Guest-guided anchoring patterns of cyclodextrin supramolecular microcrystals on droplet surfaces

The growth of cyclodextrin inclusion complexes (ICs) on oil/water interfaces represents a beautiful example of spontaneous pattern formation in nature. How the supramolecules evolve remains a challenge because surface confinement can frustrate microcrystal growth and give rise to unusual phase transitions. Here we investigate the self-assembly of ICs on droplet surfaces using microfluidics, which allows directly visualizing packing, wetting and ordering of the microcrystals anchored on the surface. The oil guests of distinct molecular structures can direct the assembly of the ICs and largely affect anchoring dynamics of the ICs microcrystals, leading to a range of behaviors including orientating, slipping, buckling, jamming, or merging. We discuss the behaviors observed in terms of the flexibility of the building blocks, which offers a new degree of freedom through which to tailor their properties and gives rise to a striking feature of anchoring patterns that have no counterpart in normal colloidal crystals.

Ejected microcrystals probe jammed states of droplets in cyclodextrin-based emulsions

The cyclodextrin (CD)-based emulsions exhibit complex instability behaviors such as rapid flocculation and creaming, and how to capture droplet dispersion states of the emulsions remains a great challenge. Here we prepare the CD-based emulsions with different oil-water volume ratios and CD concentrations by using high-pressure homogenization, and characterize the emulsion droplets by using optical microscopy and confocal laser scanning microscopy. We evaluate the effects of homogenization pressure on the stability of the emulsions, identify armored droplets with different surface features, measure interfacial concentrations of adsorbed ICs microcrystals, and observe ejection of the oil/CD inclusion complexes (ICs) microcrystals from the droplet surface. The droplet dispersion states are sensitive to the dynamic buildup and evolving morphologies of the interfacial microcrystals, and there are clear correlations between the properties of the ejected microcrystals and the characteristics of the emulsions. We ascribe the subsequent ejection of ICs microcrystals from the droplet surface to consolidation and deformation of the films formed between neighboring droplets. The ejection of the ICs microcrystals affords a simple method to detect the droplet-droplet interactions and phase transitions in the CD-based emulsions, which might be a generic feature in the broader context of the creaming processes of emulsions.

Interfacial Rheological and Emulsion Properties of Self-Assembled Cyclodextrin-Oil Inclusion Complexes

To investigate the effect of the molecular size of alkanes and the cavity size of cyclodextrins (CDs) on the formation of interfacial host-guest inclusion complexes, the interfacial tension (IFT) of CD (α-CD, β-CD, γ-CD) solutions against oils (hexadecane, dodecylbenzene) was determined by interfacial dilational rheology measurements. The results show that the "space compatibility" between CDs and oil molecules is crucial for the formation of interface host-guest inclusion complexes. Hexadecane with a smaller molecular size can form host-guest inclusion complexes with small cavities of α-CD and β-CD, dodecylbenzene with a larger molecular size can form interfacial aggregates with the medium-sized cavity of β-CD easily, and the polycyclic aromatic hydrocarbon molecules in kerosene can form inclusion complexes with the large cavity of γ-CD. The formation of interfacial inclusion complexes leads to lower IFT values, higher interfacial dilational modulus, nonlinear IFT responses to the interface area oscillating, and skin-like films at the oil-water interface. What's more, the phase behavior of Pickering emulsions formed by CDs with different oils is explored, and the phenomena in alkane-CD emulsions are in line with the results in dilatation rheology. The interfacial active host-guest structure in the kerosene-γ-CD system improves the stability of the Pickering emulsion, which results in smaller emulsion droplets. This unique space compatibility characteristic is of great significance for the application of CDs in selective host-guest recognition, sensors, enhanced oil recovery, food industries, and local drug delivery.

High Interfacial Viscoelasticity of Aqueous Mixed Dodecyltrimethylammonium Bromide-Sodium Dodecyl Sulfate Surfactants Forming Inclusion Complexes with α-Cyclodextrin

Mixtures of anionic-cationic surfactants have shown high synergistic effects in the bulk solution and at the liquid/air interface. These studies have been limited to a reduced concentration range, where there is no formation of aggregates or precipitates. The addition of host molecules, such as cyclodextrins, to these systems reduces the effects of precipitation by forming inclusion complexes and also modifies the values of other surfactant properties, like the Krafft temperature and the critical aggregation concentration (CAC). We studied the interfacial synergistic effects promoted by electrostatic interactions, using the Rosen model to calculate an interaction parameter for mixtures of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in the presence of α-cyclodextrin (αCD), in aqueous solutions. We measured the CAC of SDS-DTAB-αCD mixtures using a pendant drop tensiometer, with the αCD concentration fixed at 10 mM and at 283.15 K. We performed rheological measurements on the mixtures where the surfactant total concentration is fixed below the measured CAC, varying the αCD concentration and temperature. We found that the dilatational modulus shows a clear correlation with the interaction parameter. It appears that the attractive interactions within the film are those due to the inclusion complexes formed by two αCD and one surfactant molecule, which according to the previous studies, is the dominant species in both the bulk and liquid/air interface. The synergistic effect observed here for SDS-DTAB surfactant mixtures with αCD can be applied to systems and processes (drop emission, drug delivery methods, stabilization of viral capsids and bacterial membranes, and emulsification) where interfacial processes require specific viscoelastic properties.

