Chain length effects in the cleavage of aryl esters by cyclodextrins. Different transition states for m- and p-nitrophenyl alkanoates

Tee, Oswald S.; Mazza, Charles; Du, Xian

doi:10.1021/jo00298a042

Cited by 67 publications

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“…We have shown previously that the m-nitrophenyl esters are more reactive than their para isomers towards a-CD, P-CD, and "hydroxypropyl-P-cyclodextrin" H~-P -C D~ (8,10). These results support a mechanism whereby the carbonyl group of the meta ester (1) Scheme 1.…”

Section: Introductionmentioning

confidence: 57%

“…For each ester, there is a good linear free energy relationship5 (LFER) between the rate constants and the dissociation constants for the CDePI complexes (eqs. [8] and [9], where pK1 = -log K,): [8] pNPA, log k, = 0.77pK, -0.87 (N = 13, r = 0.992) [9] pNPH, log k, = 0.74pK1 -1.52 (N = 14, r = 0.979)…”

Section: Discussionmentioning

confidence: 99%

“…The para esters, on the other hand, show very little dependence of transition state binding on chain length up to about the hexanoate, after which the transition state binding shows a strong dependence on ester chain length. This behaviour is evidence of a switch in mode of transition state binding from aryl group inclusion (3) to acyl group inclusion (4) (8,10) as the acyl chain is lengthened beyond C,.…”

mentioning

confidence: 92%

“…nitrophenyl alkanoates (8,10,11) since these compounds provide a convenient series of substrates differing in acyl chain length or position of the nitro substituent, which allows one to probe both initial state and transition state binding as a function of structural or hydrophobic differences. We have shown previously that the m-nitrophenyl esters are more reactive than their para isomers towards a-CD, P-CD, and "hydroxypropyl-P-cyclodextrin" H~-P -C D~ (8,10).…”

Section: Introductionmentioning

confidence: 99%

“…The stability of the {ester.CD} complexes shows a strong dependence on the ester chain, with the negative logarithm of the binding constant increasing linearly with the acyl chain length (8,10). For cleavage of these esters by CDs the mode of transition state binding is not as simple.…”

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confidence: 99%

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Spectator catalysis in the cleavage of p-nitrophenyl acetate and p-nitrophenyl hexanoate by "hydroxypropyl-β-cyclodextrin"

Gadosy¹,

Tee²

1996

Can. J. Chem.

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Aliphatic alcohols that form host-guest complexes with "hydroxypropyl-P-cyclodextrin" retard the cleavage of tnnitrophenyl acetate by hydroxypropyl-P-cyclodextrin in basic aqueous solution, due to competitive inhibition. By contrast, these same species do not inhibit the reaction of p-nitrophenyl acetate and p-nitrophenyl hexanoate to the same extent and, in some cases, the addition of alcohols serves to increase the rate of reaction. The observed reaction kinetics require the presence of a process that has one molecule of the "potential inhibitor" in the transition state for ester cleavage. Rate constants, k,, for the reaction of the (ester.hydroxypropy1-P-cyclodextrin) complexes with a series of potential inhibitors show a strong dependence on the ability of the potential inhibitor to bind to the cyclodextrin. On the other hand, rate constants for the kinetically equivalent reaction of the ester with the (cyclodextrin.potential inhibitor) complex show little dependence on the alcohol structure and they vary over a very limited range. The negative logarithms of the apparent dissociation constant of the potential inhibitor from the transition state show a strong dependence on the ability of the potential inhibitor to bind to hydroxypropyl-0-cyclodextrin, indicating that the binding of the potential inhibitor in the initial state and the transition state is similar. It is concluded that the cleavage of p-nitropheny I acetate and p-nitrophenyl hexanoate by hydroxypropyl-P-cyclodextrin in the presence of 14 potential inhibitors can occur with the ester largely outside of the hydroxypropyl-P-cyclodextrin cavity during the transition state, allowing the cavity to be occupied by a molecule of potential inhibitor.Key words: cyclodextrin, spectator catalysis, esterolysis.Resum6 : A cause d'une inhibition compCtitive, les alcools aliphatiques qui forment des complexes h6tes-invitCs avec l'cchydroxypropyl-P-cyclodextrinen retardent le clivage de I'acCtate de tn-nitrophknyle par l'hydroxypropyl-P-cyclodextrine en solution basique aqueuse. Par opposition, ces m&mes espkces n'inhibent pas la rCaction de I'acCtate de p-nitrophenyle et de I'hexanoate dep-nitrophenyle de la m&me faqon et, dans certains cas, I'addition d'alcools sert mCme i augmenter la vitesse de la reaction. Les rCsultats cinCtiques observCs suggkrent I'existence d'un processus qui comporte urze molCcule d'ccinhibiteur potentiel)) dans 1'Ctat de transition du clivage de l'ester. Les constantes de vitesse, k, pour les rCactions des complexes (ester.hydroxypropy1-P-cyclodextrine] avec une sCrie d'inhibiteurs potentiels montre une forte dCpendance sur I'habilitC de l'inhibiteur potentiel B se lier B la cyclodextrine. Par ailleurs, les constantes de vitesse pour la rCaction cinktiquement Cquivalente de l'ester avec le complexe (cyclodextrine.inhibiteur potentiel) ne prksente qu'une faible dCpendance sur la structure de l'alcool et leurs variations ne sont que trks faibles. Les logarithmes nCgatifs des constantes de dissociations apparentes des inhibiteur...

