Laurate Anions Research Articles

Thermodynamics and micellization behavior of ethanolammonium carboxylate surface active ionic liquids in aqueous media

A systematic experimental study of the micellization of ethanolammonium carboxylate surface active ionic liquids (SAILs) in aqueous solutions was performed. The effect of two separate anions having different alkyl chain length, laurate and palmitate on the micellization behavior was studied. The effect of different cationic head groups, n-butyl, tertiary butyl as well as phenyl group on the micellization parameters was also investigated. The critical micelle concentration (cmc) values and the surface active parameters were evaluated from tensiometric methods. The values of cmc are observed to be lower for palmitate anion SAILs in comparison to the laurate anions. The values of surface tension reduction (πcmc) and surface excess (Γmax) show considerable variation as the anion chain length and the cationic head groups changed. The thermodynamics of the micellization parameters, standard Gibbs free energy of micellization (∆Gm°), enthalpy of micellization (∆Hm°) and entropy of micellization (∆Sm°) were evaluated by conductometric measurements. Using pyrene as a probe molecule, the cmc values were evaluated by steady state fluorescence. The values of critical micelle concentration obtained from three different methods for all the studied SAILs are found to be in good match with each other. The order of cmc for the synthesized SAILs were as follows: [NPEA][PAL] < [TBEA][PAL] < [NBEA][PAL] < [NPEA][LAU] < [TBEA][LAU] < [NBEA][LAU].

Enhanced Corrosion Resistance of Superhydrophobic Layered Double Hydroxide Films with Long-Term Stability on Al Substrate.

A superhydrophobic ZnAl-layered double hydroxide (LDH)-La film was prepared by a hydrothermal method and further modification by laurate anions in this work. Comprehensive characterizations of this film were performed in terms of morphology, composition, structure, roughness, and wettability by scanning electronic microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, three-dimensional laser scanning confocal microscopy. The long-term corrosion protection effect of this superhydrophobic film was investigated deeply by monitoring the changes of the electrochemical impedance spectra for a long time of up to a month in 3.5 wt % NaCl solution. In the meantime, the changes of the contact angle were also recorded with the evolution of the immersion time. The result indicated that the stable superhydrophobic ZnAl-LDH-La film was able to provide efficient protection for the underlying Al substrate for a long time. In addition, the capability of the superhydrophobic surface against harsh conditions, including chemical damages and physical damages, was emphatically investigated. It was found that the superhydrophobic surface was chemically stable toward acid (pH ≥ 3), alkali, and heating, and it also exhibited high ultraviolet (UV) radiation resistance. This superhydrophobic coating maintained superhydrophobicity for 7 days of radiation in an UV chamber equipped with a 40 W UV lamp (λ = 254 nm), indicating superior ability of adapting to outdoor environment. This comprehensive investigation of the superhydrophobic ZnAl-LDH-La film is considerably helpful for researchers and engineers to get deep insight into its potential for practical applications in the field of corrosion and protection.

Influence of the Anion on the Oxidation of 5-Hydroxymethylfurfural by Using Ionic-Polymer-Supported Platinum Nanoparticle Catalysts.

Platinum nanoparticles stabilized by an imidazolium-based cross-linked polymer (with chloride as the counteranion) efficiently catalyzed the oxidation of 5-hydroxymethylfurfural to form 2,5-furandicarboxylic acid in water under mild conditions with oxygen as the oxidant. This catalyst system is explored herein by varying the counteranion, that is, replacing chloride by BF4 - , PF6 - , bis(trifluoromethylsulfonyl)imide, hexanoate, or laurate anions, in the cationic polymer. The counteranion influences the structure of the obtained platinum nanoparticles, the surface electronic properties, and their catalytic activity. The highest reaction rates were obtained with the weakly nucleophilic bis(trifluoromethylsulfonyl)imide anion, which also favored platinum in the zero oxidation state, leading to complete conversion of the substrate and a high yield of 2,5-furandicarboxylic acid under mild conditions.

