Ester Hydrolysis by a Cyclodextrin Dimer Catalyst with a Tridentate N,N′,N′′‐Zinc Linking Group

Abstract

A new beta-cyclodextrin dimer, 2,6-dimethylpyridine-bridged-bis(6-monoammonio-beta-cyclodextrin) (pyridyl BisCD, L), is synthesized. Its zinc complex (ZnL) is prepared, characterized, and applied as a catalyst for diester hydrolysis. The formation constant (log K(ML)=7.31+/-0.04) of the complex and deprotonation constant (pK(a1)=8.14+/-0.03, pK(a2)=9.24+/-0.01) of the coordinated water molecule were determined by a potentiometric pH titration at (25+/-0.1) degrees C, indicating a tridentate N,N',N''-zinc coordination. Hydrolysis kinetics of carboxylic acid esters were determined with bis(4-nitrophenyl)carbonate (BNPC) and 4-nitrophenyl acetate (NA) as the substrates. The resulting hydrolysis rate constants show that ZnL has a very high rate of catalysis for BNPC hydrolysis, yielding an 8.98x10(3)-fold rate enhancement over uncatalyzed hydrolysis at pH 7.00, compared to only a 71.76-fold rate enhancement for NA hydrolysis. Hydrolysis kinetics of phosphate esters catalyzed by ZnL are also investigated using bis(4-nitrophenyl)phosphate (BNPP) and disodium 4-nitrophenyl phosphate (NPP) as the substrates. The initial first-order rate constant of catalytic hydrolysis for BNPP was 1.29x10(-7) s(-1) at pH 8.5, 35 degrees C and 0.1 mM catalyst concentration, about 1600-fold acceleration over uncatalyzed hydrolysis. The pH dependence of the BNPP cleavage in aqueous buffer was shown as a sigmoidal curve with an inflection point around pH 8.25, which is nearly identical to the pK(a) value of the catalyst from the potentiometric titration. The k(BNPP) of BNPP hydrolysis promoted by ZnL is found to be 1.68x10(-3) M(-1) s(-1), higher than that of NPP, and comparatively higher than those promoted by its other tridentate N,N',N''-zinc analogues.

Enantioselective hydrolysis of amino acid esters by non-chiral copper complexes equipped with bis (β-cyclodextrin)s

“…The two copper(II) complexes, CuL 1 and CuL 2 , were synthesized and characterized according to our previously reported procedures [36,38,40,42]. [36].…”

“…However, few study focused on the cooperation between the metal cofactor and the second coordination sphere effect for enantioselective deacylation of amino acid esters [36]. Recently, we constructed a series of metallohydrolase mimics and superoxide dismutase mimics with CD domains [7,[36][37][38][39][40][41][42][43][44]. Among the hydrolase models, the secondary face pyridine-linked "face-to-face" [45] bisCD complex CuL 2 (L 2 = 2,6-bis(3-monoamino-␤-cyclodextrin-methyl)-pyridine) [38] was demonstrated to possess higher activity for bis(4-nitrophenyl)phosphate (BNPP) cleavage than the "back-to-back" analog CuL 1 (L 1 = 2,6-bis(6-mono-amino-␤-cyclodextrin-methyl)-pyridine) [40].…”

Ester catalytic hydrolysis by a tridentate N,N′,N″-copper bridged cyclodextrin dimer

“…In previous papers, we reported the zinc complexes of β-cyclodextrin dimers, respectively linked by phenanthroline with tetradentate N 4 and pyridine with tridentate N 3 ligands, which demonstrated satisified activities for diester hydrolysis [38,39]. However, structure change of the bridge from tetradentate to tridentate has no obvious rate enhancement for esters hydrolysis.…”

“…Li and Liu et al constructed copper (II) complexes of tris(2-aminoethyl)amino-cyclodextrin (Cu-tren-CD) [34] and of CD-modified gold nanoparticles as supramolecular hydrolase models [35], both mimics showed preferable activities for BNPC hydrolysis. Breslow group designed and synthesized a cyclodextrin dimer catalyst with a N,N′-bidentate bipyridine-copper linking group, which remarkably accelerated catalytic hydrolysis of carboxylic acid diesters and phosphate diesters [36,37].In previous papers, we reported the zinc complexes of β-cyclodextrin dimers, respectively linked by phenanthroline with tetradentate N 4 and pyridine with tridentate N 3 ligands, which demonstrated satisified activities for diester hydrolysis [38,39]. However, structure change of the bridge from tetradentate to tridentate has no obvious rate enhancement for esters hydrolysis.…”

Highly Effective Opening of Epoxides with Aromatic Amines in Presence of β-Cyclodextrin in Water

“…No investi-gations of ring opening of epoxides with aromatic amines in the presence of β-cyclodextrin in water have been reported. Our earlier study on ester hydrolysis successfully catalyzed by β-cyclodextrin derivatives [21][22][23] promoted us…”