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

• -0083 Tokyo, Japan 10.3762/bjoc.20.252 Abstract Owing to their dynamic natures, rotaxane-based polymers are attractive motifs for developing stimuli-responsive materials. However, the accurate control of the rotaxane structure, which can be achieved via multistep synthesis, is key to utilizing the

• material. Concurrently, implementing a scale-up synthesis procedure to exploit the application potential of rotaxane-based polymers induces structural ambiguities, thereby presenting a significant trade-off between realizing inexpensive production and defined structures. To overcome this rotaxane-synthesis

• challenge, cyclodextrin (CD) can be employed as a promising alternative owing to its low production cost. Thus, this study presents an overview of the precise synthesis of CD-based rotaxane and its application to polymers to simultaneously ensure inexpensive production and realize defined structures

Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• addition of B(C6H5)3, which may be due to the enhancement of the dienophilic nature of the cyano group due to coordination with borane. Rotaxane synthesis Push–pull chromophores with nonplanar configurations have been reported as effective stoppering motifs for rotaxane synthesis. A rational approach

• toward rotaxane synthesis involves affixing stoppers at both termini substituents and threading a molecular thread through a macrocycle. In this threading–stoppering strategy, a mild yet high-yield reaction is required for the stoppering process. The [2 + 2] CA–RE reaction, which yields push–pull

• chromophores, is the preferred method for stoppering. Accordingly, Li et al. synthesized a rotaxane 44 terminated using push–pull chromophores by incorporating concise peptide and DCNQ moieties and employing the threading–stoppering method (Scheme 16). In 44, the rod moiety and macrocycle feature short peptide

Active-metal template clipping synthesis of novel [2]rotaxanes

• Cătălin C. Anghel,
• Teodor A. Cucuiet,
• Niculina D. Hădade and
• Ion Grosu

Beilstein J. Org. Chem. 2023, 19, 1776–1784, doi:10.3762/bjoc.19.130

• the reaction used to complete rotaxane synthesis, hence the name “active template”. This strategy was first applied by Saito and co-workers [35], using a Cu(I) template to catalyze a Glaser coupling reaction. The method has been extended for other reactions, for example Ni-catalyzed homocoupling of

• primary alkyl bromides [36] and cooper(I)-catalyzed alkyne–azide cycloaddition (CuAAC) click chemistry [37]. In all these cases a templated metal ion–macrocycle complex is used to catalyze the rotaxane formation by connecting two components of the dumbbell-shaped molecule (Figure 1a). In this context, we

• obtained by CuAAC in the presence of CuCl(SIMes)(4,7-diclorophenantroline) as catalyst, with very good yields. Next, we set to study the ability of compound 6 to form copper(I) complexes able to act as active-metal templates for [2]rotaxane synthesis. Therefore, complexation studies of 6 with CuCl(SIMes

Cyclodextrins permeabilize DPPC liposome membranes: a focus on cholesterol content, cyclodextrin type, and concentration

• Ghenwa Nasr,
• Hélène Greige-Gerges,
• Sophie Fourmentin,
• Abdelhamid Elaissari and
• Nathalie Khreich

Beilstein J. Org. Chem. 2023, 19, 1570–1579, doi:10.3762/bjoc.19.115

• chains of the phospholipid and the CD molecules where many α-CD units string along the nonpolar chains of DPPC forming a rotaxane-like ring [11]. DSC studies have also proved that α-CD forms an insoluble complex with DPPC [22]. Besides, α-CD has previously demonstrated the strongest destabilizing effect

Light-responsive rotaxane-based materials: inducing motion in the solid state

• Adrian Saura-Sanmartin

Beilstein J. Org. Chem. 2023, 19, 873–880, doi:10.3762/bjoc.19.64

• Adrian Saura-Sanmartin Departamento de Química Orgánica, Facultad de Química, Universidad de Murcia, 30100 Murcia, Spain 10.3762/bjoc.19.64 Abstract Light-responsive rotaxane-based solid-state materials are ideal scaffolds in order to develop smart materials due to the properties provided by the

• scaffolds [11]. In particular, rotaxanes and pseudorotaxanes have led to a greater number of applications due to their inherent dynamics and the switching possibility through a rational design [12]. Thus, rotaxane-based materials have attracted the interest of the scientific community due to their enhanced

• , photoswitchable rotaxane-based materials have shown very interesting machine-like operation modes, highlighting the macroscopic transport of iodomethane drops along an inclined gold surface caused by light-triggered variations in the polarophobicity of interlocked fumaramide-based films [30]. Another application

