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ABSTRACT: A programmed assembly process produces rhombic grid networks from compounds L1-L4 in the crystal by pi-pi stacking interactions that generate a bimolecular grid synthon, which undergoes further NH...N hydrogen-bond-mediated assembly.
Journal of the American Chemical Society 09/2009; 131(33):11695-7. · 9.91 Impact Factor
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ABSTRACT: In a process reminiscent of RNA folding, acyclic glycoluril decamer (+/-)-1 undergoes double helical assembly (red/green strands) in water triggered by the neutralization of regions of high electrostatic surface potential by metal cations (Li(+), Na(+), K(+), Ca(2+)).
Organic Letters 09/2009; 11(17):3918-21. · 5.86 Impact Factor
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ABSTRACT: In this paper, we report the interaction of the CB[7] molecular container with crown ether styryl and (bis)styryl dyes 1-6. The interaction of monostyryl dyes (1 and 2) with CB[7] results in the formation of 1:1 complexes where the CB[7] molecule is located on the region of the guest encompassing the pyridinium ring, C=C double bond, and a portion of the aryl ring of benzocrown ethers 1 and 2. For (bis)styryl dyes (3-5), the formation of two types of complexes with composition dye.CB[7].dye and CB[7].dye.CB[7] was confirmed by a combination of optical and electrospray ionization mass spectroscopy (ESI-MS) methods. In the case of (bis)styryl dye (6), both 2:1 and 1:1 compositions 6.CB[7].6 and CB[7].6 were formed. Complex formation is accompanied by substantial changes in the optical characteristics of the dyes and formation of long-lived excimer species. We tested the stimuli responsiveness of this system in response to metal ions. We find that the metal ions prefer to bind to the electrostatically negative ureidyl C=O portals of the CB[7] rather than with the crown ether moiety of the styryl dyes.
The Journal of Physical Chemistry B 08/2009; 113(30):10149-58. · 3.70 Impact Factor
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ABSTRACT: We report the synthesis, X-ray crystal structure, and photophysics of a fluorescent molecular clip (1). Binding studies of 1 toward phenols 2a-j were carried out using fluorescence, (1)H NMR, and IR spectroscopy, which revealed a high affinity and selectivity for 4-nitrophenol (2a) due to formation of the 1.2a complex driven by H-bonding and pi-pi stacking interactions.
Organic Letters 06/2009; 11(12):2603-6. · 5.86 Impact Factor
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Lyle Isaacs
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ABSTRACT: This feature article details some of the unusual recognition properties of the cucurbit[n]uril family (CB[n]) of molecular containers. It discusses the mechanism of CB[n] formation, which proceeds from glycoluril via methylene bridged glycoluril oligomers, along with descriptions of the structures and recognition properties of some kinetically stable macrocyclic intermediates along the way. These partially formed CB[n]-type receptors known as nor-seco-CB[n] display intriguing properties such as chiral recognition, homotropic allostery, and function as aldehyde reaction cucurbituril synthons.
Chemical Communications 03/2009; · 6.17 Impact Factor
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ABSTRACT: The first organic-inorganic hybrid complexes between CB[n] and polyoxometalates not only display a surprisingly high structural complementarity, the right pairing also allows their chemical and physical properties to be coupled, as illustrated by two examples.
Journal of the American Chemical Society 01/2009; 131(2):432-3. · 9.91 Impact Factor
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ABSTRACT: Glycoluril derivative--whose bulky Ph-C[triple bond]C- substituents prevent formation of H-bonded tapes--undergoes solvent dependent assembly in the crystal; a tetrameric molecular bowl is formed by R(24) H-bonding interactions from CH(2)Cl(2) whereas DMF results in H-bond dimerization followed by oligomerization via C-H...pi interactions.
Chemical Communications 08/2008; · 6.17 Impact Factor
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ABSTRACT: In contrast to the high yield formation of cucurbit[n]uril (CB[n]) from a 1:2 ratio of glycoluril to formaldehyde, the condensation of glycoluril with less than 2 equiv of formaldehyde delivers a reaction mixture that contains glycoluril oligomers (2-6) and CB[n] compounds that lack one or more methylene bridges known as nor-seco-cucurbit[n]urils (ns-CB[n]). In this paper we report the chromatographic purification of C-shaped glycoluril oligomers (dimer-hexamer), their characterization in solution, and their X-ray crystal structures. Quite interestingly, despite being acyclic glycoluril pentamer 5 and hexamer 6 retain the ability to bind to guests typical of CB[6] but are also able to expand their cavity to accommodate larger guests like cationic adamantane derivatives. We performed product resubmission experiments with glycoluril oligomers 2-6 and found preferences for the formation of specific ring sizes during CB[n] formation. A comprehensive mechanistic scheme is proposed that accounts for the observed formation of 2-6 and ns-CB[n]. Overall, the experiments establish that a step-growth cyclo-oligomerization process operates during CB[n] formation.