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Section: Introductionmentioning

confidence: 57%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Spectator catalysis in the cleavage of p-nitrophenyl acetate and p-nitrophenyl hexanoate by "hydroxypropyl-β-cyclodextrin"

Gadosy¹,

Tee²

1996

Can. J. Chem.

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Cyclodextrine als Bausteine supramolekularer Strukturen und Funktionseinheiten

Wenz¹

1994

Angewandte Chemie

215

103

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Cyclodextrine werden gerne als Bau-molekule auf ein passendes Gastmole-higkeit zur molekularen Erkennung zur steine eingesetzt, da sie sich gezielt so-kul aufgefadelt werden. Solche supra-chromatographischen Trennung von wohl kovalent, als auch nichtkovalent molekularen Strukturen entstehen meist komplexen Stoffgemischen, insbesondeverknupfen lassen. So wurden an ein in Losung, so daD sie durch hochauflo-re von Racematen, genutzt. Auch kon-/I-Cyclodextrinmolekul regioselektiv ein, sende spektroskopische Methoden cha-nen Cyclodextrine oder deren Derivate zwei, drei, sieben, vierzehn, achtzehn rakterisiert werden konnen. Sie lassen bemerkenswerte katalytische Aktivitaoder zwanzig Substituenten kovalent ge-sich weiter in sonst sehr schwer zugang-ten aufweisen. SchlieDlich kann man mit bunden. Cyclodextrine sind zudem or-liche molekulare Architekturen wie Ca-Cyclodextrinen die Verfiigbarkeit von ganische Wirtmolekiile. In ihrem Innen-tenane, Rotaxane. Polyrotaxane und Wirkstoffen giinstig beeinflussen, was raum finden ein oder zwei Gastmolekule Rohren effizient umwandeln. Cyclodex-sicherlich in nachster Zeit zu vielen AnPlatz. Umgekehrt konnen ein, zwei oder trine konnen auch recht interessante wendungen fuhren wird. viele (hundert und mehr) Cyclodextrin-Funktionen ausubcn. So wird ihre Fa-<

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Cyclodextrins as Building Blocks for Supramolecular Structures and Functional Units

Wenz¹

1994

Angew. Chem. Int. Ed. Engl.

1,317

682

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Cyclodextrins are frequently used as building blocks, because they can be linked both covalently and noncovalently with specificity. Thus one, two, three, seven, fourteen, eighteen, or twenty substituents have been linked to one β‐cyclodextrin molecule in a regioselective manner. Furthermore, Cyclodextrins may serve as organic host molecules. Their internal cavity is able to accommodate one or two guest molecules. Conversely, suitable guest molecules can be used to thread one, two, or many (one hundred or more) cyclodextrin rings. The resulting supramolecular structures are often formed in solution, which allows characterization by high‐resolution spectroscopic methods. Chemical conversion of these structures provides molecular architectures such as catenanes, rotaxanes, polyrotaxanes, and tubes, which are not readily prepared by other methods. The particular properties of Cyclodextrins can also be employed, for example, for the chromatographic separation of complex mixtures of substances, even racemates, by molecular recognition. Cyclodextrins and their derivatives have been found to be remarkably active catalysts as well. Finally, since Cyclodextrins can favorably influence the release of drugs, many new applications will certainly be developed in the near future.

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Chain length effects in the cleavage of aryl esters by cyclodextrins. Different transition states for m- and p-nitrophenyl alkanoates

Cited by 67 publications

References 0 publications

Spectator catalysis in the cleavage of p-nitrophenyl acetate and p-nitrophenyl hexanoate by "hydroxypropyl-β-cyclodextrin"

Spectator catalysis in the cleavage of p-nitrophenyl acetate and p-nitrophenyl hexanoate by "hydroxypropyl-β-cyclodextrin"

Cyclodextrine als Bausteine supramolekularer Strukturen und Funktionseinheiten

Cyclodextrins as Building Blocks for Supramolecular Structures and Functional Units

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