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The adsorption behavior of NH4+ and Mg2+ at kaolinite surfaces was investigated by using molecular dynamics (MD) simulations, considering the factors such as ion concentration, NH4+/Mg2+ mixing ratio, and layer charge of kaolinite. The results showed that the increase in ion concentration did not affect the adsorption modes of NH4+ and Mg2+ ions but promote the increase in the adsorption capacity. The total adsorption capacities of Mg2+ and NH4+ were 3.25 × 10−6 and 2.85 × 10−6 μmol·mm−2 at the ion concentration of 1.5 mol·L−1, respectively. When NH4+ and Mg2+ were co‐adsorbed, they could inhibit the adsorption of each other at the surface of kaolinite, except that the inner‐sphere (IS) adsorption of NH4+ at aluminum hydroxyl (Al–OH) surface could be enhanced by the presence of Mg2+. Both NH4+ and Mg2+ tended to adsorb at the siloxane (Si–O) surface of kaolinite rather than Al–OH surface. When layer charge occurred in kaolinite, a small number of Mg2+ began to adsorb in the IS complexes at 1.7 and 2.3 Å above the Al and O atoms of the lattice‐substituted tetrahedra of the Si–O surface, and at 1.7 Å above the hexahedra of the Al–OH surface. However, most of NH4+ were adsorbed in IS complexes at 1.7 Å above the center of the oxygen six‐membered ring of the Si–O surface and above the hexahedron of the Al–OH surface. The adsorption capacity of Mg2+ changed little with the increase of layer charge density, while the IS and total adsorption capacity of NH4+ increased significantly. [ABSTRACT FROM AUTHOR]

• Visual microfluidic chip technology to visually investigate the flow patterns of liquid displacing and replacing gas in porous media. • When porous media contains low-permeability geological inclusions, the solution will bypass and flow around the low-permeability area. • The low-permeability geological inclusions will slow down the rate of solution infiltration. • The larger the volume of low-permeability geological inclusions, the lower the liquid saturation after the stable flow of liquid displacing and replacing gas in porous media. Ionic rare earth deposits often contain semi-weathered or slightly weathered low-permeability geological inclusions (LPGI), which significantly impact the permeation process and leaching efficiency of in-situ liquid leaching mining. To investigate the influence of LPGI with varying developmental degrees on the seepage process of ionic rare earth leaching mining, we developed six microfluidic chip models using Polydimethylsiloxane (PDMS). A visual experiment was conducted, employing water to drive gas at a rate of 0.5 μl/min, enabling observation of the seepage and displacement process. Using MATLAB image processing technology in conjunction with time-history diagrams, we analyzed the evolution patterns of the infiltration front position and saturation over time. Our findings revealed distinct capillary fingering and side wall flow phenomena during the process of liquid phase displacing gas phase infiltration, accompanied by horizontal and counter flows perpendicular to the solution's direction of advancement. Notably, when the solution traversed the LPGI, we observed significant flow-around phenomena and low saturation of the LPGI. These inclusions hindered solution infiltration, with wider LPGI resulting in greater inhibition. Additionally, the LPGI acted as a protective barrier, preventing solution intrusion into the underlying ore body. However, due to the air discharge is not timely, it was sealed by the outlet solution, forming a substantial leaching blind area near the outlet. This study unveils the seepage laws of ionic rare earth earth leaching mining involving LPGI of various developmental degrees, signifying its vital engineering significance in the efficient extraction of ionic rare earth. [ABSTRACT FROM AUTHOR]

