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-Asp molecules have been determined from high-resolution X-ray diffraction data 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.H2O, Mr = 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) A, V= 1397.1 (6) A3, Dx = 1.49 g cm(-3), mu = 1.2 cm(-1) for lambdaMo = 0.7107 A. Crystal data for Gly-Asp: C6H10N2O5.2H2O, Mr = 212, orthorhombic, 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) A, V= 1003.3 (4) A3, Dx = 1.40 g cm(-3), mu = 1.3 cm(-1) for lambda(Mo)= 0.7107 A.