Alkyl Tail Length Research Articles

Delinkage of Metal Surface Saturation Concentration and Micellization in Corrosion Inhibition

Long-distance transmission of oil is usually performed in large-diameter steel pipelines, where water present therein may cause severe internal corrosion. An effective method of mitigating such corrosion is to inject organic corrosion inhibitors (CIs). Their surface adsorption, via heteroatom functionalities, can markedly enhance the corrosion resistance of metals. In this study, three CI model compounds with different head groups but the same alkyl tail length (-C14H29), specifically tetradecyltetrahydropyrimidinium (THP-C14), tetradecylphosphate ester (PE-C14), and tetradecylimidazolinium (IMID-C14), were synthesized, their purities being determined using nuclear magnetic resonance spectroscopy. The critical micelle concentrations (CMCs) of each compound were measured using surface tensiometry (Du Noüy ring) and fluorescence spectroscopy techniques, with differences being found between these indirect and direct methods. In addition, linear polarization resistance was used to determine inhibition efficiencies (IEs) for carbon steel immersed in a 5 wt% NaCl electrolyte saturated with CO2. CI surface saturation concentrations, with maximum IEs, were compared with the determined CMCs. Excellent IEs were observed at concentrations of THP-C14, PE-C14, and IMID-C14 which do not correspond with their CMCs, the differences involved being significantly greater than what was previously reported for tetradecylbenzyldimethylammonium (BDA-C14). These results demonstrate that there is no direct link between CMC and metal surface saturation/corrosion IE that can be made on a generalized basis for the different head groups but with the same tail length CI, indicating that the selection of the appropriate CI concentration for an industrial application should not be based on CMC alone.

Co(III)-tetra(4-sulfonatophenyl)porphyrin complexes with bidentate ligands in aqueous buffer media

The processes of hydrophilic Co(III)-tetra(4-sulfonatophenyl)porphyrin supramolecular assembly with 4,4-bipyridyl in aqueous buffer media have been studied by UV-vis, 1D and 2D 1H NMR-spectroscopy. In the case of 1,4-diazabicyclo[2.2.2]octane, pyrazine and piperazine in aqueous solutions, no assembly was observed. Interactions of the hydrophilic Co(III)-tetraarylporphyrin with ionic micelles (cationic surfactants with different alkyl tail lengths) in buffer media were investigated. These studies were performed by the UV-vis, 1D NOESY-spectroscopy and dynamic lightscattering (DLS) methods. The metalloporphyrins were incorporated into the hydrophobic part of micelles, which led to Co(III) reduction to Co(II) in the Co-porphyrinate composition. The rate of Co(III) reduction accompanied by detachment of additional ligands coordinated on Co(III)-porphyrins or disruption of supramolecular dimers and depends on the surfactant concentration and nature. The results obtained indicate the possibility of creating supramolecular porphyrin-based assemblies with the preprogrammed lifetime (from several hours to several days) and could be used in the creation of host-guest systems for recognition, selective binding and the prolonged release of bioactive substrates as the means in the designing of biomimetic systems with effective binding affinities to heterocycles, DNA base pairs and RNA.

Supramolecular assembly of hydrophilic Co(III)-porphyrin with bidentate ligands in aqueous buffer media

The processes of hydrophilic Co(III)-tetra(4-sulfonatophenyl)porphyrin supramolecular assembly with 4,4-bipyridyl in aqueous buffer media have been studied by UV–vis, 1D and 2D 1H NMR-spectroscopy. In the case of 1,4-diazabicyclo[2.2.2]octane, pyrazine and piperazine in aqueous solutions, no assembly was observed. Interactions of the hydrophilic Co(III)-tetraarylporphyrin with ionic micelles (cationic surfactants with different alkyl tail lengths) in buffer media were investigated. These studies were performed by the UV–vis, 1D NOESY-spectroscopy and dynamic lightscattering (DLS) methods. The metalloporphyrins were incorporated into the hydrophobic part of micelles, which led to Co(III) reduction to Co(II) in the Co-porphyrinate composition. The rate of Co(III) reduction accompanied by detachment of additional ligands coordinated on Co(III)-porphyrins or disruption of supramolecular dimers and depends on the surfactant concentration and nature. The results obtained indicate the possibility of creating of supramolecular porphyrin-based assembles with the preprogrammed lifetime (from several hours to several days) and could be used in the creation of host–guest systems for recognition, selective binding and prolonged release of bioactive substrates as the means in the designing of biomimetic systems with effective binding affinities to heterocycles, DNA base pairs and RNA.