Clay minerals have a specific adsorption capability for anions, which increases the amount of net negative charge on the surface, leading to the increased adsorption of rare-earth ions in clay minerals and some change from exchangeable to non-exchangeable. Further, anions show a shielding effect on rare-earth ions. The shielding capacity of anions in the leaching agents for rare-earth ions was measured in this study. The relationship between the solid-phase concentration of rare-earth ions shielded and the anion concentration was consistent with the Langmuir model. Based on the Kerr model describing the exchange of rare-earth ions by ammonium ions, an ion-exchange model considering the shielding influence of anions was proposed. The accuracy of the proposed model was higher than that of the Kerr model. When the leaching agent was ammonium sulfate, the calculation accuracy of XW and AY samples was increased by 1.15% and 5.75%, respectively. The improvement in accuracy positively correlated with the proportion of iron oxides, aluminium oxides, and Kaolin. The established ion-exchange model can provide accurate source and sink terms for the numerical simulation of the leaching process of ion-adsorption-type rare-earth ores. [ABSTRACT FROM AUTHOR]

The residual and release of ammonium in ion-adsorption rare earth tailings and soil are related to the interaction of NH 4 + with clay minerals. Molecular dynamics simulations were used to study the adsorption and diffusion of NH 4 + on the external surface of smectite. The factors, such as layer charge position (octahedral and tetrahedral substitution) and charge density (0.5, 1.0 and 1.5 e⋅uc−1, where uc denotes unit cell), initial NH 4 + concentration (from 0.64 to 1.60 mol⋅L−1), and anion types (Cl−, NO 3 − and SO 4 2−) were considered. The results of NH 4 + adsorption on the external surface were also compared with that in the interlayer. The layer charge of smectite significantly affected the interaction between NH 4 + and smectite. With increasing charge density, the major NH 4 + surface complexes were changed from outer-sphere to inner-sphere, resulting in increased adsorption density and stability, which was verified by calculated hydration structure and adsorption free energies. The inner-sphere NH 4 + complexes were located above the centers of the hexagonal rings and the Si tetrahedras for montmorillonite at a charge density of 1.0 e⋅uc−1, while only located in the vicinity of tetrahedral substitutions for beidellite. NO 3 − promoted the adsorption of NH 4 + as inner-sphere complexes relative to Cl− and SO 4 2−. As the water content in the interlayer increased, the confinement effect weakened and the mobility of NH 4 + increased, and the NH 4 + adsorption in the interlayer exhibited similar characteristics to that on the external surface at a water content of 10 H 2 O⋅uc−1. [Display omitted] • The inner-sphere complexes of NH 4 + on smectite external surface vary with the charge location. • With increasing charge density, the major NH 4 + complexes are changed from outer- to inner-sphere. • Increasing of NH 4 + concentration increase adsorption amount rather than change adsorption pattern. • NO 3 − promote the adsorption of NH 4 + as inner-sphere complexes relative to Cl− and SO 4 2−. • NH 4 + in the interlayer have similar adsorption features to on external surface at 10 H 2 O⋅uc−1. [ABSTRACT FROM AUTHOR]

