Aggregation and reactivity in aqueous solutions of cationic surfactants and aromatic anions across concentration scales

The SARS-CoV2 envelope differs from host cells, exposes procoagulant lipids, and is disrupted in vivo by oral rinses

The lipid envelope of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an essential component of the virus; however, its molecular composition is undetermined. Addressing this knowledge gap could support the design of antiviral agents as well as further our understanding of viral-host protein interactions, infectivity, pathogenicity, and innate immune system clearance. Lipidomics revealed that the virus envelope comprised mainly phospholipids (PLs), with some cholesterol and sphingolipids, and with cholesterol/phospholipid ratio similar to lysosomes. Unlike cellular membranes, procoagulant amino-PLs were present on the external side of the viral envelope at levels exceeding those on activated platelets. Accordingly, virions directly promoted blood coagulation. To investigate whether these differences could enable selective targeting of the viral envelope in vivo, we tested whether oral rinses containing lipid-disrupting chemicals could reduce infectivity. Products containing PL-disrupting surfactants (such as cetylpyridinium chloride) met European virucidal standards in vitro; however, components that altered the critical micelle concentration reduced efficacy, and products containing essential oils, povidone-iodine, or chlorhexidine were ineffective. This result was recapitulated in vivo, where a 30-s oral rinse with cetylpyridinium chloride mouthwash eliminated live virus in the oral cavity of patients with coronavirus disease 19 for at least 1 h, whereas povidone-iodine and saline mouthwashes were ineffective. We conclude that the SARS-CoV-2 lipid envelope i) is distinct from the host plasma membrane, which may enable design of selective antiviral approaches; ii) contains exposed phosphatidylethanolamine and phosphatidylserine, which may influence thrombosis, pathogenicity, and inflammation; and iii) can be selectively targeted in vivo by specific oral rinses.

Acid Hydrotropic Fractionation of Lignocelluloses for Sustainable Biorefinery: Advantages, Opportunities, and Research Needs

This Minireview provides a comprehensive discussion on the potential of using acid hydrotropes for sustainably fractionating lignocelluloses for biorefinery applications. Acid hydrotropes are a class of acids that have hydrotrope properties toward lignin, which helps to solubilize lignin in aqueous systems. With the capability of cleaving ether and ester bonds and even lignin-carbohydrate complex (LCC) linkages, these acid hydrotropes can therefore isolate lignin embedded in the plant biomass cell wall and subsequently solubilize the isolated lignin in aqueous systems. Performances of two acid hydrotropes, that is, an aromatic sulfonic acid [p-toluenesulfonic acid (p-TsOH)] and a dicarboxylic acid [maleic acid (MA)], in terms of delignification and dissolution of hemicelluloses, and reducing lignin condensation, were evaluated and compared. The advantages of lignin esterification by MA for producing cellulosic sugars through enzymatic hydrolysis and lignin-containing cellulose nanofibrils (LCNFs) through mechanical fibrillation from the fractionated water insoluble solids (WIS), and for obtaining less condensed lignin with light color, were demonstrated. The excellent enzymatic digestibility of maleic acid hydrotropic fractionation WISs was also demonstrated by comparing with WISs from other fractionation processes. The recyclability and reusability of acid hydrotropes were also reviewed. Finally, perspectives on future research needs to address key technical issues for commercialization were also provided.

Strong influence of surfactants on virgin hydrophobic microplastics adsorbing ionic organic pollutants

Microplastic (MP) pollution has become an area of increasing concern because MPs accumulate various types of pollutants. Many previous studies have explored the interactions between MPs and hydrophobic pollutants. However, little research has been conducted on hydrophilic pollutants, which are of much higher concentration and ubiquitous in environment. Surfactants cause hydrophobic MPs to become hydrophilic, which may significantly enhance their capacities to adsorb hydrophilic pollutants. This study explored the influence of co-existing surfactants on the adsorption of ionic organic pollutants by MPs, and found that the presence of an ionic surfactant could significantly enhance the capacity of polyvinyl chloride (PVC, 0.2 mm) MPs to adsorb pollutants with opposite charges. The Langmuir methylene blue adsorption capacity of PVC could be increased from 172 to 4417 ppm in the presence of a sodium dodecyl benzene sulfonate surfactant. Nonionic surfactants impeded the adsorption of both cationic and anionic pollutants due to the steric resistance of the hydrophilic polyethelene glycol chains. The electrostatic interaction mechanism dominated the interfacial behaviors of ionic pollutants on surfactant-adsorbed MP interfaces. The effects of the surfactants were further verified using four different model pollutants and six surfactants. The adsorption capacities of real environmental MPs, including PVC, polyethylene (PE), polypropylene (PP), and polystyrene (PS), increased by three to twenty-six times. The adsorption properties of MPs may be determined by the presence of co-existing surfactants, rather than their polymer species or additives.

