Cationic Surfactants: Self-Assembly, Structure-Activity Correlation and Their Biological Applications

Engineering a nanoantibiotic system displaying dual mechanism of action

In recent decades, peptide amphiphiles (PAs) have established themselves as promising self-assembling bioinspired materials in a wide range of medical fields. Herein, we report a dual-therapeutic system constituted by an antimicrobial PA and a cylindrical protease inhibitor (LJC) to achieve broad antimicrobial spectrum and to enhance therapeutic efficacy. We studied two strategies: PA-LJC nanostructures (Encapsulation) and PA nanostructures + free LJC (Combination). Computational modeling using a molecular theory for amphiphile self-assembly captures and explains the morphology of PA-LJC nanostructures and the location of encapsulated LJC in agreement with transmission electron microscopy and two-dimensional (2D) NMR observations. The morphology and release profile of PA-LJC assemblies are strongly correlated to the PA:LJC ratio: high LJC loading induces an initial burst release. We then evaluated the antimicrobial activity of our nanosystems toward gram-positive and gram-negative bacteria. We found that the Combination broadens the spectrum of LJC, reduces the therapeutic concentrations of both agents, and is not impacted by the inoculum effect. Further, the Encapsulation provides additional benefits including bypassing water solubility limitations of LJC and modulating the release of this molecule. The different properties of PA-LJC nanostructures results in different killing profiles, and reduced cytotoxicity and hemolytic activity. Meanwhile, details in membrane alterations caused by each strategy were revealed by various microscopy and fluorescent techniques. Last, in vivo studies in larvae treated by the Encapsulation strategy showed better antimicrobial efficacy than polymyxin B. Collectively, this study established a multifunctional platform using a versatile PA to act as an antibiotic, membrane-penetrating assistant, and slow-release delivery vehicle.

Structure-Activity Relationship Study to Develop Peptide Amphiphiles as Species-Specific Antimicrobials

Antimicrobial peptide amphiphiles (PAs) are a promising class of molecules that can disrupt the bacterial membrane or act as drug nanocarriers. In this study, we prepared 33 PAs to establish supramolecular structure-activity relationships. We studied the morphology and activity of the nanostructures against different Gram-positive and Gram-negative bacterial strains (such as Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii). Next, we used principal component analysis (PCA) to determine the key contributors to activity. We found that for S. aureus, the zeta potential was the major contributor to the activity while Gram-negative bacteria were more influenced by the partition coefficient (LogP) with the following order P. aeruginosa>E. coli>A. baumannii. We also performed a study of the mechanism of action of selected PAs on the bacterial membrane assessing the membrane permeability and depolarization, changes in zeta potential and overall integrity. We studied the toxicity of the nanostructures against mammalian cells. Finally, we performed an in vivo study using the wax moth larvae to determine the therapeutic efficacy of the active PAs. This study shows cationic PA nanostructures can be an intriguing platform for the development of nanoantibacterials.

Piperidinium surfactants functionalized with carbamate fragment: Aggregation, antimicrobial activity and cytotoxicity

The biomimetic nature of supramolecular systems, the structural similarity of synthetic surfactants to biomolecules (lipids, proteins), provide them with high membranotropy, the ability to overcome biological barriers, and affinity towards biosubstances. Despite rather high toxicity cationic surfactants are of importance as antimicrobial agents, gene nanocarriers and mitochondria targeted ligands. To minimize this limitation, cationic amphiphilic matrix undergoes modification with various functional groups. In this work, new piperidinium cationic surfactants containing one or two carbamate fragments were prepared; their aggregation behavior was systematically studied by tensiometery, spectrophotometry and fluorimetry. The presence of a carbamate fragment leads to a 2-3-fold decrease in critical micelle concentration and to a significant increase in solubilization capacity compared to unsubstituted analogue. Evaluation of the antimicrobial effect showed that all compounds exhibit high bactericidal and fungicidal activity against a wide range of pathogenic microorganisms, including their resistant forms. Importantly, the introducing carbamate moiety allows of decreasing hemolytic activity of cationic surfactants. The data obtained make it possible to recommend carbamate piperidinium surfactants as effective biocompatible and biodegradable nanocontainers for hydrophobic probes with high antimicrobial effect and moderate hemolytic activity.

SDBS induces multiple catalase conformations in a dose-dependent manner

Amyloid fibrils have been linked to several incurable diseases. They are long and thin fibrous proteins that self-assemble into fibrils. Small molecules can stimulate amyloid fibrillation, but the mechanism by which this happens is not well understood. This study examined how a negatively charged benzene ring containing surfactant, sodium dodecylbenzene sulphonate (SDBS), affects the fibrillation of bovine liver catalase (BLC). After SDBS treatment, BLC conformational changes were examined in vitro using turbidity, RLS kinetics, intrinsic fluorescence, ThT fluorescence, far-UV CD, and TEM. BLC in the native state was alpha-helical at pH 7.4, while it was converted to a random coil structure at pH 2.0. Far-UV CD and intrinsic fluorescence data showed that at concentrations <0.1 mM of SDBS, randomly coiled BLC assumed a native-like alpha-helical structure. However, between 0.1 and 1.0 mM SDBS, BLC was aggregated. ThT fluorescence and far-UV CD measurements showed the amyloid-like structures in the aggregated BLC. At higher SDBS concentrations (>1.0 mM) at pH 2.0, BLC again attains a native-like alpha-helical structure. It is essential for therapeutic purposes to clearly understand the process underlying surfactant- or lipid-induced fibrillation.

