Efficient Synthesis of High-Performance Anion Exchange Membranes by Applying Clickable Tetrakis(dialkylamino)phosphonium Cations.

Tetrakis(dialkylamino)phosphonium (TKDAAP) compounds exhibit extraordinary base resistance, a prerequisite feature for high-performance anion exchange membranes (AEMs). It is, however, challenging to synthesize a TKDAAP compound with reactive functionality that can be used to link the cation to a polymer backbone. In this study, two TKDAAP compounds with alkyne functionality were synthesized and incorporated into an azide-modified SBS triblock copolymer backbone via Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC) "click" chemistry. The properties of the resulting AEMs were characterized. It was found that (1) the triazole linker between the cation and the polymer backbone was stable under alkaline conditions; (2) varying the substituents of TKDAAP compounds could dramatically alter the stability; and (3) increasing the hydrophilicity of the AEM was an efficient way to enhance its ionic conductivity. Using clickable TKDAAP compounds makes it easy to combine various cations into polymer backbones with adjustable cation content, thus potentially leading to an efficient way to screen a wide variety of polyelectrolyte structures to identify the most promising candidates for high-performance AEMs.

Enhanced Pb(II) adsorption onto functionalized ordered mesoporous carbon (OMC) from aqueous solutions: the important role of surface property and adsorption mechanism.

Functionalized ordered mesoporous carbon (MOMC-NP) was synthesized by chemical modification using HNO3 and H3PO4 to enhance Pb(II) adsorption. The phosphate functional group represented by P-O-C bonding onto the surface of OMC was verified by FT-IR and XPS. Batch adsorption experiments revealed the improvement of adsorption capacity by 39 times over the virgin OMC. Moreover, the Pb(II) adsorption results provided excellent fits to Langmuir model and pseudo-second-order kinetic model. The adsorption mechanism of Pb(II) onto MOMC-NP revealed the formation of metal complexes with carboxyl, hydroxyl, and phosphate groups through ion exchange reactions and hydrogen bondings. The calculated activation energy was 22.09 kJ/mol, suggesting that Pb(II) adsorption was a chemisorption. At pH>pHpzc, the main Pb(II) existing species of Pb(II) and Pb(OH)+ combine with the carboxyl, hydroxyl, and phosphate functional groups via electrostatic interactions and hydrogen bonding. All these findings demonstrated that MOMC-NP could be a useful and potential adsorbent for adsorptive removal of Pb(II). Graphical abstract.

Electrorheological Effects of Synthesized Octa-cyanopropylsilsesquioxane Cage Structure.

This article introduces a new electrorheological (ER) fluid. A molecular cage structure for electrorheological applications has been synthesized, and the ER behavior of the octa-functionalized polyhedral oligomeric silsesquioxane (POSS) variant in silicone oil (PDMS) has been shown. The hydrolyzation route has been used in the synthesis, the microstructure has been displayed using scanning electron microscopy, the yield has been ascertained, and the compound has been characterized. The rheological properties are demonstrated on the ER fluid through steady flow and oscillatory tests to investigate the effects of change in concentration on the functional group attached to the inorganic silicon-oxygen core structure of the POSS compound. The electrorheological efficiency was analyzed, and dielectric characterization was done. The flow curve was described by the Herschel-Bulkley model, and yield stress values were derived from the model. The octa-cyanoPOSS/PDMS electrorheological fluid has been shown to have ER activity.

Comparing the Electrorheological Effect of Polyhedral Silsesquioxane Cage Structures with Different Numbers of Cyanopropyl Functional Groups.

Previous research has shown that polyhedral oligomeric silsesquioxane (POSS) particles in silicone oil show electrorheological (ER) activity. The effect of the number of same functional groups attached to POSS cage structures on the ER activity of these structures is discussed in this article. Two compounds of the octahedral geometry (T8) of cyanopropyl POSS (cPOSS) were used for this investigation. One of the compounds (monofunctionalized cPOSS) was commercially available, and the other (octafunctionalized cPOSS) was synthesized. The effects of the number of cyanopropyl functional groups attached to the inorganic silicon-oxygen core structure of the POSS compounds on the rheological properties are demonstrated through steady flow and oscillatory tests. Particular attention is paid to how the number of cyano functional groups affects the behavior of these suspensions of cPOSS compounds in silicone oil under increasing electric field strength. The research also contributed answers to the effects of changing the concentration of the cPOSS particles in the suspension. The flow curve was described by the Herschel-Bulkley model, and the yield stress values were ascertained from the model. The dielectric characterization was also done to support the ER response results, which showed that the octafunctionalized compound gave a better response. The differences in the ER properties of these compounds have also been discussed with the tests.

Bone Glue Modified Asphalt: A Step towards Energy Conservation and Environment Friendly Modified Asphalts.