The influence of tail chain length on oil film detachment: C2nTAB series (n = 4 − 9)

Employing molecular dynamic simulations, the detachment process of oil film from silica surface in six cationic surfactants with same head group and different alkyl tail length was investigated. In this work, the surfactant C2nTAB series (n = 4 − 9) were selected to investigate the effect of tail chain length on oil detachment capability. In all surfactants systems, the oil film detachment processes undergone three stages: at initial stage, the surfactants adsorb on the oil-water interface. And then water molecules penetrate the oil film and form a water channel. At last stage, the water molecules spread on the silica surface and the oil film are detached gradually. Quantitative evaluation indicates that the detachment capability of these three surfactants follows C12TAB > C14TAB ≈ C16TAB≈C8TAB > C10TAB > C18TAB. Our results indicated that the chain length of surfactant play important role in tertiary oil recovery, and a compatibility should be considered.

Controlling the Balance of Photoluminescence and Photothermal Effect in Cyanostilbene‐Based Luminescent Liquid Crystals

Comprehensive SummaryMolecular motions of the luminescent liquid crystals (LLCs) show a significant effect on fluorescent emission and heat generation. In this article, a series of cyanostilbene‐based LLCs (CSs: CS1‐6, CS1‐12, CS2‐6 and CS2‐12) are synthesized to investigate how the photoluminescence and photothermal effect balanced. Among these materials, the mesogens peripheried by single alkyl chains formed enantiotropic nematic (CS1‐6) or smectic C (CS1‐12) phase with different alkyl tail lengths. When the single aliphatic chain is replaced by mini‐dendrons, room temperature (RT) monotropic hexagonal columnar phase (CS2‐12) or molecular liquid (CS2‐6) is formed. The results revealed that all these materials exhibited high efficiency emission with the highest quantum yield reaching 59.0%. The photoluminescence and photothermal effect can be effectively tuned by dispersing CSs into a commercially available RT liquid crystal matrix 8CB, which output significantly improved photothermal conversion efficiency of 63.2%. Furthermore, the photothermal can rapidly trigger the Smectic A‐Nematic‐Isotropic sequence transitions of 8CB doped with CSs. This work paves a way of adjusting the balance of photoluminescence and photothermal properties of the LLC materials.

Poly(l-cysteine) Peptide Amphiphile Derivatives Containing Disulfide Bonds: Synthesis, Self-Assembly-Induced β-Sheet Nanostructures, pH/Reduction Dual Response, and Drug Release