Synthesis, Properties, and Biomedical Application of Dicationic Gemini Surfactants with Dodecane Spacer and Carbamate Fragments

A synthesis procedure and aggregation properties of a new homologous series of dicationic gemini surfactants with a dodecane spacer and two carbamate fragments (N,N'-dialkyl-N,N'-bis(2-(ethylcarbamoyloxy)ethyl)-N,N'-dimethyldodecan-1,6-diammonium dibromide, n-12-n(Et), where n = 10, 12, 14) were comprehensively described. The critical micelle concentrations of gemini surfactants were obtained using tensiometry, conductometry, spectrophotometry, and fluorimetry. The thermodynamic parameters of adsorption and micellization, i.e., maximum surface excess (Гmax), the surface area per surfactant molecule (Amin), degree of counterion binding (β), and Gibbs free energy of micellization (∆Gmic), were calculated. Functional activity of the surfactants, including the solubilizing capacity toward Orange OT and indomethacin, incorporation into the lipid bilayer, minimum inhibitory concentration, and minimum bactericidal and fungicidal concentrations, was determined. Synthesized gemini surfactants were further used for the modification of liposomes dual-loaded with α-tocopherol and donepezil hydrochloride for intranasal treatment of Alzheimer's disease. The obtained liposomes have high stability (more than 5 months), a significant positive charge (approximately + 40 mV), and a high degree of encapsulation efficiency toward rhodamine B, α-tocopherol, and donepezil hydrochloride. Korsmeyer-Peppas, Higuchi, and first-order kinetic models were used to process the in vitro release curves of donepezil hydrochloride. Intranasal administration of liposomes loaded with α-tocopherol and donepezil hydrochloride for 21 days prevented memory impairment and decreased the number of Aβ plaques by 37.6%, 40.5%, and 72.6% in the entorhinal cortex, DG, and CA1 areas of the hippocampus of the brain of transgenic mice with Alzheimer's disease model (APP/PS1) compared with untreated animals.

L-Rhamnose and Phenolic Esters-Based Monocatenar and Bolaform Amphiphiles: Eco-Compatible Synthesis and Determination of Their Antioxidant, Eliciting and Cytotoxic Properties

Symmetrical and dissymmetrical bolaforms were prepared with good to high yields from unsaturated L-rhamnosides and phenolic esters (ferulic, phloretic, coumaric, sinapic and caffeic) using two eco-compatible synthetic strategies involving glycosylation, enzymatic synthesis and cross-metathesis under microwave activation. The plant-eliciting activity of these new compounds was investigated in Arabidopsis model plants. We found that the monocatenar rhamnosides and bolaforms activate the plant immune system with a response depending on the carbon chain length and the nature of the hydrophilic heads. Their respective antioxidant activities were also evaluated, as well as their cytotoxic properties on dermal cells for cosmetic uses. We showed that phenolic ester-based compounds present good antioxidant activities and that their cytotoxicity is low. These properties are also dependent on the carbon chains used.

Mitochondria-Targeted Delivery Strategy of Dual-Loaded Liposomes for Alzheimer's Disease Therapy

Liposomes modified with tetradecyltriphenylphosphonium bromide with dual loading of α-tocopherol and donepezil hydrochloride were successfully designed for intranasal administration. Physicochemical characteristics of cationic liposomes such as the hydrodynamic diameter, zeta potential, and polydispersity index were within the range from 105 to 115 nm, from +10 to +23 mV, and from 0.1 to 0.2, respectively. In vitro release curves of donepezil hydrochloride were analyzed using the Korsmeyer-Peppas, Higuchi, First-Order, and Zero-Order kinetic models. Nanocontainers modified with cationic surfactant statistically better penetrate into the mitochondria of rat motoneurons. Imaging of rat brain slices revealed the penetration of nanocarriers into the brain. Experiments on transgenic mice with an Alzheimer's disease model (APP/PS1) demonstrated that the intranasal administration of liposomes within 21 days resulted in enhanced learning abilities and a reduction in the formation rate of Aβ plaques in the entorhinal cortex and hippocampus of the brain.

Green Surfactants (Biosurfactants): A Petroleum-Free Substitute for Sustainability-Comparison, Applications, Market, and Future Prospects

Surfactants are a group of amphiphilic molecules (i.e., having both hydrophobic and hydrophilic domains) that are a vital part of nearly every contemporary industrial process such as in agriculture, medicine, personal care, food, and petroleum. In general surfactants can be derived from (i) petroleum-based sources or (ii) microbial/plant origins. Petroleum-based surfactants are obvious results from petroleum products, which lead to petroleum pollution and thus pose severe problems to the environment leading to various ecological damages. Thus, newer techniques have been suggested for deriving surfactant molecules and maintaining environmental sustainability. Biosurfactants are surfactants of microbial or plant origins and offer much added advantages such as high biodegradability, lesser toxicity, ease of raw material availability, and easy applicability. Thus, they are also termed "green surfactants". In this regard, this review focused on the advantages of biosurfactants over the synthetic surfactants produced from petroleum-based products along with their potential applications in different industries. We also provided their market aspects and future directions that can be considered with selections of biosurfactants. This would open up new avenues for surfactant research by overcoming the existing bottlenecks in this field.