Jamming to unjamming: Phase transition in cyclodextrin-based emulsions mediated by sodium casein

HYPOTHESIS

Cyclodextrin (CD) can spontaneously build up the solid particle membrane with CD-oil inclusion complexes (ICs) by a self-assembly process. Sodium casein (SC) is expected to preferentially adsorb at the interface to transform the type of interfacial film. The high-pressure homogenization can increase interfacial contact opportunities of the components, which promote the phase transition of the interfacial film.

EXPERIMENTS

We added SC by sequential and simultaneous orders to mediate the assembly model of the CD-based films, examined the patterns in which the films adopt phase transitions to retard emulsion flocculation, and studied the physic-chemical properties of the emulsions and films from the structural arrest, interface tension, interfacial rheology, linear rheology, and nonlinear viscoelasticities through Fourier transform (FT)-rheology and Lissajous-Bowditch plots.

FINDINGS

The interfacial and large amplitude oscillatory shear (LAOS) rheological results showed that the films changed from jammed to unjammed. We divide the unjammed films into two types: one is SC dominated liquid-like film, which is fragile and related to droplet coalescence; the other is cohesive SC-CD film, which helps droplet rearrangement and retards droplet flocculation. Our results highlight the potential of mediating phase transformation of interfacial films to improve emulsion stability.

Effect of cyclodextrin glucosyltransferase extracted from Bacillus xiaoxiensis on wheat dough and bread properties

In this study, the cyclodextrin glucosyltransferase (CGTase) was extracted from Bacillus xiaoxiensis. CGTase had negative effects on dough viscoelastic properties and gluten strength but had positive effects on bread baking qualities and anti-staling properties. Adding an appropriate amount of CGTase (less than 0.3 U/g) could improve the specific volume, crumb texture, crust color, moisture content, and crumb hardness of bread. The bread crumb with 0.4 U/g CGTase (based on flour weight) had the lowest retrogradation enthalpy of 0.53 ± 0.10 J/g and the lowest relative crystallinity of 16.1%, which indicated the alleviating effect of amylopectin crystallization. Moreover, CGTase reduced the moisture from forming crystal lattices and limited starch molecule migration. The T₂ transverse relaxation results showed that the increase of immobilized water content in the bread with CGTase was lower than the control after 5 days of storage, which implied the water-holding capacity of the bread was enhanced and provided information on the inhibition of water migration. Hence, the CGTase could be a potential bread improver.

Drug-Loaded Nanocarriers Composed of Cholesteryl Oleate Crystal Cores and Multiple-Nanosheet Shells of γ-Cyclodextrin Inclusion Complex Crystals

In this study, we prepared drug-loaded nanocarriers made of cholesteryl oleate (ChO) and γ-cyclodextrin (γ-CD). A nanosuspension (nanosuspension-I, NS-I) containing nanoparticles with a mean size of approximately 170 nm was obtained through the solvent-diffusion method using ethanol. A second nanosuspension (nanosuspension-II, NS-II), which was prepared by freeze-drying and redispersion of NS-I, exhibited an increased particle size of approximately 210 nm. Cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM) force-distance curves indicated that the nanoparticles in NS-I were oblong and soft. However, those in NS-II were angular and stiff, and, interestingly, multiple nanosheets covered the solid-liquid interface. Synchrotron wide-angle X-ray diffraction (WAXD) analysis of NS-II indicated that the nanoparticles in it had a core-shell structure, where the ChO crystal in the inner core was covered by multiple nanosheets of ChO/γ-CD inclusion complex crystals. The X-ray peak analysis suggested that the γ-CD columns of the nanosheets were vertically stacked onto the ChO crystal interface. It was found that the nanosheets on the nanoparticle interface were formed during the freezing process. A model drug carbamazepine (CBZ) was loaded into the ChO/γ-CD nanoparticles by pre-dissolving CBZ in ethanol during the solvent-diffusion process. Cryo-TEM, ¹H NMR, ζ-potentials, and synchrotron WAXD indicated that CBZ was unexpectedly loaded into the shell as a CBZ/γ-CD inclusion complex crystalline nanosheet. The specific nanosheet structure, where ChO and CBZ coexisted in the same crystal of γ-CD, could achieve CBZ loading in the nanoparticles. ChO/γ-CD nanoparticles with the unique core-shell structure are expected to perform as practical carriers for drug delivery.