Ion-adsorption-type rare-earth ores (IATREOs) that have experienced granite weathering have good permeability, and their leaching process involves the solute transport problem, which is dominated by convection. Because of the oscillation and dispersion errors of existing numerical methods for solving the convective-dominated solute transport equation, the results have low precision in the twin leaching process. In this paper, the convection–dispersion equation is decoupled into the dispersion equation, the convection equation, and the source-sink equation; the Crank–Nicolson and implicit difference methods are used to solve the dispersion equation and the source-sink equation, respectively. The solution of the convection equation is achieved on the basis of its physical interpretation. Therefore, a decoupling method for the convective-dominated solute transport equation is established. In comparison to the two examples with analytical solutions, the calculation errors of the method established in this paper are less than 2.00%, and it can solve the oscillation and dispersion problems. The rationality of the method is further demonstrated through the column leaching experiment of IATREOs. In comparison to the test results, the coefficients of determination of the breakthrough curves of rare-earth ions and ammonium ions calculated by the proposed method are all greater than 0.850, and the peak concentration error of rare-earth ions is less than 7.00%. This indicates that the proposed method can simulate the leaching process well. Furthermore, by combining the multiple/half method and the dichotomy method, an optimization method for determining the leaching agent amount was established to analyze the relationship between the leaching agent and the ratio of dispersion to pillar length. The results can provide a solution that can be used to mine IATREOs from experience to theory. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interlayer spacing of NH 4 +-smectites decreased with increasing charge density. • Hydration more easily occurred in NH 4 +-smectites with tetrahedral substitution. • Affinity of the surface for NH 4 + increased with increasing charge density. • NH 4 + in high-charge smectites (–1.5 e ·uc–1) were always in inner-sphere complexes. Classical molecular dynamics (MD) simulations were performed to quantify the possible effects of layer charge density and location on NH 4 + and the water structure, energetics and dynamics of hydrated NH 4 +-smectites. The results showed that the layer spacing decreased with increasing charge density. Hydration occurred more easily in NH 4 +-smectites with tetrahedral substitution than those with octahedral substitution. Stable monolayer hydrates and hypothetical bi- and trilayer hydrates were found at a water content of 4, 10 and 15 H 2 O·uc–1 (H 2 O per unit cell), respectively. The binding affinity of the surface towards NH 4 + increased as the charge density of the smectites increased. For low- and medium-charge smectites (σ = –0.5 and –1.0 e ·uc–1), the affinity was also dependant on the hydration level: some of the NH 4 + in inner-sphere complexes with the surface turned into outer-sphere complexes and even formed bulk water–like structures as hydration levels increased. However, for high-charge smectites (σ = –1.5 e ·uc–1), NH 4 + was still present in inner-sphere complexes with the oxygens of the surface hexagonal cavities regardless of hydration level. The layer charge also affected the NH 4 + diffusion coefficient in the interlayer regions; NH 4 + in T-substituted smectites diffused more slowly than in O-substituted ones and increasing the charge density of smectites inhibited the mobility of NH 4 +. Quantification of these interactions can provide a basis for understanding the swelling process of clay and the release process of NH 4 + during the ion-type rare earth mining. [ABSTRACT FROM AUTHOR]

The interaction of ammonium ions (NH 4 +) with clay is closely associated with many geochemistry, engineering, and environment issues. Molecular dynamics (MD) simulations were performed to investigate to the structure, energetics, and dynamics properties of ammonium-montmorillonite (NH 4 -Mt) at different hydration levels. The simulation results show that the layer spacing, immersion and hydration energy, atomic density, coordination number, self-diffusion coefficient and residence time of NH 4 -Mt vary with the water contents. The one-layer hydrate is the most energetically favorable at the water content of 5 H 2 O/uc but up to three-layer hydrate of NH 4 -Mt can potentially be formed at the high water content (13 H 2 O/uc). As the water content increases, some NH 4 + ions which adsorbed in inner-sphere (IS) complexes at low hydration level can change to outer-sphere (OS) complexes, and further to random ions in a diffuse aqueous layer, with the interaction between NH 4 + ions and basal surfaces becoming weaker. The H-bonding of N-H n ···O s , donated by hydrogen atoms of NH 4 + to surface oxygen atoms, contributes to the adsorption of NH 4 + ions besides the electrostatic attraction. NH 4 + ions in inner-sphere complexes can reside above the hexagonal cavities longer and have more stable hydration shell at the low hydration level. Unlabelled Image • Monolayer hydrate is the most energetically favorable for NH 4 -Mt. • H-bonds between NH 4 + and Mt. contribute to the adsorption of NH 4 +. • Interaction between NH 4 + and Mt. weakens as the water content increases. • NH 4 + in IS complexes reside above surface cavity longer at low water content. [ABSTRACT FROM AUTHOR]

The role of DNA topoisomerase III (Topo III) in bacterial cells has proven elusive. Whereas eukaryotic Top IIIa homologs are clearly involved with homologs of the bacterial DNA helicase RecQ in unraveling double Holliday junctions, preventing crossover exchange of genetic information at unscheduled recombination intermediates, and Top IIIβ homologs have been shown to be involved in regulation of various mRNAs involved in neuronal function, there is little evidence for similar reactions in bacteria. Instead, most data point to Topo III playing a role supplemental to that of topoisomerase IV in unlinking daughter chromosomes during DNA replication. In support of this model, we show that Escherichia coli Topo III associates with the replication fork in vivo (likely via interactions with the single-stranded DNA-binding protein and the β clamp-loading DnaX complex of the DNA polymerase III holoenzyme), that the DnaX complex stimulates the ability of Topo III to unlink both catenated and precatenated DNA rings, and that ΔtopB cells show delayed and disorganized nucleoid segregation compared to that of wild-type cells. These data argue that Topo III normally assists topoisomerase IV in chromosome decatenation by removing excess positive topological linkages at or near the replication fork as they are converted into precatenanes. [ABSTRACT FROM AUTHOR]

