Guest Compounds Research Articles

A Water‐Soluble Cycloparaphenylene: Supramolecular Receptor with Visible Fluorescence

AbstractWe report the first synthesis of a water‐soluble [9]cycloparaphenylene derivative containing three hydrindacene (1,2,3,5,6,7‐hexahydro‐s‐indacene) units with four carboxylates at the 2,6‐positions via a macrocyclic gold complex. This crown‐shaped macrocyclic compound exhibits remarkable water solubility, of up to 16 mmol L−1 (2.6 g/100 mL), as well as strong visible fluorescence in water (λem=447 nm, ϕF=0.64, brightness (ϵ×ϕF)=5.1×104). This molecule effectively encapsulates cationic guest compounds, such as methyl viologen dichloride, as indicated by a change in visible fluorescence.

Effect of inclusion complex formation and mechanoactivation on the structure and rheological behavior of starch-oleic acid mixtures

In the present work, for the first time, mechanical activation implemented in a rotor-stator device (RSD) has been used to enhance the formation of the amylоse-fatty acid complex in gelatinized starch at a moderate temperature (40 °C) using oleic acid (ОА) as a model guest compound. Mechanical activation was found to cause an increase in the complexing index from 10 to 30 % for non-activated mixtures to 83–92 %. The study of aqueous and dried starch-OA mixtures using optical and AFM microscopy and dynamic light scattering methods revealed a uniform distribution of amylose-OA complex particles with a size of 125–260 nm in the starch matrix. The freeze-dried starch-ОА sample prepared using mechanical activation exhibited a V-type crystalline structure. By rotational viscometry and dynamic rheometry, it was found that mechanical activation causes the gelation of aqueous starch-OA mixtures, which accompanies a decrease in their fluidity and an increase in elasticity. The developed method can be recommended for large-scale production of thickening and texture modifying materials based on gelatinised starch containing a fatty acid as a nutritional or structuring additive.

Introduction of Cyclic Structures into Phosphonium Salts As Potential Guest Substances for Ionic Clathrate Hydrates

An ionic clathrate hydrate composed of tri-n-butylbenzyl-phosphonium chloride has been investigated from the viewpoint of phase equilibrium (temperature-composition) relations in comparison with an ionic clathrate hydrate with tri-n-butyl(cyclohexylmethyl)phosphonium bromide. The highest dissociation temperature of the ionic clathrate hydrates composed of tri-n-butylbenzylphosphonium chloride and tri-n-butyl(cyclohexyl-methyl)phosphonium bromide were 274.4 ± 0.1 K and 276.0 ± 0.1 K, respectively at the atmospheric pressure. The dissociation enthalpy of tri-n-butylbenzyl-phosphonium chloride ionic clathrate hydrate was 192 ± 3 kJ·kg−1. These results allow us to suggest that controlling steric structures in the guest compounds might be one of the options for tuning the equilibrium temperatures of ionic clathrate hydrates.

Guest-Induced Conformational Transformations in Tiara[5]arene Crystals: A Pathway for Molecular Sieving.

In pursuit of environmental sustainability and energy efficiency, assorted macrocyclic compounds have recently emerged as crystalline adsorbents for the efficient molecular sieving of various chemical commodities. Herein, we delve into the conformational characteristics and solid-state packing modes of tiara[5]arenes (T[5]), a rim-differentiated pillar[5]arene derivative. By meticulously exploring the conformational space, we have successfully identified a multitude of distinct T[5] conformers within a relatively narrow energy range of 22 kJ/mol. This finding underscores the inherent conformational flexibility of this macrocyclic scaffold, enabling T[5] to adapt diverse packing arrangements in the solid state. While solvent-free T[5] crystals do not exhibit permanent porosity, they undergo solvomorphic interconversions when exposed to various guest compounds. Our study demonstrates that T[5]-based crystalline materials exhibit a notable preference for selectively capturing aromatic and olefinic solvents, such as benzene, toluene, chlorobenzene, and cyclohexene, over their aliphatic hydrocarbon counterparts from equivalent volume liquid mixtures, achieving up to 10:1 selectivity between benzene and cyclohexane.

