

Vitrinite reflectance is the most commonly used index in the study of source rock evaluation, diagenetic stage division, basin simulation, and diagenesis. Because data on vitrinite reflecta...

Fluorescent single crystals that respond to multiple external stimuli are of great interest in molecular machines, sensors, and displays. The integration of photo- or acid-induced fluorescence enhancement and bending in one organic crystal, however, has not been reported yet. Herein, we report the interesting plastic photomechanical bending and switching on of the fluorescence of an azine crystal in a single-crystal transformation, due to extended π-conjugation and molecular slippage. Moreover, the fluorescent plastic bending driven by multiple volatile acid vapors was firstly observed, and attributed to the synergistic effect of push-pull electronic structure and hydrogen bonding. The single crystal also shows high elasticity under external force. In addition, reversible fluorescence switching can be triggered by grinding and solvent fuming, as well as by the adsorption and desorption of HCl vapor. The integration of plastic, elastic bending and switch-on fluorescence into one single crystal provides a new strategy for next-generation smart materials.

The utilization of readily available and non-toxic water by photocatalytic water splitting is highly attractive in green chemistry. Herein we report that light-induced oxidative half-reaction of water splitting is effectively coupled with reduction of organic compounds, which opens up, for the first time, an avenue to use water as an electron donor to enable reductive transformations of organic substances. The used photocatalyst (Pd/g-C3N4*) was synthetized by a novel method where Pd/g-C3N4 was irradiated by light in the presence of Na2CO3 and H2O. The present strategy allowed a series of aryl bromides to undergo the reductive coupling to provide biaryl products in low to high yields. Preliminary mechanistic investigation suggests that the reaction proceeds through the single electron transfer from Pd to aryl bromides. This work will guide chemists to use water as a reducing agent to develop green procedures for various organic reactions.

The utilization of readily available and non-toxic water by photocatalytic water splitting is highly attractive in green chemistry. Herein we report that light-induced oxidative half-reaction of water splitting is effectively coupled with reduction of organic compounds, which provides a light-induced avenue to use water as an electron donor to enable reductive transformations of organic substances. The present strategy allows various aryl bromides to undergo smoothly the reductive coupling with Pd/g-C3N4* as the photocatalyst, giving a pollutive reductant-free method for synthesizing biaryl skeletons. Moreover, the use of green visible-light energy endows this process with more advantages including mild conditions and good functional group tolerance. Although this method has some disadvantages such as a use of environmentally unfriendly 1,2-dioxane, an addition of Na2CO3 and so on, it can guide chemists to use water as a reducing agent to develop clean procedures for various organic reactions.

Nitrogen transfer from cyanide anion to an aldehyde is emerging as a promising method for the synthesis of aromatic nitriles. However, this method still suffers from a disadvantage that a use of stoichiometric Cu(II) or Cu(I) salts is required to enable the reaction. As we report herein, we overcame this drawback and developed a catalytic method for nitrogen transfer from cyanide anion to an alcohol via the complete cleavage of the C≡N triple bond using phen/Cu

Oligonucleotides hold great promise as therapeutic agents to specifically and selectively inhibit gene expression. In order to achieve better targeting efficiency and treatment efficacy, nanocarriers that are dual-responsive to both temperature and pH are more attractive and suitable due to the fact that certain malignancies can cause a slight increase of local temperature and a minor decrease in extracellular pH around the tumor site at the same time. Here, we systematically study oligonucleotide adsorption on the poly(ethyleneimine)-b-poly(N-isopropylacrylamide) (PEI-b-PNIPAm) copolymer layer grafted on a planar surface and nanoparticles with various radii, where the single effect of temperature or pH alone on oligonucleotide adsorption has been extensively investigated, but the combined effect of temperature and pH is less discussed. The theoretical results show that the surface density of the adsorbed oligonucleotides exhibits thermo and pH dual-responsive behavior, in which temperature and pH exhibit a combined effect on the loading capacity of the oligonucleotides. The underlying molecular mechanism of the dual-responsive behavior is revealed. Besides, the effect of important but coupled parameters in nanocarrier design such as polymer surface coverage and length, salt concentration as well as surface curvature (inverse nanoparticle radius) that may influence the dual-responsive behavior of oligonucleotide adsorption is further discussed, which is of great significance to direct the optimal design of PNIPAm/PEI-based nanocarriers to improve the transfection efficiency by achieving the maximal loading capacity of oligonucleotides at different temperatures and pH values.