Probing the Molecular Assembly of a Metabolizer Drug with β-Cyclodextrin and Its Binding with CT-DNA in Augmenting Antibacterial Activity and Photostability by Physicochemical and Computational Methodologies

The assembly of an inclusion complex in an aqueous medium using a metabolizer drug (dyphylline) as guest and β-cyclodextrin as host has been established, which is extremely appropriate for a variety of applications in modern biomedical sciences. The formation of the inclusion complex is established by ¹H NMR, and surface tension and conductivity measurements demonstrate that the inclusion complex was produced with 1:1 stoichiometry. The thermodynamic parameters based on density, viscosity, and refractive index measurements were used to determine the nature of the complex. This research also forecasts how dyphylline will release in the presence of CT-DNA without any chemical modifications. The produced insertion complex (IC) has a higher photostability due to the drug dyphylline being protected by β-CD. The antibacterial activity of dyphylline greatly improved after complexation and exhibited higher toxicity against Gram-negative (highest against Escherichia coli) in comparison to Gram-positive bacteria. The encapsulation mode of the dyphylline molecule into the cavity of the β-CD was also investigated using DFT to confirm preliminary results.

Pickering emulsions stabilized by β-cyclodextrin and cinnamaldehyde essential oil/β-cyclodextrin composite: A comparison study

Here, a cinnamaldehyde essential oil (CEO)/β-Cyclodextrin (β-CD) composite with a high embedding rate (91.74 ± 0.82%) was prepared. Its structure was characterized by Fourier transform infrared spectrometer (FT-IR) and X-ray diffractometer (XRD). Pickering emulsions prepared by β-CD and CEO/β-CD at different concentrations (1-5%) were comparatively investigated. The CEO/β-CD emulsions had better storage stability. Rheological results confirmed the emulsions were all gel-like elastic emulsions and had shear thinning phenomenon. Fluorescence microscopy and scanning electron microscopy (SEM) results confirmed that the most of excessive β-CD was adsorbed on the surface of emulsion droplets as crystals, formed thick protective shell in β-CD emulsions, while the most of excessive composites were distributed in the aqueous phase forming a stable network structure in CEO/β-CD emulsions. It caused these two emulsions had different rheological properties, and different changing trends in droplet size.

Droplet Dispersion States of Cyclodextrin-Based Emulsions from Nonlinear Rheological Properties

Polymers are desirable to improve emulsion stability by stuffing them into the continuous phase. How to get information on the droplet dispersion states of the emulsions remains a challenge, as the emulsion characteristics are dictated by two intertwining components, the polymer matrix and the droplets. Herein, we use an amphiphilic polymer, gum arabic (GA), to mediate the droplet flocculation of cyclodextrin (CD)-based emulsions and compare them with our previous studies on the stabilization of CD-based emulsions by a nonamphiphilic polymer, methylcellulose (MC). We characterize the emulsions by using optical microscopy, confocal laser scanning microscopy, and laser particle analysis, explore their rheological behavior through large-amplitude oscillatory shear experiments, and analyze the nonlinear viscoelasticities through Fourier transform (FT)-rheology and Lissajous-Bowditch plots. There is a great difference between GA and MC in the viscosity effect and the arrangement around emulsion droplets. GA is not an effective flocculation inhibitor due to a bridging flocculation mechanism rather than a direct viscosity effect. Our analysis highlights the role of the intrinsic nonlinearity parameter (Q₀) extracted by FT analysis in reflecting the droplet dispersion states of the emulsions by decoupling structural contributions from the polymers and the emulsion droplets.

Cyclodextrin-based Pickering emulsions: functional properties and drug delivery applications

Cyclodextrins (CDs) are biocompatible, cyclic oligosaccharides that are widely used in various industrial applications and have intriguing interfacial science properties. While CD molecules typically have low surface activity, they are capable of stabilizing emulsions by inclusion complexation of oil-phase components at the oil/water interface, which results in Pickering emulsion formation. Such surfactant-free formulations have gained considerable attention in recent years, owing to their enhanced physical stability, improved tolerability, and superior environmental compatibility compared to conventional, surfactant-based emulsions. In this review, we critically describe the latest insights into the molecular mechanisms involved in CD stabilization of Pickering emulsions, including covering practical aspects such as methods to prepare CD-based Pickering emulsions, lipid encapsulation, and relevant stability issues. In addition, the rheological and textural features of CD-based Pickering emulsions are discussed and particular attention is focused on promising examples for drug delivery, cosmetic, and nutraceutical applications. The functionality of currently developed CD-based Pickering emulsions is also summarised, including examples such as antifungal uses, and we close by discussing emerging possibilities to utilize the molecular encapsulation of CD-based emulsions for translational medicine applications in the antiviral and antibacterial spaces.

