Self-assembly of nonionic surfactant Tween 20@2β-CD inclusion complexes in dilute solution

Pickering nanoemulsion loaded with eugenol contributed to the improvement of konjac glucomannan film performance

Konjac glucomannan (KGM) is becoming a very potential food packaging material due to its good film-forming properties and stability. However, KGM film has several shortcomings such as low mechanical strength, strong water absorption, and poor self-antibacterial performance, which limits its application. Therefore, in order to enhance the mechanical and functional properties of KGM film, this study prepared Pickering nanoemulsion loaded with eugenol and added it to the KGM matrix to explore the improvement effect of Pickering nanoemulsion on KGM film properties. Compared to pure KGM film and eugenol directly added film, the mechanical strength of Pickering-KGM film was significantly improved due to the establishment of ample hydrogen bonding interactions between the β-cyclodextrin inclusion complex system and KGM. Pickering-KGM film had significant antioxidant capacity than pure KGM film and eugenol directly added KGM film (eugenol-KGM film) (~3.21 times better than KGM film, ~0.51 times better than eugenol-KGM film). In terms of antibacterial activity, Pickering-KGM film had good inhibitory effect on Escherichia coli, Staphylococcus aureus, and Candida albicans, and raspberry preservation experiment showed that the shelf life of the Pickering-KGM film could be extended to about 6 days. To sum up, this study developed a novel means to improve the film performance and provide a new insight for the development and application of food packaging film.

New opportunities for cyclodextrins in supramolecular assembly: metal organic frameworks, crystalline self-assembly, and catalyzed assembly

Cyclodextrins (CDs) are widely used macrocycles in supramolecular assembly due to their easy availability, versatile functionality and excellent biocompatibility. Although they are well-known for forming host-guest complexes with a wide range of guests and this host-guest chemistry has long been utilized in industry and academia, new opportunities have arisen in recent years, particularly in supramolecular assembly. In the present review, we will first provide a basic introduction to CDs and then summarize their emerging roles in the fields of supramolecular chemistry and materials. This includes their involvement in hybrid frameworks with inorganic components such as metal ions and polyoxometalates, crystalline self-assembly with amphiphilic molecules, and their new possibility of "catassembly" and induced chiral supramolecular structures that have previously been overlooked. Finally, we will comment on the future perspectives of CDs to inspire more ideas and efforts, with the aim of promoting diverse applications of CDs in supramolecular materials.

Rheological dynamics and structural characteristics of supramolecular assemblies of β-cyclodextrin and sulfonic surfactants

Cyclodextrins are highly functional compounds with a hydrophobic cavity capable of forming supramolecular inclusion complexes with various classes of molecules including surfactants. The resultant rich nanostructures and their dynamics are an interesting research problem in the area of soft condensed matter and related applications. Herein, we report novel dynamical supramolecular assemblies based on the complexation of β-cyclodextrin with 3 different sulfonic surfactants, which are sodium hexadecylsulfate, sodium dodecylbenzenesulfonate, and myristyl sulfobetaine. It was observed that a β-cyclodextrin : surfactant/2 : 1 molar ratio was ideal for inducing axial growth and imparting large viscosities in the suspensions. Such complexation processes were accompanied by intriguing nanostructural phase behaviors and rheological properties that were very sensitive to the molecular architecture of sulfonic surfactants. The presence of an amino group in the head group of the surfactant allowed for large viscosities that reached 2.4 × 10⁴ Pa s which exhibited gel-like behavior. In contrast, smaller viscosity values with a lower consistency index were observed when a bulky aromatic ring was present instead. DIC microscopy was used to visually probe the microstructure of the systems with respect to sulfonate molecular architecture. Additionally, surface tension measurements, and FTIR and NMR spectroscopies were used to gain insights into the nature of interactions that lead to the complexation and nanostructural characteristics. Finally, mechanics correlating the supramolecular morphologies to the rheological properties were proposed.

