Aggregation behavior of gemini surfactants and their interaction with macromolecules in aqueous solution

Self-assembly and antimicrobial activity of cationic gemini surfactants containing triazole moieties

1,2,3-Triazole-based gemini bis-quaternary ammonium surfactants with varying hydrophobic chain length and ethylene or butylene spacers were synthesized and characterized. Their surface and aggregation properties were analyzed using tensiometry and conductimetry. The gemini surfactants showed significantly lower CMC values compared to their single-tail counterparts and conventional gemini surfactants described in the literature. The micellization and surface adsorption processes in water can be tailored according to the hydrophobic chain and the spacer length and were substantially improved by the presence of the heterocycle. These surfactants are active against various Gram-positive and Gram-negative bacterial stains, as well as fungi. The gemini surfactant with tetradecyl chain and ethylene spacer (Bis 14-2-14) exhibited the highest activity against all investigated microbial strains.

The effect of water in THF/water mixtures on CMC, aggregation sizes, and fluorescence quenching of a new calix[4]resorcinarene macrocycle

This study explores how water content modulates the self-assembly and fluorescence behavior of a novel calixarene, C1. C1 forms large, flattened structures in pure THF, but water addition triggers a transition to smaller, unimodal clusters. A critical micellar concentration (CMC) is identified, decreasing with increasing water content. Fluorescence quenching is observed upon water addition, attributed to nonradiative deactivation. These findings highlight water as a key regulator of C1's assembly and fluorescence, paving the way for further development of water-responsive calixarene systems.

Evaluation of the antiviral potential of gemini surfactants against influenza virus H1N1

Influenza A virus (IAV) affects human health worldwide as a high-risk disease. It can neither be easily controlled by current vaccines and nor be treated by conventional drugs. Gemini surfactants (GS) have shown several properties including antiviral activity. In this study, the antiviral capacity of some GS compounds with different levels of hydrophobicity was examined. The 50% cytotoxic (CC₅₀) and non-cytotoxic (NCTC) concentrations of the compounds were determined by MTT method. The NCTCs, the same as effective concentrations (EC₅₀s), were tested for the antiviral capacity against IAV in different combination treatments for 1 h incubation on MDCK cells. The HA and MTT assays were used to evaluate the virus titer and cell viabilities, respectively. The hemolytic activity of the compounds was also assessed using an HA inhibition assay. To evaluate the apoptotic effect of GS compounds, Annexin V-PI kit was used. The HA titers decreased between 1-6.5 logs, 1-4.5 logs, and 1-5.5 logs in simultaneous, pre- and post-penetration combination treatments, respectively. The cell viability values in all combination treatments were favorable. The HI assay indicated the hemolytic potential of GSs and their physical interaction with viral HA. The apoptosis test results highlighted anti-apoptotic capacity of the GS compounds alone and in the presence of influenza virus especially for the hydrophobic ones. Gemini surfactants were generally more efficacious in simultaneous treatment. Their antiviral potential may be attributed to their physical interaction with viral membrane or HA glycoprotein that disrupts viral particle or blocks viral entry to the cell and inhibits its propagation.

Activation and Inhibition of Isomerization of a Cationic Azobenzene Surfactant in the Large Void Space of Polyglycerol Dendron Micelles

Owing to the unique geometric structure of dendritic amphiphiles with voluminous dendrons, their micelles can harbor a large void space, which provides a new research focus and approach for micellar functionalization. In this work, we used the void space to construct a UV responsive micelle system of the mixed dendritic amphiphile (C₁₂-(G3)₂) and cationic azobenzene surfactant (C4AzoTAB). The synthesized C₁₂-(G3)₂ that possesses double third generation polyglycerol (PG) dendrons and a single alkyl chain is expected to highlight the large void space within the inside of the micelles. Thus, the aims of this work are to achieve the isomerization of C4AzoTAB in situ and to deeply understand the intermolecular interaction in the mixed micelles. The effect of the large void room with a wall decorated with the ether oxygen atoms on the isomerization of C4AzoTAB was studied by isomerization kinetics, conductivity measurements, isothermal titration calorimetry (ITC), and ¹H NMR and 2D NOESY spectroscopies. The isomerization behavior of C4AzoTAB in C₁₂-(G3)₂ micelles was presented in terms of its kinetic constant, counterionic association, interaction enthalpy, and position and orientation of C4AzoTAB. The results of NMR and conductivity show that the quaternary ammonium group of C4AzoTAB situates on the surface of the mixed micelles with C₁₂-(G3)₂ both before and after UV-irradiation, while the position of azobenzene group in C₁₂-(G3)₂ micelles depends on its conformation. The C₁₂-(G3)₂ micelles can inhibit the UV response of the trans-isomer and activate the thermal relaxation of the cis-isomer, which has a potential application in the field of light-controlled smart nanocarriers.