Stress buffering in cyclodextrin-based membranes coated on emulsion droplet surfaces

Surface instability of membranes not only plays a critical role in the morphological evolution observed in natural and biological systems, but also underpins a promising way for the bottom-up fabrication of novel functional materials. There is an urgent need for the design of novel building blocks into membranes, and the understanding of the abilities of the membranes to cope with mechanical stress is therefore of considerable importance. Here, we design membranes built with cyclodextrin-oil inclusion complexes, which are formed spontaneously at the oil/water interface by a self-assembly process. We select the oil phases of distinct molecular structures, namely, branched triglyceride oil and straight-chain n-dodecane, and examine the patterns in which the membranes adopt morphological transitions to buffer stress. We discuss two possible buffering scenarios for the behaviors observed in view of structural arrest and interfacial rheology, which are most closely linked to the rigidity of the membranes. The membranes represent fascinating models and shed some light on the origin of arrested stress relaxation.

Fabrication of food-grade Pickering high internal phase emulsions stabilized by the mixture of β-cyclodextrin and sugar beet pectin

Food-grade Pickering high internal phase emulsions (HIPEs) stabilized by a mixture of β-cyclodextrin (β-CD) and sugar beet pectin (SBP) were fabricated for the first time. The factors affecting the microstructures, mechanical properties, and stabilities of the Pickering HIPEs were systematically investigated. The corresponding hybrid particles were also separated and characterized to reveal the formation mechanism. The results indicated that the mixture could induce the formation of HIPEs with an oil phase volume fraction (φ) of 75% using a one-step high-speed shearing process at room temperature. The composition (the mass ratio of β-CD to SBP, R_c/s) and concentration (W) of the mixture had significant effects on the formation and properties of HIPEs. When W ≥ 1.0% and R_c/s = 2:2 or 3:1, HIPEs had smaller oil droplets, higher gel strengths, better centrifugation stabilities and lutein protection effects. The spectral analysis suggested that SBP could adhere to the surface of β-CD particles to form hybrid particles during the homogenization. Compared with native β-CD particles, these hybrid particles had higher ζ-potential absolute values, and the SBP could also increase the viscosity of the aqueous phase, which contributed to the formation and properties of these HIPEs.

Bulk and Interfacial Contributions to Stabilization of Cyclodextrin-Based Emulsions Mediated by Bacterial Cellulose

Cyclodextrin (CD)-based emulsions have a characteristic of rapid droplet flocculation, which limits their application as functional material templates, so it is very important to improve the stability of CD-based emulsions. In this study, we select bacterial cellulose (BC) as a nonadsorbing inhibitor to prevent flocculation of CD-based emulsions. We map a phase diagram of the aqueous dispersions of CD inclusion complexes (ICs) and BC from morphological observations and investigate the effects of BC on properties of the IC-laden films. We further explore the effects of BC concentration on the stability of the CD-based emulsions and investigate rheological behavior of the emulsions through large-amplitude oscillatory shear experiments. It shows that BC can effectively suppress the flocculation of CD-based emulsion droplets even at a concentration as low as 0.01 wt %. We propose that BC has dual effects from bulk and interfacial contributions on increasing emulsion stability. At low concentrations, BC mainly results in higher packing density of ICs on the emulsion droplet surface through excluded volume repulsion, and at high concentrations, BC creates a network structure that confines the motion of emulsion droplets and retards flocculation.

Stabilization and Release of Palm Tocotrienol Emulsion Fabricated Using pH-Sensitive Calcium Carbonate

Calcium carbonate (CaCO3) has been utilized as a pH-responsive component in various products. In this present work, palm tocotrienols-rich fraction (TRF) was successfully entrapped in a self-assembled oil-in-water (O/W) emulsion system by using CaCO3 as the stabilizer. The emulsion droplet size, viscosity and tocotrienols entrapment efficiency (EE) were strongly affected by varying the processing (homogenization speed and time) and formulation (CaCO3 and TRF concentrations) parameters. Our findings indicated that the combination of 5000 rpm homogenization speed, 15 min homogenization time, 0.75% CaCO3 concentration and 2% TRF concentration resulted in a high EE of tocotrienols (92.59-99.16%) and small droplet size (18.83 ± 1.36 µm). The resulting emulsion system readily released the entrapped tocotrienols across the pH range tested (pH 1-9); with relatively the highest release observed at pH 3. The current study presents a potential pH-sensitive emulsion system for the entrapment and delivery of palm tocotrienols.

Synthesis of Poly(Methyl Methacrylate)-Based Polyrotaxane via Reversible Addition-Fragmentation Chain Transfer Polymerization

A polyrotaxane (PR) with poly(methyl methacrylate) (PMMA) as the main chain polymer was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Because of the special mechanism of RAFT, the suprastructure of a PMMA-based PR is established by synthesizing inclusion complexes of methyl methacrylate and gamma-cyclodextrin (γCD) into the middle of the poly-N-(3-dimethylamino) propyl methacrylamide segments. The presence of threaded γCD was determined via diffusion ordered spectroscopy from the alignment of the mobility of γCD and the main chain polymer. A PMMA-based PR with 2-20% CD coverage and a molecular weight of 7K-60K g/mol of PMMA-based PR was synthesized with a targeted molecular structure by mediating the RAFT polymerization. The PMMA-based PR prepared in this study is expected to be suitable for wide applications of tough materials with good heat resistance. Moreover, the investigation of this synthetical approach opened possibilities for more variety of PR with controllable properties.