The implementation of non-close-packed structures in colloids is challenging. Using Brownian dynamics simulations, we study the nonequilibrium self-assembly in suspensions of oppositely charged particles, whose charge magnitude is responsive to the pH of the solution. Under the fast pH-oscillating condition, various non-close-packed (e.g., graphitelike and diamondlike) structures are obtained. Here, changing the amplitude of the pH oscillation is an effective way to fabricate colloidal dynamic structures. To clarify the underlying mechanism of the dynamic self-assembly, the analysis of effective potential is adopted. A dimensionless parameter, the ratio of effective repulsion and attraction, is introduced to reflect the subtle interactions in the system. We find that the imbalance between repulsion and attraction is the cause of structural diversity. Madelung energy is used to study the stability of these structures. Our results provide a new way to fabricate non-close-packed structures in colloids, which has potential applications in the synthesis of photonic crystals. Accepted version

Monophenols in pyrolysis bio-oil can be used to produce renewable fuels and various other materials; their clean separation, however, remains a great challenge. This study provides an economical and feasible strategy for efficiently extracting monophenols from bio-oil. In order to determine the interaction between bio-oil components and different solvents, Hansen solubility parameter theory was used to predict the dissolution trend of several model compounds (e.g., 6 monophenols and 2 dimeric phenols) with a relatively high concentration and/or typical dissolution characteristics in the bio-oil feedstock. A new three-dimensional graphical model was then established by observing the distribution of the extractant coordinate points (Hansen solubility parameters) to predict the selectivity of the extraction of monophenols in a specific extraction process. Under the guidance of this dissolution model, a multistep extraction process with a mono phenol yield of 88.2 wt% was established, and the mass percentage of mono phenols in the separation product was about 86.3%. We performed catalytic hydrodeoxygenation on the separation product, and results showed that the yield and aromatic selectivity of the product were significantly higher than those of water-washed bio-oil. Since the separation strategy proposed in this study does not involve acids or alkalis and the solvent is easily recyclable, the method is expected to find practical application in the efficient separation of bio-oil and its downstream value-added refinement.

Porphyrins and metalloporphyrins (or porphyrin coordination complexes) have been wildly investigated as photocatalysts in recent years. Herein we synthesized two new A3B porphyrins, a new asymmetric A3B zinc-porphyrin ligand with peripheral chelate group (pyridine dicarboxylate), and a ruthenium(II) complex of the porphyrin ligand. Their photo-physical properties were characterized and investigated by UV-Vis and fluorescent emission. The modeling of the molecular structures was optimized by DFT theoretical calculation. All porphyrin compounds exhibited strong absorbance at the Soret bands and Q bands. The free base of porphyrin possessed a higher quantum yield and a longer life time than the other two zinc-porphyrins and ruthenium-porphyrin in terms of fluorescence. Furthermore, the ruthenium-porphyrin complex can be used as a promising photocatalyst under visible light for two kinds of organic reactions: ketone-related oxidative aminothiocyanation (above 90% yield) and indole-related oxidative thiocyanation (around 80% yield) with a remarkable low amount (0.1 mmol %).

