New insight into the mechanism of biofouling-resistant thiazole-linked covalent organic frameworks for selective uranium capture from seawater.

The extraction of uranium from seawater is crucial for the sustainable production of nuclear fuel. Traditional amidoxime-functionalized adsorbents suffer from competitive adsorption of vanadium ion and biofouling. These challenges motivate the development of novel adsorbents for selective uranium extraction from seawater. Herein, four kinds of thiazole-linked covalent organic frameworks (COFs) were investigated to harvest uranium from seawater. The selectivity and anti-biofouling performance were systematically investigated through the molecular dynamics (MD) simulations. Driven by the pore size sieving effect and electrostatic interaction, the Ca2UO2(CO3)3 complex and vanadate anions were selectively separated by different COFs in special areas. On one hand, benefits from the small steric partition factor, the Ca2UO2(CO3)3 complex can stick on the surface of COFs. On the other hand, the dispersive negatively and positively charged areas of studied COFs work as potential binding sites for the Ca2UO2(CO3)3 complex and vanadate anions, respectively. Moreover, an analysis of pulling force and desorption time between uranium and vanadium ions further confirmed the selectivity of various thiazole-linked COFs. The anti-biofouling property was comparatively investigated by dynamic trajectory and solvent accessible surface area. Our outcomes illustrate that the hydroxyl and zwitterionic groups in the thiazole-linked COFs endow their strong surface hydrations to resist marine biofouling. In particular, the TpBdsaPa is identified as a promising candidate due to charge dispersed zwitterionic group as well as remarkable anti-biofouling ability. The present study sheds an atomic-level understanding of the thiazole-linked COFs for selective uranium uptaking from seawater, which will provide aid to design novel adsorbent with highly selective uranium extraction capacity and strong anti-biofouling property.

Alkyl modified cationic COFs for preferential trapping of charge dispersed perrhenate: Synergistic hydrophobicity and anion-recognition effects.

Charge dispersed oxoanionic pollutants (such as TcO4- and ReO4-) with low hydrophilicity are typically difficult to be preferentially extracted. Recently, cationic covalent organic frameworks (COFs) have received considerable attention for anions trapping. Two cationic COFs, denoted as Tp-S and Tp-D, were synthesized by incorporating ethyl and cyclic alkylated diquats into 2,2'-bipyridine-based COF. A synergistic effect of hydrophobic channel and anion-recognition sites were achieved by branched chains, which effectively surmounted the Hofmeister bias. Both Tp-S and Tp-D exhibited raising removal performance for surrogate ReO4- at high acidity with adsorption capacities of 435.6 and 291.4 mg g-1, respectively. Obvious variations caused by side chains were displayed in microstructures and adsorption performance. Specially, compared with Tp-D, Tp-S demonstrated desirable priority in uptake capacity and selectivity. In a real-scenario experiment, Tp-S could remove 72.8 % of ReO4- in a simulated Hanford LAW stream, which was attributed to the spatial effects and charge distribution arising from the open and flexible side chains of Tp-S. Otherwise, the rigid cyclic chains endowed pyridine-base Tp-D material an unprecedented alkaline stability. Spectra and theoretical calculations revealed a mechanism of preferential capture based on electrostatic interaction and hydrogen bonding between charge dispersed ReO4-/TcO4- and Tp-S/Tp-D. This work provides an innovative perspective to tailored materials for the treatment of oxoanionic contaminants.

Can a heavy trinitromethyl group always result in a higher density?

Density is an important property of energetic materials and is believed to increase with the addition of heavy trinitromethyl groups, as shown in previous literature. However, this study determined that the introduction of these groups produced a decrease in density, as evidenced by the lower density of 1-trinitromethyl-4-amino-3,5-dinitropyrazole ((TN-116), 1.899 g cm-3) compared to that of its precursor (4-amino-3,5-dinitropyrazole (LLM-116), 1.900 g cm-3). Mechanistic studies indicated that the reduced density was due to the significantly weaker H-bonding and π-π interactions of TN-116, which produced looser stacking compared to that of LLM-116.

Simultaneous Recognition and Separation of Organic Isomers Via Cooperative Control of Pore-Inside and Pore-Outside Interactions.