Tomato Oil Encapsulation by α-, β-, and γ-Cyclodextrins: A Comparative Study on the Formation of Supramolecular Structures, Antioxidant Activity, and Carotenoid Stability

Cyclodextrins (CDs) are oligosaccharides, comprising 6 (α), 7 (β), or 8 (γ) glucose residues, used to prepare oil-in-water emulsions and improve oil stability towards degradation. In this research, the aptitude of α-, β-, and γ-CDs to form complexes with a supercritical CO₂ extracted lycopene-rich tomato oil (TO) was comparatively assessed. TO/CD emulsions and the resulting freeze-dried powders were characterized by microscopy, Fourier transform infrared-attenuated total reflection (FTIR-ATR), and differential scanning calorimetry (DSC), as well as for their antioxidant activity. Furthermore, carotenoid stability was monitored for 90 days at 25 and 4 °C. Confocal and SEM microscopy revealed morphological differences among samples. α- and β-CDs spontaneously associated into microcrystals assembling in thin spherical shells (cyclodextrinosomes, Ø ≈ 27 µm) at the oil/water interface. Much smaller (Ø ≈ 9 µm) aggregates were occasionally observed with γ-CDs, but most TO droplets appeared "naked". FTIR and DSC spectra indicated that most CDs did not participate in TO complex formation, nevertheless structurally different interfacial complexes were formed. The trolox equivalent antioxidant capacity (TEAC) activity of emulsions and powders highlighted better performances of α- and β-CDs as hydrophobic antioxidants-dispersing agents across aqueous media. Regardless of CDs type, low temperature slowed down carotenoid degradation in all samples, except all-[E]-lycopene, which does not appear efficiently protected by any CD type in the long storage period.

Encapsulation of tributyrin by gamma-cyclodextrin: Complexation, spray drying, and in vitro fermentation

Butyrate is a short-chain fatty acid (SCFA) known for support in gastrointestinal (GI) health. Tributyrin (TB) could be used as an alternate source of butyrate. The objectives of this study were to encapsulate TB using gamma-cyclodextrin (CD) by spray-drying and to investigate the physicochemical and the fermentation properties of TB/CD complex. The TB/CD complex precipitated in water with an average stoichiometry of 1:1.3 of TB:CD. At a 1:2 molar ratio of TB:CD, TB was fully retained in the spray-dried TB/CD complex. The spray-dried TB/CD complex showed crystalline structure, supported by both X-ray diffraction spectra and scanning electron microscopy images. The TB/CD complex at 1:2 molar ratio was fermented and several SCFAs, including butyrate, were produced in an in vitro test using piglets' ileal and colonic contents. A dose-dependent increase in the butyrate concentration in both ileum and ascending colon was observed. Approximately, 426 and 1189 μmole butyrate was produced per gram of TB/CD powder at 9 mM treatment in ileum and ascending colon, respectively. Thus, the production of the TB/CD complex using spray drying is feasible and the complex has the potential for food applications to improve intestinal health. PRACTICAL APPLICATION: The findings in this study can be applied to produce encapsulated tributyrin with gamma-cyclodextrin efficiently using spray-drying. The TB/CD complex was highly fermentable and caused an increase in the butyrate concentration in both ileum and ascending colon, which can be incorporated in foods to enhance butyrate delivery to the GI tract to assist gut health.

Preparation and characterization of molecularly imprinted polymers based on β-cyclodextrin-stabilized Pickering emulsion polymerization for selective recognition of erythromycin from river water and milk

Molecularly imprinted polymers were prepared via β-cyclodextrin-stabilized oil-in-water Pickering emulsion polymerization for selective recognition and adsorption of erythromycin. The synthesized molecularly imprinted polymers were spherical in shape, with diameters ranging from 20 to 40 µm. The molecularly imprinted polymers showed high adsorption capacity (87.08 mg/g) and adsorption isotherm data fitted well with Langmuir model. Adsorption kinetics study demonstrated that the molecularly imprinted polymers acted in a fast adsorption kinetic pattern and the adsorption features of molecularly imprinted polymers followed a pseudo-first-order model. Adsorption selectivity analysis revealed that molecularly imprinted polymers had a much better specificity for erythromycin than that for spiramycin or amoxicillin, and the relative selectivity coefficient values on the bases of spiramycin and amoxicillin were 3.97 and 3.86, respectively. The Molecularly imprinted polymers also showed a satisfactory reusability after four times of regeneration. In addition, molecularly imprinted polymers exhibited good adsorption capacities for erythromycin under complicated environment, that is, river water and milk. These results proved that the as-prepared molecularly imprinted polymers is a potent absorbent for selective recognition of erythromycin, and therefore it may be a promising candidate for practical applications, such as wastewater treatment and detection of erythromycin residues in food.