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

• Prodip Howlader and
• Michael Schmittel

Beilstein J. Org. Chem. 2022, 18, 597–630, doi:10.3762/bjoc.18.62

• procedure developed by Sauvage on the basis of topological control [33] has found ample use in the preparation of rotaxane-based machines and devices [34]. A key element is a macrocyclic phenanthroline with an endotopic binding site as it precludes homoleptic complex formation. A further principle

• state of the second click reaction, leads to an astounding synthetic efficiency, although there is a major distance mismatch between the copper(I) ions in [FeCu2(104)2]4+ and two triazole units of the rotaxane. For instance, the system [FeCu2(104)2]4+ (dCu–Cu = 34 Å) afforded the formation of both 109a

• (73%) and 109b (82%) in high yield (Figure 23b) [110], although the relevant distances in the pseudo-rotaxane 110a,b (prior to the second click reaction) are 14.3 and 21.1 Å. Actually, the yield with [FeCu2(104)2]4+ was far better than with a dicopper reference catalyst, where the separation of the

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

• chemosensing or in asymmetric catalysis. The selection of suitable stereogenic elements is of great importance [26][27][28]. The most straightforward way to create a chiral rotaxane or catenane is the introduction of classical chiral elements, such molecular parts with axial chirality, point chirality, or

• . Accordingly, demetalation leads to an almost complete disappearance of the CD signals in this area (see Figure 2). Saito and coworkers demonstrated that the homochiral [2]rotaxane (R)-10 can be efficiently synthesized using an active metal template approach [44][45]. The macrocyclic phenanthroline (R)-7 was

• treated with copper iodide to obtain the phenanthroline–Cu(I) complex (R)-8. A Glaser-type coupling with the terminal alkynes 9, followed by demetalation, proceeds smoothly in 78% yield. This furnishes the desired chiral rotaxane (R)-10, consisting of a BINOL-based macrocycle and a diyne thread. The CD

Diametric calix[6]arene-based phosphine gold(I) cavitands

• Gabriele Giovanardi,
• Andrea Secchi,
• Arturo Arduini and
• Gianpiero Cera

Beilstein J. Org. Chem. 2022, 18, 190–196, doi:10.3762/bjoc.18.21

• devised a new family of triphosphine calix[6]arene gold(I) complexes (Figure 1c) [30]. These cavitands are able to form (pseudo)rotaxane species, by threading viologen-based guests, with a conformational control operated by the sulfonamido hydrogen-bonding donor domain [31][32]. Furthermore, their

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• two different weakly coordinating anions, a surprising relation between the enthalpic and entropic binding contributions of the pseudorotaxanes was discovered. These findings were applied to the synthesis of an NDI-[2]rotaxane, which retains similar spectroelectrochemical properties compared to the

• synthesis of crown ether-based rotaxanes in 1995, crown ethers played a crucial role in the development of mechanically interlocked molecules (MIMs) [22][23]. This rotaxane synthesis was facilitated by the formation of a threaded complex (pseudorotaxane) between a secondary ammonium ion and dibenzo-24-crown

• differential pulse voltammetry (DPV) and compared to those of their corresponding pseudo[2]rotaxanes. Additionally, we report the synthesis of a novel NDI-[2]rotaxane and study the impact of the mechanical bond on the optoelectronic properties of the NDI unit by CV and spectroelectrochemical measurements

Five-component, one-pot synthesis of an electroactive rotaxane comprising a bisferrocene macrocycle

• Natalie Lagesse,
• Luca Pisciottani,
• Maxime Douarre,
• Pascale Godard,
• Brice Kauffmann,
• Vicente Martí-Centelles and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2020, 16, 1564–1571, doi:10.3762/bjoc.16.128

• ]rotaxane is a homologue of the versatile benchmark tetraamide variant developed by Leigh and co-workers. The relative templating effect of different hydrogen-bonding motifs in rotaxane and pseudorotaxane generation is compared, with yields varying from 0 to 41%. The electrochemical properties and single

• crystal X-ray structure of a doubly ferrocene-decorated [2]rotaxane are further reported. Keywords: ferrocene; macrocycle; rotaxane; single crystal X-ray structure; template; Introduction The development of interlocked molecules with tailored properties allowed the preparation of molecular machines able

• to perform several functions as artificial molecular switches [1]. The template-directed synthesis of such sophisticated catenane and rotaxane molecular architectures allowed the expansion of chemical diversity and properties. Among these architectures, electroactive rotaxanes have been described to

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• receptors for molecular recognition of anionic species, pH sensors, mechanically interlocked molecules, molecular machines, and molecular reactors. Keywords: anion recognition; catenane; chalcogen bonding; click reaction; molecular reactor; hydrogen bonding; pH sensor; rotaxane; supramolecular; 1,2,3

