Search Results (422)

The Gibbs equation describes the relationship between the enthalpy (∆H), entropy (∆S), and Gibbs energy (∆G) changes in physicochemical processes: ∆G = ∆H − T∆S. It remains a cornerstone of chemical thermodynamics, yet it has features that need to be understood. The linear correlations between ∆S and ∆H (or ∆G and ∆H) are often found across various series of processes. These correlations do not follow from the laws of thermodynamics, thus meaning that there may be additional restrictions on the variation in the thermodynamic potentials. In this study, we attempted to establish the quantitative principles governing the ∆G vs. ∆H relationship across various processes involving non-covalent interactions at 298.15 K, from solvation and vaporization to molecular complexation and supramolecular recognition. The baseline for the analysis was the linear ∆G vs. ∆H correlation for solvation in non-associated solute–solvent systems, first noted by Barclay and Butler. The classification of the solute–solvent systems enabled quantification of the deviations associated with conformational flexibility, complexation and solvophobic effects upon solvation. These regularities necessarily meant that the ∆G vs. ∆H for solution- and gas-phase molecular complexation processes should be described by similar linear relationships, having the same slope as the Barclay–Butler baseline. Furthermore, this framework was applied to α-cyclodextrin host–guest systems. The validity of the established relationships was checked against more than 4500 experimental thermodynamic values. They enable the calculation of the enthalpy change from a single equilibrium constant measurement at 298.15 K, with the deviation comparable to an experimental uncertainty. The predictive power does not depend on the process (solvation, vaporization, and complexation), the phase it takes place in (gas, liquid), or the dominating interaction type (collective/pairwise, van der Waals forces/hydrogen bonding/charge transfer), highlighting the uniform character of the discussed relationships. Full article

Previous molecular dynamics studies have examined the conformational stability and concentration-dependent complexation of amylose–LA systems, but persistence after explicit removal of a host–guest distance restraint has not been directly addressed. Here, atomistic molecular dynamics simulations were used to examine linoleic acid (LA) retention in a preformed 27-residue amylose inclusion structure at 363 K. A 400 ns pull-restrained trajectory was followed by four 100 ns post-pull runs in which the amylose–LA distance restraint was removed while the amylose glycosidic dihedral restraints remained active; all four runs were initiated from the same structural endpoint with independently assigned initial velocities. LA remained closely associated with amylose in all four runs. Across the run means, the amylose radius of gyration was 0.923 ± 0.011 nm, the minimum amylose–LA heavy-atom distance was 0.316 ± 0.004 nm, the contact count within 0.45 nm was 92.7 ± 1.8, and the O3_n–C5_n+3 cavity descriptor was 1.268 ± 0.003 nm. Direct amylose–LA hydrogen bonds were rare, whereas preserved cavity geometry and distributed close contacts characterized the retained state. Although the extent of host conformational relaxation varied among runs, it did not lead to sustained guest loss over the sampled 100 ns period. These results indicate that short-timescale LA retention in this preorganized complex is characterized by preserved cavity geometry and close host–guest contacts, while direct amylose–LA hydrogen bonding remains rare. Full article

Determination of supramolecular host–guest complex stability constants often relies on ¹H NMR spectroscopy, particularly when it comes to reactants lacking chromophores. This is usually the case for hydrophobically driven complexation, where hosts such as cyclodextrins and cucurbiturils interact with small, scarcely soluble guests in aqueous media. Even sophisticated solvent suppression techniques still require a small percentage of deuterated water, so the reactions are usually affected by the solvent isotope effect, either kinetically or thermodynamically, the latter being significantly less investigated. In this work, we report a systematic calorimetric study of the influence of solvent deuteration on the thermodynamic reaction parameters (Δ_rX°, where X = G, H, S, C_p) in 278−338 K temperature range for the reactions involving cyclodextrins and cucurbiturils and two hydrophobic alcohols. In accord with previous systematic investigations carried out solely at 298 K, the complex stability constants did not vary significantly when transferred from H₂O to D₂O. This was, in the case of cyclodextrins, a consequence of a partial enthalpy–entropy compensation, as the differences between Δ_rH° and –TΔ_rS° in two media were similar in magnitude but opposite in sign (up to 5 kJ mol⁻¹, excluding one outlier). Thus, our finding indicates that differences in the hydration of the hosts and guests in regular and heavy water partially compensate for each other. Full article

