Journal of Inclusion Phenomena and Macrocyclic Chemistry最新文献

In the present investigation, the wheel-and-axle host compound, 1,4-phenylene-bis(di-p-fluorophenylmethanol) (H1), was revealed to have inclusion ability for three saturated heterocyclic organic solvents, namely DIO, MOR and PIP, in addition to the previously reported complex with PYR. Guest competition experiments demonstrated H1 to possess an affinity for PIP and PYR while, in 20:80 PYR/DIO, 40:60 PYR/DIO and 20:80 PIP/DIO binary solutions, the host affinity for PYR, PYR and PIP, respectively, was overwhelming (K > 10). Crystal structure analysis of the complexes showed that favoured PYR was held in the crystals of its complex by means of a much shorter (guest)N‒H···O(host) hydrogen bond compared with the other nitrogen-containing guest solvents (DIO was also retained in its complex by means of a classical hydrogen bond). Plausibly as a result of this observation, the PYR-containing complex had the higher crystal density and was thermally more stable than the other complexes, explaining the affinity of H1 for PYR. The reasons for the host selectivity for PIP was less clear.

Camphor, a crystalline white substance with diverse biological benefits, faces limitations in human health applications due to its volatile and hydrophobic nature, which impedes its solubility and stability. This study addresses these challenges by investigating the encapsulation of camphor within various cyclodextrins (CDs), particularly focusing on α-cyclodextrin (α-CD), to enhance its solubility and protect it from environmental degradation. The formation of camphor-CD inclusion complexes was confirmed through a combination of infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Among the CDs tested, α-CD demonstrated the highest efficiency, achieving a solubility coefficient of 23.38 M⁻¹ and inclusion efficiencies of 24.37% and 34.63% for 1:1 and 1:2 stoichiometries, respectively. Biological evaluations revealed that the Camphor/α-CD complex exhibited significant preservative effects on sperm motility at low concentrations while demonstrating a toxic effect on red blood cells. Additionally, the complex showed promising radical scavenging activity as assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. These findings suggest that camphor, when complexed with α-CD, holds considerable potential for novel applications in drug delivery and cryopreservation technologies.

Mono-6-deoxy-(m-aminobenzylthio)-β-cyclodextrin, a novel ligand, and its two Co(II) and Zn(II) complexes were synthesized and they were extensively characterized using a range of spectroscopic techniques, including ¹H-NMR, IR, UV-Vis, and MS, providing detailed structural insights. To further understand the electronic properties and stability of the complexes, Density Functional Theory (DFT) calculations were performed, revealing optimized structures and confirming their stability. The antimicrobial potential of the ligand and both metal complexes was evaluated in vitro against a variety of naturally occurring Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coli and Klebsiella pneumonia) microorganisms, demonstrating promising inhibitory activity. In Klebsiea pneumonia plates, the Zn(II) complex (4a) produced the maximum inhibition zone, whereas Staphylococcus aureus produced the least inhibition zone. Additionally, molecular docking studies were conducted to validate the interaction mechanisms of the complexes with key bacterial proteins, supporting the experimental findings and offering deeper insights into their mode of action. This comprehensive approach highlights the potential of these complexes as novel antimicrobial agents with well-characterized structural and biological properties.

Cyclodextrin derivatives prepared either in laboratory or industrially are often mixtures of several isomers. Single isomer heptakis(2,6-di-O-methyl) β-cyclodextrin (2,6-DIMEB) has distinct methylation pattern compared to various commercially available methylated cyclodextrins. It has been used in the production of acellular pertussis vaccine as an auxiliary material improving toxin secretion since the 1980s. 2,6-DIMEB has since gained significance in other biotechnological processes, too. Characterization of the isomeric purity and differentiation of 2,6-DIMEB from other methylated cyclodextrin types having different degree and pattern of substitution has therefore a critical relevance. A rapid test by hot crystallization is proposed here based on the peculiar behavior of this compound upon heating in aqueous solution. The temperature at the onset of crystallization is informative on the 2,6-DIMEB content of a mixture of methylated β-cyclodextrins. The test was validated by using HPLC and NMR studies. Comparing the samples from different manufacturers we show that industrially produced methylated cyclodextrins labeled as “DIMEB” contains usually at least 40% of the desired 2,6-DIMEB isomer. Using these techniques, we demonstrated an example of such “DIMEB” labeled products that do not even contain detectable amount of 2,6-DIMEB.