Despite the desirability of organic isomer recognition and separation, current strategies are expensive and complicated. Here, a simple strategy for simultaneously recognizing and separating organic isomers using pillararene-based charge-transfer cocrystals through the cooperative control of pore-inside and pore-outside intermolecular interactions is presented. This strategy is illustrated using 1-bromobutane (1-BBU), which is often produced as an isomeric mixture with 2-bromobutane (2-BBU). According to its structure, perethylated pillar[5]arene (EtP5) and 3,5-dinitrobenzonitrile (DNB) are strategically chosen as a donor and an acceptor. As a result, their cocrystal exhibited stronger pore-inside interactions and much weaker pore-outside interactions with 1-BBU than with 2-BBU. Consequently, nearly 100% 1-BBU selectivity is achieved in two-component mixtures, even in those containing trace 1-BBU (1%), whereas free EtP5 only achieved 89.80% selectivity. The preference for linear bromoalkanes is retained in 1-bromopentane/3-bromopentane and 1-bromohexane/2-bromohexane mixtures, demonstrating the generality of this strategy. Selective adsorption of linear bromoalkanes induced a naked-eye-detectable color change from red to white. Moreover, the cocrystal are used over multiple cycles without losing selectivity.

Full-nitro-nitroamino cooperative action: Climbing the energy peak of benzenes with enhanced chemical stability.

More nitro groups accord benzenes with higher energy but lower chemical stability. Hexanitrobenzene (HNB) with a fully nitrated structure has stood as the energy peak of organic explosives since 1966, but it is very unstable and even decomposes in moist air. To increase the energy limit and strike a balance between energy and chemical stability, we propose an interval full-nitro-nitroamino cooperative strategy to present a new fully nitrated benzene, 1,3,5-trinitro-2,4,6-trinitroaminobenzene (TNTNB), which was synthesized using an acylation-activation-nitration method. TNTNB exhibits a high density (d: 1.995 g cm-3 at 173 K, 1.964 g cm-3 at 298 K) and excellent heat of detonation (Q: 7179 kJ kg-1), which significantly exceed those of HNB (Q: 6993 kJ kg-1) and the state-of-the-art explosive CL-20 (Q: 6534 kJ kg-1); thus, TNTNB represents the new energy peak for organic explosives. Compared to HNB, TNTNB also exhibits enhanced chemical stability in water, acids, and bases.

Optimal control of stochastic system with Fractional Brownian Motion.

In this paper, we introduce a class of stochastic harvesting population system with Fractional Brownian Motion (FBM), which is still unclear when the stochastic noise has the character of memorability. Stochastic optimal control problems with FBM can not be studied using classical methods, because FBM is neither a Markov pocess nor a semi-martingale. When the external environment impact on the system of FBM, the necessary and sufficient conditions for the optimization are offered through the stochastic maximum principle, Hamilton function and ItÔ formula in our work. To illustrate our study, we provide an example to demonstrate the obtained theoretical results, which is the expansion of certainty population system.

Highly Selective Separation Intermediate-Size Anionic Pollutants from Smaller and Larger Analogs via Thermodynamically and Kinetically Cooperative-Controlled Crystallization.

Selective separation of organic species, particularly that of intermediate-size ones from their analogs, remains challenging because of their similar structures and properties. Here, a novel strategy is presented, cooperatively (thermodynamically and kinetically) controlled crystallization for the highly selective separation of intermediate-size anionic pollutants from their analogs in water through one-pot construction of cationic metal-organic frameworks (CMOFs) with higher stabilities and faster crystallization, which are based on the target anions as charge-balancing anions. 4,4'-azo-triazole and Cu2+ are chosen as suitable ligand and metal ion for CMOF construction because they can form stronger intermolecular interaction with p-toluenesulfonate anion (Ts-) compared to its analogs. For this combination, a condition is established, under which the crystallization rate of a Ts--based CMOF is remarkably high while those of analog-based CMOFs are almost zero. As a result, the faster crystallization and higher stability cooperatively endow the cationic framework with a close-to-100% selectivity for Ts- over its analogs in two-component mixtures, and this preference is retained in a practical mixture containing more than seven competing (analogs and inorganic) anions. The nature of the free Ts- anion in the cationic framework also allows the resultant CMOF to be recyclable via anion exchange.

Highly Efficient Separation of Anionic Organic Pollutants from Water via Construction of Functional Cationic Metal-Organic Frameworks and Mechanistic Study.

Organic anions possess various functional properties; however, their presence in wastewater causes environmental pollution. Thus, coupling the separation of such species with the resultant function could be highly desirable. Herein, we propose a "killing two birds with one stone" strategy for highly efficient separation of organic pollutant anions from water at room temperature through direct construction of functional cationic metal-organic frameworks (CMOFs) based on the organic anions as charge-balancing anions. To illustrate this strategy, 2,4,6-trinitrophenolate anion (PA-) is chosen as a typical anion, while 4,4'-azo-triazole (atrz) is strategically chosen as a suitable neutral ligand. The resultant positive framework exhibits a high adsorption capacity and selectivity for PA-. Remarkably, its adsorption capacity is 869.6 mg g-1, which is more than 30 times that of multiwalled carbon nanotubes and 15 times that of activated carbon. Its capacity is even higher than that of BUT-13 (865 mg g-1), the highest adsorbent ever known. 1H NMR and single-crystal X-ray diffraction show that the high capacity is attributed to strong electrostatic interaction between the positive framework and PA-, which leads to all the pores being completely occupied by PA- anions. 1H NMR titration reveals that the selectivity comes from stronger hydrogen-bonding interaction between the ligand of the positive framework and PA-, which is confirmed from the eight times length of the shifted signal of atrz due to the addition of PA- compared with the competing anions. The stronger interaction is further confirmed from the high stability of the resultant CMOF in high-concentration salt solutions containing the competing anions, particularly in 100-fold molar NaNO3 and Na2SO4 solutions. Meanwhile, first-principles simulation shows that the high binding energy between the positive framework and PA- contributes to enhancing the selectivity. Moreover, the resultant CMOF is a potential energetic material with an improved oxygen balance, high heat of formation, and heat of detonation.