Arene–ruthenium complexes have emerged as versatile building blocks in supramolecular chemistry because of their structural stability and predictable coordination geometry. This review summarizes the development of arene–ruthenium assemblies, from early coordination-driven designs to more advanced functional systems. We discuss the strategies enabling the construction of well-defined 2D and 3D supramolecular structures, with a focus on how geometry controls cavity formation, guest encapsulation and functionality. The introduction of chirality in these assemblies and its implication for stereochemical control is also discussed. Moreover, the reactivity and stability of arene–ruthenium systems under biological conditions are discussed, including their sensitivity to nucleophiles, amino acids and proteins. In addition to structural and functional aspects, applications of arene–ruthenium assemblies are presented, including host–guest chemistry, drug delivery, and anticancer activity, confirming their role as multifunctional supramolecular platforms. Full article

To develop self-healing materials with mechanical strength, we designed a three-dimensional network polymer primarily composed of [c2]daisy-chain rotaxanes. Although polymeric materials incorporating [c2]daisy-chain rotaxanes have been reported, they all exhibit topological properties based on the non-dissociative nature of the rotaxane structure and do not undergo reversible host–guest association and dissociation. In this study, we designed a novel self-healing polymer that enables the reversible formation and dissociation of [c2]daisy-chain rotaxane. Specifically, a diacrylate containing a [c2]daisy-chain rotaxane was synthesized from a symmetrical Guest–Host–Guest (GHG) compound, in which two secondary ammonium salt units (Guests) were introduced into a single 24-membered dibenzo-crown ether (Host) unit. Subsequent Michael addition with a tetrafunctional thiol afforded a network polymer exhibiting reversible inclusion complex in response to various external stimuli. For example, under heating and cooling conditions, the gel underwent a gel-to-sol transition. In addition, the resulting organogel was readily remoldable after fracture and exhibited mechanical strength comparable to that before fracture. Furthermore, when the network polymer in either the dry or wet state was cut and the resulting surfaces were brought into contact, the fractured surfaces re-adhered. These results suggest the potential of this network polymer as a novel recyclable material. Full article

Molecular docking is widely used to predict cyclodextrin host–guest structures, yet its ability to reproduce the directional orientation of asymmetric guests within the β-cyclodextrin (β-CD) cavity has rarely been evaluated systematically. Here, 20 crystallographically characterized 1:1 β-CD complexes containing asymmetric 1,4-disubstituted benzene guests were selected from the Cambridge Structural Database. Each guest was docked into each of 20 experimentally derived β-CD conformations, yielding 7916 retained poses. Poses reproducing the crystallographic direction of inclusion were classified as Up, whereas the opposite orientation was classified as Down. Across the complete dataset, approximately 26% of poses were Up, with guest-dependent frequencies ranging from 5% to 83%. Importantly, only one β-CD conformation generated Up poses for all 20 guests, whereas the complete receptor set sampled at least one crystal-consistent pose for every compound. However, GlideScore-based orientation recovery was 65% for Top-1, 95% for Top-2, and 100% for Top-3, demonstrating that successful sampling does not necessarily ensure correct top-ranked prediction. Selected poses were subsequently optimized using dispersion-corrected DFT. DFT-based energetic ranking did not consistently favour the crystallographic orientation and could either decrease or increase guest heavy-atom RMSD. Overall, the results demonstrate that reliable validation of β-CD docking requires explicit separation of pose generation, pose ranking, energetic refinement, and structural similarity, and support the use of structurally diverse crystal-derived receptor sets to broaden orientational sampling. Full article

