Self-assembly of colloids with competing interactions confined in spheres.

At low temperatures, colloidal particles with short-range attractive and long-range repulsive interactions can form various periodic microphases in bulk. In this paper, we investigate the self-assembly behaviour of colloids with competing interactions under spherical confinement by conducting molecular dynamics simulations. We find that the cluster, mixture, cylindrical, perforated lamellar and lamellar structures can be obtained, but the details of the ordered structures are different from those in bulk systems. Interestingly, the system tends to form more perforated structures when confined in smaller spheres. The mechanism behind this phenomenon is driven by the relationship between the energy of the ordered structures and the bending of the confinement wall, which is different from the mechanism in copolymer systems.

Methylmercury Degradation by Trivalent Manganese.

Methylmercury (MeHg) is a potent neurotoxin and has great adverse health impacts on humans. Organisms and sunlight-mediated demethylation are well-known detoxification pathways of MeHg, yet whether abiotic environmental components contribute to MeHg degradation remains poorly known. Here, we report that MeHg can be degraded by trivalent manganese (Mn(III)), a naturally occurring and widespread oxidant. We found that 28 ± 4% MeHg could be degraded by Mn(III) located on synthesized Mn dioxide (MnO2-x) surfaces during the reaction of 0.91 µg·L-1 MeHg and 5 g·L-1 mineral at an initial pH of 6.0 for 12 h in 10 mM NaNO3 at 25 °C. The presence of low-molecular-weight organic acids (e.g., oxalate and citrate) substantially enhances MeHg degradation by MnO2-x via the formation of soluble Mn(III)-ligand complexes, leading to the cleavage of the carbon-Hg bond. MeHg can also be degraded by reactions with Mn(III)-pyrophosphate complexes, with apparent degradation rate constants comparable to those by biotic and photolytic degradation. Thiol ligands (cysteine and glutathione) show negligible effects on MeHg demethylation by Mn(III). This research demonstrates potential roles of Mn(III) in degrading MeHg in natural environments, which may be further explored for remediating heavily polluted soils and engineered systems containing MeHg.

Periodicity and global order parameter of hexagonally packed cylinders in a periodic box.

In all molecular simulations of periodic ordered morphologies (such as those formed by block copolymers), the periodic boundary conditions (PBCs) of the simulation box usually do not match the bulk periodicity L0 of the morphology, thus changing the structure and even the stability of the morphologies obtained in the simulations. To address this problem for hexagonally packed cylinders, we first proposed a general method of calculating the periodicity of such cylinders in a cuboid simulation box with the PBCs applied in all directions, which further allows one to enumerate all possible orientations and periodicities of such cylinders within an estimated range that can fit into a cuboid box of given lengths. We then showed how to choose the lengths of a cuboid box such that regular-hexagonally packed (RHP) cylinders with given intercylinder distance and orientation can fit into the box. Next, taking as an example the dissipative particle dynamics (DPD) simulations of a cylinder-forming diblock copolymer melt, we showed that L0 of RHP cylinders oriented along the body diagonal of a cubic box is found when all the off-diagonal elements of the pressure tensor vanish. Finally, based on our general method of calculating the periodicity of hexagonally packed cylinders, we designed a global order parameter for such cylinders, which takes into account their ordering only for the orientations that can fit into the simulation box. Using again the DPD simulations, we showed that our global order parameter can be used to quantify the formation of hexagonally packed cylinders in each collected configuration and to monitor their orientation (thus periodicity) during the simulation run.

Finding the bulk periodicity of lamellar and cylindrical structures using the pressure tensor.

It has been known for nearly thirty years that in all molecular simulations of periodic ordered morphologies (such as those formed by block copolymers), when the periodic boundary conditions of the simulation box do not match the bulk periodicity L0 of the morphology, they change the structure and even the stability of the morphologies obtained in the simulations. Few studies, however, have focused on finding L0 in simulations. Taking dissipative particle dynamics simulations of asymmetric diblock copolymer melts as an example, we found a simple way of using the pressure tensor, which can be readily calculated in molecular simulations in the continuum, to find L0 of lamellae and (regular-hexagonally packed) cylinders regardless of their orientation in (cuboid) simulation boxes. Variation of the diagonal and off-diagonal elements of the pressure tensor with the orientation of lamellae and cylinders in the box is explained by coordinate system rotation and confirmed by our simulation results. We also showed that the pressure tensor cannot be used to find L0 of 3D periodic ordered structures with a cubic symmetry such as the double gyroid.

