Synthesis and Surface Properties of N-Alkyl-N-methylgluconamides and N-Alkyl-N-methyllactobionamides

Machine learning hybrid approach for the prediction of surface tension profiles of hydrocarbon surfactants in aqueous solution

HYPOTHESIS

Predicting the surface tension (SFT)-log(c) profiles of hydrocarbon surfactants in aqueous solution is computationally non-trivial, and empirically challenging due to the diverse and complex architecture and interactions of surfactant molecules. Machine learning (ML), combining a data-based and knowledge-based approach, can provide a powerful means to relate molecular descriptors to SFT profiles.

EXPERIMENTS

A dataset of SFT for 154 model hydrocarbon surfactants at 20-30 °C is fitted to the Szyszkowski equation to extract three characteristic parameters (Γ_max,K_L and critical micelle concentration (CMC)) which are correlated to a series of 2D and 3D molecular descriptors. Key (∼10) descriptors were selected by removing co-correlation, and employing a gradient-boosted regressor model to rank feature importance and carry out recursive feature elimination (RFE). The hyperparameters of each target-variable model were fine-tuned using a randomised cross-validated grid search, to improve predictive ability and reduce overfitting.

FINDINGS

The ML models correlate favourably with test experimental data, with R²= 0.69-0.87, and the merits and limitations of the approach are discussed based on 'unseen' hydrocarbon surfactants. The incorporation of a knowledge-based framework provides an appropriate smoothing of the experimental data which simplifies the data-driven approach and enhances its generality. Open-source codes and a brief tutorial are provided.

Synthesis and Aggregation of Novel Sugar-based Gemini Surfactants in Aqueous Solution

Novel sugar-based gemini surfactants with a 1,3-propan-2-ol spacer (1, 3-(N- alkyl-2-D-glucosaminyl acetyl) propan-2-ol, Glu(n)-3(OH)-Glu(n), n = 12, 14) were synthesized with D-(+)-glucono-1,5-lactone as starting material in two steps, whose structures were confirmed using proton nuclear magnetic resonance spectroscopy (1H NMR) and carbon nuclear magnetic resonance carbon spectroscopy (13C NMR). The micellization of Glu(n)-3(OH)-Glu(n) (n = 12, 14) in aqueous solution at 25.0°C was investigated by using surface tension measurement. The results show that the critical micelle concentration (CMC) of Glu(12)-3(OH)-Glu(12) is around 10–5 mol × L–1, and is one order of magnitude smaller than that of Glu(14)-3(OH)-Glu(14), indicating that the surface activity of Glu(12)-3(OH)-Glu(12) is superior to that of Glu(14)-3(OH)-Glu(14). Moreover, the aggregation behavior of Glu(12)-3(OH)-Glu(12) in aqueous solution at different pH values was investigated by surface tension, dynamic light scattering (DLS), and cryogenic transmission electron microscopic (Cryo-TEM) measurements. The results indicate that the CMC slightly increases with the decrease of the solution pH. The microstructure of Glu(12)-3(OH)-Glu(12) aggregates transitions from micelle to vesicle with the solution pH from acidic to neutral and alkaline. The microstructural transformation of Glu(12)-3(OH)-Glu(12) with the solution pH is mainly determined by the protonation of the two tertiary amine nitrogen atoms in its hydrophilic headgroups.

Formulation of Environmentally Safe Graffiti Remover Containing Esterified Plant Oils and Sugar Surfactant

The removal of graffiti or over-painting requires special attention in order to not induce the surface destruction but to also address all of the important eco-compatibility concerns. Because of the necessity to avoid the use of volatile and toxic petroleum-based solvents that are common in cleaning formulations, much attention has recently been paid to the design of a variety of sustainable formulations that are based on biodegradable raw materials. In the present contribution we propose a new approach to graffiti cleaning formulations that are composed of newly synthesized green solvents such as esterified plant oils, i.e., rapeseed oil (RO), sunflower oil (SO), or used cooking oil (UCO), ethyl lactate (EL), and alkylpolyglucosides (APGs) as surfactants. Oil PEG-8 ester solvents were synthesized through the direct esterification/transesterification of these oils using monobutyltin(IV) tris(2-ethylhexanoate) and titanium(IV) butoxide catalysts under mild process conditions. The most efficient formulations, determined by optimization through the response surface methodology (RSM) was more effective in comparison to the reference solvents such as the so-called Nitro solvent (denoting a mixture of toluene and acetone) and petroleum ether. Additionally, the optimal product was found to be effective in removing graffiti from glass, metal, or sandstone surfaces under open-field conditions in the city of Wrocław. The performed studies could be an invaluable tool for developing future green formulations for graffiti removal.

