Cyclic Oligomers Research Articles

Polymerization of six-membered propylene oxalate

Ring-opening polymerization (ROP) of the six-membered cyclic propylene oxalate was studied for the first time. The reaction proceeded with a high limiting conversion of about 96 % at 100 °C in the presence of tin(II) octoate. Linear macromolecules, Mw of 20–30 × 103, Ð ∼ 2, represented 86 % of the product, 4 % came from the equilibrium concentration of monomer, while the rest 10 % were cyclic oligomers consisting of 3–10 repeat units. ROP was accompanied by partial (about 30 %) conversion of the catalyst into the insoluble tin(II) oxalate in the course of polymer cross-linking reaction. The kinetics of polymerization obeyed first-order law, indicating typical for ROP constant number of active centers during the process. Polymerization without catalyst was 2000 times slower and also resulted in formation of polymer with Ð ∼ 2. Addition of benzyl alcohol to the polymerization mixture resulted in its inclusion into linear macromolecules and a decrease in their molecular weight. The results point to the possibility of synthesizing propylene oxalate block copolymers using macroinitiators with hydroxyl end groups.

Enhancing antibacterial efficacy through macrocyclic host complexation of fluoroquinolone antibiotics for overcoming resistance

The use of supramolecular assemblies in pharmaceuticals has garnered significant interest. Recent studies have shown that the activities of antibacterial agents can be enhanced through complexation with cyclic oligomers and metal ions. Notably, these complexes sometimes possess greater therapeutic properties than the parent drugs. To develop microbiologically potent supramolecular drugs, the complexation of macrocyclic hosts with fluoroquinolone (FQ) antibiotics was investigated. FQs are a successful family of antibiotics that target the bacterial enzymes DNA gyrase and DNA topoisomerase IV, leading to bacterial cell death through the inhibition of DNA synthesis. However, antibiotic resistance resulting from the repeated use of FQs over time has limited their effectiveness against resistant pathogens. To overcome this issue, the encapsulation of FQs in polyphenolic macrocycles was investigated. This study highlights resorcinarene, a polyphenolic host with antibacterial properties, and its ability to chemically interact with FQs. The inclusion complexation process was analyzed using NMR and FTIR techniques. The binding constants determined by 1H-NMR titration revealed that levofloxacin forms more stable complexes with resorcinarene than with β-cyclodextrin, which aligned with MD simulations. Assessment of the geometric characteristics of the inclusion complexes using 2D NMR analysis confirmed that different moieties of various FQs can fit into a single host cavity and improve activity against gram-negative bacteria. Overall, these findings suggest that encapsulation in polyphenolic macrocycles is a promising strategy for utilizing FQs against antibiotic-resistant bacteria.

Photothermal synergistic curing of one-component epoxy resin adhesive based on active monomer mechanism

ABSTRACT One-component epoxy resin adhesives with Ethylamine-boron trifluoride (BF3-MEA) have become popular choices for electronic applications due to their lower curing temperatures and excellent storage stability. However, in the traditional thermal curing process for these adhesives, which relies on the Active Chain End (ACE) mechanism, the formation of cyclic oligomers can compromise their mechanical performance. In this study, we prepared a series of novel one-component adhesives using Diglycidyl-4,5-epoxy-cyclohexane-1,2-dicarboxylate (TDE-85) epoxy resin, Bis [4-(diphenylsulfonio) phenyl] sulfide bis (hexafluoroantimonate) (Photoinitiator 1176), and BF3-MEA through blending, and successfully achieved photothermal dual-curing. We systematically explored various adhesive ratios and curing conditions. Compared to adhesives treated solely by thermal curing, those subjected to photothermal dual-curing exhibited the best shear strength of 13.9 ± 0.7 MPa and a hardness of 88 ± 4 Shore A, representing improvements of 118.2% and 18.9%, respectively. Additionally, the study demonstrated that hydroxyl groups produced by photocuring effectively inhibit the ACE mechanism and promote the Active Monomer (AM) mechanism, which becomes dominant. In summary, the photothermal synergistic curing approach, with the AM mechanism as dominant, prevents the formation of cyclic oligomers and enhances mechanical performance. This study offers a new approach for adhesives used in electronic devices.