Rhamnolipid Self-Aggregation in Aqueous Media: A Long Journey toward the Definition of Structure–Property Relationships

The need to protect human and environmental health and avoid the widespread use of substances obtained from nonrenewable sources is steering research toward the discovery and development of new molecules characterized by high biocompatibility and biodegradability. Due to their very widespread use, a class of substances for which this need is particularly urgent is that of surfactants. In this respect, an attractive and promising alternative to commonly used synthetic surfactants is represented by so-called biosurfactants, amphiphiles naturally derived from microorganisms. One of the best-known families of biosurfactants is that of rhamnolipids, which are glycolipids with a headgroup formed by one or two rhamnose units. Great scientific and technological effort has been devoted to optimization of their production processes, as well as their physicochemical characterization. However, a conclusive structure–function relationship is far from being defined. In this review, we aim to move a step forward in this direction, by presenting a comprehensive and unified discussion of physicochemical properties of rhamnolipids as a function of solution conditions and rhamnolipid structure. We also discuss still unresolved issues that deserve further investigation in the future, to allow the replacement of conventional surfactants with rhamnolipids.

The Application of Polyethersulfone Ultrafiltration Membranes for Separation of Car Wash Wastewaters: Experiments and Modelling

The wastewater generated as a result of car washes is considered a new source of water. However, recovered water must meet the required quality criteria for reuse. For this purpose, the ultrafiltration (UF) process can be successfully used. The main aim of the present work was to investigate the influence of the membrane's molecular weight cut-off (MWCO) on the UF performance in terms of the fouling phenomenon and retention degree of car wash wastewater. Moreover, for a better understanding of the fouling mechanisms, Hermia's model was used. The experimental studies were conducted with the use of two polyethersulfone (PES) membranes (MWCO of 10 kDa and 100 kDa). It has been noted that the used membranes provided a high-quality permeate and excellent turbidity removal, up to 99%. Moreover, it has been noted that the MWCO membrane has a significant impact on the fouling mechanism. Generally, a much greater intensity of fouling for the membrane with MWCO of 100 kDa was observed. Results obtained in the present study showed that both real wastewaters and the clean solutions used for washing cars cause the fouling phenomenon. It has been proven that rinsing the membranes with water is not sufficient to recover the initial membrane's performance. Hence, periodic chemical cleaning of the membranes was required. Fitting the experimental data to Hermia's model allowed us to indicate that membranes with MWCO of 100 kDa are more prone to intermediate blocking. To sum up, the findings suggest that for the UF of the car wash wastewater, the use of membranes with MWCO equal to 10 kDa is recommended.

Biofouling in Membrane Bioreactors: Mechanism, Interactions and Possible Mitigation Using Biosurfactants

Biofouling roots damage to membrane bioreactors (MBRs), such as physical, functional and organisational changes and even therefore clogging of the membrane pores and successive microbial degradation. Further, it blocks the pores, results into a biomass cake and in due course reduces the membrane flux and leads to an increase in the operational costs. MBR fouling contributed to the rise in transmembrane pressure (TMP) and decrease in permeate flux (in case of constant pressure operation mode). Chemical surfactants adopted for the cleaning of membrane surfaces have certain disadvantages such as toxicity manifestations, damage to the membranes and high CMC concentrations. Biosurfactant surfactants have attained increasing interest due to their low toxicity, biodegradability, stability to extreme environmental conditions such as temperatures, pH and tolerance to salinity. The biosurfactants trapped the foulants via micelle formation, which distresses hydrophobic interactions amongst bacteria and the surface. Rhamnolipids as an anionic biosurfactant pose a significant interfacial potential and have affinity to bind organic matter. The present review discusses the problem of biofouling in MBRs, type and interactions of foulants involved and also highlights the mechanisms of biosurfactant cleaning, effect of different parameters, effect of concentration, TMP, flux recovery, permeability, mitigation practices and challenges.

The mechanism of thrombocytopenia caused by cholesterol-conjugated antisense oligonucleotides

In this study, we investigated thrombocytopenia caused by cholesterol-conjugated antisense oligonucleotides (Chol-ASO). First, we evaluated platelet activation induced by Chol-ASO in mice by flow cytometry after administration of platelet-rich plasma (PRP). An increase in the number of large particle-size events with platelet activation was detected in the Chol-ASO-treated group. In a smear study, numerous platelets were observed to attach to nucleic acid-containing aggregates. A competition binding assay showed that the conjugation of cholesterol to ASOs increased their affinity for glycoprotein VI. Platelet-free plasma was then mixed with Chol-ASO to form aggregates. The assembly of Chol-ASO was confirmed by dynamic light scattering measurements in the concentration range in which the formation of aggregates with plasma components was observed. In conclusion, the mechanism by which Chol-ASOs causes thrombocytopenia is proposed to be as follows: (1) Chol-ASOs form polymers, (2) the nucleic acid portion of the polymers interacts with plasma proteins and platelets, which cross-links them to form aggregates, and (3) platelets bound to aggregates become activated, resulting in platelet aggregation, leading to a decrease in platelet count in vivo. The details of the mechanism revealed in this study could contribute to creating safer oligonucleotide therapies without the risk of thrombocytopenia.

