Cationic Head Groups Research Articles

PH and reduction dual-responsive dipeptide cationic lipids with α–tocopherol hydrophobic tail for efficient gene delivery

A series of tocopherol-based cationic lipid 3a-3f bearing a pH-sensitive imidazole moiety in the dipeptide headgroup and a reduction-responsive disulfide linkage were designed and synthesized. Acid-base titration of these lipids showed good buffering capacities. The liposomes formed from 3 and co-lipid 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) could efficiently bind and condense DNA into nanoparticles. Gel binding and HPLC assays confirmed the encapsulated DNA could release from lipoplexes 3 upon addition of 10 mM glutathione (GSH). MTT assays in HEK 293 cells demonstrated that lipoplexes 3 had low cytotoxicity. The in vitro gene transfection studies showed cationic dipeptide headgroups clearly affected the transfection efficiency (TE), and arginine-histidine based dipeptide lipid 3f give the best TE, which was 30.4 times higher than Lipofectamine 3000 in the presence of 10% serum. Cell-uptake assays indicated that basic amino acid containing dipeptide cationic lipids exhibited more efficient cell uptake than serine and aromatic amino acids based dipeptide lipids. Confocal laser scanning microscopy (CLSM) studies corroborated that 3 could efficiently deliver and release DNA into the nuclei of HeLa cells. These results suggest that tocopherol-based dipeptide cationic lipids with pH and reduction dual-sensitive characteristics might be promising non-viral gene delivery vectors.

Size and temperature dependency on structure, heat capacity and phonon density of state for colloidal silver nanoparticle in 1-Ethyl-3-methylimidazolium Hexafluorophosphate ionic liquid

Abstract Phonon detector can be designed by using colloidal silver nanoparticle (Ag NP) in presence of 1-Ethyl-3-methylimidazolium Hexafluorophosphate [EMim][PF6] ionic liquid (IL) via computational technique as the first time for many and high performance biosensors applications. Density functional theory as a quantum chemistry calculation method has been used to get the potential interaction between silver metal and ionic solvent. Molecular dynamics simulation shows that in small sizes of colloidal Ag NP in [EMim][PF6], electrical effect of IL makes one main phonon peak and in big size of colloidal Ag NP, splitting of phonon density occurs with two peaks due to the lower electrical field of IL with the surface metal. There is non-monotonic behavior for phonon mean collision time in terms of colloidal Ag NP size in IL; however, phonon mean collision time for Ag NP in gas phase decreases monotonically as the Ag NP size increases. In big size of colloidal Ag NP in IL the distance frequency of main phonon peak is closer than those in gas phase. The size of colloidal Ag NP does not have a significant effect on charge separation; cation head group and anion coincide in the vicinity of the NP for the all sizes of Ag NP. Metal dipole moment due to electrical field of IL has an effect around metal surface, reducing heat capacity of colloidal silver nanoparticle in comparison with the gas phase of Ag NP and finally heat capacity of colloidal silver nanoparticle approaches to the gas phase as the size of Ag NP increases. MD simulation shows that there is non-monotonic behavior for stabilization energy as a function of Ag NPs sizes. Our result regarding phonon DOS for Ag NP and Ag bulk are in agreement with the available experimental data.

Thermal stability of tetrabutyl-phosphonium and -ammonium exchanged montmorillonite: Influence of acid treatment

