Identical Alkyl Chains Research Articles

Impact of organic solvents on the micellization and interfacial behavior of ionic liquid based surfactants

To elucidate the role of organic solvents, in altering the micellization and interfacial behavior of Ionic Liquid based Surfactants (ILBSs), we had investigated the effect of formamide (FA), glycerol (GLY), ethylene glycol (EG) and 1-propanol (PRO) on the micellization and interfacial behavior of 1-tetradecyl-3-methylimidazolium bromide (C14mimBr) and 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) ILs, in aqueous solution by conductometric and tensiometric techniques at 298.15K. The micellization behavior has been determined by studying the changes in critical micelle concentration (cmc), degree of counter ion binding (β), gibbs free energy of micellization (ΔGm0) and interfacial behavior by studying various surface parameters. Micellization behavior was mainly studied in light of altering the relative permittivity of the medium and displacement of water layer, which disfavors the micellization and as a result increases cmc. Effect of solvophobic parameter (Sp) and packing parameter (P) on the micellization was also examined. Results have been compared with the conventional cationic surfactants with identical alkyl chain.

Non-Amide Kinetic Hydrate Inhibitors: Investigation of the Performance of a Series of Poly(vinylphosphonate) Diesters

The kinetic hydrate inhibitor (KHI) performances of a series of poly(dialkyl vinylphosphonate)s (PDAVPs) containing pendant phosphonate groups fully esterified with two identical alkyl chains have been assessed by conducting a suite of slow constant cooling tests at 76 bar in steel rocking cell equipment using a synthetic natural gas (SNG) that preferably forms structure II gas hydrates. The KHI performances of three PDAVPs, of roughly the same molecular weights (28–38 kDa), comprising methyl (M), ethyl (E,) and isopropyl (IP) groups, respectively, were evaluated. As a result, the following ranking was disclosed: P(DIPVP) > P(DEVP) > P(DMVP). The diisopropylated P(DIPVP) homopolymer gave an average onset temperature from 10 experiments of To of 8.3 °C compared to 17.3 °C with deionized water and no additive. The good performance is likely related to the low cloud point (1 wt % solution in deionized water), which was measured to be 18 °C. Three ethylated P(DEVP)s, with molecular weights in the range 30–60 kDa, were tested for KHI performances. The two higher molecular weight samples gave the best performance, which we surmise is related more to the lower cloud point of these samples than the molecular weight. A P(DMVP:DIPVP) copolymer with a high cloud point showed weak KHI effect (To = 13.1 °C).

Ionic liquids as novel quartz collectors: Insights from experiments and theory

Application of quaternary ammonium based ionic liquids (IL’s) as flotation collectors of quartz has been investigated. Effect of number of carbon atoms in the four identical alkyl chains of the IL’s has been studied. The adsorption behaviour of the IL’s on the quartz surface is ascertained through FTIR, XPS and molecular modelling. The FTIR peak at 2900cm−1 indicates the adsorption of the IL’s onto the quartz surface, which is further substantiated by the appearance of the N (1S) peak in the X-ray photoelectron spectra (XPS). Curve splitting data of C (1S) suggests the maximum adsorption for the IL tetrahexylammonium iodide (THEX). Flotation results of pure quartz using ionic liquids are found to be better compared to the conventional collectors such as dodecylamine (DDA) or cetyltrimethylammonium bromide (CTAB). It is possible to float 92–100% quartz by using a THEX concentration of 4.8 × 10−5M. IL collectors are further applied in the flotation of a low grade banded hematite quartzite (BHQ) iron ore with ∼38% Fe. It is possible to achieve an iron concentrate of 63.6% Fe at 63.2% recovery by using THEX as the collector. Molecular simulations using the COMPASS forcefield explains the IL–quartz adsorption mechanism comprising of both electrostatic and van der Waals forces. Floatability of quartz has been correlated with the surface coverage and adsorption energy calculations. The IL’s used here are found to be better quartz collectors than the conventional ones as they show better collecting efficiency in lower dosages. Flotation using these IL’s does not require frothers which is an added advantage compared to the conventional collectors.

Growth Mechanisms of 2D Organic Assemblies Generated from Dialkylated Melaminium Derivatives: The Length Difference of the Two Alkyl Chains That Matters

This research is aimed to understand the growth mechanisms for self-assembly of dialkylated melamine derivatives. The dialkylated melamine derivatives with different alkyl chains (Mela-m-n) are able to self-assemble with hydrochloric acid in dichloromethane to form 2D organic assemblies, exhibiting similar lamellar structures as Mela-n·HCl with identical alkyl chains. The most interesting finding is that the growth mechanism of Mela-n·HCl with identical alkyl chains is revealed to be layer growth, while Mela-m-n·HCl with asymmetric alkyl chains adopts a spiral growth mechanism. The asymmetric alkyl chains in Mela-m-n may lead to the formation of dislocation, which is responsible for the spiral growth mechanism.