Study of Cationic Surfactants Raw Materials for COVID-19 Disinfecting Formulations by Potentiometric Surfactant Sensor

The behavior of a new 1,3-dioctadecyl-1H-imidazol-3-ium tetraphenylborate (DODI-TPB) surfactant sensor was studied in single and complex mixtures of technical grade QACs-benzalkonium chloride (BAC), N,N-didecyl-N,N-dimethylammonium chloride (DDAC), and N,N-dioctyl-N,N-dimethylammonium chloride (DOAC) usually used in COVID-19 disinfecting agents formulations. The results obtained with the new DODI-TPB sensor were in good agreement with data measured by a 1,3-dihexadecyl-1H-benzo[d]imidazol-3-ium-tetraphenylborate (DMI-TPB) surfactant sensor, as well as two-phase titration used as a reference method. The quantitative titrations of a two-component mixture of the cationic homologs (a) DDAC and DOAC; and (b) BAC and DOAC showed that the new DODI-TPB surfactant sensor can clearly distinguish two separate mixture components in a single potentiometric titration curve with two characteristic inflexion points. The consumption of SDS (used as a titrant) in the end-point 1 (EP 1) corresponded to the content of DDAC (or BAC), whereas the consumption in the end-point 2 (EP 2) corresponded to the total content of both cationic surfactants in the mixture. DOAC content in both mixtures can be calculated from the difference of the titrant used to achieve EP1 and EP2. The addition of nonionic surfactants resulted in the signal change decrease from 333.2 mV (1:0; no nonionic surfactant added) to 243.0 mV (1:10, w/w). The sensor was successfully tested in ten two-component COVID-19 disinfecting formulations.

Soluplus® promotes efficient transport of meloxicam to the central nervous system via nasal administration

In our present series of experiments, we investigated the nasal applicability of the previously developed Soluplus® - meloxicam polymeric micelle formulation. Utilizing the nasal drug investigations, moderately high mucoadhesion was experienced in nasal conditions which alongside the appropriate physicochemical properties in liquid state, contributed to rapid drug absorption through human RPMI 2650 cell line. Ex vivo studies also confirmed that higher nasal mucosal permeation could be expected with the polymeric micelle nanoformulation compared to a regular MEL suspension. Also, the nanoformulation met the requirements to provide rapid drug permeation in less 1 h of our measurement. The non-toxic, non-cell barrier damaging formulation also proved to provide a successful passive transport across excides human nasal mucosa. Based on our in vivo investigations, it can be concluded that the polymeric micelle formulation provides higher meloxicam transport to the central nervous system followed by a slow and long-lasting elimination process compared to prior results where physical particle size reduction methods were applied. With these results, a promising solution and nanocarrier is proposed for the successful transport of non-steroidal anti-inflammatory drugs with acidic character to the brain.

Double Stimuli-Responsive di- and Triblock Copolymers of Poly(N-isopropylacrylamide) and Poly(1-vinylimidazole): Synthesis and Self-Assembly

For the first time, double stimuli-responsive properties of poly(N-isopropylacrylamide) (PNIPA) and poly(1-vinylimidazole) (PVIM) block copolymers in aqueous solutions were studied. The synthesis of PNIPA₆₀-b-PVIM₉₀ and PNIPA₂₈-b-PVIM₆₂-b-PNIPA₂₉ was performed using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymers were characterized by size exclusion chromatography and ¹H NMR spectroscopy. The conformational behavior of the polymers was studied using dynamic light scattering (DLS) and fluorescence spectroscopy (FS). It was found that PNIPA and block copolymers conformation and ability for self-assembly in aqueous medium below and above cloud point temperature depend on the locus of hydrophobic groups derived from the RAFT agent within the chain. Additionally, the length of PVIM block, its locus in the chain and charge perform an important role in the stabilization of macromolecular micelles and aggregates below and above cloud point temperature. At 25 °C the average hydrodynamic radius (R_h) of the block copolymer particles at pH 3 is lower than at pH 9 implying the self-assembling of macromolecules in the latter case. Cloud points of PNIPA₆₀-b-PVIM₉₀ are ~43 °C and ~37 °C at a pH of 3 and 9 and of PNIPA₂₈-b-PVIM₆₂-b-PNIPA₂₉ they are ~35 °C and 31 °C at a pH of 3 and 9. Around cloud point independently of pH, the R_h value for triblock copolymer rises sharply, achieves the maximum value, then falls and reaches the constant value, while for diblock copolymer, it steadily grows after reaching cloud point. The information about polarity of microenvironment around polymer obtained by FS accords with DLS data.

Synthesis and Biological Evaluation of Amphotericin B Formulations Based on Organic Salts and Ionic Liquids against Leishmania infantum

Nowadays, organic salts and ionic liquids (OSILs) containing active pharmaceutical ingredients (APIs) are being explored as drug delivery systems in modern therapies (OSILs-API). In that sense, this work is focused on the development of novel OSILs-API based on amphotericin B through an innovative procedure and the evaluation of the respective biological activity against Leishmania infantum. Several ammonium, methylimidazolium, pyridinium and phosphonium organic cations combined with amphotericin B as anion were synthesized in moderate to high yields and high purities by the water-reduced buffer neutralization method. All prepared compounds were characterized to confirm the desired chemical structure and the specific optical rotation ([α]_D²⁵) was also determined. The biological assays performed on L. infantum promastigotes showed increased activity against this parasitic disease when compared with the starting chloride forms and amphotericin B alone, highlighting [P_6,6,6,14][AmB] as the most promising formulation. Possible synergism in the antiprotozoal activity was also evaluated for [P_6,6,6,14][AmB], since it was proven to be the compound with the highest toxicity. This work reported a simple synthetic method, which can be applied to prepare other organic salts based on molecules containing fragile chemical groups, demonstrating the potential of these OSILs-AmB as possible agents against leishmaniasis.

