Thermodynamic Properties of Peptide Solutions. Part 18. Partial Molar Isentropic Compressibilities of Gly-X-Gly Tripeptides (X = Tyr, Pro, Gln, Asp and Glu), and the Peptide Salts K[GlyAspGly], Na[GlyGluGly] and GlyLysGly Acetate in Aqueous Solution at 25 ∘C

Thermodynamic properties of peptide solutions 19. Partial molar isothermal compressions at T=298.15K of some peptides of sequence gly-X-gly in aqueous solution

“…In two recent papers [19,20], we reported E 2 values for several gly-X-gly tripeptides in aqueous solution at T = 298.15 K. These results have been combined herein with K S;2 and C p;2 values available from previous work [1][2][3][21][22][23][24][25]] to obtain K T;2 values for 13 gly-X-gly peptides with X = alanine (ala), valine (val), leucine (leu), isoleucine (ile), phenylalanine (phe), methionine (met), proline (pro), serine (ser), threonine (thr), asparagine (asn), glutamine (gln), histidine (his), and tyrosine (tyr). For the peptide glysergly, a new value for K S;2 at T = 298.15 K was also determined.…”

“…The partial molar heat capacities at infinite dilution, C p;2 , and the partial molar expansions at infinite dilution, E 2 , for the gly-Xgly peptides at T = 298.15 K, which are available from previous work [14,[19][20][21][22][23][24][25], are given in table 2. These quantities, along with various properties of the solvent, were used to convert the K S;2 values for the tripeptides [1][2][3]36], which are also shown in table 2, into the more useful partial molar isothermal compressions at infinite dilution, K T;2 . The expression used for this conversion is [18,37] …”

“…In previous papers of this series [1][2][3], the partial molar isentropic compressions at infinite dilution, K S;2 , were reported for several tripeptides of sequence glycyl-X-glycine (gly-X-gly), where X represents an amino acid, in aqueous solution at T = 298.15 K. These small peptides are of interest primarily because they are ideal compounds with which to model the amino acid side-chains in proteins. In these tripeptides, the single side-chain of amino acid X is flanked by two peptide groups, which is structurally identical to that found in proteins.…”

“…Since proteins are large complex molecules, a better understanding of this hydration contribution to protein compression can be gleaned from the study of small compounds chosen to model specific functional groups of a protein [4,8]. This model compound approach has been widely used in previous studies, generally with a focus either on the amino acid sidechain residues of a protein [2,3,[9][10][11][12] or on the repeating unit of the backbone chain [13,14].…”

Partial Molar Isentropic Compressions of Some Tetra- and Pentapeptides in Aqueous Solution: Implications for Group Additivity Schemes for Unfolded Proteins

“…Although any additivity scheme can only give, at best, a good approximation of the quantity Y • 2 , the ultimate success of any scheme depends upon how well the various group contributions can be estimated. One distinguishing feature of [15] the peptide-based group additivity model we have proposed [27][28][29] is that the compounds chosen as models are themselves parts of proteins, i.e. peptide molecules.…”