This work investigated the interaction between a 4-sulfocalix[4]arene (SC4) as the host molecule and para-aminobenzoic acid (PABA) as the guest molecule, driven by the outstanding properties of both SC4 and PABA for the development of a PABA nanosensor. PABA drugs are used in medical and pharmaceutical fields, but their potential carcinogenicity restricts their application. SC4 was chosen as the host molecule role because of its water-soluble property, contributing to its remarkable quality as a nanosensor and drug carrier. In this work, PABA was aimed to be detected. Based on an ultraviolet–visible spectroscopy (UV–Vis) study, the SC4 and SC4-PABA liquid samples were characterised. Tauc plot was applied to determine the band gap value. Besides, density functional theory (DFT), a first principle study of the sensing of PABA by SC4 was conducted using the Quantum ESPRESSO (QE) program. The band gap, density of state (DOS), and binding energy of the optimised novel SC4-PABA host–guest complexes were calculated. By comparing the absorbance and band gap of the host molecule to those of the host–guest complex, the reactivity of the host and guest molecules was indicated by the rise in absorbance and the decrease in band gap. Absorbance obtained based on Beer–Lambert law showed the formation of SC4-PABA complexes with the direct allowed transition. Furthermore, the complexes' negative binding energy showed their stability and favourable reactions. The optimum formation of complexes by SC4 and PABA was proven at the host–guest ratio of 1:1. Applying ultrasoft pseudopotential in the band gap calculation was more precise than applying norm-conserving pseudopotential. Both the computational and experimental studies proved the detection of PABA by SC4. The study's findings suggested the role of SC4 as a promising nanosensor for PABA drugs, which can be utilised in the future development of drug sensors.

In this work, the behaviour of host compounds N,N’-bis(9-phenyl-9H-xanthen-9-yl)propane-1,3-diamine (H1) and N,N’-bis(9-phenyl-9H-xanthen-9-yl)butane-1,4-diamine (H2) was investigated in the presence of four saturated six-membered ring guest solvents, namely dioxane (DIO), morpholine (MOR), piperidine (PIP) and tetrahydropyran (THP). After crystallization experiments from each solvent, H1 was observed to only furnish a complex with DIO (the host: guest (H: G) ratio was 2:3), while H2 formed inclusion compounds with each one (H: G ratios were either 1:1 or 1:2). SCXRD analysis revealed that the guest molecules in complex H2·PIP occupied discrete cages, all other guests being located in channels of the inclusion compounds with H2 (in the THPb-containing complex with H2, these channels were extremely constricted, THPb being a second polymorph identified in the H2·2(THP) complex). Competition experiments involving H2 revealed that DIO and MOR were, more usually, the favoured guest species. Guest competition experiments were not performed with H1 owing to extremely slow rates of crystallization. The relative thermal stabilities of the complexes of H2 were in agreement with the host selectivity behaviour: the complexes with DIO and MOR were the more stable ones (T_on 56.7 and 48.2 °C) compared with those with PIP and THP. Finally, the lack of any host···guest interactions between H2 and PIP explained the observation that PIP was never a favoured guest species in the guest competition experiments.

Shape-fixed and persistent aromatic amide hexamer macrocyclic molecules are synthesized via a one-pot method utilizing pyridone diacid and m-phenylenediamine as precursor units, facilitated by intramolecular three-center hydrogen bonds. In ¹H NMR, the significant chemical shift of the macrocyclic amide hydrogen absorption peak indicates the recognition between the macrocyclic system and alkali metal cesium ions. The binding affinity between the cesium ion and the host macromolecule is determined to be 1:1 using the job method, and as 1.00 × 10⁴ M-1 through ¹H NMR titration. X-ray single crystal diffraction confirms that the macrocyclic host is bound to the cesium ion in a ratio of 1:1. The single crystal of pyridone macro ring combined with Cs ion is obtained, which further confirmed that Cs is located in the center of the macro ring cavity, which is very consistent with the theoretical structure prediction.