Three disulfide bond-containing peptide amphiphiles (PA1-3) with different lengths of alkyl tails (PA1 for C6, PA2 for C12, and PA3 for C18) were synthesized by ring-opening polymerization of α-amino acid N-carboxyanhydride followed by post-polymerization modification. The peptide segments were composed of 3-mercaptopropionic acid-modified poly(l-cysteine) [P(Cys-SS-CH2CH2COOH)]. We characterized the chemical structure and molecular parameters by 1H NMR, 13C NMR, gel permeation chromatography, Fourier transform infrared spectroscopy, and circular dichroism spectroscopy. It is found that alkyl-P(Cys-SS-CH2CH2COOH) mainly presents a β-sheet conformation at the solid state. However, the PAs present predominant random coils at pH 7.4 in aqueous solutions. The β-sheet conformation increased dramatically when the concentration of the PA exceeded its critical micelle concentration (ca. 0.3 mg/mL for PA3), indicating the formation of self-assembly-induced β-sheet nanostructures. Elongation of the alkyl chain length or a decrease of the pH of the PA solution can promote the formation of the β-sheet conformation. The three PAs can self-assemble into spherical micelles or nanofibrous hydrogels, which can be utilized as nanocarriers for systemic drug delivery or implants for localized drug delivery, respectively. Cisplatin (CDDP) was loaded as a model medicine to examine the drug delivery potential of PA3. We found that the CDDP-loaded PA3 micelles are stable at pH 7.4, have a spherical morphology with a hydrodynamic diameter of ca. 52 nm, and accomplish pH/reduction dual-responsive release of CDDP. In addition, alkyl-P(Cys-SS-CH2CH2COOH) can self-assemble into nanofibrous hydrogels at pH 5.0-6.0 or upon the addition of certain metal ions and show excellent dynamic reversibility. Moreover, the CDDP-loaded PA3 hydrogel exhibits a sustained release profile and a nearly linear release over 48 h. In vitro cytotoxicity of PA3 also indicates its nontoxicity. Thus, our findings suggest that alkyl-P(Cys-SS-CH2CH2COOH) has great potential for both systemic and localized delivery of therapeutics.

Shorter Alkyl Chains Enhance Molecular Diffusion and Electron Transfer Kinetics between Photosensitisers and Catalysts in CO2 -Reducing Photocatalytic Liposomes.

Covalent functionalisation with alkyl tails is a common method for supporting molecular catalysts and photosensitisers onto lipid bilayers, but the influence of the alkyl chain length on the photocatalytic performances of the resulting liposomes is not well understood. In this work, we first prepared a series of rhenium‐based CO2‐reduction catalysts [Re(4,4’‐(CnH2n+1)2‐bpy)(CO)3Cl] (ReCn ; 4,4’‐(CnH2n+1)2‐bpy=4,4’‐dialkyl‐2,2’‐bipyridine) and ruthenium‐based photosensitisers [Ru(bpy)2(4,4’‐(CnH2n+1)2‐bpy)](PF6)2 (RuCn ) with different alkyl chain lengths (n=0, 9, 12, 15, 17, and 19). We then prepared a series of PEGylated DPPC liposomes containing RuCn and ReCn , hereafter noted Cn , to perform photocatalytic CO2 reduction in the presence of sodium ascorbate. The photocatalytic performance of the Cn liposomes was found to depend on the alkyl tail length, as the turnover number for CO (TON) was inversely correlated to the alkyl chain length, with a more than fivefold higher CO production (TON=14.5) for the C9 liposomes, compared to C19 (TON=2.8). Based on immobilisation efficiency quantification, diffusion kinetics, and time‐resolved spectroscopy, we identified the main reason for this trend: two types of membrane‐bound RuCn species can be found in the membrane, either deeply buried in the bilayer and diffusing slowly, or less buried with much faster diffusion kinetics. Our data suggest that the higher photocatalytic performance of the C9 system is due to the higher fraction of the more mobile and less buried molecular species, which leads to enhanced electron transfer kinetics between RuC9 and ReC9 .

Characterizing and Tuning the Properties of Polydiacetylene Films for Sensing Applications.

