Octyl Tail Research Articles

Photoresponsive arylazopyrazole surfactant/PDADMAC mixtures: reversible control of bulk and interfacial properties.

In many applications of polyelectrolyte/surfactant (P/S) mixtures, it is difficult to fine-tune them after mixing the components without changing the sample composition, e.g. pH or the ionic strength. Here we report on a new approach where we use photoswitchable surfactants to enable drastic changes in both the bulk and interfacial properties. Poly(diallyldimethylammonium chloride) (PDADMAC) mixtures with three alkyl-arylazopyrazole butyl sulfonates (CnAAP) with -H, -butyl and -octyl tails are applied and E/Z photoisomerization of the surfactants is used to cause substantially different hydrophobic interactions between the surfactants and PDADMAC. These remotely controlled changes affect significantly the P/S binding and allows for tuning both the bulk and interfacial properties of PDADMAC/CnAAP mixtures through light irradiation. For that, we have fixed the surfactant concentrations at values where they exhibit pronounced surface tension changes upon E/Z photoisomerization with 365 nm UV light (Z) and 520 nm green (E) light and have varied the PDADMAC concentration. The electrophoretic mobility can be largely tuned by photoisomerisation of CnAAP surfactants and P/S aggregates, which can even exhibit a charge reversal from negative to positive values or vice versa. In addition, low colloidal stability at equimolar concentrations of PDADMAC with CnAAP surfactants in the E configuration lead to the formation of large aggregates in the bulk which can be broken up by irradiation with UV light when the surfactant's alkyl chain is short enough (C0AAP). Vibrational sum-frequency generation (SFG) spectroscopy reveals changes at the interface similar to the bulk, where the charging state at air-water interfaces can be modified with light irradiation. Using SFG spectroscopy, we interrogated the O-H stretching modes of interfacial H2O and provide qualitative information on surface charging that is complemented by neutron reflectometry, from which we resolved the surface excesses of PDADMAC and CnAAP at the air-water interface, independently.

Effect of side chain modifications in imidazolium ionic liquids on the properties of the electrical double layer at a molybdenum disulfide electrode.

Knowledge of how the molecular structures of ionic liquids (ILs) affect their properties at electrified interfaces is key to the rational design of ILs for electric applications. Polarizable molecular dynamics simulations were performed to investigate the structural, electrical, and dynamic properties of electric double layers (EDLs) formed by imidazolium dicyanamide ([ImX1][DCA]) at the interface with the molybdenum disulfide electrode. The effect of side chain of imidazolium on the properties of EDLs was analyzed by using 1-ethyl-3-methylimidazolium ([Im21]), 1-octyl-3-methylimidazolium ([Im81]), 1-benzyl-3-methylimidazolium ([ImB1]), and 1-(2-hydroxyethyl)-3-methylimidazolium ([ImO1]) as cations. Using [Im21] as reference, we find that the introduction of octyl or benzyl groups significantly alters the interfacial structures near the cathode because of the reorientation of cations. For [Im81], the positive charge on the cathode induces pronounced polar and non-polar domain separation. In contrast, the hydroxyl group has a minor effect on the interfacial structures. [ImB1] is shown to deliver slightly larger capacitance than other ILs even though it has larger molecular volume than [Im21]. This is attributed to the limiting factor for capacitance being the strong association between counter-ions, instead of the free space available to ions at the interface. For [Im81], the charging mechanism is mainly the exchange between anions and octyl tails, while for the other ILs, the mechanism is mainly the exchange of counter-ions. Analysis on the charging process shows that the charging speed does not correlate strongly with macroscopic bulk dynamics like viscosity. Instead, it is dominated by local displacement and reorientation of ions.

