Surfactant self-assembly structures and multilayer formation at the solid-solution interface induces by electrolyte, polymers and proteins

Protecting monoclonal antibodies via competitive interfacial adsorption of nonionic surfactants

HYPOTHESIS

Bioengineered monoclonal antibodies (mAbs) have gained significant recognition as medical therapies. However, during processing, storage and use, mAbs are susceptible to interfacial adsorption and desorption, leading to structural deformation and aggregation, and undermining their bioactivity. To suppress antibody surface adsorption, nonionic surfactants are commonly used in formulation. But how surface hydrophobicity affects the adsorption and desorption of mAbs and nonionic surfactants individually and as a mixture remains inconclusive.

EXPERIMENTS

The rapid tuning of the siliconized surface from hydrophobic to hydrophilic was controlled by the UV oxidation time of a self-assembled trimethoxy(7-octen-1-yl)silane (TMOS) monolayer. Spectroscopic ellipsometry and neutron reflection were used to determine the dynamic adsorption and structural changes of the co-adsorbed mAb (COE-3) and the commercial nonionic surfactant PS80, which is composed primarily of polyoxyethylene-sorbitan monooleate with an average molecular weight of about 1310 g/mol.

FINDINGS

COE-3 adsorption on both TMOS or UV-TMOS surface was irreversible. However, nonionic surfactant PS80 could partially remove pre-adsorbed COE-3 from these surfaces, forming a co-adsorption layer. Interestingly, while the hydrophobic TMOS surface prevented mAb adsorption when pre-treated with PS80, the amphiphilic UV-TMOS did not. Furthermore, when COE-3 and PS80 were injected as a mixture, PS80 formed a preventative layer on both surfaces against COE-3 adsorption. These results highlight the significance of surface hydrophobicity in controlling mAb adsorption in the presence of nonionic surfactants.

Functional surfactant-directing ultrathin metallic nanoarchitectures as high-performance electrocatalysts

Ultrathin nanosheets possess a distinctive structure characterized by an abundance of active sites fully accessible on their surface. Concurrently, their nanoscale thickness confers an extraordinarily high specific surface area and promising electronic properties. To date, numerous strategies have been devised for synthesizing precious metal nanosheets that exhibit excellent electrocatalytic performance. In this paper, recent progress in the controlled synthesis of two-dimensional, ultrathin nanosheets by a self-assembly mechanism using functional surfactants is reviewed. The aim is to highlight the key role of functional surfactants in the assembly and synthesis of two-dimensional ultrathin nanosheets, as well as to discuss in depth how to enhance their electrochemical properties, thereby expanding their potential applications in catalysis. We provide a detailed exploration of the mechanisms employed by several long-carbon chain surfactants commonly used in the synthesis of nanosheets. These surfactants exhibit robust electrostatic and hydrophobic effects, effectively confining the crystalline growth of metals along lamellar micelles. Moreover, we present an overview of the electrocatalytic performance demonstrated by the ultrathin nanosheets synthesized through this innovative pathway. Furthermore, it offers valuable insights that may pave the way for further exploration of more functional long-chain surfactants, leading to the synthesis of ultrathin nanosheets with significantly enhanced electrocatalytic performance.

Thermodynamic Analysis of Silk Fibroin-Graphite Hybrid Materials and Their Morphology

Silk fibroin (SF) is a β-sheet-rich protein that is responsible for the remarkable tensile strength of silk. In addition to its mechanical properties, SF is biocompatible and biodegradable, making it an attractive candidate for use in biotic/abiotic hybrid materials. A pairing of particular interest is the use of SF with graphene-based nanomaterials (GBNs). The properties of this interface drive the formation of well-ordered nanostructures and can improve the electronic properties of the resulting hybrid. It was previously demonstrated that SF can form lamellar nanostructures in the presence of graphite; however, the equilibrium morphology and associated driving interactions are not fully understood. In this study, we characterize these interactions between SF and SF lamellar with graphite using molecular dynamics (MD) simulations and umbrella sampling (US). We find that SF lamellar nanostructures have strong orientational and spatial preferences on graphite that are driven by the hydrophobic effect, destabilizing solvent-protein interactions and stabilizing protein-protein and protein-graphite interactions. Finally, we show how careful consideration of these underlying interactions can be applied to rationally modify the nanostructure morphology.

Promoting the adsorption of saponins at the hydrophilic solid-aqueous solution interface by the coadsorption with cationic surfactants

HYPOTHESIS

Saponins are highly surface active glycosides, and are extensively used to stabilise emulsions and foams in beverages, foods, and cosmetics. Derived from a variety of plant species these naturally occurring biosurfactants have wider potential for inclusion in many low carbon and or sustainably sourced products. Although their adsorption at the air-solution and liquid-liquid interfaces has been extensively studied, the nature of their adsorption at solid surfaces is much less clear. The aim of this study was to establish the criteria for and nature of the adsorption of saponins at both hydrophilic and hydrophobic solid surfaces.

EXPERIMENTS

Adsorption at the hydrophilic and hydrophobic solid surfaces was investigated using neutron reflectivity. Measurements were made for the saponins escin, quillaja and glycyrrhizic acid. At the hydrophilic surface measurements were also made for escin / cetyltrimethyl ammonium bromide, C16TAB, mixtures; using deuterium labelling to determine the surface structure and composition.

