Small Guest Research Articles

Ambiguous Faces of Water-Based Inclusion Compounds: L4(4)8(8) Intercalato-Clathrate Hydrate of Pt(II) Complex.

Clathrate hydrates are among the most intensively studied H-bond inclusion compounds. Despite the broad definition for this class of compounds, their meaning commonly refers to closed polyhedral nanocages that encapsulate small guest molecules. On the other hand, larger solutes enforce another type of encapsulation because of the solute size effect. Herein, we report a series of structures containing various molecules encapsulated by intercalated water layers constructed of polycyclic moieties of L4(4)8(8) topology. We parametrized the corrugation of individual layers and characterized interactions governing their formation. We suggested that these could be categorized as two-dimensional clathrates based on the character of intra-layer interactions and the effects observed between entrapped molecules and water-based intercalators.

Designing a Novel Wide Bandgap Small Molecule Guest for Enhanced Stability and Morphology Mediation in Ternary Organic Solar Cells with over 19.3% Efficiency.

In this study, a novel wide-bandgap small molecule guest material, ITOA, designed and synthesized for fabricating efficient ternary organic solar cells (OSCs) ITOA complements the absorbance of the PM6:Y6 binary system, exhibiting strong crystallinity and modest miscibility. ITOA optimizes the morphology by promoting intensive molecular packing, reducing domain size, and establishing a preferred vertical phase distribution. These features contribute to improved and well-balanced charge transport, suppressed carrier recombination, and efficient exciton dissociation. Consequently, a significantly enhanced efficiency of 18.62% for the ternary device is achieved, accompanied by increased short-circuit current density (JSC), fill factor (FF), and open-circuit voltage (VOC). Building on this success, replacing Y6 with BTP-eC9 leads to an outstanding PCE of 19.33% for the ternary OSCs. Notably, the introduction of ITOA expedites the formation of the optimized morphology, resulting in an impressive PCE of 18.04% for the ternary device without any postprocessing. Moreover, the ternary device exhibits enhanced operational stability under maximum power point (MPP) tracking. This comprehensive study demonstrates that a rationally designed guest molecule can optimize morphology, reduce energy loss, and streamline the fabrication process, essential for achieving high efficiency and stability in OSCs, paving the way for practical commercial applications.

Modification of the van der Waals and Platteeuw model for gas hydrates considering multiple cage occupancy.

This study reviews available van der Waals- and Platteeuw-based hydrate models considering multiple occupancy of cavities. Small guest molecules, such as hydrogen and nitrogen, are known to occupy lattice cavities multiple times. This phenomenon has a significant impact on hydrate stability and thermodynamic properties of the hydrate phase. The objective of this work is to provide a comprehensive overview and required correlations for the implementation of a computationally sufficient cluster model that considers up to five guest molecules per cavity. Two methodologies for cluster size estimation are evaluated by existing nitrogen hydrate models showing accurate results for phase equilibria calculations. Furthermore, a preliminary hydrogen hydrate model is introduced and compared with the results of other theoretical studies, indicating that double occupancy of small sII cavities is improbable and four-molecule clusters are predominant in large sII cavities for pressures above 300 MPa. This work lays the foundation for further exploration and optimization of hydrate-based technologies for small guest molecules, e.g., storage and transportation, emphasizing their role in the future landscape of sustainable energy solutions.

Isomerism of Cyclodextrin Tetramer Induced by Alkali Halide Cluster Ions Observed by Ion Mobility Spectrometry-Mass Spectrometry.

Cyclodextrins (CDs) exhibit versatile self-assembly properties due to their hydrophilic and hydrophobic components, with applications such as drug delivery and selective binding. While research on CD self-assembly is extensive, limited studies have explored their aggregation behavior, particularly in interactions with small ionic guests. The present work investigates the structure of β-CD tetramers aggregated with alkali metal chloride clusters using ion mobility spectrometry-mass spectrometry (IMS-MS). The results revealed that diverse structures emerge in the tetramer depending on the alkali metal cluster size. Notably, the doubly charged tetramer exhibits distinct aggregation trends with specific numbers of MCl clusters for Na+ and K+ ions. After initially adopting a bucket-wheel structure with two internal cations, the structure transforms into a new isomer with a tetrahedral configuration upon cluster addition. The formation of the new isomer structure is closely linked to filling the cavity volume with MCl clusters and ionic interactions, which possibly compensate for the weakened hydrogen bonds between CDs. Theoretical calculations further support the structures, showing well-matched collision cross-section (CCS) values compared with the experimental CCS values. This study highlights the role of alkali metal chloride clusters as potential templates, leading to the formation of novel CD assemblies.

