Krause J A, Baures P W, Eggleston D S
Department of Physical and Structural Chemistry, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406.
Acta Crystallogr B. 1991 Aug 1;47 ( Pt 4):506-11. doi: 10.1107/s0108768191000915.
D,L-Histidyl-L,D-histidine pentahydrate, C12H16-N6O3.5H2O, Mr = 382.38, F(000) = 408, crystallizes in the monoclinic space group Pc with the cell dimensions a = 9.971 (2), b = 4.745 (2), c = 19.572 (3) A and beta = 96.08 (1) degree, V = 920.6 A3, Z = 2, D chi = 1.379 g cm-3. mu = 1.083 cm-1, T = 295 K, Mo K alpha, lambda = 0.71073 A. Final R (on F) = 0.040 for 1658 observed reflections with I greater than or equal to 3 sigma (I). This dipeptide crystallizes in a zwitterionic form with protonation of the C-terminal imidazole ring. Both histidine units exist in the g+ or 'closed' conformation with C alpha-C beta torsion angles of 67.2 (3) and 63.6 (3) degrees. Principal torsion angles, omega = 176.8 (2). psi 1 = 161.8 (3) and phi 2 = -152.1 (3) degrees, are indicative of a highly extended trans conformation. Intramolecular hydrogen bonding occurs between the imidazole rings [N2D-H2D1...N1D = 2.724 (4) A]. Intermolecular hydrogen bonding occurs between symmetry-related histidine molecules forming chains along the gamma axis and includes another short [2.764 (4) A] N-H...N interaction. The five water molecules occupy channels between adjacent histidine layers.
D，L-组氨酰-L，D-组氨酸五水合物，C12H16N6O3·5H2O，Mr = 382.38，F(000) = 408，以单斜晶系空间群Pc结晶，晶胞参数a = 9.971(2)，b = 4.745(2)，c = 19.572(3) Å，β = 96.08(1)°，V = 920.6 Å3，Z = 2，Dχ = 1.379 g cm-3。μ = 1.083 cm-1，T = 295 K，Mo Kα，λ = 0.71073 Å。对于1658个I大于或等于3σ(I)的观测反射，最终R(F) = 0.040。该二肽以两性离子形式结晶，C端咪唑环质子化。两个组氨酸单元均以g+或“封闭”构象存在，Cα-Cβ扭转角分别为67.2(3)和63.6(3)°。主要扭转角ω = 176.8(2)、ψ1 = 161.8(3)和φ2 = -152.1(3)°，表明为高度伸展的反式构象。咪唑环之间发生分子内氢键[N2D-H2D1...N1D = 2.724(4) Å]。对称相关的组氨酸分子之间发生分子间氢键，沿γ轴形成链，还包括另一个短的[2.764(4) Å] N-H...N相互作用。五个水分子占据相邻组氨酸层之间的通道。
