Short Side Chains Research Articles

Effect of nonionic side chain length of polycarboxylate-ether-based high-range water-reducing admixture on properties of cementitious systems

Despite the large variations in the behaviors of water-reducing admixtures upon changes in their structures, most previous reports on the cement-admixture compatibility did not provide sufficient information on the structure of the admixture. Hence, the evaluation and generalization of the reports on the cement-admixture compatibility are challenging. In this study, three different polycarboxylate-ether-based water-reducing admixtures with the same free nonionic content, anionic/nonionic molar ratio, and main chain length and different side chain lengths were produced. The compatibility of these admixtures with a CEM I 42.5 R-type cement was investigated. In addition, an analysis of variance was performed on the experiment results to evaluate the contributions of the admixture type, admixture/cement ratio, and elapsing time to the Marsh funnel flow time, mini-slump, slump flow, and compressive strength. The water-reducing admixtures having long or short side chains reduced the initial flow characteristics of the cementitious systems. However, the admixture having the shortest side chain was better with regard to flow retention. The side chain length of the admixture did not have significant effects on the compressive strength and water absorption capacity of the mortar mixtures and mini-slump performances of the cement paste mixtures. Regarding the behaviors of the admixtures in the cementitious systems, an optimal admixture side chain molecular weight is proposed.

Tryptic Stability and Antimicrobial Activity of the Derivatives of Polybia-CP with Fine-Tuning Modification in the Side Chain of Lysine

Antimicrobial peptides (AMPs) were believed to be a class of promising antimicrobials to combat the increasing resistant microbes. However, AMPs could be easily degraded by endogenous proteases, which limited their clinic use. Considering that lysine is the only one cationic amino acid residue in polybia-CP which were related to the cleavage of trypsin like serine protease’s digestion, we introduced lysine’s mimics which kept the key function group side chain –NH2 and only varied the methylene chains in the sequence of polybia-CP to investigate the effect of the introduction of non-proteinogenic amino acids on the activity and stability of antimicrobial peptides. In addition, two analogs in which lysine were substituted by the other two proteinogenic cationic amino acids arginine and histidine also were synthesized to evaluate the effect of fine tuning the function group in lysine on its antimicrobial activity and stability. We found that the introduction of amino acids with shortened side chain length of lysine could enhance the trypsin resistance of the derivatives of polybia-CP, while maintain the same or comparable antimicrobial activity with the parent peptide. In addition, while lysine was substituted by histidine, His-CP demonstrated comparable antimicrobial activity and dramatically improved trypsin resistance. Although the analog exhibited excellent antimicrobial activity while lysine was substituted by Arginine residue (Arg-CP), its enzymatic stability was almost the same as its parent peptide. These results suggest that the fine-tuning of side chain of lysine may offer a promising strategy to improve the tryptic stability and retain the antimicrobial activity of antimicrobial peptide.

Uptake and metabolism of nonylphenol in plants: Isomer selectivity involved with direct conjugation.

Nonylphenol (NP), an environmental estrogen, is actually a complicated mixture of isomers, although it is commonly considered to be a single compound. There are many routes for crops to come into contact with NP; however, little is known about the plant uptake and metabolism of NP, especially at the isomer level. This study comparatively evaluated the uptake and in-planta metabolism of 4-n-NP and its 10 isomers using both carrot cells and intact plants. The rapid metabolism of 4-n-NP was observed in the callus tissues and intact plants with half-lives of 2h and 4.72d, respectively. Six conjugates of 4-n-NP were identified in the cell extracts using high resolution mass spectrometry. The primary transformation pathway was found to be the direct conjugation (Phase II metabolism) with the parent compound at the hydroxyl. Furthermore, 4-NP isomers with short side chains and/or bulky α-substituents were more resistant to plant metabolism and showed a greater tendency for accumulation. The influence of the side chains to the isomer selectivity was verified by the molecular docking between glycosyltransferase and 4-NP isomers. This study highlighted the necessity to consider isomer-specificity in the plant accumulation of NP and the environmental and human health implications of NP conjugates.