Steady structures originating from dynamic self-assembly have begun to show their advantages in new generation materials, and pose challenges to equilibrium self-assembly. In view of the important role of confinement in self-assembly, here, we propose a new type of confinement leading to dynamic steady structures, which opens a new window for the conventional confinement. In our model, we consider the self-assembly of ellipsoids in 2D circular confinement via the boundary performing periodically stretching and contracting oscillation. Langevin dynamics simulations reveal the achievement of non-equilibrium steady structures under appropriate boundary motions, which are novel smectic structures with stable topological defects. Different from the confinement with a static boundary, ellipsoids close to the boundary have variable orientations depending on the boundary motion. Order-order structural transitions, accompanied by the symmetry change and varied defect number, occur with the change of oscillating amplitude and/or frequency of the boundary. Slow and fast dynamics are distinguished according to whether structural rearrangements and energetic adjustment happen or not. The collective motion of confined ellipsoids, aroused by the work performed on the system, is the key factor determining both the structure and dynamics of the self-assembly. Our results not only achieve novel textures of circular confined liquid crystals, but also inspire us to reconsider the self-assembly within the living organisms.

Readily available CuO was demonstrated to be effective as the catalyst for the conversion of arylacetic acids to aromatic nitriles with non-toxic and inexpensive K4Fe(CN)6 as the nitrogen source via the complete cleavage of the C N triple bond. The present method allowed a series of arylacetic acids including phenylacetic acids, naphthaleneacetic acids, 2-thiopheneacetic acid and 2-furanacetic acid to be converted into the targeted products in low to high yields.

Taking PEO/PS polymer blends doped with lithium salt as example, we study the effects of cross-linking of the EO segments by the Li+ ions on the phase behavior. Combining the Flory–Huggins theory with a statistical model accounting for the combinatorics in forming the cross-links and accounting for the charge neutrality due to the presence of anions, we find an entropic driving force that favors phase separation when the number of EO segments coordinating an Li+ ion exceeds 2. As a result of the asymmetric interaction between the ions and the two polymers, the phase diagram in the polymer composition becomes asymmetric upon addition of the lithium salts. In addition, we examine the effects of preferential solvation energy of the ions which has been shown previously to lead to an increase in the effective χ parameter between the two polymers. We find that the magnitudes of these two driving forces are comparable, but their effects are nonadditive.

In immunosensors, antibody orientation is a key factor that determines the sensitivity of a device. To date much effort has been devoted to exploring strategies for the direct control of the orientation of antibodies immobilized on a bioactive surface, but less attention has been paid to controlling the orientation of intermediate proteins (though usually used when immobilizing antibodies), which may greatly limit the sensitivity of immunological activities. Therefore, it is of great significance to seek novel methods for controlling protein orientation. Here, we design a new strategy for controlling protein orientation. The main idea is to bind proteins to a ligand-functionalized poly(N-isopropylacrylamide) (PNIPAm) layer, and then the protein orientation can be mediated by environmental temperature. The theory predicts that the protein orientation can show unexpected triple-thermo-responsive behavior. Based on the fraction of ligand adsorbed by the protein, the reponsive behavior can be either complete adsorption or partial adsorption, which is determind by the polymer's surface coverage and the protein's properties. We expect that the present strategy can enrich the methods for controlling intermediate protein orientation and can guide the design of novel immunosensors with superior sensitivity.

The behavior of polymer chains under stretching is a classical problem in polymer science. However, a fundamental question still in mist is how the stretching affects the interactions between polymer chains, especially when the tensions on the chains are unequal. In this work, we combine statistical theory and molecular simulations to study the influence of this tension disparity on the miscibility of athermal polymer systems. Through a minimal model, we demonstrate that when polymer chains of different lengths are under the same stretching disparate tension states among polymer chains can lead to either macroscopic or microscopic phase separation, depending on whether their ending points are mobile or not. Generally, the immiscibility found here is an entropic effect arising from conformational asymmetry between unequally stretched polymer chains. Our findings provide a new mechanism to explain the flow-induced demixing in polymer blends and indicate that heterogeneous structure can occur during stretchi...

