Cyclodextrin-based rotaxanes for polymer materials: challenge on simultaneous realization of inexpensive production and defined structures

• Yosuke Akae

Beilstein J. Org. Chem. 2024, 20, 3026–3049, doi:10.3762/bjoc.20.252

• from the chiral nature of the CD molecule, and its behavior fits well with the theoretical consideration. As comprehensively described [32], CD-based rotaxanes are typically synthesized by two methods: (1) the end-capping method (route a1, a2) in which the formation of a pseudorotaxane structure first

• proceeds through the formation of CD and an axle molecule, followed by the end-capping of the axle end; (2) the slipping method (route b) involving threading a dumbbell molecule comprising bulky axle-end groups through CD. As the latter is likely to produce a pseudorotaxane framework, the end-capping

• methods are more popular than the slipping method. However, this end-capping method must fulfill the following seven points to appropriately realize a rotaxane framework, and this causes several complexities (Figure 3): (1) The axle molecule must form a stable inclusion complex with CD, (2) the axle

Quinoxaline derivatives as attractive electron-transporting materials

• Zeeshan Abid,
• Liaqat Ali,
• Sughra Gulzar,
• Faiza Wahad,
• Raja Shahid Ashraf and
• Christian B. Nielsen

Beilstein J. Org. Chem. 2023, 19, 1694–1712, doi:10.3762/bjoc.19.124

• enhanced electron hopping and reduced geminate recombination. Qx12 and Qx13 achieved remarkable PCEs of 13.31% and 16.64%, respectively, with PBDB-TF donor in OSC devices [28]. Zhu et al. reported a modification in Qx13 by incorporating an imide-functionalized Qx moiety in its core and end-capping groups

BINOL as a chiral element in mechanically interlocked molecules

• Matthias Krajnc and
• Jochen Niemeyer

Beilstein J. Org. Chem. 2022, 18, 508–523, doi:10.3762/bjoc.18.53

• -based axle and an achiral macrocycle was also synthesized. This design was chosen to investigate the difference between a covalently and a mechanically linked chiral unit with regard to the chiral induction in asymmetric catalysis. By acylative end-capping, followed by introduction of the thiazole unit

• desymmetrization of meso-1,2-diols [58]. The [2]rotaxane (R)-42 was synthesized by interaction of the ammonium salt 41 with the BINOL-based macrocycle (R)-12 and end-capping with 3,5-di-tert-butylbenzoic acid (see Figure 10). In the asymmetric desymmetrization reaction of meso-hydrobenzoin, rotaxane (R)-42 gave

• 2004, Takata and co-workers synthesized thiazolium-based chiral [2]rotaxanes as catalysts for the asymmetric benzoin condensation [56][57]. For the synthesis of the rotaxane, ammonium salts 34a/b and the BINOL-based macrocycle (R)-12 were interlocked via tributylphosphine-catalyzed acylative end

Structure–property relationships and third-order nonlinearities in diketopyrrolopyrrole based D–π–A–π–D molecules

• Jan Podlesný,
• Lenka Dokládalová,
• Oldřich Pytela,
• Adam Urbanec,
• Milan Klikar,
• Numan Almonasy,
• Tomáš Mikysek,
• Jaroslav Jedryka,
• Iwan V. Kityk and
• Filip Bureš

Beilstein J. Org. Chem. 2017, 13, 2374–2384, doi:10.3762/bjoc.13.235

• °C, respectively. The 2,5-thienylene linker decreased the melting point approximately by 40 °C (e.g., 2a/4a with Tm = 244/200 °C). End-capping the DPP derivative with a ferrocene donor brings improved thermal stability (e.g., compound 5b with the second highest Tm and Td values within the series b

Versatile synthesis of end-reactive polyrotaxanes applicable to fabrication of supramolecular biomaterials

• Atsushi Tamura,
• Asato Tonegawa,
• Yoshinori Arisaka and
• Nobuhiko Yui

Beilstein J. Org. Chem. 2016, 12, 2883–2892, doi:10.3762/bjoc.12.287

• acids To investigate whether PRXs could be obtained via 4-substituted benzoic acids, the end capping reaction of commonly utilized pseudopolyrotaxanes comprising bis(aminopropyl) PEG (PEG-NH2) (1) and α-CD was performed using 4-azidobenzoic acid as a model compound (Scheme 1A). The synthesis of PRXs was

• % (calculated based on the molecular equivalents of the PEG axle). Many mechanisms can reduce the yield of PRXs including dethreading of CDs from the axle polymer in the process of the end capping reaction, the limited reaction efficiency of the stopper molecules in a heterogeneous system, and the loss of PRXs