A Review on Recent Progress of Glycan-Based Surfactant Micelles as Nanoreactor Systems for Chemical Synthesis Applications

The nanoreactor concept and its application as a modality to carry out chemical reactions in confined and compartmentalized structures continues to receive increasing attention. Micelle-based nanoreactors derived from various classes of surfactant demonstrate outstanding potential for chemical synthesis. Polysaccharide (glycan-based) surfactants are an emerging class of biodegradable, non-toxic, and sustainable alternatives over conventional surfactant systems. The unique structure of glycan-based surfactants and their micellar structures provide a nanoenvironment that differs from that of the bulk solution, and supported by chemical reactions with uniquely different reaction rates and mechanisms. In this review, the aggregation of glycan-based surfactants to afford micelles and their utility for the synthesis of selected classes of reactions by the nanoreactor technique is discussed. Glycan-based surfactants are ecofriendly and promising surfactants over conventional synthetic analogues. This contribution aims to highlight recent developments in the field of glycan-based surfactants that are relevant to nanoreactors, along with future opportunities for research. In turn, coverage of research for glycan-based surfactants in nanoreactor assemblies with tailored volume and functionality is anticipated to motivate advanced research for the synthesis of diverse chemical species.

Impact of the chemical structure on amphiphilic properties of sugar-based surfactants: A literature overview

In this review, structure-property trends are systematically analyzed for four amphiphilic properties of sugar-based surfactants: critical micelle concentration (CMC), its associated surface tension (γ_CMC), efficiency (pC₂₀) and Krafft temperature (T_K). First, the impact on amphiphilic properties of the alkyl chain size and the presence of branching and/or unsaturation is investigated. Then, various polar head parameters are explored, such as the degree of polymerization of the sugar unit (mono- or oligosaccharides), the chemical nature of the linker and the sugar configuration. Some systematic comparisons between ethoxylated surfactants and sugar-based surfactants are also carried out. While some structural trends with the impact of alkyl chain length or the polar head size are now well understood, this analysis points out that systematic studies of more specific effects of alkyl chain (e.g. branching, unsaturation, presence of rings, position on the polar head) and polar head (e.g. linker, anomeric configuration, internal stereochemistry, cyclic vs. acyclic sugar residues) were scarcer or not available to date. This work encourages the use of these structural trends in the perspective of developing new bio-based surfactants and their consideration in predictive models. It also highlights the need of further experimental tests to fill remaining gaps notably to explore some specific structural features (such as the introduction of rings in the alkyl chain or the position of the alkyl chain on the polar head) and towards applicative properties (like foaming capacity or wettability).

Hemolysis by surfactants--A review

An overview of the use of surfactants for erythrocyte lysis and their cell membrane action mechanisms is given. Erythrocyte membrane characteristics and its association with the cell cytoskeleton are presented in order to complete understanding of the erythrocyte membrane distortion. Cell homeostasis disturbances caused by surfactants might induce changes starting from shape modification to cell lysis. Two main mechanisms are hypothesized in literature which are osmotic lysis and lysis by solubilization even if the boundary between them is not clearly defined. Another specific mechanism based on the formation of membrane pores is suggested in the particular case of saponins. The lytic potency of a surfactant is related to its affinity for the membrane and the modification of the lipid membrane curvature. This is to be related to the surfactant shape defined by its hydrophobic and hydrophilic moieties but also by experimental conditions. As a consequence, prediction of the hemolytic potency of a given surfactant is challenging. Several studies are focused on the relation between surfactant erythrolytic potency and their physico-chemical parameters such as the critical micellar concentration (CMC), the hydrophile-lipophile balance (HLB), the surfactant membrane/water partition coefficient (K) or the packing parameter (P). The CMC is one of the most important factors considered even if a lytic activity cut-off effect points out that the only consideration of CMC not enough predictive. The relation K.CMC must be considered in addition to the CMC to predict the surfactant lytic capacity within the same family of non ionic surfactant. Those surfactant structure/lytic activity studies demonstrate the requirement to take into account a combination of physico-chemical parameters to understand and foresee surfactant lytic potency.