Physicochemical Properties of Monolayers of a Gemini Surfactant with a Minimal-Length Spacer

Fundamental physical chemical properties of monolayers formed from a new anionic gemini surfactant with a minimal-length (single-bond) spacer unit have been investigated at the air-water interface and compared with those of monolayers formed from affiliated comparator surfactants. The minimal spacer surfactant, dubbed C₁₈-0-C₁₈, exhibited strikingly different packing characteristics from an anionic gemini surfactant with a comparatively bulkier headgroup, including the formation of close-packed, crystalline films, and shared similar characteristics to simple fatty acid-based monolayers. Monolayers of C₁₈-0-C₁₈ also exhibited good stability at the air-water interface and transferred with reasonable efficiency to solid substrates, although the film integrity was compromised during the transfer. Results from this work suggest that the single-bond spacer approach might be more broadly useful for designing gemini surfactants that pack efficiently into ordered monolayers.

Fabrication of Encapsulated Gemini Surfactants

(1) Background: Encapsulation of surfactants is an innovative approach that allows not only protection of the active substance, but also its controlled and gradual release. This is primarily used to protect metallic surfaces against corrosion or to create biologically active surfaces. Gemini surfactants are known for their excellent anticorrosion, antimicrobial and surface properties; (2) Methods: In this study, we present an efficient methods of preparation of encapsulated gemini surfactants in form of alginate and gelatin capsules; (3) Results: The analysis of infrared spectra and images of the scanning electron microscope confirm the effectiveness of encapsulation; (4) Conclusions: Gemini surfactants in encapsulated form are promising candidates for corrosion inhibitors and antimicrobials with the possibility of protecting the active substance against environmental factors and the possibility of controlled outflow.

Ability to Inhibit H+ Transmission of Gemini Surfactants with Different Chain Lengths under Different Ca2+ Circumstances

To study the ability to inhibit ion transmission of the Gemini surfactant under different Ca²⁺ circumstances, three kinds of Gemini surfactants with different alkyl chain lengths are synthesized (Cn-4-Cn, n = 12, 14, and 16), which are characterized using ¹H NMR, ¹³C NMR, and Fourier transform infrared spectroscopy. To analyze the property of inhibition of the acid-rock reaction rate, surface tension and contact angle measurements and atomic force microscopy (AFM) results are obtained with different surfactants and under different Ca²⁺ concentrations. Inhibition rates with different alkyl chain lengths and an acid-etched surface morphology are also studied carefully. The result shows that all cationic Gemini surfactants significantly impact the control of the reaction rate, and the reaction rate decreased remarkably by 44.4% after adding 12-4-12. The ΔG and W_A indicate that 12-4-12 has the best adsorption ability on the rock with added Ca²⁺ compared with the other two Gemini surfactants. It is revealed through the AFM that Ca²⁺ can significantly change the adsorption morphology of the surfactant. The surfactant adsorption area decreased when Ca²⁺ is dispersed in the solution as well. These two phenomena can lead to the reduced ability to block H⁺ of 14-4-14 and 16-4-16. However, the presence of Ca²⁺ affects the adsorption area of 12-4-12 slightly. Thus, the reaction rate, including that of 12-4-12, is almost unchanged. Because 12-4-12 is adsorbed tightly on the rock surface, H⁺ can only react with the rock on the unabsorbed dot, resulting in rock surface nonuniformity after being etched, which is beneficial for maintaining the conductivity of the crack.

Study of interactions of the cationic 12–2–12 Gemini surfactant with saccharides in aqueous solution: volumetric, compressibility and viscometric analysis

In the present study, the interaction behaviour of 12–2–12 Gemini surfactant in aqueous saccharide solutions (lactose and maltodextrin solutions) is investigated using density, sound velocity and viscosity measurements. The density and sound velocity data were used to determine the volume and compressibility parameters. The effects of temperature and concentration/strength of the solutions on the interaction behaviour were analysed by conductivity studies over a wide temperature (293.15–313.15) K and concentration range of the saccharides as well as of the surfactant. It was found that predominantly hydrophobic interactions together with ionic/hydrophilic interactions between 12–2–12 Gemini surfactant and the saccharides maltodextrin and lactose play a role. In addition, the structural changes in the 12–2–12 Gemini solutions induced by lactose and maltodextrin were investigated by viscosity measurements. The results confirm the observations from the volume and compressibility studies. The study of the different hydrophobic/hydrophilic interactions in the Gemini surfactant-sacharide-water mixtures are very helpful to understand the structural behaviour of Gemini surfactants in the view of their biological significance.