Altering polythiophene derivative substrates to explore the mechanism of heterogeneous lithium nucleation for dendrite-free lithium metal anodes

Lithium metal batteries (LMBs) possess outstanding theoretical energy density and have attracted widespread attention as the next generation of energy storage devices for various crucial applications. However, the commercialization of LMBs has to simultaneously overcome numerous challenges, such as inferior Coulombic efficiency and cycling performance, high self-discharge, and complicated interfacial reactions. It has traditionally been an enormous challenge about the uniform deposition of lithium on the surface of current collector to relieve the formation of lithium dendrites. In this study, a novel efficient strategy of plating uniform lithiophilic polythiophene derivatives substrates on Cu foils was developed and the nucleation mechanism of Li ions on polythiophene derivatives substrates was further explored. We first explored the interaction between polythiophene derivatives substrates and Li ions by first-principles calculations, and found shorter side chains of polythiophene derivatives can enhance the adsorption energy and promote the diffusion rate of Li ions. Polythiophene derivatives substrates have a large number of dispersive lipophilic sites and Li ions diffusion channels in the main chain, which can effectively regulate the nucleation and growth stages of Li ions deposition. We further found polythiophene derivatives with different side chains can induce the electrodeposition of Li ions with different morphology, while the polythiophene derivatives with the shortest side chains can contribute to the most excellent cycle efficiency, resulting in a uniform lithium deposition with less lithium dendritic growth experimentally.

Extraction of Au(III) using aromatic ethers via ion solvation from acidic chloride media: Structural factors that influence extraction

Ethereal compounds, such as the commercially available extractant dibutyl carbitol (DBC), can extract Au(III) from acidic chloride media by ion solvation. Herein, various aromatic ether compounds comprising an aromatic ring and aliphatic chains were prepared to compare the extraction affinity toward Au(III) without dilution. Aromatic monoethers are not useful for the extraction of Au(III). Conversely, the extraction of Au(III) using aromatic 1,2-diethers increases as a function of hydrochloric acid concentration. For aromatic 1,2-diethers, the shorter the aliphatic chain, the higher the extraction affinity toward Au(III). 1,2-Dimethoxybenzene (o-DMB), which has the shortest side chains, exhibits the highest extraction affinity. 1,3-Dimethoxybenzene (m-DMB), which is a regioisomer for o-DMB, was not suitable for the extraction of Au(III). The extraction selectivity toward Au(III) over that of Fe(III) and Ga(III) using o-DMB, under high concentrations of hydrochloric acid, is higher than that using DBC. Selected aromatic 1,2-diethers, including o-DMB, show a significantly higher extraction capacity toward Au(III) than the industrial requirement of 30 g/dm3. Au(III) extracted using o-DMB was quantitatively recovered by reduction with oxalic acid. In a separation test from a mixed system comprising seven metals, Au(III) was selectively extracted and with a recovery percentage, after reduction, reaching 95.7%.

Steering polymer growth by molding nanochannels: 1,5-hexadiene polymerization in high silica mordenite

Zeolites are known as scaffolds for the assembly of molecules via non-covalent interactions yielding organized supramolecular materials. Yet their potential in driving the growth of low-dimensional systems requiring covalent bond formation is still unexplored. We incorporated 1,5-hexadiene in the channels of a high-silica mordenite and analyzed the material by infrared spectroscopy, X-ray powder diffraction, thermogravimetry and modeling techniques. Due to the few zeolite acid sites, 1,5-hexadiene experiences a slow conversion to a polymer mainly formed by cyclopentane units and featuring short side chains that are able to fit the channels. The shape-directing abilities of zeolite frameworks play a two-fold role, involving first the organization of the monomers inside the void-space and then the linear growth of the chain dictated by the channel geometry. These findings highlight the molding action of zeolites in directing transformations of covalent bonds under ambient conditions and may provide insights for obtaining confined polymers with intriguing prospective applications.