Tuning the spin-crossover properties of [Fe2] metal-organic cages.

A computational study on the interplay between ligand functionalization and guest effects on the transition temperature (T1/2) in the [Fe2(L1R)3]@X (L1 = 1,3-bis-(3-(pyridin-2-yl)-1H-pyrazol-5-yl)benzene, X = H-, F-, Cl-, Br-, I- and [BF4]-, R = H, F, or CH3) family of metal-organic cages (MOCs) is presented. Our results indicate that ligand functionalization with electron-donating or electron-withdrawing groups can significantly impact the T1/2 as expected, while the guest effect in lowering the T1/2 has a linear correlation with the increasing guest size. More importantly, small guests can move away from the center of the cavity, thus enhancing the two-step characteristic of the transition. All the data can be understood by analyzing the underlying electronic structure of the studied systems in terms of the relevant d-based molecular orbitals. These results can help in the rational design of new MOCs that can operate as sensors at specific temperatures, thus accelerating the discovery of new SCO devices with tailored properties.

Investigation of the effects on proton relaxation times upon encapsulation in a water-soluble synthetic receptor.

Sequestration of small molecule guests in the cavity of a water-soluble deep cavitand host has a variety of effects on their NMR properties. The effects of encapsulation on the longitudinal (T1) and transverse (T2) relaxation times of the protons in variably sized guest molecules are analyzed here, using inversion recovery and spin-echo experiments. Sequestration of neutral organic species from the bulk solvent reduces the overall proton relaxation times, but the magnitude of this effect on different protons in the same molecule has a variety of contributors, from the motion of the guest when bound, to the position of the protons in the cavity and the magnetic anisotropy induced by the aromatic walls of the host. These subtle effects can have large consequences on the environment experienced by the bound guest, and this sheds light on the nature of small molecules in enclosed environments.

Exploring the host–guest interactions of small molecules in UoC-9(Ca)

In a proof of concept study, the MOF UoC-9(Ca) is investigated as a crystalline sponge material by embedding a variety of small guest molecules in its pores via liquid exchange in single crystal to single crystal transformations using SCXRD analysis.

Water Solubilization and Guest Molecule-Induced Fluorescence Changes of Porous Host Molecules via Complexing with Polysaccharide or Polypeptide.

To detect small aromatic molecules in water, we prepared functional host molecules based on water-soluble N,N'-bis(2-aminobenzophenone)-1,4,5,8-naphthalenetetracarboxylic diimide (1) and a solubilizing agent using a high-speed vibration milling apparatus. The fluorescence response of host 1-solubilizing agent complexes before and after extraction of small aromatic guest molecules was large and the fluorescence maxima were dependent on the small aromatic guest molecules.

Effective encapsulation of noble and small gases and molecules by tubularene molecule

AbstractBased on computational chemistry calculations (ωB97XD/def2‐tzvp//ωB97XD/def2‐svp/svpfit+ZPE(ωB97XD/def2‐svp/svpfit)), binding energy of tubular[3,6,6,6]arene to accommodate noble gases and a series of 29 small gases were calculated. Based on the gained results, Rn (−17.52 kcal/mol) from the series of noble gases is best suited to be accommodated. In the series of noble gases, the binding energy increases linearly with increasing gas radii. From the series of 29 small guests, IF3 and C2I2 (~ −23 kcal/mol) have the best proclivity to be most effectively accommodated in the tubularene, with other 26 exhibiting favorable encapsulation energies on various scales depending on their voluminosity and structure, and only NI3 with the unfavorable complexation energy of 13.87 kcal/mol. Investigated gases, depending on the size, are placed at the different position inside the tube‐like cavity of the tubularene. The structure of the tubularene, independent of the hosted guest species, has remained very rigid, with its atom's rearrangements withing an error margin.

Lamellar structure formed from block copolymer for structural color

Certain brilliant colors in living species, such as, in plants, animals, insects, fungi, seaweed, and so on, known as structural colors, have attracted tremendous attention from researchers worldwide. Block copolymers are an interesting class of material that has been proven effective in fabricating structural colors due to their capability to self-assemble into structures on the scale of the wavelength of visible light. Lamellar structure is one of these structures. The demand on the high-quality structural colors in large scale application requires the easy modification of commercial block copolymers to obtain structural colors. In this project, a method to easily prepare structural colors is presented. First, an already commercialized block polymer was purchased. Then, the block copolymer is mixed with the small molecule guest to prepare a supramolecular complex solution. By slowly evaporating the solution, these supramolecular complexes can be assembled into a lamellar structure that displays structural color. By changing the ratio of polymer to small molecular guest and using different small molecular guests, polymer films of different colors can be obtained and tuned.