Cholesterol as a Subsidiary Component of Sorbitan Surfactant-Based Aggregates: A Study of Formation, Hydrophobicity, and Estimation of Localization of Embedded Molecules

Aggregates of amphiphilic molecules can be used as drug carriers, for which the properties can be modified by mixing with other molecules such as cholesterol. It is important to understand the effects of such additives on the properties because they directly define the material functions. In this work, we investigated the effect of cholesterol on the formation and hydrophobicity of aggregates of sorbitan surfactants. As cholesterol changed its formation from micelles to vesicles, an increase in hydrophobicity was seen, particularly in the middle regions compared with the shallow and deep regions. We show that this gradual hydrophobicity is related to the localization of the embedded molecules. 4-Hydroxy-TEMPO and 4-carboxy-TEMPO were preferentially localized in the shallow region of the aggregates, whereas 4-PhCO₂-TEMPO was preferentially localized in the deep region of the vesicle. The localization of molecules depends on their chemical structure. However, the localization of 4-PhCO₂-TEMPO in micelles was not observed, despite the similar hydrophobicity in the hydrophobic region within the aggregates. The localization of embedded molecules was related to other properties, such as molecular mobility.

Thermoresponsive behavior of cyclodextrin inclusion complexes with weakly anionic alkyl ethoxy carboxylates

This study investigates the temperature responsive behavior of inclusion complexes formed by weakly anionic alkyl ethoxy carboxylates and α (αCD) and β-cyclodextrins (βCD). Small-angle neutron scattering (SANS) was performed to probe the structural behaviour at the 1-100 nanometer scale of the hierarchical assemblies at different temperatures. The phase transitions and thermodynamics were systematically monitored as a function of the degree of ionization of the surfactant by differential scanning calorimetry (DSC). Herein, we investigate the effect of the surfactant degree of ionization on the thermoresponsive properties of the inclusion complex supramolecular assemblies. Inclusion complexes formed with the ionized surfactant spontaneously assemble into multilayered structures, which soften with increasing temperature. We also found that the presence of charges is not only required to impart order to the supramolecular assemblies, but also induced in-plane crystallization of the inclusion complexes. Finally, the use of a weakly anionic surfactant allows us to probe the interplay between the charge density and temperature on the assembly of surfactant-cyclodextrin inclusion complexes. This study helps to improve the design of multi-responsive supramolecular systems based on cyclodextrins.

Hierarchical assembly of pH-responsive surfactant-cyclodextrin complexes

In this work, the inclusion complexes of alkyl ethoxy carboxylates with α-cyclodextrin (αCD) and β-cyclodextrin (βCD) were investigated. The thermodynamics of the complexation process was probed by isothermal titration calorimetry (ITC) and volumetry as a function of the degree of ionization of the surfactant. The complexation process was shown to be an enthalpically driven pH-independent process. For both types of cyclodextrins, the complexes were found to spontaneously self-assemble into highly-ordered supramolecular aggregates probed by small-angle neutron scattering and electron and optical microscopy. Herein, we report the formation of thin platelets for nonionized surfactant systems and equally spaced multilayered hollow cylinders for ionized systems in a hierarchical self-assembly process. In addition, the analysis allowed unveiling the effect of the number of ethylene oxides in the surfactants and the CD cavity size on the morphology of the aggregates. Finally, this study also highlights the importance of examining the tuning parameters' influence on the short and long-range interactions involved in the control of the assembly process.

Physicochemical and Stability Evaluation of Topical Niosomal Encapsulating Fosinopril/γ-Cyclodextrin Complex for Ocular Delivery

This study aimed to develop a chemically stable niosomal eye drop containing fosinopril (FOS) for lowering intraocular pressure. The effects of cyclodextrin (CD), surfactant types and membrane stabilizer/charged inducers on physiochemical and chemical properties of niosome were evaluated. The pH value, average particle size, size distribution and zeta potentials were within the acceptable range. All niosomal formulations were shown to be slightly hypertonic with low viscosity. Span® 60/dicetyl phosphate niosomes in the presence and absence of γCD were selected as the optimum formulations according to their high %entrapment efficiency and negative zeta potential values as well as controlled release profile. According to ex vivo permeation study, the obtained lowest flux and apparent permeability coefficient values confirmed that FOS/γCD complex was encapsulated within the inner aqueous core of niosome and could be able to protect FOS from its hydrolytic degradation. The in vitro cytotoxicity revealed that niosome entrapped FOS or FOS/γCD formulations were moderate irritation to the eyes. Furthermore, FOS-loaded niosomal preparations exhibited good physical and chemical stabilities especially of those in the presence of γCD, for at least three months under the storage condition of 2–8 °C.

