Influence of cyclodextrin on the solubility and the polymerization of (meth)acrylated Triton^® X-100

• Melanie Kemnitz and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 2176–2183, doi:10.3762/bjoc.8.245

• , and fluorescence studies, were used to determine the equilibrium constant [4][5][6][7][8][9][10][11][12]. The results also differ in the stoichiometry of the formed complexes [4][7][9][10][11]. Host/guest ratios of 1:1 [4][7], 2:1 [9] and the coexistence of 1:1 and 2:1 [10][11] complexes of β-CD and

• RAMEB-CD The reaction of Triton® X-100 (1) with methacryloyl chloride and acryloyl chloride gave the corresponding methacrylic ester 2 [2] and acrylic ester 3, respectively. Both monomers 2 and 3 were insoluble in water, but readily formed water-soluble host–guest complexes with RAMEB-CD (4 to 7) within

• possible after the complexation of (meth)acrylated Triton® X-100 (2 and 3) with RAMEB-CD (Scheme 3). The polymers 10 and 12 complexed with 1 equiv of RAMEB-CD precipitated during the polymerization, whereas the double complexed polymers 11 and 13 did not precipitate, as a consequence of the stronger host

New enzymatically polymerized copolymers from 4-tert-butylphenol and 4-ferrocenylphenol and their modification and inclusion complexes with β-cyclodextrin

• Adam Mondrzyk,
• Beate Mondrzik,
• Sabrina Gingter and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 2118–2123, doi:10.3762/bjoc.8.238

• investigated until now. Hence, in the present paper we report the HRP-catalyzed synthesis of novel copolymers from 2 and 3. Click reaction of the propargyl modified polyphenol 5 with mono-(6-azido-6-deoxy)-β-cyclodextrin (6) was also investigated. Based on former studies, host–guest structures were created [24

• subsequent click chemistry with N3-β-CD. The covalently bound cyclodextrin moiety and the covalently bound Fc or tert-butyl group form host/guest complexes as proven by DLS measurement. The cyclic voltammetry data shows that the central iron atom of the Fc moiety is present in the copolymer and can be

Cyclodextrin-induced host–guest effects of classically prepared poly(NIPAM) bearing azo-dye end groups

• Gero Maatz,
• Arkadius Maciollek and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 1929–1935, doi:10.3762/bjoc.8.224

• observed. Additionally, this azo-dye-end-group-labeled polymer was complexed with hyperbranched polyglycerol (HPG) decorated with β-CD to generate hedgehog-like superstructures. Keywords: azo-dye; cyclodextrins; end-group functionalization; host–guest interaction; supramolecular aggregation; Introduction

• functionalization by condensation with an azo dye. We also investigated the host–guest interaction of the azo-dye-labeled end group with randomly methylated β-cyclodextrin (RAMEB-CD), and with HPG bearing β-CD on top. Thus, the focus of the present study was directed towards the preparation and superstructure

• predominant form in the red acidic aqueous solution [17][18][19]. Due to our general interest in the use of CD in polymer chemistry [3], the interaction of polymer 6 with RAMEB-CD was investigated. The proposed formation of the host–guest structure between the azo-dye end group and the RAMEB-CD cavity was

Influence of intramolecular hydrogen bonds on the binding potential of methylated β-cyclodextrin derivatives

• Gerhard Wenz

Beilstein J. Org. Chem. 2012, 8, 1890–1895, doi:10.3762/bjoc.8.218

• ]. The host–guest complexes, so-called cyclodextrin inclusion compounds, find many applications such as solubilization of pharmaceutical drugs, dispersion of cosmetics, catalysis, or chromatographic separation of enantiomers [2][7][8]. Application of β-CD 1 is hampered by its low solubility of 18.8 g L−1

• host–guest complexes. Thermodynamic data obtained for the guests 4-tert-butylbenzoate and adamantane-1-carboxylate are listed in Table 1 and Table 2, respectively. Remarkable differences in the binding constants for 4-tert-butylbenzoate were found for the β-CD derivatives 2–7. The completely methylated

