Studies of plant proteins and their solutions become increasingly important due to the growing demand for the replacement of the proteins of animal origin in cosmetic, medical and food industries. At the same time, the information on the relationship between the structure of plant proteins and their functional properties at liquid interfaces is rather scarce. This study considers the influence of the intrinsic flexibility of four plant globulins 7S, 8S, 11S and 12S from legumes and oat on the dynamic surface properties of their solutions. The dilatational surface rheology and ellipsometry allowed identification of the key differences between the dynamic properties of the adsorption layers of plant proteins, while the calculations using IUPred3 predictor gave a possibility to determine the distribution of flexible intrinsically disordered regions in protein chains. It was found that the 7S, 8S, and 12S proteins subunits have only short flexible regions with less than 20 amino acid residues on average, and they almost do not influence the properties of the layers at the liquid-gas interface. As a result, the kinetic dependencies of the dynamic surface elasticity are monotonic and its steady-state values vary in the range of 40 - 55 mN/m depending on the protein. In contrast, 11S globulin from chickpea has a long, intrinsically disordered region, over 50 amino acid residues, that can be displaced from the interface in the form of loops to form a distal region of the surface layer. The exchange of the segments between the proximal and distal regions of the surface layer in the course of the surface compression/expansion leads to non-monotonic dependences of the dynamic surface elasticity on the surface age and surface pressure with the values corresponding to a local maximum and steady-state of 32 mN/m and 19 mN/m, respectively.

The dynamic properties of spread and adsorbed layers of amyloid-like silk fibroin fibrils (ALF) differ significantly from the properties of native protein layers (RSF). In the former case, the dynamic dilational surface elasticity and the steady-state adsorbed amount are considerably lower than in the latter case. This high dynamic elasticity of RSF layers is close to that of the layers of solid nanoparticles and is provided by the spontaneous formation of various interconnected supramolecular structures at the interface. The ALF produced at elevated temperatures is also intertwined at the interface but does not form a continuous network. In this case, the layer properties are close to those of the layers of amyloid fibrils of globular proteins. If the ALF dispersion is purified from admixtures of unreacted protein molecules, the dynamic surface elasticity reaches about 140 mN/m, similar to the results for dispersions of amyloid fibrils of globular proteins. The admixtures of unreacted protein molecules of high surface activity significantly influence the dynamic surface properties participating in the self-assembly, thereby leading to a slight increase in the surface elasticity. At the same time, the ALF acts as an effective inhibitor of the formation of supramolecular structures in the surface layer for mixed systems. Under the influence of amyloid fibrils, neither the impurities nor the addition of native RSF lead to mechanical surface properties close to those of native fibroin systems.

This study presents a novel approach to composite membranes production. Our membranes are based on polysulfone matrix and filled with inorganic hydroxyapatite nanoparticles (HAp NPs) as new green pore-forming agent. A non-classical HAp growth mechanism - oriented attachment (OA) - was utilized for the NPs' size control. The rod-shaped HAp NPs were investigated using XRD, WPPM, FTIR and TEM analyses complemented by quantum-chemical calculations to estimate the role of inorganic ion regulators in surface blocking and coalescence course. The HAp nanofillers with different sizes and aspect ratios were incorporated into polysulfone membranes, with structural and morphological characterization via XRD, ATR-FTIR, SEM and AFM methods. Filler size dictated the morphology of obtained defect-free membranes: larger filler increased surface roughness, while smaller HAp sample induced irregular pore formation. Ultrafiltration performance of composite membranes was evaluated using water and model protein solution with comparison to polyethylene glycol 2000 plasticized blank membrane. HAp-modified membranes exhibited a substantial increase in pure water flux versus blanks, while protein flux rose moderately, indicating enhanced desirable protein retention. It was established that the use of HAp nanofillers of different sizes allows to control the transport properties of ultrafiltration membranes and achieve greater separation efficiency during the purification of protein medium. Post-treatment revealed a decline in water flux recovery compared to blanks, attributed to temporary binding of BSA to HAp surface highlighting the need for optimized membrane washing protocols. These outcomes demonstrate great prospects of OA-synthesized HAp nanofillers to tailor polysulfone membranes for biomedical and food-industry applications.