Coagulation mechanisms of humic acid in metal ions solution under different pH conditions: A molecular dynamics simulation.

Humic acid (HA) exerts a variety of significant environmental and geochemical influences on the soils, sediments and aqueous environments. The interaction with metal ions induces strong HA-metal complexation, thus effecting the transport of the toxic metals as well as the colloidal aggregation of HA. In the present work, we systematically report and analyze the aggregation mechanisms of HAs in solutions filled with different heavy cations (Ag+, Cd2+ and Cr3+) or common metal ions (Na+, Ca2+ and Al3+) under neutral and low pH conditions by using molecular dynamic simulations. We aim to explore the effects of pH, metal ions type and other possible weak interactions on the aggregation capabilities of HA. Scrutiny of the simulation results showed that the aggregation of HAs under neutral condition was driven by the HA-metal complexation which combined the effects of electrostatic attraction and inter-molecular bridging between cations and COO- groups. Larger extent of aggregation was found in heavy metal ions compared with the common ones. On the other hand, under low pH condition, due to the protonation states of carboxyl and phenolic group, the aggregation of HAs was stabilized mainly by weak forces, such as hydrogen bonds between different functional groups. In addition, other weak interactions such as the hydrophilic and hydrophobic effects, the cation-π interactions have also been proposed to be progressive effects on the coagulation behavior. Our computational studies give supplement to the experimental observation and provide insights into the intrinsic mechanisms of the aggregation behavior of HAs and their complexation with metal ions. Such computational modelling supplied a highly effective tool for qualitatively evaluating their roles in environmental remediation.

Effect of co-existing Co2+ ions on the aggregation of humic acid in aquatic environment: Aggregation kinetics, dynamic properties and fluorescence spectroscopic study.

The fate and transport of humic substances in the aquatic environments depend significantly on their interactions with co-existing ions. Herein, we employed dynamic light scattering (DLS) measurement, molecular dynamic (MD) simulation and fluorescence spectrometry to investigate the aggregation of humic acid (HA) in the presence of Co2+ ions. The aggregation kinetics was depicted by hydrodynamic diameter () and the attachment efficiency (α) of HA aggregates. α increases gradually in the reaction-limited (slow) regime due to the decrease of the double layer repulsion, and the energy barrier is eliminated to a certain extent in the diffusion-limited reaction while α close to unity. The complexation between functional groups (i.e. carboxylic and phenolic groups) of HA and Co2+ ions contributes significantly to the aggregation process of HA. MD simulation and density functional theory (DFT) calculation demonstrate that the aggregation process of HA can be promoted by Co2+ through several inter- or intra-molecular interactions between HA and the Co2+ ions. The results provide a pathway for insight into the interactions between HA and metal ions, which is important for deeply understanding the environmental behaviors of HA in natural aqueous systems.

Computational Study on the Excited-State Decay of 5-Methylcytosine and 5-Hydroxymethylcytosine: The Common Form of DNA Methylation and Its Oxidation Product.

5-Methylcytosine (5mC) is the predominant epigenetic modification of DNA. 5mC and its sequential oxidation product, 5-hydroxymethylcytosine (5hmC), are crucial epigenetic markers which have a profound impact on gene stability, expression, and regulation. In the present work, ab initio electronic structure computations were performed to investigate the excited-state decay pathways for 5mC and 5hmC in both the neutral and protonated forms. Based on the theoretical quantities, four nonradiative decay pathways via conical intersections (CIs) were identified: ring distortion, ring opening, N-H dissociation, and intersystem crossing (ISC) pathways. Additional calculated potential energy surfaces revealed that ring distortion and ISC pathways were the most effective routes for 5mC and 5hmC, respectively. The influence of environmental factors, such as the solution and an acidic environment, was also explored in this study. Our study demonstrated that excited-state decay pathways via CIs are indispensable for the photostability of DNA epigenetic modifications and may be involved in ingenome stability and mammalian development.