Journal of the American Chemical Society 08/2008; 130(26):8446-54. · 9.91 Impact Factor
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ABSTRACT: We report the isolation and characterization of two top-bottom differentiated CB[n]-type receptors, namely ns-CB[6] and cucurbituril derivative 2, which display diastereoselective recognition toward unsymmetrical guests. Compound 2 also promotes the back-folding of long chain alkanediammonium ions in water.
Organic Letters 07/2008; 10(12):2577-80. · 5.86 Impact Factor
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ABSTRACT: We report the synthesis and characterization of 12 C-shaped methylene-bridged glycoluril dimers (1-12) bearing H-bonding groups on their aromatic rings. Compounds 1, 2, (+/-)-4a, (+/-)-5, (+/-)-7, and 8 form tightly associated homodimers in CDCl3, due to the combined driving force of pi-pi and H-bonding interactions. Compounds 2, (+/-)-5, and 8, having disparate spatial distribution of their H-bonding groups, display the ability to efficiently distinguish between self and nonself even within three-component mixtures in CDCl3. When the spatial distributions of the H-bonding groups of the molecular clips are similar (e.g., 1 and 2), a mixture of homodimers and heterodimers is formed. The effect of various structural modifications (e.g., chirality, side chain steric bulk, number and pattern of H-bonds) on the strength of self-assembly and the fidelity of self-sorting are presented. On the basis of these results we prepared self-sorting systems comprising three (e.g., 1, (+/-)-5, and (+/-)-7) and even four ( 2, (+/-)-5, 9, and 10) components. The potential of molecular clips 1-12 as robust, functionalizable, self-sorting modules to control the noncovalent interaction network in systems chemistry studies is described.
The Journal of Organic Chemistry 07/2008; 73(15):5915-25. · 4.45 Impact Factor
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Angewandte Chemie International Edition 02/2008; 47(14):2657-60. · 13.45 Impact Factor
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ABSTRACT: The ability of cucurbit[8]uril (CB[8]) to control the folding of diaryl ureas 1 and 2 in water was investigated. Compounds 1 and 2 contain two ureidyl C–N bonds which can each populate two conformational states resulting in a conformational ensemble comprising at least three states. We find that the presence of CB[8] results in the selective population of the (E,E)-2 conformer by the formation of CB[8]·(E,E)-2 complex at CB[8]:2 stoichiometries of 1: < 1; at higher stoichiometries, an unfolding process takes place during the formation of CB[8]·(Z,Z)-2 2. In contrast, compound 1 forms the 2:2 complex CB[8]2·(Z,Z)-1 2 over a broad range of CB[8]:2 stoichiometries. The absolute stoichiometries of these complexes were established by diffusion ordered spectroscopic methods (DOSY). The folding of 2 into the (E,E)-2 conformer under the formation of CB[8]·(E,E)-2 is responsive to the presence of guests in its environment. For example, the addition of 8 results in the expulsion of (E,E)-2 from the cavity of CB[8] followed by its unfolding to the thermally preferred mixture of (Z,Z)- and (Z,E)-2 conformers. These results suggest that complexation within synthetic molecular containers—just like their natural counterparts the chaperones—may be an efficient route to control the folding behaviour of non-natural oligomers in aqueous solution.
Supramolecular Chemistry 01/2008; 20(1–2):191-199. · 2.14 Impact Factor
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Mikhail V Rekharsky,
Tadashi Mori,
Cheng Yang,
Young Ho Ko,
N Selvapalam,
Hyunuk Kim,
David Sobransingh,
Angel E Kaifer,
Simin Liu, Lyle Isaacs,
Wei Chen,
Sarvin Moghaddam,
Michael K Gilson,
Kimoon Kim,
Yoshihisa Inoue
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ABSTRACT: The molecular host cucurbit[7]uril forms an extremely stable inclusion complex with the dicationic ferrocene derivative bis(trimethylammoniomethyl)ferrocene in aqueous solution. The equilibrium association constant for this host-guest pair is 3 x 10(15) M(-1) (K(d) = 3 x 10(-16) M), equivalent to that exhibited by the avidin-biotin pair. Although purely synthetic systems with larger association constants have been reported, the present one is unique because it does not rely on polyvalency. Instead, it achieves its extreme affinity by overcoming the compensatory enthalpy-entropy relationship usually observed in supramolecular complexes. Its disproportionately low entropic cost is traced to extensive host desolvation and to the rigidity of both the host and the guest.
Proceedings of the National Academy of Sciences 01/2008; 104(52):20737-42. · 9.68 Impact Factor
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ABSTRACT: The title inclusion complex, C(36)H(36)N(24)O(12)·C(8)H(14)N(2) (2+)·2I(-)·10H(2)O, displays a large ellipsoidal deformation of the cucurbit[6]uril (CB[6]) skeleton upon complex formation. The benzene ring of the cation is rotationally disordered between two orientations in a ratio of 3:1. The solvent H(2)O mol-ecules form a hydrogen-bonded network by inter-action with the carbonyl groups of CB[6] and the I(-) counterions. The crystal studied exhibited non-merohedral twinning. Both CB[6] and the cation are centrosymmetric.