Rings, Hexagons, Hetals, and Dipolar Moment Sink-Sources: The Fanciful Behavior of Water around Cyclodextrin Complexes

The basket-like geometry of cyclodextrins (CDs), with a cavity able to host hydrophobic groups, makes these molecules well suited for a large number of fundamental and industrial applications. Most of the established CD-based applications rely on trial and error studies, often ignoring key information at the atomic level that could be employed to design new products and to optimize their use. Computational simulations are well suited to fill this gap, especially in the case of CD systems due to their low number of degrees of freedom compared with typical macromolecular systems. Thus, the design and validation of solid and efficient methods to simulate and analyze CD-based systems is key to contribute to this field. The behavior of supramolecular complexes critically depends on the media where they are embedded, so the detailed characterization of the solvent is required to fully understand these systems. In the present work, we use the inclusion complex formed by two α-CDs and one sodium dodecyl sulfate molecule to test eight different parameterizations of the GROMOS and AMBER force fields, including several methods aimed to increase the conformational sampling in computational molecular dynamics simulation trajectories. The system proved to be extremely sensitive to the employed force field, as well as to the presence of a water/air interface. In agreement with previous experiments and in contrast to the results obtained with AMBER, the analysis of the simulations using GROMOS showed a quick adsorption of the complex to the interface as well as an extremely exotic behavior of the water molecules surrounding the structure both in the bulk aqueous solution and at the water surface. The chirality of the CD molecule seems to play an important role in this behavior. All together, these results are expected to be useful to better understand the behavior of CD-based supramolecular complexes such as adsorption or aggregation driving forces, as well as to introduce new methods able to speed up general MD simulations.

A cyclodextrin surfactant for stable emulsions with an accessible cavity for host–guest complexation

Oil-in-water-emulsions stabilized by an anionic β-cyclodextrin surfactant show long term stability and accessibility of the cavity for host–guest-complexation.

Highly viscoelastic films at the water/air interface: α-Cyclodextrin with anionic surfactants

This work showcases the remarkable viscoelasticity of films consisting of α-cyclodextrin (α-CD) and anionic surfactants (S) at the water/air interface, the magnitude of which has not been observed in similar systems. The anionic surfactants employed are sodium salts of a homologous series of n-alkylsulfates (n = 8-14) and of dodecylsulfonate. Our hypothesis was that the very high viscoelasticity can be systematically related to the bulk and interfacial properties of the system. Through resolution of the bulk distribution of species using isothermal titration calorimetry, the high dilatational modulus is related to (α-CD)₂:S₁ inclusion complexes in the bulk with respect to both the bulk composition and temperature. Direct interfacial characterization of α-CD and sodium dodecylsulfate films at 283.15 K using ellipsometry and neutron reflectometry reveals that the most viscoelastic films consist of a highly ordered monolayer of 2:1 complexes with a minimum amount of any other component. The orientation of the complexes in the films and their driving force for adsorption are discussed in the context of results from molecular dynamics simulations. These findings open up clear potential for the design of new functional materials or molecular sensors based on films with specific mechanical, electrical, thermal, chemical, optical or even magnetic properties.

Droplet clustering in cyclodextrin-based emulsions mediated by methylcellulose

Rapid droplet aggregation in cyclodextrin (CD)-stabilized emulsions limits their practical use as material templates. Herein, we formulate mixtures of submicron CD-based emulsion droplets suspended in aqueous solutions of methylcellulose (MC) with various concentrations and molecular weights. We evaluate the effects of MC on the microstructure and stability of the emulsions using different techniques including optical microscopy, laser particle analysis, confocal laser scanning microscopy and multiple light scattering, explore the rheological behavior of the emulsions through large amplitude oscillatory shear experiments, and study the viscoelastic nonlinearities of the emulsions as a function of strain and strain-rate space through nondimensional elastic and viscous Lissajous-Bowditch plots. It is demonstrated that the emulsion droplets are present in the form of small clusters and their size is almost independent of MC concentration and molecular weight. The clustering pattern is also supported by the changes in viscoelastic properties of the emulsions and the intracycle nonlinear behavior of the Lissajous-Bowditch plots. We propose for the first time that glass-like dynamic arrest takes place with the formation of small equilibrium droplet clusters in the situation where the CD-based emulsion droplets are forced by depletion flocculation and kinetic trapping simultaneously exerted by MC.