CNSL, a Promising Building Blocks for Sustainable Molecular Design of Surfactants: A Critical Review

Surfactants are crystallizing a certain focus for consumer interest, and their market is still expected to grow by 4 to 5% each year. Most of the time these surfactants are of petroleum origin and are not often biodegradable. Cashew Nut Shell Liquid (CNSL) is a promising non-edible renewable resource, directly extracted from the shell of the cashew nut. The interesting structure of CNSL and its components (cardanol, anacardic acid and cardol) lead to the synthesis of biobased surfactants. Indeed, non-ionic, anionic, cationic and zwitterionic surfactants based on CNSL have been reported in the literature. Even now, CNSL is absent or barely mentioned in specialized review or chapters talking about synthetic biobased surfactants. Thus, this review focuses on CNSL as a building block for the synthesis of surfactants. In the first part, it describes and criticizes the synthesis of molecules and in the second part, it compares the efficiency and the properties (CMC, surface tension, kraft temperature, biodegradability) of the obtained products with each other and with commercial ones.

Cationic gemini surfactant properties, its potential as a promising bioapplication candidate, and strategies for improving its biocompatibility: A review

Gemini surfactants consist of two cationic monomers of a surfactant linked together with a spacer. The specific structure of a cationic gemini surfactant is the reason for both its high surface activity and its ability to decrease the surface tension of water. The high surface activity and unique structure of gemini surfactants result in outstanding properties, including antibacterial and antifungal activity, anticorrosion properties, unique aggregation behaviour, the ability to form various structures reversibly in response to environmental conditions, and interactions with biomacromolecules such as DNA and proteins. These properties can be tailored by selecting the optimal structure of a gemini surfactant in terms of the nature and length of its alkyl substituents, spacer, and head group. Additionally, regarding their properties, comparison with their monomeric counterparts demonstrates that gemini surfactants have higher performance efficacy at lower concentrations. Hence, less material is needed, and the toxicity is lower. However, there are some limitations regarding their biocompatibility that have led researchers to develop amino acid-based and sugar-based gemini surfactants. Owing to their remarkable properties, cationic gemini surfactants are promising candidates for bioapplications such as drug delivery systems, gene carriers, and biomaterial surface modification.

On the Effect of pH, Temperature, and Surfactant Structure on Bovine Serum Albumin-Cationic/Anionic/Nonionic Surfactants Interactions in Cacodylate Buffer-Fluorescence Quenching Studies Supported by UV Spectrophotometry and CD Spectroscopy

Due to the fact that surfactant molecules are known to alter the structure (and consequently the function) of a protein, protein–surfactant interactions are very important in the biological, pharmaceutical, and cosmetic industries. Although there are numerous studies on the interactions of albumins with surfactants, the investigations are often performed at fixed environmental conditions and limited to separate surface-active agents and consequently do not present an appropriate comparison between their different types and structures. In the present paper, the interactions between selected cationic, anionic, and nonionic surfactants, namely hexadecylpyridinium chloride (CPC), hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), polyethylene glycol sorbitan monolaurate, monopalmitate, and monooleate (TWEEN 20, TWEEN 40, and TWEEN 80, respectively) with bovine serum albumin (BSA) were studied qualitatively and quantitatively in an aqueous solution (10 mM cacodylate buffer; pH 5.0 and 7.0) by steady-state fluorescence spectroscopy supported by UV spectrophotometry and CD spectroscopy. Since in the case of all studied systems, the fluorescence intensity of BSA decreased regularly and significantly under the action of the surfactants added, the fluorescence quenching mechanism was analyzed thoroughly with the use of the Stern–Volmer equation (and its modification) and attributed to the formation of BSA–surfactant complexes. The binding efficiency and mode of interactions were evaluated among others by the determination, comparison, and discussion of the values of binding (association) constants of the newly formed complexes and the corresponding thermodynamic parameters (ΔG, ΔH, ΔS). Furthermore, the influence of the structure of the chosen surfactants (charge of hydrophilic head and length of hydrophobic chain) as well as different environmental conditions (pH, temperature) on the binding mode and the strength of the interaction has been investigated and elucidated.

Modulating the Excited State Chirality of Dynamic Chemical Reactions in Chiral Micelles

Chirality generation and transfer is not only of critical importance in resolving the origin of biological homochirality, but also is of great significance for exploring the chirality-related functionalities in nanomaterials and supramolecular systems. Although modulating the ground state chirality in chiral nanomaterials has been widely demonstrated, it remains a big challenge to steer the excited state chirality (circularly polarized luminescence, CPL). Herein, we present a kind of chiral spherical micelles constructed by chiral cationic gemini surfactants, whose surfaces and cavities could co-assemble with hydrophilic and hydrophobic emitters concurrently. Subsequently, the hydrophilic and hydrophobic emitters could be endowed with CPL activity in the aqueous phase. Additionally, the cavities of such micelles can be regarded as the powerful chiral confined space, which could effectively modulate the excited state chirality of dynamic chemical reactions, enabling color-adjustable CPL emission.