• /lysosomes and nuclei are stained with LysoTracker Red DND-99 and Hoechst 33342, respectively. Scheme for the end-capping of the PEG-NH2 (1)/α-CD pseudopolyrotaxane with 4-(azidomethyl)benzoic acid (2a) (Reaction 1). Synthesis of end-reactive PRXs (4a–c) by the end-capping of the PEG-Ph-NH2 (3)/α-CD

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

• Stefan Naumann,
• Johannes Klein,
• Dongren Wang and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 2261–2266, doi:10.3762/bjoc.11.246

• end-capping with TMS-Cl. Discussed mechanisms proposed to operate in NHC-mediated polymerization of D4 in presence/absence of BnOH. Polymerization of D4 in bulk using different protected NHCs (80 °C, 16 h). Supporting Information Supporting Information File 512: Details on the synthesis of NHC-CO2

Synthesis of a resin monomer-soluble polyrotaxane crosslinker containing cleavable end groups

• Ji-Hun Seo,
• Shino Nakagawa,
• Koichiro Hirata and
• Nobuhiko Yui

Beilstein J. Org. Chem. 2014, 10, 2623–2629, doi:10.3762/bjoc.10.274

• , e.g., α-cyclodextrin (α-CD), threaded on a linear guest molecule, e.g., poly(ethylene glycol) (PEG) [1]. The threaded α-CD molecules are known to be reversibly disassembled when a cleavable end-capping group was introduced in the PEGs, and the cleavable reaction was triggered by proper signals [2][3

• ][4]. For example, if cleavable end-capping groups such as disulfide groups are introduced at both ends of PRX, the threaded α-CD molecules could be completely released by disassembling the PRX structure when a preferable stimulation such as dithiothreitol (DTT) is applied to the cleavable end-capping

• with minimal chemical reaction, methacrylate-functionalized PRX with degradable end-capping groups is anticipated to be a useful molecular platform for the development of degradable crosslinking agents. In this study, resin monomer-soluble, methacrylate-functionalized PRX with degradable end-capping

Synthesis of graft polyrotaxane by simultaneous capping of backbone and grafting from rings of pseudo-polyrotaxane

• Kazuaki Kato,
• Katsunari Inoue,
• Masabumi Kudo and
• Kohzo Ito

Beilstein J. Org. Chem. 2014, 10, 2573–2579, doi:10.3762/bjoc.10.269

• reaction yielded graft polyrotaxanes in a good yield, demonstrating a significant simplification of the synthesis of graft polyrotaxanes. Keywords: branch structure; cyclodextrin; end capping; graft polyrotaxane; polyrotaxane; Introduction Polyrotaxanes, interlocked molecules composed of polymer chains

• inclusion complex with CDs, 3) end capping, 4) chemical modification of CDs, and 5) grafting. The first three steps constitute the synthesis of polyrotaxane. The fourth process is necessary to dissociate the columnar crystal of CDs formed by hydrogen bonds and to disperse the CDs within the backbone

• force for complexation, are not formed [3][15][16]. The end-capping process should be carried out before chemical modification; otherwise the modification will induce the dissociation of the inclusion complex. Therefore, although the crystal formation (driven by the hydrogen bonds of the CDs) is

Loose-fit polypseudorotaxanes constructed from γ-CDs and PHEMA-PPG-PEG-PPG-PHEMA

• Tao Kong,
• Lin Ye,
• Ai-ying Zhang and
• Zeng-guo Feng

Beilstein J. Org. Chem. 2014, 10, 2461–2469, doi:10.3762/bjoc.10.257

• impact of end-capping groups on the self-assembly direction of γ-CDs with an incoming polymer chain, a PPO-PEO-PPO, triblock copolymer was studied. The copolymer had an average degree of polymerization (DP) of five PPO flanking blocks instead of pure PEG in order to enlarge the volume of the end-capping

• the conformational differences in the double-chain and single-chain stranded PPRs. This implies that PEG tends to be bent in order to quickly pass through the inner cavity of γ-CDs when the 2-bromoisobutyryl initiating groups are attached to two ends. However, if these end-capping groups were replaced

• end-capping reaction with a fourfold molar excess of 2-bromoisobutyryl bromide in CH2Cl2. PPO-PEO-PPO (9.16 g, 2 mmol), DMAP (488 mg, 4 mmol) and TEA (404 mg, 4 mmol) were dissolved in 20 mL CH2Cl2 in a 100 mL three-neck round-bottom flask. Thereafter, another 20 mL of CH2Cl2 containing 2

The effect of permodified cyclodextrins encapsulation on the photophysical properties of a polyfluorene with randomly distributed electron-donor and rotaxane electron-acceptor units

• Aurica Farcas,
• Ana-Maria Resmerita,
• Pierre-Henri Aubert,
• Flavian Farcas,
• Iuliana Stoica and
• Anton Airinei