Enzyme-Responsive Molecular Assemblies Based on Host-Guest Chemistry

Recent years have witnessed a growing interest in the design of enzyme-responsive molecular assemblies that hold appealing applications in the fields of disease-related sensing, imaging, and drug delivery. Cyclodextrins (CDs) are amylase-cleavable host molecules that can associate with surfactants, alkanes, alkyl amines, fatty alcohols, and aromatic compounds to form diverse supramolecular structures. In this work, we report a versatile supramolecular platform to construct enzyme-responsive nanosystems via host-guest interactions, in which complexation between CDs and surfactants eventually leads to the formation of a variety of nanostructures such as vesicles and microtubes. These supramolecular structures are capable of loading water-soluble molecules or functional nanoparticles, which can be actively released on-demand in the presence of α-amylase. This universal strategy to fabricate enzyme-responsive supramolecular systems was further demonstrated with a range of surfactants with anionic, cationic, and nonionic headgroups. Our results highlight a versatile platform for the exploration of biologically responsive self-assembly with potential applications as controlled-release systems and microrobots.

Visual recognition of ortho-xylene based on its host-guest crystalline self-assembly with α-cyclodextrin

HYPOTHESIS

Distinguishing substituted aromatic isomers is a challenging task because of the great similarity of their physicochemical properties. Considering xylene isomers have drastically different geometrical shapes, we predict this would show great impact on the self-assembling behavior of various xylene isomer@cyclodextrin inclusion complex.

EXPERIMENTS

Through host-guest crystalline self-assembly, among three isomers, only ortho-xylene is capable to form hydrogels with α-cyclodextrin. ROESY NMR, molecular simulations and circular dichroism spectra suggest that the ortho selectivity comes from the difference in the conformation of host-guest building block. The larger volume, and steric hinderance of the ortho isomer make it most possibly decrease their tendency to adopt more mobile orientations in cyclodextrin-based complex as meta and para isomers do, resulting in gel formation.

FINDINGS

Herein, we report a novel, facile and environmentally-friendly protocol on the recognition of ortho benzene isomers using α-cyclodextrin through host-guest crystalline self-assembly. Visual recognition of ortho-xylene is achieved through amplifying the structural difference of xylene isomers at molecular scale into macroscopic scale. We believe this work unveils subtle rules to control macroscopic assemblies at the molecular level and highlights the potential of using macrocyclic compounds to improve the quality and reduce the energy bill for separation in petrochemical industry.

Double-Encapsulated Microcapsules for the Adsorption to Cotton Fabrics

Double-encapsulated microcapsules (DEMs) were prepared and effectively adsorbed onto the cotton fabric surfaces during impregnation without crosslinking agents to obtain functional cotton fabrics. Specifically, Fourier transform infrared spectrometer (FTIR) and confocal laser scanning microscope (CLSM) showed two different molecules (lavender essence and dye indigo) were encapsulated into the microcapsules simultaneously, with loading capacity of 10% and 9.73%, respectively. The spherical shape of DEMs was confirmed by transmission electron microscopy (TEM), confocal laser scanning microscope (CLSM) and average particle sizes were about 617 nm, as measured by dynamic light scattering (DLS). According to the results of IR and X-ray photoelectron spectroscopy (XPS) experiments, DEMs was combined with cotton fabrics by hydrogen bond. The superior thermal stability of microcapsules and functional cotton fabrics was also demonstrated. The adsorption behavior and mechanism of microparticles onto cotton fabrics were further examined by chemical property characterization in combination with adsorption kinetic model. The kinetic adsorption process included three stages: fast adsorption, slow adsorption rate, and adsorption equilibrium. Finally, the good color fastness of the functional cotton fabrics was demonstrated by the tests of rubbing and accelerated laundering. Herein, this study will be beneficial to the development of functional cotton fabrics-based materials.