Synthesis and Characterization of a Pyrene-Labeled Gemini Surfactant Sensitive to the Polarity of Its Environment

The cationic gemini surfactant PyO-3-12 was designed to include two dimethyl ammonium groups, one dodecyl tail, and 1-pyrenemethyl hexyl ether tail into the structure of the surfactant. The pyrenyl label ensured that the fluorescence of pyrene could be employed to probe the behavior of PyO-3-12 at the molecular level. The introduction of the oxygen atom in the β-position to pyrene was found to be critical for restoring the sensitivity of the pyrenyl label to the polarity of its environment. The properties of PyO-3-12 were characterized in water by surface tension and a fluorescence methodology that involved the global model-free analysis (MFA) of the pyrene monomer and excimer fluorescence decays to provide quantitative information about the state (unassociated-vs-aggregated) of PyO-3-12. The MFA was combined with a fluorescence quenching study with 2,6-dinitrotoluene to determine the size of the PyO-3-12 micelles. PyO-3-12 was found to behave like a typical gemini surfactant, exhibiting a critical micelle concentration (CMC) of 0.38 (±0.05) mM and an aggregation number (N_agg) equal to 23 (±2). Besides allowing PyO-3-12 to probe the polarity of its environment, the oxygen atom in the β-position next to pyrene brought some pyrenyl labels closer to the interface between the micellar interior and the aqueous phase, in a process that increased the effective volume of the hydrophobic part of PyO-3-12. This led to an increase in the packing parameter of PyO-3-12 and, consequently, an increase in N_agg compared to the N_agg value of 14 (±0.2) obtained for Py-3-12, a gemini surfactant, whose chemical structure was similar to that of PyO-3-12 but without the oxygen in the β-position to pyrene. The methodology described in this study to prepare and characterize pyrene-labeled surfactants is general and can be applied to study any pyrene-labeled surfactant and its interactions with oppositely charged macromolecules.

A Systematic Approach: Molecular Dynamics Study and Parametrisation of Gemini Type Cationic Surfactants

The spreading of antibiotic-resistant bacteria strains is one of the most serious problem in medicine to struggle nowadays. This triggered the development of alternative antimicrobial agents in recent years. One of such group is Gemini surfactants which are massively synthesised in various structural configurations to obtain the most effective antibacterial properties. Unfortunately, the comparison of antimicrobial effectiveness among different types of Gemini agents is unfeasible since various protocols for the determination of Minimum Inhibitory Concentration are used. In this work, we proposed alternative, computational, approach for such comparison. We designed a comprehensive database of 250 Gemini surfactants. Description of structure parameters, for instance spacer type and length, are included in the database. We parametrised modelled molecules to obtain force fields for the entire Gemini database. This was used to conduct in silico studies using the molecular dynamics to investigate the incorporation of these agents into model E. coli inner membrane system. We evaluated the effect of Gemini surfactants on structural, stress and mechanical parameters of the membrane after the agent incorporation. This enabled us to select four most likely membrane properties that could correspond to Gemini’s antimicrobial effect. Based on our results we selected several types of Gemini spacers which could demonstrate a particularly strong effect on the bacterial membranes.

Rhamnolipids as Effective Green Agents in the Destabilisation of Dolomite Suspension

In this paper, we describe an application of mono- and dirhamnolipid homologue mixtures of a biosurfactant as a green agent for destabilisation of a dolomite suspension. Properties of the biosurfactant solution were characterised using surface tension and aggregate measurements to prove aggregation of rhamnolipids at concentrations much lower than the critical micelle concentration. Based on this information, the adsorption process of biosurfactant molecules on the surface of the carbonate mineral dolomite was investigated, and the adsorption mechanism was proposed. The stability of the dolomite suspension after rhamnolipid adsorption was investigated by turbidimetry. The critical concentration of rhamnolipid at which destabilisation of the suspension occurred most effectively was found to be 50 mg·dm-3. By analysing backscattering profiles, solid-phase migration velocities were calculated. With different amounts of biomolecules, this parameter can be modified from 6.66 to 20.29 mm·h-1. Our study indicates that the dolomite suspension is destabilised by hydrophobic coagulation, which was proved by examining the wetting angle of the mineral surface using the captive bubble technique. The relatively low amount of biosurfactant used to destabilise the system indicates the potential application of this technology for water treatment or modification of the hydrophobicity of mineral surfaces in mineral engineering.

Activity of Polyphenoloxidase in red Fuji Apples Promoted with Cationic Surfactant – Role of Surfactant Structure

In this study, we observed the activity of polyphenoloxidase (PPO) in red Fuji apples in the presence of single-chained surfactants (including cetyl trimethyl ammonium bromide (CTAB), and dodecyl trimethyl ammonium bromide (DTAB)) and gemini surfactants (pentamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide), octamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide, dodecamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide), pentamethylene-α,ω-bis(cetyl dimethyl ammonium bromide), and octamethylene-α,ω-bis(cetyl dimethyl ammonium bromide)). It was found that all these surfactants enhanced the activity of PPO in a wide range of temperature at low content. When PPO was denatured by incubating at high temperature, the surfactants caused reactivation of PPO. Compared to the single-chained surfactants, the gemini surfactants increased PPO activity at a much lower concentration. Moreover, the single-chained surfactant and the gemini surfactant acted together to further increase PPO activity, and the synergistic effect reduced the amount of surfactant used. In addition, the Michaelis-Menten constant for PPO did not change in the presence of the surfactants, suggesting the active site should remain well with the surfactants.