The formation of mixed adsorption layers of amyloid fibrils of a plant protein, oat globulin (OG), and a strong polyelectrolyte, sodium polystyrene sulfonate (PSS), at the liquid–gas interface was studied by measurements of the kinetic dependencies of surface tension, dynamic surface elasticity, and ellipsometric angle. The micromorphology of the layers was determined by atomic force microscopy. A strong increase in the surface elasticity was discovered when both components had similar concentrations and formed a network of threadlike aggregates at the interface, thereby explaining the high foam stability in this concentration range. The sequential adsorption of PSS and OG resulted in the formation of thick mixed multilayers and the surface elasticity increased with the number of duplex layers.

Although the formation of the layers of fibrillar aggregates at liquid–liquid and liquid–gas interfaces can significantly increase the stability of disperse systems, like foams and emulsions, any information on their structure and properties is rather limited. In the present work, surface properties of the adsorption layers of fibrils of intrinsically disordered β-casein are investigated. For unpurified dispersions of the fibrils of this protein, the dynamic surface elasticity proved to be close to the values for the native protein solutions. This behavior is typical for dispersions of fibrils of globular proteins. However, previously studied fibrils of another intrinsically disordered protein, κ-casein, do not demonstrate this similarity. The contribution of β-casein fibrils to the dynamic surface properties becomes noticeable only after the purification of the dispersions from impurities of high surface activity. The dynamic surface elasticity increases up to 48 mN/m after two purification cycles, i.e., to values 4 times higher than the steady-state values of native protein adsorption layers at the same protein bulk concentrations.

Dynamic surface properties of the dispersions of a plant protein, oat globulin, were determined in a broad concentration range. The dilational dynamic surface elasticity of the dispersions exceeded significantly the values for native protein solutions indicating that fibrils can effectively stabilize multiphase disperse systems; thus, they can find various applications in the production of new materials.

Silk fibroin (SF)-based materials attract significant interest because of their biocompability and great diversity of possible morphologies. One of the approaches to obtain SF materials is the use of an air-water or oil-water interface as a template for protein self-assembly. Surfactants can change the surface properties of adsorbed SF layers by promoting or preventing the formation of SF fiber networks. This study focuses on the influence of two typical ionic surfactants, cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS), on the dynamic properties of SF layers adsorbed at the air-water interface. The dynamic surface elasticity, surface tension, ellipsometric angle Δ, and the film thickness were measured as a function of the surface age and surfactant concentration. The morphology of the layers was evaluated by atomic force microscopy (AFM). For the adsorption layers of globular proteins, the main effect of the surfactants consists in the protein unfolding at high concentrations and in a decrease in the electrostatic adsorption barrier. In the case of SF layers, CTAB and SDS strongly influence the protein aggregation at the air-water interface. Regardless of the sign of the surfactant charge, its addition to SF solutions results in a decrease in the surface elasticity and the destruction of the ordered structure of protein fibers at concentrations higher than 1 × 10-4 M. With the further increase in the surfactant concentration, the thread-like aggregates disappear, the packing of thin fibers becomes less tight, a uniform layer disintegrates into separate islands, and finally, the protein is displaced from the interface.