FINDINGS

At a range of solution concentrations, from below to well in excess of the critical micelle concentration, cmc, there was no saponin adsorption evident at either the hydrophilic or hydrophobic surface. This implies an inherent incompatibility between the surface OH- groups at the hydrophilic surface and the saponin sugar groups, and a reluctance for the hydrophobic triterpenoid group of the saponin to interact with the octadecyltrichlorosilane, OTS, hydrophobic solid surface. Above a critical composition or concentration escin / C16TAB mixtures adsorb at the hydrophilic solid surface; with a surface composition which is dominated by the escin, and a structure which reflects the disparity in the molecular arrangement of the two surfactant components. The results provide an important insight into how cooperative adsorption can be utilised to promote adsorption of saponins at the solid- solution interface.

Strong Synergistic Molecular Interaction in Catanionic Surfactant Mixtures: Unravelling the Role of the Benzene Ring

Noncovalent interactions play a crucial role in driving the formation of diverse self-assembled structures in surfactant systems. Surfactants containing a benzene ring structure are an important subset of surfactants. These surfactants exhibit unique colloid and interfacial properties, which give rise to fascinating transformations in the aggregate structures. These transformations are directly influenced by specific noncovalent interactions facilitated by the benzene ring structure including cation-π and π-π interactions. Investigating catanionic surfactant systems that incorporate benzene ring structures provides valuable insights into the distinct noncovalent interactions observed in mixed surfactant systems. Our approach involved studying the enthalpy change ΔH during the titration process, utilizing isothermal titration calorimetry (ITC). Simultaneously, we employed cryogenic transmission electron microscopy (cryo-TEM) to observe the corresponding self-assembly structures. To gain further insight, we delved into the noncovalent interactions of the mixed systems by analyzing the molecular environments variations through chemical shifts of the aggregates using proton magnetic resonance (1H NMR). The intermolecular interaction was also confirmed by the two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). We conducted a systematic study of the effects of NaCl concentrations, molar ratios, and molecular structures of surfactants on aggregate structures. The existence forms of surfactants are closely linked to the shape of the titration curve and the transition of the aggregate structures. When cationic surfactants were titrated into sodium dodecylbenzenesulfonate (SDBS) micelle solutions, the dominant cation-π interaction leads to the direct formation of vesicle structures. Conversely, when the SDBS system is titrated into benzyldimethyldodecylammonium chloride (DDBAC) micelles, a delicate balance of multiple noncovalent interactions, including cation-π, π-π, hydrophobic, and electrostatic forces, results in a range of aggregate structure transformations such as worm-like micelles and vesicular structures.

Role of Polyanions and Surfactant Head Group in the Formation of Polymer-Colloid Nanocontainers

OBJECTIVES

This study was aimed at the investigation of the supramolecular systems based on cationic surfactants bearing cyclic head groups (imidazolium and pyrrolidinium) and polyanions (polyacrylic acid (PAA) and human serum albumin (HSA)), and factors governing their structural behavior to create functional nanosystems with controlled properties. Research hypothesis. Mixed PE-surfactant complexes based on oppositely charged species are characterized by multifactor behavior strongly affected by the nature of both components. It was expected that the transition from a single surfactant solution to an admixture with PE might provide synergetic effects on structural characteristics and functional activity. To test this assumption, the concentration thresholds of aggregation, dimensional and charge characteristics, and solubilization capacity of amphiphiles in the presence of PEs have been determined by tensiometry, fluorescence and UV-visible spectroscopy, and dynamic and electrophoretic light scattering.

RESULTS

The formation of mixed surfactant-PAA aggregates with a hydrodynamic diameter of 100-180 nm has been shown. Polyanion additives led to a decrease in the critical micelle concentration of surfactants by two orders of magnitude (from 1 mM to 0.01 mM). A gradual increase in the zeta potential of HAS-surfactant systems from negative to positive value indicates that the electrostatic mechanism contributes to the binding of components. Additionally, 3D and conventional fluorescence spectroscopy showed that imidazolium surfactant had little effect on HSA conformation, and component binding occurs due to hydrogen bonding and Van der Waals interactions through the tryptophan amino acid residue of the protein. Surfactant-polyanion nanostructures improve the solubility of lipophilic medicines such as Warfarin, Amphotericin B, and Meloxicam.

PERSPECTIVES

Surfactant-PE composition demonstrated beneficial solubilization activity and can be recommended for the construction of nanocontainers for hydrophobic drugs, with their efficacy tuned by the variation in surfactant head group and the nature of polyanions.

Tuning Properties of Polyelectrolyte-Surfactant Associates in Two-Phase Microfluidic Flows

This work focuses on identifying and prioritizing factors that allow control of the properties of polyelectrolyte-surfactant complexes in two-phase microfluidic confinement and provide advantages over synthesis of such complexes in macroscopic conditions. We characterize the impact of polymer and surfactant aqueous flow conditions on the formation of microscale droplets and fluid threads in the presence of an immiscible organic solvent. We perform an experimental and selected numerical analysis of fast supramolecular reactions in droplets and threads. The work offers a quantitative control over properties of polyelectrolyte-surfactant complexes produced in two-phase confinement by varying capillary numbers and the ratio of aqueous and organic flowrates. We propose a combined thread-droplet mode to synthesize polyelectrolyte-surfactant complexes. This mode allows the production of complexes in a broader size range of R ≈ 70-200 nm, as compared with synthesis in macroscopic conditions and the respective sizes R ≈ 100-120 nm. Due to a minimized impact of undesirable post-chip reactions and ordered microfluidic confinement conditions, the dispersity of microfluidic aggregates (PDI = 0.2-0.25) is lower than that of their analogs synthesized in bulk (PDI = 0.3-0.4). The proposed approach can be used for tailored synthesis of target drug delivery polyelectrolyte-surfactant systems in lab-on-chip devices for biomedical applications.