One-pot formation of sugar-immobilized monodisperse polymethylmethacrylate particles by soap-free emulsion polymerization

Soap-free emulsion polymerization was applied to fabricate monodisperse submicron-sized polymethylmetacrylate (PMMA) particles with β-D-glucopyranoside (glucose) groups immobilized on the surface. The immobilization was induced not by the direct surface chemical modification but rather by the coexistence of octyl-β-D-glucopyranoside dissolved in the starting water solvent. The presence of the immobilized glucose components on the particle surface was proven by the specific affinity for concanavalin A (ConA). Due to the hydrophobic nature of the PMMA matrix, the relatively hydrophilic glucose components tend to be oriented toward the outer aqueous phase, giving rise to the markedly increased adsorption of ConA, where the nonpolar octyl tail acts as the anchor to the relatively hydrophobic polymeric matrix.

Dynamics of cytochrome c in surface active ionic liquid: A study of preferential interactions towards denaturation

Surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium octyl sulfate ([C4mim][C8OSO3]) having octyl tail on anionic moiety have been very less investigated with proteins. Herein, we present a study of the structural change of horse heart cytochrome c (h-cyt c) in aqueous solutions of SAIL ([C4mim][C8OSO3]) by optical spectroscopy and molecular docking methods. Time-resolved fluorescence, UV–vis and circular dichroism (CD) spectra indicated that the addition of up to 25 mM of [C4mim][C8OSO3] induces structural changes of h-cyt c resulting from disruption of tertiary structure and after 25 mM of [C4mim][C8OSO3], h-cyt c denatures completely and loses its tertiary structure. Thermodynamic parameters for denaturation of h-cyt c by [C4mim][C8OSO3] were also obtained having ΔG°D and m-value of the unfolded state. The values were found to be lower when compared to the reported for urea denatured h-cyt c. The midpoint concentration of unfolding of h-cyt c by [C4mim][C8OSO3] was found ~25 mM. The results showed that the presence of alkyl chain on the anionic moiety destabilizes the protein. The docking results confirm the preferential interactions of ions of SAIL to residues of h-cyt c and suggest the dominant role of anion [C8OSO3]− by the electrostatic interaction that drives local destabilization of the h-cyt c.

Solvent Isotopic Effects on a Surfactant Headgroup at the Air–Liquid Interface

The geometry, arrangement, and orientation of a quaternary ammonium surfactant flanked by two methyl groups, a benzyl head, and an octyl tail were assessed at the air–water and air-deuterium oxide (D2O) interfaces using sum frequency generation vibrational spectroscopy. Remarkably, symmetric and asymmetric N–CH3 stretches (at ∼2979 and ∼3045 cm–1, respectively, in the SSP polarization combination) were visible in water but negligible in deuterium oxide. We concluded that D2O addition triggers the average reorientation of the dimethyl amino units parallel to the interface and possibly changes the overall conformation of the surfactant. A reduced number of gauche defects in the surfactant octyl chain is also observed in D2O. Tilt angles for the octyl chain (1.0–10.8°) are consistent with an ordered monolayer at the air–liquid interface.

Structures of Ionic Liquids Having Both Anionic and Cationic Octyl Tails: Lamellar Vacuum Interface vs Sponge-Like Bulk Order.

Numerous experimental and computational studies have shown that the structure of ionic liquids is significantly influenced by confinement and by interactions with interfaces. The nature of the interface can affect the immediate ordering of cations and anions, changing important rheological characteristics relevant to lubrication. Most studies suggest that such changes are local or short-ranged and that bulk properties are reestablished on a length scale of a few nanometers. The current study focuses on the 1-methyl-3-octylimidazolium octylsulfate ionic liquid for which both the cation and anion have moderate length linear alkyl tails. For this system, we find that the bulk phase is dominated by the very common sponge-like morphology characteristic of many ionic liquids. However, at the vacuum interface, a lamellar structure is observed that is not restricted to the vicinity of the surface but instead extends across the full 9 nm slab of our simulation. We suspect that in reality it could extend significantly beyond this.

Preparation of novel cross-linked and octylated caseinates using a biphasic enzymatic procedure and their functional properties.