Cracks at the boundary of the brittle inclusions inside heavy forgings are major defects detrimental to the forgings’ the fatigue life and impact performance. In the forging process, the stress field around brittle inclusions is the key factor determining whether cracks appear at the boundary. To study the influences of the stress field on the crack initiation, a definition of the Average Stress Intensity (ASI) and its mathematical expression analytic are given. Average Spherical Stress Intensity (ASSI) is used as an index to investigate the rule of the stress field’s influence on the brittle inclusion boundary crack initiation. Numerical simulation results indicate that ASSI is highly relevant to crack initiation at brittle inclusion boundary and it is practical to use it as a parameter to represent the effect of the stress field on the crack initiation at the boundary of the brittle inclusion. As the algebraic value of the ASSI decreases, the crack size decreases. When the algebraic value of the ASSI is less than-2.3, there will have no cracks at the boundary of the brittle inclusion. Hot compression tests at 1220°C are conducted on a Gleeble-3180 thermal mechanical simulator with dedicated specimens and shape anvils. Scanning Electron Microscopy (SEM) is employed to observe the cracks at the boundary of the brittle inclusions inside the specimens. Observed results agree well with the numerical simulation results.

Using a molecular theory for dilute PEO-b-PNIPAm solutions, we first take the formation of hydrogen bonds between copolymer monomers and water molecules into account, which enables us to study the impact of temperature on PEO-b-PNIPAm self-assembly effectively by quantitatively describing the different changes in water affinities of two blocks. With the increase of temperature, hydrogen bonds between PNIPAm and water break down dramatically, resulting in the hydrophobic character of PNIPAm while PEO remains hydrophilic. Amphiphilic copolymers in the aqueous surrounding can aggregate into various structures: micelles and vesicles. According to the equilibrium criterion of the excess grand potential under the conditions of the grand canonical ensemble, we find that both structures are stable and can coexist. Theoretically calculated potentials of mean force of aggregates further verify the coexistence of micelles and vesicles, although the low critical solution temperatures of different aggregates are different under these conditions. A phase diagram as functions of temperature and the weight fraction of PEO (fPEO) is obtained, which shows different regions of micelles, vesicles and their coexistence. It implies the appearance of two types of micelle-vesicle transition: spontaneous and temperature-induced. Since PEO-b-PNIPAm as a thermoresponsive material has a broad range of applications, a systematic investigation of the phase behavior is very useful not only for the scientific interest but also for the practical applications.

Water transportation inside carbon nanotubes is of great importance for designing novel nanodevices. In this article, by using molecular dynamics simulations, we systematically investigate the pumping of water by rotating carbon nanotube (CNT). It is found that the chirality and rotation of the CNT are two preconditions for stable water flux inside it. Besides, we find that the water flux shows an approximately logarithmic dependence on the angular velocity of the rotation, a linear dependence on the radius of the CNT, and interestingly, independence of its length within a certain range of CNT size and angular velocity. Further, we also use a dragging theory which successfully describes the water flux behaviors inside the CNT and can fit well with the results obtained from simulations. The present study provides insight into the designing of nanodevices based on the CNT for real applications.

Based on the fluid-structure interaction theory, FLAC3D was adopted to conduct a numerical simulation on the excavation of hong shigou hard rock tunnel. The basic mechanical properties for rock mass changed significantly during the process of secondary stress adjustments, and the rock deterioration constitutive model (RDM) can accurately reflect both the abruptness of the rock yield failure and the changes of mechanical parameters after yield. On the basis of RDM, the permeability coefficient with equivalent plastic strain function was introduced which can update the permeability coefficient. The results showed that both the surrounding rock displacement and the volume of plastic zone increased significantly because of the seepage action. Therefore, the seepage of fissure water on the hard rock should be fully considered during excavating and supporting in order to prevent accidents such as water inrush and sudden collapse.

Combining self-consistent-field theory and density-functional theory, we systematically study the deformation of copolymer micelles induced by the presence of amphiphilic dimer particles. Due to the amphiphilic nature, dimer particles tend to accumulate onto the interface of the copolymer micelle. With increasing concentration of the symmetric dimer particles, which are made of two identical spherical particles, the micelle deforms from the initial sphere to ellipse, dumbbell, and finally separates into two micelles. Furthermore, asymmetric dimer particles, composed by two particles with different sizes, are considered to investigate the influence of geometry of dimer particles on the deformation of the micelle. It is found that the micelle inclines to deform into dumbbell due to the additional curvature originating in the gathering of asymmetric dimer particles onto the interface of the micelle. The present study on the deformation of micelles is useful to understand the possible shape variation in the course of cell division/fusion.

