Complexation Thermodynamics of Cyclodextrins

Size-dependent compression of threaded alkyldiphosphate in head to head cyclodextrin [3]pseudorotaxanes

The encapsulation of guests in a confined space enables unusual conformations and reactivities. In particular, the compression of akyl chains has been obtained by self-assembled molecular capsules but such an effect has not been reported in solution for pseudorotaxane architectures. By exploiting the tendency of cyclodextrin (CD) to form head to head [3]pseudorotaxanes and the hydrogen bonding abilities of phosphate groups, we have studied the effect of the CD dimer cavity on the conformation of threaded α,ω-alkyl-diphosphate axles. The formation of [2]pseudorotaxanes and [3]pseudorotaxanes was investigated by a combination of NMR, ITC and X-ray diffraction techniques. In the solid state, the [3]pseudorotaxane with a C₈ axle presents a fully extended conformation with both terminal phosphate groups interacting with hydroxyl groups of the primary rim of CDs. Such hydrogen bonding interactions are also present with the C₉ and C₁₀ axles resulting in a compression of the alkyl chain with gauche conformations in the solid state. NMR studies have shown that this effect is maintained in solution resulting in a size-dependent progressive compression of the alkyl chain by the CD [3]pseudorotaxane architecture for C₉, C₁₀ and C₁₁ axles.

Alkyl chain compression of alkanediphosphate guests was achieved by head-to-head cyclodextrin [3]pseudorotaxanes in a mechanostereoselective self-assembly process.

Reliable prediction of association (free) energies of supramolecular complexes with heavy main group elements – the HS13L benchmark set

We introduce a set of 13 supramolecular complexes featuring diverse non-covalent interactions with heavy main group elements (Zn, As, Se, Te, Br, I), high charges (−2 up to +4), and large systems with up to 266 atoms (HS13L).

Locally superengineered cascade recognition–quantification zones in nanochannels for sensitive enantiomer identification

As an intriguing and intrinsic feature of life, chirality is highly associated with many significant biological processes. Simultaneous recognition and quantification of enantiomers remains a major challenge. Here, a sensitive enantiomer identification device is developed on TiO₂ nanochannels via the design of cascade recognition–quantification zones along the nanochannels. In this system, β-cyclodextrin (β-CD) is self-assembled on one side of the nanochannels for the selective recognition of enantiomers; CuMOFs are designed as the target-responsive partners on the other side of the nanochannels for the quantification of enantiomers that pass through the nanochannels. As a proof-of-principle of the cascade design, arginine (Arg) enantiomers are tested as the identification targets. The l-Arg molecules selectively bind in the recognition zone; d-Arg molecules pass through the recognition zone and then interact with the quantification zone via a specialized reduction reaction. As verified by nanofluidic simulations, because of the confinement effect of nanoscale channels combined with the condensation effect of porous structure, the in situ reaction in the quantification zone contributes to an unprecedented variation in transmembrane K⁺ flux, leading to an improved identification signal. This novel cascade-zone nanochannel membrane provides a smart strategy to design multifunctional nanofluidic devices.

A design of the cascade recognition–quantification zone is developed along TiO₂ nanochannels. The asymmetric nanochannels exhibit a predominant sensitivity and selectivity for enantiomer discrimination.

FePd nanowires modified with cyclodextrin as improved catalysts: effect of the alloy composition on colloidal stability and catalytic capacity

FePd nanowires of different compositions are thoroughly characterized and assessed as catalysts for the reduction reaction of 4-nitrophenol to 4-aminophenol.

Unravelling binding effects in cyclodextrin inclusion complexes with diamondoid ammonium salt guests

A hydrophobic tornado – complexation of diamondoid ammonium salts with cyclodextrins in water.

Water content and guest size dictate the mechanical properties of cyclodextrin mediated hydrogels

Steric bulkiness and water content plays an important role in mechanical properties of supramolecular hydrogels consisting of host-guest complexation as cross-links. With low and high water contents, the network mobility and the kinetics of the cross-links become dominant to the mechanical properties, respectively.

Thermally induced disassembly mechanism of pseudo-polyrotaxane nanosheets consisting of β-CD and a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer

PPRNSs dissolved in two steps during heating owing to the anisotropy of the topological constraint of β-CD by axis polymers.