Thermal stability of acid-treated organo-montmorillonites was investigated by thermogravimetric analysis (TA) coupled with infrared (IR) spectroscopic analysis of evolved gasses, and by in-situ measurement of near-IR (NIR) spectra of solid samples. The organoclays prepared from Na-form of SAz-1 montmorillonite (Na-S) and tetrabutylphosphonium (Bu4P+) and tetrabutylammonium (Bu4N+) salts were treated with 6M HCl at 80°C for 2–12h. Elemental analysis revealed higher resistance of Bu4P-S and Bu4N-S to decomposition compared to Na-S, leaving 44 and 52% of the octahedral Mg and/or Al in the solid reaction products after 12h treatment. Bu4N-S decomposed in slightly lower extent than Bu4P-S, pointing thus to the influence of the type of cation headgroup on its stability in HCl. The TG/DTG profiles of both samples showed pronounced mass loss due to decomposition of organic cations within temperature 200–800°C. While Bu4N-S showed onset temperature of near 200°C, significantly higher temperatures, above 300°C, was found for Bu4P-S. The intensities of the absorption bands related to CH vibrations of aliphatic hydrocarbons in the IR spectra reached maxima at 277°C and 446°C for Bu4N-S and Bu4P-S, respectively. The mass loss attributed to the organic cation decomposition for acid-treated samples dropped down below 50% of its initial value due to the leaching of organic phase. Moreover, the onset temperature of organic phase release was shifted to higher temperature indicating that only more strongly held cations remained in the samples. NIR spectra showed that the intensity decrease of the first 2νCH overtones band due to organic cation release began at lower temperature for Bu4N-S (above 380°C) than for Bu4P-S (above 500°C).

Toll-like receptor 2 promiscuity is responsible for the immunostimulatory activity of nucleic acid nanocarriers

Lipopolyamines (LPAs) are cationic lipids; they interact spontaneously with nucleic acids to form lipoplexes used for gene delivery. The main hurdle to using lipoplexes in gene therapy lies in their immunostimulatory properties, so far attributed to the nucleic acid cargo, while cationic lipids were considered as inert to the immune system. Here we demonstrate for the first time that di-C18 LPAs trigger pro-inflammatory responses through Toll-like receptor 2 (TLR2) activation, and this whether they are bound to nucleic acids or not. Molecular docking experiments suggest potential TLR2 binding modes reminiscent of bacterial lipopeptide sensing. The di-C18 LPAs share the ability of burying their lipid chains in the hydrophobic cavity of TLR2 and, in some cases, TLR1, at the vicinity of the dimerization interface; the cationic headgroups form multiple hydrogen bonds, thus crosslinking TLRs into functional complexes. Unravelling the molecular basis of TLR1 and TLR6-driven heterodimerization upon LPA binding underlines the highly collaborative and promiscuous ligand binding mechanism. The prevalence of non-specific main chain-mediated interactions demonstrates that potentially any saturated LPA currently used or proposed as transfection agent is likely to activate TLR2 during transfection. Hence our study emphasizes the urgent need to test the inflammatory properties of transfection agents and proposes the use of docking analysis as a preliminary screening tool for the synthesis of new non-immunostimulatory nanocarriers.

Detection of sulfate surface-active substances via fluorescent response using new amphiphilic thiacalix[4]arenes bearing cationic headgroups with Eosin Y dye

New ammonium-containing derivatives of p-tert-butylthiacalix[4]arene in 1,3-alternate stereoisomeric form were synthesized via copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction of corresponding azides with N-propargyl-N,N,N-triethylammonium bromide. Critical aggregation concentration (CAC) of new amphiphilic thiacalixarenes 1-3 (with butyl, octyl and tetradecyl substituents) determined by pyrene micellization method are 91, 59 and 33μM, respectively. According to DLS data the diameter of these aggregates is around 130nm. Anionic dye Eosin Y (EY) forms the associates with positive charged thiacalixarenes 1-3, shifts CAC to the low concentration region (2μM) and decreases nanoaggregates size up to 90nm. Thiacalixarene/EY associates were investigated as fluorescent probe for the determination of different surface active substances (SAS) in the solution. It was found that only sodium dodecyl sulfate (SDS) and sodium laureth sulfate (SLES) causes EY release, while other anionic, cationic and zwitterionic SAS form only mixed aggregates. Fluorescent response of thiacalixarene/EY associates is considerable from 3.5μM concentration of SDS.

Probing Molecular Interactions between Ammonium-Based Ionic Liquids and N,N-Dimethylacetamide: A Combined FTIR, DLS, and DFT Study.

