Physicochemical and antimicrobial activities of cationic gemini surfactants with polyether siloxane linked group

Anti-adhesive, anti-biofilm and fungicidal action of newly synthesized gemini quaternary ammonium salts

Newly synthesized gemini quaternary ammonium salts (QAS) with different counterions (bromide, hydrogen chloride, methylcarbonate, acetate, lactate), chain lengths (C12, C14, C16) and methylene linker (3xCH2) were tested. Dihydrochlorides and dibromides with 12 carbon atoms in hydrophobic chains were characterized by the highest biological activity against planktonic forms of yeast and yeast-like fungi. The tested gemini surfactants also inhibited the production of filaments by C. albicans. Moreover, they reduced the adhesion of C. albicans cells to the surfaces of stainless steel, silicone and glass, and slightly to polystyrene. In particular, the gemini compounds with 16-carbon alkyl chains were most effective against biofilms. It was also found that the tested surfactants were not cytotoxic to yeast cells. Moreover, dimethylcarbonate (2xC12MeCO3G3) did not cause hemolysis of sheep erythrocytes. Dihydrochlorides, dilactate and diacetate showed no mutagenic potential.

Study on the Synthesis, Surface Activity, and Self-Assembly Behavior of Anionic Non-Ionic Gemini Surfactants

The use of surfactants in oil recovery can effectively improve crude oil recovery rate. Due to the enhanced salt and temperature resistance of surfactant molecules by non-ionic chain segments, anionic groups have good emulsifying stability. Currently, there are many studies on anionic non-ionic surfactants for oil recovery in China, but there is relatively little systematic research on introducing EOs into hydrophobic alkyl chains, especially on their self-assembly behavior. This article proposes a simple and effective synthesis method, using 3-aminopropane sulfonic acid, fatty alcohol polyoxyethylene ether, and epichlorohydrin as raw materials, to insert EO into hydrophobic alkyl chains and synthesize a series of new anionic non-ionic Gemini surfactants (CnEO-5, n = 8, 12, 16). The surface activity, thermodynamic properties, and self-assembly behavior of these surfactants were systematically studied through surface tension, conductivity, steady-state fluorescence probes, transmission electron microscopy, and molecular dynamics simulations. The surface tension test results show that CnEO-5 has high surface activity and is higher than traditional single chain surfactants and structurally similar anionic non-ionic Gemini surfactants. Additionally, thermodynamic parameters (e.g., ΔG°mic ΔH°mic ΔS°mic et al. indicate that CnEO-5 molecules are exothermic and spontaneous during the micellization process. DLS, p-values, and TEM results indicate that anionic non-ionic Gemini surfactants with shorter hydrophobic chains (such as C8EO-5) tend to form larger vesicles in aqueous solutions, which are formed in a tail to tail and staggered manner; Negative non-ionic Gemini surfactants with longer hydrophobic chains (such as C12EO-5, C16EO-5) tend to form small micelles. The test results indicate that CnEO-5 anionic non-ionic Gemini surfactants have certain application prospects in improving crude oil recovery.

Molecular guidelines for promising antimicrobial agents

Antimicrobial resistance presents a pressing challenge to public health, which requires the search for novel antimicrobial agents. Various experimental and theoretical methods are employed to understand drug-target interactions and propose multistep solutions. Nonetheless, efficient screening of drug databases requires rapid and precise numerical analysis to validate antimicrobial efficacy. Diptool addresses this need by predicting free energy barriers and local minima for drug translocation across lipid membranes. In the current study employing Diptool free energy predictions, the thermodynamic commonalities between selected antimicrobial molecules were characterized and investigated. To this end, various clustering methods were used to identify promising groups with antimicrobial activity. Furthermore, the molecular fingerprinting and machine learning approach (ML) revealed common structural elements and physicochemical parameters in these clusters, such as long carbon chains, charged ammonium groups, and low dipole moments. This led to the establishment of guidelines for the selection of effective antimicrobial candidates based on partition coefficients (logP) and molecular mass ranges. These guidelines were implemented within the Reinforcement Learning for Structural Evolution (ReLeaSE) framework, generating new chemicals with desired properties. Interestingly, ReLeaSE produced molecules with structural profiles similar to the antimicrobial agents tested, confirming the importance of the identified features. In conclusion, this study demonstrates the ability of molecular fingerprinting and AI-driven methods to identify promising antimicrobial agents with a broad range of properties. These findings deliver substantial implications for the development of antimicrobial drugs and the ongoing battle against antibiotic-resistant bacteria.

Synthesis, surface activities and aggregation properties of asymmetric Gemini surfactants

A series of Gemini surfactants with an asymmetric structure (PKO 15-3(OH)-n; n = 12, 14 and 16) were synthesized through a simple two-step reaction consisting of a ring-opening reaction followed by a quaternization reaction. The surface tension measurements indicated that the surface activities of PKO 15-3(OH)-n were higher than those of traditional single-chain and symmetrical Gemini surfactants. The thermodynamic parameters obtained from electrical conductivity measurements showed that the micellization processes of PKO 15-3(OH)-n were spontaneous and entropy-driven. Transmission electron microscopy and dynamic light scattering measurements confirmed that PKO 15-3(OH)-n molecules with a higher asymmetric degree could form vesicles, in which surfactant molecules were interdigitated side-by-side in the vesicle membrane. The obtained results are not in accordance with those calculated from the critical packing theory, which can further complement the theory.

