Amino Acid Surfactants Research Articles

Effect of electrolytes on the interfacial rheological behaviors of N-cocoyl glycinate

Amino acid surfactants have been applied to numerous areas of science and are often used in the presence of electrolytes. In this study, the interfacial rheological behaviors of potassium N-cocoyl glycinate (KCGl), an amino acid surfactant, with three kinds of electrolytes (KCl, CaCl2 and tetrabutylammonium bromide (TBABr)) have been investigated using the oscillating drop method. The interfacial tensions (IFTs) and dilational rheological parameters show that KCGl in conjunction with electrolytes has enhanced interfacial activity and stronger intermolecular interaction than pure KCGl, indicating that electrolytes contribute to denser molecular packing at the oil–aqueous interface. Interestingly, the butyl groups of TBA+ hinder closer arrangement of molecules at the interface, hindering KCGl ability to form a tightly packed layer compared with K+ and Ca2+ electrolytes. The relaxation processes, such as diffusion exchange of surfactant molecules between the aqueous phase and interface, are more probable to occur. Therefore, more viscoelastic films are formed in the presence of TBABr.

Contrastive Study of the Foaming Properties of N-Acyl Amino Acid Surfactants with Bovine Serum Albumin and Gelatin.

A detailed study on the foamability, foam stability, foam liquid-carrying capacity, and foam morphology of two N-acyl amino acid surfactants with bovine serum albumin (BSA) and gelatin were performed by foam scanning. The results showed that the foamability of the mixed system increased gradually and then tended to be stable with increasing surfactant concentration. The foamability of the high-concentration BSA system was stronger than that of the low-concentration BSA system. The foamability and foam stability of sodium N-lauroyl phenylpropanoic acid (N-C12P)/BSA were better than those of sodium N-lauroyl propylamino acid (N-C12A)/BSA, and the foamability and foam stability of N-C12A/gelatin was better than those of N-C12P/gelatin. The liquid-carrying capacity of the foam initially increased and then decreased with increasing time, and the maximum liquid-carrying capacity increased with increasing surfactant concentration. When the concentration of the surfactant was 8 mM, the drainage rate of N-C12A/protein was higher than that of N-C12P/protein. The morphology of the bubble gradually changed from spherical to polyhedron and the number of bubbles gradually decreased with time increasing. Differences in surfactant structure and protein type had an important effect on the number and area of foam.

Effects of fatty acyl chains on the interfacial rheological behaviors of amino acid surfactants

Amino acid surfactants derived from vegetable oils have attracted significant interest in the scientific community due to their excellent biocompatibility and low environmental impact. Because of the wide variety of vegetable oils, derived N-acyl amino acid surfactants may feature various fatty acyl groups and therefore offer diverse properties. According to the composition of commonly used vegetable oils, three main characteristics of fatty acyl structures, namely fatty acyl chain length, the number of CC bonds, and hydroxyl substituent, were summarized in this paper and a series of N-fatty acyl glycinate surfactants were synthesized. The specific effects of these three structural factors on the surface tension and interfacial rheological properties were systematically studied. In doing so, we found that an increase of fatty acyl chain length enhanced the interfacial activity and intermolecular interactions of N-fatty acyl glycinate surfactants. Thus, glycinate surfactants with longer fatty acyls could generate more compact adsorption films with a higher dilational modulus. The cis CC bonds in oleoyl and linoleoyl chains were found to bend the long hydrophobic tails, which might affect the compact arrangement of surfactant molecules and increased the viscoelasticity of interfacial films. In addition, the hydroxyl group on ricinoleoyl was found to inhibit the close packing of the hydrophobic tails and reduced intermolecular interactions. As a result, more viscoelastic films were formed by sodium N-ricinoleoylglycinate. The obtained results gained insights into the relationships between fatty acyl structural characteristics and the interfacial arrangements of N-acyl amino acid surfactants, which present a theoretical foundation for surfactant design and further application.