Antimicrobial Activity of Gemini Surfactants with Ether Group in the Spacer Part

Due to their large possibility of the structure modification, alkylammonium gemini surfactants are a rapidly growing class of compounds. They exhibit significant surface, aggregation and antimicrobial properties. Due to the fact that, in order to achieve the desired utility effect, the minimal concentration of compounds are used, they are in line with the principle of greenolution (green evolution) in chemistry. In this study, we present innovative synthesis of the homologous series of gemini surfactants modified at the spacer by the ether group, i.e., 3-oxa-1,5-pentane-bis(N-alkyl-N,N-dimethylammonium bromides). The critical micelle concentrations were determined. The minimal inhibitory concentrations of the synthesized compounds were determined against bacteria Escherichia coli ATCC 10536 and Staphylococcus aureus ATCC 6538; yeast Candida albicans ATCC 10231; and molds Aspergillus niger ATCC 16401 and Penicillium chrysogenum ATCC 60739. We also investigated the relationship between antimicrobial activity and alkyl chain length or the nature of the spacer. The obtained results indicate that the synthesized compounds are effective microbicides with a broad spectrum of biocidal activity.

pH-Responsive Rheological Properties and Microstructure Transition in Mixture of Anionic Gemini/Cationic Monomeric Surfactants

Surfactant aggregates have long been considered as a tool to improve drug delivery and have been widely used in medical products. The pH-responsive aggregation behavior in anionic gemini surfactant 1,3-bis(N-dodecyl-N-propanesulfonate sodium)-propane (C₁₂C₃C₁₂(SO₃)₂) and its mixture with a cationic monomeric surfactant cetyltrimethylammonium bromide (CTAB) have been investigated. The spherical-to-wormlike micelle transition was successfully realized in C₁₂C₃C₁₂(SO₃)₂ through decreasing the pH, while the rheological properties were perfectly enhanced for the formation of wormlike micelles. Especially at 140 mM and pH 6.7, the mixture showed high viscoelasticity, and the maximum of the zero-shear viscosity reached 1530 Pa·s. Acting as a sulfobetaine zwitterionic gemini surfactant, the electrostatic attraction, the hydrogen bond and the short spacer of C₁₂C₃C₁₂(SO₃)₂ molecules were all responsible for the significant micellar growth. Upon adding CTAB, the similar transition could also be realized at a low pH, and the further transformation to branched micelles occurred by adjusting the total concentration. Although the mixtures did not approach the viscosity maximum appearing in the C₁₂C₃C₁₂(SO₃)₂ solution, CTAB addition is more favorable for viscosity enhancement in the wormlike-micelle region. The weakened charges of the headgroups in a catanionic mixed system minimizes the micellar spontaneous curvature and enhances the intermolecular hydrogen-bonding interaction between C₁₂C₃C₁₂(SO₃)₂, facilitating the formation of a viscous solution, which would greatly induce entanglement and even the fusion of wormlike micelles, thus resulting in branched microstructures and a decline of viscosity.

Scrutinizing Self-Assembly, Surface Activity and Aggregation Behavior of Mixtures of Imidazolium Based Ionic Liquids and Surfactants: A Comprehensive Review

The desire of improving various processes like enhanced oil recovery (EOR), water treatment technologies, biomass extraction, organic synthesis, carbon capture etc. in which conventional surfactants have been traditionally utilized; prompted various researchers to explore the self-assembly and aggregation behavior of different kinds of surface-active molecules. Ionic liquids (ILs) with long alkyl chain present in their structure constitute the advantageous properties of surfactant and ILs, hence termed as surface-active ionic liquids (SAILs). The addition of ILs and SAILs significantly influence the surface-activity and aggregation behavior of industrially useful conventional surfactants. After a brief review of ILs, SAILs and surfactants, the prime focus is made on analyzing the self-assembly of SAILs and the mixed micellization behavior of conventional surfactants with different ILs.

Determination of the Aggregation Number of Pyrene-Labeled Gemini Surfactant Micelles by Pyrene Fluorescence Quenching Measurements