Crystallization experiments of the wheel-and-axle host compound, 1,4-phenylene-bis(di-p-tolylmethanol), from pyridine and methylpyridine mixtures

1,4-Phenylene-bis(di-p-tolylmethanol) (H), a host compound with the wheel-and-axle design, formed complexes with organic guest solvents pyridine (PYR) and 2-, 3- and 4-methylpyridine (2MP, 3MP and 4MP). The host: guest (H: G) ratios were 1:3, 1:2, 1:2 and 1:1, respectively. Host crystallization experiments from mixed guests demonstrated H to prefer both PYR and 4MP; however, it was established that these difficult-to-separate (by fractional distillations) guest mixtures cannot be purified/separated by means of H through supramolecular chemistry strategies owing to these selectivities for PYR and 4MP being less than optimal. Single crystal X-ray diffraction experiments showed that each guest compound was held in its complex by means of a classical hydrogen bond with H, and that one of the preferred guests, PYR, experienced a significantly shorter contact of this type than the other guests. Hirshfeld surface analyses demonstrated that PYR was also involved in a greater percentage of (guest)N···H(host) interactions compared with the other guest molecules. Thermal analyses, on the other hand, revealed that 4MP (also a favoured guest species) formed the most stable complex of the four in this investigation. These results with H were compared to those obtained when employing a closely related host compound from a previous report, 1,4-bis(diphenylhydroxymethyl)benzene: while both host species preferred the same guests (PYR and 4MP), the extent of the selectivity of that host compound compared with H in the present work was significantly more enhanced. Thus, minor modifications may deleteriously affect the selectivity behaviour of closely related host compounds.

Rational design of disulfide bonds to improve the thermostability and γ-cyclodextrin production capacity of γ-cyclodextrin glycosyltransferase

The ability of γ-cyclodextrin(γ-CD)to form inclusion complexes with various guest compounds, together with its relatively high solubility, gives γ-CD advantages over both α-cyclodextrin(α-CD) and β-cyclodextrin(β-CD). The thermostability of γ-cyclodextrin glycosyltransferases (γ-CGTase) which can produce γ-CD discovered so far is poor, which is one of the problems limiting its industrial application. To enhance the thermostability of γ-CGTase from Bacillus clarkii 7364, potential disulfide bond mutants were predicted by Disulfide by Design. Five pairs of mutants were constructed by analyzing the predicted results. The t1/2 of S172C-R183C was 2.25 h, which was 3.17 times of WT. Molecular dynamics simulations confirmed that the increase of thermostability of S172C-R183C may be due to the formation of disulfide bond, which leads to the increase of structure rigidity of protein. Then the ability of S172C-R183C mutant to produce cyclodextrins(CDs) was tested. Compared with WT, the maximum CD yield, γ-CD yield and γ-CD specificity of S172C-R183C in the non-complexant catalysed reaction were increased by 6.9 %, 8.8 %, and 2.4 % respectively. In the complexant catalyzed reaction, the CDs yield of S172C-R183C increased by 17.0 %, in which the γ-CD yield increased by 21.7 %, and the γ-CD specificity increased by 3.9 %. Molecular docking results showed that S172C-R183C formed more hydrogen bonds with γ-CD, especially Y186, which was the key central site affecting product specificity. This work involving rational protein engineering provided a new method for adjusting γ-CGTase thermostability.

Retraction of: Direct Joining of a Heterogeneous Pair of Supramolecular Nanotubes and Reaction Control of a Guest Compound by Transportation in the Nanochannels

Retraction of: Direct Joining of a Heterogeneous Pair of Supramolecular Nanotubes and Reaction Control of a Guest Compound by Transportation in the Nanochannels

Synthesis and Characterization of Amido-Thiourea Based p-tert-butylcalix[4]arene Compound and Investigation of Transition Metal Complex Properties