Eco-Friendly Tadalafil Surfactant-Free Dry Emulsion Tablets (SFDETs) Stabilized by In Situ Self-Assembled Aggregates of Natural Oil and Native Cyclodextrins

The main principles of green chemistry and engineering were extended to pharmaceutical formulations to prepare eco-friendly surfactant-free dry emulsion tablets (SFDETs) devoid of solvents or synthetic surfactants. Surfactant-free emulsions were stabilized by in situ cyclodextrins/sweet almond oil inclusion complexes and assessed for creaming stability. Formulation variables' effects on the emulsion droplet size and tadalafil solubility were studied using 2² × 3 factorial design. The emulsions exhibited nanometric and micrometric droplet sizes. The optimized nanoemulsion was loaded with tadalafil, morphologically evaluated, and utilized for preparing lyophilized SFDETs using different gelatin/Pearlitol® ratios. The tablets were characterized and the selected formulation was subjected to storage for 6 months. The emulsions prepared using β-cyclodextrin or higher concentrations of α-cyclodextrin showed little or no phase separation. Statistical analysis revealed significant influence of cyclodextrin type and amount on droplet size, while cyclodextrin type and oil volume exhibited significant effect on drug solubility. Morphological examination revealed non-aggregated spherical emulsion droplets. The prepared tablets showed satisfactory mechanical strength, short disintegration times, and enhanced drug dissolution. The selected tablet formulation (gelatin/Pearlitol®, 4:2 w/w) showed acceptable stability at 25°C/60% relative humidity. An overall conclusion claims that the absence of surfactants is expected to minimize the proposed tablets' in vivo toxicity and environmental concerns.

The Addition of α-cyclodextrin and γ-cyclodextrin Affect Quality of Dough and Prebaked Bread During Frozen Storage

The effects of the addition of 0–3.0 wt% α-cyclodextrin (α-CD) and γ-cyclodextrin (γ-CD) on the quality of wheat flour as well as the texture and the aging of prebaked bread were evaluated. The addition of α-CD and γ-CD increased the ability of wheat flour to absorb water and shortened the times of dough formation and stabilization. Amylase activity slightly increased after using 2.0 and 3.0 wt% of α-CD and γ-CD, respectively. Moreover, the addition of α-CD and γ-CD increased the fermentation height and gas retention ability of dough. Dough samples containing 2.0 wt% α-CD and 3.0 wt% γ-CD showed the highest fermentation heights and gas retention volumes, respectively. Dough gas production increased with the addition of γ-CD. Gas production by dough samples containing more than 2.0 wt% α-CD exceeded that by samples in the control group. The results of the texture crumb of bread and specific volume tests revealed that the addition of 2.0 wt% α-CD and 3.0 wt% γ-CD reduced bread hardness and increased bread elasticity, resilience, and specific volume. The optimal α-CD and γ-CD contents were identified as 2.0 wt% and 3.0 wt%, respectively. The addition of 2.0 wt% α-CD and 3.0 wt% γ-CD delayed the aging of prebaked bread and reduced the hardness of prebaked bread during different weeks of storage, which may be due to decreasing the melting enthalpy of starch crystals. This work elucidated the mechanisms underlying the effects of CD addition on prebaked bread quality.

Effect of Emulsifier Type, Maltodextrin, and β-Cyclodextrin on Physical and Oxidative Stability of Oil-In-Water Emulsions

The effect of emulsifiers, emulsion stabilizer (maltodextrin, MD), and β-cyclodextrin (BCD) on physical and oxidative properties of oil-in-water (O/W) emulsions (5%, 20%, 40% of oil, w/w) was investigated. Four different emulsifiers were selected based on their structure: two types of protein-based emulsifiers (sodium caseinate, SC; and whey protein isolate, WPI), and two types low molecular weight emulsifiers (LMEWs: lecithin, LEC; and Citrem, CITREM). Physical and oxidative stability of emulsions prepared with these emulsifiers together with MD were compared based on their creaming index (CI), viscosity, droplet size, zeta potential, peroxide and p-anisidine values. LMWE-stabilized emulsions (with LEC or CITREM) had better creaming stability with lower droplet sizes whereas protein-stabilized emulsions (with SC or WPI) had higher viscosities. Droplet size was the lowest when CITREM was used, which increased with increasing oil concentration for all emulsifiers. Formulation with the lowest CI value and droplet size was considered to be more prone to oxidation; therefore, a 1:1 (w/w) combination of CITREM with BCD was used to stabilize the emulsions to improve the oxidative as well as physical stability. Added BCD significantly increased the storage stability of emulsions by reducing CI and droplet size values with a simultaneous increase in the viscosity, both at room temperature and at storage conditions (at 4 and 55 ^o C). However, the oxidative as well as physical stability of BCD added emulsions were not improved, neither toward heat- nor light-induced lipid oxidation. PRACTICAL APPLICATION: This work investigated the effects of emulsifiers and dextrins on the stability of oil-in-water (O/W) emulsions. Both maltodextrin (MD) and β-cyclodextrin (BCD) addition resulted in enhanced physical stability, the latter being more effective. The findings can be applied to formulate emulsions with improved shelf life within the limits of allowed daily intake (ADI) level of BCD (5 mg/kg bw per day).

