Urea-diketopiperazine interactions: a model for urea induced denaturation of proteins.
The solubility of diketopiperazine (DKP) in aqueous urea (U) solutions with molalities ranging from 0 to 16 mol kg-1 (corresponding to urea activities ranging from 0 to 10 mol kg-1) has been measured as a function of the urea activity at 298.15 K. In accordance with a previous study the solubility of diketopiperazine increases with increasing urea activity but drops sharply at a urea activity of 5.7 +/- 0.2 mol kg-1. This drop in solubility can be attributed to the formation of a DKP.U2 cocrystal. The solubility data were fitted to a simple model based on the stoichiometry of the DKP.U2 to yield an intrinsic equilibrium constant kappa describing the interactions occurring between a urea molecule and a peptide group of diketopiperazine in aqueous solution, its value being kappa = 0.0447 +/- 0.0007 kg mol-1. When the activity of water is taken into account, kappa has a lower value of 0.0398 +/- 0.0007 kg mol-1.
Sijpkes
A H
AH
Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309-0215.
van de Kleut
G J
GJ
Gill
S C
SC
D003460:Crystallization; D054659:Diketopiperazines; D004151:Dipeptides / Q000737:chemistry; D008956:Models, Chemical; D010879:Piperazines / Q000737:chemistry*; D011489:Protein Denaturation; D014508:Urea / Q000737:chemistry*
D054659:Diketopiperazines; D004151:Dipeptides; D010879:Piperazines; D014508:Urea