Asphalt has been modified for the past several decades using various additives, including synthetic polymers. Polymer modification improves structural and engineering characteristics of the binder, which is a result of improvement in rheological characteristics of binder as well as its adhesion capability with the aggregate. Such enhancement inevitably enhances the performance characteristics of hot mix asphalts (HMA) such as fatigue life, resistance to rutting, and thermal cracking. Even though polymer-modified HMA is popular in North America and European countries, its use is still limited in developing countries of Southeast Asia due to high costs associated with its manufacturing, processing, and energy consumption. In this study, a new kind of asphalt modifier derived from animal wastes, such as bones, hides, and flesh commonly known as Bone Glue, is studied. This biomaterial which is a by-product of food and cattle industries is cheap, conveniently available, and produced locally in developing countries. The results of the research study showed that the bone glue can easily be mixed with asphalt without significantly altering the asphalt binder's viscosity and mixing and compaction temperatures of HMA. Additionally, improvements in complex shear modulus for a range of temperatures were also determined and it was found that complex shear modulus was improved by bone glue modification.

Direct synthesis of ß-alkyl N-aryl aza Baylis-Hillman adducts via nitroso-ene reaction.

A new approach for the direct Fe-catalyzed synthesis of ß-alkyl N-aryl aza Baylis-Hillman (ABH) adducts is reported. This approach involves the formation of a C-N bond via a nitroso-ene reaction. This is a simple, fast, and best alternate method to overcome the substrate scope limitations of the ABH reaction, which converts allyl esters and carbonyl compounds to novel ABH adducts. A variety of arylhydroxylamines reacted with esters, aldehydes, ketone, and nitriles to yield the corresponding products in moderate to excellent yields.

CH···π interactions do not contribute to hydrogen transfer catalysis by glycerol dehydratase.

The role of the nonbonded CH···π interaction in the hydrogen abstraction from glycerol by the coenzyme B(12)-independent glycerol dehydratase (GDH) was examined using the QM/MM (ONIOM), MP2, and CCSD(T) methods. The studied CH···π interaction included the hydrogen atom of the -C(2)H(OH)- group of the glycerol substrate and the tyrosine-339 residue of the dehydratase. A contribution of this interaction to the stabilization of the transition state for the transfer of a hydrogen atom from the adjacent terminal C(1)H(2)(OH) group to cysteine 433 was determined by ab initio HF, MP2, and CCSD(T) calculations with the aug-cc-pvDZ basis set for the corresponding methane/benzene, methanol/phenol, and glycerol radical/phenol subsystems. The calculated CH···π distance, defined as the distance between the H atom and the center of the phenol ring, shortened from 2.62 to 2.52 Å upon going from the ground- to the transition-state of the GDH-catalyzed reaction. However, this shortening was not accompanied by the expected lowering of the CH···π interaction free energy. Instead, this interaction remained weak (about -1 kcal/mol) along the entire reaction coordinate. Additionally, the mutual orientation of the CH group and the phenol ring did not change significantly during the reaction. These results suggest that the phenol group of the tyrosine-339 does not contribute to lowering the activation barrier in the enzyme, but do not exclude the possibility that tyrosine 339 facilitates proper orientation of glycerol for the electrostatic catalysis, or inhibits side-reactions of the reactive glycerol radical intermediate.

QM/MM (ONIOM) study of glycerol binding and hydrogen abstraction by the coenzyme B12-independent dehydratase.

Glycerol binding and the radical-initiated hydrogen transfer by the coenzyme B(12)-independent glycerol dehydratase from Clostridium butyricum were investigated by using quantum mechanical/molecular mechanical (QM/MM) calculations based on the high-resolution crystal structure (PDB code: 1r9d). Our QM/MM calculations of enzyme catalysis considered the electrostatic coupling between the quantum-mechanical and molecular-mechanical subsystems and two alternative mechanisms. In addition to performing QM/MM calculations in the enzyme, we evaluated energetics along the same reaction pathway in aqueous solution modeled by the polarized dielectric and in the virtual enzyme site that included full steric component from the enzyme residues described by molecular mechanics but lacked the electrostatic contribution of these residues. In this way, we established significant enzyme catalytic effect with respect to reference reactions in both an aqueous solution and a nonpolar cavity. Structurally, four hydrogen bonds formed between glycerol and H164, S282, E435, and D447 anchor glycerol for hydrogen abstraction by thiyl radical on C433. These hydrogen-bond partners orient glycerol molecule to facilitate the formation of the transition state for hydrogen abstraction from carbon C1. This reaction then proceeds with the activation free energy of 6.3 kcal/mol and the reaction free energy of 6.1 kcal/mol. The polarization effects imposed by these hydrogen bonds represent a predominant contribution to a 7.5 kcal/mol enzyme catalytic effect. These results demonstrate the importance of electrostatic catalysis and hydrogen-bonding in enzyme-catalyzed radical reactions and advance our understanding of the catalytic mechanism of B(12)-independent glycerol dehydratases.

The diversity and molecular modelling analysis of B12 and B12-independent glycerol dehydratases.

To broaden our knowledge on the diversity of glycerol dehydratases, comprehensive sequence and molecular modelling analyses of these enzymes were performed. Our sequence analysis showed that B12-dependent and B12-independent glycerol dehydratases are not related, suggesting that they evolved from different ancestors. Second, our study demonstrated that a gene fusion event occurred between α and ß subunits of B12-dependent glycerol dehydratases in several bacteria during enzyme evolution. In addition, our sequence and molecular modelling analyses revealed more B12-independent glycerol dehydratases including hypothetical proteins. Furthermore, we found that some microorganisms contain both B12-dependent and B12-independent glycerol dehydratases in their genomes.