Mean-field coarse-grained model for poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer systems

The microscopic modeling of surfactant systems is of the utmost importance in understanding the mechanisms related to the micellization process because it allows for prediction and comparison with experimental data of diverse equilibrium system properties. In this work, we present a coarse-grained model for Pluronics, a trademarked type of triblock copolymer, from simulations based on a single-chain mean-field theory (SCMF). This microscopic model is used to quantify the micellization process of these nonionic surfactants at 37 °C and has been shown to be able to quantitatively reproduce experimental data of the critical micelle concentration (CMC) along with other equilibrium properties. In particular, these results correctly capture the experimental behavior with respect to the lengths of the hydrophobic and hydrophilic moieties of the surfactants for low and medium hydrophobicities. However, for the more highly hydrophobic systems with low CMCs, a deviation is found which has been previously attributed to nonequilibrium effects in the experimental data (Garcı́a Daza, F. A.; Mackie, A. D. Low Critical Micelle Concentration Discrepancy between Theory and Experiment. J. Phys. Chem. Lett. 2014, 5, 2027-2032).

Synthesis and Characterization of N-alkyl-N′-glucosylhexanediamine Surfactant

The synthesis and structural analysis of glucosamide surfactants of the general formula CnH2n+1NH(CH2)6NHCO(CHOH)4CH2OH (n = 8, 10, 12) were described, and the surface activity properties of the surfactants were studied, and the interfacial tensions between n-octane and the aqueous surfactant solution were measured. N-alkylhexanediamines were synthesized by the alkylation of the 1,6-hexanediamine with alkyl bromide. The glucosamide surfactants, N-alkyl-N′-glucosylhexanediamine (C n GA), were prepared by amidation of the precursor diamine with D-gluconic acid δ-lactone. They were structurally characterized by IR, 1H NMR and MS. They reduced the surface tension of water to approximately 28–33 mN · m−1 at concentration levels of (0.2–1.0) × 10−3 mol · L−1, and reduced the interfacial tensions between n-octane and the aqueous surfactant solution to approximately 1–2 mN · m−1 at concentration levels of (0.3–4.2) × 10−3 mol · L−1.

Low Critical Micelle Concentration Discrepancy between Theory and Experiment

Experimental measurements for a variety of surfactants unexpectedly show that the critical micelle concentration (CMC) becomes constant with respect to increasing the size of the hydrophobic tail. This observation disagrees with theoretical models where it is expected to continue to decrease exponentially. Because of the lack of a satisfactory explanation for such a discrepancy from theory, we have studied these systems using a coarse-grained model within the single-chain mean field (SCMF) theory combined with relevant micellar kinetic effects. In particular, a microscopic model for poly(ethylene oxide) alkyl ether was applied to describe a series of nonionic gemini surfactants. When kinetic effects are used to correct the equilibrium CMC values from the SCMF scheme together with the loss of surfactants due to adsorption on the experimental recipient, it is possible to reproduce the correct order of magnitude of the experimental CMC results. Hence it appears that the experimental values disagree with the theoretical predictions because they are not true equilibrium values due to the fact that the time scales for these low CMC values become astronomically large.

Structure-Activity Relationships for Sorption of Alkyl Trimethyl Ammonium Compounds on Activated Sludge

Association of quaternary ammonium based surfactants with activated sludge from wastewater treatment plants has been studied. Adsorption isotherms on activated sludge particles and surface properties of a series of alkyl trimethyl ammonium compounds have been investigated. The effect of alkyl chain length and the water hardness in those physical-chemical properties have been evaluated. Adsorption on sludge increased with increasing the alkyl chain length in the cationic surfactant molecule. Linear relationships between critical micelle concentration (-log CMC) and efficiency of adsorption at the liquid/gas interface (pC20), and the number of carbon atoms in the alkyl chain length were found for the alkyl trimethyl ammonium compounds. Water hardness decreased the CMC values of the tested alkyl trimethyl ammonium homologues and the extent of their sorption to activated sludge. Langmuir and Freundlich adsorption isotherms described satisfactorily the equilibrium adsorption of the cationic surfactants on activated sludge.