Excited-State Decay Pathways of Flavin Molecules in Five Redox Forms: The Role of Conical Intersections.

Flavin molecules play an important role in light-driven biological activities. They have drawn significant interest for decades because of their rich photochemistry. In addition to the well-explored FADH- (anionic hydroquinone), which is supposed to be the only catalytic active state to repair DNA lesions, other four flavin molecules (i.e., FAD, FAD·-, FADH·, and FADH2) in three redox forms combined the redox cycle of flavins. Although extensive studies have been carried out for steady-state spectroscopic properties of five redox flavins in various proteins and solutions, the photochemistry and photophysical properties of those different redox states significantly complicate the corresponding theoretical studies. In present work, we employed the ab initio wave function based CASSCF method to systematically investigate the excited state decay pathways of flavins in five redox forms through two approaches. First, the comparison of the absorption and emission spectra from both theoretical calculation and experiment allows a detailed mapping of the transition properties of different redox states in flavins. Second, we identified four kinds of conical intersections (CIs) for five different redox states as the possible deactivation mechanisms responsible for internal conversion or intersystem crossing from the initially populated excited state. The theoretical calculations provide atomic details for the photochemical and photophysical properties of flavins on photoinduced processes. Our findings highlight the indispensable effects of CIs in the excited state decay of flavin molecules and thereby provide basic theoretical information for light-driven biological activities.

[Treatment of humeral shaft fractures in children with closed reduction and external fixation].

OBJECTIVE: To explore the clinical effect of closed reduction and minimally invasive treatment of humeral shaft fractures in children. METHODS: From July 2011 to April 2015, 39 cases of pediatric humeral shaft fractures were treated by closed reduction and external fixation, including 27 males and 12 females with a mean age of 8.6 years old ranging from 3 to 14 years old. Time from injury to the treatment was 2 h to 7 days with an average of 2.7 days. There were 6 cases of upper fracture, 21 cases of middle fracture and 12 cases of lower fracture. All children were closed injury, appeared pain, swelling, local deformity and limited mobility and other symptoms after injury. X-ray examination showed humeral shaft fracture. Neer score of shoulder joint function and HSS score of elbow joint function were used to record and analyze the pain, function and activity of shoulder and elbow joint before and after treatment. RESULTS: All the 39 cases were followed up for 6 to 12 months with a mean of 8.6 months. Two cases appeared postoperative superficial infection of the needle, and healed after dress; other cases gained good pinhole healing. There were significant differences in the pain, function and activity of the shoulder of Neer score before and after the treatment (P<0.05). There were significant differences in the pain and function of the elbow of HSS before and after treatment (P<0.05). According to the evaluation of Neer score of shoulder function, the total score was 88.82±2.50, 29 cases were excellent, 9 cases were good, and 1 case was fair. According to the evaluation of HSS score of elbow joint function evaluation, the total score was 91.51±5.09, 30 cases were excellent, 7 cases were good, 2 cases were general. CONCLUSIONS: Manual closed reduction combined with external fixation for the treatment of humeral shaft fractures in children has advantages of less trauma, definite reduction effect, reliable fixation and benefit for early functional exercise of the shoulder and elbow joint. This therapy can be used as one of clinical methods for the treatment of humeral shaft fractures in children.

[Bone setting manipulative reduction for the treatment of children's distal radioulnar fracture and dorsal dislocation].

OBJECTIVE: To observe the effect of different manipulative reduction for children's distal radioulnar fracture and dorsal dislocation. METHODS: From June 2013 to June 2014, 80 children with distal radioulnar fracture and dorsal dislocation were treated by bone setting manipulative reduction including 51 males and 29 females with an average age of 6.5 years old ranging from 3 to 14 years old. Time from injury to treatment was 1 h to 6 d, 31 cases were on the right, 49 cases were on the left. Among them, 45 cases were type I of overlapping displacement, 35 cases were type II. The displacement of the fracture was observed by clinical manifestations and X-ray examination. Under fluoroscopy, different techniques were used for reduction and fixation. After 3 weeks of over wrist fixation, the splints were overturned and fixed again for 1 to 2 weeks, then were removed. The wrist joint function was evaluated based on Dienst criteria. RESULTS: Eighty cases of fracture were successfully operated one time, all reached anatomic reduction or near anatomic reduction. Eighty children were followed up for 3 months to 1 year. All the fractures healed, and the healing time was 4 to 5 weeks with an average of 4.6 weeks. All patients removed the splint 3 months later, the results were excellent in 72 cases, good in 7 cases and fair in 1 case, the excellent and good rate was 98.75%. CONCLUSIONS: Bone setting manipulation for children's distal radioulnar fracture and dorsal dislocation can get good reduction. At 1 month after the removal of the splint, wrist function and finger strength gradually recovered and returned to normal after 3 months.