Transformable Colloidal Polymer Particles with Ordered Internal Structures.

Based on studies combining experiments and simulations, internally ordered colloidal particles that are able to undergo morphological transformations both in shape and internal structure are presented. The particles are prepared by emulsion solvent evaporation-induced 3D soft confined assembly of di-block copolymer polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP). Control over the solvent selectivity leads to a dramatic change in shape and internal structure for particles. Pupa-like particles of lamellar morphology are obtained when using a non-selective solvent, while patchy particles possessing a plum pudding structure formed when the solvent is selective for PS-block. More interestingly, 3D soft confined annealing drives order-order morphological transformation of the particles. The morphology of reshaped particles can be well controlled by varying the solvent selectivity, annealing time, and interfacial interaction. The experimental results can be explained based on simulations. This study can offer considerable scope for the design of new stimuli-responsive colloidal particles for potential applications in photonic crystal, drug delivery and release, sensor and smart coating, etc.

Controlling the chirality and number of strands of helices self-assembled from achiral block copolymers confined inside a nanopore: a simulation study.

Achiral block copolymers can self-assemble into helical structures when confined inside a cylindrical nanopore. However, controlling the chirality and the number of strands of helices is challenging. We present our simulation results of the influence of a chiral patch added to the confining nanopore on the structures and chirality of helices self-assembled from achiral cylinder-forming diblock copolymers under the confinement. Our results indicate that, when the designed patch is of proper geometry, it can induce the formation of helical structures and exhibit good control over their chirality. The bottom surface of the patch can induce the formation of a characteristic local structure near and parallel to it. It is the characteristic local structure that directs the formation of helices and of their chirality consistent with that of the patch. A large patch angle or the top/bottom surface of a weakly selective pore promotes the formation of double-helices compared to single-helices by enlarging the pitch of the helices near the patch or through the entropic attraction of the top surface of the pore to the minority blocks.

A simulation study of the self-assembly of ABC star terpolymers confined between two parallel surfaces.

The phase behavior of ABC star terpolymers confined between two identical parallel surfaces is systematically studied using a simulated annealing method. Several phase diagrams are constructed for systems with different bulk phases or with different interfacial interaction strength ratios in the space of surface distance (D) and surface preference for different arms, or in the space of D and the arm-length ratio x. Phases, including tiling patterns [6.6.6], [8.8.4], [8.6.6; 8.6.4], [8.6.6; 8.6.4; 10.6.6; 10.6.4] and hierarchical lamellar structures of lamella + cylinders and lamella + rods, are identified both in the bulk and in the films. Our results suggest that the self-assembled structure of a phase is largely controlled by x, while an increase of the interfacial interaction strength ratio shifts the x-window for each phase to the smaller x side. The orientation of a confined phase depends on the "effective surface preference" which is a combined effect of the interfacial interaction strength ratio, the surface preference, and the entropic preference. In the case of neutral or weak "effective surface preference", phases with a perpendicular orientation are usually observed, while in the case of strong "effective surface preference" phases with a perpendicular orientation or also with outermost wetting-layers can be frequently observed under some circumstances.

Simple-to-use nomogram for predicting the risk of syphilis among MSM in Guangdong Province: results from a serial cross-sectional study.

BACKGROUND: The purpose of this study was to develop and validate a simple-to-use nomogram for the prediction of syphilis infection among men who have sex with men (MSM) in Guangdong Province. METHODS: A serial cross-sectional data of 2184 MSM from 2017 to 2019 was used to develop and validate the nomogram risk assessment model. The eligible MSM were randomly assigned to the training and validation dataset. Factors included in the nomogram were determined by multivariate logistic regression analysis based on the training dataset. The receiver operating characteristic (ROC) curves was used to assess its predictive accuracy and discriminative ability. RESULTS: A total of 2184 MSM were recruited in this study. The prevalence of syphilis was 18.1% (396/2184). Multivariate logistic analysis found that age, the main venue used to find sexual partners, condom use in the past 6 months, commercial sex in the past 6 months, infection with sexually transmitted diseases (STD) in the past year were associated with syphilis infection using the training dataset. All these factors were included in the nomogram model that was well calibrated. The C-index was 0.80 (95% CI 0.76-0.84) in the training dataset, and 0.79 (95% CI 0.75-0.84) in the validation dataset. CONCLUSIONS: A simple-to-use nomogram for predicting the risk of syphilis has been developed and validated among MSM in Guangdong Province. The proposed nomogram shows good assessment performance.

