An Asymmetric Carceplex and New Crystal Structure Yield Information Regarding a 1 Million-Fold Template Effect

Fraser, James E.; Borecka, Bozena; Trotter, James; Sherman, John C.

doi:10.1021/jo00110a025

Cited by 64 publications

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“…Tetrol 4 and diester 6 were prepared by methods described elsewhere. [24] , [25] 1 H NMR spectra were obtained with a Varian Unity-plus NMR spectrometer. Hexaester diol (7): To a solution of tetrol 4 [24] (0.5 g, 0.76 mmol) in dry 1-methyl-2-pyrrolidinone (NMP) (500 mL) was added anhydrous Cs 2 CO 3 (4.0 g) and the solution was degassed.…”

mentioning

confidence: 99%

“…[24] , [25] 1 H NMR spectra were obtained with a Varian Unity-plus NMR spectrometer. Hexaester diol (7): To a solution of tetrol 4 [24] (0.5 g, 0.76 mmol) in dry 1-methyl-2-pyrrolidinone (NMP) (500 mL) was added anhydrous Cs 2 CO 3 (4.0 g) and the solution was degassed. The degassed solution of diester 6 [25] (0.47 g, 1.1 mmol; 1.5 equivalents) was added dropwise over 16 h to the solution of tetrol 4.…”

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confidence: 99%

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Highly Organized Spherical Hosts That Bind Organic Guests in Aqueous Solution with Micromolar Affinity: Microcalorimetry Studies

Piatnitski

Flowers

Deshayes³

2000

Chem. Eur. J.

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Two novel closed-shell hemicarcerand-like hosts with spherical cavities of 11 A diameter that are soluble in aqueous solution were constructed. The binding of xylenes, aryl ethers, polyaromatic compounds, ferrocene derivatives, and bicyclic aliphatic compounds were examined by NMR spectroscopy and microcalorimetry. NMR binding studies indicated that binding depended upon guest hydrophobicity and shape. No binding was detected for guests in which a charge must be desolvated as part of inclusion or for guests that can not fit within the cavity of the host. Three complexes 2.naphthalene, 2.p-xylene, and 2.ferrocene were isolated and found to be indefinitely stable in the solid phase and in aqueous solution. The binding constants for these complexes are estimated to be greater than 10(8) M-1. Thirteen guests were examined by microcalorimetry with binding constants ranging between 10(7) and 10(3) M-1. A comparison of results obtained here with those from previous work with beta-cyclodextrin and cyclophane hosts, along with analysis of the entropy-enthalpy compensation data, indicate that there is a higher degree of guest desolvation with this host structure than with open-shell hosts. This accounts at least partially for the increase in affinity observed with these closed-shell hosts. Replacing a hydroxy group in the host portal with a hydrogen atom does not affect the binding constant, a finding consistent with the guest residing deeply buried within the host cavity. It was observed that aromatic guests are bound with higher affinity than aliphatic ones in agreement with results that point to the importance of London dispersion forces in the association of aromatic components in face-to-edge orientations. The correlation of changes in NMR chemical shift with microcalorimetry data supports a model in which increased CH-pi interactions strengthen association between host and guest due to the dominant role of van der Waals dispersion forces. Remarkably, the binding constant for the 1,4 isomer of dimethoxybenzene is 32 times higher than for the 1,2 isomer, and even greater discrimination is observed between the xylene guests since the binding constant for p-xylene is 80 times greater than that for o-xylene. This discrimination between isomeric guests by a rigid host indicates that changes in specific hydrophobic interactions have substantial effects upon binding affinity.

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confidence: 99%

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confidence: 99%

Highly Organized Spherical Hosts That Bind Organic Guests in Aqueous Solution with Micromolar Affinity: Microcalorimetry Studies

Piatnitski

Flowers

Deshayes³

2000

Chem. Eur. J.

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“…Various suggestions have been put forward as to the nature of the host-guest interactions that may result in such large differences in the template ratio. 31,33 We have found that parameters such as dipole moment, polarizability, and size of the guest do not successfully explain the observed trends in the template ratio. The electronic structure of the X-ray structure of 5a.pyrazine was examined using AM1 and Extended Hückel (EH) theory, to see if this could shed some light on why pyrazine forms the carceplex 5a.pyrazine so readily.…”

Section: Modeling the 4-methylene-bridged System 5amentioning

confidence: 88%

“…No X-ray coordinates have been reported for the three-bridged systems 1a.guest or 1b.guest, and to compare the host-guest geometries on more than a qualitative basis, we optimized the structure of 5a.pyrazine (a four-bridge carceplex related to .guest) for which coordinates from an X-ray structure 31 have been deposited with the Cambridge Crystallographic Data Collection. Illustrated in Figure 5 are AM1 and X-ray structures of 5a.pyrazine.…”

