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Hydrolysis of Dipeptides Catalyzed by a Zirconium(IV)‐Substituted Lindqvist Type Polyoxometalate
Author(s) -
Ly Hong Giang T.,
Absillis Gregory,
Bajpe Sneha R.,
Martens Johan A.,
ParacVogt Tatja.
Publication year - 2013
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201300270
Subject(s) - chemistry , hydrolysis , amide , deprotonation , polyoxometalate , hydrolysis constant , reaction rate constant , zirconium , inorganic chemistry , imidazole , catalysis , medicinal chemistry , kinetics , organic chemistry , ion , physics , quantum mechanics
The hydrolysis of a series of unactivated dipeptides in the presence of a zirconium(IV)‐substituted Lindqvist type polyoxometalate, (Me 4 N) 2 [W 5 O 18 Zr(H 2 O) 3 ] (designated as ZrW 5 ), was studied by kinetic experiments and NMR spectroscopy. Among the dipeptides examined, those with the X–Ser amino acid sequence were most effectively hydrolyzed. The kinetics of the hydrolysis of histidylserine (His–Ser) was studied in detail; a rate constant of 95.3 (± 0.1) × 10 –7 s –1 (pD 7.4 and 60 °C) in the presence of an equimolar amount of ZrW 5 was calculated. The binding of His–Ser to ZrW 5 was examined by UV/Vis, 1 H, 13 C, and 183 W NMR spectroscopy, and the data indicate that at physiological pD His–Ser chelates the Zr IV through its imidazole nitrogen, amine nitrogen, and amide carbonyl oxygen. In the presence of ZrW 5 , the pD profile of k obs is bell‐shaped, with a maximum reaction rate at pD 7.5. At high pD values an inactive complex is formed as a result of the deprotonation of the amide nitrogen, resulting in inhibition of His–Ser hydrolysis. The effects of pH, temperature, inhibitors, and ionic strength on the hydrolysis rate constant were also investigated, and a full account of the mechanism of this novel reaction is given.