Phase behavior of ABC cyclic terpolymer melts: a simulation study.

The phase behavior of ABC cyclic terpolymer melts is investigated using a simulated annealing technique. A ternary phase diagram is constructed by tuning the volume fractions of the three blocks (fA, fB, and fC) in the case of symmetric interactions. 11 phases are predicted, including lamellae with spheres at the interfaces, lamellae with spheres inside a domain, lamellae with spheres inside domains, cylinders in perforated lamellae, [6.6.6] tiling patterns, lamella + cylinder, hierarchical double-gyroid, columnar piled disk, patched spheres, cylinders with spheres at the interfaces and double gyroid with spheres at the interfaces. In these structures, the end segments of the three blocks tend to distribute uniformly on the A/B, B/C, or A/C interfaces, which may result in superior mechanical properties of the structures in cyclic terpolymer systems than those of the same structures formed in star or linear terpolymer systems. The physical reason for the similarities and differences between the phases formed in ABC cyclic and star terpolymer systems is investigated. Our simulation results are compared with related experimental observations and theoretical calculations.

Lattice self-consistent field calculations of confined symmetric block copolymers of various chain architectures.

The effects of chain architecture and confinement on the structure and orientation of lamellae formed by incompressible and symmetric AB-type block copolymer melts confined between two parallel and identical surfaces are investigated using self-consistent field calculations on a simple cubic lattice. Five systems of various chain architectures (linear, ring, and star) and lengths are studied, with their bulk lamellar period L0 chosen such that they have comparable L0/Rg, where Rg denotes the ideal-chain radius of gyration. For thin films of thickness D = L0 confined between two neutral surfaces, we define the rescaled volume fraction profiles of A, B, chain end, and joint segments in the parallel and perpendicular lamellae such that these profiles can be directly compared among the five systems to quantitatively reveal the interplay between the chain-end enrichment near confining surfaces and the surface-induced A-B compatibilization, and how such interplay is affected by the chain architectures (for example, the chain-crowding effects in the star block copolymers). The effects of D and surface preference for one of the blocks are also investigated.

Formation Mechanisms of Porous Particles from Self-Assembly of Amphiphilic Diblock Copolymers inside an Oil-in-Water Emulsion Droplet upon Solvent Evaporation.

The formation mechanisms of porous particles from self-assembly of amphiphilic diblock copolymers inside an oil-in-water emulsion droplet upon evaporation of the organic solvent are investigated based on Monte Carlo simulations for the first time. A morphological diagram of particles is constructed as a function of the surfactant concentration (φ) and the copolymer composition characterized by the volume fraction of the hydrophilic B block ( fB). Particles with various morphologies are predicted. Morphological sequences from non-porosity to closed-porosity to capsules and finally to open-porosity particles are usually observed with increasing φ when fB ≤ 1/2, with the only exception that capsules do not occur when fB = 1/6. Furthermore, the critical φ value for a given morphological transition usually decreases with increasing fB. Micelles are always observed at higher φ regions when fB > 1/2. It is found that the specific surface area falls on almost the same regime for particles with the same kind of morphology, indicating that the morphology of a particle largely determines its specific surface area. The chain stretching varies with the particle morphology. It is the presence of the surfactant that makes the formation of porous particles possible, while when φ > 0, multiple morphological transitions can be induced by changing fB. In the process of organic solvent removal, the value of fB may affect the shape of pores inside the droplet and hence leads to the fB dependence of the morphological sequences. When the solvent evaporation is not too fast, the resulting morphological sequence does not depend on the evaporation rate. Our results are compared with related experiments.

Pharmacokinetics and safety of tadalafil in a paediatric population with pulmonary arterial hypertension: A multiple ascending-dose study.