The present study investigates the effects of the alkyl chain length of the cationic head-group of some ammonium-based ionic liquids (ILs) (having the same anion) on the interaction between the ILs and N,N-dimethylacetamide (DMA). The molecular interactions between the studied ILs, tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), and their binary mixtures with DMA were studied using the Fourier transform infrared spectroscopy (FTIR) technique, dynamic light scattering (DLS) experiments, and quantum chemical calculations. It was observed from both experimental FTIR analysis and theoretical studies that the strength of intermolecular interactions, such as hydrogen bonding, ion-ion interactions, and induced dipole interactions, between the ILs and DMA depends on the alkyl chain length of the IL cation head-group. The interaction of DMA with IL is energetically favorable and occurs via direct interactions between the IL anion and the carbonyl oxygen of DMA. The results further revealed that the shorter the alkyl chain length of the cationic head-group of the ILs, the stronger the interaction with the DMA molecule, such that the strength of interactions between the ILs and DMA follows the order TEAH > TPAH > TBAH. This trend can be attributed to the increased self-organized aggregation with increasing alkyl chain length of the IL cation.

Hiding the Headgroup? Remarkable Similarity in Alkyl Coverage of the Surfaces of Pyrrolidinium- and Imidazolium-Based Ionic Liquids

The liquid–vacuum interfaces of a series of ionic liquids (ILs) containing 1-alkyl-1-methylpyrrolidinium ([Cnmpyrr]+) cations of different alkyl chain lengths have been studied by reactive-atom scattering with laser-induced fluorescence detection (RAS-LIF) and molecular dynamics (MD) simulations. A direct, quantitative comparison has been performed between [Cnmpyrr]+ and the previously better-characterized 1-alkyl-3-methylimidazolium ([Cnmim]+) ILs with the same chain lengths, n, and common anion, bis(trifluoromethylsulfonyl)imide ([Tf2N]−). Both RAS-LIF experiments, using O(3P) as the projectile and monitoring OH yield, and MD simulations indicate that the coverage of the surface by alkyl chains is almost independent of the identity of the cation headgroup. Moreover, the potentially abstractable H atoms of the saturated pyrrolidinium ring do not contribute appreciably to the experimental OH yield. In both these senses, therefore, the headgroup is “hidden” from the probe particles approaching from vacuum....

Laccase Activity in CTAB-Based Water-in-Oil Microemulsions.

The aim of this study was to develop a microemulsion system as a medium for laccase-catalyzed reactions. Phase behavior studies were conducted by constructing partial pseudo-ternary phase diagrams for systems comprising of cetyltrimethylammonium bromide (CTAB), various organic solvents as the oil phase (i.e., hexane, cyclohexane, heptane, octane, isooctane, toluene, isopropyl myristate), two co-surfactants (i.e., 1-butanol and 1-hexanol) and citrate buffer solution, at various surfactant/co-surfactant weight ratios (Rsm). A monophasic, transparent, non-birefringent area (designated as microemulsion domain) was seen to occur in some phase diagrams along the surfactant/organic solvent axis, the extent of which was dependent mainly upon the nature of co-surfactant and Rsm. On each phase diagram, three different water-in-oil (w/o) microemulsion systems with less than 50 wt% surfactant mixture and less than 20 wt% of aqueous phase were selected for laccase loading and activity measurements. Results revealed that the catalytic activity of laccase in CTAB-based w/o microemulsions decreased considerably, compared with its activity in the buffer solution, the extent of which depended upon the type of component and their compositions in the microemulsions. It was suggested that the conformational changes due to the electrostatic interactions between the cationic head group of CTAB and the negative enzyme might be the reason for the reduction of laccase activity, once entrapped in the microemulsion.

Reactive-Atom Scattering from Liquid Crystals at the Liquid-Vacuum Interface: [C12mim][BF4] and 4-Cyano-4'-Octylbiphenyl (8CB).

Two complementary approaches were used to study the liquid-vacuum interface of the liquid-crystalline ionic liquid 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C12mim][BF4]) in the smectic A (SmA) and isotropic phases. O atoms with two distinct incident translational energies were scattered from the surface of [C12mim][BF4]. Angle-dependent time-of-flight distributions and OH yields, respectively, were recorded from high- and low-energy O atoms. There were no significant changes in the measurements using either approach, nor the properties derived from them, accompanying the transition from the SmA to the isotropic phase. This indicates that the surface structure of [C12mim][BF4] remains essentially unchanged across the phase boundary, implying that the bulk order and surface structure are not strongly correlated for this material. This effect is ascribed to the strong propensity for the outer surfaces of ionic liquids to be dominated by alkyl chains, over an underlying layer rich in anions and cation head groups, whether or not the bulk material is a liquid crystal. In a comparative study, the OH yield from the surface of the liquid crystal, 8CB, was found to be affected by the bulk order, showing a surprising step increase at the SmA-nematic transition temperature, whose origin is the subject of speculation.