Effect of main and side chain length change of polycarboxylate‐ether‐based water‐reducing admixtures on the fresh state and mechanical properties of cementitious systems

AbstractIn this study, the effect of both main and side chain length changes of the admixtures on some properties of cementitious systems were investigated. Three different polycarboxylate‐ether‐based water‐reducing admixtures (WRA) having constant molecular weights and different main and side chain lengths were synthesized. Single type of raw material and carboxylate functional group were used in all WRAs. The molecular weights, free nonionic contents, and anionic/nonionic ratios of the admixtures were kept constant. Test results showed that degree of fluidity was observed in cement paste and mortar mixtures in case the admixture main and side chain length is more or less than a critical value. This negative effect is thought to be due to the weakening of the adsorption ability by the chain length change of the admixtures, the being tendency of polymers to intertwine and the adsorbing of admixture on several cement particles simultaneous. Admixtures having excessive long or short main chain and side chain improved the time‐dependent slump‐flow retention of the mortar mixtures. The admixtures with short main and side chains had insufficient adsorption ability and the admixture with excessive long main and side chains had the interlacing risk of polymers. In both cases, time‐dependent behavior improved because the amount of free admixture in solution increased. The change in the chain lengths of the WRAs affected the 1‐day compressive strength of the mortar mixtures.

Effect of Annealing on Proton Conductivity of Aquivion-Like Proton-Exchange Membrane

Proton-conducting membranes were fabricated from a new short-side chain ionomer Inion (Russian analogue of Aquivion) by solution casting method. A series of temperature treatment experiments was conducted to show that annealing of Inion membranes at the temperature range from 160 °C to 170 °C leads to a significant increase of specific proton conductivity to values even higher than those of commercial membrane Nafion NR212. An explanation of this fact can be given by considering the membranes’ proton transport mechanism and water behavior models in nanopores. Matching the proton conductivity mechanism of the membranes, which is realized in nanostructured channels with the diameter of about several nanometers according to the Grotthuss proton hopping mechanism, and the model of water and ice states in nanopores leads to the comprehensive understanding for the further optimization of the membranes to achieve high transport characteristic. For example, it can be improved by increasing the number of side-chain branches of the polymer.

Impact of the microstructure of polycarboxylate superplasticizers on the dispersion of graphene

Graphene can not only toughen cement-based materials, but also give them sensing ability. However, the uniform dispersion of graphene in a cement matrix is the major problem in the fabrication process. Four polycarboxylate superplasticizers (PCEs) with different charge densities and side-chain lengths were synthesized and the effects of their microstructures on the dispersibility of graphene in deionized water and in solution in cement pores were examined by UV-Vis spectroscopy, dynamic light scattering and optical microscopy with a large depth of field. A mechanism for the dispersion of graphene in the two media was also proposed. In deionized water, PCEs with a higher charge density showed more electrostatic repulsion, which improved the graphene dispersion efficiency. Conversely,PCEs with a lower charge density and longer side-chains gave a lower graphene dispersion. In solution in the cement pores, however, a PCE with a high charge-density produced a low graphene dispersibility, due to a cross-linking Ca2+-bridging effect. This effect was insignificant in cement pores for a solution containing low charge-density PCEs. Moreover, it was found that PCEs with the longer side-chains produced the worst graphene dispersion efficiency in both media. Overall, PCEs with a low charge density and relatively short side chains are more suitable for the preparation of graphene-composited cement pastes.

Impact of DAA/water composition on PFSA ionomer conformation

Performance of a proton exchange membrane fuel cell (PEMFC) is significantly determined by the structure and composition of the electrode layer. Electrode layers are formed from inks consisting of platinum-doped carbon black particles, perfluorosulfonic acid (PFSA) ionomer and a dispersing solvent. Interaction between these materials mainly influences suspension stability, ionomer conformation and therewith layer morphology.We characterize the interplay between a short sidechain (SSC) PFSA ionomer (Aquivion® D79-25BS) and a solvent mixture (diacetone alcohol (DAA) and water with different weight ratios) by using Hansen solubility/dispersibility parameters (HSP) and by experimental tests. It was found that HSPs are well suitable to describe the ionomer/solvent interactions. In particular, the HSP difference in terms of the hydrogen bonds is responsible for the poor affinity between ionomer and solvent at low DAA concentrations. With increasing DAA content the affinity between ionomer and solvent increases as indicated by better matching HSPs. For an ionomer concentration of 4 wt%, Aquivion always forms molecular solutions for all DAA-in-water mixing ratios. Self-organization of the ionomer molecules changes from densely packed/collapsed molecules with highly deprotonated sulfonic acid side groups at low DAA concentrations to unfolded Aquivion molecules with a low dissociation degree of the sulfonic acid groups at high DAA concentrations.