The ion-adsorbed rare earth is mainly concentrated in the in situ leaching process using NH4+ as the leaching agent. The adsorption mechanisms of Y3+ and NH4+ on kaolinite (001) and (00-1) surfaces were studied by density functional theory based on plane wave pseudopotential. The adsorption structures and energies, electrostatic potential, frontier orbital, Mulliken bond population and atomic charge, and electron density difference were calculated. The calculated results showed that the activity sites of kaolinite surfaces are located around the lying OH groups on (001) surface and above the center of the six-membered oxygen ring on (00-1) surface. Y3+ is adsorbed on kaolinite (001) surface primarily through covalent interaction while on kaolinite (00-1) surface primarily through Coulomb interaction. NH4+ is adsorbed on surface by electrostatic interaction and hydrogen bonding. The adsorption energy order on kaolinite (001) surface is Y3+ > NH4+ > H2O while NH4+ > Y3+ > H2O on kaolinite (00-1) surface. The presence of both the ligand water of cations and surface water can increase the Eads of NH4+/Y3+. The hydrated Y3+ can be still more strongly adsorbed on hydrated kaolinite surface than NH4+. When NH4+ is used as the leaching agent for ion-adsorption-type rare earth, it is necessary to increase the concentration of NH4+ to a certain value so that Y3+ could be effectively exchanged by NH4+. [ABSTRACT FROM AUTHOR]