Navigating a 1E+60 Chemical Space of Peptide/Peptoid Oligomers.

Herein we report a virtual library of 1E+60 members, a common estimate for the size of the drug-like chemical space. The library consists of linear or cyclic oligomers forming molecules within the size range of peptide drugs. We demonstrate ligand-based virtual screening using a genetic algorithm.

Phosphoric acid salts of amino acids as a source of oligopeptides on the early Earth

Because of their unique proton-conductivity, chains of phosphoric acid molecules are excellent proton-transfer catalysts. Here we demonstrate that this property could have been exploited for the prebiotic synthesis of the first oligopeptide sequences on our planet. Our results suggest that drying highly diluted solutions containing amino acids (like glycine, histidine and arginine) and phosphates in comparable concentrations at elevated temperatures (ca. 80 °C) in an acidic environment could lead to the accumulation of amino acid:phosphoric acid crystalline salts. Subsequent heating of these materials at 100 °C for 1–3 days results in the formation of oligoglycines consisting of up to 24 monomeric units, while arginine and histidine form shorter oligomers (up to trimers) only. Overall, our results suggest that combining the catalytic effect of phosphate chains with the crystalline order present in amino acid:phosphoric acid salts represents a viable solution that could be utilized to generate the first oligopeptide sequences in a mild acidic hydrothermal field scenario. Further, we propose that crystallization could help overcoming cyclic oligomer formation that is a generally known bottleneck of prebiotic polymerization processes preventing further chain growth.

The third-order nonlinear optical responses of zinc porphyrin oligomers: Cycles vs linear chains

Porphyrins are widely used as potential nonlinear optical (NLO) materials because of their highly delocalized π electrons and feasible synthesis and functionalization with broad biological applications. A variety of linear and cyclic porphyrin derivatives have been synthesized, and the correlation between their structures and NLO properties awaits being disclosed. In this work, the electronic structures and third-order NLO properties of linear and cyclic butadiyne-linked zinc porphyrin oligomers have been studied by quantum chemical methods and sum-over-states model. The static second hyperpolarizability (<γ0>) increases exponentially with the number of zinc porphyrin units ([<γ0>n] = 0.67[<γ0>1]n2.63, n = 2 ∼ 6) in linear π-conjugated oligomers, and the <γ0> of the linear hexamer is about 74 times that of the monomer. Such enhancement of <γ0> in linear oligomers originates from closely-lying frontier molecular orbitals available for low energy electron excitations and strong charge transfer-based excitations across porphyrins. The <γ0>s of cyclic porphyrins are lower than that of the linear hexamer, though the interaction between the ring and the ligand enhances the <γ0> of some cyclic zinc porphyrin complexes. The large two-photon absorption cross sections confer on these zinc porphyrin derivatives excellent candidates for two-photon absorption applications.

Durable and dense zwitterionic polymer brushes initiated from surface-segregated cyclic initiator via atom transfer radical polymerization

Immobilization of initiators on a polymer surface for surface-initiated polymerization has primarily been achieved via covalent bonds. However, this approach is subject to limitations, such as the requirement for additional processing steps and different customized methods tailored to the specific characteristics of each polymer. In this study, initiator immobilization was achieved by surface segregation, a phenomenon observed in polymer blends wherein one component spontaneously enriches the surface, thereby enabling the modification of surface properties. Specifically, we designed cyclic oligomers containing an atom transfer radical polymerization (ATRP) initiator. The enhanced performance of surface segregation mediated by the cyclic topology was evaluated, along with the surface-initiated polymerization initiated by the surface-segregated oligomer. The kinetics of the ATRP reaction for the cyclic initiators were investigated, and the zwitterion polymer brush density was also calculated. The robustness of the brushes was evaluated through leaching tests, which revealed no notable alterations before and after the assessments. The antifouling effect of the brushes was confirmed through protein adsorption, platelet adhesion, bacterial attachment, and whole-blood circulation experiments. These antifouling examinations demonstrated reduced substance attachment of zwitterionic polymer brushes. Lastly, experiments on optimizing the ATRP catalyst loading during the surface-initiated ATRP were conducted. The excellent performance of the cyclic initiators is expected to provide new insights and opportunities in the field of surface-initiated polymerization. Moreover, the formation of zwitterion brushes via cyclic initiators holds promise for versatile applications in the field of long-term utilization in biointerfaces, offering a wide range of potential uses.