Wetting- and fouling-resistant hollow fiber membranes for dissolved methane recovery from anaerobic wastewater treatment effluents

Anaerobic wastewater treatment processes are becoming increasingly widespread due to their advantages in sludge management and net energy consumption. One major reason behind the energy benefit of the mainstream anaerobic processes is methane (CH4) production. Nevertheless, over one-third of the produced CH4 typically remains in effluent streams in dissolved form. To recover the dissolved CH4 (dCH4) from anaerobic effluents, the membrane contactor (MC) process enabled by porous membranes offers a promising way. However, membrane wetting and fouling issues hinder the practical implementation of the concept. Here we report a wetting- and fouling-resistant hollow fiber membrane that can operate with realistic anaerobic effluents. Coating of a highly porous (~85%) hollow fiber support with a conformal layer of polydimethylsiloxane (PDMS) provides resistance to wetting, but fouling persists. To tackle the fouling issue, we post-treated the uncured PDMS-coatings with PDMS-based amphiphilic copolymers with short (147 Da) or long (~1570 Da) side chains. Both types of post-treated membranes exhibited an improved performance when tested against effluent samples taken not only from an anaerobic membrane bioreactor but also from an upflow anaerobic sludge blanket (UASB) reactor. The membrane treated with the short-side-chain copolymer could sustain 7 days of continuous operation with UASB effluent with a performance loss of only ~10%. We observed that the fouling layers were much richer in proteins rather than subtances similar to humic and fulvic acids and microbial byproducts. Besides, we calculated that our wetting/fouling-resistant membranes provide a net energy benefit for the MC process (when the recovered CH4 is retrofitted to the process as fuel). Thus, our results suggest that the MC-based dCH4 recovery process is a viable alternative for industrial practices in case the demonstrated custom-designed membranes are employed.

The behavior of free radicals during the carbonization of anthracite briquette

The variation in behavior of free radicals during the pyrolysis and co-pyrolysis of anthracite and coal-based binder (AS) was determined by Electron paramagnetic resonance (EPR). Besides, Thermogravimetry (TG) and Carbon-13 nuclear magnetic resonance (13C NMR) were also applied to investigate the nature of pyrolysis and structural characterization of the coal samples. The results indicated that the induced effect of free radical existed in the co-pyrolysis of anthracite and AS, such that the free radical concentration (Ng) of AS carbonized briquette (ASB) at 300–500 °C is far higher than the additive value of Ng when anthracite and AS are separately carbonized. When the temperature exceeds 500 °C, the timely release of AS free radicals could combine with the aromatic free radicals of anthracite, leading to a slight decrease in the Ng value of ASB. Due to the limited combination, the rapid polycondensation of aromatic free radicals in anthracite was inhibited and more number of short side-chains and cross-links were generated in ASB. These effects delay the major polycondensation process of ASB to a higher temperature compared with other samples. As a result, the Ng value of ASB drops significantly above 700 °C and the line shape of it transforms closer to the Lorentz line shape. The lapping of free radical variation in anthracite and binder would broaden the temperature range for bonding-polymerization, which makes the free radicals of the blend components to rearrange and to form strong carbon–carbon bonds. Thus, the mechanical strength (M40) of carbonized briquette would be improved.

Structural design of asymmetric diketopyrrolopyrrole polymers for organic solar cells processed from a non-halogenated solvent