The design and the synthesis of molecule-based crystalline salts made up of simple cationic and/or anionic building blocks with multiple, occasionally stimulus-responsive, chemical (host–guest, catalytic, acid–base, or redox) and physical (optical, magnetic, or conducting) properties constitute two major goals in inorganic, organic, organometallic, and coordination chemistries. A deep knowledge of the basic features of molecular and supramolecular interactions that occur in the solid state is needed to progress along these tasks to obtain new advanced multifunctional materials. Inspired by the outstanding research of several groups on magnetic molecular salts from the mid-1970s to the present day, this review offers a personal portrayal of the history of molecular magnetism and molecular electronics and its current evolution toward molecular spintronics and quantum computing. We focus on the well-known families of molecular salts based on paramagnetic tetrathiafulvalenium/tetraselenafulvalenium or tetracyanoethenide/tetracyanoquinodimethanide organic radicals, cyclopentadienide/cyclooctatetraenide metallocenium complexes, and polyhalide/polycyanide, porphyrin/phthalocyanine, oxalate/dithiooxalate, or dithiolene/dithiolate metal complexes with first-, second-, or third-row transition metal (nd, n = 3–5) and lanthanide (4f) ions. This old but evergreen class of magnetic molecular salts provides illustrative “textbook” examples of advanced multifunctional materials such as molecular magnets and conductors, molecular magnetic conductors, molecular nanomagnets, and molecular quantum bits with potential nanotechnological applications in quantum information storage and processing. Full article

Methotrexate (MTX) remains central to the treatment of rheumatoid arthritis and several malignancies, yet its use is complicated by dose-dependent toxicity, variable oral exposure, photolability, and pH-dependent solubility. Cyclodextrins (CDs) can alter the molecular environment of MTX, but the literature often conflates true inclusion complexes with formulations in which CD merely forms part of a larger carrier. This review critically distinguishes direct MTX–CD complexes, dosage forms built from a preformed complex, CD-containing carriers without direct evidence of cavity occupancy, and covalent MTX–CD conjugates. Particular attention is given to binding stoichiometry, apparent association constants, guest orientation, preparation methods, and the evidence needed to establish inclusion. Both solution-state host–guest association and isolated solid products are considered; however, solid-state changes are treated as supportive evidence rather than as stand-alone proof of cyclodextrin cavity occupancy. Among the limited head-to-head comparisons of native cyclodextrins, β-CD generally showed more favorable MTX recognition than α- or γ-CD, although the magnitude of this difference is method- and condition-dependent. Complexation can improve dissolution, photostability, and oral or local delivery; however, greater solubilization does not necessarily enhance membrane transport. In carrageenan hydrogels, β-CD increased MTX loading and release while reducing membrane permeation, illustrating the importance of the equilibrium between complexed and freely permeating drug. The most promising systems remain preclinical. Progress toward translation will require clearer nomenclature, orthogonal structural characterization, mechanism-resolving controls, and standardized pharmacokinetic and safety studies. Full article

The present study investigates the physicochemical behavior of the first-line anti-tuberculosis drugs isoniazid (INH) and ethambutol, in the form of dihydrochloride (E·(HCl)₂), in aqueous solutions containing the synthetic macrocyclic resorcinarene, C-tetra(propyl)resorcin[4]tetrasulfonate (Na₄PRA) at 298.15 K. Taylor dispersion experiments were conducted to determine the ternary diffusion coefficients of these systems, offering valuable insights into their transport properties. Non-zero cross-diffusion coefficients (${\mathit{D}}_{12}$ and ${\mathit{D}}_{21}$) demonstrate significant coupled transport, collectively indicating interactions between these antibiotics and the resorcinarene host. This behavior is highly consistent with the formation of a host–guest complex. These diffusion measurements were complemented by NMR spectroscopy, which confirmed the formation of host–guest complexes between the respective drugs and this resorcinarene, Na₄PRA. Full article