Diptool-A Novel Numerical Tool for Membrane Interactions Analysis, Applying to Antimicrobial Detergents and Drug Delivery Aids

The widespread problem of resistance development in bacteria has become a critical issue for modern medicine. To limit that phenomenon, many compounds have been extensively studied. Among them were derivatives of available drugs, but also alternative novel detergents such as Gemini surfactants. Over the last decade, they have been massively synthesized and studied to obtain the most effective antimicrobial agents, as well as the most selective aids for nanoparticles drug delivery. Various protocols and distinct bacterial strains used in Minimal Inhibitory Concentration experimental studies prevented performance benchmarking of different surfactant classes over these last years. Motivated by this limitation, we designed a theoretical methodology implemented in custom fast screening software to assess the surfactant activity on model lipid membranes. Experimentally based QSAR (quantitative structure-activity relationship) prediction delivered a set of parameters underlying the Diptool software engine for high-throughput agent-membrane interactions analysis. We validated our software by comparing score energy profiles with Gibbs free energy from the Adaptive Biasing Force approach on octenidine and chlorhexidine, popular antimicrobials. Results from Diptool can reflect the molecule behavior in the lipid membrane and correctly predict free energy of translocation much faster than classic molecular dynamics. This opens a new venue for searching novel classes of detergents with sharp biologic activity.

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.

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.

Self-Assembly of Amphiphilic Compounds as a Versatile Tool for Construction of Nanoscale Drug Carriers

This review focuses on synthetic and natural amphiphilic systems prepared from straight-chain and macrocyclic compounds capable of self-assembly with the formation of nanoscale aggregates of different morphology and their application as drug carriers. Since numerous biological species (lipid membrane, bacterial cell wall, mucous membrane, corneal epithelium, biopolymers, e.g., proteins, nucleic acids) bear negatively charged fragments, much attention is paid to cationic carriers providing high affinity for encapsulated drugs to targeted cells. First part of the review is devoted to self-assembling and functional properties of surfactant systems, with special attention focusing on cationic amphiphiles, including those bearing natural or cleavable fragments. Further, lipid formulations, especially liposomes, are discussed in terms of their fabrication and application for intracellular drug delivery. This section highlights several features of these carriers, including noncovalent modification of lipid formulations by cationic surfactants, pH-responsive properties, endosomal escape, etc. Third part of the review deals with nanocarriers based on macrocyclic compounds, with such important characteristics as mucoadhesive properties emphasized. In this section, different combinations of cyclodextrin platform conjugated with polymers is considered as drug delivery systems with synergetic effect that improves solubility, targeting and biocompatibility of formulations.

Can the Isothermal Calorimetric Curve Shapes Suggest the Structural Changes in Micellar Aggregates?

Inspired by the unusual shapes of the titration curve observed for many surfactants and mixed colloidal systems, we decided to extend the analysis to isothermal titration calorimetric curves (ITC) by paying special attention to potential structural changes in micellar aggregates. In this paper, we used isothermal titration calorimetry in conjunction with Scanning Transmission Electron Microscopy (STEM), Small-Angle Neutron Scattering (SANS) and X-ray Scattering (SAXS) methods support by Monte Carlo and semiempirical quantum chemistry simulations to confirm if the isothermal calorimetric curve shape can reflect micelle transition phenomena. For that purpose, we analysed, from the thermodynamic point of view, a group of cationic gemini surfactants, alkanediyl-α,ω-bis(dimethylalkylammonium) bromides. We proposed the shape of aggregates created by surfactant molecules in aqueous solutions and changes thereof within a wide temperature range. The results provide evidence for the reorganization processes and the relationship (dependence) between the morphology of the created aggregates and the conditions such as temperature, surfactant concentration and spacer chain length which affect the processes.

Gemini quaternary ammonium compound PMT12-BF4 inhibits Candida albicans via regulating iron homeostasis

Quaternary ammonium compounds (QACs) are classified as cationic surfactants, and are known for their biocidal activity. However, their modes of action are thus far not completely understood. In this study, we synthesized a gemini QAC, PMT12-BF4 and found that it exerted unsurpassed broad-spectrum antifungal activity against drug susceptible and resistant Candida albicans, and other pathogenic fungi, with a minimal inhibitory concentration (MIC) at 1 or 2 μg/mL. These results indicated that PMT12-BF4 used a mode of action distinct from current antifungal drugs. In addition, fungal pathogens treated with PMT12-BF4 were not able to grow on fresh YPD agar plates, indicating that the effect of PMT12-BF4 was fungicidal, and the minimal fungicidal concentration (MFC) against C. albicans isolates was 1 or 2 μg/mL. The ability of yeast-to-hyphal transition and biofilm formation of C. albicans was disrupted by PMT12-BF4. To investigate the modes of action of PMT12-BF4 in C. albicans, we used an RNA sequencing approach and screened a C. albicans deletion mutant library to identify potential pathways affected by PMT12-BF4. Combining these two approaches with a spotting assay, we showed that the ability of PMT12-BF4 to inhibit C. albicans is potentially linked to iron ion homeostasis.