AIMS: To evaluate the pharmacokinetics and safety of once-daily (QD) tadalafil in paediatric patients with pulmonary arterial hypertension (PAH) to establish an appropriate dose range for further research. METHODS: This was an open-label, multicentre, international, multiple-ascending-dose study. Patients aged ≥2 years were enrolled into 1 of 3 cohorts based on body weight: heavy-weight (≥40 kg), middle-weight (25 to <40 kg), and light-weight (<25 kg). Each patient received tadalafil QD for 10 weeks: 5 weeks at a low dose, then 5 weeks at a high dose. The doses for each cohort were intended to produce plasma tadalafil concentrations within the range produced by 5-10 mg (for the low dose) or 20-40 mg (for the high dose) of tadalafil in adults with PAH. Area under the plasma concentration-time curve during 1 dosing interval (AUCτ ), maximum concentration, and apparent clearance were assessed throughout the trial, as were safety and tolerability. RESULTS: The study enrolled 19 patients aged 2-17 years, weighing 9.9-76.0 kg. Tadalafil's median (range) steady-state AUCτ at the high dose was 7243 (3131-13 088) ng•h/mL across all patients. Concentrations were higher in no bosentan-treated patients than in bosentan-treated patients, but both populations were within the range of respective adult patients taking 20-40 mg QD. Tadalafil had an acceptable safety profile consistent with the known safety profile of tadalafil in adults. CONCLUSIONS: Tadalafil 40 mg QD for patients ≥40 kg, and 20 mg QD for patients <40 kg and aged ≥2 years, are suitable for further research in paediatric patients with PAH.

Modulation of thermodynamic and kinetic inverted phase behavior of block copolymers by inorganic polyoxometalates.

The Keggin polyoxometalates (POM) H3PW12O40 (PW) electrostatically complexed with poly(styrene-block-2-vinyl pyridine) (PS-b-P2VP) in DMF, and ordered microphase separation occurred through solvent evaporation. The phase behaviors of PS-b-P2VP/PW in bulk were systematically investigated by using SAXS and TEM to discover the effect of POM content and molecular weight of the block copolymers. Computational simulation was also performed to reveal the same phase transition sequence as the experimental results. As the POM content increases, the PS-b-P2VP/PW complex with a low molecular weight changed from lamellar phase (LAM) to hexagonal cylindrical phase (HEX), and finally transited into spherical phase (SPH). Unexpectedly, PS-b-P2VP/PW complexes with a high molecular weight were inclined to form a kinetic-trapped intermediate phase (inverted HEX). The mechanism of formation of inverted phases was proposed based on simulation that asymmetric swelling in the concentrated DMF solution would result in the ultimate kinetic-trapped nanostructure in the bulk.

Effect of Chain Architecture on Self-Assembled Aggregates from Cyclic AB Diblock and Linear ABA Triblock Copolymers in Solution.

The self-assembly behaviors of two block copolymers with the same chain length but different chain architectures (cyclic AB, linear ABA) in B-selective solvents are investigated using Monte Carlo simulations. A morphological transition sequence, from spherical micelles to cylindrical micelles, to vesicles and then to multicompartment vesicles, is observed for both copolymer systems when the interaction between the solvophobic A-block and the solvent is increased. In particular, toroidal micelles could be formed in triblock systems due to the presence of the bridging chains at the parameter region between cylindrical micelles and vesicles whereas disklike micelles are formed in cyclic systems. The simulation results demonstrated that the architecture of block copolymers could be used to regulate the structural characteristics and thermal stability of these self-assembled aggregates.

Lattice self-consistent field calculations of ring polymer brushes.

We reported the first systematic study using lattice self-consistent field (LSCF) calculations of ring homopolymer brushes grafted onto a flat and homogeneous surface and immersed in an explicit and athermal solvent, which are either uncompressed, compressed by a flat and impenetrable surface, or compressed by an identical brush. Our results clearly show that ring brushes are slightly less stretched than, thus nearly but not completely identical to, the "equivalent" linear brushes having half the chain length and double the grafting density. Our LSCF results are consistent with the molecular simulation results reported in the literature (Reith et al., Europhys. Lett., 2011, 95, 28003; Erbas and Paturej, Soft Matter, 2015, 11, 3139), except that Erbas and Paturej reported that the normal pressure of two opposing ring brushes is only half of the "equivalent" linear brushes at melt density.