Molecular solubilization of fullerene C₆₀ in water by γ-cyclodextrin thioethers

• Hai Ming Wang and
• Gerhard Wenz

Beilstein J. Org. Chem. 2012, 8, 1644–1651, doi:10.3762/bjoc.8.188

• hampered by the toxicities of the employed organic solvents or surfactants. The most successful strategy to carry the extremely hydrophobic C60 molecule into water is the use of appropriate water-soluble carriers that can form host–guest complexes, such as calixarenes [19][20] and cyclodextrins (CDs) [21

Mannose-decorated cyclodextrin vesicles: The interplay of multivalency and surface density in lectin–carbohydrate recognition

• Ulrike Kauscher and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2012, 8, 1543–1551, doi:10.3762/bjoc.8.175

• be modified by host–guest interactions with functional guest molecules. In this article, we investigate the multivalent interaction of the lectin concanavalin A (ConA) with cyclodextrin vesicles decorated with mannose–adamantane conjugates with one, two or three adamantane units as well as one or two

• , the stoichiometry appears to be less than 1:1, the binding constant is somewhat lower, and the thermodynamic parameters are different (notably, ΔS is negative). This observation can be explained by steric hindrance in the trivalent host–guest complex: apparently, three β-cyclodextrins are too large to

• , the guest molecules are expected to form inclusion complexes at the surface of vesicles of amphiphilic cyclodextrin 5. More importantly, guest molecules 2–4 are expected to form multivalent host–guest complexes with a much higher effective binding constant than the monovalent binding constant reported

Influence of cyclodextrin on the solubility of a classically prepared 2-vinylcyclopropane macromonomer in aqueous solution

• Helmut Ritter,
• Jia Cheng and
• Monir Tabatabai

Beilstein J. Org. Chem. 2012, 8, 1528–1535, doi:10.3762/bjoc.8.173

• different types of molecules with fitting size through van-der-Waals interactions. By formation of such host–guest complex properties, the dissolution behavior of the guest molecules can be changed. Based on this fact numerous applications of β-CDs are reported [17][18][19][20][21][22][23][24][25

• vinylcyclopropane unit, this water insoluble macromonomer 5 is able to form a host–guest complex with Me2-β-CD, which is located at the polymerizable vinyl end group. This supramolecular complex 7 becomes completely water-soluble, so that a typical LCST effect could be observed. Since the bulky macromonomer 5

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• (Figure 6) [94]. The photochromic properties of azobenzenes also find applications in “host–guest” recognition [95][96]. For example, the bis-azo compound 3 behaves as an excellent receptor of guanidinium ions by hydrogen-bonding interactions. The recognition is very effective when the azobenzene adopts

Synthesis and anion recognition properties of shape-persistent binaphthyl-containing chiral macrocyclic amides

• Marco Caricato,
• Nerea Jordana Leza,
• Claudia Gargiulli,
• Giuseppe Gattuso,
• Daniele Dondi and
• Dario Pasini

Beilstein J. Org. Chem. 2012, 8, 967–976, doi:10.3762/bjoc.8.109

• loss of the initial symmetry. From the preliminary data in our hands, it is clear that there is a slow-exchanging equilibrium on the NMR time scale: the bulkier acetoxy group presumably inhibits a binding mechanism based on a fast host–guest exchange. A slow encapsulation mechanism, with multiple modes

Low-generation dendrimers with a calixarene core and based on a chiral C₂-symmetric pyrrolidine as iminosugar mimics

• Marco Marradi,
• Stefano Cicchi,
• Francesco Sansone,
• Alessandro Casnati and
• Andrea Goti

Beilstein J. Org. Chem. 2012, 8, 951–957, doi:10.3762/bjoc.8.107

• , such as calixarenes, with the advantages of a dendrimeric presentation of iminosugar analogues. Calixarenes [11] have been widely employed in host–guest chemistry, first as ligands for small ions and neutral molecules [12][13] and, more recently, for biologically relevant molecules and macromolecules