Computational Modeling of Lauric Acid at the Organic–Water Interface

Where water meets an immiscible liquid, the orientation and hydrogen bonding patterns of the molecules nearest the interface differ significantly from those in the bulk. These differences drive important interface-specific phenomena, including interfacial tension and the adsorption of other molecular species. Additionally, surfactants and other amphiphilic molecules present at the interface interact with both the aqueous and hydrophobic layers in a complex fashion that can dramatically change the characteristics of the interface as a whole. In this study, classical molecular dynamics computer simulations have been employed to investigate the accommodation of lauric acid at the water–hexane and water–carbon tetrachloride interfaces. Our results show that the behavior of surfactant molecules in the interfacial region is strongly influenced by the protonation of their headgroups. Deprotonated lauric acid molecules cause a larger increase in interfacial width than their protonated counterparts. The carboxylate headgroups of laurate anions in the interfacial region consistently point toward the water layer, while the orientation of the protonated lauric acid headgroups changes with depth into the water layer.

SIMULTANEOUS ESTERIFICATION AND TRANSESTERIFICATION OF ACID OILS USING LAYERED ZINC CARBOXYLATES AS BIFUNCTIONAL CATALYSTS

Palm oil containing 40% fatty acids was converted to methyl esters using zinc carboxylates as the esterification/transesterification catalyst. The reaction was optimized using a factorial design in which the effects of the alcohol:fatty acids molar ratio (MRAG) and the catalyst concentration (CAT) were assessed. The best conversion was achieved with CAT at 4 wt% and MRAG at 4:1. However, the solid catalyst presented significant structural changes after use. For instance, laurate anions were replaced by carboxylates of higher molecular mass, leading to the formation of a new catalytically active layered structure. Also, the glycerin obtained as a co-product contained 86 wt% glycerol.

Oriented CuZnAl Ternary Layered Double Hydroxide Films: In situ Hydrothermal Growth and Anticorrosion Properties

Oriented dense thin films of CuZnAl–NO3 layered double hydroxide (CuZnAl–NO3 LDH) have been grown on the surface of copper foil by an in situ hydrothermal method with Cu substrate as Cu source, boehmite sol as Al source, and Zn(NO3)2 aqueous solution as Zn source. The structure and morphology of the as-prepared CuZnAl–NO3 LDH films were studied by X-ray diffraction, elemental analysis, room temperature Fourier transform infrared spectra, and scanning electron microscopy analysis. The results showed that the [00l] direction (or ab plane) of CuZnAl–NO3 LDH platelets was parallel to the surface of the Cu substrate. By a facial immersion method, intercalation of laurate anions by ion exchange with the CuZnAl–NO3 LDH film precursors endowed hydrophobic properties on Cu substrate. Moreover, the corrosion behavior of the hydrophobic laurate intercalated LDH films was then investigated by detecting the contact angle, potentiodynamic polarization, and electrochemical impedance properties, which showed that the cor...

Synthesis and characterization of laurate-intercalated Mg–Al layered double hydroxide prepared by coprecipitation

Effective utilization of layered double hydroxides (LDH) for industrial applications requires the synthesis of pure and well-defined LDH phases. In the present study, dodecanoate (laurate) anions were intercalated into Mg–Al-layered double hydroxide (LDH-C12) by coprecipitation in the presence of an aqueous ethanolic laurate solution at a constant pH of 9 and room temperature. The effect of varying the Mg:Al molar ratio (2:1 or 3:1), the Al:laurate molar ratio, and ethanol concentration (0, 30 or 40% v/v ) was investigated. A pure LDH-C12 phase was obtained using a Mg:Al molar ratio of 2:1, a Al:laurate molar ratio of 1:1 and 30% v/v ethanol, and a post-synthesis hydrothermal treatment at 75°C for 12h. An additional impurity phase formed in syntheses having a Mg:Al molar ratio at 3:1 and/or in the presence of excess laurate anions. This phase has previously been misinterpreted as a particular LDH-C12 intercalated structure, but we here demonstrate it to be magnesium laurate (Mg-C12). The LDH-C12 compound showed high structural order with a basal spacing of 2.41nm. Fourier-transform IR-spectra confirmed the intercalation of the laurate anions in the interlayer. Transmission electron microscopy showed plate-like, irregularly shaped crystals with lateral dimensions in the range of 100–200nm and plate thickness smaller than 40nm. Scanning electron microscopy revealed nonporous aggregates of LDH-C12.

