Constrictive binding of large guests by a hemicarcerand containing four portals

Quan, Mimi L.; Cram, Donald J.

doi:10.1021/ja00007a060

Cited by 180 publications

(132 citation statements)

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“…The ferrocene hemicarceplexes were prepared by heating a mixture of the corresponding hemicarcerand host with a large excess of ferrocene in tripiperidinophosphine oxide for several days. [14] Electrochemistry: The ferrocene (Fc) complex of 1 was found to be extremely insoluble in most solvents commonly used for H NMR spectroscopy. The half-life for these processes was found to be quite long (t 1/2 b 300 h in all cases) which is consistent with Crams reported value [14] of t 1/2 19.6 h obtained with Fc´1 at a much higher temperature (112 8C in C 2 D 2 Cl 4 ).…”

Section: Resultsmentioning

confidence: 99%

“…[14] Electrochemistry: The ferrocene (Fc) complex of 1 was found to be extremely insoluble in most solvents commonly used for H NMR spectroscopy. The half-life for these processes was found to be quite long (t 1/2 b 300 h in all cases) which is consistent with Crams reported value [14] of t 1/2 19.6 h obtained with Fc´1 at a much higher temperature (112 8C in C 2 D 2 Cl 4 ). These data clearly indicate that the kinetic stability of the two ferrocene hemicarceplexes is sufficient to provide a convenient time window in which the electrochemical behavior of the fully encapsulated ferrocene guest can be investigated.…”

Section: Resultsmentioning

confidence: 99%

“…The preparation of a ferrocene hemicarceplex with host 1 by Quan and Cram [14] played a crucial role in our decision to explore the electrochemistry of these systems. Ferrocene has frequently been used as a redox-active building block in the preparation of a variety of supramolecular assemblies [29] and is attractive from the electrochemical standpoint because it has a wellcharacterized and reversible anodic electrochemistry.…”

Section: Discussionmentioning

confidence: 99%

“…[14] Guests of appropriate size and shape can access the hemicarcerand cavity through the four equatorial openings or portals defined by the four bridges joining the two cavitand halves of the host. However, the formation of the corresponding inclusion complexes, or hemicarceplexes, can be extremely slow at room temperature if the sizes of the guest and the portals are similar.…”

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Electrochemistry of Encapsulated Guests: Ferrocene inside Cram's Hemicarcerands

1998

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The voltammetric behavior of ferrocene encapsulated inside two hemicarcerand hosts was investigated in dichloromethane and tetrachloroethane solutions. Molecular encapsulation led to substantial changes in the anodic voltammetric behavior of the ferrocene nucleus. Generally, encapsulated ferrocene exhibited a more positive halfwave oxidation potential and a lower apparent standard rate constant of heterogeneous electron transfer than uncomplexed ferrocene under identical experimental conditions. Whereas the anodic shift of the half-wave potential probably results from the hindered solvation of the positively charged, oxidized ferrocene inside the nonpolar hemicarcerand cavities, the observed decrease in electron transfer rate seems to arise primarily from the increased molecular mass of the electro-inactive species and the longer distance of maximum approach between the ferrocene center and the electrode surface which is imposed by the encapsulating host. Generally, electrochemical oxidation did not significantly alter the slow rate of ferrocene guest dissociation or release from the hemicarceplexes surveyed.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Electrochemistry of Encapsulated Guests: Ferrocene inside Cram's Hemicarcerands

1998

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“…A similar result is observed with anthracenene, which is too long to fit within the confines of 2. In an earlier study, Quan and Cram [11] demonstrated that a kinetically stable complex could be formed between anthracene and a host with an enforced cavity similar to 1. The contrast between the results from molecular incarceration and equilibrium binding studies points out that different factors determine kinetic and thermodynamic stability.…”