Materials formed with a base of silk fibroin (SF) are successfully used in tissue engineering since their properties are similar to those of natural extracellular matrixes. Mixing SF with different polymers, for example, polyethylene oxide (PEO) and polyvinylpyrrolidone (PVP), allows the production of fibers, hydrogels, and films and their morphology to be controlled. The impact of PEO and PVP on formation and structure of SF adsorption layers was studied at different was studied at different polymer concentrations (from 0.002 to 0.5 mg/mL) and surface lifetimes. The protein concentration was fixed at 0.02 and 0.2 mg/mL. These concentrations are characterized by different types of spontaneously formed structures at the air-water interface. Since both synthetic polymers possess surface activity, they can penetrate the fibroin adsorption layer, leading to a decrease in the dynamic surface elasticity at almost constant surface tension and a decrease in ellipsometric angle Δ and adsorption layer thickness. As shown by AFM, the presence of polymers increases the porosity of the adsorption layer, due to the possible arrangement of protein and polymer molecules into separate domains, and can result in various morphology types such as fibers or tree-like ribbons. Therefore, polymers like PEO and PVP can be used to regulate the SF self-assembly at the interface, which in turn can affect the properties of the materials with high surface areas like electrospun matts and scaffolds.

The influence of dithiothreitol (DTT) and β-mercaptoethanol (β-MEt) or their mixtures with a chaotropic denaturant, namely guanidine hydrochloride or urea, on the surface properties of lysozyme aqueous solutions was studied by the methods of dilatational surface rheology and ellipsometry. Adding 0.32 mM DTT to lysozyme solutions led to a considerable increase of the dynamic surface elasticity and a decrease of the dynamic surface tension compared with the results for native protein solutions. The observed effect was even more pronounced after a preliminary heating of the solutions. The rearrangement of disulfide bonds under the influence of a reducing agent and the subsequent cross-linking of lysozyme molecules resulted in the formation of a dense layer of adsorbed protein aggregates stabilized by intermolecular disulfide bridges at the liquid-gas interface. In the case of lysozyme solutions containing β-MEt, a significantly weaker effect ruled out the dense film formation, yet it also assumed some limited perturbations of the protein structure. The influence of reducing agents on the surface properties of lysozyme solutions differed from that of chaotropic denaturants and surfactants. At the same time, the simultaneous addition of both a reducing agent and a chaotropic denaturant led to a decrease of steady-state values of the dynamic surface elasticity due to the slow loosening of the cross-linked layer of lysozyme aggregates. Furthermore, unlike the protein solutions with urea, the molten globule state was not observed for solutions with both urea and a reducing agent, and the surface layer structure in the latter case was presumably similar to that in the layer in solutions containing guanidine hydrochloride where unfolded protein molecules formed loops and tails in the surface layer. The ellipsometric results corroborated these conclusions and revealed a decrease in the ellipsometric angle Δ in the case of both lysozyme/DTT/GuHCl and lysozyme/DTT/urea solutions.

Microgels serve as versatile colloidal building blocks and stabilizers in multiphase systems due to their deformability, surface activity, and environmental responsiveness. Among them, microgels constructed from protein coacervates hold promise for high-protein colloidal ingredients and food emulsion products. However, their interfacial properties, particularly in relation to their swelling behavior induced by environmental stimuli, remain largely unexplored but are critical for their successful application. In this study, soy protein (SPI) coacervates, formed via self-coacervation, were thermally transformed into microgels, and their interfacial behavior including adsorption kinetics, interfacial structure and rheological properties at the oil-water interface, was investigated in relation to pH-induced swelling. SPI microgels remain unswollen under neutral pH conditions (pH 7) but swell in acidic (pH 3) or alkaline (pH 10) conditions. Unswollen SPI microgels exhibit faster diffusion and adsorption due to their smaller particle size and lower electrostatic barrier. Upon adsorption to the interface, swollen SPI microgels assemble into an interfacial network more rapidly, whereas unswollen microgels form denser interfacial structures. The adsorption dynamics and interfacial structure are primarily governed by size and charge variations rather than microgel softness or deformability, as SPI microgels exhibit relatively high stiffness. Nevertheless, microgel softness influences the mechanical properties of the interfacial layer; swollen softer microgels form stretchable gel-like networks, while unswollen microgels form glassy-like layers exhibiting higher brittleness and yielding more readily under nonlinear deformations. These findings highlight the unique interfacial properties of soy protein microgels derived from protein coacervates, which provide valuable insights for the design of plant-based multiphase food formulations.