Effect of 1,2-propanediol on the Critical Micelle Concentration of Decyltrimethylammonium Bromide at Temperatures from 293.15 K to 308.15 K

It is well known that polar organic compounds, such as alcohols and polyols, exert an appreciable influence on water structure and thus have important effects on surfactant micellization. These substances are often used to modify the properties of surfactants in aqueous solutions, increasing the practical applications they have in diverse industries. In this work, the critical micelle concentration (CMC) of decyltrimethylammonium bromide (C₁₀TAB) in water and in 1,2-propanediol aqueous solutions was determined from both sound velocity and surface tension measurements as a function of surfactant concentration in the temperature range of (293.15 to 308.15) K. The critical micelle concentration of the surfactant increases as the concentration of 1,2-propanediol becomes higher, while the effect on temperature does not show important changes within the range considered. At the selected temperatures, the standard thermodynamic parameters of micellization suggests that the addition of 1,2-propanediol makes the micellization process less favorable. Thermodynamic analysis suggests that the micelle formation of C₁₀TAB is an entropy-driven process at the temperatures considered in this study.

Cationic Surfactants Based on Arginine-Phenylalanine and Arginine-Tryptophan: Synthesis, Aggregation Behavior, Antimicrobial Activity, and Biodegradation

Cationic surfactants have great potential as drug vehicles and for use in gene therapy (cationic vesicles made from cationic surfactants can encapsulate RNA or DNA for cellular transfer). They can also be used as antimicrobial and antifungal agents to treat human infections. In an era of increasing antimicrobial resistance, the development of new biocompatible surfactants suitable for application as antimicrobial agents is of high interest. In this work, a library of amino acid-based surfactants was synthesized, characterized and tested for antimicrobial activity. The head group architecture (number and type of amino acids, density of cationic charge, ionic character) and the hydrophobic moiety (alkyl chain length and position of the hydrophobic group) were systematically modified, and the effect on the surfactant biological and aggregation behavior was studied. Thus, the pKa values, micellization process, antimicrobial efficiency and biodegradability were evaluated. The critical micelle concentration values of the surfactants depended on their hydrophobic character, but changes in the polar head as well as the position and length of the alkyl chain also significantly affected activity against some of the tested microorganisms. Moreover, biodegradability was closely related to the hydrophobic character of the surfactant and attachment of the alkyl chain to the polar head. The structure-activity relationships established here may open perspectives for the design of effective biodegradable antimicrobial materials that can overcome emerging resistance.

Toxicity of metal-based nanoparticles: Challenges in the nano era

With the rapid progress of nanotechnology, various nanoparticles (NPs) have been applicated in our daily life. In the field of nanotechnology, metal-based NPs are an important component of engineered NPs, including metal and metal oxide NPs, with a variety of biomedical applications. However, the unique physicochemical properties of metal-based NPs confer not only promising biological effects but also pose unexpected toxic threats to human body at the same time. For safer application of metal-based NPs in humans, we should have a comprehensive understanding of NP toxicity. In this review, we summarize our current knowledge about metal-based NPs, including the physicochemical properties affecting their toxicity, mechanisms of their toxicity, their toxicological assessment, the potential strategies to mitigate their toxicity and current status of regulatory movement on their toxicity. Hopefully, in the near future, through the convergence of related disciplines, the development of nanotoxicity research will be significantly promoted, thereby making the application of metal-based NPs in humans much safer.

Studies on the interactions of tiny amounts of common ionic surfactants with unsaturated phosphocholine lipid model membranes

In order to provide the fundamental information about the interactions of common anionic surfactants with the basic unsaturated phospholipids the influence of three cationic (dodecyltrimethylammonium bromide, DTAB; tetradecyltrimethylammonium bromide, TTAB and hexadecyltrimethylamonium bromide, CTAB) and one anionic (sodium dodecylsulfate, SDS) surfactants on the properties of the 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) layers was investigated. The studies proved that a tiny amount of the ionic surfactant added to the already synthesized liposome suspension is sufficient to change the zeta potential of the POPC and DOPC liposomes significantly. This impact increases with the surfactant concentration, the alkyl chain length of the surfactant and the degree of lipid saturation. Moreover, this effect is greater for the anionic surfactant than for the cationic one of the same alkyl chain length. The observed findings were confirmed in the course of the research carried out with the use of the corresponding Langmuir monolayers where the surface pressure - mean area isotherms, the compressibility modulus - surface pressure dependences, the monolayer penetration tests, the surface potential - mean molecular area isotherms and Brewster angle microscopy were discussed. It was found that the presence of the surfactants shifts the isotherms towards larger molecular area, to the higher extent for the SDS than DTAB. This effect increases with the increasing surfactant concentration in the subphase. Moreover, the investigated surfactants remain in the monolayer even at high surface pressure. Nevertheless, no effect on the morphology of the POPC and DOPC monolayers was detected from the BAM images. The surface potential and surface charge of the liposomes calculated on the basis of the zeta potential results reflected the interactions between the surfactant and the lipid layers.

Didecyldimethylammonium Chloride- and Polyhexamethylene Guanidine-Resistant Bacteria Isolated from Fecal Sludge and Their Potential Use in Biological Products for the Detoxification of Biocide-Contaminated Wastewater Prior to Conventional Biological Treatment

Simple Summary

Every year, more than a million tons of fecal sludge (FS) containing biocides based on quaternary ammonium compounds and guanidine derivatives, which are widely used for FS deodorization and control of microbial activity, are generated in the environmentally safe toilet complexes of Russian Railways trains. Higher disposal costs for such biocide-contaminated FS due to activated sludge toxicity increases pressure on sanitary equipment servicing companies («Ecotol Service» LLC) to more efficiently discharge FS to wastewater treatment plants. In this work, we have developed a new environmentally friendly approach to reducing the toxicity of FS, based on the use of biological products from biocide-resistant bacterial strains isolated from FS. Our approach has proven to be effective in a series of FS biodegradation experiments, biological oxygen demand tests, and a newly developed disk-diffusion bioassay.