Unique interfacial adsorption behavior of a hydroxy group-containing amino acid surfactant

The interfacial adsorption properties of the novel hydroxy-group-containing amino-acid-type surfactant, N-alkanoyl-N-(2-hydroxyethyl)-β-alanine (Cn-EtOH-βAla, where n is the length of the alkyl chain; n = 8, 10, 12, 14, and 16; EtOH is the hydroxyethyl group; βAla is β-alanine), and the hydroxy-group-free conventional amino-acid-type surfactant, N-dodecanoyl-N-methyl-β-alanine (C12-Me-βAla), were investigated for comparison purposes in an alkaline solution. Cn-EtOH-βAla (where n = 10–14) possessed a significant minimum critical micelle concentration (CMC) in surface tension vs. concentration plots, contrary to the conventional surfactant C12-Me-βAla. The area occupied per molecule for C12-EtOH-βAla (0.316 nm2) was considerably decreased compared with C12-Me-βAla (0.683 nm2); this was attributed to hydrogen bonding between the hydroxy group and water/carboxylate ions in Cn-EtOH-βAla, which facilitated the dense adsorption and efficient orientation of the surfactant at the air/water interface. The relationship between the logarithm of the CMC and the n value of Cn-EtOH-βAla indicated that the surfactant exhibited nonionic-like behavior because the hydrogen bonding between the hydroxy groups and carboxylate ions suppressed the electrostatic repulsion between hydrophilic groups.

Analysis of Derivatized N-Acyl Amino Acid Surfactants Using HPLC and HPLC/MS

A method for the analysis of weak anionic surfactants based on N-acyl amino acids was developed. The surfactants were derivatized using 2,4′-dibromoacetophenone yielding 4′-bromophenacyl esters suitable for spectrophotometric detection. Surfactants containing glycine, threonine and glutamic acid were analyzed after derivatization using reversed-phase liquid chromatography with UV/Vis and MS detection. The gradient profile was optimized using isocratic retention data of N-acyl-linked fatty acid homologues. The relative content of the homologues of N-acyl-linked fatty acids was expressed using the determined method. The intraday repeatability and stability of the prepared derivatives was tested. The relative content of fatty acids in the surfactants was correlated with the most common sources of fatty acids, showing high Pearson’s correlation coefficients with the typical fatty acids profile of a coconut oil.

Supramolecular Hydrogels with Chiral Nanofibril Structures Formed from β-Cyclodextrin and a Rosin-Based Amino Acid Surfactant.

The rational combination of natural molecules is expected to provide new soft material building blocks. Herein, a rosin-based amino acid surfactant was synthesized using dehydroabietic acid and l-serine as the starting materials (denoted as R-6-Ser). Supramolecular hydrogels were formed when β-cyclodextrin (β-CD) was mixed with R-6-Ser at molar ratios of over 0.5:1 and above certain concentrations. The hydrogels were investigated using rheometry, small-angle X-ray scattering, CD spectroscopy, and cryo-transmission electron microscopy (cryo-TEM). The β-CD associated with the isopropyl benzyl group of the dehydroabietic acid unit in R-6-Ser and formed R-6-Ser@β-CD complexes. The complexes and R-6-Ser self-assembled to form elongated right-handed rigid fibers with a diameter of approximately 7-8 nm, which were responsible for the elasticity of the hydrogels. This work demonstrated the feasibility of preparing supramolecular hydrogels from a diterpenoid-based surfactant and β-CD and provides a new means of utilizing the secretions of pine trees.

Microstructural Characterization of Foam Formed by a Hydroxy Group-Containing Amino Acid Surfactant Using Small-Angle Neutron Scattering.