HP-β-CD for the formulation of IgG and Ig-based biotherapeutics

The main challenge to develop HCF for IgG and Ig-based therapeutics is to achieve essential solubility, viscosity and stability of these molecules in order to maintain product quality and meet regulatory requirement during manufacturing, production, storage, shipment and administration processes. The commonly used and FDA approved excipients for IgG and Ig -based therapeutics may no longer fulfil the challenge of HCF development for these molecules to certain extent, especially for some complex Ig-based platforms. 2-Hydroxypropyl beta-cyclodextrin (HP-β-CD) is one of the promising excipients applied recently for HCF development of IgG and Ig-based therapeutics although it has been used for formulation of small synthesized chemical drugs for more than thirty years. This review describes essential aspects about application of HP-β-CD as excipient in pharmaceutical formulation, including physico-chemical properties of HP-β-CD, supply chain, regulatory, patent landscape, marketed drugs with HP-β-CD, analytics and analytical challenges, stability and control strategies, and safety concerns. It also provides an overview of different studies, and outcomes thereof, regarding formulation development for IgGs and Ig-based molecules in liquid and solid (lyophilized) dosage forms with HP-β-CD. The review specifically highlights the challenges for formulation manufacturing of IgG and Ig-based therapeutics with HP-β-CD and identifies areas for future work in pharmaceutical and formulation development.

Cyclodextrin/surfactant inclusion complexes: An integrated view of their thermodynamic and structural properties

Cyclodextrins (CDs) play an important role in self-assembly systems of amphiphiles. The structure of CDs provides distinguished physicochemical properties, including the ability to form host-guest complexes. The complexation affects the properties of guest molecules and can produce supramolecular aggregates with desirable characteristics for fundamental and practical applications. Surfactants are particularly attractive host molecules due to their wide variety, availability, responsiveness to different stimuli, and high relevance in different fields, e.g. medical, cosmetic, pharmaceutical, and food industries. The tendency of organization in higher-order supramolecular aggregates arises the interest in applying such versatile complexes in the development of novel materials. In this review, we provide a comprehensive overview of the thermodynamics aspects of surfactants and CDs inclusion complexes formation in aqueous environment, emphasizing the assessment of the interactions, thermodynamic driving forces, and structural aspects. Also, the most common analytical techniques used to gather deep insight into the aspects of CDs complexes are discussed and the perspectives for the surfactant-cyclodextrin complexes are pointed out.

The intrinsic microstructure of supramolecular hydrogels derived from α-cyclodextrin and pluronic F127: nanosheet building blocks and hierarchically self-assembled structures

Supramolecular hydrogels derived from the self-assembly of α-cyclodextrin with pluronic F127 were found to be built up with polypseudorotaxane nanosheets with a thickness of 30-40 nm and possessed flower-like hierarchically assembled structures. The findings in this work could provide critical guidance for material design for biomedical purposes.

Nanoparticles containing β-cyclodextrin potentially useful for the treatment of Niemann-Pick C

β-Cyclodextrin (β-CD) is being considered a promising therapy for Niemann-Pick C (NPC) disease because of its ability to mobilise the entrapped cholesterol from lysosomes, however, a major limitation is its inability to cross the blood-brain barrier (BBB) and address the central nervous system (CNS) manifestations of the disease. Considering this, we aimed to design nanoparticles able to cross the BBB and deliver β-CD into the CNS lysosomes. The physicochemical characteristics of β-CD-loaded nanoparticles were evaluated by dynamic light scattering, small-angle X-ray scattering, and cryogenic transmission electron microscopy. The in vitro analyses were performed with NPC dermal fibroblasts and the β-CD-loaded nanoparticles were tracked in vivo. The nanoparticles showed a mean diameter around 120 nm with a disordered bicontinuous inner structure. The nanoparticles did not cause decrease in cell viability, impairment in the antioxidant enzymes activity, damage to biomolecules or release of reactive species in NPC dermal fibroblasts; also, they did not induce genotoxicity or alter the mitochondrial function in healthy fibroblasts. The β-CD-loaded nanoparticles were taken up by lysosomes reducing the cholesterol accumulated in NPC fibroblasts and reached the CNS of mice more intensely than other organs, demonstrating advantages compared to the free β-CD. The results demonstrated the potential of the β-CD-loaded nanoparticles in reducing the brain impairment of NPC.

