SOLUBILITY OF DIKETOPIPERAZINE IN AQUEOUS SOLUTIONS OF UREA¹

Abstract

Diketopiperazine has been used as a model compound to investigate hydrogen bond interactions between the peptide bond and urea. The solubility has been measured in aqueous urea solutions as a function of temperature and urea concentration.The heats of solution obtained from this temperature relation serve to evaluate the hydrogen bond interaction of diketopiperazine with urea. The fraction of peptide-urea interactions is estimated by simple equilibrium considerations. The heat of association of urea with a cis peptide bond can then be evaluated from experimental data as -3.4 f 0.5 kcal. An equilibrium constant of 0.096 is found for the association of urea with the peptide bond in aqueous solution. The strong hydrogen bond interaction between urea and peptides is further illustrated by the discovery of a 2 urea: 1 diketopiperazine solid complex which was 0bservt.d to form from 8 M urea solutions below 30'.It is obEerved that the solubility follows a simple exponential dependence upon l / T .

Ammonium based ionic liquids act as compatible solvents for glycine peptides

“…Further, we have used scheme 1b to evaluate the IL dependences of Dg 0 tr contribution of glycyl residue from the DG 0 tr values of c(GG) model compound [54]. The results of these predicted Dg 0 tr from scheme 1b are also included in table 3.…”

Metrics that Differentiate the Origins of Osmolyte Effects on Protein Stability: A Test of the Surface Tension Proposal

“…54 Amino acid side-chain transfer free energies from water to 1 M solutions of TMAO, sarcosine, betaine, proline, sorbitol, sucrose, and urea were obtained from our previous publications. [26][27][28][29] Solvent-accessible surface areas Solvent-accessible surface areas of native RNase T1 (PDB 2BU4), RNase P protein (1A6F), and SNase (1STN) were calculated from the crystal coordinate data obtained from the Protein Data Bank, 55 using the Lesser and Rose 56 modification of the static surface area algorithm of Lee and Richards, 57,58 with a hard sphere probe radius for water of 1.4 Å.…”

Urea effects on protein stability: Hydrogen bonding and the hydrophobic effect

“…Other studies have determined the enthalpies of interaction of urea with constituent groups either from temperature-dependent properties [4][5][6] or from direct calorimetric studies. [6][7][8][9] These studies suggest that the urea-amide unit interaction is exothermic and the urea-apolar interaction is endothermic.…”