• analogous experiment was done with benzoate, due to the precipitation of an insoluble ferrocenium complex [40]. 2.4. Mechanically interlocked catenanes containing 1,2,3-triazolium macrocycles Mechanically interlocked molecules like rotaxane and catenane have attracted much attention in the field of

• nanoscale molecular machines and switches [41] and their importance has been recognized by the 2016 Nobel prize. Anion recognition can be used as an impediment for rotary movement in the rotaxane structure. Besides, catenanes possessing a mechanically interlocked ring, have attracted considerable attention

Multiple threading of a triple-calix[6]arene host

• Veronica Iuliano,
• Roberta Ciao,
• Emanuele Vignola,
• Carmen Talotta,
• Patrizia Iannece,
• Margherita De Rosa,
• Annunziata Soriente,
• Carmine Gaeta and
• Placido Neri

Beilstein J. Org. Chem. 2019, 15, 2092–2104, doi:10.3762/bjoc.15.207

• dialkylammonium axles. The formation of pseudo[2]rotaxane, pseudo[3]rotaxane, and pseudo[4]rotaxane by threading one, two, and three, respectively, calix-wheels of 6 has been studied by 1D and 2D NMR, DOSY, and ESI-FT-ICR MS/MS experiments. The use of a directional alkylbenzylammonium axle led to the

• stereoselective formation of endo-alkyl pseudo[n]rotaxane stereoisomers. Keywords: calixarene; multiple-threading; pseudo[n]rotaxane; stereoisomers; Introduction The self-assembly [1] of smaller components to larger aggregates represents one of the most spectacular phenomena in supramolecular chemistry [2][3][4

• -catenanes [25]. On the basis of these results, we were also able to assemble high-order architectures by double-threading of bis-calix[6]arene hosts with ammonium axles [27]. In particular, handcuff (pseudo)rotaxane architectures (e.g., 32+ in Figure 2) [27] were obtained by double-threading of bis-calix[6

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer

• Jason Yin Hei Man and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2019, 15, 1829–1837, doi:10.3762/bjoc.15.177

• respect to the orthogonal plane of the axle, only one stereoisomer of the [6]rotaxane was obtained. Keywords: cucurbit[6]uril; cyclodextrin; macrocycles; mechanostereoisomer; rotaxane; Introduction Cyclodextrins (CDs) are macrocycles composed of glucoses linked via α-1,4-glycosidic bonds. CDs of six (α

• building blocks for the construction of complex molecular topology such as rotaxanes and catenanes [12][13][14][15]. For example, by making use of hydrophobic-driven binding of simple alkyl groups in water to α-CD, Ogino has reported one first example of a rotaxane assembly featuring an alkyldiamine

• threaded through an α-CD [16]. The corresponding rotaxane with a β-CD was obtained in lower yield, probably due to a weaker binding of the alkyl group to β-CD as a result of a size mismatch [17]. For β-CD with a larger cavity, interlocked molecules derived from aromatic units such as biphenyl, stilbene

A heteroditopic macrocycle as organocatalytic nanoreactor for pyrroloacridinone synthesis in water

• Piyali Sarkar,
• Sayan Sarkar and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2019, 15, 1505–1514, doi:10.3762/bjoc.15.152

• supramolecular assemblies like molecular rotors (pseudorotaxane, rotaxane, catenane), molecular switches, molecular shuttles, etc. [32][33][34][35][36][37][38][39][40][41][42][43]. Furthermore, macrocycles have been applied in the area of ion–ion pair recognition and heterometallic complex formation [44][45][46

Molecular recognition using tetralactam macrocycles with parallel aromatic sidewalls

• Dong-Hao Li and
• Bradley D. Smith

Beilstein J. Org. Chem. 2019, 15, 1086–1095, doi:10.3762/bjoc.15.105

• effect; macrocycles; rotaxane; supramolecular; Review 1. Introduction A large fraction of host–guest chemistry research uses macrocyclic compounds as the host molecules [1][2]. There are several reasons for this circumstance. Macrocycles are often relatively easy to synthesize and they have inherently

• following sections, we divide the guest structures into two large categories; those that associate with a tetralactam host in a reversible solution-state equilibrium and those that are permanently trapped inside a tetralactam macrocycle as an interlocked rotaxane or catenane. It is important to emphasize

• ] macrocycle and a larger amount of the corresponding [2]catenane. Subsequent work found that conducting the reaction in the presence of a dumbbell-shaped template was a general way to make a wide range of [2]rotaxanes [28]. Listed in Scheme 2 are the yields of [2]rotaxane produced using various biscarbonyl