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system

• Caterina Fraschetti,
• Matthias C. Letzel,
• Antonello Filippi,
• Maurizio Speranza and
• Jochen Mattay

Beilstein J. Org. Chem. 2012, 8, 539–550, doi:10.3762/bjoc.8.62

• simplified models under conditions, such as the gas phase, in which the noncovalent interactions in the guest–host complex are not perturbed by effects owing to the medium. As biological function and morphology are strongly correlated, knowledge of the supramolecular host–guest structures is expected to shed

• of tunable macrocycles largely studied in the context of host–guest chemistry, as cavitands [5] and capsules [6]. The great ability of resorcin[4]arenes to trap several classes of compounds makes them very suitable for the subtle study of the chemicophysical properties of their host–guest systems

Synthesis of mesomeric betaine compounds with imidazolium-enolate structure

• Nina Gonsior,
• Fabian Mohr and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 390–397, doi:10.3762/bjoc.8.42

• relatively low values of the formation constant calculated for both a 1:1 complex (K1 = 1.6 × 102 M−1) and a 1:2 complex (K2 = 0.2 × 102 M−1) indicates only weak host/guest interactions and therefore only a slight increase of solubility in water was achieved. However, the value of K1 is in good agreement

Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• species. Applications in fields as diverse as ion selective electrode modifiers, fluorescence sensors, fullerene separations and biomimetic chemistry are described. Keywords: calixarenes; host–guest chemistry; macrocycles; oxacalixarenes; Introduction Calixarenes, macrocycles which are widely used in

• -substituted phenol; however, in host–guest chemistry an asymmetric macrocycle can provide a site for enantioselective molecular recognition. In the case of p-tert-butylcalix[n]arenes the tert-butyl substituent can be removed, as mentioned previously, through a retro-Friedel–Crafts acylation, and replaced by

• absorption features at 425 or 430 nm in toluene. The strongest binding was observed for 3a (35.6 M−1) and the weakest for 3h (9.1 M−1). Although spectroscopic methods are widely used to determine host–guest association constants, Georghiou has argued persuasively that spectral changes in solution may be due

Efficient, highly diastereoselective MS 4 Å-promoted one-pot, three-component synthesis of 2,6-disubstituted-4-tosyloxytetrahydropyrans via Prins cyclization

• Naseem Ahmed and
• Naveen Kumar Konduru

Beilstein J. Org. Chem. 2012, 8, 177–185, doi:10.3762/bjoc.8.19

• phorboxazoles (A and B) [1], (−)-centrolobine [2], GEX1A/herboxidiene [3], bryostatins [4], and pheromones [5] (Figure 1). Tetrahydropyran derivatives are also used as materials in photographic films [6] and host–guest chemistry [7]. In particular, 2,4,6-trisubstituted tetrahydropyrans have tremendous

On the mechanism of action of gated molecular baskets: The synchronicity of the revolving motion of gates and in/out trafficking of guests

• Keith Hermann,
• Stephen Rieth,
• Hashem A. Taha,
• Bao-Yu Wang,
• Christopher M. Hadad and
• Jovica D. Badjić

Beilstein J. Org. Chem. 2012, 8, 90–99, doi:10.3762/bjoc.8.9

• the basket: Specifically, the greater the affinity of the guest for occupying the basket, the less effective the gates are in “sweeping” the guest as the gates undergo their revolving motion. Keywords: dynamic NMR; host–guest chemistry; linear free-energy relationships; molecular encapsulation

• proportional to the concentration of the host–guest complex, [basket–CH3CCl3], but inversely proportional to the concentration of CH3CCl3. At higher concentrations of CH3CCl3, however, there should be a negligible variation in the concentration of basket–CH3CCl3 and the magnetization rate coefficient k*in

Binding of group 15 and group 16 oxides by a concave host containing an isophthalamide unit

• Jens Eckelmann,
• Vittorio Saggiomo,
• Svenja Fischmann and
• Ulrich Lüning

Beilstein J. Org. Chem. 2012, 8, 11–17, doi:10.3762/bjoc.8.2

• to be obtained by curve fitting, which adds to the overall error. In our host–guest systems, saturation was not reached even when 20 equivalents of guests were used. An even larger excess of guest changed the polarity of the solvent to such an extent that all signals were affected, not only those