Pickering Emulsions Containing Cellulose Microfibers Produced by Mechanical Treatments as Stabilizer in the Food Industry

Pickering emulsions are emulsions stabilized by solid particles, which generally provide a more stable system than traditional surfactants. Among various solid stabilizers, bio-based particles from renewable resources, such as micro- and nanofibrillated cellulose, may open up new opportunities for the future of Pickering emulsions owing to their properties of nanosize, biodegradability, biocompatibility, and renewability. The aim of this research was to obtain oil-in water (O/W) Pickering emulsions using cellulose microfibers (CMF) produced from cotton cellulose linters by mechanical treatment through a high-pressure homogenizer. The O/W Pickering emulsions were prepared with different O/W ratios by mixing edible oil (sunflower oil) with water containing CMF at concentrations of up to 1.0 wt%. The apparent viscosity of the separated emulsion phase was measured. Results showed the feasibility of using low concentration of CMF for preparing and stabilizing Pickering emulsions, with the apparent viscosity of the emulsion phase increasing 60–90 times with respect to the sunflower oil, for a shear rate of 1 s−1. In addition, theoretical nutrition facts of the emulsions were calculated and compared with other fats used in foods, showing that they can be a promising low-calorie product containing dietary fiber, replacing trans and saturated fats in foods.

Application of Pickering Emulsion with Cyclodextrin as an Emulsifier to a Transdermal Drug Delivery Vehicle

The emulsion prepared with β-cyclodextrin as an emulsifier (βCDE) is considered to be a Pickering emulsion. We examined the characteristics of βCDEs using captopril (CP) as a model drug, and studied the in vitro skin permeation of CP from βCDEs through hairless mouse skin. The stability of βCDE was increased with increasing βCD concentration and conversely decreased with increasing CP concentration. The yield stress value from the rheological measurement results was suggested to be one of the factors determining the stability of the βCDE, and βCDEs with higher yield stress values were more stable. We found that the skin permeability of CP could be improved by using βCDE with isopropyl myristate as the oil phase and that the flux of CP depended on the free CP concentration in the water phase of βCDE.

Tailoring the Wettability of Colloidal Particles for Pickering Emulsions via Surface Modification and Roughness

Pickering emulsions are water or oil droplets that are stabilized by colloidal particles and have been intensely studied since the late 90s. The surfactant-free nature of these emulsions has little adverse effects such as irritancy and contamination of environment and typically exhibit enhanced stability compared to surfactant-stabilized emulsions. Therefore, they offer promising applications in cosmetics, food science, controlled release, and the manufacturing of microcapsules and porous materials. The wettability of the colloidal particles is the main parameter determining the formation and stability of Pickering emulsions. Tailoring the wettability by surface chemistry or surface roughness offers considerable scope for the design of a variety of hybrid nanoparticles that may serve as novel efficient Pickering emulsion stabilizers. In this review, we will discuss the recent advances in the development of surface modification of nanoparticles.

Get Beyond Limits: From Colloidal Tectonics Concept to the Engineering of Eco-Friendly Catalytic Systems

The interactions between two or more molecules or colloidal particles can be used to obtain a variety of self-assembled systems called supramolecules or supracolloids. There is a clear, but neglected, convergence between these two fields. Indeed, the packing of molecules into colloidal or supracolloidal particles emerges as a smart solution to build an infinite variety of reversible systems with predictable properties. In this respect, the molecular building blocks are called "tectons" whereas "colloidal tectonics" describes the spontaneous formation of (supra)colloidal structures using tectonic subunits. As a consequence, a bottom-up edification is allowed from tectons into (supra)colloidal particles with higher degrees of organization (Graphical Abstract). These (supra)colloidal systems can be very useful to obtain catalysts with tunable amphiphilic properties. In this perspective, an overview of colloidal tectonics concept is presented as well as its use for the design of new, smart, and flexible catalytic systems. Finally, the advantages of these catalytic devices are discussed and the perspective of future developments is addressed especially in the context of "green chemistry."

Joint Effects of Granule Size and Degree of Substitution on Octenylsuccinated Sweet Potato Starch Granules As Pickering Emulsion Stabilizers

The granules of sweet potato starch were size fractionated into three portions with significantly different median diameters ( D₅₀) of 6.67 (small-sized), 11.54 (medium-sized), and 16.96 μm (large-sized), respectively. Each portion was hydrophobized at the mass-based degrees of substitution (DS_m) of approximately 0.0095 (low), 0.0160 (medium), and 0.0230 (high). The Pickering emulsion-stabilizing capacities of modified granules were tested, and the resultant emulsions were characterized. The joint effects of granule size and DS_m on emulsifying capacity (EC) were investigated by response surface methodology. For small-, medium-, and large-sized fractions, their highest emulsifying capacities are comparable but, respectively, encountered at high (0.0225), medium (0.0158), and low (0.0095) DS_m levels. The emulsion droplet size increased with granule size, and the number of freely scattered granules in emulsions decreased with DS_m. In addition, the term of surface density of the octenyl succinic group (SD_-OSG) was first proposed for modified starch granules, and it was proved better than DS_m in interpreting the emulsifying capacities of starch granules with varying sizes. The present results implied that, as the particulate stabilizers, the optimal DS_m of modified starch granules is size specific.