Self-assembled, polymerized diacetylene (DA) nanostructures and two-dimensional films have been studied over the past two decades for sensor applications because of their straightforward visual readout. DA monomers, when exposed to UV light, polymerize to produce a visibly blue polymer. Blue phase polydiacetylenes (PDAs) when exposed to an external stimuli, such as temperature or UV light, undergo a chromatic phase transition to a fluorescent, visibly red phase. The tunability of the monomer to blue to red chromatic phase transitions by choice of diacetylene monomer in the presence of metal cations is systematically and comprehensively investigated to determine their effects on the properties of PDA Langmuir films. The polymerization kinetics and domain morphology of the PDA films were characterized using polarized fluorescent microscopy, UV-vis-fluorescent spectroscopy, and Fourier transform infrared spectroscopy (FTIR). Increasing the monomer alkyl tail length was found to strongly increase the UV dose necessary to produce optimally blue films and fully red films. A decrease in the polymer domain size was also correlated with longer-tailed DA molecules. Metal cations have a diverse effect on the film behavior. Alkaline-earth metals such as Mg, Ca, and Ba have a negligible effect on the phase transition kinetics but can be used to tune PDA polymer domain sizes. The Ni and Fe cations increase the UV dose necessary to produce red phase PDA films and significantly decrease the polymer domain sizes. The Zn, Cd, and Cu ions exhibit strong directed interactions with the PDA carboxylic acid headgroups, resulting in quenched fluorescence and a unique film morphology. FTIR analysis provides insight into the metal-PDA binding mechanisms and demonstrates that the coordination between the PDA film headgroups and the metal cations can be correlated with changes in the film morphology and kinetics. The findings from these studies will have broad utility for tuning PDA-based sensors for different applications and sensitivity ranges.

Molecular Dynamics Study on Performance of Olefin Sulfonate at the Decane–Water Interface: Effect of Molecular Architecture

Surfactant flooding has been widely employed to recover the residual oil in the oilfields. Among the various oil-displacing chemicals, olefin sulfonate isomers have been identified as effective chemical agents by many experiments due to the realization of low interfacial tension (IFT) at the oil–water interface, and tolerance for high salinity and high temperature under reservoir conditions. The molecular architecture (e.g. degree of branching) of the surfactant can significantly affect the oil–water interfacial properties and hence its performance. Herein, molecular dynamics simulations were performed to investigate the adsorption processes of alpha olefin surfactant (AOS with single-tailed structure) and internal olefin surfactant (IOS with twin-tailed structure) at the oil (n-decane) - water interface under oil reservoir condition. The results show that IOS can significantly reduce the IFT at high concentrations, and the formed monolayers at the interface are more stable compared with AOS. The steric hindrance effect by the short chain of IOS can inhibit the aggregation behavior, thus leading to larger interfacial coverage, which are favorable to separation of the water and decane phases. The larger distance between the headgroups of IOS molecules is conducive to formation of hydrogen bonds between the surfactant and water molecules, and hence enhances the interaction between the IOS and water molecules at the inerface. Based on the analysis of order parameter, the middle segment of AOS molecules and the long chain of IOS molecules are mainly contributed to the Van der Waals’ interaction between the surfactant alkyl tails and decane molecules. Meanwhile, the twin-tailed structure of IOS has more favorable effective alkyl tail length (i.e. better miscibility with the oil phase) compared with the single-tailed structure of AOS. Consequently, the twin-tailed structure is superior to the single-tailed structure in terms of interfacial performance, and it is strongly suggested for the design of advanced surfactants in EOR implementation.

Boosting cell proliferation in three-dimensional polyacrylates/nanohydroxyapatite scaffolds synthesized by deep eutectic solvent-based emulsion templating

Among three-dimensional (3D) scaffold fabrication methods, porous polymers templated using high internal phase emulsions (HIPEs) have emerged as an attractive method due to the facile generation of interconnected porosity through a variety of synthetic routes. These include a bottom-up approach to selectively incorporate nanomaterials onto the inner walls in a nonaqueous environment. In this work, novel nonaqueous HIPEs made of different (meth)acrylate monomers and a deep eutectic solvent (DES) were formulated with nonfunctionalized nanohydroxyapatite (NHA), which also played the role of cosurfactant. Free radical polymerization of HIPEs yielded free-standing nanocomposites with 3D interconnected macroporosity and nonfunctionalized NHA selectively decorating the scaffolds’ inner surface. The influence of different polymer functionalities, acrylate or methacrylate, their alkyl tail length, and the presence of NHA on MC3T3-E1 preosteoblast cell proliferation in vitro, reactive oxygen species (ROS) production and alkaline phosphatase (ALP) activity were evaluated. All materials presented promising biocompatibility, non-hemolytic activity, negligible inflammatory response along to remarkably enhanced cell proliferation (e.g., up to 160-fold cell proliferation increase compared with polystyrene plate) in vitro, which open the path for the development of scaffolds in regenerative medicine. It is noteworthy that polyHIPEs studied here were obtained using a green synthetic protocol where nonfunctionalized nanoparticles can be selectively incorporated into a scaffolds’ inner walls. This versatile technique allows for the simple construction of 3D bioactive nanocomposite scaffolds with varied compositions for cell culture.