Interactions between a zwitterionic phospholipid, 1, 2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and four anionic phospholipids dihexadecyl phosphate (DHP), 1, 2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG), 1, 2-dipalmitoyl-sn-glycero-3-phosphate (DPP) and 1, 2-dipalmitoyl-sn-glycero-3-phospho ethanol (DPPEth) in combination with an additional amount of 30 mol% cholesterol were separately investigated at air-buffer interface through surface pressure (π) - area (A) measurements. π-A isotherm derived parameters revealed maximum negative deviation from ideality for the mixtures comprising 30 mol% anionic lipids. Besides the film functionality, structural changes of the monomolecular films at different surface pressures in the absence and presence of polyamidoamine (PAMAM, generation 4), a cationic dendrimer, were visualised through Brewster angle microscopy and fluorescence microscopic studies. Fluidity/rigidity of monolayers were assessed by surface dilatational rheology studies. Effect of PAMAM on the formation of adsorbed monolayer, due to bilayer disintegration of liposomes (DPPC:anionic lipids= 7:3 M/M, and 30 mol% cholesterol) were monitored by surface pressure (π) - time (t) isotherms. Bilayer disintegration kinetics were dependent on lipid head group and chain length, besides dendrimer concentration. Such studies are considered to be an in vitro cell membrane model where the alteration of molecular orientation play important roles in understanding the nature of interaction between the dendrimer and cell membrane. Liposome-dendrimer aggregates were nontoxic to breast cancer cell line as well as in doxorubicin treated MDA-MB-468 cell line suggesting their potential as drug delivery systems.

Background: Understanding how surface area (SA) fluctuation affects the dilational modulus (E) of globular protein films is crucial for evaluating their mechanical properties and practical utility. However, limited reports are available in the literature and the measurement error is unclear. Method: The impact of SA fluctuation and large, forced perturbation on the E of bovine serum albumin (BSA) and human serum albumin (HSA) film was investigated. The E was evaluated by analyzing surface tension (ST) and SA relaxation data obtained using a pendant bubble tensiometer. Significant findings: The data revealed that a large fluctuation in SA exerted a notable influence on the E: a distinct peak and minima in E being detected at the onset and end, respectively (at magnitude Delta A/A > similar to 3 % and at oscillation frequency f = 0.3 - 1.1 mHz for adsorbed BSA/HSA film). In contrast, a comparatively smaller SA fluctuation caused only a slight variation in E. Furthermore, a large, forced perturbation led to a rise in E, exhibiting a distinctly high value after a rapid bubble compression, followed by a subsequent decrease to a distinctly low E.

Kinetic dependences have been determined for the surface tension, dilatational dynamic surface elasticity, and ellipsometric angles of solutions of styrene copolymers with 4-vinylbenzyl chloride modified with N,N-dimethyldodecylamine. The micromorphology of the adsorbed and spread layers of these polyelectrolytes has also been studied. All kinetic dependences of the dynamic surface elasticity have turned out to be monotonic in contrast to those observed for previously studied solutions of polyelectrolytes free of polystyrene fragments. The peculiarities of the surface properties of the studied solutions may be related to the formation of microaggregates in the surface layers, because these microaggregates suppress the formation of loops and tails of polymer chains at the interfaces, and, consequently, decrease the surface elasticity after the local maximum. Atomic force microscopy data also indicate the formation of aggregates with sizes in the Z direction of 1–4 nm in the surface layers. The obtained results confirm the conclusions previously made about the formation of aggregates in the surface layers of solutions of polyelectrolytes containing fragments of sodium poly(styrene sulfonate). A 2D phase transition to a denser surface phase and the formation of aggregates with a size of 40 nm in the Z direction have been observed at surface pressures of 25–30 mN/m for the layers of the studied styrene-free polyelectrolyte spread over an aqueous substrate.