Summary Many essential cellular processes, such as gene control, employ elaborate mechanisms involving the coordination of large, multi-component molecular assemblies. Few structural biology tools presently have the combined spatial-temporal resolution and molecular specificity required to capture the movement, conformational changes, and subunit association-dissociation kinetics, three fundamental elements of how such intricate molecular machines work. Here, we report a 3D single-molecule super-resolution imaging study using modulation interferometry and phase-sensitive detection that achieves <2 nm axial localization precision, well below the few-nanometer-sized individual protein components. To illustrate the capability of this technique in probing the dynamics of complex macromolecular machines, we visualize the movement of individual multi-subunit E. coli RNA polymerases through the complete transcription cycle, dissect the kinetics of the initiation-elongation transition, and determine the fate of σ 70 initiation factors during promoter escape. Modulation interferometry sets the stage for single-molecule studies of several hitherto difficult-to-investigate multi-molecular transactions that underlie genome regulation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Y(OH) 3-n n+ ions are adsorbed on kaolinite mainly via Y atom and surface O atoms. • Ion hydrolysis and surface deprotonation affect the adsorption of Y(OH) 3-n n+ ions. • Adsorption energies increase with the increase of kaolinite deprotonation degree. • Adsorption energies decrease with the increase of the hydrolysis degree of Y3+ ion. Abstract The interaction of rare earth elements (REEs) ions with clay minerals is crucial for understanding the processing of mineralization, extraction and recovery of ion-adsorption rare earth. Theoretical studies based on density functional theory (DFT) were performed to investigate the adsorption of rare earth Y(OH) 3-n n+ (n = 1–3) ions on kaolinite surfaces of varying deprotonation degree depending on the solution pH. The Conductor-like Screening Model (COSMO) was used to simulate the water environment of adsorption. The calculated results showed that the surface electrostatic potential and frontier orbital are enhanced and increasingly localized around the exposed oxygen atoms with the increase of the deprotonation degree of kaolinite (0 0 1) surface hydroxyls. Y(OH) 3-n n+ ions are adsorbed mainly via the Y atom and the surface O atoms, and located over the center of Al-hexagonal ring on kaolinite (0 0 1) surface, and the center of Si-hexagonal ring on kaolinite (0 0 −1) surface. The adsorption energies increase with the increase of deprotonation degree of kaolinite (0 0 1) surface, and decrease with the increase of the hydrolysis degree of Y3+. The results of Mulliken bond length and population, atomic charge, electron density and density of states (DOS) revealed that Y(OH) 3-n n+ ions interact with kaolinite (0 0 1) surface through the combination of covalent and electrostatic bonding, while with (0 0 −1) surface mainly through electrostatic bonding. The above calculated results would provide some atomic-level insights for the interaction of rare earth ions with kaolintie surfaces in aqueous solution. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • F&Ti codoped heptazine/triazine g-C 3 N 4 heterostructure is explored by hybrid DFT. • F&Ti codoping induces a narrow bandgap of heptazine/triazine g-C 3 N 4 heterostructure. • The formed type-II heterostructure promotes the separation of electron-hole pairs. • F&Ti codoped heptazine/triazine g-C 3 N 4 has enough redox potential as photocatalyst. Abstract Graphitic carbon nitride (g-C 3 N 4) has been widely investigated as a metal-free photocatalyst for water splitting. However, the rapid recombination of photoexcited carriers and narrow visible-light response region substantially limit its performance. In this work, we have systematically studied the geometrical, electronic, optical, charge transfer and photocatalytic mechanism of (F, Ti) codoped heptazine/triazine based g-C 3 N 4 heterostructure using hybrid density functional approach. The interface interaction between heptazine and triazine g-C 3 N 4 shows heptazine and triazine g-C 3 N 4 form a Van Der Waals heterostructure. The bandgap of (F, Ti) codoped heptazine/triazine based g-C 3 N 4 heterostructure is narrow (2.39 eV), which enhances the absorption of visible light and leads to an obvious redshift of absorption edge. A type-II heterostructure is formed at the interface of (F, Ti) codoped heptazine/triazine based g-C 3 N 4 heterostructure, and leads to high photocatalytic activity. Furthermore, Bader charge and charge density difference indicate that the internal electric field promotes the separation of electron-hole pairs in the heptazine/triazine g-C 3 N 4 interface and inhibits carrier recombination. Meanwhile, electrons in the conduction band of triazine g-C 3 N 4 and holes in the valence band of (F, Ti) codoped heptazine g-C 3 N 4 have enough redox ability. This work is helpful in understanding the mechanism of photocatalytic water splitting and relevant experimental observations. [ABSTRACT FROM AUTHOR]

The geometrical, electronic and optical properties of Cu or/and N (co)doped TiO 2 /g-C 3 N 4 heterostructure systems have been investigated systematically on the basis of spin-polarized density functional theory calculations. Our calculated results indicate that the band gap of TiO 2 /g-C 3 N 4 heterostructure has an obvious narrowing compared with pure TiO 2 (1 0 1) surface, and (Cu, N) codoping can induce some impurity states of N 2 p and hybridized states of Cu 3 d and N 2 p appearing in the forbidden gap of TiO 2 /g-C 3 N 4 heterostructure, which lead to a decrease of the photon excitation energy and an obvious redshift of the optical absorption edge. Moreover, the charge density difference calculations of Cu or/and N (co)doped TiO 2 /g-C 3 N 4 heterostructure systems show that the excited electrons and holes will eventually accumulate in (co)doping TiO 2 (1 0 1) surface and g-C 3 N 4 monolayer, respectively, which can effectively reduce the recombination of the photogenerated electron-hole pairs by the interfacial coupling of between TiO 2 (1 0 1) surface and g-C 3 N 4 monolayer. This work not only investigates systematically the electronic and optical properties of Cu or/and N (co)doped TiO 2 /g-C 3 N 4 heterostructure, but also suggests that (Cu, N) codoped TiO 2 /g-C 3 N 4 heterostructure is a preferable visible-light photocatalyst. [ABSTRACT FROM AUTHOR]