Section: Modeling the 4-methylene-bridged System 5amentioning

confidence: 99%

An AM1 semiempirical study of host–guest complexation in hemicarcerand complexes

et al. 2004

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Semiempirical AM1 calculations have been carried out on host-guest complexes of model hemicarcerands 1a and 2a. The justification for the choice of the AM1 Hamiltonian was based on a comparison between reported X-ray data for the smaller tetrabromocavitand 4a and computational results obtained using several different Hamiltonians. The complexation behavior of hemicarcerands 1a and 2a have been compared with experimental results reported by Cram et al. for the related hemicarcerands 1b and 2b. Based on this comparison, a criterion for predicting guest encapsulation was developed, E(complexation), which relies on the calculation of AM1 heats of formation for host, guest, and hemicarceplex. If E(complexation) is lower than 10 kcal/mol, then a guest will be encapsulated, while if it is greater than 30 kcal/mol, a guest will not be encapsulated. The use of constrained-path AM1 optimizations to determine the energy barriers to guest entry and exit from the host was found to be a useful tool for examining suitable host-guest combinations when the E(complexation) criteria does not hold. We have computed the barriers to exit of N, N-dimethylformamide (dmf) and furan from the hemicarcerand 1a, the former has been compared with the experiment and shows excellent agreement. Based on the success of the above computational methods in predicting which host-guest combinations will form stable hemicarceplexes we have synthesized a new target hemicarceplex 1b.furan.

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“…Several groups have reported the synthesis of cavitands with an enhanced solubility in water. This requires the introduction of either charged moieties, such as quaternary ammonium, [8] amidinium, [9] pyridinium, [10] carboxylate, [11] phosphoric acid salt, [12] phenoxide, [13] etc., or neutral substituents, such as peptides, [14] diethanolamine, [15] dendritic wedges, [16] Pd-organometallic centers. [17] Saccharides have been used as water-solubilizing moieties in the cases of calix [4]arenes [18] and resorcinols, [19] and there is one example of a cavitand.…”

Section: Introductionmentioning

confidence: 99%

Anion Complexation by Glycocluster Thioureamethyl Cavitands: Novel ESI‐MS‐Based Methods for the Determination of K_a Values

Oshovsky

Verboom

Fokkens

et al. 2004

Chemistry A European J

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A series of saccharide-thiourea functionalized cavitands was prepared in good yields (72-86 %) by reaction of a tetrakis(aminomethyl) cavitand with the thiocyanate derivatives of acetylated glucose, galactose, and cellobiose. The anion complexation behavior of the acetylated and deacetylated glycocluster thioureamethyl cavitands was studied with electrospray ionization mass spectrometry (ESI-MS) in acetonitrile and in a 1:1 acetonitrile/water mixture, respectively. All compounds show a preference for Cl(-). A linear relationship was found between the square root of the intensity and the concentration of the formed host-guest complex. Based on this relationship, novel methods have been developed to determine K(a) values, by means of direct titration and competition experiments.

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An Asymmetric Carceplex and New Crystal Structure Yield Information Regarding a 1 Million-Fold Template Effect

Cited by 64 publications

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Highly Organized Spherical Hosts That Bind Organic Guests in Aqueous Solution with Micromolar Affinity: Microcalorimetry Studies

Highly Organized Spherical Hosts That Bind Organic Guests in Aqueous Solution with Micromolar Affinity: Microcalorimetry Studies

An AM1 semiempirical study of host–guest complexation in hemicarcerand complexes

Anion Complexation by Glycocluster Thioureamethyl Cavitands: Novel ESI‐MS‐Based Methods for the Determination of K_a Values

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An Asymmetric Carceplex and New Crystal Structure Yield Information Regarding a 1 Million-Fold Template Effect

Cited by 64 publications

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Highly Organized Spherical Hosts That Bind Organic Guests in Aqueous Solution with Micromolar Affinity: Microcalorimetry Studies

Highly Organized Spherical Hosts That Bind Organic Guests in Aqueous Solution with Micromolar Affinity: Microcalorimetry Studies

An AM1 semiempirical study of host–guest complexation in hemicarcerand complexes

Anion Complexation by Glycocluster Thioureamethyl Cavitands: Novel ESI‐MS‐Based Methods for the Determination of Ka Values

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Anion Complexation by Glycocluster Thioureamethyl Cavitands: Novel ESI‐MS‐Based Methods for the Determination of K_a Values