A novel microbial transglutaminase-catalyzed aqueous-organic biphasic reaction system was successfully developed to prepare caseinate derivatives by cross-linking and incorporating nonpolar octyl tails for the first time. SDS-PAGE and (1)H NMR analysis confirmed that cross-linking and octyl conjugation occurred simultaneously. The octyl substitution degree (SD) was measured by (1)H NMR and used as an index to determine a suitable reaction condition. It was found that at the condition of 0.125% (w/v) protein concentration and 6 h of reaction time, the modified caseinate had the highest SD of 28.96%. The modified caseinate also had an increased surface hydrophobicity, better emulsifying activity, and improved thermal and salt stabilities. However, its emulsion stability or in vitro enzymatic digestibility was slightly lower than that of the native caseinate.

Linker Effects on Amino Acid and Peptide Recognition by Molecular Tweezers (Eur. J. Org. Chem. 34/2013)

The cover picture shows the crystal structure of an unsymmetrically substituted molecular tweezer derivative for peptide and protein surface recognition. The phosphate group is necessary for lysine binding, the octyl tail is intended to explore nonpolar patches on the protein surface. In front of the open tweezers two Lys-Val dipeptides are waiting for their chance to enter the cavity. Details are discussed in the article by F.-G. Klärner, T. Schrader et al. on p. 7705 ff.

Orientational Ordering of Ionic Liquids near a Charged Mica Surface

The self-assembly of ions in room-temperature ionic liquids adsorbed on a mica surface is studied using molecular dynamics simulations. Four liquids from the 1-methyl,n-alkylimidazolium bis(trifluoromethylsulfonyl)imide ([C(n)mim][NTf(2)]) family are investigated, where n ranges between 2 and 8. Cations with ethyl or butyl groups are found to orient with the hydrocarbon tails lying parallel to the surface, while the hexyl and octyl tails of cations are observed to be oriented perpendicular to it. The crossover in the orientational preference matches recent observations of surface forces of these liquids.

Cyclic Nucleotide-Gated Channel Block by Hydrolysis-Resistant Tetracaine Derivatives

To meet a pressing need for better cyclic nucleotide-gated (CNG) channel antagonists, we have increased the biological stability of tetracaine-based blockers by synthesizing amide and thioamide linkage substitutions of tetracaine (1) and a higher affinity octyl tail derivative (5). We report the apparent K(D) values, the mechanism of block, and the in vitro hydrolysis rates for these compounds. The ester linkage substitutions did not adversely affect CNG channel block; unexpectedly, thioamide substitution in 1 (compound 8) improved block significantly. Furthermore, the ester linkage substitutions did not appear to affect the mechanism of block in terms of the strong state preference for closed channels. All ester substituted compounds, especially the thioamide substitutions, were more resistant to hydrolysis by serum cholinesterase than their ester counterparts. These findings have implications for dissecting the physiological roles of CNG channels, treating certain forms of retinal degeneration, and possibly the current clinical uses of compound 1.

Formation of Linear Supramolecular Polymers That Is Driven by CH⋅⋅⋅π Interactions in Solution and in the Solid State

Copillararene convoy: A linear supramolecular polymer can be efficiently constructed in solution with a copillararene monomer (see picture). Single-crystal X-ray analysis and NMR spectroscopy revealed that aggregation was enthalpically driven by quadruple CH⋅⋅⋅π interactions between the octyl tail (blue) and the aromatic cavity (red). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Spectral insights into gelation microdynamics of N-octyl-D-gluconamide in water

Near infrared spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and perturbation correlation moving window (PCMW) technique is employed to illustrate the gelation microdynamic mechanism of hydrogelator N-octyl-D-gluconamide (8-GA), which can rapidly self-agglomerate into helical bilayer micellar fibers upon cooling from spherical micelles. Boltzmann fitting and PCMW easily determined the gelation temperature to be ca. 72 °C and the transition temperature range to be 70–75 °C. Moreover, band shifting and splitting phenomena can be observed for CH-related overtones, indicating the formation of much ordered and tight hydrophobic core from octyl tails. On the other hand, 2Dcos was used to discern the sequential orders during the gelation process and concluded that all the group motions have a continuous transfer from the octyl tail to the chiral carbohydrate head followed by the final immobilization of the solvent, which meanwhile, is actually a continuous dehydration process from the hydrophobic core to the outer hydrophilic chiral head. The driving force of the gelation process in microdynamics can only be the dehydration process of hydrophobic octyl chains, but with final helical superstructures being stabilized by amide-associated hydrogen bonding and the “chiral bilayer effect” of carbohydrate heads.