Conformation transitions of a single polyelectrolyte chain in a poor solvent: a replica-exchange lattice Monte-Carlo study.

The thermodynamic behaviors of a strongly charged polyelectrolyte chain in a poor solvent are studied using replica-exchange Monte-Carlo simulations on a lattice model, focusing on the effects of finite chain length and the solvent quality on the chain conformation and conformation transitions. The neutralizing counterions and solvent molecules are considered explicitly. The thermodynamic quantities that vary continuously with temperature over a wide range are computed using the multiple histogram reweighting method. Our results suggest that the strength of the short-range hydrophobic interaction, the chain length, and the temperature of the system, characterized by ε, N, and T, respectively, are important parameters that control the conformations of a charged chain. When ε is moderate, the competition between the electrostatic energy and the short-range hydrophobic interaction leads to rich conformations and conformation transitions for a longer chain with a fixed length. Our results have unambiguously demonstrated the stability of the n-pearl-necklace structures, where n has a maximum value and decreases with decreasing temperature. The maximum n value increases with increasing chain length. Our results have also demonstrated the first-order nature of the conformation transitions between the m-pearl and the (m-1)-pearl necklaces. With the increase of ε, the transition temperature increases and the first-order feature becomes more pronounced. It is deduced that at the thermodynamic limit of infinitely long chain length, the conformational transitions between the m-pearl and the (m-1)-pearl necklaces may remain first order when ε > 0 and m = 2 or 3. Pearl-necklace conformations cannot be observed when either ε is too large or N is too small. To observe a pearl-necklace conformation, the T value needs to be carefully chosen for simulations performed at only a single temperature.

Long Noncoding RNA PVT1 as a Potent Predictor of Prognosis in Cancers: a Meta-Analysis.

BACKGROUND: Plasmacytoma variant translocation 1 (PVT1), an oncogenic long noncoding RNA located in a recognized cancer-risk gene region-8q24, is significantly overexpressed in various cancers. Many studies have found that high expression of PVT1 was correlated with poor prognosis. METHODS: This meta-analysis was performed by searching electronic databases Pubmed, Web of Science, Chinese National Knowledge Infrastructure, WanFang, and ChongQing VIP for eligible papers on the prognostic impact and clinicopathological characteristics of PVT1 expression in cancer from inception to January 31, 2017. The hazard ratio (HR) and odds ratio (OR) with 95% confidence intervals (CI) were computed to estimate the pooled effect of PVT1 on prognosis of cancers using Stata 12.0 version software. RESULTS: Thirteen studies were finally included in this review with a total of 1559 patients. The pooled result indicated that overexpressed PVT1 predicts a poorer prognosis of cancerous patients for overall survival (HR = 1.91, 95% CI: 1.61 - 2.26, p < 0.001) and disease-free survival (HR = 1.90, 95% CI: 1.46 - 2.48, p < 0.001) or recurrencefree survival (HR = 1.77, 95% CI: 1.24 - 2.52, p = 0.002) or progression-free survival (HR = 2.84, 95% CI: 1.67 - 4.82, p < 0.001). High expression of PVT1 was closely associated with tumor-node-metastasis (TNM) stage (III/IV vs. I/II: OR = 3.19, 95% CI: 2.43 - 4.18, p < 0.001), and the significant correlation between PVT1 expression and TNM stage is found in T classification (T3/4 vs. T1/2: OR = 6.48, 95% CI: 2.93 - 14.31, p < 0.001) and lymph node metastasis (present vs. absent: OR = 2.56, 95% CI:1.36 - 4.80, p = 0.003), but not in distant metastasis of patients with cancers (yes vs. no: OR = 2.50, 95% CI: 0.72 - 8.66, p = 0.15). Furthermore, the cancerous patients with high PVT1 expression had a worse histological differentiation than those with low PVT1 expression (undifferentiated/poorly vs. moderately/well: OR = 1.48, 95% CI: 1.02 - 2.14, p = 0.039). CONCLUSIONS: PVT1 could serve as a potent predicator of prognosis in different types of cancers.

Influence of Grafting Point Distribution on the Surface Structures of Y-Shaped Polymer Brushes in Solution.