Tensiometric determination of Gibbs surface excess and micelle point: a critical revisit

Amphiphile adsorption at the air/water interface lowers the surface tension (γ) of the solution. After a critical surfactant concentration (C), γ becomes constant (with a break in the γ-logC plot), which is considered the critical micelle concentration (CMC). At very low amphiphile concentration, γ decreases slowly, forming a plateau, then decreases sharply and often nonlinearly by a co-operative adsorption process till the second plateau is reached at CMC. To get the Gibbs surface excess (Γ) of the amphiphile relative to water, a polynomial equation of appropriate degree needs to be used, since the drop in γ progresses with continuous changing slope, which maximizes at CMC and becomes zero afterward. Recent research has evidenced that a complete saturated Gibbs monolayer may not always form at CMC; there may be formation of multilayer of micelles below the Gibbs monolayer, which cannot be assessed by ST measurements. A method like neutron reflectometry (NR) can evaluate the Γ beyond CMC. A procedure for determining Γ(max) from tensiometric results is herein proposed. Amphiphiles do sometimes show a linear decline in γ with logC followed by a break with a plateau at CMC. There, a single slope leading to a single surface excess quantity is obtained for the Gibbs equation at all concentrations up to CMC. Possible reasons for such results are given. Current conflicting ideas and criticisms on the issue of Gibbs equation and determination of Γ and Γ(max) have been addressed.

Carbohydrate-modified siloxane surfactants and their adsorption and aggregation behavior in aqueous solution

Four carbohydrate-modified siloxane surfactants, Si(n)N-GA and Si(n)N-LA (n = 3, 4), were designed and synthesized. Their surface activities, adsorption, and aggregation behavior in aqueous solution were investigated by surface tension measurements, dynamic light scattering (DLS) and transmission electron microscopy (TEM). Due to the bulky siloxane moiety at the end of hydrophobic chains, the surfactant solutions displayed low critical aggregation concentration (cac) and low surface tension. Surface tension measurement for all three surfactants are under 22 mN x m(-1), much lower than those of ordinary hydrocarbon surfactants. Due to its poor solubility in water, surface tension of Si(4)N-GA could not be measured. DLS and TEM analysis of Si(3)N-GA, Si(3)N-LA, and Si(4)N-LA aqueous solutions revealed self-assembled spherical vesicles, indicating potential applications as microsphere drug delivery systems and as models of biomembranes.

Re-evaluating the Gibbs analysis of surface tension at the air/water interface

Molecular areas of soluble films at the air/water interface have traditionally been calculated by applying the Gibbs equation to the steep linear decline in surface tension as the bulk concentration increases. This approach presupposes that the interface is saturated in the "Gibbs region," thereby allowing a single unique area to be calculated. We show that the areas derived by the Gibbs equation (typically 50-60 A(2)/molecule) are much too large to account for the abrupt surface tension decline. Moreover, a surface tension/concentration plot was observed for a system where micelle formation does not interfere with the Gibbs region. Nonetheless, the surface tension plot leveled off, ostensibly owing to saturation, when the Gibbs approach predicted a continued linear decline, proving that the interface in the Gibbs region is not saturated as generally assumed. This conclusion means that the hundreds of published molecular areas obtained by the Gibbs approach should be reconsidered.

Adsorption and aggregation properties of heterogemini surfactants containing a quaternary ammonium salt and a sugar moiety

A novel heterogemini surfactant comprising two hydrocarbon chains and two different hydrophilic groups such as a quaternary ammonium cation and gluconamide nonion N,N-dimethyl-N-[2-(N'-alkyl-N'-gluconamide)ethyl]-1-alkylammonium bromides (2CnAmGlu, where n represents hydrocarbon chain lengths of 8, 10, 12, and 14) was synthesized by reacting N,N-dimethylethylenediamine with alkyl bromide, followed by a reaction with 1,5-D(+)-gluconolactone. The adsorption properties of 2CnAmGlu were characterized by surface tension measurements made using the Wilhelmy plate method, and their aggregation properties were investigated by dynamic light scattering and cryogenic transmission electron microscopy techniques. The relationship between the hydrocarbon chain length and the logarithm of the critical micelle concentration (cmc) for 2CnAmGlu exhibited a linear decrease when the chain length was increased up to 12 and then a departure from linearity at n=14. The surface tension reached 24-26 mN m-1 at each cmc, indicating high efficiency in lowering the surface tension of water. Furthermore, it was found that the structure of the aggregate formed for 2CnAmGlu in solution was influenced by the hydrocarbon chain length; that is, for n=10 and 12, micelles with a hydrodynamic radius of 2-5 nm were formed, whereas vesicles were also observed for n=14.