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• milling frequency of 22.5 Hz (Figure 6b) [59]. The stoppers were constructed in situ with 1,8-diaminonaphthalene through the formation of an imine via dehydration of the amine and aldehyde. Interestingly, a synthesis of the smallest [2]rotaxane also has been demonstrated by the same group [60]. They

• applied a Diels–Alder reaction of 1,2,4,5-tetrazine with a terminal alkyne unit in a 21-crown-7-based [2]pseudorotaxane 14. The [2]rotaxane 15 was produced in 81% yield having pyridazine groups as stoppers (Figure 7). Very recently, Nierengarten and co-workers reported a solvent-free mechanochemical

• under milling conditions (30 Hz for 1–2 h). When for example, N-methyl-1,1,-diphenylmethanamine was used as one of the stoppers, diamido [2]rotaxane 17 was obtained with high yield (ca. 87%) [61] (Figure 8). In 2017, Wang and co-workers reported an efficient method for the synthesis of neutral donor

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• is transferred into a controlled molecular motion in MIMs, the TTF-based pseudo[1]rotaxane 12 recently reported by us is shown in Figure 9 [70]. In a pseudo[1]rotaxane, the axle molecule is covalently bound to the wheel component. The self-inclusion structure mimics the conformation of a molecular

• machines to the molecular level may be limited and may even be misleading. In contrast to macroscopic piston engines, the translation of the wheel in a rotaxane occurs through Brownian motion and the switching processes cause merely a shift of the equilibrium between the two positional isomers of the

• rotaxane. Thus, a transfer of work on the molecular level that is created by wheel translation into a macroscopic force is quite difficult (but not impossible) to achieve. Closely after the discovery of the donor–acceptor complex 13, Stoddart and co-workers reported the synthesis of the first TTF-based

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

• Carmine Gaeta,
• Carmen Talotta and
• Placido Neri

Beilstein J. Org. Chem. 2018, 14, 2112–2124, doi:10.3762/bjoc.14.186

• their ability to adopt novel forms of isomerism. More in detail, (pseudo)rotaxane or catenane architectures can show novel stereoisomeric forms as a result of the "social" [14] relationship between their components. Recently, Goldup’s group assembled a mechanically planar chiral rotaxane [15][16] (I and

• -flat wheels, such as calixarenes or cyclodextrins, are threaded along an axle to give a pseudo[3]rotaxane architecture V–VII (Figure 2), where three sequential stereoisomers can arise. We showed that this stereoisomerism can be effectively controlled when two calix[6]arene wheels are threaded along a

• bis(benzylalkylammonium) axle [19], where the stereoselective formation of the pseudo[3]rotaxane with endo-alkyl orientation VIII was observed [19]. Calixarene macrocycles [22] have found numerous applications in several areas of supramolecular chemistry, such as (bio)molecular recognition [23] and

A switchable [2]rotaxane with two active alkenyl groups

• Xiu-Li Zheng,
• Rong-Rong Tao,
• Rui-Rui Gu,
• Wen-Zhi Wang and
• Da-Hui Qu

Beilstein J. Org. Chem. 2018, 14, 2074–2081, doi:10.3762/bjoc.14.181

• Abstract A novel functional [2]rotaxane containing two alkenyl bonds was designed, synthesized and characterized by 1H, 13C NMR spectroscopy and HRESI mass spectrometry. The introduction of alkenyl bonds endowed the [2]rotaxane a fascinating ability to react with versatile functional groups such as alkenyl

• and thiol functional groups. The reversible shuttling movement of the macrocycle between two different recognition sites on the molecular thread can be driven by external acid and base. This kind of rotaxane bearing functional groups provides a powerful platform for preparing stimuli-responsive

• polymers. Keywords: alkenyl bond; functional crown ether; stimuli-responsiveness; switchable rotaxane; Introduction Along with the development of supramolecular chemistry, much attention has been paid to the design and synthesis of novel and complicated mechanical interlocked molecules (MIMs) [1][2][3][4

An amphiphilic pseudo[1]catenane: neutral guest-induced clouding point change

• Tomoki Ogoshi,
• Tomohiro Akutsu and
• Tada-aki Yamagishi

Beilstein J. Org. Chem. 2018, 14, 1937–1943, doi:10.3762/bjoc.14.167

• best of our knowledge, the use of a dynamic supramolecular structural change of 3 to induce an LCST change is the first example in this area. Thus, this work may open the way for the design of a new generation of molecular assembly systems using supramolecular structures such as rotaxane, catenanes

A pyridinium/anilinium [2]catenane that operates as an acid–base driven optical switch