Diketopyrrolopyrrole (DPP) polymers possess narrow optical bandgaps and high charge carrier mobilities which make them attractive for solar cell applications. DPP polymers are generally only soluble in chlorinated solvents, which is a drawback for commercial application. Solubility in non-halogenated solvents can be achieved by reducing the translational symmetry of the chain by employing two different aromatic moieties on either side of the DPP units. Here a series of polymers in which thiophene (T) and pyridine (Py) sandwich the DPP units in the main chain is reported. These asymmetric T-DPP-Py units increase the solubility dramatically. The side chain length, nature of the co-monomer, and regioregularity of the main chain are varied to investigate their effect on the solubility in toluene, the active layer morphology and the performance of organic solar cells. We demonstrate that polymers processed from both chloroform and toluene reach very similar power conversion efficiencies and blend morphologies. In general, a small co-monomer, short side chains, a regioregular main chain, and a high molecular weight give the best performance for solar cells processed from toluene. • Asymmetric substitution enhances solubility of diketopyrrolopyrrole polymers. • The asymmetry enables processing from non-halogenated solvents. • In solar cells, power conversion efficiencies are similar for both types of solvents. • Regioregular derivatives provide higher efficiencies than regiorandom polymers.

Effects of molecular structures of poly α-olefin mixture on nano-scale thin film lubrication

In order to determine how the molecular structures of poly α-olefin (PAO) mixture could impact the lubrication in nano-scale thin film, PAO models were constructed using the polymer of different polymerization degree according to published friction experiment, molecular dynamic simulations were conducted under compressed-shear condition. According to the simulation results, the PAO molecules with short side chains exhibited a rigid structure and high shear stress, while the molecules with long side chains exhibited the opposite and the tendency to orientate along the shearing direction. The syndiotactic molecular structure exhibited a lower friction coefficient than the isotactic structure. As suggested by the trajectory of lubricant molecules, the small lubricant molecules in the polymer mixture moved at a slower pace than the large ones under compressed-shear motion, indicating that the large molecules contribute more to the effect of friction than the small ones.

Structure Characterization and Solubility Analysis of the Existent Gum of the Fischer-Tropsch Synthetic Crude.

The existent gum content of the Fisher–Tropsch synthetic crude exceeded the standard seriously, affecting its transportation and use. To determine the structure of the existent gum extracted from the Fisher–Tropsch synthetic crude, elemental analysis, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) were employed to determine the chemical structure of the gum. The Brown–Ladner method is used to calculate the average structural parameters and the average molecular formula of the existent gum. The results show that the existent gum of the Fisher–Tropsch synthetic crude is composed of heterocyclic aromatic hydrocarbons and short-carbon paraffins. Compared with petroleum gums and coal tar gums, the existent gum content of the Fisher–Tropsch synthetic crude has the characteristics of high aromaticity, short side chains, and nitrogen-containing heterocycles. After being oxidized, its aromaticity further increases, more closed loops are formed, and the side chain is further shortened. This is caused by a complex oxidation reaction during the oxidation process. Molecular dynamics simulation calculations were performed to reveal the T-stacked morphology of the existent gum of the Fisher–Tropsch synthetic crude in a mixed solvent of acetone and toluene.

Side chain flexibility and the symmetry of protein homodimers.

A comprehensive analysis of crystallographic data of 565 high-resolution protein homodimers comprised of over 250,000 residues suggests that amino acids form two groups that differ in their tendency to distort or symmetrize the structure of protein homodimers. Residues of the first group tend to distort the protein homodimer and generally have long or polar side chains. These include: Lys, Gln, Glu, Arg, Asn, Met, Ser, Thr and Asp. Residues of the second group contribute to protein symmetry and are generally characterized by short or aromatic side chains. These include: Ile, Pro, His, Val, Cys, Leu, Trp, Tyr, Phe, Ala and Gly. The distributions of the continuous symmetry measures of the proteins and the continuous chirality measures of their building blocks highlight the role of side chain geometry and the interplay between entropy and symmetry in dictating the conformational flexibility of proteins.

PH-responsive micellization of an amine oxide surfactant with branched hydrophobic tail