Modification of cyclodextrin and use in environmental applications

Water pollution, which has become a global problem in parallel with environmental pollution, is a problem that needs to be solved urgently, considering the gradual depletion of water resources. The inadequacy of the water treatment methods and the materials used somehow directed the researchers to look for dual character structures such as biocompatible and biodegradable β-cyclodextrin (β-CD). β-CD, which is normally insoluble in water, is used in demanding wastewater applications by being modified with the help of different agents to be water soluble or transformed into polymeric adsorbents as a result of co-polymerization via cross-linkers. In this way, in addition to the host-guest interactions offered by β-CD, secondary forces arising from these interactions provide advantages in terms of regeneration and reusability. However, the adsorption efficiency and synthesis steps need to be improved. Based on the current studies presented in this review, in which cross-linkers and modification methods are also mentioned, suggestions for novel synthesis methods of new-generation β-CD-based materials, criticisms, and recent methods of removal of micropollutants such as heavy metals, industrial dyes, harmful biomolecules, and pharmaceutics wastes are mentioned.

Studies of the Formation and Stability of Ezetimibe-Cyclodextrin Inclusion Complexes

In the presented studies, the interactions between ezetimibe (EZE) and selected cyclodextrins were investigated. α-Cyclodextrin (αCD), β-cyclodextrin (βCD) and its modified derivatives, hydroxypropyl-β-cyclodextrin (HPβCD) and sulfobutylether-β-cyclodextrin (SBEβCD), were selected for the research. Measurements were carried out using calorimetric and spectroscopic methods. Additionally, the Hirshfeld surface and biochemical analysis were achieved. As a result of the study, the inclusion complexes with 1:1 stoichiometry were obtained. The most stable are the complexes of β-cyclodextrin and its derivatives. The comparison of βCD with its derivatives shows that the modifications have an affect on the formation of more durable and stable complexes.

Cyclodextrins: Structural, Chemical, and Physical Properties, and Applications

Due to their unique structural, physical and chemical properties, cyclodextrins and their derivatives have been of great interest to scientists and researchers in both academia and industry for over a century. Many of the industrial applications of cyclodextrins have arisen from their ability to encapsulate, either partially or fully, other molecules, especially organic compounds. Cyclodextrins are non-toxic oligopolymers of glucose that help to increase the solubility of organic compounds with poor aqueous solubility, can mask odors from foul-smelling compounds, and have been widely studied in the area of drug delivery. In this review, we explore the structural and chemical properties of cyclodextrins that give rise to this encapsulation (i.e., the formation of inclusion complexes) ability. This review is unique from others written on this subject because it provides powerful insights into factors that affect cyclodextrin encapsulation. It also examines these insights in great detail. Later, we provide an overview of some industrial applications of cyclodextrins, while emphasizing the role of encapsulation in these applications. We strongly believe that cyclodextrins will continue to garner interest from scientists for many years to come, and that novel applications of cyclodextrins have yet to be discovered.

Entropy Effects in Intermolecular Associations of Crown-Ethers and Cyclodextrins with Amino Acids in Aqueous and in Non-Aqueous Media

The analysis of the ratios of entropy and enthalpy characteristics and their contributions to the change in the Gibbs energy of intermolecular interactions of crown ethers and cyclodextrins with amino acids is carried out. Two different types of macrocycles were chosen for examination: crown ethers with a hydrophilic interior and cyclodextrins with a hydrophobic inner cavity and a hydrophilic exterior. The thermodynamics of complex formation of crown ethers and cyclodextrins with amino acids in water and aqueous-organic solvents of variable composition was examined. The contributions of the entropy solvation of complexes of 18-crown-6 with glycine, alanine, phenylalanine to the change in the entropy of complexation in water-ethanol and water-dimethyl sulfoxide solvents was calculated and analyzed. It was found that the ratios of the entropy and enthalpy solvation of the reagents for these systems have similar trends when moving from water to aqueous-organic mixtures. The relationship between the thermodynamic characteristics and structural features of the complexation processes between cyclodextrins and amino acids has been established. The thermodynamic enthalpy–entropy compensation effect was revealed, and its features for complexation of cyclodextrins and 18-crown-6 were considered. It was concluded that, based on the thermodynamic parameters of molecular complexation, one could judge the mode of the formation of complexes, the main driving forces of the interactions, and the degree of desolvation.

In Vitro and In Vivo Sequestration of Methamphetamine by a Sulfated Acyclic CB[n]-Type Receptor

We report the synthesis of two new acyclic sulfated acyclic CB[n]-type receptors (TriM0 and Me4 TetM0) and investigations of their binding properties toward a panel of drugs of abuse (1-13) by a combination of 1 H NMR spectroscopy and isothermal titration calorimetry. TetM0 is the most potent receptor with Ka ≥106  M-1 toward methamphetamine, fentanyl, MDMA and mephedrone. TetM0 is not cytotoxic toward HepG2 and HEK 293 cells below 100 μM according to MTS metabolic and adenylate kinase release assays and is well tolerated in vivo when dosed at 46 mg kg-1 . TetM0 does not inhibit the hERG ion channel and is not mutagenic based on the Ames fluctuation test. Finally, in vivo efficacy studies show that the hyperlocomotion of mice treated with methamphetamine can be greatly reduced by treatment with TetM0 up to 5 minutes later. TetM0 has potential as a broad spectrum in vivo sequestrant for drugs of abuse.

