Exploring the Assembly of Resorc[4]arenes for the Construction of Supramolecular Nano-Aggregates

Many biologically active compounds feature low solubility in aqueous media and, thus, poor bioavailability. The formation of the host-guest complex by using calixarene-based macrocycles (i.e., resorcinol-derived cyclic oligomers) with a good solubility profile can improve solubilization of hydrophobic drugs. Herein, we explore the ability of resorc[4]arenes to self-assemble in polar solutions, to form supramolecular aggregates, and to promote water-solubility of an isoflavone endowed with anti-cancer activity, namely Glabrescione B (GlaB). Accordingly, we synthesized several architectures featuring a different pattern of substitution on the upper rim including functional groups able to undergo acid dissociation (i.e., carboxyl and hydroxyl groups). The aggregation phenomenon of the amphiphilic resorc[4]arenes has been investigated in a THF/water solution by UV–visible spectroscopy, at different pH values. Based on their ionization properties, we demonstrated that the supramolecular assembly of resorc[4]arene-based systems can be modulated at given pH values, and thus promoting the solubility of GlaB.

Main Applications of Cyclodextrins in the Food Industry as the Compounds of Choice to Form Host–Guest Complexes

Cyclodextrins (CDs) are cyclic oligomers broadly used in food manufacturing as food additives for different purposes, e.g., to improve sensorial qualities, shelf life, and sequestration of components. In this review, the latest advancements of their applications along with the characteristics of the uses of the different CDs (α, β, γ and their derivatives) were reviewed. Their beneficial effects can be achieved by mixing small amounts of CDs with the target material to be stabilized. Essentially, they have the capacity to form stable inclusion complexes with sensitive lipophilic nutrients and constituents of flavor and taste. Their toxicity has been also studied, showing that CDs are innocuous in oral administration. A review of the current legislation was also carried out, showing a general trend towards a wider acceptance of CDs as food additives. Suitable and cost-effective procedures for the manufacture of CDs have progressed, and nowadays it is possible to obtain realistic prices and used them in foods. Therefore, CDs have a promising future due to consumer demand for healthy and functional products.

Triplet State Baird-Aromaticity in Macrocycles: Scope, Limitations and Complications

<p>The aromaticity of cyclic 4<i>n</i>p-electron molecules in their first pp* triplet state (T₁), labelled Baird-aromaticity, has gained growing attention in the last decade. Here we explore computationally the limitations of T₁ state Baird-aromaticity in macrocyclic compounds, <b>[<i>n</i>]CM</b>’s, which are cyclic oligomers of four different monocycles (M = <i>para</i>-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 p-electrons in their main conjugation paths we find that for their T₁ states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans (<b>[<i>n</i>]CFU</b>’s) retain Baird-aromaticity until larger <i>n</i> than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a <b>³[<i>n</i>]CFU</b> with a specific <i>n</i> is more strongly Baird-aromatic than the analogous <b>³[<i>n</i>]CPP</b> while the magnetic indices tell the opposite. To construct large T₁ state Baird-aromatic <b>[<i>n</i>]CM</b>’s the design should be such that the T₁ state Baird-aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hückel-aromaticity of one or a few monocycles and semi-localized triplet diradical character. Monomers with lower Hückel-aromaticity in S₀ than benzene (<i>e.g.</i>, furan) that do not impose steric congestion are preferred. Structural confinement imposed by, <i>e.g.</i>, methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T₁ state aromaticity we reveal the analogy to the Hückel-aromaticity of the corresponding closed-shell dications, yet, observe stronger Hückel-aromaticity in the macrocyclic dications than Baird-aromaticity in the T₁ states of the neutral macrocycles. </p>

Triplet State Baird-Aromaticity in Macrocycles: Scope, Limitations and Complications

<p>The aromaticity of cyclic 4<i>n</i>p-electron molecules in their first pp* triplet state (T₁), labelled Baird-aromaticity, has gained growing attention in the last decade. Here we explore computationally the limitations of T₁ state Baird-aromaticity in macrocyclic compounds, <b>[<i>n</i>]CM</b>’s, which are cyclic oligomers of four different monocycles (M = <i>para</i>-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 p-electrons in their main conjugation paths we find that for their T₁ states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans (<b>[<i>n</i>]CFU</b>’s) retain Baird-aromaticity until larger <i>n</i> than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a <b>³[<i>n</i>]CFU</b> with a specific <i>n</i> is more strongly Baird-aromatic than the analogous <b>³[<i>n</i>]CPP</b> while the magnetic indices tell the opposite. To construct large T₁ state Baird-aromatic <b>[<i>n</i>]CM</b>’s the design should be such that the T₁ state Baird-aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hückel-aromaticity of one or a few monocycles and semi-localized triplet diradical character. Monomers with lower Hückel-aromaticity in S₀ than benzene (<i>e.g.</i>, furan) that do not impose steric congestion are preferred. Structural confinement imposed by, <i>e.g.</i>, methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T₁ state aromaticity we reveal the analogy to the Hückel-aromaticity of the corresponding closed-shell dications, yet, observe stronger Hückel-aromaticity in the macrocyclic dications than Baird-aromaticity in the T₁ states of the neutral macrocycles. </p>

From Allenes to Spirobifluorenes: On the Way to Device-compatible Chiroptical Systems

The last decade has seen a huge growth in the construction of chiral systems to expand the scope of chiroptical applications. Dependence of chiroptical response on molecular conformation typically leads to low chiroptical intensities of chiral systems that feature several conformations in solution. In this respect, allenes were employed for the preparation of open and cyclic oligomers as well as molecular cages, presenting remarkable chiroptical responses in solution. Their molecular chirality was also transferred to metal surfaces, yet photoisomerization of allenes limited their further exploration. In search of a more robust chiral axis, theoretical and experimental studies confirmed that spirobifluorenes could give rise to stable systems with tailored optical and chiroptical properties. Additionally, incorporating a conformational lock into spirobifluorene cyclic architectures served as an efficient strategy towards the generation of distinct helical molecular orbitals. This review article outlines our results on developing device-compatible chiroptical systems through axially chiral allenes and spirobifluorenes. The contribution from other research groups is presented briefly.

Development of an LC-MS method for the semiquantitative determination of polyamide 6 contaminations in polyolefin recyclates

Recycling will be of increasing importance in the future, especially for plastic packaging waste mainly consisting of polyolefins. One major problem of recyclates comprises impurities which can have a significant negative impact on future product properties. Polyamide 6 can be found widely as contaminant in recycled polyolefins, leading to a need of quantification methods thereof. In this paper, a method development for the quantitative analysis of polyamide 6 is presented based on analysing ε-caprolactam and related cyclic oligomers as marker compounds in model recyclates of high- and low-density polyethylene and polypropylene compounded with low amounts of polyamide 6. For the method development and tentative identification of the different cyclic compounds, a HPLC-QTOF-MS was used and it was possible to detect six different compounds, ε-caprolactam and the corresponding cyclic di- to hexamer. The quantification was performed with a HPLC-QQQ-MS, equipped with a HILIC column, after sample preparation via microwave-assisted extraction. It could be shown that a good linearity from 0.2 up to 5 wt% polyamide 6 in the different polyolefins can be achieved. The cyclic trimer and tetramer show a low limit of quantification and are therefore well-suited for the quantification, whereas the other cyclic compounds can be then used as qualifiers to avoid false positives. To guarantee the applicability of the method, six real recyclate materials were analysed, whereby in three of them low amounts of polyamide 6 could be detected.