Abstract

Toxic shock caused by the discharge of biocide-contaminated fecal sludge (FS) from chemical toilets to conventional wastewater treatment plants (WWTP) can be a major problem in activated sludge operation. It is necessary to develop new environmental approaches to mitigate the toxicity of biocides in order to avoid degrading the performance of WWTP. “Latrina”, a chemical toilet additive containing didecyldimethylammonium chloride and polyhexamethylene guanidine, is widely used in environmentally safe toilet complexes (ESTC) on Russian railway trains to deodorize FS and control microbial activity. In this work, seven biocide-resistant bacterial strains were isolated and identified from the FS of ESTC. The values of the minimum inhibitory and bactericidal concentrations of biocides for the isolated strains were 4.5–10 times higher than for the collection microorganisms. The bacterium Alcaligenes faecalis DOS7 was found to be particularly resistant to “Latrina”, the minimum inhibitory concentration of which was almost 30 times higher than recommended for ESTC. Biological products based on isolated bacterial strains proved to be effective for FS biodegradation under both aerobic and anaerobic conditions. The results of the biochemical oxygen demand test and the newly developed disk-diffusion bioassay confirmed that isolated strains contribute to reducing toxicity of biocidal agents in FS. Hyper-resistance, non-pathogenicity, and potential plant growth-promoting ability make A. faecalis DOS7 promising for use in various biological products for wastewater treatment and bioremediation of soils contaminated with biocides, as well as in agriculture to increase plant productivity.

Hybrid emulsifier systems: Alkyl imidazolium lactoside surfactants derived from natural resources

A new series of hybrid surfactants comprising an imidazolium as a cation and a disaccharide as a non-ion were synthesized, and their aggregation behavior was also investigated. The synthetic approach used alkylation as an easily accessible route on an imidazole to attempt an economic production followed by coupling with bromoethyl lactoside to form lacto-imidazolium salts surfactants. The coupled surfactants were obtained in almost quantitative yield over several steps. The surfactant surface properties in aqueous media were investigated, including critical micelle concentration (CMC), Krafft temperature, and emulsion stability were studied. The CMC measurements of the alkyl imidazolium lactoside surfactants are significantly lower than normal imidazolium surfactants, while the emulsion investigations encourage the use of alkyl imidazolium lactoside surfactants owing to stabilized assemble behavior as good as APGs.

Combatting Antibiotic Resistance Using Supramolecular Assemblies

Antibiotic resistance has posed a great threat to human health. The emergence of antibiotic resistance has always outpaced the development of new antibiotics, and the investment in the development of new antibiotics is diminishing. Supramolecular self-assembly of the conventional antibacterial agents has been proved to be a promising and versatile strategy to tackle the serious problem of antibiotic resistance. In this review, the recent development of antibacterial agents based on supramolecular self-assembly strategies will be introduced.

Customized cationic nanoemulsions loading triamcinolone acetonide for corneal neovascularization secondary to inflammatory processes

Customized cationic oil-in-water nanoemulsions (NEs) have been produced to improve the bioavailability of poorly water-soluble drugs, such as triamcinolone acetonide (TA). TA is a synthetic glucocorticoid with anti-inflammatory and antiangiogenic therapeutic properties and it is widely used as an effective treatment in ocular disorders. In this work, TA-NEs were characterized using two different custom-made cationic surfactants, showing a high positive surface charge favouring corneal penetration and a particle size below 300 nm. Both TA-NE formulations demonstrated to be stable at 4 °C during the first months of storage. Furthermore, TA-NEs were able to produce antiangiogenic effects in chicken membranes. The TA-NEs safety profile was evaluated using in vitro and in vivo ocular tolerance tests. Out of the two formulations, the one showing no irritant effects was screened in vivo demonstrating capacity to ameliorate ocular inflammation in New Zealand rabbits significantly, specially to reduce the risk of ocular inflammation processes, with antiangiogenic activity, and can therefore be exploited as a suitable formulation to avoid inflammatory reactions upon ocular surgical procedures, such as cataracts.

Supramolecular Self-Assembly of Porphyrin and Metallosurfactant as a Drug Nanocontainer Design

The combined method of treating malignant neoplasms using photodynamic therapy and chemotherapy is undoubtedly a promising and highly effective treatment method. The development and establishment of photodynamic cancer therapy is closely related to the creation of sensitizers based on porphyrins. The present study is devoted to the investigation of the spectroscopic, aggregation, and solubilization properties of the supramolecular system based on 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TSPP) and lanthanum-containing surfactant (LaSurf) in an aqueous medium. The latter is a complex of lanthanum nitrate and two cationic amphiphilic molecules of 4-aza-1-hexadecylazoniabicyclo[2.2.2]octane bromide. The mixed TSPP–LaSurf complexes can spontaneously assemble into various nanostructures capable of binding the anticancer drug cisplatin. Morphological behavior, stability, and ability to drug binding of nanostructures can be tailored by varying the molar ratio and the concentration of components. The guest binding is shown to be additional factor controlling structural rearrangements and properties of the supramolecular TSPP–LaSurf complexes.