Ketoprofen is a Biopharmaceutics Classification System (BCS) class II non-steroidal anti-inflammatory drug whose therapeutic performance is limited by its poor aqueous solubility, though complexation with cyclodextrins is a well-established strategy to overcome this limitation. The aim of this work was to prepare and characterize inclusion complexes of ketoprofen with HPβCD. Complexes were obtained by the solution (magnetic-stirring) method at ketoprofen–HPβCD molar ratios of 1:1 and 2:1 and were characterized by Fourier-transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) coupled with EDX, and computer-assisted dimensional analysis and statistics (AutoCAD/MathCAD). The bulk and tapped densities were used to derive the Carr index and the Hausner ratio, respectively. FT-IR showed attenuation and shifting of the characteristic C=O, C=C, and –CH bands of ketoprofen and the presence of the 1655 cm⁻¹ band in complexes demonstrates inclusion. DSC revealed a marked reduction of the ketoprofen melting endotherm, the degree of inclusion reaching 75% (1:1) and 62% (2:1). SEM and statistical analysis confirm, individualized particles, predominantly 20–100 µm in perimeter size. The dissolution test showed a faster release of the complexes than in the case of pure ketoprofen. Therefore, HPβCD forms stable inclusion complexes with ketoprofen having pharmacotechnical properties suitable for compressed tablets. Full article

Cyclodextrin (CD)-based supramolecular nanofibers (NFs) have emerged as an advanced class of multifunctional materials for active food packaging by integrating host–guest supramolecular chemistry with electrospun nanofibrous architectures. The unique hydrophobic cavity and hydrophilic exterior of CDs enable the encapsulation of a wide range of bioactive compounds, including essential oils, natural antioxidants, antimicrobials, and volatile active agents, thereby enhancing their solubility, stability, controlled release, and preservation efficacy. This review comprehensively discusses the molecular structure and inclusion complexation mechanisms of CDs, recent advances in polymer-assisted and polymer-free electrospinning strategies, and the design of CD-based supramolecular nanofibers for food preservation. Particular emphasis is placed on the relationship between fiber morphology, supramolecular interactions, and controlled release behavior, which collectively govern antimicrobial, antioxidant, moisture management, and barrier properties. Recent developments involving biodegradable polymers, hybrid nanofibrous systems, and cyclodextrin-based metal–organic frameworks (CD-MOFs) are critically summarized, highlighting their roles in improving encapsulation efficiency, mechanical stability, and multifunctional performance. The review further compares CD-based nanofibers with other advanced encapsulation technologies, including liposomes, solid lipid nanoparticles, nanostructured lipid carriers, nanoemulsions, polymeric nanoparticles, microspheres, and conventional MOFs, providing a comprehensive evaluation of their loading capacity, release kinetics, scalability, cost, and regulatory suitability for food-contact applications. Representative applications in the preservation of fruits, vegetables, meat, seafood, dairy products, and bakery products demonstrate significant improvements in microbial inhibition, oxidation resistance, ethylene and volatile organic compound adsorption, and shelf-life extension through sustained delivery of natural preservatives. Ultimately, the current challenges, including large-scale manufacturing, long-term stability, regulatory approval, and commercialization, are discussed together with future directions, focusing on smart packaging, stimuli-responsive delivery systems, intelligent sensing, biodegradable multifunctional materials, and sustainable industrial implementation. Full article

Cyclodextrins (CDs) offer a promising solution for enhancing the aqueous solubility of various hydrophobic molecules and facilitate their transport and delivery. Although CDs possess inherent molecular recognition capabilities, their derivatization is often essential to augment solubility and functional performance. A promising strategy involves the grafting of cyclodextrins onto polysaccharides. These hybrid systems combine the molecular recognition of CDs with the structural stability and versatility of biopolymers, yielding advanced materials suitable for biomedical and environmental applications. This review provides a comprehensive overview of CDs, focusing on their unique structural characteristics and their ability to form host-guest inclusion complexes with various hydrophobic molecules. The diverse methodologies used for CD modification and their immobilization onto polysaccharide backbones are described. Furthermore, the multifaceted applications of these grafted materials are explored. While in the pharmaceutical field these systems serve as advanced drug delivery platforms to improve the bioavailability and stability of hydrophobic therapeutic agents, in the environmental sector they demonstrate exceptional efficiency in wastewater treatment, acting as potent sorbents for the removal of organic pollutants and heavy metals. By bridging fundamental chemistry with practical applications, this review highlights the potential of CD-polysaccharide hybrids as sustainable solutions to pressing clinical and ecological challenges. Full article