Small-angle neutron scattering, which has not been extensively utilized for foam characterization, can provide important insights into the microstructure of surfactant-stabilized foam. Small-angle neutron scattering in combination with several other techniques was herein employed to determine the microstructure of foams stabilized by hydroxy group-containing (C12-EtOH-βAla) and hydroxy group-free (C12-Me-βAla) surfactants of the amino acid type. Hydroxy group introduction at the amide nitrogen had no effect on the foam film thickness (∼26 nm in both cases) but increased the foam stability and suppressed draining, as hydrogen bonding between hydroxy groups and carboxylate ions increased the foam film strength. Moreover, the obtained foam films were shown to contain micelles identical to those in the bulk solution.

Comparative Study on the Syntheses and Properties of Three N‐lauroyl Aromatic Amino Acid Surfactants

AbstractThree N‐lauroyl aromatic amino acid surfactants, namely, sodium N‐lauroyl phenylalaninate (SLP), sodium N‐lauroyl tyrosinate, and sodium N‐lauroyl tryptophanate (SLTr), with aromatic group structures were synthesized via methyl ester method. Mass spectrometry, Fourier transform infrared spectroscopy, and nuclear magnetic resonance were applied for the structural representation of products. A comparative study of the three surfactants in terms of surface, foam, and emulsifying properties and decontamination performance was conducted. Results demonstrated that aromatic structure significantly influenced the properties of the three surfactants. SLTr had the best surface performance and foam property, whereas SLP had the best emulsifying property. All three surfactants exhibited strong decontamination effects on protein‐soiled swatches.

Synergistic Effect of Cocamidopropyl Betaine and Sodium Lauroyl Sarcosinate

In this study, we investigated the synergistic effect of a zwitterionic surfactant (cocamidopropyl betaine) and amino acid surfactant (sodium lauroyl sarcosinate) by measurements of surface tension, rheological properties, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The results confirm the formation of wormlike micelles in the mixed system, which leads to superior surface activity as compared to that of an individual surfactant. Stable and dynamic viscoelastic measurements were also performed to explore the characteristics of wormlike micelles at different mole fractions, pH values, and temperatures. The results indicate that the strongest wormlike structure formed under the conditions of X1 = 0.5, pH = 4.7, and CT = 600 mmol/L. The size and morphology of the mixed micelles were obtained by DLS and TEM. The results of this work offer insight into the interaction between zwitterionic and amino acid surfactants, which will contribute to the design of complex surfactants.

Interfacial rheological behavior of N-acyl amino acid surfactants derived from vegetable oils

Surfactants based on natural building blocks instead of traditional petroleum chemicals have attracted increasing attention in recent years. N-acyl amino acid surfactants derived from vegetable oils and amino acids are popular because of their excellent interfacial properties, biodegradability and low toxicity. Due to the variety of vegetable oils, it is significant to understand the effect of the composition and fatty acids structure of the vegetable oils on the interfacial properties of the synthesized amino acid surfactants. In the study presented herein, two N-acyl amino acid surfactants (Cas-Gly-Na and Cot-Gly-Na) were synthesized using glycine and different vegetable oils, i.e. castor oil and cottonseed oil. The interfacial dilational rheological behavior of the resulting surfactants were investigated. The long hydrophobic tails of Cot-Gly-Na enhanced the intermolecular van der Waals interactions, while the hydroxyl group present on the ricinoleate acyl moiety of Cas-Gly-Na inhibited the interactions between the hydrophobic tails. Thus, Cot-Gly-Na exhibited a higher interfacial activity and could generate stronger adsorption films. Moreover, the hydroxyl group on the hydrophobic tails of Cas-Gly-Na may have caused a molecular reorientation during adsorption at the interface. The obtained results demonstrated that the fatty acyls of amino acid surfactants introduced from different vegetable oils exhibited a significant influence on the interfacial properties.