Using self-consistent field and density functional theories, we investigate the self-assembly behavior of asymmetric dimer particles in a supported AB block copolymer bilayer. Asymmetric dimer particles are amphiphilic molecules composed by two different spheres. One prefers to A block of copolymers and the other likes B block when they are introduced into the copolymer bilayer. The two layer structure of the dimer particles is formed within the bilayer. Due to the presence of the substrate surface, the symmetry of the two leaflets of the bilayer is broken, which may lead to two different layer structures of dimer particles within each leaflet of the bilayer. With the increasing concentration of the asymmetric dimer particles, in-plane structure of the dimer particles undergoes sparse square, hexagonal, dense square, and cylindrical structures. In a further condensed packing, a bending cylindrical structure comes into being. Here we verify that the entropic effect of copolymers, the enthalpy of the system and the steric repulsion of the dimer particles are three important factors determing the self-assembly of dimer particles within the supported copolymer bilayer.

Exploring the mechanism of specific salt effects in electrolyte solutions is an old and attractive subject. It has been gradually realized that the competition at the molecular level plays an important role. Aiming to include molecular details as many as possible, we combine molecular dynamics (MD) simulations with a molecular theory to study specific salt effects on poly(ethylene oxide) (PEO) solutions with the addition of monovalent salt. Radial distribution functions obtained from MD simulations provide microscopic structures of different components as well as interactions between various species. On the basis of these interactions, we construct the molecular theory with four assumptions: (1) an ion along with bound water in the first shell works as a single entity; (2) short-ranged interactions among various species are modeled as hydrogen-bonding interactions; (3) the ability of a hydrated ion to provide donors/acceptors for hydrogen bonding is governed by the charge density; (4) contact ion pairs ar...

Untreated disposal of coal mine wastewaters from Shanbei loess have environmental and public health concerns in the developing Shanbei Loess Plateau, Northwest China. An in-situ experiment was conducted in the easily accessible loess to study their efficiency in removal of pollutants. Approximately 565L of wastewater was used in the test, which lasted 333min. Loess samples were collected at 5 discrete depths, 0.2m, 0.4m, 0.6m, 1m, and 1.5m from the surface before, at the end of, and 20 days after the infiltration test. Pollutants commonly found in wastewaters were analyzed for all the loess samples. The test indicates the loess is more effective for Cd and Pb.

A molecular theory to study the properties of end-tethered polymer layers, in which the polymers have the ability to form hydrogen bonds with water, is presented. The approach combines the ideas of the single-chain mean-field theory to treat tethered layers with the approach of Dormidontova (Macromolecules, 2002, 35, 987.) to include hydrogen bonds. The generalization includes the consideration of position-dependent polymer-water and water-water hydrogen bonds. The theory is applied to model poly(ethylene oxide) (PEO), and the predictions are compared with equivalent polymer layers that do not form hydrogen bonds. It is found that increasing the temperature lowers the solubility of the PEO and results in a collapse of the layer at high enough temperatures. The properties of the layer and their temperature dependence are shown to be the result of the coupling between the conformational entropy of the chains, the ability of the polymer to form hydrogen bonds, and the intermolecular interactions. The structural and thermodynamic properties of the PEO layers, such as the lateral pressure-area isotherms and polymer chemical potentials, are studied as a function of temperature and type of tethering surface. The possibility of phase separation of the PEO layer at high enough temperature is predicted due to the reduced solubility induced by breaking of polymer-water hydrogen bonds. A discussion of the advantages and limitations of the theory, together with how to apply the approach to different hydrogen-bonding polymers, is presented.