Static SIMS studies of fatty alcohols, amines and esters on gold and aluminium–magnesium alloy surfaces

AbstractStatic secondary ion mass spectrometry was used to study the chemical reactions and lateral distributions of fatty amines, alcohols and esters spin coated onto gold surfaces and commercial aluminium–magnesium (Al–Mg) alloy surfaces, cleaned using UV–ozone. The aim of this study is to develop an understanding of the interactions of model lubricants with metal surfaces, such as gold and aluminium. This static SIMS study of organic thin films has been able to identify specific reaction products on the aluminium surface for each functional group. This work demonstrates that organic molecules with alcohol, ester and amine functional groups undergo specific chemical reactions with oxidized Al–Mg alloy surfaces. For example, films composed of the fatty alcohol dodecanol were observed to emit monomers, dimers and trimers with discrete distributions. In addition, negative secondary ion mass spectra indicate that a surface carboxylate is formed from the alcohol. The formation of carboxylate reaction products was confirmed by Fourier transform infrared spectroscopy. On Al–Mg alloy surfaces, a direct interaction with the amine and aluminium oxide surface is observed by the detection of a molecular ion that corresponds to the mass of dodecylamine and AlO−, characteristic of aluminium oxide. Ethyl laurate was shown to eliminate the ethyl group, leaving the laurate anion. This study demonstrates the ability of time‐of‐flight (ToF) SIMS to discriminate and detect chemical reaction products formed between model lubricant molecules and metal surfaces. As a result of this study, the use of ToF‐SIMS to identify reaction products of model lubricants can be extended to provide a better understanding of the interactions of lubricants and metal surfaces at high temperatures and pressures that more closely resemble the conditions encountered in industrial rolling processes. Copyright © 2005 John Wiley &amp; Sons, Ltd.

X-ray investigation of compounds crystallized in aqueous solution of tetrabutylammonium laurate. The structure of (C4H9)4N(C11H23COO)·3C11H23COOH·4H2O

The crystal structure of two compounds, 1 and 2, crystallizing from tetrabutylammonium laurate solutions was studied by single crystal XRD method (T = 150 K). The structure of compound 1 is tetragonal, space group P42/m. The water lattice belongs to a known type of polyhedral water structures, tetragonal structure I (TS-I). The composition of 1 was determined as (2 + 3x)[(C4H9)4N(OH)]·(2 − 2x)[(C4H9)4N(C11H23COO)]·167H2O (x = 0–1). The stoichiometry of compound 2 is (C4H9)4N(C11H23COO)·3C11H23COOH·4H2O; the structure is triclinic, space group $$P\bar 1$$ , with unit cell dimensions a = 7.924(2) A, b = 9.665(3) A, c = 47.21(2) A, α = 89.88(2)°, β = 87.50(2)°, γ = 83.96(2)°, Z = 2. The crystal structure of 2 can be described as packing of tetrabutylammonium cations and hydrogen bonded ribbons comprising laurate anions and the molecules of lauric acid and water. Both compounds are the products of hydrolysis of tetrabutylammonium laurate in aqueous solution.