Alkaline-Stable Anion Exchange Blend Membranes (AEBMs) with a Novel Sterically Hindered Cationic Head Group

In this study, synthesis and characterization of Anion Exchange Blend Membranes (AEBMs) are introduced. AEBMs were prepared by mixing polymer solutions of a halomethylated polymer (Br-PPO, brominated poly(2,6-dimethyl-1,4-phenylene oxide)), polybenzimidazole (PBI, F6PBI or PBI-OO) and a sulfonated polymer (S-polymer, SAC 098 (a sulfonated poly(phenylethersulfone), nonfluorinated) or SFS 001 (a sulfonated aromatic polyether, partially fluorinated)). A halomethylated polymer was used as the anion exchange ionomer precursor. Polybenzimidazole was used as a matrix polymer in order to enhance the mechanical strength of the AEBN. A minor amount of sulfonated polymer was added, forming ionic cross-links, and covalent bonds were formed in the blend membrane by reaction of a small amount of the CH2Br groups of Br-PPO with imidazole N-H groups of the PBI, respectively, leading to an increase of the chemical and dimensional stability of the novel AEBMs [1]. Membranes were fabricated by following procedure 1) mixing of the polymer solutions to homogeneity, 2) solvent evaporation in oven, 3) quaternization of the blend membrane by soaking the membrane in amine solution, 4) Ion exchange into chloride form in sodium chloride solution. It is well known that many types of anion exchange membranes are chemically unstable under alkaline condition. S. Holdcroft published a novel polybenzimidazolium AEM with a mesitylene building block shielding the dimethylimidazolium moiety of the polybenzimidazolium from OH- attack, leading to excellent hydroxide stability of this AEM: after immersion of this AEM in 2M KOH for 10 days at 60°C, no significant change of the NMR spectrum was observed [2]. Therefore it can be concluded that introduction of bulky steric hindrance groups in the vicinity of the cationic groups of AEMs can prevent the quaternized amine in the polymer structure from nucleophilic attack of hydroxide ions. Consequently in this study several types of sterically hindered tertiary amines were introduced in the polymer blend system for quaternization with Br-PPO, among them 1,2,2,6,6-pentamethylpiperidine (pempidine), quinuclidine, and 1,2,4,5-tetramethyl-1H-imidazole (abbreviated TMIm). Among these AEBMs, the TMIm-based membranes showed the best properties in terms of conductivity and stability. We investigated different combinations of polymers for AEBMs. The membrane containing PBI-OO and SAC098 showed good weight maintenance than other material combinations in DMAc extraction test at 90oC. This membrane was prepared and post-treated with TMIm as mentioned above. The membrane exhibited a chloride conductivity of 6.5 mS/cm at 30oC and 90% RH which is higher than that of commercial membrane (Tokuyama A202) under the same condition. The change of ion exchange capacities (IECs) was also investigated in order to examine the hydroxide stability. The membrane was exposed to 1M KOH solution at 90oC for 10days, and ion-exchange capacities (IECs) were compared to each other before and after KOH treatment. The IECs before and after KOH treatment were 2.63 and 2.59 mmol/g respectively, indicating excellent hydroxide stability. Apart from Br-PPO, other halomethylated polymers such as polyvinylbenzylchloride and polyepichlorohydrine were also investigated as precursors for AEBMs in this study, yielding good Cl- conductivities (in excess of 30 mScm-1) and alkaline stabilities with the novel 1,2,4,5-tetramethyl-1H-imidazolium head group. Addition of a hydrophilic polymer phase to the novel AEBMs resulted in even higher Cl- conductivities (e. g. 131 mScm-1@90°C@90% r.h.) after 10 d of KOH treatment (1M, 90°C).