Hydrogels Consisting of Vesicles Constructed via the Self-Assembly of a Supermolecular Complex Formed from α-Cyclodextrin and Perfluorononanoic Acid

The self-assembly of α-cyclodextrin (α-CD) mixed with a fluorocarbon surfactant, perfluorononanoic acid (PFNA), in aqueous solution was studied. Interestingly, the 1:1 inclusion complex, PFNA@α-CD, was verified to form by ¹H nuclear magnetic resonance measurement. Also as the building block, the PFNA@α-CD complex was further self-assembled into worm-like micelles under lower concentrations while hydrogels were self-assembled under higher concentrations. The hydrogels were composed of unilamellar vesicles with polydisperse size, which were clearly detected by freeze-fracture transmission electron microscopy measurements. Besides, the vesicle hydrogels showed high viscoelasticities and a substantial elastic characteristic. Also as revealed by the results of Fourier transform infrared measurements, the driving force for the vesicle and worm-like micelle formation was the hydrogen bonding between α-CD molecules. Then, these vesicles were densely packed to form hydrogels. As far as we know, the self-assembly of CDs and fluorocarbon surfactants based on host-guest inclusion in aqueous solution has been limitedly reported. Our work successfully constructed hydrogels consisting of vesicles through the self-assembly of the α-CD/PFNA complex for the first time and will also provide a better understanding and enrich the fundamental research of the self-assembly behavior of the CD/fluorosurfactant complex.

Endowing a Light-Inert Aqueous Surfactant Two-Phase System with Photoresponsiveness by Introducing a Trojan Horse

The ability to modulate the phase behavior of an aqueous surfactant two-phase (ASTP) system reversibly with light is of great importance in both fundamental and applied science. Thus far, most of the light-responsive ASTP systems are based on covalent modification of the component molecules. In this article, we, for the first time, achieve photoresponsiveness in a light-inert ASTP system by physically introducing a phototrigger with the aid of a Trojan horse. The ASTP system formed from sodium laurate (SL) and dodecyltributylammonium bromide (DBAB) does not show light responsiveness by physically mixing a light-responsive azobenzene compound, 2-(4-(phenyldiazenyl)phenoxy)acetate sodium (Azo). However, in the presence of the host-guest complex SL@β-CD formed from β-CD and sodium laurate (SL), the ASTP turns quickly into a homogeneous suspension under visible light, which recovers to the original ASTP state again under 365 nm UV irradiation. Because the SL@β-CD complex exists harmonically with the ASTP system, it can be viewed as a "Trojan horse" that becomes fatal only when the encapsulated SL is triggered to release. In the presence of the Trojan horse, the photoresponsiveness of the ASTP system can be manipulated reversibly by alternatively exerting UV and visible light. Using this strategy, we are able to collect trace amounts of oily components from water. The current strategy points out that it is possible to achieve light responsiveness in light-inert systems with a physical method, which may have profound impact on both the fundamental and applied science.

Controllable assembly of a novel cationic gemini surfactant containing a naphthalene and amide spacer with β-cyclodextrin

A novel cationic gemini surfactant (C12NDDA) with a spacer containing naphthalene and amides was successfully synthesized. The assembly of C12NDDA with β-cyclodextrin (β-CD) was investigated using various techniques including transmission electron microscopy, proton nuclear magnetic resonance (1H NMR), and scanning electron microscopy. Tuning the C12NDDA concentration and the C12NDDA/β-CD molar ratio allowed the production of different assembled aggregate morphologies such as micelles, vesicles, nanowires, nanorods, and hydrogels. Investigation of the inclusion mechanisms of C12NDDA and β-CD by 1H NMR revealed that hydrophobic interactions, hydrogen bonding, π-π stacking, and electrostatic forces play key roles in the assembly process. The antimicrobial activities of the C12NDDA/xβ-CD (x = 0-4) inclusion complexes were tested against Gram-negative bacteria (Escherichia coli and Salmonella) and Gram-positive bacteria (Staphylococcus aureus and Streptococcus), and very low minimum inhibitory concentrations of 0.078-0.31 μg mL-1 were observed. Thus, this newly synthesized gemini surfactant and its inclusion complexes exhibit potential as superior broad-spectrum disinfectants for various biomedical and biotechnological applications.

Self-Assembly of Aggregation-Induced-Emission Molecules

The last decade has witnessed rapid developments in aggregation-induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light-emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self-assembly behavior is very attractive because the formation of a well-defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self-assemble into well-defined structures. To date, some strategies have been proposed to achieve the self-assembly of AIEgens. Herein, we summarize the most recent approaches for the self-assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.