Live cell imaging with high spatiotemporal resolution and high detection sensitivity facilitates the study of the dynamics of cellular structure and function. However, extracting high-resolution 4D (3D space plus time) information from live cells remains challenging, because current methods are slow, require high peak excitation intensities or suffer from high out-of-focus background. Here we present 3D interferometric lattice light-sheet (3D-iLLS) imaging, a technique that requires low excitation light levels and provides high background suppression and substantially improved volumetric resolution by combining 4Pi interferometry with selective plane illumination. We demonstrate that 3D-iLLS has an axial resolution and single-particle localization precision of 100 nm (FWHM) and <10 nm (1σ), respectively. We illustrate the performance of 3D-iLLS in a range of systems: single messenger RNA molecules, nanoscale assemblies of transcription regulators in the nucleus, the microtubule cytoskeleton and mitochondria organelles. The enhanced 4D resolution and increased signal-to-noise ratio of 3D-iLLS will facilitate the analysis of biological processes at the sub-cellular level. New lattice light-sheet microscopy approach improves live cell imaging. [ABSTRACT FROM AUTHOR]

Objective: To study the hemodynamic response to lower leg heating intervention (LLHI) inside the abdominal and iliac arterial segments (AIAS) of young sedentary individuals. Methods: A Doppler measurement of blood flow was conducted for 5 young sedentary adults with LLHI. Heating durations of 0, 20, and 40 min were considered. A lumped parameter model (LPM) was used to ascertain the hemodynamic mechanism. The hemodynamics were determined via numerical approaches. Results: Ultrasonography revealed that the blood flow waveform shifted upwards under LLHI; in particular, the mean flow increased significantly (p < 0.05) with increasing heating duration. The LPM showed that its mechanism depends on the reduction in afterload resistance, not on the inertia of blood flow and arterial compliance. The time-averaged wall shear stress, time-averaged production rate of nitric oxide, and helicity in the external iliac arteries increased more significantly than in other segments as the heating duration increased, while the oscillation shear index (OSI) and relative residence time (RRT) in the AIAS declined with increasing heating duration. There was a more obvious helicity response in the bilateral external iliac arteries than the OSI and RRT responses. Conclusion: LLHI can effectively induce a positive hemodynamic environment in the AIAS of young sedentary individuals. [ABSTRACT FROM AUTHOR]

• The adsorption of La onto the kaolin surface at different concentrations and pH conditions was explored as a proxy for investigations of the mineralization process of ion adsorption REE ore. • The content of REE in each phase was determined by desorption experiments, on this basis, the leaching process of ion adsorption REE ore was discussed. • The occurrence regularity of REE on clay mineral surfaces was investigated to explore the mineralization mechanism using adsorption/desorption experiments. The occurrence of rare earth elements on clay mineral surfaces and the metallogenic mechanism is significant for mining and the leaching of ion adsorption REE ore. Through experimental isothermal adsorption of La onto the kaolin surface, it was found that the unit adsorption capacity could be divided into three stages according to the La concentration in solution: a) when the concentration of La in solution is 0–0.69 mmol/L, the adsorption capacity of La on kaolin increases rapidly with the rising of La concentration; b) when the concentration is 0.69–1.69 mmol/L, the adsorption capacity of kaolin to La tends to be flat; and c) when the concentration is more than 9.95 mmol/L, the adsorption capacity of kaolin to La increases linearly. The occurrence of La on the kaolin surface was studied by desorption experiments. It was found that with increasing La concentration, the water-soluble phase La is initially adsorbed up to a maximum adsorption of 0.259 mg/g, followed by the ion-exchange phase La up to a maximum adsorption of 0.175 mg/g. Finally, when the concentration of La in solution is >9.95 mmol/L, the colloidal phase La appeared. The metallogenic process of ion adsorption REE ore is revealed through the adsorption experiment of La on kaolin surface and the "three-phase La desorption" experiment. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of g-C 3 N 4 /TiO 2 heterostructure are investigated using spin-polarized DFT+ U calculations. The equilibrium spacing (1.94 Å) and binding energy (24 meV/Å 2 ) show that g-C 3 N 4 /TiO 2 is a van der Waals heterostructure. And the calculated band gap of g-C 3 N 4 /TiO 2 is significantly reduced compared with TiO 2 . Therefore, the visible light response of g-C 3 N 4 /TiO 2 heterostructure is remarkably improved. Besides, the predicted type II band alignment would ensure that the electrons can migrate from g-C 3 N 4 monolayer to anatase TiO 2 (101) surface, which leads oxidation and redox reactions can occur on g-C 3 N 4 and TiO 2 , respectively. Finally, a built-in electric field within the interface region will be set. Above processes can benefit the separation of photoexcited carriers and enhance the hydrogen-evolution activity. In addition, compared with TiO 2 , g-C 3 N 4 /TiO 2 with higher conduction band minimum energy can effectively produce higher-energy electrons to reduce hydrogen ions. Moreover, the influence of composite distance and the number of g-C 3 N 4 layers are also investigated systematically. The results indicate that the optical absorption is enhanced over the whole spectrum with the increase of the number of g-C 3 N 4 layers. Similar visible light enhancing is also found when the composite distance is decreased. [ABSTRACT FROM AUTHOR]

