l-Leucylglycylglycine

In the title compound, C10H19N3O4, the N- and C-termini are protonated and ionized, respectively, and the molecule forms a zwitterion. The main chain is in a folded form. In the crystal, the N-terminal –NH3 + group hydrogen bonds to three C-terminal –COO groups and one carbonyl O atom, forming a three-dimensional network. In addition, an N—H⋯O hydrogen bond between the amide groups of the middle glycine residue and a C—H⋯O interaction continue along the a-axis direction. The side chains of the leucyl residues form a hydrophobic region along the a axis.

In the title compound, C 10 H 19 N 3 O 4 , the N-and C-termini are protonated and ionized, respectively, and the molecule forms a zwitterion. The main chain is in a folded form. In the crystal, the N-terminal -NH 3 + group hydrogen bonds to three Cterminal -COO groups and one carbonyl O atom, forming a three-dimensional network. In addition, an N-HÁ Á ÁO hydrogen bond between the amide groups of the middle glycine residue and a C-HÁ Á ÁO interaction continue along the a-axis direction. The side chains of the leucyl residues form a hydrophobic region along the a axis.
Data collection: CrystalClear (Rigaku, 2006); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and Yadokari-XG 2009 (Kabuto et al., 2009). In the case of the L-leucylglycylglycylglycine (Srikrishnan & Parthasarathy, 1987), the main chain is a folded form, and hydrophobic columns are formed along the a axis as in the case of L-LGG. On the other hand, the main chain of D,Lleucylglycylglycine (D,L-LGG) (Goswami et al., 1977) is in a nearly all-trans form expect the N-terminus. The main chains align parallel to the b axis in a head-to-tail manner and a β-sheetlike structure is formed parallel to the bc plane.
The hydrophobic regions of the leucyl side chains and the hydrophilic regions are aligned alternately along the a axis. As in the case of D,L-LGG, the main chain in L-leucylglycine 0.67 hydrate (Kiyotani & Sugawara, 2012) is in a extended form, and hydrophobic and hydrophilic regions are aligned alternately along the c axis.

Experimental
L-Leucylglycylglycine was purchased from Bachem Inc. Single crystals were obtained from an aqueous solution.

Refinement
H atoms were placed in calculated positions with C-H = 0.98 Å (CH 3 ), 0.99 Å (CH 2 ) or 1.00 Å (CH) and refined in a riding mode with U iso (H) = 1.2U eq (C). The other H atoms were placed in a difference Fourier map. The N-terminal H atoms were restrained to N-H = 0.87 (4) Å during refinements. The absolute configuration was known for the purchased material.

Computing details
Data collection: CrystalClear (Rigaku, 2006); cell refinement: CrystalClear (Rigaku, 2006); data reduction: CrystalClear (Rigaku, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and Yadokari-XG 2009 (Kabuto et al., 2009).    Hydrogen bonding scheme around the molecule, whose carbon atoms are colored with black. Hydrogen bonds are indicated by dotted lines. Side-chain atoms of the leucyl residues have been omitted for clarity. Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.