[show abstract][hide abstract] ABSTRACT: A supramolecular complex between benzoates and a bambusuril crystallizes out immediately after mixing in chloroform but only in the presence of residual water molecules. In this complex each of the two portals of the macrocycle is occupied by one benzoate. Carboxylate groups are connected through hydrogen bonding interactions with one molecule of water positioned between them in the center of the bambusuril cavity. Similar water assisted host-guest behavior was also observed when tosylates instead of benzoates were used.
Chemical Communications 12/2013; · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: A water-soluble methylene-bridged glycoluril dimer 2S was isolated. It was shown that 2S is only kinetic product of the reaction between glycoluril derivative 1 and paraformaldehyde. 2S is subsequently intermolecularly transformed into its diastereomer 2C. The kinetics and thermodynamics of the S- to C-shaped dimer isomerization were investigated under reaction conditions similar to cucurbituril synthesis.
The Journal of Organic Chemistry 11/2012; · 4.56 Impact Factor
[show abstract][hide abstract] ABSTRACT: Six- and seven-membered cucurbiturils form inclusion complexes with a lutidine derivative. These inclusion complexes differ in the binding mode, stability, kinetics of complexation, and sensitivity toward basic media.
New Journal of Chemistry 08/2012; 36(9):1721-1724. · 2.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: Deprotonation of the two terminal COOH groups on a 4,4'-bipyridinium linear derivative leads to a pronounced slow down on the kinetics of threading and unthreading by the cucurbituril host.
Chemical Communications 05/2012; 48(53):6693-5. · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: Since the discovery of the cucurbituril (CB6) macrocycle, the binding modes of its supramolecular complexes with organic cations have been elucidated using NMR spectroscopy. The observed changes in chemical shifts of guests induced by this complexation follow generally accepted rules. Here we report some exceptions to this usual behavior for complexes of CB6 with pyridinium and pyrazinium guests, as determined by using 1H, 13C, and 15N NMR spectroscopy. We use quantum chemical calculations to rationalize our observations by the concept of redistribution of the electron density in the aromatic part of the guest caused by complexation with the macrocycle. Furthermore, we used a simple model employing point charges that mimic the CB6 host to analyze the electron deformation density induced by complexation. It indicates that the changes in the nuclear magnetic shielding observed for the aromatic part of the guest result from the redistribution of electrons induced mainly by the electrostatic repulsion of the oxygen atoms of the CB6 portal.
New Journal of Chemistry 11/2011; 35(12):2854-2859. · 2.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: Cucurbituril (CB6) and bispyridinium ethylene form a stable inclusion complex. A rotaxane derived from this complex was prepared in which a CB6 wheel shuttles along an axle in an NMR time-resolved regime.
[show abstract][hide abstract] ABSTRACT: a b s t r a c t 1,6-Dibenzylglycoluril is not accessible via classical condensation reaction between substituted urea and glyoxal. In this paper 1,6-dibenzylglycoluril was successfully prepared by alkylation of 1,6-diacetylgly-coluril with benzylbromide for the first time. 1,6-Dibenzylglycoluril reacted with formaldehyde to give tetrabenzylglycoluril dimer. Deprotection of this dimer and the previously reported o-xylyleneglycoluril dimer was achieved by dissolving metal reduction, whereas propyleneglycoluril dimer was deprotected by action of potassium persulfate.
[show abstract][hide abstract] ABSTRACT: Electrospray ionization mass spectrometry (ESI-MS) is used to probe the binding of small anions to the macrocycle of bambusuril. For the halide ions, the experimental patterns suggest F(-) < Cl(-) < Br(-) < I(-), which is consistent with the order of anion binding found in the condensed phase. Parallel equilibrium studies in the condensed phase establish the association constants of halide anions and bambusuril in mixed solvents. A detailed analysis of the mass spectrometric data is used to shed light on the correlations between the binding constants in the condensed phase and the ion abundances observed using ESI-MS. From the analysis it becomes apparent that ESI-MS can indeed represent the situation in solution to some extent, but the sampling in the gas-phase experiment is not 1:1 compared to that in solution.
The Journal of Physical Chemistry A 09/2011; 115(41):11378-86. · 2.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: A recently discovered anion receptor is jointed by three related macrocycles differing in the number of glycoluril units and type of substitution. The synthesis is carried out in nonpolar solvents compared to aqueous media used in the case of the original macrocycle. The size of macrocycle is controlled by a template. A hexameric macrocycle with benzyl substitution binds halide anions with an affinity exceeding 10(9) M(-1) while a tetrameric analog does not bind any of the investigated anions.