Modulating MnO2 Interface with Flexible and Self-Adhering Alkylphosphonic Layers for High-Performance Zn-MnO2 Batteries.

Metal oxides are essential electrode materials for high-energy-density batteries, but it remains highly challenging to modulate their interfacial charge-transfer process and improve their cycling stability. Here, using MnO2 nanofibers as an example, we describe the application of self-assembled alkylphosphonic modification layers for significantly improved cycling stability and high-rate performance of Zn-MnO2 batteries. Two modifier organic molecules with the same phosphonic functional group but different alkyl tail lengths were employed and systematically compared, including butylphosphonic acid (BPA) and decylphosphonic acid (DPA). The phosphonic groups form strong interfacial covalent bonding and assist the generation of conformal and flexible coatings with few nanometers thickness on a MnO2 surface. The intertwined alkylphosphonic molecules in the modulation layers have interconnected phosphonic groups, which improve interfacial charge transfer of H+ ions for fast conversion of MnO2 to MnOOH without compromising electrolyte wetting. Importantly, the coating layers effectively reduce dissolutive loss of Mn2+ from MnO2 during battery cycling since diffusion of both water molecules and divalent Mn2+ cations was inhibited across the modification layers. The flexible coatings could readily adapt to the morphological changes of MnO2 during battery cycling and provide long-lasting protection. Overall, we identified that BPA has the optimal balance of hydrophobic-hydrophilic components and enabled modified MnO2 cathodes with >30% improved discharge capacity compared with unmodified MnO2 cathodes, together with substantially improved long-term cycling stability with >60% capacity retention for 400 cycles in aqueous ZnSO4 electrolytes without any Mn2+ additive. This work provides new insights into tuning electrochemical pathways that move away from the prevailing rigid, ceramic coating-based surface modifications.

Synthesis and Surface Properties of Novel Quaternary Ammonium Gemini Surfactants with Polar Head Groups Containing 2‐Hydroxypropyl Moieties

AbstractThe purpose of this paper is to comprehend in‐depth the effect of the surfactant structure on its and physicochemical properties such as surface/interfacial properties, foam stability, wettability, and biodegradability. To this end, quaternary ammonium Gemini surfactants, alkanediyl‐α,ω‐bis[(2‐hydroxypropyl)dodecylammonium] dibromide (abbreviated as Cm‐n‐Cm[iso‐Pr(OH)]2 with m = 12, 14 and n = 2, 3, 4) were synthesized via substitution and quaternization reactions, and their chemical structures were characterized by Fourier transform infrared (FT‐IR) and nuclear magnetic resonance (1HNMR) spectroscopies. The results showed that with the decrease of the spacer length, the surface tension was reduced more strongly, and with the increase of the alkyl tail length, micelles were more easily formed. Besides, the highest surface activity of C14‐2‐C14[iso‐Pr(OH)]2 was observed by increasing NaCl concentration to 200 g L−1. The temperature had a great influence on thermodynamic parameters of the adsorption and micellization. The interfacial tension between 0.26 g L−1 C14‐2‐C14[iso‐Pr(OH)]2 solution and oil could reach 0.022 mN m−1. An elongation of the spacer chain in C14‐n‐C14[iso‐Pr(OH)]2 was unfavorable to foam stability. Besides, the oil‐wetted core, which was aged in 0.6 g L−1 C14‐2‐C14[iso‐Pr(OH)]2 solution, exhibited more hydrophilicity. Cm‐n‐Cm[iso‐Pr(OH)]2 surfactants produced higher biodegradable rates in river water (≥ 90% after 28 days) than the biodegradable surfactant of international recommendation (71% after 28 days) at 30 °C.

