857800-84-1Relevant articles and documents
Methyl group steric effects on the kinetics of the copper(II)-tripeptide reactions with triethylenetetramine
Schwederski, Brigitte E.,Basile-D'Alessandro, Franco,Dickson, Peter N.,Lee, Hsiupu D.,Raycheba, John M. T.,Margerum, Dale W.
, p. 3477 - 3480 (2008/10/08)
Rates of reaction of triethylenetetramine (trien) with doubly deprotonated (tripeptido)cuprate(II) complexes are measured as a function of the number and position of methyl groups in the amino acid residues. Twelve tripeptides that consist of glycyl (G), L-alanyl (A), and α-aminoisobutyryl (Aib) residues are compared. The Cu(H-2Aib3)- complex reacts 8 orders of magnitude more slowly with trien than does the Cu(H-2G3)- complex. Methyl groups on the α-carbon of the second and third amino acid residues (from the amino terminus) decrease the rate of the trien substitution reaction to a much greater extent than methyl groups on the first residue. An empirical correlation between the second-order rate constant (Ktrien, M-1 s-1 at 25.0°C, pH ? 11) and the number and position of the methyl groups is found: log ktrien = 6.7 - 0.2C1 - 2.2C2 - 1.6C3, where Ci denotes the number of methyl groups in the ith amino acid residue. The enormous changes in reactivity are attributed primarily to steric effects in these ligand-ligand exchange reactions.