Liquid chromatography of short chain carboxylic acids using a glutamic acid surfactant coated C18 stationary phase

A C18 column was modified with the anionic amino acid surfactant lauroyl-l-glutamate (LLG) to facilitate the separation of ten short-chain aliphatic carboxylic acids (oxalic, tartaric, malic, malonic, lactic, acetic, maleic, citric, fumaric, and succinic). The developed method was proven to be fast, versatile, and environmentally friendly. After the coating of the column using 1% LLG solution and optimizing chromatographic conditions such as pH and temperature, near baseline resolution of the ten carboxylic acids within 4 min with excellent peak shape at pH = 1.8 using 100% H2O acidified with sulfuric acid was possible. Although the design of this stationary phase, with the hydrophilic group at the end of the alkyl chain, seems to be in contrast to such columns designed for a totally aqueous mobile phase that have a polar (often amide) group embedded near the silica surface, no evidence of phase collapse was noted. Linear relationships of ln retention factor (k) versus 1/Temperature (T) (van't Hoff plots) were generated for all the acids indicating a single retention mechanism was likely. As the pH of the mobile phase decreased, the analyte retention factors increased due to the increase of the fraction of the analyte with neutral charge (alpha zero). The surfactant amide linkage, being electron donating, increased the pKa of the more acidic carboxyl group of glutamic acid so both carboxyl groups were protonated (neutral) at pH 1.8. The exact nature of the retention mechanism is uncertain but there certainly seems to be a pronounced hydrophobic component due to the large difference in retention of fumaric acid and methyl fumarate at pH 1.8. In addition, eleven beverage samples were analyzed for their aliphatic carboxylic acid contents. The results showed that malic, fumaric, and citric acids were the most common carboxylic acids in natural beverages with concentrations as high as 6432 ppm of malic acid in organic apple juice, 64 ppm of fumaric acid in organic concord juice, and 6543 ppm citric acid in strawberry lemonade juice.

Amino Acid Surfactants with Hydroxy Group

Amino Acid Surfactants with Hydroxy Group

Effect of Added Tetraalkylammonium Counterions on the Dilational Rheological Behaviors of N-Cocoyl Glycinate.

Ion specific effect, which is also known as Hofmeister effect, has been reported in numerous systems including ionic surfactant aggregates. Acyl amino acid surfactants have attracted growing attentions in the field of novel surfactants research due to their environmentally benign characteristics. The objective of this study was to investigate the effect of different salts containing NH4+ and tetraalkylammonium (TAA+), where alkyl = methyl (TMA+), ethyl (TEA+), and propyl (TPA+), cations on the dilational rheological properties of interfacial film are stabilized by potassium N-cocoyl glycinate (KCGl). The interfacial behaviors were studied using oscillating drop shape analysis method. The interfacial tensions (IFTs) and dilational rheological parameters results illustrate that KCGl in the presence of salts has better interfacial activity and stronger intermolecular interaction, indicating that added cations contribute to denser molecular packing at oil-water interface. Ion specific effects were observed in the system. Among the cations, KCGl shows highest dilational modulus in the presence of NH4+. The overall interaction between cations and headgroups of KCGl decreases in the sequence NH4+ >TMA+ >TEA+ ≈TPA+, which follows Hofmeister series. The increasing hydrophobicity of TAA+ prevents the interaction between cations and KCGl's headgroup, and therefore prevent amphiphiles from packing closely at interface. The results present a theoretical origin for useful application of KCGl in cosmetics, petroleum and daily chemical industries.

Coacervation in Cationic Polyelectrolyte Solutions with Anionic Amino Acid Surfactants.

Coacervates formed by cationic polyelectrolytes and anionic surfactants are utilized to improve the user's tactile perception of shampooing hair during washing and after drying. In this study, we investigated the formation and structure of coacervates in aqueous systems containing anionic amino acid surfactants. The phase behaviors at constant temperature were investigated in aqueous systems combining cationic polyelectrolyte JR-400 with potassium cocoyl glutamate (CoGluK) or potassium cocoyl glycinate (CoGlyK) for a qualitative depiction of coacervate formation. The composition range of coacervate formation varied with the hydrophilic group of the surfactant. The surface tension was measured at different surfactant concentrations and constant polyelectrolyte concentration. The surface tension behavior revealed the critical association concentrations and critical micelle concentrations, indicating that coacervate was produced via complex formation through electrostatic interaction between opposite charges. Optical microscopy and small-angle X-ray scattering measurements revealed that the coacervates were composed of fibrous aggregates, a few microns thick, and those formed in the CoGlyK system had thicker fibers.