Impact of configuration and fluorination on the solubility of octyl ester benzoate dimers in CO 2

Data are reported on the phase behavior of hydrocarbon and semifluoroinated octyl ester benzoate dimers in CO 2 to temperatures of 100 °C and pressures of 1 600 bar. The experimental data at 75 °C demonstrate that the non-fluorinated head-to-head (H–H) dimer dissolves in CO 2 at ∼400 bar lower pressures than the non-fluorinated tail-to-tail (T–T) dimer. Even though partially fluorinating the octyl tails of the H–H and T–T dimers renders them soluble in CO 2 at pressures near 200 bar, it still takes ∼40 bar more pressure to dissolve the fluorinated T–T dimer as compared to the H–H dimer. The difference in pressures needed to dissolve these dimers is attributed to steric constraints on the coplanarity of the benzene rings imposed by the H–H regiochemistry that do not exist with T–T dimers. Semi-empirical quantum mechanics calculations suggest that the H–H dimer has a twisted, non-coplanar conformation due to the steric effect of the octyl ester groups while the T–T dimer has a less twisted conformation. Steric hindrance in the H–H dimer reduces considerably resonance or conjugation between the π electrons of the aromatic groups which also reduces the dipole moments of the H–H dimers compared to those of the T–T dimers.

Structure of the nonionic surfactant triethoxy monooctylether C8E3 adsorbed at the free water surface, as seen from surface tension measurements and Monte Carlo simulations

The adsorption layer of the nonionic surfactant triethoxy monooctylether C8E3 has been investigated at the free water surface by means of both experimental and computer simulation methods. The surface tension of the aqueous solution of C8E3 has been measured by pendant drop shape analysis in the entire concentration range in which C8E3 is soluble in water. The data obtained from these measurements are used to derive the adsorption isotherm. The critical micellar concentration and the surface excess concentration of the saturated adsorption layer are found to be 7.48 mM and 4.03 micromol/m2, respectively, the latter value corresponding to the average area per molecule of 41 A2. In order to analyze the molecular level structure of the unsaturated adsorption layer, Monte Carlo simulations have been performed at four different surface concentration values, i.e., 0.68, 1.36, 2.04, and 2.72 micromol/m2, respectively. It has been found that the water surface is already almost fully covered at the lowest surface density value investigated, and the adsorbed molecules show a strong preference for lying parallel with the interface in elongated conformations. No sign of the penetration of the hydrophilic triethoxy headgroups into the aqueous phase to any extent has been observed. With increasing surface densities the preferential orientation of the apolar octyl tails gradually turns from lying parallel with the interface to pointing toward the vapor phase by their CH3 end, whereas the conformation of the adsorbed molecules becomes gradually less elongated. Both of these changes lead to the increase of the number of C8E3 molecules being in a direct contact (i.e., forming hydrogen bonds) with water. However, the increasing number of the C8E3 molecules hydrogen bonded to water is found to be accompanied by the weakening of this binding, i.e., the decrease of both the number of hydrogen bonds a bound C8E3 molecule forms with water and the magnitude of the average binding energy of the adsorbed C8E3 molecules.