• involved in the binding [20]. If most guests only bind very moderately, an exact (and tedious) determination of all binding constants Kass is not interesting. It would be sufficient if a quick screening of the binding potentials of the hosts were possible and host–guest pairs with significant association

• between weak and strong binding. However, when NMR titrations of different host–guest pairs are carried out with identical concentrations, small and large association constants can be differentiated by the different curvatures of the titration graphs. In a titration curve of strong binding, the curvature

(How) does 1,3,5-triethylbenzene scaffolding work? Analyzing the abilities of 1,3,5-triethylbenzene- and 1,3,5-trimethylbenzene-based scaffolds to preorganize the binding elements of supramolecular hosts and to improve binding of targets

• Xing Wang and
• Fraser Hof

Beilstein J. Org. Chem. 2012, 8, 1–10, doi:10.3762/bjoc.8.1

• to achieve strong and specific binding to targeted guest molecules. Many important weak interactions are directional and lead to highly ordered host–guest complexes [1][2]. The preorganization of binding elements in a competent binding geometry can have enthalpic effects on binding when considering

• the energy that must be paid to adopt a (potentially unfavorable) binding conformation, and can also have effects on binding entropy when one considers the degrees of freedom in the host, guest, and solvated host–guest complex. Rigid macrocyclic hosts are often successful because of their high degree

• (Figure 2a) [8]. The field has since exploded, with the first all-organic host–guest system of this type constructed by Anslyn [9] (Figure 2b) and over 150 papers reporting on 900 such structures for binding organic and inorganic guests having been published in the last 30 years [10]. The preorganizing

Continuous proline catalysis via leaching of solid proline

• Suzanne M. Opalka,
• Ashley R. Longstreet and
• D. Tyler McQuade

Beilstein J. Org. Chem. 2011, 7, 1671–1679, doi:10.3762/bjoc.7.197

• been suggested. Initially, researchers gathered 1H NMR, UV, and fluorescence data to show that ureas enhance the solubility of proline through a host–guest interaction between the urea and proline carboxylate: A substrate-independent model [49][50]. However, it has been proposed that substrate–urea

Supramolecular chemistry II

• Christoph A. Schalley

Beilstein J. Org. Chem. 2011, 7, 1541–1542, doi:10.3762/bjoc.7.181

• devoted to quantifying host–guest interactions, aiming at a more profound understanding of the subtle entropic and enthalpic effects that govern the interactions between host and guest. A first Thematic Series devoted to supramolecular chemistry was assembled about two years ago and published by the

Chiral recognition of ephedrine: Hydrophilic polymers bearing β-cyclodextrin moieties as chiral sensitive host molecules

• Sabrina Gingter and
• Helmut Ritter

Beilstein J. Org. Chem. 2011, 7, 1516–1519, doi:10.3762/bjoc.7.177

• -containing polymer. The supramolecular structures obtained by complexation of ephedrine and cyclodextrin were verified by 2-D ROESY NMR measurements. Dynamic light scattering showed clear differences in the mean coil size. Keywords: chiral recognition; cyclodextrins; ephedrine; host–guest interaction

• -exclusion chromatography (SEC), dynamic light scattering (DLS) and turbidity measurements. To confirm the formation of the proposed host–guest structure of β-cyclodextrin and ephedrine in principle, 2-D ROESY NMR spectroscopy was performed at room temperature with β-CD in excess. Thus the correlation

• in the host–guest system, the LCST rises to 35 °C for polymer 2, which is 3 °C higher than the value for pure poly(NIPAAM). The increase of LCST takes place because the hydrophobic phenyl ring of ephedrine is incorporated into the CD cavity, and the hydrophilic OH and amino groups are located in the

Ratiometric fluorescent probe for enantioselective detection of D-cysteine in aqueous solution