A comparative study on the interface tension and interface dilational rheological properties of three sodium N-acyl aromatic amino acid surfactants.

Interface dilational rheology is useful for understanding and exploring the role of interface phenomena. However, relatively few studies have been conducted on the interface dilational rheological properties of N-acyl aromatic amino acid surfactants. Herein, surface tension and the dynamic interface tension and dilational rheological properties of three surfactants, namely, sodium N-lauroyl phenylalaninate (SLP), sodium N-lauroyl tyrosinate (SLTy), and sodium N-lauroyl citrate (SLTr) were investigated. The results show that the order of critical micelle concentration, which includes the surface tension at the critical micelle concentration, minimum area per surfactant molecule, and interfacial tension, was SLTr < SLTy < SLP. At a low surfactant concentration, the three surfactants exhibited a low-viscosity interfacial elastic film at the n-decane/water interface. The dilational modulus increased and the phase angle decreased with increase in frequency. However, the order of the dilational modulus was SLP < SLTy < SLTr, while the order of the phase angle change was SLTr < SLTy < SLP at the same frequency. With increase in surfactant concentration, the dilational modulus of SLP and SLTy increased and then decreased after a maximum value; however, the dilational modulus plot of SLTr demonstrated two maxima.

Effect of SiO2 nanoparticles on the performance of L-Arg and L-Cys surfactants for enhanced oil recovery in carbonate porous media

Surfactant flooding as conventional chemical enhanced oil recovery (cEOR) was widely used to improve oil from the matured-producible reservoirs. Currently, nanoparticles (NPs) earned the vast attraction in EOR applications due to their sizes and physiochemical properties that possibly influence the viscosity, attraction, and IFT specifications of the fluid system. This work studied the effect of silica NPs on the performance of two synthesized amino-acid surfactants (lauroyl-arginine (L-Arg) and lauroyl-cysteine (L-Cys)) for improving oil recovery by considering the IFT reduction and wettability alteration. The conductivity, pH and turbidity measurements were considered to discover their critical micelle concentration (CMC). While, the visual observation and zeta potential were applied to analyze the dispersion stability of nanoparticles (NPs) within the surfactant solutions. The obtained results expressed that the high stability of SiO2 NPs achieved at 1000 ppm concentration when dispersed in surfactant solutions, and 2000 and 4500 ppm concentrations of L-Arg and L-Cys nano-surfactants are determined as CMC values, respectively. By adding SiO2 into surfactants, high reductions of 58% and 66% are obtained in the values of IFT and contact angle, respectively. Therefore, higher improvement in oil recovery was achieved by nano-surfactant flooding compared with the surfactant flooding, which are 13.1% and 11.9% OOIP, respectively.

Green Synthesis, Characterization, and Properties of Acyl Lysine, Serine, Threonine, and Methionine Derived from Three Types of Natural Oils