Alkali-Resistant Anion-Exchange Membranes for Electrochemical Hydrogen Conversions

H2 fuel cells and water electrolysers containing solid alkaline electrolytes represents a promising approach for the development of a cost-effective H2-based infrastructure. The alkaline media promises the use of cheaper non-precious metal catalysts [1]. Therefore, there is a push to fulfil the current performance requirements of such electrochemical devices. The employment of alkaline anion-exchange membrane (AAEM) in fuel cells and water electrolysers allows the reduction of the inter-electrode distance with better energy efficiencies without an increase in undesirable gas crossover and a reduction of the purity of the product H2 [2]. However, the stability of the central AAEM at operation temperatures (up to 90°C) remains the biggest challenge of this technology. Numerous researchers around the world are seeking the most stable chemistries of AAEMs in strongly basic media. Among the cationic head group options, the use of quaternary ammoniums (QA) is common, due to the accessibility of the starting materials and their demonstrated ion-conducting properties. Numerous studies of hydroxide-derived degradation products have enabled the identification of the main degradation pathways with such tetraalkylammonium functionalities [3]. Herein, we have employed radiation-induced grafting for the preparation of conductive AAEMs (> 100 mS cm-2 at 80°C, fully hydrated) with various benzylic QA head-groups (cyclic and non-cyclic). The radiation induced grafting of commodity polymer films affords a reproducible method for the cost competitive, large lab-scale preparation of ion-exchange materials that is scalable for further applications [4]. The spectroscopic and composition analysis of the AAEMs after aqueous hydroxide (1 mol dm-3) treatment at 80°C revealed various degradation mechanisms are occurring. According to this, we have developed chemistries to introduce QA head groups that afforded AAEMs with improved alkali stabilities. Furthermore, fuel cell testing has demonstrated that some of these new chemistries significantly enhance the in situ electrochemical performance of the AAEMs compared to the radiation-grafted benzyltrimethylammonium benchmark [5] (> 800 mW cm-2 H2/O2 peak power densities at 60°C, no back-pressurization, with 50 μm thick AAEMs and Pt- benchmark catalysts). [1] J. R. Varcoe, P. Atanassov, D. R. Dekel, A. M. Herring, M. A. Hickner, P. A. Kohl, A. R. Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott, T. W. Xu and L. Zhuang, Energy Environ. Sci., 2014, 7 3135. [2] S. Vengatesan, S. Santhi, S. Jeevanantham and G. Sozhan, J. Power Sources, 2015, 284, 361–368. [3] A. D. Mohanty and C. Bae, J. Mater. Chem. A, 2014, 2, 17314–17320; M. G. Marino and K. D. Kreuer, ChemSusChem, 2015, 8, 513–23; M. R. Sturgeon, C. S. Macomber, C. Engtrakul, H. Long and B. S. Pivovar, J. Electrochem. Soc., 2015, 162, F366–F372. [4] M. Nasef, Chem.Rev, 2012, 114, 12278. [5] J. R. Varcoe, R. C. T. Slade, E. Lam How Yee, S. D. Poynton, D. J. Driscoll and D. C. Apperley, Chem. Mater., 2007, 19, 2686–2693. Figure 1

Role of the Electrostatic Interactions in the Stabilization of Ionic Liquid Crystals: Insights from Coarse-Grained MD Simulations of an Imidazolium Model.

In order to investigate the role of the electrostatic interactions in stabilizing various phases of ionic liquids, especially smectic ionic liquid crystals, we have employed a coarse-grained model of 1-hexadecyl-3-methylimidazolium nitrate, [C16mim][NO3], to perform molecular dynamics simulations with the partial charges artificially rescaled by a factor from 0.7 to 1.2. The simulated systems have been characterized by means of orientational and translational order parameters and by distribution functions. We have found that increasing the total charge of the ions strongly stabilizes the ionic smectic phase by shifting the clearing point (melting into the isotropic liquid phase) to higher temperatures, while a smaller effect is observed on the stability of the crystal phase. Our results highlight the importance of the electrostatic interactions in promoting the formation of ionic liquid crystals through microphase segregation. Moreover, as the total charge of the model is increased, we observe a transformation from a homogeneous to a nanosegregated isotropic structure typical of ionic liquids. Therefore, a connection can be established between the degree of nanosegregation of ILs and the stability of ILC phases. All the above can be understood by the competition among electrostatic interactions between charged groups (cationic head groups and anions), van der Waals interactions between nonpolar cationic tail groups, and thermal fluctuations.