In this article, we have studied the modulated photophysics and photodynamic of an excited state proton transfer (ESIPT) molecule1-(1H-benzo[d]imidazol-2-yl)naphthalen-2-ol (H-BINO) following host-guest inclusion complexation with water-soluble host Cucurbit[7]uril (CB7) with the help of steady-state, time-resolved spectroscopic measurements and is supported by Density Functional Theory (DFT) calculations. The change of absorbance and fluorescence enhancement with blue shift of emission maxima indicates host-guest inclusion complexation and favourable enol-keto photo-isomerisation of H-BINO inside the CB7 nanocavity. Complexation offers an increment of excited state lifetime from 0.7ns and 2.1ns observed in aqueous medium to 0.8 ns and 3.3 ns in CB7 cavity due to structural rigidity and thereby minimizing non-radiative processes. Benesi-Hildebrand (BH) plot indicates the formation of 1:1 inclusion complex (H-BINO: CB7) which is supported by time-resolved anisotropy measurement. Solvation of H-BINO inside the CB7 cavity is faster at the beginning and slows down over time with solvation correlation time of 2.46 ns. Computational structural calculations at DFT level support that inside the CB7 cavity, the reversal of stability of proton transfer keto-form with respect to the enol-form in the first excited state than the ground state. Blue shifting of experimental absorption and emission maxima inside CB7 nanocavityis well correlate with DFT calculated bands.

The present investigation demonstrated that (4R,5R)-bis(diphenylhydroxymethyl)-2-spiro-1’-cyclohexane-1,3-dioxolane (TADDOL6) possessed the ability to form 1:1 host: guest inclusion compounds with dioxane, piperidine, morpholine and pyridine (DIO, PIP, MOR, PYR) when it was crystallized from these solvents. When mixed guests were employed as the crystallization solvent, TADDOL6 showed an overwhelming preference for PYR, and the host selectivity was noted to be in the order PYR > PIP > MOR > DIO. From SCXRD analyses, it was observed that each of the four organic guest solvents was held in the crystal of the complex by means of classical hydrogen bonding interactions with the host species, with PIP experiencing, statistically, the shorter of these. Hirshfeld surfaces were also considered and demonstrated that the preferred guest species, PYR, experienced the broader range of short contact types. Finally, thermal analyses also explained the host selectivity order: PYR, which was most favoured by TADDOL6, formed a complex with the greatest thermal stability of the four, while the complex with DIO, which was least preferred by TADDOL6, possessed the lowest stability.

Various contributions have been reported concerning the inclusion of flavonoids in cyclodextrins (CDs). The association constant (({K}_{ass})) is one fundamental aspect for characterizing inclusion compounds. Distinct association constants were obtained depending on the experimental technique or the pH for flavonoids included in CD. In the present study, we applied two recently developed theoretical methodologies based on a multi-equilibrium approach to estimate the ({K}_{ass}) for the inclusion of the neutral flavonoids morin (MOR), quercetin (QUE), luteolin (LUT), and kaempferol (KAE) into β-cyclodextrin (β-CD). The analysis of the experimental data for an appropriate pH range, in conjunction with the theoretical response from quantum GFN2-xTB and classical molecular dynamics, addressed the following stability order: LUT@β-CD > QUE@β-CD ~ KAE@β-CD. The combined theoretical and experimental data suggest as more representative experimental K_ass for neutral systems, the following values (in M⁻¹): 462 (2020) – 545 (2013) for LUT@β-CD, 398 (2008) for QUE@β-CD, and 375 (2007) for KAE@β-CD. The theoretical information did not align with the experimental data previously published for MOR@β-CD at low pH, indicating the need for further studies.

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