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Formation and dissociation mechanism of amide complexes. V . Interconversion of dimeric and monomeric Cu 2+ ‐complexes with 1,8‐diamino‐3,6‐diaza‐2,7‐octanedione: Comparison between the reactivity of terminal and internal amide groups
Author(s) -
Zuberbühler Andreas D.,
Kaden Thomas A.
Publication year - 1982
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19820650313
Subject(s) - chemistry , protonation , deprotonation , amide , dissociation (chemistry) , reaction rate constant , reactivity (psychology) , yield (engineering) , monomer , medicinal chemistry , crystallography , dimer , stereochemistry , chelation , kinetics , inorganic chemistry , organic chemistry , polymer , ion , medicine , physics , alternative medicine , materials science , pathology , quantum mechanics , metallurgy
The protonation and deprotonation rates of the coordinated amide groups in the Cu 2+ ‐complexes of 1,8‐diamino‐3,6‐diaza‐2,7‐octanedione (DED = L) have been studied by stopped‐flow techniques. Starting at low pH from Cu 2+ and DED the dimeric Cu 2 L 2 4+ ‐complex, fully formed within the mixing time of the stopped‐flow instrument, reacts in two consecutive steps to yield the final product CuLH −2 . The rate constants of the forward and backward reactions have been determined and are given in Table 1. The intermediate was identified as Cu 2 L 2 H −2 2+ by measuring its VIS.‐absorption spectrum. The rate constants for the interconversion of the amide groups from the O ‐ to the N ‐coordinated form in the Cu 2+ ‐complexes of DED, 2,10‐dioxo‐1, 4, 8, 11 tetraazaundecane (DANA) and triglycine (TRIGLY) are compared with each other. It is shown that these rate constants are similar, no matter whether the amide group is terminal or internal as long as the rotation is easily possible as is the case in the dimeric species Cu 2 L 2 4+ and Cu 2 L 2 H −2 2+ . However, for CuLH −2 the inter‐conversion only takes place after opening of one of the chelate rings in a rapid protonation preequilibrium.