Hydrogen‐bonded polyurethane complexes based on 4‐alkoxybenzoic acids as the low molar mass components

AbstractSupramolecular polyurethane complexes based on a polyurethane with a pendant pyridyl unit (PUPy) as the hydrogen bond acceptor and 4‐octyloxybenzoic acid (OOBA) or 4‐butyloxybenzoic acid (BOBA) as the hydrogen bond donor were prepared. The primary driving force for the formation of these complexes is the hydrogen bonding between the pyridyl polyurethane group and the carboxylic acid group, while the urethane group only contributes to the binding of acid molecules to a minor extent. Phase separation in the BOBA/PUPy and OOBA/PUPy systems occurred at low molar ratios: BOBA and OOBA formed amorphous polyurethane complexes at a molar ratio of 0.2, while the OOBA/PUPy complex exhibited a glassy smectic mesophase at a molar ratio of 0.4. In comparison to the previously studied complexes of PUPy and 4‐dodecyloxybenzoic acid (DOBA), where side‐chain ordering prevailed, OOBA/PUPy complexes showed a high tendency of the main‐chain crystallization at molar ratios of 0.4 or higher. This is due to weak overall van der Waals interactions between the short octyl tails and effective intra‐ and/or intermolecular hydrogen bonding between the urethane and pyridyl groups of the polymer backbone. Copyright © 2004 Society of Chemical Industry

Structure and Kinetics of Oxidation of Amphiphilic Nickel(II) Pentaazamacrocycles by Peroxodisulfate and by a Nickel(III) Pendant-Arm Macrocycle

Three nickel(II) pentaazamacrocycles bearing pendant alkyl tails have been synthesized,and the crystal structure of one (bearing an octyl tail) is reported. The redox potentials of the complexes, for oxidation of the nickel(II) centre, is 0.72 V (versus S.H.E.) in all cases, indicating that the pendant alkyl tails have no effect on the redox site. The kinetics of oxidation of the complexes by peroxodisulfate, S2O8 2- and by aqua(5, 5, 7,12, 12, 14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato)nickel(III),[Ni(hmca)(OH2)]2+ have been studied. Oxidation by S2O8 2- occursby ion-pairing of the reactants, followed by electron transfer with concomitant peroxo bond fissure. Oxidation by [Ni(hmca)(OH2)]2+ occurs by an outer sphere electron transfer process. Redox kinetics at the nickel centre provides a probe for supramolecular interactions at the pendant tails in such complexes.

Rodlike mesogenic molecules consisting of two diacetylenic groups: mesomorphic behavior and photoimaging

A series of mesogenic compounds with two diacetylenic groups were synthesized. The diacetylene groups were connected to a benzene ring via ester linkages, becoming a part of a rigid rod. The thermal behavior of the compounds and their polymerization were investigated. Compounds 7, 8, 9 and 10 having long alkyl tails showed nematic mesophases. They were thermally polymerized in the isotropic state above 200 °C. Partial polymerization occurred by annealing in the liquid crystalline state. When the compounds were exposed to UV light in the liquid crystalline state, the polymerization was completed within 30 min to give amorphous polydiacetylenes. In the UV-Vis spectra, absorption of the polymers occurred up to about 600 nm, attributable to the short conjugated polydiacetylene backbones. Compound 9 with an octyl tail was fabricated into a thin film and the photopolymerization was carried out through a photomask in the liquid crystalline state resulting in a patterned image.

Characterization of hexadecanoic acid perdeuterated from carbon eight to carbon sixteen: a novel conformational probe for amphipathic systems

The molecule (9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16)-heptadecadeuterio hexadecanoic acid has been characterized as a useful tool for conformational studies of lipid chains in membranes. Calorimetric and mass spectrometry tests successfully established the sample to be of high purity 99.6 ± 0.2% and to be deuterated as specified above. Detailed Raman spectra of the sample were analyzed in all regions of interest between 50 cm −1 and 3100 cm −1. The optical skeletal bands arising from the perdeuterated octyl tail are uncoupled from the bands proceeding from the head portion of the molecule. Likewise, the very strong symmetric and antisymmetric CD 2 stretching bands fall in the region of 2000–2200 cm −1 where no other bands are present. Bands associated in the CH 2 twisting, CH 2 bending and CH 2 stretching have also been identified. The relevance of this study to conformational analyses in lipids is discussed.