Acta Crystallographica Section E Structure Reports Online 01/2008; 64(Pt 7):o1321-2. · 0.35 Impact Factor
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ABSTRACT: 1,6-Bis-(N-benzyl)-diphenylglycoluril (1,6-BPGlyc) was used as a ligand in the synthesis of a dinuclear rhodium(II) paddlewheel complex. The ligand exchange reaction from Rh2(OAc)4 was remarkably selective for the formation of Rh2(1,6-BPGlyc)2(OAc)2 with a cis-(1,3) ligand arrangement in 46% isolated yield. The bis-substitution pattern and diastereoselective ligand exchange is attributed to the steric bulk of the glycoluril backbone that prevents further ligand substitution. Rh2(1,6-BPGlyc)2(OAc)2 catalyzes cyclopropanation reactions via decomposition of diazoacetates with reactivities and selectivities that were comparable to those of dirhodium(II) tetrakis-μ-carboxamidates.
Inorganica Chimica Acta 01/2008; 361:3309-3314. · 1.85 Impact Factor
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ABSTRACT: We describe the preparation of five triazene-arylene oligomers (3, 4, 7, 8, and 11) and investigations of their folding properties in aqueous solution. These oligomers contain four 2-fold rotors and populate a conformational ensemble comprising at least 10 states. Extensive 1D and 2D NMR studies as well as X-ray crystallography establish that the presence of three members of the cucurbit[n]uril family (CB[n]), CB[10], CB[7], and CB[8], results in the selective population of the (a,a,a,a)-, (a,s,s,a)-, and (a,a,a,s)-conformers. As a result of the high affinity and highly selective binding properties of the CB[n] family, it is possible to fold a single foldamer strand (3) into the CB[8].(a,a,a,s)-3 conformer by the addition of CB[8], then unfold and refold it into the CB[7].(a,s,s,a)-3.CB[7] conformer by addition of CB[7] and 3,5-dimethylaminoadamantane (17), then unfold and refold it again into the CB[10].(a,a,a,a)-3 conformer by addition of CB[10].CB[5] and aminoadamantane (18). The transformation of CB[8].(a,a,a,s)-3 into CB[7].(a,s,s,a)-3.CB[7] proceeds through the intermediacy of CB [8].(a,a,s,a)-3.CB[7], which enhances the rate of dissociation of strand 3 from CB[8].
Journal of the American Chemical Society 10/2007; 129(36):11232-41. · 9.91 Impact Factor
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ABSTRACT: Inverted cucurbit[n]urils (iCB[n]) form as intermediates during the synthesis of cucurbit[n]urils from glycoluril and formaldehyde in HCl (85 degrees C). Product resubmission experiments establish that the diastereomeric iCB[6] and iCB[7] are kinetic products that are less stable thermodynamically than CB[6] or CB[7] (>2.8 kcal mol(-1)). When iCB[6] or iCB[7] is heated under aqueous acidic conditions, a preference for ring contraction is noted in the formation of CB[5] and CB[6], respectively. Interestingly, under anhydrous acidic conditions ring size is preserved with iCB[6] delivering CB[6] cleanly. To establish the intramolecular nature of the iCB[6] to CB[6] conversion under anhydrous, but not aqueous, acidic conditions we performed crossover experiments involving mixtures of iCB[6] and its (13)C=O labeled isotopomer (13)C(12)-iCB[6]. An unusual diastereomeric CB[6] with a Möbius geometry (13) is proposed as a mechanistic intermediate in the conversion of iCB[6] to CB[6] under anhydrous acidic conditions. The improved mechanistic understanding provided by this study suggests improved routes to CB[n]-type compounds.
The Journal of Organic Chemistry 08/2007; 72(18):6840-7. · 4.45 Impact Factor
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ABSTRACT: Chiral molecular clips constitute a robust system for crystal engineering studies and undergo several levels of orthogonal organization including heterochiral dimerization, H-bond or metal-ligand mediated tape formation, and longitudinal packing of the tapes.
Organic Letters 06/2007; 9(10):1899-902. · 5.86 Impact Factor
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ABSTRACT: The four-component ensemble comprising CB[6], beta-CD, and guests 1 and 2 forms complexes CB[6].1H+ and beta-CD.2 at pH < 7 but swaps partners forming complexes CB[6].2 and beta-CD.1 at pH > 13. The intermolecular nature of the switching process suggests application as a basis for stimuli-responsive reconfigurable systems.
Organic Letters 06/2007; 9(12):2349-52. · 5.86 Impact Factor
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Angewandte Chemie International Edition 02/2007; 46(39):7425-7. · 13.45 Impact Factor