Amphiphile self-assembly based on ionic liquids

Ionic liquids (ILs), as a class of compounds composed of ions with melting points at or near room temperature, have unusual physicochemical properties including low volatility, high temperature stability, high ionic conductivity and easy recyclability. Thus ILs have been applied widely in the range of organic synthesis, catalysis, chromatography, analytical chemistry, biochemistry and so on. Perhaps the most unique capability of ILs is to support the self-assembly of amphiphiles. Due to the extraordinary properties of ILs, the self-assembled aggregates based on ILs have attracted a lot of attentions during the last decades. ILs are now not only considered as important alternative solvents, but also as materials with unique and tuneable properties which can be easily adjusted by suitable selection of cations and anions for a specific function. Based on the unique designability of ILs, it will be expected to achieve the controllability of the nanostructures and properties of IL-based self-assembled aggregates by tailoring the structures of ILs. Here, the research progress of amphiphile self-assembly based on ILs was reviewed. Firstly, the room-temperature ILs can be considered as solvents to participate in the self-assembly process and classified as protic ionic liquids (PILs) and aprotic ionic liquids (AILs), respectively. Up to now, a number of AILs based on imidazolium cations and many alkylammonium PILs, such as ethylammonium nitrate (EAN), have been used as self-assembly media to support amphiphile to form various aggregates including micelles, vesicles, microemulsions and liquid crystals. Different from AILs, the PILs can build up hydrogen-bonding networks which are similar to water molecules due to their protic nature and general properties. The different solvent properties of PILs and AILs have significant influence on the aggregation behavior of amphiphilic molecules. Secondly, the long chain analogues of common ionic liquids, named as surfactive ionic liquids (SAILs), could possess inherent surface active properties and self-assemble to form different aggregates with specific structures, shapes and properties in aqueous solutions like traditional amphiphilic molecules. Various long-chain SILs with different cationic headgroups based on imidazolium, pyrrolidinium, piperidinium etc. have been synthesized and investigated. Except for cationic SAILs, the aggregation behaviors of a series of anionic SAILs based on organic surfactant anions and imidazolium cations have also been studied to expand the application of SAILs in the filed of colloid and interface chemistry. SILs, as a novel kind of surfactants, can self-assembly into different kinds of aggregates driven by intermolecular interactions including hydrophobic interaction, electrostatic interaction, hydrogen bonding and so on. Thus, the type of cations, the alkyl chain length, and the nature of the counterions have key effect on the aggregation behavior of SAILs. Thirdly, the physicochemical properties of the given surfactant solutions can also be modified by the addition of external ionic liquids. Due to the tailoring properties of ILs, “task-specific” ILs (TSILs) have emerged by introducing functional groups as a part of substituent to impart a particular capability to ILs and further modulate the aggregation behavior of surfactant solutions. This is also a practical way for us to determine the role of one specific intermolecular interaction on the self-assembly process. The present work summarized the amphiphile self-assembly based on ILs, including room-temperature ILs as solvents, long-chain ILs as amphiphiles and ILs as external additives. Our aim is to establish the dependence of aggregation behavior of amphiphiles on the unique structures of ILs. This review is helpful to achieve the controllability and functionalization of traditional self-assembled aggregates by the incorporation of functional ILs.

The influence of electronic polarizability of components on the electric field of an ionic micelle according to molecular simulation data

Molecular dynamics simulation of a cationic micelle having a rigid hydrophobic core and mobile cationic head groups has been performed taking into account the electronic contribution into solution polarization. As compared with an analogous micelle previously considered with no regard to the polarization effects, the latter manifest themselves as a weaker structuring of micelle crown and greater concentrating of counterions in it. Analysis of the local electric potential has indicated that the discrepancy between the data of the continual and atomistic descriptions of water remains preserved. Thus, agreement between the theory and numerical experiment cannot be achieved when describing the local electric potential with no allowance for the local character of polarization.

A novel cationic lipid with intrinsic antitumor activity to facilitate gene therapy of TRAIL DNA.