DNA-Condensed Plasmonic Supraballs Transparent to Molecules.

DNA nanotechnology offers an unrivaled programmability of plasmonic nanoassemblies based on encodable Watson-Crick basepairing. However, it is very challenging to build rigidified three-dimensional supracolloidal assemblies with strong electromagnetic coupling and a self-confined exterior shape. We herein report an alternative strategy based on a DNA condensation reaction to make such structures. Using DNA-grafted gold nanoparticles as building blocks and metal ions with suitable phosphate affinities as abiological DNA-bonding agents, a seedless growth of spheroidal supraparticles is realized via metal-ion-induced DNA condensation. Some governing rules are disclosed in this process, including kinetic and thermodynamic effects stemming from electrostatic and coordinative forces with different interaction ranges. The supraballs are tailorable by adjusting the volumetric ratio between DNA grafts and gold cores and by overgrowing extra gold layers toward tunable plasmon coupling. Various appealing and highly desirable properties are achieved for the resulting metaballs, including (i) chemical reversibility and fixation ability, (ii) stability against denaturant, salt, and molecular adsorbates, (iii) enriched and continuously tunable plasmonic hotspots, (iv) permeability to small guest molecules and antifoulingness against protein contaminates, and (v) Raman-enhancing and photocatalytic activities. Innovative applications are thus foreseeable for this emerging class of meta-assemblies in contrast to what is achieved by DNA-basepaired ones.

Tuning the Solution Self-Assembly of a Peptide-PEG (Polyethylene Glycol) Conjugate with alpha-Cyclodextrin.

Cyclodextrins are saccharide ring molecules which act as host cavities that can encapsulate small guest molecules or thread polymer chains. We investigate the influence of alpha-cyclodextrin (αCD) on the aqueous solution self-assembly of a peptide-polymer conjugate YYKLVFF-PEG3K previously studied by our group [Castelletto et al., Polym. Chem., 2010, 1, 453-459]. This conjugate comprises a designed amyloid-forming peptide YYKLVFF that contains the KLVFF sequence from Amyloid β peptide, Aβ16-20, along with two aromatic tyrosine residues to enhance hydrophobicity as well as polyethylene glycol PEG with molar mass 3000 g mol-1. The conjugate self-assembles into β-sheet fibrils in aqueous solution. Here we show that complexation with αCD leads instead can produce free-floating nanosheets in aqueous solution (with a β-sheet structure). The transition from fibrils to nanosheets is driven by an increase in the number of αCD molecules threaded on the PEG chains, as determined by 1H NMR spectroscopy.These findings point to the use of cyclodextrin additives as a powerful means to tune the solution self-assembly in peptide-polymer conjugates and potentially other polymer/biomolecular hybrids.

PERIPHERAL TOURISM ENTREPRENEURS IN A RESOURCE-CONSTRAINED ENVIRONMENT: EVIDENCE FROM EASTERN CAPE PROVINCE, SOUTH AFRICA

The tourism industry is distinguished from many other economic activities by the dominance of small-scale enterprises and micro-firms. Small tourism firms are critical change agents for destinations, local economic development and poverty reduction most especially in peripheral regions. This paper is situated within a growing international literature on tourism entrepreneurship and specifically the characteristics and motivations of small tourism entrepreneurs and their business operations. The research is conducted in Eastern Cape province of South Africa which is a resource-scarce or resource-constrained environment. Results are presented from a survey of 79 Black-owned small accommodation businesses and 19 semi-structured interviews with key stakeholders. It is shown that women own and operate the majority of these small accommodation businesses. These are mainly bed and breakfast establishments or small guest houses for which the clientele is mostly business tourists and government employees in particular. Issues under scrutiny are business motivations, start-up and operational issues. Networking emerges as an important business strategy for these peripheral entrepreneurs to address the challenges of business development. Overall, this study provides original findings and fresh insight into a segment of peripheral entrepreneurs operating in a resource-scarce context.

Hydrated electrons as nodes in porous clathrate hydrates.