Bioinspired Binding and Conversion of Linear Monoterpenes by Polyaromatic Coordination Capsules.

Linear monoterpenes, versatile reaction biosubstrates, are bound and subsequently converted to various cyclic monomers and oligomers with excellent selectivity and efficiency, only in natural enzymes. We herein report bioinspired functions of synthetic polyaromatic cavities toward linear monoterpenes in the solution and solid states. The cavities are provided by polyaromatic coordination capsules, formed by the assembly of Pt(II) ions and bent bispyridine ligands with two anthracene panels. By using the capsule cavities, the selective binding of citronellal from mixtures with other monoterpenes and its preferential vapor binding over its derivatives are demonstrated in water and in the solid state, respectively. The capsule furthermore extracts p-menthane-3,8-diol, with high product- and stereoselectivity, from a reaction mixture obtained by the acid-catalyzed cyclization of citronellal in water. Thanks to the inner and outer polyaromatic cavities, the catalytic cyclization-dimerization of vaporized citronellal efficiently proceeds in the acid-loaded capsule solid and product/stereoselectively affords p-menthane-3,8-diol citronellal acetal (∼330% yield based on the capsule) under ambient conditions. The solid capsule reactor can be reused at least 5 times with enhanced conversion. The present study opens up a new approach toward mimicking terpene biosynthesis via synthetic polyaromatic cavities.

The recent development of β‐cyclodextrin‐based catalysts system in Suzuki coupling reactions

β‐Cyclodextrin has drawn significant attention as a special class of cyclic oligomers over the past few decades. They have been employed in many organic conversions as green alternative catalysts to perform satisfactorily in catalytic activity and modify the efficiency of organic reactions. Its availability, nontoxicity, low cost, renewability, and high performance in organic transformations are several benefits of cyclodextrins that have captured the interest of many research groups worldwide. In recent decades, great progress has been made in developing metal‐catalyzed coupling reactions to create carbon–carbon bonds. For the transition‐metal‐catalyzed cross‐coupling, using modified β‐cyclodextrin derivatives as catalysts is much more pleasant due to the obvious advantages such as valuable catalytic properties and the capability to create an inclusion complex with different metals. The particular purpose of this review is to summarize the application of β‐cyclodextrin‐based catalyst systems in Suzuki coupling reaction for the synthesis of biaryl compounds covering the years 2019–2023.

Predicting Organometallic Intermediates in the Surface-Assisted Ullmann Coupling of Chrysene Isomers.

On-surface polymerization of functional organic molecules has been recently recognized as a promising route to persistent low-dimensional structures with tailorable properties. In this contribution, using the coarse-grained Monte Carlo simulation method, we study the initial stage of the Ullmann coupling of doubly halogenated chrysene isomers adsorbed on a catalytically active (111) crystalline surface. To that end, we focus on the formation of labile metal-organic precursor structures preceding the covalent bonding of chrysene monomers. Four monomeric chrysene units with differently distributed halogen substituents were probed in the simulations, and the resulting precursor structures were compared and quantified. Moreover, the effect of (pro)chirality of chrysene tectons on the structure formation was elucidated by running separate simulations in enantiopure and racemic systems. The calculations showed that suitable manipulation of the halogen substitution pattern allows for the creation of diverse precursor architectures, ranging from straight and winded chains to cyclic oligomers with enantiopure, racemic, and nonracemic composition. The obtained findings can be helpful in developing synthetic strategies for covalent polymers with predefined architecture and functionality.