Bottom-Up Solid-State Molecular Assembly via Guest-Induced Intermolecular Interactions

The manipulation of molecular motions to construct highly ordered supramolecular architectures from chaos in the solid state is considered to be far more complex and challenging in comparison to that in solution. In this work, a bottom-up molecular assembly approach based on a newly designed skeleton-trimmed pillar[5]arene analogue, namely the permethylated leggero pillar[5]arene MeP[5]L, is developed in the solid state. An amorphous powder of MeP[5]L can take up certain guest vapors to form various ordered linker-containing solid-state molecular assemblies, which can be further used to construct a thermodynamically favored linker-free superstructure upon heating. These approaches are driven by vapor-induced solid-state molecular motions followed by a thermally triggered phase-to-phase transformation. The intermolecular interactions play a crucial role in controlling the molecular arrangements in the resulting assemblies. This research will open new insights into exploring controllable molecular motions and assemblies in the solid state, providing new perspectives in supramolecular chemistry and materials.

Enantioselective synthesis of heterocyclic compounds using photochemical reactions

Different methods for the direct enantioselective photochemical synthesis of heterocycles are presented. Currently, asymmetric catalysis with templates involving hydrogen bonds or metal complexes is intensively investigated. Enzyme catalysis can be simplified under photochemical conditions. For example, in multi enzyme systems, one or more enzyme catalytic steps can be replaced by simple photochemical reactions. Chiral induction in photochemical reactions performed with homochiral crystals is highly efficient. Such reactions can also be carried out with crystalline inclusion complexes. Inclusion of a photochemical substrate and an enantiopure compound in zeolites also leads to enantioselective compounds. In all these methods, the conformational mobility of the photochemical substrates is reduced or controlled. Memory of chirality is a particular case in which a chiral information is temporally lost but the rigid conformations stabilize the molecular structure which leads to the formation of enantiopure compounds. Such studies allows a profound understanding on how particular conformations determine the configuration of the final products.Graphical abstract.

Deconstruction and Reassembly of Renewable Polymers and Biocolloids into Next Generation Structured Materials

This review considers the most recent developments in supramolecular and supraparticle structures obtained from natural, renewable biopolymers as well as their disassembly and reassembly into engineered materials. We introduce the main interactions that control bottom-up synthesis and top-down design at different length scales, highlighting the promise of natural biopolymers and associated building blocks. The latter have become main actors in the recent surge of the scientific and patent literature related to the subject. Such developments make prominent use of multicomponent and hierarchical polymeric assemblies and structures that contain polysaccharides (cellulose, chitin, and others), polyphenols (lignins, tannins), and proteins (soy, whey, silk, and other proteins). We offer a comprehensive discussion about the interactions that exist in their native architectures (including multicomponent and composite forms), the chemical modification of polysaccharides and their deconstruction into high axial aspect nanofibers and nanorods. We reflect on the availability and suitability of the latter types of building blocks to enable superstructures and colloidal associations. As far as processing, we describe the most relevant transitions, from the solution to the gel state and the routes that can be used to arrive to consolidated materials with prescribed properties. We highlight the implementation of supramolecular and superstructures in different technological fields that exploit the synergies exhibited by renewable polymers and biocolloids integrated in structured materials.

Adamantane-Substituted Purines and Their β-Cyclodextrin Complexes: Synthesis and Biological Activity

Cyclin-dependent kinases (CDKs) play an important role in the cell-division cycle. Synthetic inhibitors of CDKs are based on 2,6,9-trisubstituted purines and are developed as potential anticancer drugs; however, they have low solubility in water. In this study, we proved that the pharmaco-chemical properties of purine-based inhibitors can be improved by appropriate substitution with the adamantane moiety. We prepared ten new purine derivatives with adamantane skeletons that were linked at position 6 using phenylene spacers of variable geometry and polarity. We demonstrated that the adamantane skeleton does not compromise the biological activity, and some of the new purines displayed even higher inhibition activity towards CDK2/cyclin E than the parental compounds. These findings were supported by a docking study, which showed an adamantane scaffold inside the binding pocket participating in the complex stabilisation with non-polar interactions. In addition, we demonstrated that β-cyclodextrin (CD) increases the drug’s solubility in water, although this is at the cost of reducing the biochemical and cellular effect. Most likely, the drug concentration, which is necessary for target engagement, was decreased by competitive drug binding within the complex with β-CD.