Beilstein J. Org. Chem. 2014, 10, 2145–2156, doi:10.3762/bjoc.10.222

• of approaches were examined, e.g., copolymerization [7][8][9][10][11], end-capping with sterically hindered groups [12], introduction of donor (D) and acceptor (A) moieties, to form statistically [13][14] or alternating D–A units in the main chain [15][16][17][18]. The coupling of D–A units has been

End-labeled amino terminated monotelechelic glycopolymers generated by ROMP and Cu(I)-catalyzed azide–alkyne cycloaddition

• Ronald Okoth and
• Amit Basu

Beilstein J. Org. Chem. 2013, 9, 608–612, doi:10.3762/bjoc.9.66

• used as probes of biologically relevant recognition events and to functionalize surfaces [10]. Monotelechelic polymers have been obtained by the use of prefunctionalized initiators, direct end-capping with functionalized capping agents (terminating agents), and through the use of sacrificial monomers

• [11]. Chain termination is commonly carried out by using ethyl vinyl ether or cis-butene derivatives, although incomplete end-capping has been reported as a limitation with the former [12]. Notable examples include an enol ether derivative that introduces a β-trimethylsilylethoxy protected carboxylic

• required an even longer time for complete end-capping [14][15]. Treatment of longer or shorter polymers with 3 for 20 minutes was found to efficiently cap these polymers as well (see Supporting Information File 1). Because of the labile nature of the NHS-ester substituents in polymer 6, the stable p

Synthesis and characterization of low-molecular-weight π-conjugated polymers covered by persilylated β-cyclodextrin

• Aurica Farcas,
• Ana-Maria Resmerita,
• Andreea Stefanache,
• Mihaela Balan and
• Valeria Harabagiu

Beilstein J. Org. Chem. 2012, 8, 1505–1514, doi:10.3762/bjoc.8.170

• 1:1 5,5'-dibromo-2,2'-bithiophene inclusion complex in PS-βCD (BTc) and 9,9-dioctylfluorene-2,7-bis(trimethylene borate) (DOF) as a bulky molecule followed by a small excess of DOF at the end of polymerization and, finally, 3-bromothiophene (3T) as a monofunctional end-capping reagent, as

• illustrated in Scheme 1. In order to analyse the influence of end-capping reagents on the photophysical properties we changed the termination of the growing chains to 3T instead of bromobenzene, as in previously reported results [12]. A noncomplexed PDOF-BT copolymer was also synthesized by polycondensation

• the influence on the surface morphological properties induced by using 3T as an end-capping reagent instead of bromobenzene [12], AFM experiments were also performed. The 2D AFM images of the top surface of both copolymer films, within the same scan areas of 2 × 2 μm2 are shown in Figure 7a and Figure

Sexithiophenes as efficient luminescence quenchers of quantum dots

• Christopher R. Mason,
• Yang Li,
• Paul O’Brien,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2011, 7, 1722–1731, doi:10.3762/bjoc.7.202

• Sexithiophenes 1a and 1b, in which a 4-(dimethylamino)phenyl unit is incorporated as an end-capping group, were synthesised and characterised by cyclic voltammetry, absorption spectroscopy and UV–vis spectroelectrochemistry. Additionally, their ability to function as effective luminescence quenchers for quantum

• study due to their enhanced stability, and this can lead to improved performance in devices through enhanced intermolecular ordering [11]. Tailoring of the properties of oligothiophenes can be achieved by the appropriate choice of the end-capping functionality, for example, the incorporation of

• [14]. In this article, the role of dimethylamino end-capping groups in coordinating to nanocrystalline particles is reported. Recently, there has been significant interest in small, nanocrystalline particles, or quantum dots, from both a fundamental point of view, and also with regards to their

Syntheses and properties of thienyl-substituted dithienophenazines

• Annemarie Meyer,
• Eva Sigmund,
• Friedhelm Luppertz,
• Gregor Schnakenburg,
• Immanuel Gadaczek,
• Thomas Bredow,
• Stefan-S. Jester and
• Sigurd Höger

Beilstein J. Org. Chem. 2010, 6, 1180–1187, doi:10.3762/bjoc.6.135

• . Nevertheless we assume they are oriented along the main crystallographic direction of the HOPG substrate. Ordered adlayers were observed only for 12b, but not for 12a. Moreover, additional terminal alkyl chains terminating the end-capping thiophene substituents of 14, 15 and 18 appear to hinder the formation

Novel multi-responsive P2VP-block-PNIPAAm block copolymers via nitroxide-mediated radical polymerization

• Cathrin Corten,
• Katja Kretschmer and
• Dirk Kuckling

Beilstein J. Org. Chem. 2010, 6, 756–765, doi:10.3762/bjoc.6.89

• reactions, e.g., elimination of the end capping nitroxide group by β-elimination, can occur terminating chain growth. Hence, an increased molecular weight distribution was observed. At 130 °C the reaction was very fast leading to a strong increase in conversion. After 30 min 40% of polymer was obtained