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In the work, sulfhydryl functionalized montmorillonite nanosheets based hydrogel balls were firstly synthesized for Pb(II) adsorption, and then characterized by scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), surface area analyzer (BET), thermogravimetry (TG), and zeta potential. Effects of initial solution pH, adsorbent dosage, contact time, temperature on Pb(II) adsorption of the resulting hydrogel balls were investigated systematically. The experimental results showed that the increase amount of sulfhydryl functionalized montmorillonite nanosheets (MMTNs-SH) maintained the hydrogel balls a better porous structure and bigger specific surface area, endowing it a bigger adsorption capacity. The adsorption process was fitted well with pseudo-second-order kinetics model and Freundlich model, and more than 97% of Pb(II) could be removed under the optimum conditions. Moreover, hydrogel spheres have a certain cycle performance. In addition, the interactions between Pb(Ⅱ) ions and the oxygen atoms in the hydroxyl groups and the sulfur atoms in the sulfhydryl groups, and the ion exchange in MMTNs-SH dominated the adsorption.

Defect-containing MoS2/ reduced graphene oxide (rGO) composites were moderately prepared via chemical etching. The effects of MoS2 defect on the structure, electrochemical and desalination performance of the defect-containing MoS2/rGO composites were comparatively researched. The results showed that the defect-containing MoS2/rGO composite chemical etched with 5.0 g NaBH4 (dMSG-5) exhibited the advantages of the fewest amount of (002) interplanar layers, the smallest water contact angle and zeta potential, and the most amount of exposed edge sites. etc., which endowed it with the largest specific capacity (305.6 F/g at 1.0 A/g), the lowest interfacial charge transfer resistance and the best CDI performance with the biggest desalination capacity of 25.47 mg/g at the voltage of 0.8 V in 200 mg/L NaCl solution. The results suggested that appropriate MoS2 defect indeed could enhance the electrochemical and desalination performance of dMSG-5 via providing more adsorption sites for Na+ insertion/extraction and ion diffusion channels, and improving the ion accessibility and transport efficiency. Those pave the way for construction of other high-performance electrode materials and making dMSG-5 attractive to the electrode of CDI device.

Fluorite, barite and calcite are important industry minerals. However, they often co-exist, presenting difficulty in selectively separating them due to their similar surface properties. In this study, valonea extract and sodium fluosilicate were used as depressants to selectively separate them by flotation, with sodium oleate as the collector. The single mineral flotation results showed that valonea extract displayed the strongest depression on calcite, while sodium fluosilicate displayed the strongest depression on barite. These two depressants allowed selective separation of the three minerals through sequential flotation. The flotation of mixed minerals showed that 94% of the calcite was successfully depressed by the valonea extract, and 95% recovery of the fluorite was achieved in the subsequent flotation with sodium fluosilicate depressing barite. The different depressant–mineral interactions were investigated via electro-kinetic studies and molecular dynamics (MD) simulations using the Materials Studio 6.0 program. The valonea extract exhibited the strongest adsorption on the calcite surface, and sodium fluosilicate exhibited the strongest adsorption on the barite surface, which prevented oleate species from reacting with Ca2+ or Ba2+ surface sites. This study provides useful guidance for how to process fluorite, barite and calcite resources.

Dihydrouridine (D) is a highly conserved modified base found in tRNAs from all domains of life. Dihydrouridine synthase (Dus) catalyzes the D formation of tRNA through reduction of uracil base with flavin mononucleotide (FMN) as a cofactor. Here, we report the crystal structures of Thermus thermophilus Dus ( Tth Dus), which is responsible for D formation at positions 20 and 20a, in complex with tRNA and with a short fragment of tRNA (D-loop). Dus interacts extensively with the D-arm and recognizes the elbow region composed of the kissing loop interaction between T- and D-loops in tRNA, pulling U20 into the catalytic center for reduction. Although distortion of the D-loop structure was observed upon binding of Dus to tRNA, the canonical D-loop/T-loop interaction was maintained. These results were consistent with the observation that Dus preferentially recognizes modified rather than unmodified tRNAs, indicating that Dus introduces D20 by monitoring the complete L-shaped structure of tRNAs. In the active site, U20 is stacked on the isoalloxazine ring of FMN, and C5 of the U20 uracil ring is covalently cross linked to the thiol group of Cys93, implying a catalytic mechanism of D20 formation. In addition, the involvement of a cofactor molecule in uracil ring recognition was proposed. Based on a series of mutation analyses, we propose a molecular basis of tRNA recognition and D formation catalyzed by Dus.

Acrylic acid was used to investigate the capabilities of novel two-dimensional molecular space with regular amino groups (layered aminopropylsilica, ATMS-DS) on influencing and controlling molecular reaction processes. The acrylic acid was regularly fixed in the layer structure of layered aminopropylsilica through the formation of amide between carboxyl of acrylic acid and amino groups of layered aminopropylsilica. The acrylic acid regularly fixed in layered aminopropylsilica was completely polymerized to form a novel organic-inorganic nanocomposite material named as layered polyacryl-amidepropylsilica (ATMS-PAA) with monolayers of polyacrylamide in layer space of layered aminopropylsilica without initiator after being heated at 100 °C for 24 h. It was found that the polymerization of acrylic acid was facilitated in the novel two-dimensional molecular space with regular amino groups compared with free space. The polymeric structure of ATMS-PAA was also found to be decided by the regular structure of layered aminopropylsilica. The novel two-dimensional molecular space with regular amino groups in structure showed a potential of influencing and controlling molecular reaction processes. The formation of a novel hybrid organic-inorganic nanocomposite material (layered polyacrylamidepropylsilica) is also interesting for the research of polymer nanocomposite materials.