Broadly neutralizing antibodies and appropriate immunogens are critical for preexposure prophylaxis and therapeutic HIV vaccines. In this study, we aimed to explore effective antibodies against the genetically diverse HIV-1 strains by investigating the roles of human CD4 D1D2 domain and nonvariable immugens. The human CD4 D1D2 domain and the chimeric protein of mouse D1 domain/human D2 domain were expressed in Sf9 insect cells and purified by gel-filtration chromatography. The human CD4 D1D2 domain potently inhibited the infection of 77.8% HIV-1 pseudoviruses, including the clades AE, B' and BC, with less than 20 μg/mL of IC50. pcDNA3.1-mhD1D2m and pcDNA3.1-mhD2m plasmids were used for the production of mouse anti-human CD4 polyclonal antibodies. The neutralizing activities of the polyclonal antibodies were determined by using pseudotyped HIV-1 viruses. The antibodies induced by plasmids containing human CD4 D1D2 domain were able to potently inhibit all pseudotyped HIV-1 strains. The antibodies from mhD1D2m-immunized mice also showed strong binding capacity to CD4 expressed on the surface of TZM-bl cells. The potent and broad inhibitory activity of antibodies against the human CD4 D1D2 domain may be used to develop effective passive immunization agent to control the spread of HIV infection. [ABSTRACT FROM AUTHOR]

Transforming the vast knowledge from genetics, biochemistry, and structural biology into detailed molecular descriptions of biological processes inside cells remains a major challenge—one in sore need of better imaging technologies. For example, transcription involves the complex interplay between RNA polymerase II (Pol II), regulatory factors (RFs), and chromatin, but visualizing these dynamic molecular transactions in their native intracellular milieu remains elusive. Here, we zoom into single tagged genes using nanoscopy techniques, including an active target-locking, ultra-sensitive system that enables single-molecule detection in addressable sub-diffraction volumes, within crowded intracellular environments. We image, track, and quantify Pol II with single-molecule resolution, unveiling its dynamics during the transcription cycle. Further probing multiple functionally linked events—RF-chromatin interactions, Pol II dynamics, and nascent transcription kinetics—reveals detailed operational parameters of gene-regulatory mechanisms hitherto-unseen in vivo. Our approach sets the stage for single-molecule studies of complex molecular processes in live cells. • Real-time single-molecule detection in high-background, crowded cellular locales • Imaging and tracking Pol II at single genes during the transcription cycle • Organization, dynamics, and interdependencies of enhancer-bound regulatory factors • Dissection of enhancer mechanisms at the endogenous Pou5f1 and Nanog Key limitations of imaging single copies of highly abundant factors at specific intracellular sites of activity are overcome by an active target-locking system that achieves long-term tracking at single-molecule resolution. [ABSTRACT FROM AUTHOR]