A cationic gemini surfactant referred to as Py-3-12 and composed of two alkylated diammonium bromide head groups, a propyl spacer, and dodecyl and 1-pyrenehexyl hydrophobic tails was synthesized. Its critical micellar concentration (CMC) was determined to equal 0.15 (±0.02) mM by surface tension and time-resolved fluorescence measurements. The state of the pyrene molecules, whether they were incorporated inside the Py-3-12 micelles or unassociated in the aqueous solution, was determined by applying the global model-free analysis (MFA) to the fluorescence decays acquired with Py-3-12 aqueous solutions. The unassociated Py-3-12 surfactants emitted as pyrene monomers and showed a long fluorescence lifetime. The excited pyrenyl groups located inside Py-3-12 micelles formed an excimer by a rapid encounter with a ground-state pyrene with an average rate constant equal to 0.69 (±0.06) ns^-1. After having the photophysical properties of Py-3-12 in aqueous solution characterized, the number (N_agg) of surfactants per micelle was determined by conducting quenching experiments with dinitrotoluene (DNT). Although DNT is fairly hydrophobic, it was found to partition itself between the Py-3-12 micelles and the aqueous phase. Fluorescence quenching experiments performed on the pyrene monomer and excimer generated by the Py-3-12 aqueous solutions yielded the concentration ([Q]_b) of DNT bound to the Py-3-12 micelles and the average number ⟨n⟩_d of DNT quenching an excimer by diffusive encounters. A combination of steady-state and time-resolved fluorescence quenching experiments on the excimer yielded the number (⟨n⟩_s) of DNT molecules that were bound to the micelles and quenched the excimer in a static manner. A plot of the sum ⟨n⟩_d + ⟨n⟩_s as a function of [Q]_b yielded an N_agg value of 14.0 (±0.2) Py-3-12 units per micelle. This study represents the first example in the literature where N_agg is determined for a micelle, where each surfactant molecule is labeled with pyrene.

Biological and Physico-Chemical Characteristics of Arginine-Rich Peptide Gemini Surfactants with Lysine and Cystine Spacers

Ultrashort cationic lipopeptides (USCLs) and gemini cationic surfactants are classes of potent antimicrobials. Our recent study has shown that the branching and shortening of the fatty acids chains with the simultaneous addition of a hydrophobic N-terminal amino acid in USCLs result in compounds with enhanced selectivity. Here, this approach was introduced into arginine-rich gemini cationic surfactants. l-cystine diamide and l-lysine amide linkers were used as spacers. Antimicrobial activity against planktonic and biofilm cultures of ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) strains and Candida sp. as well as hemolytic and cytotoxic activities were examined. Moreover, antimicrobial activity in the presence of human serum and the ability to form micelles were evaluated. Membrane permeabilization study, serum stability assay, and molecular dynamics were performed. Generally, critical aggregation concentration was linearly correlated with hydrophobicity. Gemini surfactants were more active than the parent USCLs, and they turned out to be selective antimicrobial agents with relatively low hemolytic and cytotoxic activities. Geminis with the l-cystine diamide spacer seem to be less cytotoxic than their l-lysine amide counterparts, but they exhibited lower antibiofilm and antimicrobial activities in serum. In some cases, geminis with branched fatty acid chains and N-terminal hydrophobic amino acid resides exhibited enhanced selectivity to pathogens over human cells.

Newer Non-ionic A2 B2 -Type Enzyme-Responsive Amphiphiles for Drug Delivery

A new series of nonionic gemini amphiphiles have been synthesized in a multi-step chemoenzymatic approach by using a novel A₂ B₂ -type central core consisting of conjugating glycerol and propargyl bromide on 5-hydroxy isophthalic acid. A pair of hydrophilic monomethoxy poly(ethylene glycol) (mPEG) and hydrophobic linear alkyl chains (C₁₂ /C₁₅ ) were then added to the core to obtain amphiphilic architectures. The aggregation tendency in aqueous media was studied by dynamic light scattering, fluorescence spectroscopy and cryogenic transmission electron microscopy. The nanotransport potential of the amphiphiles was studied for model hydrophobic guests, that is, the dye Nile Red and the drug Nimodipine by using UV/Vis and fluorescence spectroscopy. Evaluation of the viability of amphiphile-treated A549 cells showed them to be well tolerated up to the concentrations studied. Being ester based, these amphiphiles exhibit stimuli-responsive sensitivity towards esterases, and a rupture of amphiphilic architecture was observed in the presence of immobilized Candida antarctica lipase (Novozym 435), thus facilitating release of the encapsulated guest from the aggregate.

Effective cytocompatible nanovectors based on serine-derived gemini surfactants and monoolein for small interfering RNA delivery

Non-viral gene therapy based on gene silencing with small interfering RNA (siRNA) has attracted great interest over recent years. Among various types of cationic complexation agents, amino acid-based surfactants have been recently explored for nucleic acid delivery due to their low toxicity and high biocompatibility. Monoolein (MO), in turn, has been used as helper lipid in liposomal systems due to its ability to form inverted nonbilayer structures that enhance fusogenicity, thus contributing to higher transfection efficiency. In this work, we focused on the development of nanovectors for siRNA delivery based on three gemini amino acid-based surfactants derived from serine - (12Ser)₂N12, amine derivative; (12Ser)₂COO12, ester derivative; and (12Ser)₂CON12, amide derivative - individually combined with MO as helper lipid. The inclusion of MO in the cationic surfactant system influences the morphology and size of the mixed aggregates. Furthermore, the gemini surfactant:MO systems showed the ability to efficiently complex siRNA, forming stable lipoplexes, in some cases clearly depending on the MO content, without inducing significant levels of cytotoxicity. High levels of gene silencing were achieved in comparison with a commercially available standard indicating that these gemini:MO systems are promising candidates as lipofection vectors for RNA interference (RNAi)-based therapies.