Poly(ethylene glycol) (PEG) nanofilms are used to avert the nonspecific binding of biomolecules on substrate surfaces in biomedicine and bioanalysis including modern fluorescence-based DNA sensing and sequencing chips. A fundamental and coherent understanding of the interactions between fluorophore-tagged DNA, PEG-films, and substrates in terms of molecular and energetic factors is, however, missing. Here we explore a large parameter space to elucidate how PEG layers passivate metal oxide surfaces against Cy3-labeled DNA probes. The driving force for probe adsorption is found to be the affinity of the fluorophore to the substrate, while the high-quality PEG films prevent adsorption to bare ITO surfaces. The amount of nonrepelled, surface-bound DNA strongly depends on oligonucleotide size, PEG chain length, and incubation temperature. To explain these observations, we develop an experimentally validated theory to provide a microscopic picture of the PEG layer and show that adsorbed DNA molecules reside within the film by end-tethering the fluorophore to the ITO surface. To compensate for the local accumulation of negatively charged DNA, counterions condense on the adsorbed probes within the layer. The model furthermore explains that surface passivation is governed by the interdependence of molecular size, conformation, charge, ion condensation, and environmental conditions. We finally report for the first time on the detailed thermodynamic values that show how adsorption results from a balance between large opposing energetic factors. The insight of our study can be applied to rationally engineer PEG nanolayers for improved functional performance in DNA analysis schemes and may be expanded to other polymeric thin films.

High density DNA brush is not only used to model cellular crowding, but also has a wide application in DNA-functionalized materials. Experiments have shown complicated cooperative hybridization/melting phenomena in these systems, raising the question that how molecular crowding influences DNA hybridization. In this work, a theoretical modeling including all possible inter and intramolecular interactions, as well as molecular details for different species, is proposed. We find that molecular crowding can lead to two distinct cooperative behaviours: negatively cooperative hybridization marked by a broader transition width and positively cooperative hybridization with a sharper transition, well reconciling the experimental findings. Moreover, a phase transition as a result of positive cooperativity is also found. Our study provides new insights in crowding and compartmentation in cell and has the potential value in controlling surface morphologies of DNA functionalized nano-particles.

Using self-consistent-field and density-functional theories, we first investigate colloidal self-assembly of colloid-polymer films confined between two soft surfaces grafted by polymers. With increasing colloidal concentrations, the film undergoes a series of transitions from disordered liquid --sparse square --hexagonal (or mixed square-hexagonal) --dense square --cylindrical structures in a plane, which results from the competition between the entropic elasticity of polymer brushes and the steric packing effect of colloidal particles. A phase diagram displays the stable regions of different in-layer ordering structures as the colloidal concentration is varied and layering transitions as the polymer-grafted density is decreased. Our results show a new control mechanism to stabilize the ordering of structures within the films.

C16H16F6N3P, monoclinic, P21/n, a = 8.6414(8) Å, b = 20.755(2) Å, c = 10.1157(8) Å, β = 104.686(9)°, V = 1755.0(3) Å3, Z = 4, R gt (F) = 0.0547, wR ref (F 2 ) = 0.1496, T = 291(2) K.

We investigate the pattern formation of a binary polymer mixture in the presence of chemical reaction A ⇌ B and with the inclusion of mobile particles under a modulated pinning potential. The presence of particles with a preferential attraction for one component of the mixture breaks the isotropy of the bulk phase-separating process and controls the orientational ordering of structures. On the other hand, the chemical reaction can change the relative volume of A and B components, leading to the formation of a wide variety of morphologies. We find that due to the competition among the chemical reaction, phase separation and externally-driven effect, some unusual ordering structures can be realized. The results may provide some important insights into designing novel ordering morphologies such as microporous structures and quantum dots.

A numerical tee joint valve model was set up in this paper. The numerical forming simulation was implemented. The load of the upper punch was predicted. The final temperature field shows that varying temperatures are within the feasible forging temperature region. The results from the numerical simulation were verified through the practical experiment.

The aim of this paper is to make surgeons aware of the use of cone beam computed tomography (CBCT) within the field of implantology. The paper describes one case illustrating the improved diagnostic yield using CBCT over conventional radiography thus facilitating the appropriate insertion guidance of implants.