Thermodynamic Studies of Interactions between Sertraline Hydrochloride and Randomly Methylated β-Cyclodextrin Molecules Supported by Circular Dichroism Spectroscopy and Molecular Docking Results

The interaction between sertraline hydrochloride (SRT) and randomly methylated β-cyclodextrin (RMβCD) molecules have been investigated at 298.15 K under atmospheric pressure. The method used-Isothermal Titration Calorimetry (ITC) enabled to determine values of the thermodynamic functions like the enthalpy (ΔH), the entropy (ΔS) and the Gibbs free energy (ΔG) of binding for the examined system. Moreover, the stoichiometry coefficient of binding (n) and binding/association constant (K) value have been calculated from the experimental results. The obtained outcome was compared with the data from the literature for other non-ionic βCD derivatives interacting with SRT and the enthalpy-entropy compensation were observed and interpreted. Furthermore, the connection of RMβCD with SRT was characterized by circular dichroism spectroscopy (CD) and complexes of βCD derivatives with SRT were characterized through the computational studies with the use of molecular docking (MD).

FRET-Based In-Cell Detection of Highly Selective Supramolecular Complexes of meso-Tetraarylporphyrin with Peptide/BODIPY-Modified Per-O-Methyl-β-Cyclodextrins

Artificial supramolecular systems capable of self-assembly and that precisely function in biological media are in high demand. Herein, we demonstrate a highly specific host-guest-pair system that functions in living cells. A per-O-methyl-β-cyclodextrin derivative (R8-B-CD^Me ) bearing both an octaarginine peptide chain and a BODIPY dye was synthesized as a fluorescent intracellular delivery tool. R8-B-CD^Me was efficiently taken up by HeLa cells through both endocytosis and direct transmembrane pathways. R8-B-CD^Me formed a 2 : 1 inclusion complex with tetrakis(4-sulfonatophenyl)porphyrin (TPPS) as a guest molecule in water, from which fluorescence resonance energy transfer (FRET) from R8-B-CD^Me to TPPS was observed. The FRET phenomenon was clearly detected in living cells using confocal microscopy techniques, which revealed that the formed supramolecular R8-B-CD^Me /TPPS complex was maintained within the cells. The R8-B-CD^Me cytotoxicity assay revealed that the addition of TPPS counteracts the strong cytotoxicity (IC₅₀ =16 μM) of the CD cavity due to complexation within the cells. A series of experiments demonstrated the bio-orthogonality of the supramolecular per-O-methyl-β-CD/tetraarylporphyrin host-guest pair in living cells.

Host-Guest Complexation Between Cyclodextrins and Hybrid Hexavanadates: What are the Driving Forces?

Host-guest complexes between native cyclodextrins (α-, β- and γ-CD) and hybrid Lindqvist-type polyoxovanadates (POVs) [V₆ O₁₃ ((OCH₂ )₃ C-R)₂ ]^2- with R = CH₂ CH₃ , NO₂ , CH₂ OH and NH(BOC) (BOC = N-tert-butoxycarbonyl) were studied in aqueous solution. Six crystal structures determined by single-crystal X-ray diffraction analysis revealed the nature of the functional R group strongly influences the host-guest conformation and also the crystal packing. In all systems isolated in the solid-state, the organic groups R are embedded within the cyclodextrin cavities, involving only a few weak supramolecular contacts. The interaction between hybrid POVs and the macrocyclic organic hosts have been deeply studied in solution using ITC, cyclic voltammetry and NMR methods (1D ¹ H NMR, and 2D DOSY, and ROESY). This set of complementary techniques provides clear insights about the strength of interactions and the binding host-guest modes occurring in aqueous solution, highlighting a dramatic influence of the functional group R on the supramolecular properties of the hexavanadate polyoxoanions (association constant K_1:1 vary from 0 to 2 000 M^-1 ) while isolated functional organic groups exhibit only very weak intrinsic affinity with CDs. Electrochemical and calorimetric investigations suggest that the driving force of the host-guest association involving larger CDs (β- and γ-CD) is mainly related to the chaotropic effect. In contrast, the hydrophobic effect supported by weak attractive forces appears as the main contributor for the formation of α-CD-containing host-guest complexes. In any cases, the origin of driving forces is clearly related to the ability of the macrocyclic host to desolvate the exposed moieties of the hybrid POVs.