• Sarah J. Vella and
• Stephen J. Loeb

Beilstein J. Org. Chem. 2018, 14, 1908–1916, doi:10.3762/bjoc.14.165

• molecule; molecular switch; Introduction [2]Rotaxane molecular shuttles [1][2][3][4][5] are the dynamic building blocks of a wide variety of molecular switches [6][7][8][9] and a number of sophisticated molecular machines that operate away from equilibrium [10][11][12][13][14][15]. We have previously

• reported [2]rotaxane molecular switches containing a single dibenzo[24]crown ether DB24C8 wheel and two different recognition sites; benzylanilinium and 1,2-bis(pyridinium)ethane [16]. These shuttles operate as bistable switches driven by acid/base chemistry and can be optically sensed by either a change

• ]rotaxane molecular shuttles outlined in Figure 1. This should be possible because of the structural similarities (size and shape) between the bis(pyridinium)ethane and benzylanilinium recognition sites. Each has a two-atom chain in a low energy, anti-conformation linking aromatic rings and the distance

Efficient catenane synthesis by cucurbit[6]uril-mediated azide–alkyne cycloaddition

• Antony Wing Hung Ng,
• Chi-Chung Yee,
• Kai Wang and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2018, 14, 1846–1853, doi:10.3762/bjoc.14.158

• mediate their cycloaddition inside the CB[6] cavity [21][22]. Yet, these strategies have been largely limited to the synthesis of rotaxane-based interlocked systems [23], probably because of the additional challenges associated with the macrocyclization in catenane synthesis. Previously, we have reported

• . Further extending the reaction time to 3, 5 or 8 hours resulted in similar chromatograms with no significant improvement of the yield of Cat-1. A similar observation has been reported in a CBAAC-mediated rotaxane synthesis and additional templates have been used to positively cooperate with the CB[6

• decided to first assemble a pseudo[3]rotaxane CB[6] complex with either the azide or alkyne building block, before introducing the other building block to the reaction mixture. By heating a solution of DN-N3 in the presence of two equivalents of CB[6] in 0.2 M aq HCl for 2 hours, a clear solution was

Synthesis of diamido-bridged bis-pillar[5]arenes and tris-pillar[5]arenes for construction of unique [1]rotaxanes and bis-[1]rotaxanes

• Ying Han,
• Li-Ming Xu,
• Cui-Yun Nie,
• Shuo Jiang,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2018, 14, 1660–1667, doi:10.3762/bjoc.14.142

• ]arene di(oxybutoxy)benzoic acid with monoamido-functionalized pillar[5]arenes resulted in the diamido-bridged tris-pillar[5]arenes, which successfully form the unique bis-[1]rotaxanes bearing longer than diaminopropylene diamido bridges. Keywords: bis-[1]rotaxane; mechanically interlocked molecule

• ; pillar[5]arene; [1]rotaxane; self-assembly; Introduction The construction and dynamic motion of the mechanically interlocked molecules (MIMs) have attracted significant research interests due to their intrinsic self-assembled nature and potential applications in various aspects [1][2][3][4]. Pseudo[1

• ]rotaxane and [1]rotaxane are one of particular supramolecular assembly system and are considered as an important building block in the construction of diverse MIMs [5][6][7][8][9][10]. [1]Rotaxane has a macrocyclic wheel component connected with a self-locked chain axle, and a bulky stopper at the terminal

Structural diversity in the host–guest complexes of the antifolate pemetrexed with native cyclodextrins: gas phase, solution and solid state studies

• Magdalena Ceborska,
• Magdalena Zimnicka,
• Aneta Aniela Kowalska,
• Kajetan Dąbrowa and
• Barbara Repeć

Beilstein J. Org. Chem. 2017, 13, 2252–2263, doi:10.3762/bjoc.13.222

• available in Supporting Information File 1, Figure S2a–c). The exclusive fragmentation pathway of studied complexes into two components suggests that PTX is quite loosely connected with the CD comparing to a typical rotaxane complex for which the main fragmentations, occurring at substantial high collision

• carboxylic functionalities is dangling outside the host molecule forming a rotaxane-like inclusion compound (Figure 3b). For more detailed information on the behavior of acidic protons of the guest molecule 1D measurements in DMSO-d6 were performed (see Supporting Information File 1, Figures S15, S16, S18

• )2− = 780.1; M(γ-CD/PTX − 2H)2− = 861.1]. We found that cyclodextrin with the smallest cavity, α-CD, forms exclusion type complex (as seen from 1D NMR in D2O and DMSO-d6 and 2D ROESY NMR experiments). β-CD and γ-CD form rotaxane-like structures where CD host is threaded over the PTX guest, as it is