Cationic Imidazolium Amphiphiles Bearing a Methoxyphenyl Fragment: Synthesis, Self-Assembly Behavior, and Antimicrobial Activity

Novel cationic amphiphiles of the 3-alkyl-1-(4-methoxyphenyl)-1H-imidazol-3-ium bromide series bearing methoxyphenyl fragments (MPI-n) have been synthesized. Their aggregation properties in aqueous solutions, solubilization capacity, and hemolytic and antimicrobial activities have been investigated by a number of physicochemical methods. Using tensiometry, conductometry, and fluorescence spectroscopy, it was shown that the MPI-n have lower CMCs than their nonfunctionalized counterparts. The unusual alkyl-chain-length-dependent morphology of aggregates is testified for this homological series. Amphiphiles with 12, 14, and 16 alkyl tails are characterized by the formation of micellar aggregates, while a surfactant with a decyl tail is characterized by the formation of larger aggregates with lower surface curvature. The MPI-10 aggregate morphology was rationalized in terms of the packing parameter consideration and was supported by size measurements and the fluorescence probe techniques, which showed that vesicle-like aggregates in close-packing mode probably occur. MPI-n aggregates have exhibited a high solubilization capacity toward hydrophobic azo dye Orange OT. Importantly, amphiphiles studied showed (i) high bacteriostatic activity at the level of ciprofloxacin; (ii) high bactericidal action against all Gram-positive bacteria, including methicillin-resistant strains; (iii) bactericidal properties against Gram-negative bacteria; and (iv) low hemolytic activity.

Permeability, anti-inflammatory and anti-VEGF profiles of steroidal-loaded cationic nanoemulsions in retinal pigment epithelial cells under oxidative stress

Age-related macular degeneration (AMD) is defined as a degenerative, progressive and multifactorial disorder that affects the macula with a complex etiology. The retinal pigment epithelium is a monolayer of cells that has the function to separate the surface of the choroid from the neural retina that is involved in the signal transduction leading to vision. The blood-aqueous barrier and the blood retinal barrier limit the permeation of drugs into the retina and thereby reducing their efficacy. Triamcinolone acetonide (TA) is widely used as anti-inflammatory and immunomodulatory drug that promotes the inhibition of the inflammatory processes. The factors that stimulate or inhibit angiogenesis in AMD create a local balance that is responsible for the growth of sub-retinal neovascularization. In AMD, the main angiogenic stimulus is the vascular endothelial growth factor (VEGF). In this work, nanoemulsions with cationic surfactants (mono- and dicationic DABCO and quinuclidine) were produced to deliver TA, and were found to reduce the production of tumor necrosis factor alpha (TNF-α), which stimulates the choroidal neovascularization development by upregulating the VEGF production, and consequently decreased the VEGF levels. Our results support the potential use of mono- and dicationic DABCO and quinuclidine-based cationic nanoemulsions for the delivery of TA in the treatment of AMD.

Gemini and Bicephalous Surfactants: A Review on Their Synthesis, Micelle Formation, and Uses

The use of surfactants in polymerization reactions is particularly important, mainly in emulsion polymerizations. Further, micelles from biocompatible surfactants find use in pharmaceutical dosage forms. This paper reviews recent developments in the synthesis of novel gemini and bicephalous surfactants, micelle formation, and their applications in polymer and nanoparticle synthesis, oil recovery, catalysis, corrosion, protein binding, and biomedical area, particularly in drug delivery.

Development and Characterization of Nanoemulsions for Ophthalmic Applications: Role of Cationic Surfactants

The eye is a very complex organ comprising several physiological and physical barriers that compromise drug absorption into deeper layers. Nanoemulsions are promising delivery systems to be used in ocular drug delivery due to their innumerous advantages, such as high retention time onto the site of application and the modified release profile of loaded drugs, thereby contributing to increasing the bioavailability of drugs for the treatment of eye diseases, in particular those affecting the posterior segment. In this review, we address the main factors that govern the development of a suitable nanoemulsion formulation for eye administration to increase the patient’s compliance to the treatment. Appropriate lipid composition and type of surfactants (with a special emphasis on cationic compounds) are discussed, together with manufacturing techniques and characterization methods that are instrumental for the development of appropriate ophthalmic nanoemulsions.

Antimicrobial Properties and Cytotoxic Effect of Imidazolium Geminis with Tunable Hydrophobicity

Antimicrobial, membranotropic and cytotoxic properties of dicationic imidazolium surfactants of n-s-n (Im) series with variable length of alkyl group (n = 8, 10, 12, 14, 16) and spacer fragment (s = 2, 3, 4) were explored and compared with monocationic analogues. Their activity against a representative range of Gram-positive and Gram-negative bacteria, and also fungi, is characterized. The relationship between the biological activity and the structural features of these compounds is revealed, with the hydrophobicity emphasized as a key factor. Among dicationic surfactants, decyl derivatives showed highest antimicrobial effect, while for monocationic analogues, the maximum activity is observed in the case of tetradecyl tail. The leading compounds are 2–4 times higher in activity compared to reference antibiotics and prove effective against resistant strains. It has been shown that the antimicrobial effect is not associated with the destruction of the cell membrane, but is due to specific interactions of surfactants and cell components. Importantly, they show strong selectivity for microorganism cells while being of low harm to healthy human cells, with a SI ranging from 30 to 100.