New Antifungal Compound: Impact of Cosolvency, Micellization and Complexation on Solubility and Permeability Processes

Poor solubility of new antifungal of 1,2,4-triazole class (S-119)—a structural analogue of fluconazole in aqueous media was estimated. The solubility improvement using different excipients: biopolymers (PEGs, PVP), surfactants (Brij S20, pluronic F-127) and cyclodextrins (α-CD, β-CD, 2-HP-β-CD, 6-O-Maltosyl-β-CD) was assessed in buffer solutions pH 2.0 and pH 7.4. Additionally, 2-HP-β-CD and 6-O-Maltosyl-β-CD were proposed as promising solubilizers for S-119. According to the solubilization capacity and micelle/water partition coefficients in buffer pH 7.4 pluronic F-127 was shown to improve S-119 solubility better than Brij S20. Among biopolymers, the greatest increase in solubility was shown in PVP solutions (pH 7.4) at concentrations above 4 w/v%. Complex analysis of the driving forces of solubilization, micellization and complexation processes matched the solubility results and suggested pluronic F-127 and 6-O-Maltosyl-β-CD as the most effective solubilizing agents for S-119. The comparison of S-119 diffusion through the cellulose membrane and lipophilic PermeaPad barrier revealed a considerable effect of the lipid layer on the decrease in the permeability coefficient. According to the PermeaPad, S-119 was classified as a highly permeated substance. The addition of 1.5 w/v% CDs in donor solution moves it to low-medium permeability class.

Targeted Delivery and Site-Specific Activation of β-Cyclodextrin-Conjugated Photosensitizers for Photodynamic Therapy through a Supramolecular Bio-orthogonal Approach

Targeted delivery of photosensitizers using hydrophilic and tumor-directing carriers and site-specific activation of their photocytotoxicity are two common strategies to enhance the specificity of anticancer photodynamic therapy. We report herein a novel supramolecular bio-orthogonal approach to integrate these two functions. A β-cyclodextrin-substituted aza-boron-dipyrromethene-based photosensitizer was first complexed with a ferrocene-substituted black-hole quencher to inhibit its photosensitizing ability. Upon encountering the adamantane moieties that had been delivered to target cancer cells through specific binding of the conjugated peptide to the overexpressed epidermal growth factor receptor, the ferrocene-based guest species were displaced due to the stronger binding interactions between β-cyclodextrin and adamantane, thereby restoring the photodynamic activity of the photosensitizer. Hence, this two-step process enabled targeted delivery and site-specific activation of the photosensitizer, as demonstrated through a series of experiments in aqueous media, in a range of cancer cell lines and in tumor-bearing nude mice.

Macrocycle Dynamics in a Branched [8]Catenane Controlled by Three Different Stimuli in Three Different Regions

A branched [8]catenane from an efficient one-pot synthesis (72 % HPLC yield, 59 % isolated yield) featuring the simultaneous use of three kinds of templates and cucurbit[6]uril-mediated azide-alkyne cycloaddition (CBAAC) for ring-closing is reported. Design and assembly of the [8]catenane precursors are unexpectedly complex that can involve cooperating, competing and non-influencing interactions. Due to the branched structure, dynamics of the [8]catenane can be modulated in different extent by rigidifying/loosening the mechanical bonds at different regions by using solvent polarity, acid-base and metal ions as the stimuli. This work not only highlights the importance of understanding the delicate interplay of the weak and non-obvious supramolecular interactions in the synthesis of high-order [n]catenane, but also demonstrates a complex control of dynamics and flexibility for exploiting [n]catenanes applications.

Cyclodextrin polymer-valved MoS2-embedded mesoporous silica nanopesticides toward hierarchical targets via multidimensional stimuli of biological and natural environments

Targeted delivery of pesticides towards pests and pathogens can significantly improve the bioavailability and efficacy of pesticides and minimize the impact on the environment. Cyclodextrin polymer (CDP)-valved, benzimidazole functionalized, MoS₂-embedded mesoporous silica (MoS₂@MSN@CDP) nanopesticides were constructed toward hierarchical biological targets of pests, pathogens, and foliage. The splash and bounce of the aqueous droplets containing MoS₂@MSN@CDP nanoparticles in the presence of Aersosol OT on superhydrophobic surfaces were well inhibited available for excellent wetting to prevent pesticides from losing to the environment. The multivalent supramolecular nanovalves between CDP and the functionalized benzimidazole moieties could be activated for the controlled release of pesticides in the cases of low pH and α-amylase. It is the first time to report the foliage-triggered controlled release of pesticides, owing to the competitive binding of epicuticular wax components to CDP. Furthermore, thermogenic MoS₂ cores triggered the controlled release of pesticides under irradiation of near infrared light. The fungicidal efficacies of the stimuli-responsive nanopesticides against pathogenic fungi Rhizoctonia solani and Fusarium graminearum were demonstrated. It is clear that the smart nanopesticides could realize the controlled release of pesticides toward hierarchical biological targets for enhanced pesticide bioavailability and efficacy via the multidimensional stimuli of pH, α-amylase, epicuticular waxes, and sunlight.

