Carboxy ester hydrolysis promoted by a zinc(II) 2-[bis(2-aminomethyl)amino]ethanol complex: a new model for indirect activation on the serine nucleophile by zinc(II) in zinc enzymes.
A complexation study on the new Zn(II) complexes of asymmetric tripodal ligand 2-[bis(2-aminoethyl)amino]ethanol (L) has revealed that the alcoholic OH group of complex ZnL exhibits remarkable acidity with a very low pK(a) value of 7.7 at 25 degrees C. Both the monomeric complex [ZnH(-0.25)L(H(2)O)](ClO(4))(1.75) (I) and the dimeric alkoxide-coordinating complex [Zn(2)(H(-1)L)(2)](ClO(4))(2) (II) were synthesized, and their structures were determined by X-ray diffraction. The Zn(II)-bound alkoxide, as the reactive nucleophile toward the hydrolysis of esters, has shown a second-order rate constant of 0.13 +/- 0.01 M(-1) s(-1) in 10% (v/v) CH(3)CN at 25 degrees C in 4-nitrophenyl acetate (NA) hydrolysis, which is almost the same as the corresponding value for the very reactive alcohol-dependent [12]aneN(3)-Zn complex. Present work shows for the first time that Zn(II) complexes of the asymmetric tripodal polyamine bearing an ethoxyl pod can also serve as good models of Zn(II)-containing enzymes.
Xia
J
J
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P.R. China.
Xu
Y
Y
Li
S
S
Sun
W
W
Yu
K
K
Tang
W
W
D002614:Chelating Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004798:Enzymes / Q000737:chemistry*; D006868:Hydrolysis; D007700:Kinetics; D008667:Metalloproteins / Q000737:chemistry*; D008958:Models, Molecular; D009942:Organometallic Compounds; D011199:Potentiometry; D012694:Serine / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry*
D002614:Chelating Agents; D004798:Enzymes; D008667:Metalloproteins; D009942:Organometallic Compounds; C430767:zinc(II)2-(bis(2-aminomethyl)amino)ethanol; D012694:Serine; D015032:Zinc