Self-Assembling Drug Formulations with Tunable Permeability and Biodegradability

This review focuses on key topics in the field of drug delivery related to the design of nanocarriers answering the biomedicine criteria, including biocompatibility, biodegradability, low toxicity, and the ability to overcome biological barriers. For these reasons, much attention is paid to the amphiphile-based carriers composed of natural building blocks, lipids, and their structural analogues and synthetic surfactants that are capable of self-assembly with the formation of a variety of supramolecular aggregates. The latter are dynamic structures that can be used as nanocontainers for hydrophobic drugs to increase their solubility and bioavailability. In this section, biodegradable cationic surfactants bearing cleavable fragments are discussed, with ester- and carbamate-containing analogs, as well as amino acid derivatives received special attention. Drug delivery through the biological barriers is a challenging task, which is highlighted by the example of transdermal method of drug administration. In this paper, nonionic surfactants are primarily discussed, including their application for the fabrication of nanocarriers, their surfactant-skin interactions, the mechanisms of modulating their permeability, and the factors controlling drug encapsulation, release, and targeted delivery. Different types of nanocarriers are covered, including niosomes, transfersomes, invasomes and chitosomes, with their morphological specificity, beneficial characteristics and limitations discussed.

Mono- and Dicationic DABCO/Quinuclidine Composed Nanomaterials for the Loading of Steroidal Drug: 32 Factorial Design and Physicochemical Characterization

Oil-in-water nanoemulsions (NEs) are considered a suitable nanotechnological approach to improve the eye-related bioavailability of lipophilic drugs. The potential of cationic NEs is prominent due to the electrostatic interaction that occurs between the positively charged droplets with the negatively charged mucins present in the tear film. This interaction offers prolonged NEs residence at the ocular surface, increasing the drug absorption. Triamcinolone acetonide (TA) is one of the first pharmacologic strategies applied as an intravitreal injection in the treatment of age-related macular degeneration (AMD). Newly synthesized quaternary derivatives of 1,4-diazabicyclo[2.2.2]octane (DABCO) and quinuclidine surfactants have been screened with the purpose to select the best compound to formulate long-term stable NEs that combine the best physicochemical properties for the loading of TA intended for ocular administration.

DABCO-Customized Nanoemulsions: Characterization, Cell Viability and Genotoxicity in Retinal Pigmented Epithelium and Microglia Cells

Quaternary derivatives of 1,4-diazabicyclo[2.2.2]octane (DABCO) and of quinuclidine surfactants were used to develop oil-in-water nanoemulsions with the purpose of selecting the best long-term stable nanoemulsion for the ocular administration of triamcinolone acetonide (TA). The combination of the best physicochemical properties (i.e., mean droplet size, polydispersity index, zeta potential, osmolality, viscoelastic properties, surface tension) was considered, together with the cell viability assays in ARPE-19 and HMC3 cell lines. Surfactants with cationic properties have been used to tailor the nanoemulsions’ surface for site-specific delivery of drugs to the ocular structure for the delivery of TA. They are tailored for the eye because they have cationic properties that interact with the anionic surface of the eye.

Analysis of surfactants by mass spectrometry: Coming to grips with their diversity

Surfactants are surface-active agents widely used in numerous applications in our daily lives as personal care products, domestic, and industrial detergents. To determine complex mixtures of surfactants and their degradation products, unselective and rather insensitive methods, based on colorimetric and complexometric analyses are no longer employable. Analytical methodologies able to determine low concentration levels of surfactants and closely related compounds in complex matrices are required. The recent introduction of robust, sensitive, and selective mass spectrometry (MS) techniques has led to the rapid expansion of the surfactant research field including complex mixtures of isomers, oligomers, and homologues of surfactants as well as their chemically and biodegradation products at trace levels. In this review, emphasis is given to the state-of-the-art MS-based analysis of surfactants and their degradation products with an overview of the current research landscape from traditional methods involving hyphenate techniques (gas chromatography-MS and liquid chromatography-MS) to the most innovative approaches, based on high-resolution MS. Finally, we outline a detailed explanation on the utilization of MS for mechanistic purposes, such as the study of micelle formation in different solvents.

Contrasting effect of 1-butanol and 1,4-butanediol on the triggered micellar self-assemblies of C16-type cationic surfactants

The self-assembly in aqueous solutions of three quaternary salt-based C₁₆-type cationic surfactants with different polar head groups and identical carbon alkyl chain viz., cetylpyridinium bromide (CPB), cetyltrimethylammonium tosylate (CTAT), and cetyltriphenylphosphonium bromide (CTPPB) in the presence of 1-butanol (BuOH) and 1,4-butanediol (BTD) was investigated using tensiometry, 2D-nuclear Overhauser enhancement spectroscopy (2D-NOESY) and small angle neutron scattering (SANS) techniques. The adsorption parameters and micellar characteristics evaluated at 303.15 K distinctly showed that BuOH promotes the mixed micelle formation while BTD interfered with the micellization phenomenon. The SANS data fitted using an ellipsoid (as derived by Hayter and Penfold using the Ornstein-Zernike equation and the mean spherical approximation) and wormlike micellar models offered an insight into the micelle size/shape and aggregation number (N_agg) in the examined systems. The evaluated descriptors presented a clear indication of the morphology transition in cationic micelles as induced by the addition of the two alcohols. We also offer an investigation into the acceptable molecular interactions governing the differences in micelle morphologies, using the non-invasive 2D-NOESY technique and molecular modeling. The experimental observations elucidated from computational simulation add novelty to this work. Giving an account to the structural complexity in the three cationic surfactants, the molecular dynamics (MD) simulation was performed for CPB micelles in an aqueous solution of alcohols that highlighted the micelle solvation and structural transition, which is further complemented in terms of critical packing parameter (PP) for the examined systems.