Sugar-based gemini surfactants with peptide bonds-synthesis, adsorption, micellization, and biodegradability

The sugar-based gemini surfactant with peptide bonds, N,N'-bisalkyl-N,N'-bis[2-(lactobionylamide)ethyl]hexanediamide (2C(n)peLac, in which n represents hydrocarbon chain lengths of 12 and 16), was synthesized by reacting adipoyl chloride with the corresponding monomeric surfactant N-alkyl-N'-lactobionylethylenediamine (C(n)peLac), which was obtained by reacting ethylenediamine with alkyl bromide and lactobionic acid. The adsorption and micellization properties of C(n)peLac and 2C(n)peLac were characterized by the measurement of their equilibrium and dynamic surface tension, steady-state fluorescence using pyrene as a probe, dynamic light scattering (DLS), and time-resolved fluorescence quenching (TRFQ), and their biodegradability was also investigated. The critical micelle concentration (cmc) decreases with an increase in the hydrocarbon chains from monomeric to gemini surfactants, whereas it increases with an increase in the chain length from 12 to 16 for both systems. The increases in both the hydrocarbon chain and the chain length of sugar-based surfactants reduce surface activities such as the ability to lower the surface tension, the occupied area per molecule, and the adsorption rate at the air/water interface. The sugar-based surfactants C(n)peLac and 2C(n)peLac exhibit unique aggregation behavior in aqueous solution. The DLS results indicate that the apparent hydrodynamic diameter of C(n)peLac micelles decreases sharply with increasing concentration, whereas that of 2C(n)peLac micelles decreases gradually. From the TRFQ measurement, it was observed that, as concentration increases, the aggregation numbers are almost constant for C(n)peLac, whereas they increase for 2C(n)peLac. These results imply that loosely packed micelles formed by sugar-based surfactants become tightly packed micelles as the concentration increases. Furthermore, it was found that 2C(n)peLac shows lower biodegradability than does C(n)peLac because it contains tertiary amines in the molecule.

Nucleic Acid Complexing Glycosyl Nucleoside-Based Amphiphile

A neutral amphiphile derived from uridine featuring two oleyl chains and one glucose for DNA binding was prepared using a convenient four-step synthetic route. The nucleic acid binding capabilities of this amphiphile were investigated by UV-vis, quasi-elastic light scattering (QELS), transmission electronic microscopy (TEM), gel electrophoresis, 31P NMR, IR, and circular dichroism (CD). Amphiphile-nucleic acid complex formation is a consequence of the amphiphilic character of the molecule, phosphate-sugar, and nucleobase-nucleobase interactions. This work presents for the first time a glyco-nucleo-amphiphile capable of binding efficiently the nucleic acid double helix structure.

Adsorption behavior of surface chemically pure N-cycloalkylaldonamides at the air/water interface

Equilibrium surface tension (sigma(e)) and electric surface potential (DeltaV(e)) versus concentration isotherms of the homologous series of N-cycloalkylaldonamides synthesized from cycloalkylamines (from cyclopentyl- to cyclododecylamine) and D-glucono-1,5-lactone (c-C(n)GA) or D-glucoheptono-1,4-lactone (c-C(n)GHA) (c-n(C) = 5-12) were investigated at the air/water interface. The measurements were performed with aqueous, surface chemically pure surfactant solutions. Equilibrium surface tension vs concentration isotherms were evaluated to get the adsorption parameters, i.e., standard free energy of adsorption, DeltaG degrees (ads), saturation surface concentration, Gamma(infinity), minimum surface area demand per molecule adsorbed, A(min), and interaction parameter, H(s). Increasing the size of the cycloalkyl moiety leads to a significant increase of the minimum surface area demand per molecule adsorbed. This fact, together with a decrease of the intermolecular interaction parameter suggests that the introduction of a more bulky cycloalkyl ring (c-n(C) = 7 and 8) causes an attenuation of the hydrogen-bond network. This goes in line with the exceptional finding that the higher homologues revealed improved solubility in water. In addition, surface tension investigations suggest occurrence of a phase transition for the N-cyclooctylaldonamides at relatively small surface coverage. This observation is well supported by the surface potential measurements, for which the effect of possible changes in the molecules' surface orientation is even more pronounced. Moreover, the concentration intervals of N-cyclooctylaldonamide in which the change in orientation is observed for either the surface tension or the surface potential isotherms are in very good agreement.