Synthesis and Cav2.2 Binding Data for Non-Peptide Mimetics of ω-Conotoxin GVIA based on a 5-Amino-Anthranilamide Core

A simple and efficient method has been developed for the synthesis of two anthranilamide-based non-peptide mimetics of ω-conotoxin GVIA. These anthranilamide derivatives aim to mimic the K2, R17, and Y13 residues of the peptide. The synthetic route described enables the rapid synthesis of anthranilamide analogues with identical alkyl chain lengths. The target compounds show affinity to rat N-type voltage gated calcium channels (Cav2.2) with EC50 values of 42 and 75 μM.

Chirality in Supramolecular Self-Assembled Monolayers of Achiral Molecules on Graphite: Formation of Enantiomorphous Domains from Arachidic Anhydride

The molecular arrangement and chirality of the self-assembled arachidic anhydride monolayer on graphite were investigated using scanning tunneling microscopy (STM). This molecule has two identical alkyl chains, linked by an anhydride group in the middle. In its extended form, one alkyl chain is shifted, with respect to the other, along the molecular backbone. Upon adsorption on graphite, this achiral anhydride spontaneously forms two types of homogeneous domains (denoted as m and m') with mirror symmetry. The angle from the molecular chain to the row-packing direction is 98.0 degrees +/- 0.5 degrees and 82.0 degrees +/- 0.5 degrees for domains m and m', respectively. Domain m is the mirror image of m'. The molecular arrangement of this self-assembled monolayer shows that domains m and m' are two-dimensional enantiomers with opposite chiralities. This new molecular packing motif is confirmed by line-profile analyses along the molecule-chain and the row-packing directions. This finding demonstrates the spontaneous formation of highly ordered homogeneous enantiomorphous domains on graphite resulting only from weak van der Waals forces between the achiral arachidic anhydride molecules.

Effects of Concentration and Temperature on SDS Monolayers at the Air−Solution Interface Studied by Infrared External Reflection Spectroscopy

Infrared external reflection (IER) spectra of sodium dodecyl sulfate (SDS) monolayers at the air-solution interface and infrared transmission spectra of the corresponding aqueous solutions were measured at various SDS concentrations and temperatures. A comparison between the spectra of adsorbed monolayers and bulk solutions revealed that the conformational order of the SDS alkyl-chain at the air-solution interface improved with increasing the SDS concentrations, up until the saturation adsorption, and that the conformational order of the adsorbed SDS monolayer was higher than those of monomers and micelles. In addition, below the Krafft point temperature, the adsorbed SDS was maintained in the liquid crystal state, while SDS in the bulk solution was in the crystalline state. Furthermore, the SDS adsorption density was evaluated based on the IER band intensities of the insoluble monolayer of tridecanoic acid with an identical alkyl chain length to SDS.

New bisamides gelators: relationship between chemical structure and fiber morphology

Different dialkoxybenzoic acid derivatives with identical alkyl chain lengths were synthesized and their properties as organogelators evaluated. Only the compounds bearing amide groups behave like gelators. Their gelation abilities and phase diagrams were described. A structural study was conducted by freeze-fracture electron microscopy and showed that the methyl ester formed platelet-like aggregates whereas the corresponding free acid formed thin fibers in the gel.

Dodecyl maltoside as a solubilizing agent of stratum corneum lipid liposomes

The lytic interactions of the nonionic surfactant dodecyl maltoside (DM) with liposomes formed by a mixture of lipids modeling the stratum corneum (SC) lipid composition were investigated. To this end, the surfactant to lipid molar ratios (Re) and the normalized bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light-scattering (SLS) of the system during solubilization. The fact that the free surfactant concentration was always similar to its critical micelle concentration indicates that the liposome solubilization was mainly ruled by formation of mixed micelles. In addition, the linear dependence established between the level of SLS and Re indicates a progressive incorporation of DM in the liposomes as well as the progressive formation of mixed micelles. DM showed in all cases lower bilayer activity (higher Re values) and greater affinity with vesicles (higher K values) than those reported for its interaction with phosphatidylcholine (PC) liposomes. Thus, whereas the SC lipid liposomes were more resistant to the action of this surfactant, its degree of partitioning into SC bilayers was higher throughout the solubilization process than that exhibited in PC vesicles. Comparison of the present Re values with those reported for the lytic interaction of dodecyl glucoside (DG) with SC liposomes reveals that in the case of DM the bilayer activity was more than three times higher than that for DG in spite of the identical alkyl chain length.