In host-guest complexes, the compatibility of the size and shape of the host cavity and the guest molecule is essential in the formation of the host-guest complex. Considered third-generation macrocyclic hosts, calixarenes attract the attention of researchers in supramolecular chemistry as they offer a wide range of applications in fields such as biocatalysis, enzyme analysis, pharmaceuticals, and biosensing. The synthesis of host molecules for anionic and cationic guest compounds has a very important place in coordination chemistry. Calixarenes are known as one of the important types of supramolecular compounds and are an important class of easily synthesized compounds that can act as a suitable receptors for cations, anions, and organic molecules. When calixarene compounds, which have an important place in host-guest chemistry, are derivatized appropriately, the coordination ability of the molecule against metal cations increases. These derivatizations gained importance due to the sensory properties of the molecule, and different studies were started considering that a larger cavity and functional group are required for more guest molecules. In this study, a new ligand of 1,3-disubstituted p-tert-butylcalix[4]arene derivative with increased donor atomic number with amide and thiourea groups in its structure was synthesized. Co(II), Ni(II), Cu(II), and Zn(II) complexes were synthesized with the compound and the structures of the compounds were characterized by UV-vis, FT-IR, 1H-NMR, 13C-NMR, and mass spectrometry.

Radiation-Assisted Assembly of a Highly Dispersed Nanomolybdenum-Functionalized Covalent Organic Framework.

Two-dimensional covalent organic frameworks (2D COFs), featuring a large surface area and 1D pore structure, serve as promising scaffolds for anchoring functional guest compounds, which can significantly enhance their performance and thus expand their potential applications. Postsynthetic strategy for COFs functionalization is versatile but challenging because of their tedious procedure with high time and energy consumption, generation of excess reaction waste, and damage to COF crystallinity. We report in this work a general strategy for the synthesis of inorganic nanocompound-functionalized COF composites in a one-pot way. Specifically, a high-crystallinity nanoscale molybdenum compound is successfully introduced into a COF skeleton with high dispersion in situ during the crystallization process of the COF induced by gamma ray radiation under ambient conditions. The obtained COF@Mo composites exhibit remarkable sorption performance for methylene blue and many other organic dyes in aqueous solution with the advantages of ultrarapid uptake dynamics and high removal efficiency.

Mild and Efficient Extraction of Fluorescent Chlorophyll a from Spinach Leaves for Application as the Sustainable Emitter in Light‐Emitting Electrochemical Cells

AbstractNatural pigments are sustainable compounds that can be employed as emitters, sensors and sensitisers in optoelectronics. The most abundant pigment, chlorophyll, offers advantages of easily available and plentiful feedstock, biodegradability and non‐toxicity. However, strenuous extraction and separation limit its application on larger scale. In this work, a practically mild and scalable extraction and separation method for rapid isolation of chlorophyll a from spinach is presented. Three different stationary phases for column chromatography were evaluated, and a new solvent system was developed for the elution of chlorophyll a on a neutral alumina chromatography column. The purified product was obtained with a yield of 0.98 mg ⋅ g−1 with respect to the dry leaves. A first light‐emitting electrochemical cell (LEC) based on chlorophyll a as the emitter is reported, using the extracted chlorophyll a as the guest compound dispersed in a blend‐host matrix in a concentration of 2.5 or 5 mass %. The higher‐chlorophyll‐concentration LEC exhibits emission solely from the chlorophyll emitter, with the main emission peak located at 675 nm. The lower‐chlorophyll‐concentration LEC features two distinct emission bands, one in the red region that is originating from the chlorophyll guest and one in the blue region (main peak at 430 nm) that stems from the blend host. This combined red:blue emission can be attractive for, e. g., greenhouse applications, since it matches the action spectrum of plant photosynthesis.

Photophysical properties of Pt(ii) complexes based on the benzoquinoline (bzq) ligand with OLED implication: a theoretical study.

In this study, we investigate photophysical properties of eight inorganic Pt(ii) complexes containing the bzq (benzoquinoline) ligand for OLED applications using high-level density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. We explore the radiative and non-radiative relaxation constants (k r, k nr), spin-orbit coupling (SOC) matrix elements, and spectral properties. To ensure compatibility between the host and guest compounds, we determine the HOMO and LUMO energy levels, as well as the triplet excitation energies of the selected systems, and evaluate their efficiency for OLED devices. Our findings indicate that all systems, except for 2a and 2b, exhibit a small S1-T1 energetic gap (ΔE ≤ 0.60 eV) and promising SOC matrix elements (25-93 cm-1), leading to a significant intersystem crossing (ISC) process. These complexes also show promising radiative relaxation rates (k r = ∼10-4 s-1) and high phosphorescent quantum yields (Φ > 30%). Thus, our results confirm that six out of the eight selected Pt(ii) complexes are promising candidates for use in the emitting layer (EML) of OLED devices as efficient green emitters.