We investigate the structures of hydrated electrons (e- aq) in one of water's solid phases, namely, clathrate hydrates (CHs). Using density functional theory (DFT) calculations, DFT-based ab initio molecular dynamics (AIMD), and path-integral AIMD simulations with periodic boundary conditions, we find that the structure of the e- aq@node model is in good agreement with the experiment, suggesting that an e- aq could form a node in CHs. The node is a H2O defect in CHs that is supposed to be composed of four unsaturated hydrogen bonds. Since CHs are porous crystals that possess cavities that can accommodate small guest molecules, we expect that these guest molecules can be used to tailor the electronic structure of the e- aq@node, and it leads to experimentally observed optical absorption spectra of CHs. Our findings have a general interest and extend the knowledge of e- aq into porous aqueous systems.

A Double-Walled Tetrahedron with AgI 4 Vertices Binds Different Guests in Distinct Sites.

A double-walled tetrahedral metal-organic cage assembled in solution from silver(I), 2-formyl-1,8-naphthyridine, halide, and a threefold-symmetric triamine. The AgI 4 X clusters at its vertices each bring together six naphthyridine-imine moieties, leading to a structure in which eight tritopic ligands bridge four clusters in an (AgI 4 X)4 L8 arrangement. Four ligands form an inner set of tetrahedron walls that are surrounded by the outer four. The cage has significant interior volume, and was observed to bind anionic guests. The structure also possesses external binding clefts, located at the edges of the cage, which bound small aromatic guests. Halide ions bound to the silver clusters were observed to exchange in a well-defined hierarchy, allowing modulation of the cavity volume. The principles uncovered here may allow for increasingly more sophisticated cages with silver-cluster vertex architectures, with post-assembly tuning of the interior cavity volume enabling targeted binding behavior.

A Double‐Walled Tetrahedron with AgI4 Vertices Binds Different Guests in Distinct Sites**

AbstractA double‐walled tetrahedral metal‐organic cage assembled in solution from silver(I), 2‐formyl‐1,8‐naphthyridine, halide, and a threefold‐symmetric triamine. The AgI4X clusters at its vertices each bring together six naphthyridine‐imine moieties, leading to a structure in which eight tritopic ligands bridge four clusters in an (AgI4X)4L8 arrangement. Four ligands form an inner set of tetrahedron walls that are surrounded by the outer four. The cage has significant interior volume, and was observed to bind anionic guests. The structure also possesses external binding clefts, located at the edges of the cage, which bound small aromatic guests. Halide ions bound to the silver clusters were observed to exchange in a well‐defined hierarchy, allowing modulation of the cavity volume. The principles uncovered here may allow for increasingly more sophisticated cages with silver‐cluster vertex architectures, with post‐assembly tuning of the interior cavity volume enabling targeted binding behavior.

FEATURES OF THE FORMATION OF THE ARCHITECTURE OF TOURIST OBJECTS IN THE AZOV RESORT AND RECREATIONAL ZONE OF THE KRASNODAR TERRITORY

The affordable cost of recreation on the Azov coast, as well as the presence of the sea, combined with a favorable climate, make these territories attractive for Russian tourism. However, more than half (62%) of all accommodation facilities in the regions of the Azov region are individual accommodation facilities: small private guest houses, which provokes a number of problems. The state of the resort and tourism industry in the Azov resort and recreational zone is a very topical issue, but most studies present an assessment of the current state of the resort and tourism industry from the point of view of related sciences. In this regard, the purpose of the study is to determine the features of the formation of the architecture of tourist facilities for this region, and its tasks can be determined: identifying the most developed and resort-oriented areas of the Azov region, studying iconic accommodation facilities in selected areas, systematizing the collected material, taking into account the main factors (natural and climatic, functional-planning, socio-economic) and their criteria (climate type, temperature, air humidity and terrain; typology of accommodation facilities, territory development system; capacity index of resort complexes, seasonality of work) that affect tourist attractiveness. The practical significance of the study is related not only to identifying the strengths and weaknesses of the development of the resort in this region, but also to predicting the tourist attractiveness of the Sea of Azov regions. The analysis allows you to determine which of the existing accommodation facilities will be popular and attractive to tourists in the near future, and which of them require urgent modernization. The totality of the results obtained shows the presence of real opportunities for the sustainable development of the Azov region as a resort

