Electron density and electrostatic properties of two peptide molecules: tyrosyl-glycyl-glycine monohydrate and glycyl-aspartic acid dihydrate

The electron density and electrostatic properties of Tyr-Gly-Gly and Gly-As p molecules have been determined from high-resolution X-ray diffraction dat a at 123 K. Topological properties of the charge distribution are discussed and compared with those derived from other experimental studies on peptide molecules, and the characteristics of the (3,-1) critical points of the C= O, C-N, C-C bonds are analysed. Crystal data for Tyr-Gly-Gly: C13H17N3O5. H 2O, M-r = 313, orthorhombic, P2(1)2(1)2(1), Z = 4, T = 123 +/- 2 K; lattice parameters: a = 7.984 (2), b = 9.535 (3), c = 18.352 (5) Angstrom, V = 139 7.1 (6) Angstrom(3), D-x = 1.49 g cm(-3), mu = 1.2 cm(-1) for lambda(Mo) = 0.7107 Angstrom. Crystal data for Gly-Asp: C6H10N2O5. 2H(2)O, M-r = 212, or thorhombic, P2(1)2(1)2(1), Z = 4, T = 123 +/- 2 K; lattice parameters: a = 9.659 (1), b = 9.672 (1), c = 10.739 (1) Angstrom, V = 1003.3 (4) Angstrom( 3), D-x = 1.40 g cm(-3), mu = 1.3 cm(-1) for lambda(Mo) = 0.7107 Angstrom.