pH-sensitive surfactants find applications in many fields, including responsive drug delivery and smart material design. The rational design of the surfactant molecular structure leads to species presenting strong variations of the micellization parameter (e.g., critical micelle concentration, cmc, and aggregate dimension) in a controlled pH range.In the present work, the micellization of the branched amine oxide surfactant N,N-dimethyl-2-propylheptan-1-amine oxide (C10DAO-branched) is studied as a function of pH in dilute aqueous mixtures. Its behavior is compared with that of the linear isomer N,N-dimethyldecan-1-amine oxide (C10DAO-linear). The samples are investigated by potentiometric titrations, fluorescence spectroscopy, and Dynamic Light Scattering (DLS). With increasing pH, micellized C10DAO-branched presents a higher tendency to remain in the protonated/cationic form with respect to the linear isomer. As a consequence, the minimum cmc value, observed when the protonated and the deprotonated/zwitterionic forms of the surfactant coexist in the micelles, is shifted to higher pH values. The volume of these C10DAO-branched “mixed micelles” is more than one order of magnitude higher than that of completely protonated or deprotonated aggregates. This is a singularity of the branched surfactant, not observed for the linear isomer. Overall, the results highlight that the branched molecular architecture of the surfactant tail, favoring the formation of low-curvature aggregates, enhances H-bonding between the protonated and deprotonated headgroups, which synergistically stabilizes the flatter surface of bulkier aggregates.Taking into account the good biodegradability of surfactants with a limited number of short side chains, purposely designed branched surfactants appear as a suitable option to accurately tune supramolecular aggregation in pH-responsive formulations.

Covalent coupling regulated thermal conductivity of poly(vinyl alcohol)/boron nitride composite film based on silane molecular structure

Creating covalent bonds between inorganic fillers and polymer matrix is an effective method to enhance the thermal conductivity (TC) of composite materials, while the detailed mechanism is still not clear. By introducing different silane coupling agents (SCAs) bonding poly(vinyl alcohol) (PVA) and functionalized boron nitride (fBN), intrinsic relationship between molecular structure of silane crosslinkers and TC of PVA-fBN composite has been systematically investigated. The results show that the SCAs molecules with short side chain, i.e. vinyl triethoxysilane (VTES) and tetraethyl orthosilicate (TEOS), increase the TC of composite polymer, with maximum value of 1.636 W/m·K, which is 337.3% of that of PVA/fBN. In contrast, 3-glycidoxypropyltrimethoxy silane (GPTMS) with long side chain decreases the TC to 54.4% of that of PVA-fBN. The number of hydrolyzable SiOR of SCAs molecules affects the TC of PVA-fBN composite through controlling the self-condensation degree of SCAs. Integrated with atomistic simulations, these findings provide new insights for the design of polymer-based thermal management materials.

Investigation into the molecular design and plasticizing effectiveness of HPEG-based polycarboxylate superplasticizers in alkali-activated slag

In this study, a series of HPEG PCE polymers with different anionic charge density and side chain lengths was synthesized via free-radical copolymerization from acrylic acid and α-methallyl poly (ethylene glycol) ether (HPEG) as macromonomer. The resulting PCE polymers were characterized via Size Exclusion Chromatography (SEC) and anionic charge titration. Thereafter, a correlation between their molecular structures and dispersing effectiveness was established for alkali-activated slag. A broad variety of HPEG PCE polymers was found to work in the alkali-activated slag (AAS) system. Finally, the working mechanism for best performing polymer was investigated via adsorption measurements. It was concluded that HPEG PCEs of high anionicity, high Mw and short side chain length adsorb particularity high amounts on slag, thus providing enhanced dispersion capacity as compared to other HPEG polymers.

Effect of entanglement upon branching on dispersibility, β-nucleating and mechanically strengthening ability of polystyrene in isotactic polypropylene

Polymers with benzene rings have the potential to act as macromolecular β-nucleating agents and rigid organic particles for isotactic polypropylene (iPP). The dispersibility in iPP matrix is a key factor for their β-nucleating efficiency and mechanically strengthening ability. In this paper, comb-like branched polystyrenes (cPSs) with different side chain lengths were introduced into iPP. The effect of entanglement upon branching on dispersibility, β-nucleating and mechanically strengthening ability of PS in iPP was investigated in detail. Compared with the linear polystyrene with the same length of backbone, the incorporation of side chains intensifies the entanglement between cPS chains, not facilitating their dispersion in iPP matrix. However, short side chains (chain length lower than the critical chain entanglement molecular weight of PS) facilitate the interdiffusion between the cPS and iPP chains and ultimately lead to favorable dispersibility and high β-nucleating efficiency, as well as prominent toughening and reinforcing effect on iPP.