Section: Discussionmentioning

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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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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Dynamische kovalente Chemie

et al. 2002

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Die Synthese molekularer organischer Verbindungen ist traditionell durch die Anwendung kinetisch kontrollierter Reaktionen dominiert, [1] die zu irreversiblen (starken) kovalenten Bindungen f¸hren. Dabei werden die Reagentien (oder Katalysatoren) und die Reaktionsbedingungen in Hinblick auf eine gute Ausbeute eines einzigen Produkts sorgf‰ltig ausgew‰hlt. Im Wesentlichen ist ein Reaktionsweg er-w¸nscht, der zur energetisch bevorzugten Bildung eines bestimmten Produkts f¸hrt und die Bildung anderer, uner-w¸nschter Produkte vermeidet; so wird, wie in Abbildung 1 Angew. Chem. 2002, 114, 938 ± 993 Stuart J. Rowan wurde 1969 in Edinburgh, Schottland, geboren. Er erhielt 1991 seinen B.Sc.-Titel an der University of Glasgow. Dort fertigte er auch seine Doktorarbeit mit dem Titel πSupramolecular Crystal Engineering of Inclusion Compounds™ bei Dr. David D. MacNicol an (Ph.D.-Titel 1995). 1994 ging er nach Cambridge zu Prof. Jeremy K. M. Sanders zur Erforschung von dynamischen kombinatorischen Bibliotheken mit dem Schwerpunkt Umesterungsreaktionen. 1996 wurde er zum Research Associate of Girton College in Cambridge ernannt. 1998 f¸hrte ihn sein Weg an die University of California in Los Angeles, wo er als Postdoc bei Prof. J. Fraser Stoddart seine Arbeiten fortsetzte. Dort entwickelte er zahlreiche neue Methoden zum Aufbau von mechanisch verkn¸pften Verbindungen, speziell durch Anwendung der dynamischen kovalenten Chemie, und Stoppern. 1999 wurde er zum Assistant Professor am Department of Macromolecular Science an der Case Western Reserve University in Cleveland, Ohio, ernannt. Seine Forschungsinteressen konzentrieren sich auf das Potential der dynamischen (kovalenten und nichtkovalenten) Chemie, auf den Aufbau und die Eigenschaften polymerer Stoffe und auf die Entwicklung neuer Synthesemethoden zum Aufbau komplexer polymerer Architekturen. Stuart J. Cantrill wurde 1974 in Lichfield, England, geboren. 1993 begann er an der University of Birmingham mit dem Studium der Chemie und der Bioorganischen Chemie und erhielt dort 1996 seinen B.Sc.-Titel. Seine Doktorarbeit fertigte er bei Prof. J. Fraser Stoddart an (University of Birmingham (M.Phil.-Titel)/University of California in Los Angeles). Der Schwerpunkt seiner Arbeit lag in Forschungen zur Wechselwirkung zwischen sekund‰ren Dialkylammoniumionen und Kronenethern, wobei speziell selbstkomplement‰re πdaisy chain™-Systeme untersucht wurden. 2001 erlang er an der UCLA den Ph.D.-Titel. Gegenw‰rtig forscht er als Postdoc am California Institute of Technology in der Arbeitsgruppe von Prof. Robert H. Grubbs. Graham Cousins wurde 1975 in Southampton, Gro˚britannien, geboren. Er erhielt seinen B.Sc.-Titel in Chemie 1997 an der University of Birmingham. Anschlie˚end fertigte er an der University of Cambridge bei Prof. Jeremy Sanders seine Doktorarbeit an und erhielt dort 2000 seinen Ph.D.-Titel. Sein Hauptforschungsinteresse gilt der Supramolekularen Chemie und der Kombinatorischen Chemie. In Birmingham erforschte er w‰hrend seiner Studienzeit bei Prof. J. Fraser Stoddart die mol...

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Constrictive binding of large guests by a hemicarcerand containing four portals

Cited by 180 publications

References 3 publications

Electrochemistry of Encapsulated Guests: Ferrocene inside Cram's Hemicarcerands

Electrochemistry of Encapsulated Guests: Ferrocene inside Cram's Hemicarcerands

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

Dynamische kovalente Chemie

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