The adsorption layers of cupin-1.1, one of the two evolutionary conserved beta-barrel domains of vicilin-the garden pea storage globulin-at the liquid-gas interface were studied by a few methods of the surface chemistry. The kinetic dependencies of the surface pressure of cupin-1.1 solutions in 8 M urea overlap in a single master curve if the surface pressure is plotted as a function of the normalized time. The analysis of the master curve allows separation of a few adsorption steps including the induction period, the regions of the diffusion-controlled and barrier-controlled adsorption kinetics, and a plateau region of slow adsorption. Another master curve can be constructed from the dependencies of the dynamic surface elasticity on surface pressure. This curve has some similarities with the corresponding results for recently studied cupin-1.1 spread layers on the surface of urea solutions and gliadin adsorption layers. There are also important distinctions with the master curve for adsorption layers of cupin-1.1 in the system without denaturants. This difference can be connected with the formation of larger and more rigid aggregates in pure water than the aggregates in urea solutions.

Spread layers of amorphous aggregates of the structural domain of plant protein vicilin, cupin-1.1, at the water - air interface were studied by the surface tensiometry, dilational surface rheology, Brewster angle and atomic force microscopy. The layer properties differed strongly from the results for the layers of previously studied proteins. The dependency of the dynamic elasticity of the layer on surface pressure had two local maxima with the second peak being four times higher than the first one. In the region of the first maximum the obtained results are similar to those for dispersions of polymer microgels with a hairy corona. At the beginning of surface compression separate threads of the corona are stretched along the surface and the surface elasticity increases. The further compression results in the formation of loops and tails leading to a decrease of the elasticity. The second local maximum of the dynamic surface elasticity is presumably caused by the interactions of the rigid cores of the aggregates leading finally to the formation of multilayer structures at high surface pressures. In this case, the surface elasticity starts to decrease as a result of the segment exchange between different layers at the interface.

The formation of beta-lactoglobulin (BLG)/sodium polystyrene sulfonate (PSS) complexes decelerates the change in the surface properties of the mixed solutions with the surface age and increases the steady-state dilational surface elasticity in a narrow PSS concentration range. At the same time, the changes in the surface properties are accelerated in the dispersions of BLG fibrils with and without PSS due to the influence of small peptides coexisting with fibrils. A decrease in the peptide concentration as a result of the dispersion purification leads to slower changes in the surface properties at low PSS concentrations. The increase in the polyelectrolyte concentration results in an increase in the steady-state surface elasticity due to the fibril/PSS complex formation and in very slow changes in the surface properties if the polyelectrolyte exceeds a certain critical value. The latter effect is a consequence of the formation of large aggregates and of an increase in the electrostatic adsorption barrier. The consecutive adsorption of BLG fibrils and PSS leads to the formation of regular multilayers at the liquid–gas interface. The multilayer properties change noticeably with an increase in the number of layers from four to six in agreement with previous results on the multilayers of PSS with an oppositely charged synthetic polyelectrolyte, presumably due to the heterogeneity of the first PSS layer. The dynamic elasticity of the multilayers approaches 250 mN/m, indicating that they can effectively stabilize foams and emulsions.

Amphiphilic silk fibroin (SF) forms stable adsorption layers at the air–water interface. The range of the investigated protein concentrations can be divided into two parts according to the peculiarities of the surface layer properties. At protein concentrations from 0.0005 to 0.01 mg/mL, the dynamic surface elasticity monotonically increases with the concentration and surface age and reaches values of up to 220 mN/m. In this range, the adsorption layer compression leads to a fast increase of the surface pressure. In the second part (>0.01 mg/mL), the surface elasticity decreases again and the kinetic dependences of the film thickness and adsorbed amount change only a little. In this case, the layer compression leads only to a slight increase of the surface pressure. These two types of behavior can be attributed to the distinctions in the protein aggregation in the surface layer. Atomic force microscopy (AFM) investigations of the layers transferred from the liquid surface onto a mica surface by the Langmuir–Schaefer method show some peculiarities of the layer morphology in the intermediate concentration range (~0.02 mg/mL).