Investigation of the hydrogen bonded host‧‧‧guest and guest‧‧‧guest interactions present in complexes of a polyaromatic wheel-and-axle host compound with dioxane, morpholine, piperidine and pyridine

1,4-Bis(diphenylhydroxymethyl)benzene (H), a host compound possessing wheel-and-axle geometry, was found to possess host ability for dioxane (DIO), morpholine (MOR) and piperidine (PIP), forming inclusion compounds with each one with 1:2 host:guest ratios. This observation prompted an investigation of the host behaviour in mixtures of these guest compounds but where pyridine (PYR) was also considered (PYR was reported earlier to also form a 1:2 complex with H). In mixtures, H demonstrated significant affinities for, more especially, MOR and PIP, while DIO and PYR were usually disfavoured guest species. Single crystal X-ray diffraction experiments revealed that MOR (a favoured guest species) interacted by means of three hydrogen bonds with both adjacent guest and host molecules, plausibly explaining the host preference for this guest species; each of DIO, PYR and PIP were involved in only one interaction of this type with H. Total energy calculations revealed that the host-guest molecular pairs involving preferred MOR and PIP possessed significantly lower energies than those with disfavoured DIO and PYR. Thermal analyses demonstrated that the complex containing the least favoured guest compound, H‧2(DIO), possessed the lowest thermal stability of the four complexes, but these experiments did not clearly explain the affinity of H for MOR.

Odor-scavenging capabilities of pre-formed “empty” V-type starches for beany off-flavor compounds

Off-flavors have garnered significant attention in research due to their impact on overall flavor, which leads consumers to avoid purchasing or consuming food products with off-flavors, even if they offer health benefits. However, there has been limited research on encapsulating off-flavor compounds as a means to mask them and to improve the flavor profiles of food products. Starch, particularly its amylose component, is well-known for its ability to form inclusion complexes (ICs) with various small molecules, providing protection and controlled release of these encapsulated guest molecules. The complexation interaction between starch and guest compounds is influenced by factors such as the structure and chemistry of the guest, as well as the process method and parameters. In the present study, nine different beany off-flavor compounds, including hexanal (HAL), 3-hexanol (HOL), benzaldehyde (BAL), 1-octen-3-ol (OOL), 1-octen-3-one (ONE), 2-pentylfuran (PTF), trans-2-nonenal (NAL), trans, trans-2,4-nonadienal (NAD), and trans, trans-2,4-decadienal (DEC) were used as model off-flavors to examine their complexation ability with three types of preformed “empty” V-type high amylose maize starches (HAMS), namely V6h, V7, and V8. The successful formation of inclusion complexes was characterized using complementary techniques, including X-ray diffraction (XRD), differential scanning calorimetry (DSC), and gas chromatography-mass spectrometry (GC-MS). The results revealed that the complexation of off-flavor compounds with the starches did not significantly alter the original structures of the starches. Additionally, the IC samples prepared using the gas phase (GP) approach exhibited significantly higher encapsulation efficiency compared to the direct contact (DC) approach, as indicated by GC-MS analysis. Among the V-type starches, V6h HAMS demonstrated the highest complexation efficiency for all selected beany off-flavor compounds when the ICs were prepared using the GP approach. This study suggests that both V6h and V8 starches exhibit effective scavenging abilities for beany off-flavor compounds. Further, complexation properties depend on the properties of the off-flavor compounds, the type of V starch used, and the IC preparation approach.