AbstractThe development of environmentally benign products has been the subject of growing interest in the field of surfactant chemistry. Acyl amino acid surfactants bearing lysine, serine, threonine, and methionine residues were synthesized using natural oils extracted from coconut, palm kernel, and soybean as acyl donors. The chemical structures were confirmed by high‐performance liquid chromatography (HPLC/MS) and infrared (IR) spectra. Their surface activities, ion‐specific effects, detergency, and foam properties were studied systematically. The critical micelle concentration (CMC) values depend significantly on amino acid and oil types and follow the orders: (i) Lys &gt; Thr ≈ Ser &gt; Met and (ii) Coconut ≈ Palm kernel &gt; Soybean oil. Interestingly, the ion‐specific effects showing that the γCMC value decreases with increasing counterion size and hydrophobicity were observed, and the results were consistent with the famous Hofmeister series. The detergency ability of acyl amino acid surfactants is better than multiple traditional surfactants in distilled water. Although the detergency ability of our products for oil‐soiled swatches decreased significantly in hard water, this problem was solved by the C‐Lys‐Na/AES mixed system showing excellent synergistic effects. Excellent foamability and foam stability were achieved for acyl threonine and serine bearing hydroxyl groups on their headgroups, suggesting that the packing of these surfactants at the air–water interface was assisted by hydrogen bonding.

How Promoting and Breaking Intersurfactant H-Bonds Impact Foam Stability.

On the basis of previous results revealing that intersurfactant H-bonds improve foam stability, we now focus on how foams stabilized by two different N-acyl amino acid surfactants are affected by different salts (NaF, NaCl, NaSCN), which can promote or break intersurfactant H-bonds. The chosen surfactants, namely, sodium N-lauroyl sarcosinate (C12SarcNa) and sodium N-lauroyl glycinate (C12GlyNa), differ only by one methyl group at the nitrogen of the amide bond that blocks intersurfactant H-bonds in the case of C12SarcNa. The salts were chosen because they are kosmotropic (NaF), chaotropic (NaSCN), and in between (NaCl) and thus influence the formation of an H-bond network in different ways. Surface tension measurements showed that the addition of salts decreased the cmcs of both surfactants and increased the packing density, as expected. Moreover, in presence of the salts, the head groups of the H-bond forming surfactant C12GlyNa were more tightly packed at the surface than the C12SarcNa head groups. The effect of the salts on foam stability was studied by analysis of the foam height, the foam liquid fraction, and by image analysis of the foam structure. As expected, the salts had no significant effect on foams stabilized by C12SarcNa, which is unable to form intersurfactant H-bonds. In contrast, the stability of C12GlyNa-containing foams followed the trend NaF > NaCl > NaSCN, which is in agreement with NaF promoting and NaSCN breaking intersurfactant H-bonds. Surface rheology measurements allowed us to correlate foam stability with surface elasticity. This study provides new insights into the importance of H-bond promoters and breakers, which should be used in the future design of tailor-made surfactants.

Application of Oxidative Fatty Acid Esters in Amino Acid Surfactants

Abstract The amino acid surfactants were synthesized by using natural fatty acid esters (FAE) as raw materials, but FAE with a high iodine value has thermal and oxidative instabilities in chemical reactions. The oxidation of FAE by peroxyacetic acid generated was studied under various conditions, then the oxidized FAE and different amino acids (glycine, glutamic acid and aspartic acid) were used to form sodium N-acyl amino acids in glycerol. By the surface tension method, the relationship between temperature and critical micelle concentration (CMC) has been researched. The CMC value, the surface tension at the CMC (γCMC), and the maximum surface excess concentration Γmax were calculated, respectively. For different amino acids surfactants, the surface tension of the solution was greatly reduced at the low CMC value, and the γCMC constantly decreases with rising temperature.

Amino-Acid Surfactants in Personal Cleansing (Review)

Abstract The consumer demand for greener, sustainable and skin friendly chemicals is driving the use of amino-acid based surfactants in the personal care area. Acyl glutamates and glycinates are already being used in commercial products. Available literature clearly shows that the amino acid based surfactants are generally milder than their corresponding alkyl sulfates and carboxylates. However, they do offer some interesting challenges in the area of structuring and consumer desired lather properties. Furthermore, the amino acid surfactants, unlike alkyl sulfates, have pH as an interesting variable for fine-tuning their functional properties. In this paper, the solution, interfacial and skin mildness properties of commercially relevant amino acid surfactants are reviewed and the opportunities and challenges for their wider application are outlined.