Aggregation Behavior of "Linear" Trisiloxane Surfactant with Different Terminal Groups (CH3-, ClCH2-, and CF3-) in Aqueous Solution

Novel "linear" trisiloxane surfactants with different terminal groups (CH₃-, ClCH₂-, CF₃-) and two polyether hydrophilic groups were successfully synthesized and confirmed using ¹H NMR, ¹³C NMR, ²⁹Si NMR, and FT-IR spectroscopy. The aggregation and adsorption behavior of the "linear" trisiloxane surfactants in aqueous solution was studied by surface tension, dynamic light scattering (DLS), transmission electron microscopy (FF-TEM), and TEM. Owing to the introduction of two polyether hydrophilic groups in the terminal positions of the trisiloxane hydrophobic part, "linear" trisiloxane surfactants (Me-Si₃-EO₈, Cl-Si₃-EO₈, and F-Si₃-EO₈) tend to lie flat in the air/water interface and result in an increasing the surface tension at the CMC ( γ_CMC) and single trisiloxane surfactant molecule at the air/water interface ( A _min) values. Following the difference in the intermolecular forces and molecular volumes (CH₃- < ClCH₂- < CF₃-), the γ_CMC values decrease following the order Me-Si₃-EO₈ > Cl-Si₃-EO₈ > F-Si₃-EO₈, and the adsorption efficiency ( p C₂₀), surface pressure at the CMC ( π_CMC), CMC/ C₂₀ , and A _min values increase following the order Me-Si₃-EO₈ < Cl-Si₃-EO₈ < F-Si₃-EO₈. As comparison, fluorinated trisiloxane surfactant (F-Si₃-EO₈) has greater surface activity attributed to the terminal CF₃- group. The TEM and FF-TEM results illustrated that all the investigated "linear" trisiloxane surfactants can form nonuniform size spherical aggregates.

Antimicrobial Activities of Hydrophobically Modified Poly(Acrylate) Films and Their Complexes with Different Chain Length Cationic Surfactants

Multilayer films from hydrophobically modified poly(acrylic acid) (HMPA) and their complexes with cationic surfactants were successfully prepared using the layer-by-layer (LbL) method. Alkyl trimethylammonium bromide derivatives with various lengths of the hydrophobic chain (C10–C18) were used to interact with the HMPA polymer, generating highly hydrophobic domains in the films and contributing to the antimicrobial properties of the prepared coating. The antimicrobial efficiency against common pathogens such as Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans was investigated in relationship with the morphology and composition of the thin films. The wettability and roughness of the multilayered systems were evaluated using atomic force microscopy (AFM) and contact angle measurements. The effects of the microbial exposure on the surface properties of the prepared films were investigated in order to assess the stability of the HMPA-deposited multilayers and the durability of the antimicrobial activity. The hydrophobically modified films exhibited antimicrobial activity against the studied pathogens. The best efficiency was registered in the case of S. aureus, which showed an inhibition of growth up to 100% after 2 h. C. albicans proved to be less sensitive to the effect of the multilayers deposited from HMPA–surfactant complexes. These results suggest that HMPA and HMPA–surfactant complex LbL multilayer films can be used as promising materials in antimicrobial surface coatings with increased resistance to pathogens during exposure.

Aggregation Behavior of Polyether Based Siloxane Surfactants in Aqueous Solutions: Effect of Alkyl Groups and Steric Hindrance

A series of polyether based siloxane surfactants with different branched chain and alkyl groups were synthesized by thiol-ene reaction and Piers-Rubinsztajn reaction. The effect of the siloxane structures (alkyl groups and branched chains) on the adsorption and aggregation behavior in aqueous solution was investigated by surface tension, fluorescence, dynamic light scattering (DLS), freeze-fracture transmission electron microscopy (TEM), and TEM. The molecular structures of siloxane can obviously influence their surface activities and thermodynamics. Replacing the methyl of trimethylsiloxyl groups with longer alkyl groups (ethyl, propyl, and butyl) and branching trimethylsiloxyl resulted in an obvious decrease of the values of critical micelle concentration (CMC) and surface tension at CMC (γ_CMC). Dense surface films packed with CH₃ groups result in the lower surface tensions being disordered by longer alkyl groups or branched chains of siloxane hydrophobic groups. And the minimum surface area per surfactant molecule ( A_min) values of Si₃-PG, Et-Si₃-PG, Pro-Si₃-PG, and But-Si₃-PG successively decrease about 3.5 Å with each increasing -CH₂- group. All polyether based siloxane surfactants can form nonuniform size spheroidal aggregates in aqueous solution. Concerning the driving force, the micellization process was spontaneous but less spontaneous compared with adsorption.

The adsorption and aggregation properties of dendritic cationic tetrameric surfactants

A series of dendritic cationic tetrameric surfactants (4C_ntetraQ, n = 12, 14, 16) were synthesized with raw materials that are commercially available.