A spectrofluorimetric method for the determination of pindolol in natural waters using various organic and cyclodextrin media

A simple, sensitive, and rapid spectrofluorimetric method was developed for the determination of the β-blocker pindolol. The native fluorescence of pindolol was measured in different organic solvents and in cyclodextrin aqueous media. The highest fluorescence signal was obtained in 2-propanol at λ_em = 303 nm with λ_ex = 260 nm. Analytical figures of merit for the spectrofluorimetric determination of pindolol were satisfactory, with wide linear dynamic range (LDR) values of two orders of magnitude, and rather low limit of detection (LOD) values between 0.2 and 8.7 ng/mL. Moreover, the addition of cyclodextrins (HP-β-CD and β-CD) in aqueous media enhanced the fluorescence of pindolol. In addition, the inclusion complexes of pindolol with cyclodextrins were investigated and the stability constants of complexes were calculated by means of the method of nonlinear regression (NLR). The method was successfully applied to the analysis of tap water and natural water samples, spiked with pindolol.

Engineering hydrogels with homogeneous mechanical properties for controlling stem cell lineage specification

Hydrogels are extensively used for cell culture, tissue engineering, and flexible electronics. In all of these applications, mechanical properties of hydrogels play an important role. Although tremendous studies have been devoted to optimizing the stiffness, strain, toughness, and dynamic mechanical response, the mechanical homogeneity of hydrogels has rarely been considered. By developing a general strategy to control the mechanical homogeneity of hydrogels, here we show that nanoscale variation in matrix stiffness can considerably affect the lineage specification of human embryonic stem cells. Inhomogeneous hydrogels suppress mechanotransduction and facilitate stemness maintenance, while homogenous hydrogels promote mechanotransduction and osteogenic differentiation. Therefore, engineering hydrogels with controllable and well-defined nanoscale homogeneity may have considerable implications in stem cell culture and regenerative medicine.

The extracellular matrix (ECM) is mechanically inhomogeneous due to the presence of a wide spectrum of biomacromolecules and hierarchically assembled structures at the nanoscale. Mechanical inhomogeneity can be even more pronounced under pathological conditions due to injury, fibrogenesis, or tumorigenesis. Although considerable progress has been devoted to engineering synthetic hydrogels to mimic the ECM, the effect of the mechanical inhomogeneity of hydrogels has been widely overlooked. Here, we develop a method based on host–guest chemistry to control the homogeneity of maleimide–thiol cross-linked poly(ethylene glycol) hydrogels. We show that mechanical homogeneity plays an important role in controlling the differentiation or stemness maintenance of human embryonic stem cells. Inhomogeneous hydrogels disrupt actin assembly and lead to reduced YAP activation levels, while homogeneous hydrogels promote mechanotransduction. Thus, the method we developed to minimize the mechanical inhomogeneity of hydrogels may have broad applications in cell culture and tissue engineering.

Red-Emitting Fluorophores as Local Water-Sensing Probes

Fluorescent probes are known for their ability to sense changes in their direct environment. We introduce here the idea that common red-emitting fluorophores recommended for biological labeling and typically used for simple visualization of biomolecules can also act as reporters of the water content in their first solvent sphere by a simple measurement of their fluorescence lifetime. Using fluorescence spectroscopy, we investigated the excited-state dynamics of seven commercially available fluorophores emitting between 650 and 800 nm that are efficiently quenched by H₂O. The amount of H₂O in their direct surrounding was modulated in homogeneous H₂O-D₂O mixtures or, in heterogeneous systems, by confining them into reverse micelles, by encapsulating them into host-guest complexes with cyclodextrins, or by attaching them to peptides and proteins. We found that their fluorescence properties can be rationalized in terms of the amount of H₂O in their direct surroundings, which provides a general mechanism for protein-induced fluorescence enhancements of red-emitting dyes and opens perspectives for directly counting water molecules in key biological environments or in polymers.

A rapid screening method to select microdialysis carriers for hydrophobic compounds

Microdialysis is a minimally invasive sampling technique which is widely applied in many fields including clinical studies. This technique usually has limitation on sampling hydrophobic compounds as aqueous solutions are commonly used as the perfusates. The relative recovery of hydrophobic compounds is often low and irreproducible because of the non-specific binding to microdialysis membranes or catheter tubing. Carriers such as cyclodextrins have been used to improve the recovery and consistency, however the identification of an optimal carrier can only be achieved after time-consuming and costly microdialysis experiments. We therefore developed a rapid, convenient, and low-cost method to identify the optimal carriers for sampling hydrophobic compounds with the use of centrifugal ultrafiltration. Doxorubicin was used as the model compound and its relative recoveries obtained from centrifugal ultrafiltration and from microdialysis were compared. The results show that the relative recoveries are highly correlated (correlation coefficient ≥ 0.9) between centrifugal ultrafiltration and microdialysis when different types or different concentrations of cyclodextrins were used as the carriers. In addition to doxorubicin, this method was further confirmed on three other drugs with different hydrophobicity. This method may facilitate and broaden the use of microdialysis perfusion on sampling or delivering hydrophobic substances in various applications.