Layers of pulmonary lipids on an aqueous substrate at non-equilibrium conditions can decrease the surface tension of water to quite low values. This is connected with different relaxation processes occurring at the interface and the associated changes in the surface layer structure. Results of measurements by the combination of methods like surface rheology, ellipsometry, Brewster angle microscopy, and IRRAS for spread layers of lipid mixtures open a possibility to specify the dynamics of structural changes at conditions close to the physiological state. At sufficiently low surface tension values (below 5 mN/m) significant changes in the ellipsometric signal were observed for pure DPPC layers, which can be related to a transition from 2D to 3D structures caused by the layer folding. The addition of other lipids can accelerate the relaxation processes connected with squeezing-out of molecules or multilayer stacks formation hampering thereby a decrease of surface tension down to low values corresponding to the folding of the monolayer.

Physicochemical investigations on the inclusion of anionic polyamidoaminesuccinamic acid dendrimer, generation 5 (PAMAM-SA, G5) with positively charged hybrid vesicles (HCV), prepared using soylecithin, ion pair amphiphile (IPA), cholesterol and dihexadecyldimethylammonium bromide, were investigated by dynamic light scattering, transmission electron/atomic force microscopy (TEM/AFM), differential scanning calorimetry, fluorescence spectroscopy and surface pressure-time isotherm studies. Adsorption of dendrimer onto vesicle surface and subsequent bilayer disruption strongly depends on the bilayer composition and dendrimer concentration. Change in the zeta potential value with increasing dendrimer concentration suggests the dendrimer-vesicle interaction to be electrostatic in nature. AFM studies also confirm the adsorption of dendrimer as well as hole formation in the bilayer. Impact of the inclusion of dendrimer into the bilayer were further investigated through differential scanning calorimetry by monitoring the chain melting temperature and enthalpy of the chain melting processes. Dendrimer at low concentration does not alter bilayer integrity, while hole formations are noted at higher dendrimer concentration. Fluorescence anisotropy studies confirm the adsorption and subsequent bilayer disruption due to dendrimer inclusion. Dendrimer induced vesicle disintegration kinetics conclusively illustrate the transformation of cationic bilayer to monolayer and thereby exposing the role of IPA. In vitro cytotoxicity studies on PAMAM-SA, G5 and HCVs mixtures against human breast cancer cell line suggest that dendrimer-liposome aggregates (dendriosomes) exhibit substantial anticancer activities with insignificant side effects. It is expected that the dendriosomes may have application to host and deliver anticancer drug in the field of targeted drug delivery.

Dicarboxylate metallosurfactants (AASM), synthesized by mixing N -dodecyl aminomalonate, -aspartate and -glutamate with CaCl 2 , MnCl 2 and CdCl 2 , were characterized by XRD, FTIR, and NMR spectroscopy. Layered structures, formed by metallosurfactants, were evidenced from differential scanning calorimetry and thermogravimetric analyses. Solvent-spread monolayer of AASM in combination with soyphosphatidylcholine (SPC) and cholesterol (CHOL) were studied using Langmuir surface balance. With increasing mole fraction of AASM mean molecular area increased and passed through maxima at ~60 mol% of AASMs, indicating molecular packing reorganization. Systems with 20 and 60 mol% AASM exhibited positive deviations from ideal behavior signifying repulsive interaction between the AASM and SPC, while synergistic interactions were established from the negative deviation at other combinations. Dynamic surface elasticity increased with increasing surface pressure signifying formation of rigid monolayer. Transition of monolayer from gaseous to liquid expanded to liquid condensed state was established by Brewster angle microscopic studies. Stability of the hybrid vesicles, formed by AASM+SPC+CHOL, were established by monitoring their size, zeta potential and polydispersity index values over 100 days. Size and spherical morphology of hybrid vesicles were confirmed by transmission electron microscopic studies. Biocompatibility of the hybrid vesicles were established by cytotoxicity studies revealing their possible applications in drug delivery and imaging.