The [4+2] cycloaddition remains one of the most intriguing transformations in synthetic and natural products chemistry. In nature, however, there are remarkably few enzymes known to have this activity. We herein report an unprecedented enzymatic [4+2] cyclization cascade that has a central role in the biosynthesis of pyrroindomycins, which are pentacyclic spirotetramate natural products. Beginning with a linear intermediate that contains two pairs of 1,3-diene and alkene groups, the dedicated cyclases PyrE3 and PyrI4 act in tandem to catalyze the formation of two cyclohexene rings in the dialkyldecalin system and the tetramate spiro-conjugate of the molecules. The two cyclizations are completely enzyme dependent and proceed in a regio- and stereoselective manner to establish the enantiomerically pure pentacyclic core. Analysis of a related spirotetronate pathway confirms that homologs are functionally exchangeable, establishing the generality of these findings and explaining how nature creates diverse active molecules with similar rigid scaffolds.

Avermectins (AVEs), which are widely used for the treatment of agricultural parasitic diseases, belong to a family of 6,6-spiroketal moiety-containing, macrolide natural products. AVE biosynthesis is known to employ a type I polyketide synthase (PKS) system to assemble the molecular skeleton for further functionalization. It remains unknown how and when spiroketal formation proceeds, particularly regarding the role of AveC, a unique protein in the pathway that shares no sequence homology to any enzyme of known function. Here, we report the unprecedented, dual function of AveC by correlating its activity with spiroketal formation and modification during the AVE biosynthetic process. The findings in this study were supported by characterizing extremely unstable intermediates, products and their spontaneous derivative products from the simplified chemical profile and by comparative analysis of in vitro biotransformations and in vivo complementations mediated by AveC and MeiC (the counterpart in biosynthesizing the naturally occurring, AVE-like meilingmycins). AveC catalyzes the stereospecific spiroketalization of a dihydroxy-ketone polyketide intermediate and the optional dehydration to determine the regiospecific saturation characteristics of spiroketal diversity. These reactions take place between the closures of the hexene ring and 16-membered macrolide and the formation of the hexahydrobenzofuran unit. MeiC can replace the spirocyclase activity of AveC, but it lacks the independent dehydratase activity. Elucidation of the generality and specificity of AveC-type proteins allows for the rationalization of previously published results that were not completely understood, suggesting that enzyme-mediated spiroketal formation was initially underestimated, but is, in fact, widespread in nature for the control of stereoselectivity.

Dihydrouridine synthase (Dus) is responsible for catalyzing dihydrouridine formation in RNA by the reduction of uridine. To elucidate its RNA-recognition mechanism, Dus from Thermus thermophilus (TthDus) and its complex with tRNA were crystallized. Diffraction data sets were collected from crystals of native and selenomethionine-substituted TthDus to resolutions of 1.70 and 2.30 Å, respectively. These crystals belonged to space group P1. Preliminary X-ray crystallographic analysis showed that two molecules of TthDus were contained in an asymmetric unit. In addition, diffraction data were collected to 3.51 Å resolution from a crystal of selenomethionine-substituted TthDus in complex with tRNA, which belonged to space group P4(1)2(1)2. Preliminary structural analysis showed that the asymmetric unit contained two TthDus-tRNA complexes.

A novel two-dimensional molecular space (layered carboxylpropylamidephenylsilica, CPAPhS) with regular carboxyl groups was successfully synthesized through grafting carboxyl groups in the structure of layered (aminophenyl)silica using butanedioic anhydride. The carboxyl groups regularly arranged in the layered CPAPhS can react with various organic molecules with amino and hydroxyl groups through formation of reactive intermediate with catalyzers, such as SOCl2. In this research, an example was used to prove the reaction properties of regular carboxyl groups in layered CPAPhS. The layered CPAPhS was reacted with SOCl2 to form layered acyl chloridepropylamidephenylsilica (ACPAPhS) and then reacted with n-butylamine and n-butyl alcohol to form layered n-butylamidepropylamidephenylsilica (BAPAPhS) and n-butylesterpropylamidephenylsilica (BEPAPhS) with regular molecular structures. Layered CPAPhS showed the potential as a starting material for formation of a series of novel two-dimensional molecular space with various regular molecular structures, and as a solid acceptor for chemical reagent with amino and hydroxyl groups for chemical processes.

A novel reactive layered two-dimensional molecular space material [layered chloroacetamide phenyl silica (CAAPhS)] with regular chlorine groups was synthesized by grafting chlorine groups into the layer structure of layered aminophenyl silica. The reactive activity of chlorine groups regularly arranged in the layer structure of layered CAAPhS was confirmed through a substitution reaction with n-butylamine. Layered CAAPhS showed potential as a starting material for the formation of a series of two-dimensional layered materials with various regular functional molecules and organic-inorganic composite materials.