We report a simulated annealing study of surface structures of the Y-shaped copolymers grafted onto a planar substrate in nonselective solvents. The influences of the lateral size of the grafting surface and the distribution manner of the grafting point on the order degree of the ripple structures are investigated. Under uniformly distribution conditions, it is found that the well-defined ripple structures can be formed when the lateral size less than a threshold which depends on the solvent quality and grafting density. However, introducing a density fluctuation into the uniformly distribution grafting points in different ways, the defects with different degrees are observed in the ripple structures. The influence of the density fluctuations on the ripple phase are studied quantitatively. Furthermore, the possibility of the formation of surface structures with long-range order induced by directed self-assembly is investigated. The findings provide guidelines for fabricating patterned surfaces with highly ordered structures.

Phase behavior of ABC-type triple-hydrophilic block copolymers in aqueous solutions.

The phase behavior of symmetric ABC triple-hydrophilic triblock copolymers in concentrated aqueous solutions is investigated using a simulated annealing technique. Two typical cases, in which the hydrophilicity of the middle B-block is either stronger or weaker than that of the end A- and C-blocks, are studied. In these two cases, a variety of phase diagrams are constructed as a function of the volume fraction of the B-block and the copolymer concentration ([Formula: see text] for both non-frustrated and frustrated copolymers. Structures, such as two-color alternatingly packed cylinders or gyroid, and lamellae-in-lamellae etc. that do not occur in the melt system, are obtained in solutions. Rich phase transition sequences, especially re-entrant phase transitions involving complex continuous networks of alternating gyroid and alternating diamond are observed for a given copolymer with decreasing [Formula: see text] . The difference in hydrophilicity among different blocks can result in inhomogeneous distribution of solvent molecules in the morphology, and with the decrease of [Formula: see text] , the distribution of solvent molecules presents a non-monotonic variation. This results in a non-monotonic variation of the effective volume fraction of each domain with the decrease of [Formula: see text] , which induces the re-entrant phase transitions. The presence of a good solvent for all the blocks can cause changes in the effective segregation strengths between different blocks and also in chain conformations, hence can alter the bulk phases and results in the occurrence of new structures and phase transitions. Especially, structures having A-C interfaces or A-C mixed domains can be obtained even in the non-frustrated copolymer systems, and structures obtained in the frustrated systems may be similar to those obtained in the non-frustrated systems. The window of the alternating gyroid structures may occupy a large part of the phase diagram for non-frustrated copolymers with stronger B-hydrophilicity. This behavior can be used to tune the self-assembled structures of block copolymers.

Complexation behavior of oppositely charged polyelectrolytes: Effect of charge distribution.

Complexation behavior of oppositely charged polyelectrolytes in a solution is investigated using a combination of computer simulations and experiments, focusing on the influence of polyelectrolyte charge distributions along the chains on the structure of the polyelectrolyte complexes. The simulations are performed using Monte Carlo with the replica-exchange algorithm for three model systems where each system is composed of a mixture of two types of oppositely charged model polyelectrolyte chains (EGEG)5/(KGKG)5, (EEGG)5/(KKGG)5, and (EEGG)5/(KGKG)5, in a solution including explicit solvent molecules. Among the three model systems, only the charge distributions along the chains are not identical. Thermodynamic quantities are calculated as a function of temperature (or ionic strength), and the microscopic structures of complexes are examined. It is found that the three systems have different transition temperatures, and form complexes with different sizes, structures, and densities at a given temperature. Complex microscopic structures with an alternating arrangement of one monolayer of E/K monomers and one monolayer of G monomers, with one bilayer of E and K monomers and one bilayer of G monomers, and with a mixture of monolayer and bilayer of E/K monomers in a box shape and a trilayer of G monomers inside the box are obtained for the three mixture systems, respectively. The experiments are carried out for three systems where each is composed of a mixture of two types of oppositely charged peptide chains. Each peptide chain is composed of Lysine (K) and glycine (G) or glutamate (E) and G, in solution, and the chain length and amino acid sequences, and hence the charge distribution, are precisely controlled, and all of them are identical with those for the corresponding model chain. The complexation behavior and complex structures are characterized through laser light scattering and atomic force microscopy measurements. The order of the apparent weight-averaged molar mass and the order of density of complexes observed from the three experimental systems are qualitatively in agreement with those predicted from the simulations.