Physicochemical characterization of a novel surfactant peptide containing an arginine cation and laurate anion

A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized. The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45°C). Cmc is also determined in the presence of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45°C). The standard free energy change (ΔG m 0 ) and standard enthalpy change (ΔH m 0 ) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS m 0 ). The peptide aggregate seems to undergo phase transition above 50°C as observed from UV-vis and fluorescence spectroscopy. From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34°C to 8.77 at 50°C and further decreases with increase in temperature indicating a phase change at 50°C. Also, the ratio of excimer intensity to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a change at 50°C indicating a phase change.

Effects of ionic strength and pH on the binding of medium-chain fatty acids to human serum albumin.

Binding equilibria for the interactions of the medium-chain fatty acid anions, laurate and myristate, with defatted human serum albumin have been investigated under varying environmental conditions such as ionic strength and pH. Since these ligands bind strongly to albumin (Kass approximately 10(7) M-1), conventional equilibrium dialysis is not a feasible method for these investigations. Consequently, we employed a dialysis method, allowing determination of very low concentrations of unbound ligand by measuring the rate of exchange of labelled ligand across a dialysis membrane under conditions of chemical equilibrium. Over a range of ionic strength, 8-68 mM, the binding of the first few molecules of laurate to albumin was weakened with increasing ionic strength, whereas the binding of subsequent molecules seemed to proceed independently of ionic strength. The binding of myristate by albumin, however, appeared to be independent of ionic strength in the observed range of concentrations. The influence of pH in the range 5.1-9.0 on the binding of the two fatty acid anions by albumin was more complicated. The first molecule of laurate appeared to bind with a slightly weaker affinity to albumin at low pH, compared to pH 7 and high pH, while the trends for the following molecules varied. The binding of myristate (irrespective of concentration) seemed to strengthen monotonously with pH, but this conclusion depends critically on the interpretation of the kinetic behaviour of the myristate anion. We have previously shown [Pedersen, A. O., Honoré, B. & Brodersen, R. (1990) Eur. J. Biochem. 190, 497-502] that the strength of binding of the first few molecules of the two fatty acid anions to albumin decreases with increasing temperature, whereas binding of subsequent molecules seems to proceed independently of temperature. We explain these findings as follows. The binding of the first few (3 or 4) molecules of the C12 laurate anion is clearly driven by formation of ionic bonds between the fatty acid anion and positively charged groups, such as lysine residues, in the albumin molecule, whereas the binding of subsequent molecules of laurate seems to depend more on hydrophobic interactions. In the case of the C14 myristate anion, the binding of the first few (only 1 or 2) molecules may depend on ionic forces, but binding of the following molecules of myristate seems to depend on hydrophobic interactions only.(ABSTRACT TRUNCATED AT 250 WORDS)

Human Skin Permeability Enhancement by Lauric Acid under Equilibrium Aqueous Conditions

An in vitro method was developed to investigate the enhancement of hydrocortisone transport across human stratum corneum (SC) by a model enhancer, lauric acid, in aqueous solutions under equilibrium conditions with respect to the enhancer. In contrast to classical (i.e., nonequilibrium) loading techniques, in which the enhancer is applied only to the donor side of SC either in pure form or in an organic solvent while enhancer‐free aqueous buffers are placed in the receptor phase, this method allowed the investigation of pH effects, concentration effects, and reversibility of both enhancer uptake and enhancement of drug transport under thermodynamically well‐defined conditions. The SC–buffer partition coefficients for lauric acid were linear with concentration and sigmoidal with pH, suggesting that both the neutral species and laurate anion partition into SC. Comparisons of partition coefficients in delipidized and untreated SC as a function of pH indicated that the uptake of lauric acid in neutral form is governed primarily by the lipid domain, whereas the protein domain accounts for anion uptake. The effects of lauric acid on skin permeability were >80% reversible upon extraction of the enhancer from the membrane. However, the degree of enhancement of hydrocortisone permeability was nonlinearly dependent on the equilibrium concentration of lauric acid in either the aqueous buffer or the membrane, exhibiting thresholds in the appearance of enhancement with concentration. The enhancer concentration necessary to achieve isoenhancement of about 6‐fold varied from ∼1 × 10−5M at pH < pKato ∼1 × 10−2M at high pH (pH > 8) demonstrating the higher influence of the free acid species. Maximum enhancement, however, occurred at high pH, reflecting the significantly higher solution concentration of laurate anion attainable in saturated solutions at high pH.