Designed construction of tween 60@2β-CD self-assembly vesicles as drug delivery carrier for cancer chemotherapy

We report a simple strategy to prepare Tween 60@2β-CD self-assembly vesicles in aqueous solution as a new drug delivery carrier for cancer chemotherapy. The spherical shape of vesicles was confirmed by transmission electron microscopy (TEM) and mean particle sizes were about 33.7 nm, as measured by dynamic light scattering, micro-IR results indicated that the self-assembly vesicles was driven by hydrogen bonding. Hydrophilic doxorubicin (DOX) was successfully loaded into the self-assembly vesicles with drug loading content of 7.85% and loading efficiency of 42%. In addition, an in vitro cytotoxicity study and cellular uptake assays demonstrated that the DOX-loaded Tween 60@2β-CD vesicles markedly enhanced the cellular uptake and cytotoxicity of DOX toward the Hela cells. Furthermore, when used to evaluate the in vivo therapeutic efficacy in mice bearing the breast cell line (4T1), DOX-loaded vesicles exhibited superior inhibition of tumor growth compared with the DOX solutions.

Cyclodextrin modified niosomes to encapsulate hydrophilic compounds

Niosomes were prepared from equimolar mixtures of two non-ionic surfactants, Span 80 and Tween 80. The capability of the vesicular systems was studied through the encapsulation of two azo dyes as molecular probes of different hydrophobicity (methyl orange (MO) and methyl yellow (MY)). To improve the efficiency of the niosomes to encapsulate the dyes, we employed an additional modification of the vesicular system, adding β-cyclodextrin (β-CD) or a modified amphiphilic β-CD (Mod-β-CD) to the niosomes. Neither the inclusion of dyes nor the incorporation of β-CD to the niosomes produces considerable modifications in size and morphology of the vesicles. However, in the presence of Mod-β-CD the niosomes became smaller, probably due to the anchoring of the cyclodextrin at the surface of vesicles through the hydrophobic chain, altering the curvature of the outer monolayer and reducing the surface charge of the interphase. The entrapment efficiency (EE) for MY was higher than that for MO in niosomes without cyclodextrin, however, the content of MO in the presence of β-CD increased considerably. Besides, the release of this dye under the same conditions was faster and reached 70% in 24 hours whereas in the absence of the macrocycle, the release was 15%, in the same time. UV-visible spectrophotometry and induced circular dichroism analysis allowed it to be established that MO is complexed with cyclodextrins inside vesicles, whereas MY interacts mainly with the niosome bilayer instead of with CD. Besides, the cavity of cyclodextrins is probably located in the interphase and preferably in the polar region of niosomes.

Incorporation of β-cyclodextrin into niosomes considerably increased the encapsulated amount and the delivery rate of a hydrophilic molecular probe.

Interfacial rheological behaviors of inclusion complexes of cyclodextrin and alkanes

The transformation of cyclodextrins (CDs) and alkanes from separated monomers to inclusion complexes at the interface is illustrated by analyzing the evolution of interfacial tension along with the variation of interfacial area for an oscillating drop. Amphiphilic intermediates are formed by threading one CD molecule on one alkane molecule at the oil/aqueous interface. After that, the amphiphilic intermediates transform into non-amphiphilic supramolecules which further assemble through hydrogen bonding at the oil/aqueous interface to generate a rigid network. With the accumulation of supramolecules at the interface, microcrystals are formed at the interface. The supramolecules of dodecane@2α-CD grow into microrods which form an unconsolidated shell and gradually cover the drop. However, the microcrystals of dodecane@2β-CD are significantly smaller which fabricate into skin-like films at the interface. The amphiphilic intermediates during the transformation increase the feasibility of self-emulsification and the skin-like films enhance the stability of the emulsion. With these unique properties, CDs can be promising for application in hydrophobic drug delivery, food industry and enhanced oil recovery.

Self-Aggregation, Antibacterial Activity, and Mildness of Cyclodextrin/Cationic Trimeric Surfactant Complexes