Odd-Even Effect of Polyesters‘ Cyclic Oligomers and the Definition of Oligomers Based on Physicochemical Properties

This work explores the definition and characterization of synthetic polymeric oligomers, chemical substances comprising a small number of repeated organic molecules. It highlights the lack of clarity surrounding the range of repeated units that can be classified as an oligomer, and how this definition is field-dependent. The present study focused on PET cyclic oligomers and revealed that the progression of the ring length from smaller to longer oligomers followed the well-known odd-even effect. This phenomenon affects the physical and chemical properties of oligomers and can also be observed with analytical techniques such as differential scanning calorimetry (DSC), high resolution mass spectrometry (HR-MS) and NMR. Similarities between PET and PBT oligomers were also observed, and an alternative potential definition for oligomers in the polymeric field is suggested based on physical behaviour of the longer cyclic oligomers.

Unraveling The Impact of Isomerism on Enzymatic Polymerization of Furanic Polyesters

AbstractAs awareness of the environmental impact of fossil‐based polymers grows, the demand for biobased alternatives rises. In this context, combining eco‐friendly synthesis techniques with renewable resources is important to produce polymers efficiently and sustainably. Furandicarboxylic acid (FDCA) is one of the key building blocks for producing biobased polymers. However, most studies predominantly focus on 2,5‐FDCA, while FDCA encompasses other noteworthy isomers, namely, 2,4‐ and 3,4‐FDCA. The polymers derived from these two isomers have recently gained attention due to their promising properties. In this study, an environmentally friendly approach for producing biobased polyesters from 2,5‐, 2,4‐, and 3,4‐FDCA dimethyl ester isomers is proposed. The synthesis is conducted under greener conditions, utilizing Candida antarctica lipase B (CALB) enzyme as a biocatalyst. The performance of the enzyme is assessed, revealing CALB preference for polymerizing 2,5‐FDCA over 2,4‐ and 3,4‐FDCA dimethyl ester, which is elucidated by docking analysis. Moreover, CALB shows varying rates of cyclic oligomer formation for each isomer, favoring 2,5‐FDCA cyclization. The structure‐property relationship, encompassing the variation in isomeric structure, is evaluated through structural characterization, thermal analysis, and surface properties. This study primarily emphasized enzymatic polymerization and highlighted its versatility in accommodating different monomer isomeric substitutions.

Safety profile of ZnO active packaging PBAT based biomaterial for food packaging. First tier evaluation

Materials produced with polybutylene adipate terephthalate (PBAT) and starch are raising great interest for packaging and food contact applications, including as support for active antimicrobial agents such as zinc oxide nanoparticles (ZnO). Studies focusing on the safety of these materials as evaluated with the current reference rules for food contact materials, are lacking. A commercially available PBAT/starch-based material was incorporated with ZnO and the overall and specific migration of the films were studied at different conditions of simulants and temperature. The overall migration (OM) limit is exceeded due to the release of starch as confirmed by infrared spectroscopy. The impact of temperature on the OM was higher for the ethanol 10%. The incorporation of ZnO particles reduced the OM, for both temperatures tested for ethanol 10%. The impact of incorporating ZnO in the migration into acetic acid was relevant at 20 °C only. Beside starch, most relevant migrants were PBAT oligomers made of butanediol and two different kinds of diacids, terephthalic acid or adipic acid. The cyclic diester of 1,4-butanediol and adipic acid, butenyl butanediol adipate in either cyclic and linear form and oligomers terephthalic acid, but-3-enyl hexadecyl ester were detected in an untargeted screening with GC-MS. A second TPA oligomer was not fully identified. The specific migration was in several cases, depending on the simulant and on the temperature, higher than 50 μgkg−1 (semi-quantification), the threshold value for requiring additional toxicity test (genotoxicity tests applied to oligomers below 1000 Da). This indicates the need for more detailed studies with more precise quantification to verify the need for toxicity tests.

Calixarene: A Supramolecular Material for Treating Cancer.

Cancer is a disease with a high mortality rate; therefore, research on new treatment strategies is essential. There has been increased interest in novel drug delivery systems (DDS) in recent years, such as calixarene, one of the most important principal molecules in supramolecular chemistry. Calixarene is a cyclic oligomer of phenolic units linked by methylene bridges that belongs to the third generation of supramolecular compounds. By modifying the phenolic hydroxyl end (lower edge) or the para-position, a wide range of calixarene derivatives can be obtained (upper edge). Drugs are combined with calixarenes to modify and have new properties, such as strong water solubility, the ability to bond with guest molecules, and excellent biocompatibility. In this review, we summarize the applications of calixarene in the construction of anticancer drug delivery systems and its application in clinical treatment and diagnosis. It provides theoretical support for the diagnosis and treatment of cancer in the future.