Control of the electron transfer reactions between c-type cytochromes and lipid-modified electrodes

The electron transfer reactions between a lipid-modified pyrolytic graphite (PG) electrode and four c-type cytochromes (monoheme cytochrome c and cytochrome c553 from Desulfovibrio vulgaris Hildenborough, tetraheme cytochromes c3 from D. vulgaris Hildenborough and D. desulfuricans Norway) have been studied by cyclic and square-wave voltammetry. No signal was detected at the PG electrode simply coated with a mixed layer of phosphatidylcholine (PC) and cholesterol (CH). The peaks corresponding to the reduction—reoxidation of cytochrome c553 were restored by doping the lipid layer with laurate anions (LA). In the case of cytochrome c, a rapid electron transfer reaction has been observed at the (PCCH + LA)-modified PG electrode, accompanied by the progressive incorporation of protein molecules.By studying the effect of pH on the cv peak heights, it has been shown that the profiles for the four cytochromes depend on the protonation of the laurate anions and the protonation—deprotonation of protein species.The results support the electrostatic nature of the interactions between the cytochrome and the lipid layer but other factors (eg hydrophobic effects) are not excluded.

Electrochemistry of cytochrome c3 at a lipid-modified graphite electrode

The electron transfer reactions between a lipid-modified, pyrolytic graphite (PG) electrode and tetraheme cytochromes c 3 have been studied at different ionic strengths by cyclic and square-wave voltammetry. In 0.1 M phosphate buffer (pH 7.6), no signal was detected at the PG electrode coated with a mixed layer of phosphatidylcholine (PC) and cholesterol (CH) (containing 5 mg ml −1 PC). The signals corresponding 1to the reduction-re-oxidation of cytochrome c 3 from Desulfovibrio vulgaris Hildenborough (DvH) were restored by doping the lipid layer with laurate anions. At low ionic strengths (10 mM phosphate), using the same (PC-CH + LA)-modified PG electrode, DvH cytochrome c 3 molecules are incorporated into the lipid layer. The stability of the film has been studied after transfer into an electrolyte solution. No incorporation was observed in the case of cytochrome c 3 from Desulfovibrio desulfuricans Norway. The results support the electrostatic nature of the interactions between cytochrome c 3 and the lipid layer. This approach to the electrochemistry of cytochrome c 3 opens new ways for the study of protein | lipid interfaces.

The effect of long‐chain alcohols on the properties of sodium laurate solutions. Part II. Critical micelle concentration

AbstractThe effect of monohydric alcohols from hexanol to decanol and of the dihydric alcohols, 1,2‐decanediol and 1,10‐decanediol, on the critical micelle concentration (CMC) of sodium laurate in aqueous solution at pH 11 has been investigated at 24°C.Only up to a certain alcohol concentration was a linear relation found to apply between the CMC and the alcohol concentration. The break points in the CMC against alcohol concentration curves are attributed to complex formation between the laurate anion and the alcohol molecule. When, however, complex formation between the solutes does not occur, as is assumed to be the case for 1,10‐decanediol and sodium laurate, the CMC is found to be a linear function of the alcohol concentration up to the saturation concentration of the diol in aqueous solution, and no break point is observed in the CMC against alcohol concentration curve.

The effect of long‐chain alcohols on the properties of sodium laurate solutions: Part I. Surface tension

AbstractThe surface tensions of sodium laurate solutions containing aliphatic alcohols from hexanol up to decanol have been measured at pH 11. The occurrence of break points in the surface‐tension concentration curves for higher alcohol concentrations are explained by assuming complex formation to occur between the laurate anion and the alcohol molecule.