Pushing and Pulling: A Dual pH Trigger Controlled by Varying the Alkyl Tail Length in Heme Coordinating Peptide Amphiphiles.

Some organisms in nature that undergo anaerobic respiration utilize 1D nanoscale arrays of densely packed cytochromes containing the molecule heme. The assemblies can be mimicked with 1D nanoscale fibrils composed of peptide amphiphiles designed to coordinate heme in dense arrays. To create such materials and assemblies, it is critical to understand the assembly process and what controls the various aspects of hierarchical assembly. MD simulations suggest that shorter alkyl chains on the peptide lead to more dynamic structures than the peptides with longer chains that yield kinetically trapped states. The hydration parameters manifest themselves experimentally through the observation of a dual pH trigger, which controls the peptide assembly rate, the heme binding affinity, and heme organization kinetics. Great strides in understanding the relative complexity of the self-assembly process in relation to incorporating a functional moiety like heme opens up many possibilities in developing abiotic assemblies for bioelectronic devices and assemblies.

Structural Effects of Gas Hydrate Antiagglomerant Molecules on Interfacial Interparticle Force Interactions.

Gas hydrate interparticle cohesive forces are important to determine the hydrate crystal particle agglomeration behavior and subsequent hydrate slurry transport that is critical to preventing potentially catastrophic consequences of subsea oil/gas pipeline blockages. A unique high-pressure micromechanical force apparatus has been employed to investigate the effect of the molecular structure of industrially relevant hydrate antiagglomerant (AA) inhibitors on gas hydrate crystal interparticle interactions. Four AA molecules with known detailed structures [quaternary ammonium salts with two long tails (R1) and one short tail (R2)] in which the R1 has 12 carbon (C12) and 8 carbon (C8) and saturated (C-C) versus unsaturated (C═C) bonding are used in this work to investigate their interfacial activity to suppress hydrate crystal interparticle interactions in the presence of two liquid hydrocarbons (n-dodecane and n-heptane). All AAs were able to reduce the interparticle cohesive force from the baseline (23.5 ± 2.5 mN m-1), but AA-C12 shows superior performance in both liquid hydrocarbons compared to the other AAs. The interfacial measurements indicate that the AA with an R1 longer alkyl chain length can provide a denser barrier, and the AA molecules may have higher packing density when the AA R1 alkyl tail length is comparable to that of the liquid hydrocarbon chain on the gas hydrate crystal surface. Increasing the salinity can promote the effectiveness of an AA molecule and can also eliminate the effect of longer particle contact times, which typically increases the interparticle cohesive force. This work reports the first experimental investigation of high-performance known molecular structure AAs under industrially relevant conditions, showing that these molecules can reduce the interfacial tension and increase the gas hydrate-water contact angle, thereby minimizing the gas hydrate interparticle interactions. The structure-performance relation reported in this work can be used to help in the design of improved AA inhibitor molecules that will be critical to industrial hydrate crystal slurry transport.

Formation of catanionic vesicles by threonine-derived surfactants and gemini surfactants based on conventional or serine-derived headgroups: designing versatile and cytocompatible nanocarriers.