The recent development of β‐cyclodextrin‐based catalysts system in click reactions: A review

A significant challenge for scientists today is to design green and eco‐friendly catalysts based on green chemistry with high catalytic performance and recycling properties. Many studies have aimed to address environmental issues by developing green chemical processes and catalysts that reduce the production of harmful substances. β‐Cyclodextrin (β‐CD), a class of cyclic oligomers, has garnered considerable attention in recent decades. It has been utilized as a green alternative catalyst in various organic conversions, demonstrating satisfactory catalytic activity and improved efficiency of organic reactions. The availability, non‐toxicity, low cost, renewability, and high performance in organic transformations are several benefits of cyclodextrins that have attracted interest from research groups worldwide. The click reaction is well‐known in green chemistry for its high selectivity and efficiency in producing 1,2,3‐triazoles with significant medicinal activities. This reaction involves aryl/alkyl halides, alkynes, and NaN3 under ambient conditions to generate necessary scaffolds called 1,2,3‐triazoles. Therefore, finding green approaches for synthesizing 1,2,3‐triazoles is of great interest. In recent decades, significant advancements have been made in developing metal‐catalyzed click reactions to synthesize 1,2,3‐triazole derivatives. Carolyn Bertozzi, Morten Meldal, and Barry Sharpless were awarded the Nobel Prize in Chemistry in 2022 for their contributions to the foundations of click and bio‐orthogonal chemistry. In transition, metal‐catalyzed click reactions, using modified β‐CD derivatives as catalysts is particularly advantageous because of their valuable catalytic properties and their ability to form inclusion complexes with different metals. This review focuses on the catalyzed click reaction using β‐CD‐based catalysts to prepare triazoles. Using biodegradable β‐CD has made the method safe, sustainable, and eco‐friendly. The click reaction has provided access to various 1,2,3‐triazoles essential in pharmaceutical products and exhibits diverse biological activities. The specific purpose of this review is to summarize the application of β‐CD‐based catalyst systems in click reactions.

Selective synthesis of α-vinyl-ω-vinylidene-oligoisoprene as a macromonomer via ethenolysis of polyisoprene

Oligoisoprene macromonomer, which bears a terminal vinyl group, was prepared by the metathesis degradation of high-molecular-weight polyisoprene with ethylene for coordination polymerization. The ethenolysis of polyisoprene using the 2nd-generation Grubbs catalyst (G2) at ambient pressure gave heterotelechelic (α-vinyl-ω-vinylidene) oligoisoprene, keeping the stereoregularity in high yield, whereas the 1st generation Grubbs catalyst was immediately deactivated. In such metathesis degradation, an intramolecular side reaction giving cyclic oligomers may be competitive, but ethenolysis proceeded with high selectivity, probably because of the least steric effect of ethylene. The ethenolysis is also applicable for the degradation of natural rubber-derived polyisoprene, although the catalytic activity decreased. The prepared oligoisoprene macromonomer was successfully copolymerized with ethylene using a phenoxyimine-ligated titanium catalyst, and the reactivity of the macromonomer was almost the same as that of 1-hexadecene. The oligoisoprene-grafted polyethylene showed a typical stress‒strain curve, of which the tensile modulus and yielding stress are comparable to those of linear low-density polyethylene.

Computational design of boron-free triangular molecules with inverted singlet-triplet energy gap.

A novel, computationally designed, class of triangular-shape organic molecules with an inverted singlet-triplet (IST) energy gap is investigated with ab initio electronic structure methods. The considered molecular systems are cyclic oligomers and their common feature is electronic conjugation along the molecular rim. Vertical excitation energies from the electronic ground state to the lowest singlet and triplet excited states were computed, as well as vertical emission energies from these states to the ground state. The results underscore the significance of optimizing excited-state geometries to accurately describe the optoelectronic properties of IST molecules, in particular with respect to their application in OLEDs.