Synthesis of Silver Nanoparticles with Gemini Surfactants as Efficient Capping and Stabilizing Agents

The scientific community has paid special attention to silver nanoparticles (AgNPs) in recent years due to their huge technological capacities, particularly in biomedical applications, such as antimicrobials, drug-delivery carriers, device coatings, imaging probes, diagnostic, and optoelectronic platforms. The most popular method of obtaining silver nanoparticles as a colloidal dispersion in aqueous solution is chemical reduction. The choice of the capping agent is particularly important in order to obtain the desired size distribution, shape, and dispersion rate of AgNPs. Gemini alkylammonium salts are named as multifunctional surfactants, and possess a wide variety of applications, which include their use as capping agents for metal nanoparticles synthesis. Because of the high antimicrobial activity of gemini surfactants, AgNPs stabilized by this kind of surfactant may possess unique and strengthened biocidal properties. The present paper presents the synthesis of AgNPs stabilized by gemini surfactants with hexadecyl substituent and variable structure of spacer, obtained via ecofriendly synthesis. UV-Vis spectroscopy and dynamic light scattering were used as analyzing tools in order to confirm physicochemical characterization of the AgNPs (characteristic UV-Vis bands, hydrodynamic diameter of NPs, polydispersity index (PDI)).

Synthesis and Aggregation Behavior of Jellyfish-Shaped Triazine Hexamer Quaternary Ammonium Chloride Surfactant

A novel jellyfish-shaped triazine hexamer quaternary ammonium chloride surfactant (TH₁₂QC) was synthesized, which consisted of one triazine spacer group and six long flexible hydrophobic chains. The molecular structure and aggregation behavior of TH₁₂QC was investigated by nuclear magnetic resonance (NMR), surface tension, electrical conductivity, dynamic light scattering (DLS), transmission electron microscope (TEM), etc. The results show that the jellyfish-shaped TH₁₂QC has better surface activity and lower surface tension than traditional ionic and Gemini surfactants in aqueous solution. There are two inflection points in the curve of conductivity versus concentration of the TH₁₂QC aqueous solution, which correspond to the critical aggregation concentration (CAC) and the critical micelle concentration (CMC) respectively. The existence of CAC indicates that there is a pre-aggregation process before TH₁₂QC forms micelles. The results of DLS and TEM show that network pre-aggregation, spherical aggregation and dense spherical aggregation were observed in different concentration of TH₁₂QC aqueous solution, and the electrostatic equilibrium of the system subtly depends on the concentration of the solution. In addition, intramolecular and intermolecular hydrogen bonding is also an important factor. This study provides a method for studying the aggregation behavior and morphology of oligomeric surfactants with rigid spacer groups.

Dicationic Amino Substituted Gemini Surfactants and their Nanoplexes: Improved Synthesis and Characterization of Transfection Efficiency and Corneal Penetration In Vitro

PURPOSE

To formulate and characterize nanoparticles from m-7NH-m gemini surfactants, synthesized by a new improved method, for non-invasive gene delivery including optimization of composition for transfection efficiency and corneal penetration.

METHODS

A one-pot, solvent-free, DMAP-free method was developed for the synthesis of m-7NH-m (m = 12-18) gemini surfactant series. Lipoplexes (LPXs) and nanoplexes (NPXs) of gemini surfactant-plasmid DNA were formulated with and without DOPE helper lipid, respectively, at various charge ratios and characterized by dynamic light scattering and zeta potential measurements. Transfection efficiency, cellular toxicity, effect of DOPE and gene expression kinetic studies were carried out in A7 astrocytes by flow cytometry and confocal microscopy. Corneal penetration studies of 18-7NH-18 NPXs were carried out using 3D EpiCorneal^® tissue model.

RESULTS

The new synthesis method provides a two-fold improved yield and the production of a pure species of m-7NH-m without DMAP and trimeric m-7N(m)-m surfactants as impurities. Structure and purity was confirmed by ESI-MS, ¹H NMR spectroscopy and surface tension measurements. Particle size of 199.80 ± 1.83 nm ± S.D. and a zeta potential value of +30.18 ± 1.17 mV ± S.D. was obtained for 18-7NH-18 5:1 ratio NPXs showed optimum transfection efficiency (10.97 ± 0.11%) and low toxicity (92.97 ± 0.57% viability) at the 48-h peak expression. Inclusion of DOPE at 1: 0.5 and 1:1 ratios to gemini surfactant reduced transfection efficiency and increased toxicity. Treatment of EpiCorneal^® tissue model showed deep penetration of up to 100 μm with 18-7NH-18 NPXs.

CONCLUSION

Overall, 18-7NH-18 NPXs are potential gene delivery systems for ophthalmic gene delivery and for further in vivo studies.