On Crying While Stripping Wallpaper

On Crying While Stripping Wallpaper Stevie Edwards (bio) Keywords Stevie Edwards, poetry, home renovation, nursery, children, grief Three days into strippingthe third layer of painted wallpaperin a poorly ventilated powder roomand I am a sorrow river. My husbandsticks his head in to ask why I’m standing on a ladder, sobbingugly and snotty, a steamer in my left handspitting at the wall, a scraper in the right:I’m not sure. Too many hoursof quiet in close quarters. No, I’ve been choosing colors and namesin my sleep. My mind keeps its secretPinterest board of nursery décorpadlocked in its dingiest corner:the wallpaper border with baby animals, the mobile and cribI circled in my Grandma’s JCPenneycatalogue when I was sevenand knew how to want without guilt.There’s a small guest bedroom across the hall from mine, perfectfor the child my husband doesn’t wantenough, the child I spent yearsnot being sure I deserved. I am notredecorating that room in lambs [End Page 101] or unicorns. Not carefully choosingeach rattle and onesie for a registry.Scraping three decades offthe same four walls for days, my prettyfingers haggard with hangnails, I am chanting the name of a daughterI, more than likely, will never teachto strip wallpaper like my mothertaught me in the hallway one summerwith no air conditioning and too much July. I only teach the children of strangers,and I never teach them anythingas useful as how to undo the shortsighteddecisions of homeowners with too many recitalsand soccer practices to do the job right. [End Page 102] Stevie Edwards stevie edwards holds a PhD in creative writing from University of North Texas and an MFA in poetry from Cornell University. Stevie’s poems have appeared in Poetry Magazine, American Poetry Review, Crazyhorse, and elsewhere. She is a lecturer at Clemson University and author of Sadness Workshop (Button Poetry), Humanly (Small Doggies Press), and Good Grief (Write Bloody Publishing). Edwards is currently poetry editor of The South Carolina Review, and her third full-length collection of poetry, Quiet Armor, is forthcoming from Northwestern University Press’s Curbstone imprint. Originally a Michigander, she now lives in South Carolina with her husband and a small herd of rescue pitbulls (Daisy, Tinkerbell, and Peaches). Stevie uses she/they pronouns. Copyright © 2023 The Massachusetts Review, Inc

Encapsulating Semiconductor Quantum Dots in Supramolecular Cages Enables Ultrafast Guest-Host Electron and Vibrational Energy Transfer.

In the field of supramolecular chemistry, host-guest systems have been extensively explored to encapsulate a wide range of substrates, owing to emerging functionalities in nanoconfined space that cannot be achieved in dilute solutions. However, host-guest chemistry is still limited to encapsulation of small guests. Herein, we construct a water-soluble metallo-supramolecular hexagonal prism with a large hydrophobic cavity by anchoring multiple polyethylene glycol chains onto the building blocks. Then, assembled prisms are able to encapsulate quantum dots (QDs) with diameters of less than 5.0 nm. Furthermore, we find that the supramolecular cage around each QD strongly modifies the photophysics of the QD by universally increasing the rates of QD relaxation processes via ultrafast electron and vibrational energy transfer. Taken together, these efforts expand the scope of substrates in host-guest systems and provide a new approach to tune the optical properties of QDs.

Reversible Molecular Capture and Release in Microfluidics by Host-Guest Interactions in Hydrogel Microdots.

The integration of microscopic hydrogels with high specific surface area and physically reactive groups into microfluidic systems for selective molecular interactions is attracting increasing attention. Herein, the reversible capture and release of molecules through host-guest interactions of hydrogel dots in a microfluidic device is reported, which translates the supramolecular chemistry to the microscale conditions under continuous flow. Polyacrylamide (PAAm) hydrogel arrays with grafted β-cyclodextrin (β-CD) modified poly(2-methyl-2-oxazoline) (CD-PMOXA) chains are fabricated by photopolymerization and integrated into a polydimethylsiloxane (PDMS)-on-glass chip. The β-CD/adamantane (β-CD/Ada) host-guest complex is confirmed by two dimensional Nuclear Overhauser Effect Spectroscopy NMR (2D NOESY NMR) prior to transfer to microfluidics. Ada-modified molecules are successfully captured by host-guest interaction formed between the CD-PMOXA grafted chains in the hydrogel network and the guest molecule in the solution. Furthermore, the captured molecules are released by perfusing free β-CD with higher binding affinity than those grafted in the hydrogel array. A small guest molecule adamantane-fluorescein-isothiocyanate (Ada-FITC) and a macromolecular guest molecule (Ada-PMOXA-Cyanine 5 (Cy5)) are separately captured and released for three times with a release ratio up to 46% and 92%, respectively. The reproducible capture and release of functional molecules with different sizes demonstrates the stability of this hydrogel system in microfluidics and will provide an opportunity for future applications.