Cyclodextrin Chemistry

Bender, Myron L.; Komiyama, Makoto

doi:10.1007/978-3-642-66842-5

Cited by 1,369 publications

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“…As expected from earlier work (6) hydrolysis by OH-is dominant. This behaviour parallels that seen earlier for other phenyl esters (4, 5 ) , the levelling-off being due to the cyclodextrin pK,s around 12.1 (4,5,7). At fixed pH and varying CD concentration the observed first-order rate constants (k,,,) ( Table 2) vary in a curvilinear manner (Fig.…”

Section: Resultssupporting

confidence: 87%

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The cleavage of aspirin by α- and β-cyclodextrins in basic aqueous solution

Tee¹,

Takasaki²

1985

Can. J. Chem.

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The deacetylation of aspirin is promoted by a-and P-cyclodextrins (aCD and PCD) in basic aqueous solution. From saturation kinetics the dissociation constants (K,) for the aspirin anion -CD complexes are 12 mM (aCD) and 20 mM (PCD). At pH 12.25 the limiting rate constant for ester cleavage is 14 times (aCD) and 7 times (PCD) that in the medium alone. For the 4-chloroaspirin anion (K, = 3.8 mM) the cleavage induced by aCD is 240 times that in the medium, but 5-chloroaspirin shows a very small effect. The results are discussed in terms of a model derived from that of Bender and co-workers (1967) and are compared to earlier work. For the aCD anion, the 4-chloroaspirin anion is almost as good as "substrate" as m-chloroand m-tert-butylphenyl acetates. Compared to hydroxide ion, the aCD anion is better at cleaving 4-chloroaspirin (2000x) and aspirin (36 X).OSWALD S. TEE et BRYAN K. TAKASAKI. Can. J. Chem. 63, 3540 (1985). The solubility of aspirin (0-acetylsalicylic acid, ASA) in water is quite low (1 g/300 mL) (1). However, it can be increased substantially by the addition of the complexing agents a -and P-cyclodextrin, the effect of the latter being greater (2). P-Cyclodextrin also stabilizes solid aspirin (3). Any attempts to use these effects for pharmaceutical purposes (2,3) should take into account the ability of cyclodextrins to promote the deacylation of phenyl acetates in aqueous solution (4). In the strictest sense of the word, cyclodextrins do not catalyze the hydrolysis of these esters since their deacylation results in the formation of an acetylcyclodextrin, which undergoes hydrolysis relatively slowly (4).The seminal studies carried out by Bender and co-workers (4, 5) included m-andp-carboxyphenyl acetates ( 2 , 3 ) but not, OAc 0 A c 0 Acsurprisingly, ASA (1) (4). In view of the lack of a prior study and the potential interest of its results, it seemed worthwhile to examine the behavior of ASA under hydrolytic conditions in the presence of cyclodextrins. For comparative purposes, 4-chloro-and 5-chloroaspirin were also studied briefly.'Author to whom correspondence should be addressed 'N.S.E.R.C. summer student, 1984. Results and discussion The rate of hydrolysis of aspirin is very slow at intermediate pHs but it rises monotonically with hydroxide ion in aqueous base (6). For the sake of convenience we chose the pH range 11 -14 which is close to that used by Bender and co-workers (4, 5). Moreover, within this range lie the apparent pK,s of the secondary hydroxyls of cyclodextrins that are involved in ester cleavage (4, 5, 7). Table 1 and Fig. 1 show pH-rate data for the deacylation of ASA in the absence of and in the presence of a-and P-cyclodextrin (aCD and PCD). As expected from earlier work (6), the rate constant for hydrolysis in the absence of cyclodextrin simply increases linearly with [OH-]. However, with aCD or PCD present the cleavage is faster at lower pH, the effect levelling off above pH 12 until by pH 13.5 normal Can. J. Chem. Downloaded from www.nrcresearchpress.com by 34.218.44.141 on 0...

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Section: Resultssupporting

confidence: 87%

“…For the sake of convenience we chose the pH range 11 -14 which is close to that used by Bender and co-workers (4,5). Moreover, within this range lie the apparent pK,s of the secondary hydroxyls of cyclodextrins that are involved in ester cleavage (4,5,7). Table 1 and Fig.…”

Section: Resultsmentioning

confidence: 96%

The cleavage of aspirin by α- and β-cyclodextrins in basic aqueous solution

Tee¹,

Takasaki²

1985

Can. J. Chem.

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“…The 'induced-fir-type mechanism is valid only for a-CD. For fl-and y-CD, the homologous compounds with seven and eight glucose residues, no conformational differences between 'empty' and complexed fl-CD are observed but release of highly disordered water within the cavity ('activated water') upon complex formation seems to provide substantial driving force for this process (Lindner & Saenger, 1978;McLennan & Stezowski, 1980;Bender & Komiyama, 1978).…”

Section: Discussionmentioning

confidence: 99%

Topography of cyclodextrin inclusion complexes. XVI. Cyclic system of hydrogen bonds: structure of α-cyclodextrin hexahydrate, form (II): comparison with form (I)

Lindner¹,

Saenger²

1982

Acta Crystallogr B Struct Sci

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“…The three most commonly known CDs contain 6 (α), 7 (β) and 8 (γ) glucose units which are linked together by α-(1,4) linkages (Bender and Komiyana, 1978). Liu et al (2003) reported that CDs have a non-polar cavity which provides a micro-environment for the encapsulation of non-polar, low molecular weight compounds (formation of an inclusion complex) (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Cyclodextrin-ionic liquid polyurethanes for application in drinking water treatment

Malefetse¹,

Mamba²,

Krause³

et al. 2009

WSA

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The prevalence of toxic contaminants in water remains a huge challenge for water-supplying companies and municipalities. Both organic and inorganic (especially heavy metals) pollutants are often present in water distribution networks. The presence of these contaminants in drinking water poses a major risk to human health. Organic and inorganic pollutants often co-occur in drinking water networks. However, at present there is no water treatment intervention that simultaneously removes both organic and inorganic pollutants from water to desirable levels. In our laboratories, recent studies have shown that both functionalised and un-functionalised cyclodextrin (CD) polymers are capable of removing organic pollutants from water, with the functionalised CD polymers showing an enhanced absorption capability. Ionic liquids (ILs), on the other hand, have been reported to absorb heavy metals from aqueous media. In this paper, we report on the synthesis of several cyclodextrin-ionic liquid (CD-IL) polymers, a dual system capable of removing both organic and inorganic pollutants from water. This system has been tested and has proved to possess excellent capabilities for the removal of model pollutants such as p-nitrophenol (PNP), 2,4,6-trichlorophenol (TCP) and chromium (Cr 6+ ) from aqueous media.

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Cyclodextrin Chemistry

Cited by 1,369 publications

References 0 publications

The cleavage of aspirin by α- and β-cyclodextrins in basic aqueous solution

The cleavage of aspirin by α- and β-cyclodextrins in basic aqueous solution

Topography of cyclodextrin inclusion complexes. XVI. Cyclic system of hydrogen bonds: structure of α-cyclodextrin hexahydrate, form (II): comparison with form (I)

Cyclodextrin-ionic liquid polyurethanes for application in drinking water treatment

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