Synthesis and characterization of geminis and implications of their micellar solution on ninhydrin and metal amino acid complex

In our study, three gemini dicationic surfactants with different methylene group spacer (16-6-16, 16-5-16 and 16-4-16) have been synthesized and characterized in solution by 1H NMR spectroscopic technique. The implications of gemini micellar solution on ninhydrin and metal amino acid complex ([Cu(II)-Trp]+) were performed by the means of single-beam UV-visible spectroscopy. The absorbance was noted at regular time intervals and values of rate constant (kψ ) were determined by using a computer-based program. Synthesized surfactants proved as an efficient catalyst on the interaction of ninhydrin with metal amino acid complex as compared with conventional surfactant and aqueous systems. The required description regarding the implications of gemini dicationic surfactants are provided in the text in detail. The conductivity technique was applied in order to get critical micelle concentration (cmc) of geminis in the presence and absence of reactants. Catalytic results developed in gemini dicationic surfactant system were explained effectively by pseudo-phase model. Various thermodynamic quantities, viz., activation energy, E a, activation enthalpy, ΔH #, and activation entropy, ΔS #, were obtained on interaction of ninhydrin with [Cu(II)-Trp]+ in gemini systems by applying Eyring equation. A detailed explanation about these evaluated parameters was also made.

Chemoenzymatic Synthesis of D-Glucitol-Based Non-Ionic Amphiphilic Architectures as Nanocarriers

Newer non-ionic amphiphiles have been synthesized using biocompatible materials and by following a greener approach i.e., D-glucitol has been used as a template, and hydrophobic and hydrophilic segments were incorporated on it by using click chemistry. The hydrophilic segments in turn were prepared from glycerol using an immobilized Candida antarctica lipase (Novozym-435)-mediated chemoenzymatic approach. Surface tension measurements and dynamic light scattering studies reflect the self-assembling behavior of the synthesized amphiphilic architectures in the aqueous medium. The results from UV-Vis and fluorescence spectroscopy establish the encapsulation of guests in the hydrophobic core of self-assembled amphiphilic architectures. The results of 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay indicate that the amphiphiles are well tolerated by the used A549 cell lines at all tested concentrations.

Role of Different States of Solubilized Water on Solvation Dynamics and Rotational Relaxation of Coumarin 490 in Reverse Micelles of Gemini Surfactants, Water/12-s-12.2Br- (s = 5, 6, 8)/n-Propanol/Cyclohexane

The present study demonstrates how the different states of solubilized water viz. quaternary ammonium headgroup-bound, bulklike, counterion-bound, and free water in reverse micelles of a series of cationic gemini surfactants, water/12-s-12 (s = 5, 6, 8).2Br^-/n-propanol/cyclohexane, control the solvation dynamics and rotational relaxation of Coumarin 490 (C-490) and microenvironment of the reverse micelles. The relative number of solubilized water molecules of a given state per surfactant molecule decides major and minor components. A rapid increase in the number of bulklike water molecules per surfactant molecule as compared to the slow increase in the number of each of headgroup- and counterion-bound water molecules per surfactant molecule with increasing water content (W _o) in a given reverse micellar system is responsible for the increase in the rate of solvation and rotational relaxation of C-490. The increase in the number of counterion-bound water molecules per surfactant molecule and the concomitant decrease in the number of bulklike water molecules per surfactant molecule with increasing spacer chain length of gemini surfactants at a given W _o are ascribed to the slower rates of both solvation and rotational relaxation. Relative abundances of different states of water have a role on the microenvironment of the reverse micelles as well. Thus, a comprehensive effect of different states of water on dynamics in complex biomimicking systems has been presented here.

Synthesis and Properties of a Quaternary Ammonium Salt Gemini Surfactant with Diethyl Ether as the Spacer Group

A quaternary ammonium salt gemini surfactant (C12N)2O with diethyl ether as the spacer group was synthesized by dodecyl dimethyl amine and 2-chloroethyl ether. The structure of the product was confirmed by Fourier transform infrared spectra (FT-IR) and proton nuclear magnetic resonance spectra (1H NMR), which showed that the structure of the synthesized product was consistent with the theoretical structure. We tested the surface tension of (C12N)2O at 25°C and found the critical micelle concentration (CMC) was roughly 2 orders of magnitude lower than that of dodecyl trimethylamine chloride (DTAC). Gemini structure and the unique diethyl ether spacer group endowed the novel amphiphile excellent properties including low contact angle and high antistatic property. (C1 2N)2O showed good compatibility with alcohol ether sulfate (AES) and dodecylbenzene sulfonate (LAS) in surfactant mixed systems. When the ratio of (C12N)2O:AES was 1:4 and (C12N)2O:LAS 1:9, the emulsifying properties were preferable to single surfactant.

Stimuli-responsive non-ionic Gemini amphiphiles for drug delivery applications

This paper shows the synthesis of stimuli responsive Gemini amphiphiles sensitive to Glutathione and hydrolase.