Ternary Cu(II) complexes, Cu(H-1L)(ACys-) and Cu(H-2L)(ACys-);: L = peptides, ACys- = N-acetyl-cysteinate.: Analogous complexes to the intermediates in the transport of Cu(II) from Cu(H-2L) to cysteine

The Cu(II) in Cu(H-2L) has been postulated to be successively transported to cysteine (Cys) as follows; Cu(H-2L) reversible arrow Cu(H-2L)(Cys*(-)) reversible arrow Cu(H-1L)(Cys*(-)) Cu(H-1L)(Cys(-)), where Cys*(-) denotes the monodentate Cys(-). N-acetyl-cysteinate (ACys(-)) complexes Cu(H-2L)(ACys(-)) and Cu(H-1L)(ACys(-)), having similar coordination modes to Cu(H-2L)(Cys*(-)) and Cu(H-1L)(Cys*(-)), respectively, exhibited the S -> Cu(II) charge transfer absorption at 325-355 nm and the d-d absorption at 530610 nm. A linear interrelation existed between the energies of the CD and d-d absorptions. Cu(H-2L)(ACys(-)) were in rapid equilibrium with Cu(H-1L)(ACys(-)). Upon forming the ternary complex, pK(c2) of the parent Cu(H-1L) was raised to more than 1.0. The formation constants (K) of the Cu(H-1L)(ACys(-)) species from Cu(H-1L) were bigger than those of Cu(H-2L)(ACys(-)) from Cu(H-2L). The linear free-energy relationship existed between the free-energy change (Delta G) and the entropy change (Delta S) for the ternary complex formation. The rate constants (k(1+)) for the Cu(H-1L)(Cys(-)) formation closely correlated with the Kvalues for Cu(H-2L)(ACys(-)). The ternary complexes containing ACys are considered to be analogous complexes to the intermediates in the transport of Cu(II) from peptides to cysteine. (c) 2005 Elsevier Inc. All rights reserved.