Effect of melting point and drying technique on encapsulation of hydrophobic active compounds by coprecipitation with starch nanoparticles

This study aims to optimize the coprecipitation method for the encapsulation of hydrophobic active compounds using starch nanoparticles (SNP). Saturated fatty acids with varying chain lengths (8, 18, and 22) were used as model compounds. Differential scanning calorimetry analysis revealed that various reaction conditions influenced the encapsulation efficiency of fatty acids, with 30% ethanol, an addition level of 10 mg/mL, heating for 30 min, and a cooling rate of 10 k/min, producing the highest melting enthalpy of the shifted thermal transition peak. Specifically, heating near the melting point of the guest compound resulted in substantial structural modifications between the guest compound and the SNP. D-δ-tocopherol, coenzyme Q10, and curcumin were then encapsulated under optimized conditions and dehydrated via spray- and freeze-drying. Transmission electron microscopy, Fourier transform-infrared spectroscopy, and X-ray diffraction analyses revealed that each compound underwent spherical aggregation with SNP in an amorphous state via hydrogen bonding and hydrophobic interactions. Freeze-drying generally resulted in higher encapsulation efficiency than spray-drying. For D-δ-tocopherol and curcumin, freeze-dried composites exhibited higher storage stability under varying pH, UV irradiation, and thermal treatment conditions. However, for coenzyme Q10, spray-drying resulted in higher storage stability.

Cucurbit[8]uril-based water-dispersible assemblies with enhanced optoacoustic performance for multispectral optoacoustic imaging

Organic small-molecule contrast agents have attracted considerable attention in the field of multispectral optoacoustic imaging, but their weak optoacoustic performance resulted from relatively low extinction coefficient and poor water solubility restrains their widespread applications. Herein, we address these limitations by constructing supramolecular assemblies based on cucurbit[8]uril (CB[8]). Two dixanthene-based chromophores (DXP and DXBTZ) are synthesized as the model guest compounds, and then included in CB[8] to prepare host-guest complexes. The obtained DXP-CB[8] and DXBTZ-CB[8] display red-shifted and increased absorption as well as decreased fluorescence, thereby leading to a substantial enhancement in optoacoustic performance. Biological application potential of DXBTZ-CB[8] is investigated after co-assembly with chondroitin sulfate A (CSA). Benefiting from the excellent optoacoustic property of DXBTZ-CB[8] and the CD44-targeting feature of CSA, the formulated DXBTZ-CB[8]/CSA can effectively detect and diagnose subcutaneous tumors, orthotopic bladder tumors, lymphatic metastasis of tumors and ischemia/reperfusion-induced acute kidney injury in mouse models with multispectral optoacoustic imaging.

Confinement of Pyridine Derivatives into a Metal-Organic Framework Host as Electron Acceptors to Achieve Photoinduced Electron-Transfer.

The photoinduced electron-transfer (ET) process plays an irreplaceable role in chemical and biological fields exemplified by enzymatic catalysis, artificial photosystems, solar energy conversion, and so forth. Searching for a new photoinduced ET system is of great importance for the development of functional materials. Herein, a series of host-guest compounds based on a magnesium metal-organic framework (Mg-MOF) as a host and pyridine derivatives as guests have been presented. Notably, strong O-H···N hydrogen bond between the oxygen atom of μ2-H2O and the nitrogen atom of pyridine enables proton delocalization between water molecule and pyridine guest. Despite the absence of photochromic modules in these host-guest compounds, long-lived charge-separated states with distinct color changes can be formed after UV-light irradiation. The substituents in pyridines and the proton delocalization ability between the host and guests have a great influence on their photoinduced ET process to endow the MOF materials with tunable photoinduced charge-separated states.

Supramolecular Host–Guest Assemblies of [M6Cl14]2–, M = Mo, W, Clusters with γ-Cyclodextrin for the Development of CLUSPOMs

Host–guest assemblies open up opportunities for developing novel functional CLUSPOM multicomponent systems based on transition metal clusters (CLUS), polyoxometalates (POMs) and macrocyclic organic ligands. In water–ethanol solution γ-cyclodextrin (γ-CD) interacts with halide metal clusters [M6Cl14]2– (M = Mo, W) to form sandwich-type structures. The supramolecular association between the clusters and CDs, however, remains weak in solution, and the interactions are not strong enough to prevent the hydrolysis of the inorganic guest. Although analysis of the resulting crystal structures reveals inclusion complexation, 1H NMR experiments in solution show no specific affinity between the two components. The luminescent properties of the host–guest compounds in comparison with the initial cluster complexes are also studied to evaluate the influence of CD.

