Copper(II)- cis, cis-1,3,5-triaminocyclohexane complex-promoted hydrolysis of dipeptides: kinetic, speciation and structural studies.
The hydrolysis of glycylglycine (GylGly), glycyl-L-leucine (GlyLeu), L-leucylglycine (LeuGly) and glycyl-DL-serine (GlySer) promoted by a copper(II)- cis, cis-1,3,5-triaminocyclohexane complex [Cu(II)TACH] was investigated at 70 degrees C and pH 7-10, using HPLC. The observed pseudo-first-order rate constants (k(obs)) and rate enhancing factors (REF) were as follows: 4.1x10(-3 )h(-1)(REF=23) for GylGly, 1.6x10(-3 )h(-1)(REF=21) for GlyLeu, 5.1x10(-3 )h(-1)(REF=64) for LeuGly and 9.2x10(-2 )h(-1)(REF=47) for GlySer [pH 8.1, dipeptide 2 mM, copper(II) 2 mM and TACH 2 mM]. Based on the pH dependence and dipeptide concentration dependence of the initial rates and speciation of the Cu(II)-TACH-dipeptide system at 25 degrees C and I=0.1, the reactions proceed via the formation of a ternary complex [Cu(TACH)(dipeptide)](+) as an intermediate followed by OH(-)-dependent and OH(-)-independent paths to give amino acid(s). GylGly, GlyLeu and LeuGly preferred the OH(-)-dependent path, while GlySer preferred the OH(-)-independent path. The latter can be explained by the intramolecular attack of the amide carbonyl group coordinated with its oxygen atom by the OH group in the serine residue. The X-ray crystal structure of [Cu(TACH)(GlyGly)]BPh(4).MeOH confirmed that GlyGly coordinates to copper(II) ion with its terminal amino N and amide O atoms. The crystal structures of [Cu(TACH)(Gly)]BPh(4) and [Cu(2)(TACH)(2)(OH)(2)](ClO(4))(2).NaClO(4).H(2)O are also reported.
Department of Chemistry, Faculty of Science, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512, Japan. yuki@mito.ipc.ibaraki.ac.jp
Yuki
Y
Fujii
Tamas
T
Kiss
Tamas
T
Gajda
Xiang Shi
XS
Tan
Tsuyoshi
T
Sato
Yoshiharu
Y
Nakano
Yoshihito
Y
Hayashi
Morio
M
Yashiro
D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray; D003514:Cyclohexylamines / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007202:Indicators and Reagents; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D011522:Protons
C472375:(1,3,5-triaminocyclohexane)copper(II); D003514:Cyclohexylamines; D004151:Dipeptides; D007202:Indicators and Reagents; D009942:Organometallic Compounds; D011522:Protons