Metformin (dimethylbiguanide) has been found to be effective for the treatment of a wide range of cancer. Herein, a novel lipid (1,2-di-(9Z-octadecenoyl)-3-biguanide-propane (DOBP)) was elaborately designed by utilizing biguanide as the cationic head group. This novel cationic lipid was intended to act as a gene carrier with intrinsic antitumor activity. When compared with 1,2-di-(9Z-octadecenoyl)-3-trimethylammonium-propane (DOTAP), a commercially available cationic lipid with a similar structure, the blank liposomes consisting of DOBP showed much more potent antitumor effects than DOTAP in human lung tumor xenografts, following an antitumor mechanism similar to metformin. Given its cationic head group, biguanide, DOBP could encapsulate TNF-related apoptosis-inducing ligand (TRAIL) plasmids into Lipid-Protamine-DNA (LPD) nanoparticles (NPs) for systemic gene delivery. DOBP-LPD-TRAIL NPs demonstrated distinct superiority in delaying tumor progression over DOTAP-LPD-TRAIL NPs, due to the intrinsic antitumor activity combined with TRAIL-induced apoptosis in the tumor. These results indicate that DOBP could be used as a versatile and promising cationic lipid for improving the therapeutic index of gene therapy in cancer treatment.

Synthesis of Thermally Stable Geminal Dicationic Ionic Liquids and Related Ionic Compounds: An Examination of Physicochemical Properties by Structural Modification

Geminal dicationic ionic liquids (ILs) often display higher thermal stabilities, viscosities, and densities compared to traditional monocationic ILs. Also, dicationic ILs have advantages in terms of tuning of their physicochemical properties by different structural modifications. They can be considered as a combination of three structural moieties: (1) cationic head groups, (2) an alkane linker chain, and (3) the associated anions. Two types of each imidazolium, pyrrolidinium, and phosphonium cations were joined by different alkane linkages (C6, C9, and C12) to develop 18 different dications. These dications were paired with two different anions (NTf2– and PFOS–) to synthesize 36 different dicationic ILs. The effect of variations in the structural moieties of these related ILs on their physicochemical properties, including melting points, densities, viscosities, solubilities, and thermal stabilities, were evaluated. ILs synthesized in this study displayed TGA thermal stabilities in the range 330–467 °C. A...

External surface structure of organoclays analyzed by transmission electron microscopy and X-ray photoelectron spectroscopy in combination with molecular dynamics simulations

HypothesisInterface properties of organoclay particles can be related directly to type of organic cation, and density and arrangement of organic coating at clay surfaces. ExperimentsThis study provides detailed nanoscale insights on surface structure of hexadecyltrimethylammonium/hexadecylpyridinium-montmorillonite (HDTMA+/HDPy+-M) organoclays by combining several experimental methods (e.g. transmission electron microscopy, TEM, and X-ray photoelectron spectroscopy, XPS) with molecular simulations. FindingsTEM showed a relation between the thickness of the organic coating and the amount of organic cation loading. Furthermore, coating thickness varied for the same sample indicating a heterogeneous surface of clay particles. The changes in elemental composition determined by XPS were correlated with the thickness of the organic coating. High resolution XPS showed changes in binding energies of CN bonds, which were attributed to varying local environment of head groups of organic cations. Classical molecular dynamics (MD) simulations showed a successive transformation of the organic cation coating of the montmorillonite surface from thin disordered monolayers at low up to disordered bilayer or quasi paraffin-type arrangements at high surfactant coverages. For organoclays with low cation loading no significant difference was observed between HDTMA+ and HDPy+. However, at high cation loading, surface packing density was higher for HDTMA+ than for HDPy+.