Continuous hydrate-based CO2 separation from H2 + CO2 gas mixture using cyclopentane as co-guest

CO2 separation from H2 + CO2 gas mixture is a necessary technology for a stable supply of blue hydrogen. Among CO2 separation technology, hydrate-based CO2 separation is an environmentally and economically superior technology. Cyclopentane (CP) was selected as guest compound to enable hydrate-based CO2 separation under thermodynamic conditions closer to normal pressure and temperature. Hydrate-based continuous CO2 separation experiments are conducted in the H2 + CO2 + CP + H2O system at 284 K. The results of these experiments showed that mole fraction of H2 in the gas phase reached 0.9 at the steady state in the H2 + CO2 + CP + H2O system after the CO2 was extracted via hydrate formation. At the same time, more H2 was incorporated into the mixed hydrate during this process as the concentration of H2 in the gas phase increases post hydrate formation. Therefore, it was demonstrated that hydrate-based CO2 separation was successful in H2 + CO2 + CP + H2O system at 284 K but there is also increase of energy costs caused by H2 loss. The PXRD results identified H2 + CO2 + CP hydrate as structure II hydrate. Although H2 + CO2 + Tetrahydropyran (THP) hydrate also forms structure II hydrate, more H2 is encapsulated in the H2 + CO2 + CP mixed hydrate than in the H2 + CO2 + THP mixed hydrate. This difference may be caused by the difference in the lattice constants of CP and THP hydrates, which arises from the difference in molecular size of CP and THP, from the differences between the large guest–host interactions, and from differences arising from hydrogen bonding of THP with the host water framework which can decrease the H2 holding capacity. In this study, it was revealed that the molecular diameter of the guest molecules need also to be considered in addition to the phase equilibrium conditions of the hydrates when selecting guest compound of hydrates.

Color‐Tunable Dual‐Mode Organic Afterglow from Classical Aggregation‐Caused Quenching Compounds for White‐Light‐Manipulated Anti‐Counterfeiting

AbstractColor‐tunable dual‐mode organic afterglow excited by ultraviolet (UV) and white light was achieved from classical aggregation‐caused quenching compounds for the first time. Specifically, two luminescent systems, which could produce significant organic afterglow composed of persistent thermally activated delayed fluorescence and ultralong organic phosphorescence under ambient conditions, were constructed by doping fluorescein sodium and calcein sodium into aluminum sulfate. Their lifetimes surpassed 600 ms, and the dopant concentrations were as low as 5×10−6 wt %. Moreover, the persistent luminescence colors of the materials could be tuned from blue to green and then to yellow by simply varying the concentrations of guest compounds or the temperature in the range of 260–340 K. Inspired by these exciting results, the afterglow materials were used for UV‐ and white‐light‐manipulated anti‐counterfeiting and preparation of elastomers with different colors of persistent luminescence.

Color-Tunable Dual-Mode Organic Afterglow from Classical Aggregation-Caused Quenching Compounds for White-Light-Manipulated Anti-Counterfeiting.

Color-tunable dual-mode organic afterglow excited by ultraviolet (UV) and white light was achieved from classical aggregation-caused quenching compounds for the first time. Specifically, two luminescent systems, which could produce significant organic afterglow composed of persistent thermally activated delayed fluorescence and ultralong organic phosphorescence under ambient conditions, were constructed by doping fluorescein sodium and calcein sodium into aluminum sulfate. Their lifetimes surpassed 600 ms, and the dopant concentrations were as low as 5×10-6 wt %. Moreover, the persistent luminescence colors of the materials could be tuned from blue to green and then to yellow by simply varying the concentrations of guest compounds or the temperature in the range of 260-340 K. Inspired by these exciting results, the afterglow materials were used for UV- and white-light-manipulated anti-counterfeiting and preparation of elastomers with different colors of persistent luminescence.