Mono-6-Substituted Cyclodextrins-Synthesis and Applications

Cyclodextrins are well known supramolecular hosts used in a wide range of applications. Monosubstitution of native cyclodextrins in the position C-6 of a glucose unit represents the simplest method how to achieve covalent binding of a well-defined host unit into the more complicated systems. These derivatives are relatively easy to prepare; that is why the number of publications describing their preparations exceeds 1400, and the reported synthetic methods are often very similar. Nevertheless, it might be very demanding to decide which of the published methods is the best one for the intended purpose. In the review, we aim to present only the most useful and well-described methods for preparing different types of mono-6-substituted derivatives. We also discuss the common problems encountered during their syntheses and suggest their optimal solutions.

Polyaniline/Biopolymer Composite Systems for Humidity Sensor Applications: A Review

The development of polyaniline (PANI)/biomaterial composites as humidity sensor materials represents an emerging area of advanced materials with promising applications. The increasing attention to biopolymer materials as desiccants for humidity sensor components can be explained by their sustainability and propensity to absorb water. This review represents a literature survey, covering the last decade, which is focused on the interrelationship between the core properties and moisture responsiveness of multicomponent polymer/biomaterial composites. This contribution provides an overview of humidity-sensing materials and the corresponding sensors that emphasize the resistive (impedance) type of PANI devices. The key physicochemical properties that affect moisture sensitivity include the following: swelling, water vapor adsorption capacity, porosity, electrical conductivity, and enthalpies of adsorption and vaporization. Some key features of humidity-sensing materials involve the response time, recovery time, and hysteresis error. This work presents a discussion on various types of humidity-responsive composite materials that contain PANI and biopolymers, such as cellulose, chitosan and structurally related systems, along with a brief overview of carbonaceous and ceramic materials. The effect of additive components, such as polyvinyl alcohol (PVA), for film fabrication and their adsorption properties are also discussed. The mechanisms of hydration and proton transfer, as well as the relationship with conductivity is discussed. The literature survey on hydration reveals that the textural properties (surface area and pore structure) of a material, along with the hydrophile-lipophile balance (HLB) play a crucial role. The role of HLB is important in PANI/biopolymer materials for understanding hydration phenomena and hydrophobic effects. Fundamental aspects of hydration studies that are relevant to humidity sensor materials are reviewed. The experimental design of humidity sensor materials is described, and their relevant physicochemical characterization methods are covered, along with some perspectives on future directions in research on PANI-based humidity sensors.

Self-Assembly and Photochemistry of a Pyrene-Methyl Viologen Supramolecular Fiber System

This paper reports the self-assembly of a donor-acceptor system into nanoscopic structures and the photo processes taking place within these structures. The donor employed is pyrene linked to two β-cyclodextrin molecules (CD-PY-CD), and adamantane-linked methyl viologen attached to the three arms of mesitylene (Ms-(MV²⁺-AD)₃) is the acceptor. CD-PY-CD and Ms-(MV²⁺-AD)₃ when dissolved in water self-assembled into vesicles, which joined together to give long fibers. The self-assembly was studied using spectroscopic and microscopic techniques. Fluorescence of the pyrene chromophore was quenched within the self-assembled system due to efficient photoinduced electron transfer to methyl viologen. Photoinduced electron transfer within the assembly is confirmed through identification of product radical ions in flash photolysis experiments. Steady-state irradiation of the self-assembled system in an optical bench led to the formation of methyl viologen radical cation, which was stable for a few hours. Longevity of the radical cation was attributed to the fast reaction of pyrene radical cation with adjacent pyrene to give an unstable adduct, which slows down the back electron transfer process.

Self-Assembled Open Porous Nanoparticle Superstructures

Imparting porosity to inorganic nanoparticle assemblies to build up self-assembled open porous nanoparticle superstructures represents one of the most challenging issues and will reshape the property and application scope of traditional inorganic nanoparticle solids. Herein, we discovered how to engineer open pores into diverse ordered nanoparticle superstructures via their inclusion-induced assembly within 1D nanotubes, akin to the molecular host-guest complexation. The open porous structure of self-assembled composites is generated from nonclose-packing of nanoparticles in 1D confined space. Tuning the size ratios of the tube-to-nanoparticle enables the structural modulation of these porous nanoparticle superstructures, with symmetries such as C₁, zigzag, C₂, C₄, and C₅. Moreover, when the internal surface of the nanotubes is blocked by molecular additives, the nanoparticles would switch their assembly pathway and self-assemble on the external surface of the nanotubes without the formation of porous nanoparticle assemblies. We also show that the open porous nanoparticle superstructures can be ideal candidate for catalysis with accelerated reaction rates.