A novel process for recovery and exploitation of polyesters and polyamides from waste polymeric artifacts

Plastic waste is one of the world's biggest sources of pollution. Despite the growing trend towards recycling, there are currently no effective technologies to offset the continuous increase in plastic production. Polyesters and polyamides are among the most widely produced single-use plastics, mainly used in the manufacture of textiles and soft drink bottles. Currently, only a small proportion of these polymers can be effectively recycled. The two primary methods employed for this purpose are mechanical and chemical recycling. Presently, mechanical recycling remains the more widely adopted process within the industrial sector. However, the treatment process is limited to a narrow range of waste materials as it is impossible to remove dyes and the mechanical properties deteriorate due to incompatibility between different plastic materials. Another critical limit of this recycling technology is the limited number of recycling loops that can be done due to the thermal degradation that occurs during the extrusion process. The alternative option is chemical recycling, which allows the depolymerization of the original product to recover the monomers directly. The main drawbacks are the long reaction times and the many solvents needed to achieve high-purity products. As a results, chemical recycling is only economically feasible for large companies that can produce the virgin polymer in situ. In this work, a new technology has been patented. This process consists of three main steps. The first one is the distillation-assisted cyclodepolymerization (DA-CDP), introduced as a modification of the CDP process. In this unit, cyclic oligomers together with high molecular weight compounds are produced. Then, after polymer purification, it is possible to achieve the same molecular weight as the initial polymer in less than 30 min, exploiting the ring-opening polymerization (ROP) of the next step.

Monomeric, Oligomeric, Polymeric, and Supramolecular Cyclodextrins as Catalysts for Green Chemistry.

This review comprehensively covers recent developments of cyclodextrin-mediated chemical transformations for green chemistry. These cyclic oligomers of glucose are nontoxic, eco-friendly, and recyclable to accomplish eminent functions in water. Their most important feature is to form inclusion complexes with reactants, intermediates, and/or catalysts. As a result, their cavities serve as sterically restricted and apolar reaction fields to promote the efficiency and selectivity of reactions. Furthermore, unstable reagents and intermediates are protected from undesired side reactions. The scope of their applications has been further widened through covalent or noncovalent modifications. Combinations of them with metal catalysis are especially successful. In terms of these effects, various chemical reactions are achieved with high selectivity and yield so that valuable chemicals are synthesized from multiple components in one-pot reactions. Furthermore, cyclodextrin units are orderly assembled in oligomers and polymers to show their cooperation for advanced properties. Recently, cyclodextrin-based metal-organic frameworks and polyoxometalate-cyclodextrin frameworks have been fabricated and employed for unique applications. Cyclodextrins fulfill many requirements for green chemistry and should make enormous contributions to this growing field.

Untargeted screening of NIAS and cyclic oligomers migrating from virgin and recycled polyethylene terephthalate (PET) food trays

Polyethylene terephthalate is considered one of the most used and approved recycled plastic polymer as food contact materials (FCM); however, the fundamental details arising from the recycled content of PET trays in relation to processing conditions or extent of recycling are not well understood. In the present work, the presence and migration of different series of PET cyclic oligomers from industrially recycled trays were investigated using official food simulant D1 at 40 °C for 10 days. The trays were produced in two different facilities, using different extrusion processing technology, namely single and twin-screw extruder. Tested food packaging trays were produced from different ratios of virgin (vPET) and recycled PET (rPET), varying from 0% up to 100% w/w content. Analysis of the trays using MALDI-TOF-MS revealed a decrease in the molecular weight distribution (Mw) in rPET compared to virgin PET plastic. Untargeted screening with UHPLC-QTOF-MS, revealed the presence and migration of several intentionally added substances (IAS) as well as non-intentionally added substances (NIAS). The results demonstrated differences of the cyclic oligomers migration into the selected food simulant, depending on the rPET/vPET ratios as well as among the applied extrusion technology applied. Following multivariate analysis, marker compounds found to be benzyl butyl phthalate (BBP), butyl lactate, dodecenamide, 2-methyl-1,3-dioxolane, PET 2nd series cyclic dimer as well as PET 1st series cyclic dimer can be considered as marker compounds.