In this work, we explore the ability of newly synthesized threonine-derived surfactants to form robust, versatile and cytocompatible catanionic vesicles when mixed with gemini surfactants, as potential effective nanocarriers for biomolecules. The threonine surfactants consist of single-tailed amphiphiles with carboxylate headgroups and varying alkyl tail length, CnThr, where n is the (even) number of tail C atoms, varying from 8 to 16. After an initial characterization of the micellization behavior of the neat CnThr surfactants (at pH = 7 and 12), the dodecyl derivative, C12Thr, was selected as the optimal surfactant to investigate regions of formation of spontaneous catanionic vesicles. Phase behavior studies and microstructural characterization of mixtures involving both conventional bis-quat n-s-n gemini (where n and s are the tail and spacer number of C atoms) and biocompatible serine-derived gemini surfactants were carried out. Light and electron microscopy, dynamic light scattering and zeta potential measurements show spontaneous vesicles indeed form and exhibit versatile features in terms of average size, morphology, polydispersity, surface charge and pH. The toxicological profile of the neat surfactants and C12Thr/gemini vesicles based on MTT assays with a L929 cell line was also evaluated, showing good levels of in vitro cytocompatibility. Overall, the assortment of developed catanionic vesicles offers very attractive physicochemical and biological features to be explored for delivery purposes.

Interplay between surfactant self-assembly and adsorption at hydrophobic surfaces: insights from dissipative particle dynamics

ABSTRACT We study the self-organisation of aqueous surfactants in bulk phase, and the adsorption and self-organisation of the aqueous surfactants at a planar hydrophobic surface by dissipative particle dynamics. Nonionic surfactants, n-alkyl poly(ethylene oxide) CE, and water are coarse-grained into mesoscopic beads comprising 1–3 heavy atoms and two water molecules, respectively. The size of the mesoscopic beads is related to the molar volume of the underlying molecular fragments while the bead–bead interaction parameters are calibrated against the water-octanol partition coefficients. We focus on the CE, CE, CE, and CE surfactants in water that form spherical micelles in the bulk. The bulk micellization is primarily affected by the alkyl tail length which is demonstrated by an order of magnitude decrease in the critical micelle concentration when going from the aqueous CE to aqueous CE solutions. Surfactants strongly adsorb on the hydrophobic surface, adopting lying-down configurations and forming hemispheres which are in equilibrium with the spherical micelles in the bulk. In contrast to the bulk phase, the surfactant adsorption behaviour is influenced by both the alkyl tail and head chain lengths.

Synergistic interactions of ionic liquids and antimicrobials improve drug efficacy.

SummaryCombinations of ionic liquids (ILs) with antimicrobial compounds have been shown to produce synergistic activities in model liposomes. In this study, imidazolium chloride-based ILs with alkyl tail length variations are combined with commercially available, small-molecule antimicrobials to examine the potential for combinatorial and synergistic antimicrobial effects on P. aeruginosa, E. coli, S. aureus, and S. cerevisiae. The effects of these treatments in a human cell culture model indicate the cytotoxic limits of ILs paired with antimicrobials. The analysis of these ILs demonstrates that the length of the alkyl chain on the IL molecule is proportional to both antimicrobial activity and cytotoxicity. Moreover, the ILs which exhibit synergy with small-molecule antibiotics appear to be acting in a membrane permeabilizing manner. Collectively, results from these experiments demonstrate an increase in antimicrobial efficacy with specific IL + antimicrobial combinations on microbial cultures while maintaining low cytotoxicity in a mammalian cell culture model.

Amphiphile Organization in Organic Solutions: An Alternative Explanation for Small-Angle X-ray Scattering Features in Malonamide/Alkane Mixtures.