Despite efficacious antimicrobial activity, cationic oligomeric surfactants show strong skin irritation potential due to their larger cationic charge numbers and multiple hydrophobic chains. This work reports that the incorporation of α-, β-, and γ-CDs with different cavity sizes can effectively improve the mildness of cationic ammonium trimeric surfactant DTAD with a star-shaped spacer while maintaining its high antibacterial activity. On the basis of the different cavity sizes of CDs and the asymmetry in the spacer of DTAD, the CD/DTAD mixtures form α-CD@DTAD, 2α-CD@DTAD, β-CD@DTAD, and γ-CD@DTAD complexes. Compared to DTAD, these CD/DTAD complexes show much stronger self-assembly ability with much lower critical aggregation concentrations (CAC) and form more diverse aggregates with reduced zeta potential. Just above their CACs, the CD/DTAD complexes form vesicles or solid spherical aggregates of ∼50 nm and then transform into small micelles of ∼10 nm as the concentration increases. The strong self-assembly ability and the multiple sites of hydrogen bonds of the CD/DTAD complexes endow them with high antibacterial activity against E. coli, showing a very low minimum inhibitory concentration (2.22-2.48 μM) comparable to that of DTAD. In particular, the addition of CDs significantly reduces the abilities of DTAD in solubilizing zein (a skin model protein) and in binding with zein, and the mildness decreases in the order of 2α-CD@DTAD > β-CD@DTAD > γ-CD@DTAD > α-CD@DTAD. This tendency depends on their different self-assembling structures, and the formation of vesicles is approved to be in favor of the improvement of the mildness.

Kinetic trapping - a strategy for directing the self-assembly of unique functional nanostructures

Supramolecular self-assembly into various nano- or microscopic structures based on non-covalent interactions between molecules has been recognized as a very efficient approach that leads to functional materials. Since most non-covalent interactions are relatively weak and form and break without significant activation barriers, the thermodynamic equilibrium of many supramolecular systems can be easily influenced by processing pathways that allow the system to stay in a kinetically trapped state. Thus far, kinetic traps have been found to be very important in producing more elaborate structural and functional diversity of self-assembled systems. In this review, we try to summarize the approaches that can produce kinetically trapped self-assemblies based on examples made by us. We focus on the following subjects: (1) supramolecular pathway dependent self-assembly, including kinetically trapped self-assemblies facilitated by host-guest chemistry, coordination chemistry, and electrostatic interactions; (2) physical processing pathway dependent self-assembly, including solvent quality controlled self-assembly, evaporation induced self-assembly and crystallization induced self-assembly.

Sodium dodecyl sulfate/β-cyclodextrin vesicles embedded in chitosan gel for insulin delivery with pH-selective release

In an answer to the challenge of enzymatic instability and low oral bioavailability of proteins/peptides, a new type of drug-delivery vesicle has been developed. The preparation, based on sodium dodecyl sulfate (SDS) and β-cyclodextrin (β-CD) embedded in chitosan gel, was used to successfully deliver the model drug-insulin. The self-assembled SDS/β-CD vesicles were prepared and characterized by particle size, zeta potential, appearance, microscopic morphology and entrapment efficiency. In addition, both the interaction of insulin with vesicles and the stability of insulin loaded in vesicles in the presence of pepsin were investigated. The vesicles were crosslinked into thermo-sensitive chitosan/β-glycerol phosphate solution for an in-situ gel to enhance the dilution stability. The in vitro release characteristics of insulin from gels in media at different pH values were investigated. The insulin loaded vesicles–chitosan hydrogel (IVG) improved the dilution stability of the vesicles and provided pH-selective sustained release compared with insulin solution–chitosan hydrogel (ISG). In vitro, IVG exhibited slow release in acidic solution and relatively quick release in neutral solutions to provide drug efficacy. In simulated digestive fluid, IVG showed better sustained release and insulin protection properties compared with ISG. Thus IVG might improve the stability of insulin during its transport in vivo and contribute to the bioavailability and therapeutic effect of insulin.

Chain length dependent alkane/β-cyclodextrin nonamphiphilic supramolecular building blocks

In this work we report the chain length dependent behavior of the nonamphiphilic supramolecular building blocks based on the host-guest inclusion complexes of alkanes and β-cyclodextrins (β-CD). (1)H NMR, ESI-MS, and SAXS measurements verified that upon increasing the chain length of alkanes, the building blocks for vesicle formation changed from channel type 2alkane@2β-CD via channel type alkane@2β-CD to non-channel type 2alkane@2β-CD. FT-IR and TGA experiments indicated that hydrogen bonding is the extensive driving force for vesicle formation. It revealed that water molecules are involved in vesicle formation in the form of structural water. Upon changing the chain length, the average number of water molecules associated with per building block is about 16-21, depending on the chain length.