Effect of ethylene glycol and its derivatives on the aggregation properties of reactive Orange 13 dye aqueous solution

The aggregation behavior of dyes especially in the dyeing and printing of different textile materials is an important phenomenon which affects the process of dye adsorption and diffusion. In order to avoid the aggregation of dyes, scientists are looking for materials which can inhibit the aggregation process by fabricating the dye solution. Organic solvents have found important influence in the aggregation of dye molecules. Therefore, herein, we report the fabrication of reactive orange 13 dye solutions with the aid of ethylene glycol and its derivative organic solvents to investigate the aggregation behavior of dye molecules by UV-vis absorption spectrum, fluorescence spectrum, surface tension, rheological and particle size measurements. IR spectra were performed to understand the effect of hydrogen bonding on the aggregation behavior of dye molecules. Moreover, transmission electron microscopy was also tested to confirm the effect of organic solvents on the surface morphology of dye molecules. The results show that the reactive Orange 13 dye molecules show aggregation in terms of dimeric and multimeric structures at high dye concentrations due to π–π interaction of naphthalene rings. Moreover, on introducing the ethylene glycol and its derivatives, the dye molecules disaggregate by hydrophobic interactions of dye molecules and organic solvents which destroyed the ice-like structure between the dye molecules and the water molecules. Among the three organic solvents, DME solvent caused more disaggregation of reactive Orange 13 dye molecules due to extra hydrophobic methyl groups in its structure. The results also show that the interaction between Orange 13 dyes and ethylene glycol and its derivatives could decrease the surface tension and particle size of the dye, and increase the quantum yield and viscosity. This research will help to understand the aggregation behavior of dyes and help the textile industries to choose the suitable formulations of dye solutions for coloration of different textile substrates via dyeing and printing methods.

The interaction between Orange 13 dye and ethylene glycol and its derivatives was determined by the dispersion force.

Self-Assembled Quaternary Ammonium-Containing Comb-Like Polyelectrolytes for the Hydrolysis of Organophosphorous Esters: Effect of Head Groups and Counter-Ions

The aim of this work was to increase the efficiency of catalytic systems for the hydrolytic cleavage of 4-nitrophenyl esters of phosphonic acids. Quaternary ammonium-containing comb-like polyelectrolytes («polymerized micelles») with ester cleavable fragments and a low aggregation threshold were used as catalysts. The synthesis of poly(11-acryloyloxyundecylammonium) surfactants with different counterions (Br^- , NO₃ ^- , CH₃ C₆ H₄ SO₃ ^- ) and head groups was realized by micellar free-radical polymerization. Molecular weight, critical association concentration, particle sizes and solubilization properties toward Orange OT were determined. Self-assemblies organized by poly(11-acryloyloxyundecyltrimethyl ammonium) bromide successfully catalyze the hydrolysis of 4-nitrophenyl butylchloromethylphosphonate up to two orders of magnitude compared to aqueous alkaline hydrolysis. The development of these catalysts is promising for industrial applications and organophosphorus compound detoxification.

Surfactant stealth effect of microplastics in traditional coagulation process observed via 3-D fluorescence imaging

Microplastics (MPs) have aroused rising social concerns. Although amounts of surfactants exist in wastewater and are expected to alter the surface properties of MPs significantly as they are designed to be adsorbed by hydrophobic particles. However, rare works have been done on the influence of surfactants on the coagulation removal process of MPs which was thought to be an effective way to remove MPs together with other natural particles, such as clay. We used 3-D fluorescence imaging to track the coagulation removal process of polystyrene MPs. Our results indicate that nonionic surfactant, tween 20 in ppm scale, could inhibit the coagulation removal of polystyrene MPs significantly. Residue MPs in the effluent is proportional with the surfactant concentration and increases up to tens of times, which will lead to a dramatic increase in their potential environmental risks. Apparent size effect exists in the coagulation in which smaller MPs can escape from the coagulation removal more easily. Mechanism study suggests that the steric resistance of the hydrophilic flexible polyethylene glycol (PEG) layer formed by tween 20 adsorbed on MP surface inhibits clay deposition and thus hinders subsequent agglomeration and precipitation. A surfactant stealth effect, which is used in the design of nanomedicine to avoid the human immune recognition and clearance of nano-drugs from blood circulation, also exists in the coagulation removal process of MPs. Our finding not only proves the strong influence of surfactants on MPs but also will stimulate related studies on other latent surfactant effects of MPs.

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

The development of biotechnological protocols based on cationic surfactants is a modern trend focusing on the fabrication of antimicrobial and bioimaging agents, supramolecular catalysts, stabilizers of nanoparticles, and especially drug and gene nanocarriers. The main emphasis given to the design of novel ecologically friendly and biocompatible cationic surfactants makes it possible to avoid the drawbacks of nanoformulations preventing their entry to clinical trials. To solve the problem of toxicity various ways are proposed, including the use of mixed composition with nontoxic nonionic surfactants and/or hydrotropic agents, design of amphiphilic compounds bearing natural or cleavable fragments. Essential advantages of cationic surfactants are the structural diversity of their head groups allowing of chemical modification and introduction of desirable moiety to answer the green chemistry criteria. The latter can be exemplified by the design of novel families of ecological friendly cleavable surfactants, with improved biodegradability, amphiphiles with natural fragments, and geminis with low aggregation threshold. Importantly, the development of amphiphilic nanocarriers for drug delivery allows understanding the correlation between the chemical structure of surfactants, their aggregation behavior, and their functional activity. This review focuses on several aspects related to the synthesis of innovative cationic surfactants and their broad biological applications including antimicrobial activity, solubilization of hydrophobic drugs, complexation with DNA, and catalytic effect toward important biochemical reaction.