Kinetics of glycolipid phase transitions: ms laser T‐jump synchrotron studies

AbstractThe kinetics of the lamellar gel (Lβ) to inverse hexagonal (HII) phase transition as well as the LC→Lα phase change of aqueous suspensions of glycolipids were characterized using ms laser T‐jump techniques in combination with synchrotron X‐ray diffraction. The glycolipids employed were 1,2‐di‐O‐alkyl‐3‐O‐β‐D‐glucosyl‐snglycerols with identical alkyl chains of 16 and 18 carbon atoms, respectively, and 1,2‐di‐O‐alkyl‐3‐O‐β‐D‐galactosyl‐sn‐glycerol with C16 chains. The time course of the LC→Lα phase transition was probed using 1,2‐di‐O‐hexadecyl‐3‐O‐β‐D‐lactosyl‐sn‐glycerol, whose head group consists of the disaccharide β‐D‐galactopyranosyl‐(1→4)‐β‐D‐glucopyranoside. Surprisingly the phase change from the lamellar to the inverse hexagonal topology is very fast despite the major structural changes involved in the lipid‐water interface. The overall phase change of both glucolipids can be quantitatively described by a sequential mechanism of the type \documentclass{article}\pagestyle{empty}\usepackage{amsmath}\begin{document}$ {\rm L}_\beta \xrightarrow{{k_1}}{\rm I}\xrightarrow{{k_2}}{{\rm H}}_{\rm II} $\end{document}$\end{document}. The intermediate I is thinner than both the Lβ and the HII phases. It has a relatively broad distribution of d‐spacings and relaxes into the HII phase with half times of approximately 125 ms (16‐1,2‐Glc) and 244 ms (18‐1,2‐Glc), respectively. Both rate constants, k1 and k2, are chain length dependent.The galactolipid transforms into the HII phase following a sequential mechanism of the type \documentclass{article}\pagestyle{empty}\usepackage{amsmath}\begin{document}$ {{\rm L}}_\beta \xrightarrow{{k_1}}{{\rm I'}}\xrightarrow{{k_2}}{{\rm I}}\xrightarrow{{k_3}}{{\rm H}}_{\rm II} $\end{document}. The additional intermediate I' can be assigned to a lamellar phase bearing similarity to a thin Lα phase. The specific features of the galactose head group compared to glucose as head group that have been previously observed in equilibrium studies are also evident in the kinetic mechanism in that comparative structural changes in the intermediates are slower in the galactolipid than in the chain‐homologous glucolipid. There is evidence from the X‐ray data that the general transition mechanism is identical for gluco‐ and galacto‐lipids. However, the first intermediate I' disappears too fast in the glucolipid phase change to be detectable with the present time resolution of the X‐ray measurements.The kinetics of the phase change of the lactolipid is characterized within the resolution of the X‐ray sequence (5 ms) by a strict two‐state mechanism \documentclass{article}\pagestyle{empty}\usepackage{amsmath}\begin{document}$ {{\rm L}}_{{\rm C}} \xrightarrow{k}{{\rm L}}_{\alpha} $\end{document} with transient coexistence of the initial and final phase during the kinetic phase transformation. The relaxation time has been found to be highly temperature dependent, being 57 ms at 79.1 ° and 14 ms at 81.1 °.It is worth noting that there appears to be a principal difference in the phase change mechanism between glycolipids with mono‐ or disaccharide head groups in that the latter (16‐1,2‐Lac) shows no sign of any kinetic intermediate state.

Liposome formation from synthetic polyhydroxyl lipids

The preparation of liposomes from synthetic dialkyl amphiphiles is described. Two of these lipids were synthesised with mixed chains of 18:0,14:0 and 18:0,22:0 and one contained two identical alkyl chains of 18:0,18:0. Based on electron microscopic observations and encapsulation studies, liposomes formed from these lipids resemble those prepared from natural lipids. The polyhydroxyl head group of these lipids was designed to mimic the oligosaccharide rich surface of natural cells. SPLVs of all lipid compositions investigated, had higher encapsulation efficiency compared with that of MLVs. With SPLVs the encapsulation efficiency obtained with EPC liposomes were similar to those with novel lipids. However, the optimum was obtained with 4a: cholesterol. Encapsulation efficiency in both MLVs and SPLVs was higher with novel lipid containing different side chain length.