• Xiao-bo Zhou,
• Wing-Hong Chan,
• Albert W. M. Lee and
• Chi-Chung Yeung

Beilstein J. Org. Chem. 2011, 7, 1508–1515, doi:10.3762/bjoc.7.176

• health [32]. On the basis of multipoint electrostatic interactions and structure complementarity of the host–guest, we have rationally designed and synthesised a bis(spiropyran) as a fluorescence turn-on probe for selective binding of GSH [33]. We have also developed the first spiropyran–metal sensing

• enantioselectivity of 3.35 conferred by the chiral trans-1,2-diaminocyclohexane moiety for recognizing D-cysteine in 1% ACN/HEPES buffered solutions (pH 7.4) (Figure 5). Apparently, owing to the structure complementarity of the host–guest, D-cysteine outperforms its enantiomer in forming a more stable complex with

PEG-embedded KBr₃: A recyclable catalyst for multicomponent coupling reaction for the efficient synthesis of functionalized piperidines

• Sanny Verma,
• Suman L. Jain and
• Bir Sain

Beilstein J. Org. Chem. 2011, 7, 1334–1341, doi:10.3762/bjoc.7.157

• accessible catalytic protocol for the synthesis of functionalized piperidines by the one-pot coupling of aldehyde, amine and β-keto ester with PEG-wrapped KBr3 as a recyclable catalyst. The PEG-embedded tribromide could easily be synthesized through the concept of host–guest complexation [34] of PEGs with

• poly(ethylene)glycol to prepare an efficient and highly stable tribromide reagent through the concept of host–guest chemistry. The prepared PEG-embedded tribromide was found to be a highly efficient catalyst for the synthesis of highly substituted piperidines in the one-pot coupling reaction of aniline

NMR studies of anion-induced conformational changes in diindolylureas and diindolylthioureas

• Damjan Makuc,
• Jennifer R. Hiscock,
• Mark E. Light,
• Philip A. Gale and
• Janez Plavec

Beilstein J. Org. Chem. 2011, 7, 1205–1214, doi:10.3762/bjoc.7.140

• along the C7–N7α bonds and the syn–syn conformer was preferred for anion–receptor complexes. The conformational changes upon anion binding are in good agreement with energetic preferences established by ab initio calculations. Keywords: anion recognition; conformation analysis; host–guest systems; NMR

Hyperbranched polyethylenimine bearing cyclodextrin moieties showing temperature and pH controlled dye release

• Indra Böhm,
• Susanne Katharina Kreth and
• Helmut Ritter

Beilstein J. Org. Chem. 2011, 7, 1130–1134, doi:10.3762/bjoc.7.130

• compounds for a drug delivery system in combination with hyperbranched cationic polyethylenimine bearing covalently attached β-CDs 3. As outlined in Scheme 1, each dye, 1 and 2, was mixed with 3 in water to form a salt 4 and a host–guest complex 5, respectively. Additionally, both dyes were mixed together

• dye 1 could not be measured since the dye is not water-soluble and cannot be enclosed by CD. Complex 6 exhibits enlarged networks with a dH of 480 nm, which verifies an inclusion of both dyes (1 and 2) through salt formation and host-guest complexation (Supporting Information File 1, Figure S4). In

• -1,4-dihydroxyanthraquinone (AQ-OH) can be dissolved by pH adjustment. In contrast, the adamantyl modified compound 1,4-di-N-adamantylaminoanthraquinone (AQ-Ada) forms a host–guest complex with the PEI attached CDs and can be released by heating. These dyes serve as model compounds to illustrate the

Tribenzotriquinacenes bearing three peripheral or bridgehead urea groups stretched into the 3-D space

• Jörg Tellenbröker and
• Dietmar Kuck

Beilstein J. Org. Chem. 2011, 7, 329–337, doi:10.3762/bjoc.7.43

• units. Research on the formation and chemical properties of host–guest compounds bearing urea units as linker groups has become an exciting field of scientific interest over the past few decades [8][9][10][11][12][13][14][15]. For example, cone-like building blocks such as those based on calix[4]arenes