Adaptive soft molecular self-assemblies

Adaptive molecular self-assemblies provide possibility of constructing smart and functional materials in a non-covalent bottom-up manner. Exploiting the intrinsic properties of responsiveness of non-covalent interactions, a great number of fancy self-assemblies have been achieved. In this review, we try to highlight the recent advances in this field. The following contents are focused: (1) environmental adaptiveness, including smart self-assemblies adaptive to pH, temperature, pressure, and moisture; (2) special chemical adaptiveness, including nanostructures adaptive to important chemicals, such as enzymes, CO2, metal ions, redox agents, explosives, biomolecules; (3) field adaptiveness, including self-assembled materials that are capable of adapting to external fields such as magnetic field, electric field, light irradiation, and shear forces.

Smart stimuli-responsive fluorescent vesicular sensor based on inclusion complexation of cyclodextrins with Tyloxapol

Novel fluorescent vesicles based on inclusion complexes of β-cyclodextrins (β-CD) with Tyloxapol were constructed.

Enzyme-responsive protein/polysaccharide supramolecular nanoparticles

Biocompatible and enzyme-responsive supramolecular assemblies have attracted more and more interest in biomaterial fields, and find many feasible applications especially in the controlled drug release at specific sites where the target enzyme is located. In this work, novel supramolecular nanoparticles were successfully constructed from two biocompatible materials, i.e. a cyclic polysaccharide named sulfato-β-cyclodextrin (SCD) and a protein named protamine, through non-covalent association, and fully characterized by means of atomic force microscopy (AFM) and high-resolution transmission electron microscopy (TEM). Significantly, the disassembly of the resulting nanoparticles can respond especially to trypsin over other enzymes. Owing to their trypsin-triggered disassembly behaviors, these nanoparticles can efficiently release the encapsulated model substrate in a controlled manner. That is, the model substrate can be encapsulated inside the nanoparticles with a high stability and released when treated with trypsin.

Controllable self-assemblies of sodium benzoate in different solvent environments

Sodium benzoate is an important and widely used food additive, however, it's self-assembly properties in diverse solvents have been rarely studied. Here, we systematically report its various self-assemblies in different solvents environments.

Self-assembly of channel type β-CD dimers induced by dodecane

Cyclodextrins (CDs) can hardly self-assemble into well-defined structures. Here we report if they preassemble into channel type dimers assisted by dodecane, well-defined vesicles and bricks can be formed. Unlike the traditional self-assembly of amphiphilic molecules driven by hydrophobic effect, the self-assembly of the channel type dodecane@2β-CD supramolecular building block is predoninantly driven by hydrogen-bonds. More water molecules are found in the lyophilized vesicles than in the bricks, suggesting water molecules play an important role in the self-assembly of the channel-type dimers of β-CD. The amount of structural water in the self-assembly is closely related to the curvature of the final self-assembled structures. Our work reveals that the channel-type dimer of β-CD may represent a new sort of building block for advanced structures.

Advanced molecular self-assemblies facilitated by simple molecules

Advanced materials are often based on smart molecular self-assemblies that either respond to external stimuli or have hierarchical structures. Approaches to this goal usually stem from complicated molecular design and difficult organic synthesis. In this invited feature article, we demonstrate that desired molecular self-assemblies can be made conveniently by introducing simple functional molecules into amphiphilic systems. We show that upon introducing specific small molecules which serve as responders, modulators, or even building blocks, smart supramolecular architectures can be achieved which avoid complicated organic synthesis. We expect that this could be a general and economical way to produce advanced materials in the near future.

Self-assembly of triangular amphiphiles into diverse nano/microstructures and release behavior of the hollow sphere

Amphiphilic triangular derivatives containing imine bond have been designed and used as building blocks for the construction of soft colloidal materials. The acylhydrazone derivative was found to form various nano/microstructures in different solvents. The microspheres, flower-like, and hollow spheres were formed in the polar solvents, while organogels with microporous structures were formed in nonpolar solvents. However, the simple Schiff base amphiphile without amide group did not form any ordered structures in the tested solvents. Therefore, besides the π-π stacking between the aromatic core and the van der Waals interactions between the alkyl chains, the hydrogen bonding between the acylhydrazone moieties played an important role in promoting the formation of various organized structures. More interestingly, the hollow sphere structure which was formed in THF could be used to encapsulate and release the rhodamine B. It was found that rhodamine B was encapsulated within their interiors under neutral conditions and released in an acidic condition due to the breakage of the imine bond.