Influence of interfacial interactions on the properties of polybenzimidazole/clay nanocomposite electrolyte membrane

Abstract Despite the wide range of studies illustrating the influence of type and quantity of nanoclay on the macro properties of polymer nanocomposites, it has always remained a biggest challenge to study the chemistry of organic/inorganic interface on the final properties of polymer nanocomposites, a study that can indeed aid us in designing tailor-made materials e.g. proton exchange membranes (PEM). Hence in this study, we aimed to explore the influence of interface chemistry of nano-clay on the properties of poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI)/clay nanocomposite PEM for fuel cell. Cloisite clay modified organically with three surfactant molecules differing structurally in their cationic head group – cetyltrimethyl ammonium bromide (CTAB), cetylpyridinium bromide (CPyB) and cetylimidazolium bromide (CImiB) was utilized for making OPBI nanocomposite membranes by a simple solution blending route. 13 C CP MAS solid state NMR confirmed the hydrogen bonding interactions between the OPBI chains and clay particles. Formation of intercalated clay nanostructures in the OPBI matrix was revealed by WAXD and TEM analyses and this morphology was found to influence different properties in a favorable manner. TGA and DMA studies highlighted the influence of the different surfactants on the interfacial interactions in elevating/decreasing the thermal and glass transition temperatures of the nanocomposite membranes. The use of different surfactant modified clays induced sufficient hydrophobicity in the membranes that led to higher phosphoric acid (PA) loading and controlled dimensional swelling in both water and PA. The proton conductivity data particularly underscored the different degrees of interfacial interactions each of the three differently modified clays had in creating efficient proton transport pathways giving rise to higher proton conductivity while decreasing the activation energy barrier for the proton hopping. The results also revealed the critical role played by the clay particles especially by the organic modifier in preventing the leaching away of the doped acid from the nanocomposites membranes.

Water Structure at the Lipid Multibilayer Surface: Anionic Versus Cationic Head Group Effects.

Membrane water interface is a potential reaction site for many biochemical reactions. Therefore, a molecular level understanding of water structure and dynamics that strongly depend on the chemical structure of lipid is prerequisite for elucidating the role of water in biological reactions on membrane surface. Recently, we carried out femtosecond infrared pump-probe studies of water structure and dynamics at multibilayer surfaces of zwitterionic phosphatidylcholine-analogue lipid ( J. Phys. Chem. Lett. 2016 , 7 , 741 ). Here, to further elucidate the anionic and cationic headgroup effects on water, we study vibrational dynamics of water on lipid multibilayers formed by anionic phospho-glycerol lipid molecules as well as by cationic choline-derivatized lipid molecules. We observed two significantly different vibrational lifetime components (very fast 0.5 ps and slow 1.9 ps) of the OD stretch mode of HOD molecules at the negatively charged phospho-lipid multibilayer whereas only one vibrational lifetime component (1.6 ps) was observed at the positively charged choline-derivatized lipid multibilayer. From the detailed analyses about the vibrational energy and rotational relaxations of HOD molecules in lipid multibilayers composed of anionic lipid with phosphate and cationic lipid without phosphate, the role of phosphate group in structuring water molecules at phospholipid membrane interface is revealed.

A study of the interaction between polyvinylpyrrolidone and gemini surfactant G12-3-12 by NMR

The interaction between a water-soluble polymer polyvinylpyrrolidone (PVP) and a gemini surfactant N,N'-didodecyl-N,N,N',N'-tetramethyl-N,N'-propanediyl-diammonium dibromide (G12-3-12) was investigated by means of NMR in a D2O solution at 298 K. The critical micelle concentration (СMC), critical aggregation concentration (СAC) and adsorption reached the saturated concentration (C2) were confirmed by chemical shift and self-diffusion coefficients, respectively. The results of the relaxation time ratio (T R = T 2/T 1) of G12-3-12 show that the motion of the ionic head N+–CH 3 * proton (G6) is seriously restricted, and thus, it can be proved that the cationic head groups are situated in the hydrophilic layer of the micelle. The size of the mixed-aggregates in the G12-3-12/PVP solution is larger than pure G12-3-12 micelles according to self-diffusion coefficients, indicating that the G12-3-12 and PVP has formed mixed micelles, and ionic heads N+–CH 3 * become more tightly packed in the hydrophilic layer of the micelle shell. On the other hand, strong cross peaks, such as G1-P2, G1-P3, and G2-P3, appear in the 2D nuclear Overhauser enhancement spectroscopy (2D NOESY) spectra of the G12-3-12/PVP system, further indicating that the interaction sites are located between the hydrophobic tail of G12-3-12 and PVP ring.