The role of different intermolecular interactions in the aggregation of amphiphiles in an organic solvent is studied for systems of relevance to liquid-liquid extraction (LLE), a chemical process used to selectively recover metals from complex mixtures. Of specific interest is the role, or lack thereof, of hydrogen bonding, which is often assumed to be a main driver of the organic phase structural organization that has been linked to separation efficacy. Toward that end, a series of malonamide extractants in n-dodecane have been studied in the absence of any extracted aqueous solutes, including water. The series of extractants includes N,N'-dimethyl-N,N'-dibutyltetradecylmalonamide (DMDBTDMA), two of its homologs, and N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA). This simplified model LLE system enables systematic investigation of the role of dipole-dipole and alkyl tail steric interactions in amphiphile aggregation. Small-angle X-ray scattering (SAXS) profiles computed from molecular dynamics trajectories are in good agreement with experimental SAXS data. Molecular dynamics simulations show that malonamide aggregation results from dipole-driven self-association and lacks characteristic aggregate sizes. Mid-q correlation peaks in the SAXS profiles emerge at high concentration for each malonamide. In those densely packed solutions, the correlation peaks are observed to result from alkyl tail-induced spacing between electron-rich polar head groups, with peak positions determined by the different alkyl tail lengths present in the malonamide molecule. This explanation of the SAXS correlation peaks contrasts with the prevailing literature, which attributes mesoscale features observed in small-angle scattering to the formation of microemulsions. Instead, this work finds that these features are present in the absence of water or any reverse micellar organization of the malonamides. As such, molecular-scale malonamide self-association and packing, rather than microemulsion-based colloidal-scale descriptions, is a more appropriate framework for these LLE systems.

Controllable Synthesis and Structure-Performance Relationship of Silicalite-1 Nanosheets in Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime

Bulky silicalite-1 shows high catalytic activity for vapor phase Beckmann rearrangement of cyclohexanone oxime. However, it often deactivates rapidly and the structure-performance relationship is unclear. Here, a series of well-crystallized silicalite-1 catalysts from three-dimensional micron particles (n < 10) to two-dimensional nanosheets (10 ≤ n ≤ 18) were controllably synthesized using diquaternary ammoniums [CnH2n+1-N+(CH3)2-C6H12-N+(CH3)2-C6H13](Br−)2 (n = 6–18) as the structure directing agent. The influence of morphology of catalysts on active sites distribution and the pore confinement effect on caprolactam selectivity and the catalytic stability were studied by XRD, SEM, TEM, In situ vacuum IR, 29Si MAS NMR and N2 adsorption/desorption isotherms. The silicalite-1 nanosheets with relatively high crystallinity exhibited superior catalytic activity to almost 100% and remarkably high caprolactam selectivity (92%). The catalytic lifetime of silicalite-1 nanosheets could be increased by 28 times in comparison to bulky silicalite-1 zeolite. The external surface area and mesopore volume of the synthesized catalyst dramatically increase with increasing the tail length of surfactant from C6 to C18, leading to high active sites and coke tolerance capacity. It was found the lifetime of the catalysts is almost linearly related to the product of area of silanol nest and volume of mesopore (Asilanol·nest*Vmeso) with correlation coefficient of 0.97, which strongly supports the excellent performance of nanosheets results from the synergetic effect of its high active sites and high coke tolerance capacity. This provides a theoretic guide for designing new catalysts with high catalytic activity. Silicalite-1 nanosheets were controllable synthesized through adjusting alkyl tail length of diquaternary ammoniums, resulting in large mesoporous volume and external surface area, which effectively improve high coke tolerance capacity and active sites of catalysts and exhibit much longer catalytic lifetime and high selectivity.

Effects of fatty acids having different alkyl tail lengths on rigidness of the shell region surrounding an ionic core and mechanical properties of poly(ethylene-co-methacrylic acid) ionomer/fatty acid blends

Herein, we suggest the importance of the rigidness of the shell region surrounding the ionic core in controlling the tensile mechanical properties of sodium-neutralized poly(ethylene-co-methacrylic acid) (EMAA) ionomers blended with several fatty acids with different alkyl tail lengths. When dodecyl acid (DA) or lauric acid (LA) was blended, the local Tg of most of the shell region decreased to lower than room temperature, whereas the ionic core was still glassy at room temperature. However, the local Tg of the shell region was almost equal to room temperature when stearic acid or behenic acid was blended. The EMAA ionomers blended with DA and LA exhibited higher stretchability and toughness in the tensile test and shorter relaxation time in the stress–relaxation test than the other samples because some neutralized and/or unneutralized carboxy groups attached to highly stressed polyethylene chains detachfrom the ionic cores when the shell region was soft.