Complexation of phenylalanine and histidine by β -cyclodextrin, 6 A -(3-aminopropylamino)-6 A -deoxy- β -cyclodextrin and its metallocyclodextrins in aqueous solution
Date
1995
Authors
Brown, S.
Haskard, C.
Easton, C.
Lincoln, S.
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Advisors
Journal Title
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Type:
Journal article
Citation
Journal of the Chemical Society, Faraday Transactions, 1995; 91(6):1013-1018
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Abstract
A pH titration study shows that for the complexation of phenylalanine anion [(R)- and (S)-Phe<sup>-</sup>] by β-cyclodextrin (βCD), log(K<inf>1R</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 2.91 ± 0.08 and log(K<inf>1S</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 2.83 ± 0.06, and that by 6<sup>A</sup>-(3-aminopropylamino)-6<sup>A</sup>-deoxy-β-cyclodextrin (βCDpn) is characterized by log(K<inf>2R</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 2.51 ± 0.07 and log(K<inf>2S</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 2.74 ± 0.05. No complexation of histidine (HisH) by βCD was detected, but for the complexation of histidine anion (His<sup>-</sup>) by βCDpnH<sup>+</sup> log(K<inf>3R</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 2.50 ± 0.02 and log(K<inf>3S</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 2.37 ± 0.09; and for the complexation of HisH by βCDpnH<sup>+</sup> log(K<inf>4R</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 2.31 ± 0.05 and log(K<inf>4S</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 2.18 ± 0.05. For the complexation of Phe<sup>-</sup> by the metallocyclodextrin, [M(βCDpn)]<sup>2+</sup>, log(K<inf>11R</inf>/dm<sup>3</sup> mol<sup>-1</sup>) and log(K<inf>11S</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 3.6 ± 0.2 and 3.69 ± 0.06, <3.6 and 4.4 ± 0.1, 7.2 ± 0.1 and 6.9 ± 0.1, 4.7 ± 0.1 and 4.7 ± 0.2, when M<sup>2+</sup> = Co<sup>2+</sup>, Ni<sup>2+</sup>, Cu<sup>2+</sup> and Zn<sup>2+</sup>, respectively. For the complexation of His<sup>-</sup> by [Cu(βCDpn)]<sup>2+</sup>, log(K<inf>11R</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 8.38 ± 0.04 and log(K<inf>11S</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 8.42 ± 0.02, and for the complexation of a second His<sup>-</sup> log(K<inf>12R</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 7.75 ± 0.05 and log(K<inf>12S</inf>/dm<sup>3</sup> mol<sup>-1</sup>) = 7.6 ± 0.1. The roles of the cyclodextrins, divalent metal ions and amino acids affecting complexation are discussed.