[show abstract][hide abstract] ABSTRACT: Methods for the preparation of anion-free bambusuril (BU6) are presented. They are based on the oxidation of iodide anion, which is bound inside the macrocycle, utilizing dark oxidation by hydrogen peroxide or photooxidation in the presence of titanium dioxide. Anion-free BU6 was found to be insoluble in any of the investigated solvents; however, it dissolves in methanol/chloroform (1:1) or acetonitrile/water (1:1) mixtures in the presence of the tetrabutylammonium salt of a suitable anion. The association constants with halide ions, BF(4)(-), NO(3)(-), and CN(-), were measured by (1)H NMR spectroscopy. The highest association constant (8.9×10(5) M(-1)) was found for the 1:1 complex of BU6 with I(-) in acetonitrile/water mixture. A number of crystal structures of BU6 complexes with various anions were obtained. The influence of the anion size on the macrocycle diameter is discussed together with an unusual arrangement of the macrocycles into separate layers.
[show abstract][hide abstract] ABSTRACT: We report here on supramolecular objects containing glycoluril units and functioning as host molecules. The present paper contains a detailed discussion on the synthetic approaches leading to methylene bridged glycoluril oligomers, as well as a description of their supramolecular properties. We also discuss the recently obtained macrocycle, bambusuril, and its affinity towards anions.
Israel Journal of Chemistry. 04/2011; 51(5‐6):592 - 599.
[show abstract][hide abstract] ABSTRACT: We have prepared organic guest molecules in which two pyridinium rings are connected through an aromatic/aliphatic bridge bearing a carboxyl group. The supramolecular interactions between these guests and macrocyclic hosts cucurbituril (CB7) and cucurbituril (CB8) has been studied. We have demonstrated that the binding modes of the complexes depend on the type of central bridge present in the guest molecules and the size of the macrocycle. We have also showed that the binding mode between cucurbiturils and guests with aromatic bridges is pH independent. On the other hand, a guest containing an aliphatic bridge and CB7 formed a pseudorotaxane, which behaved as a pH-driven molecular switch.
Chemistry - An Asian Journal 11/2010; 5(11):2386-92. · 4.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: The reaction of substituted glycolurils or a glycoluril dimer with a dialdehyde (o-phthalaldehyde) delivers S-shaped dimers and an S-shaped tetramer selectively. A combination of X-ray crystallography, PM3 calculations, and product resubmission experiments establish that the S-shaped isomers are thermodynamically more stable than the C-shaped diastereomers which we attribute to the conformational preferences of the newly formed benzo bicyclo[3.3.2]decane ring system. The preferential formation of S-shaped subunits is one reason why o-phthalaldehyde and possibly other aldehydes do not usually participate in CB[n] forming reactions. We also present evidence that points toward an equilibrium between glycoluril monomer + phthalaldehyde and S-shaped dimer + water that responds to concentration over the 1-50 mM range. This result suggests a second reason, insufficient reactivity (e.g., low equilibrium constant), why o-phthalaldehyde and possibly other aldehydes do not participate in CB[n] forming reactions. Delineation of the reasons why some aldehydes fail in these reactions is the first step toward devising methods to overcome these limitations.
The Journal of Organic Chemistry 03/2010; 75(9):2934-41. · 4.56 Impact Factor
[show abstract][hide abstract] ABSTRACT: The first selective synthesis of glycoluril trimers is described. Trimers framed by o-xylylene walls represent new supramolecular hosts which are able to encapsulate bispyridinium ethylene and methylviologen guests in the solid state and aqueous solution.
[show abstract][hide abstract] ABSTRACT: The supramolecular complex formed by partial inclusion of methylviologen in MeCB6 was described both in solution and in the solid state. The association constant of the complex was determined using (1)H NMR and UV-vis spectrophotometric titration. An extraordinary 2000-fold drop in the association constant of the complex was observed when pure water was replaced by 50 mM NaCl solution.
The Journal of Physical Chemistry B 08/2009; 113(32):11054-7. · 3.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this study, we have investigated the supramolecular interaction between series of 1-alkyl-3-methylimidazolium guests with variable alkyl substituent lengths and cucurbituril (CB6) in the solution and the solid state. Correct interpretation of (1)H NMR spectra was a key issue for determining the binding modes of the complexes in solution. Unusual chemical shifts of some protons in the (1)H NMR spectra were explained by the polarization of the imidazolium aromatic ring upon the complexation with the host. The formation of 1:1 complex between 1-ethyl-3-methylimidazolium and CB6 is in disagreement with previously reported findings describing an inclusion of two guest molecules in the CB6 cavity.
[show abstract][hide abstract] ABSTRACT: A selective method for the synthesis of 1,6-substituted glycolurils has been developed. The glycolurils have been used for the synthesis of methylene-bridged glycoluril dimers bearing hydrogen atoms on their convex face. Depending on the side walls of the dimers, different modes of self-assembly in the solid state have been described using X-ray crystallography.
The Journal of Organic Chemistry 07/2008; 73(12):4671-5. · 4.56 Impact Factor