Two thiourea-based chiral solvating agents (CSAs), S-1 and S-2, were evaluated for the enantiomeric discrimination of representative α-arylacetic acids by ¹H NMR spectroscopy in the presence of DMAP. Enantiomeric discrimination was assessed by monitoring chemical shift nonequivalence (ΔΔδ) arising from the formation of diastereomeric host–guest complexes. S-1 exhibited concentration-dependent enantiomeric discrimination toward all investigated carboxylic acid derivatives, reaching a maximum ΔΔδ value of 0.021 ppm. In contrast, S-2 failed to produce detectable signal splitting under identical experimental conditions. A 1D ROESY experiment together with association constant measurements supported the proposed diastereomeric host–guest complexation model and the preferential binding of one enantiomer by S-1. To further expand the substrate scope, two thiohydantoin derivatives were also examined, and S-1 produced measurable chemical shift nonequivalences, with the largest ΔΔδ value reaching 0.019 ppm. Comparison with previously reported thiourea-based CSAs further highlighted the importance of hydrogen-bonding ability, aromatic anisotropy, and overall molecular architecture in governing enantiomeric discrimination. Overall, these findings provide useful structural insights for the rational design of thiourea-based chiral solvating agents for NMR enantiomeric analysis. Full article

The accurate discrimination of structurally analogous neurotransmitters remains a formidable challenge due to their high structural similarity and overlapping chemical properties. To address the limitations of low specificity in single-probe sensors and the fabrication complexity of multi-component arrays, we developed a simplified fluorescence sensing array based on a single pyrene-functionalized MOF, In-TBAPy. This strategy leverages the distinctive monomer-to-excimer luminescence transition of In-TBAPy, triggered by the tunable π-π stacking of pyrene units within the crystalline framework. The results demonstrate that the array, integrated with Linear Discriminant Analysis (LDA) across four optimized emission channels, achieves a classification accuracy of 93.75% in identifying four highly similar neurotransmitters: serotonin (5-HT), dopamine (DA), adrenaline (A), and norepinephrine (NA). Notably, the sensing platform exhibits exceptional robustness in simulated physiological environments and complex multi-analyte mixtures, enabling reliable quantitative analysis: 0–100 μM for 5-HT and adrenaline (A), 0–40 μM for dopamine (DA), and 0–80 μM for norepinephrine. Mechanistic studies suggest that the differential quenching of monomer and excimer peaks stems from the synergistic effect of competitive absorption and host–guest interactions. This work effectively overcomes the cross-interference issues of traditional sensors and validates a high-efficiency solution for high-throughput neurotransmitter analysis using a single-material-based array strategy, significantly reducing operational costs and preparation time. Full article

The micellization behavior of binary mixtures of the nonionic surfactants Triton X-100 and Brij S20 was investigated in aqueous solution in the absence and presence of β-cyclodextrin (βCD) over the temperature range 283.15–318.15 K. Critical micelle concentrations (CMC) were determined and analyzed using regular solution theory to evaluate mixed micelle composition, interaction parameters, activity coefficients, and excess Gibbs free energies. The Triton X-100/Brij S20 system exhibited pronounced synergistic interactions, reflected by negative interaction parameters, reduced CMC values, and negative excess Gibbs free energies over the entire composition range. The addition of βCD systematically increased CMC values and reduced the magnitude of the interaction parameters, indicating that inclusion complex formation competes with micellization and weakens surfactant–surfactant interactions. Corrected micellar compositions revealed significant redistribution of surfactants between the aqueous phase and mixed micelles due to host–guest complexation. Thermodynamic analysis demonstrated spontaneous formation of βCD inclusion complexes with both surfactants, characterized by negative Gibbs free energy, enthalpy, and entropy changes. Triton X-100 exhibited a higher affinity toward βCD than Brij S20. The results demonstrate that coupled equilibria between micellization and inclusion complex formation govern the behavior of the system and suggest that conformational contributions should be considered when interpreting interaction parameters in cyclodextrin–surfactant systems. Full article