Upper Critical Solution Temperature-Type Responsive Cyclodextrins with Characteristic Inclusion Abilities

Water-soluble and thermoresponsive macrocycles with stable inclusion toward guests are highly valuable to construct stimuli-responsive supramolecular materials for versatile applications. Here, we develop such macrocycles - ureido-substituted cyclodextrins (CDs) which exhibit unprecedented upper critical solution temperature (UCST) behavior in aqueous media. These novel CD derivatives showed good solubility in water at elevated temperature, but collapsed from water to form large coacervates upon cooling to low temperature. Their cloud points are greatly dependent on concentration and can be mediated through oxidation and chelation with silver ions. Significantly, the amphiphilicity of these CD derivatives is supportive to host-guest binding, which affords them inclusion abilities to guest dyes. The inclusion complexation remained nearly intact during thermally induced phase transitions, which is in contrast to the switchable inclusion behavior of lower critical solution temperature (LCST)-type CDs. Moreover, ureido-substituted CDs were exploited to co-encapsulate a pair of guest dyes whose fluorescence resonance energy transfer process can be switched by the UCST phase transition. We therefore believe these novel thermoresponsive CDs may form a new strategy for developing smart macrocycles and allow for exploring smart supramolecular materials.

Cyclodextrins in drug delivery: applications in gene and combination therapy

Gene therapy is a powerful tool against genetic disorders and cancer, targeting the source of the disease rather than just treating the symptoms. While much of the initial success of gene delivery relied on viral vectors, non-viral vectors are emerging as promising gene delivery systems for efficacious treatment with decreased toxicity concerns. However, the delivery of genetic material is still challenging, and there is a need for vectors with enhanced targeting, reduced toxicity, and controlled release. In this article, we highlight current work in gene therapy which utilizes the cyclic oligosaccharide molecule cyclodextrin (CD). With a number of unique abilities, such as hosting small molecule drugs, acting as a linker or modular component, reducing immunogenicity, and disrupting membranes, CD is a valuable constituent in many delivery systems. These carriers also demonstrate great promise in combination therapies, due to the ease of assembling macromolecular structures and wide variety of chemical derivatives, which allow for customizable delivery systems and co-delivery of therapeutics. The use of combination and personalized therapies can result in improved patient health-modular systems, such as those which incorporate CD, are more conducive to these therapy types. Graphical abstract.

Attachment of cyclodextrin acids to PEGA resin and study of binding with fluorescence microscopy

Three different cyclodextrin acids, 6^A,6^D-di-O-(prop-2-carboxy-1,3-dienyl)-α-cyclodextrin (1), 6-deoxy-β-cyclodextrin-6-carboxylic acid (2), 6-deoxy-β-cyclodextrin-6-ethylenecarboxylic acid (3), were prepared and attached to amino PEGA resin as amides using coupling conditions with COMU and NEM. Host-guest binding to the resins was studied by fluorescence microscopy using 8-anilinoaphtalene-1-sulfonic acid (ANS) as guest, and was found to follow the equation I_F = I_Fmax*[ANS]/([ANS] + K_d) where F, F_max and K_d are the fluorescence, maximum fluorescence and K_d the dissociation constant for the ANS-cyclodextrin complex, respectively. K_d was 4.4, 2.4 and 4.9 × 10^-4 M for the three resins. Competitive inhibition of ANS binding was performed with 1-adamantanylamine and octyl β-d-glucoside with the latter being selective for the α-cyclodextrin as expected.

Removal of Pesticides from Waters by Adsorption: Comparison between Synthetic Zeolites and Mesoporous Silica Materials. A Review

Pesticides are pollutants found in wastewater due to increasing agricultural activities over the years. Inappropriate dosing of pesticides results in the dispersal of active ingredients in the environment. The complete removal of pesticides from wastewater is an immediate concern due to their high toxicity and mobility. At present, adsorption is one of the most widely used methods for pesticide removal, in which synthetic zeolites and mesoporous silica materials are extensively applied. This article presents a systematic and comparative review of the applications and comparison of these adsorbents, based on the data reported in the literature. The paper summarizes the information collected from various studies, including the type of adsorbents and pesticides used, experimental conditions, and results of each work. The studies analyzed were laboratory-based and show potential advantages for the treatment of pesticide-bearing waters using functionalized and unfunctionalized synthetic zeolites and mesoporous silica materials. As a whole, functionalized materials are reported to exhibit better removal performance for different pesticides than conventional materials. It is expected that the results of this review will help researchers to establish a powerful strategy for the abatement of pesticides in wastewater.