l‐Phenyl­alanyl‐l‐isoleucine 0.88‐hydrate

The asymmetric unit in the crystal structure of the title compound, C₁₅H₂₂N₂O₃·0.88H₂O, contains two peptide mol­ecules with completely different conformations. The structure is divided into hydro­phobic and hydro­philic layers, with channels of water mol­ecules at the layer interface.     

l‐Phenyl­alanyl‐l‐alanine dihydrate

A new type of molecular arrangement for dipeptides is observed in the crystal structure of l ‐phenyl­alanyl‐l ‐alanine dihydrate, C₁₂H₁₆N₂O₃·2H₂O. Two l ‐Phe and two l ‐Ala side chains aggregate into large hydro­phobic columns within a three‐dimensional hydrogen‐bond network.     

l‐Isoleucyl‐l‐serine 0.33‐hydrate,l‐phenyl­alanyl‐l‐serine and l‐methionyl‐l‐serine 0.34‐hydrate

The structures of the title dipeptides, C₉H₁₈N₂O₄·0.33H₂O, C₁₂H₁₆N₂O₄ and C₈H₁₆N₂O₄S·0.34H₂O, complete a series of investigations focused on l ‐Xaa‐l ‐serine peptides, where Xaa is a hydro­phobic residue. All three structures are divided into hydro­philic and hydro­phobic layers. The hydro­philic layers are thin for l ‐phenyl­alanyl‐l ‐serine, rendered possible by an unusual peptide conformation, and thick for l ‐isoleucyl‐l ‐serine and l ‐methionyl‐l ‐serine, which include cocrystallized water mol­ecules on the twofold axes.     

Water polymers in l‐alanyl‐l‐methionine hemihydrate

The side chains of l ‐alanyl‐l ‐me­thionine hemihydrate, C₈H₁₆N₂O₃S·0.5H₂O, form hydro­phobic columns within a three‐dimensional hydrogen‐bond network that includes extended polymers of cocrystallized water mol­ecules and C^α—H⋯S interactions.     

An NH3+⃛phenyl interaction in l‐­phenyl­alanyl‐l‐valine

One of the amino H atoms of l ‐phenyl­alanyl‐l ‐valine, C₁₄H₂₀N₂O₃, participates in a rare secondary interaction in being accepted by the aromatic ring of the phenyl­alanine side chain. The phenyl group is also a donor in a weak hydrogen bond to the peptide carbonyl group.     

N‐(l‐2‐Aminobutyryl)‐l‐alanine and 2‐(l‐alanylamino)‐l‐butyric acid 0.33‐hydrate

The crystal structure of N‐(l ‐2‐amino­butyryl)‐l ‐alanine, C₇H₁₄N₂O₃, is closely related to the structure of l ‐alanyl‐l ‐alanine, both being tetragonal, while the retro‐analogue 2‐(l ‐alanyl­amino)‐l ‐butyric acid 0.33‐hydrate, C₇H₁₄N₂O₃·­0.33H₂O, forms a new type of molecular columnar structure with three peptide mol­ecules in the asymmetric unit.     

l‐Phenyl­alanine–4‐nitro­phenol (1/1)

In the 1:1 adduct formed between l ‐phenyl­alanine and 4‐nitro­phenol [alternative IUPAC name: (2S)‐2‐ammonio‐3‐phenyl­propanoate–4‐nitro­phenol (1/1)], C₉H₁₁NO₂·C₆H₅NO₃, the l ‐phenyl­alanine mol­ecule is in the zwitterionic state. The overall structure is stabilized via strong hydrogen bonding between polar zones and van der Waals inter­actions between non‐polar zones, which alternate with the polar zones.     

l‐Isoleucyl‐l‐asparagine 1.094‐hydrate: a hybrid hydrogen‐bonding pattern

The title compound, C₁₀H₂₀N₃O₄·1.094H₂O, crystallizes with two dipeptide molecules in the asymmetric unit, each participating in two head‐to‐tail chains with hydrogen bonds between the terminal amino and carboxylate groups. As with many other dipeptides, the resulting structure is divided into distinct layers, but as the amide groups of the two peptide molecules participate in different types of interaction, the observed hydrogen bonds within a peptide main‐chain layer (as distinct from the side‐chain/solvent regions) cannot adapt to any of the four basic patterns observed previously for dipeptides. Instead, a rare hybrid pattern is formed.     

Two modifications of l‐alanyl‐l‐tyrosyl‐l‐alanine with different solvent mol­ecules in the crystal lattice

The low‐temperature crystal and mol­ecular structure analyses of two modifications of l ‐alanyl‐l ‐tyrosyl‐l ‐alanine with water, C₁₅H₂₁N₃O₅·2.63H₂O [(I), at 9 K], and ethanol, C₁₅H₂₁N₃O₅·C₂H₅O [(II), at 20 K], solvent mol­ecules in the crystal lattice show that the overall conformations of both modifications of the title tripeptide are practically the same. Moreover, despite the presence of different solvent mol­ecules in the crystal lattice, the specific inter­molecular inter­actions characteristic for individual tripeptide mol­ecules of (I) and (II) are conserved. The crystal packing of the two modifications of Ala‐Tyr‐Ala differ from each other only in the solvent region. The tight arrangements of tripeptide mol­ecules seem to be responsible for similar displacement parameters for all non‐H atoms, despite the different distances from the mol­ecular centre of mass. Comparison of the displacement parameters between the room‐ and low‐temperature structures shows that an average U_eq value decrease of about 80% takes place at 9 K [for (I)] and 20 K [for (II)] with respect to room temperature.     

2‐Phenyl­malon­amide

In the title compound, C₉H₁₀N₂O₂, the amide groups are rotated out of the C(ONH₂)—C(HPh)—C(ONH₂) plane by ca 25–47° and the phenyl ring is almost perpendicular to this plane. The crystal structure is stabilized by intra‐ and intermolecular N—H?O hydrogen bonds.     

2‐Phenyl­malonpiperadide and 2‐phenyl­malonmorpholide

The structures of 2‐phenyl­malonpiperadide [systematic name: 2‐phenyl‐1,3‐bis­(piperidin‐1‐yl)­propane‐1,3‐dione, C₁₉H₂₆N₂O₂, (I)] and 2‐phenyl­malonmorpholide [systematic name: 1,3‐dimorpholino‐2‐phenyl­propane‐1,3‐dione, C₁₇H₂₂N₂O₄, (II)], have been determined and both their molecular conformations and packing arrangements compared. Although chemically similar, compounds (I) and (II) exhibit different molecular conformations. The only general conformational similarities are that their respective carbonyl groups are orientated in the same direction and the heterocyclic rings exist in the chair arrangement. General similarities in the packing arrangements arise due to both compounds having the same space group (P2₁2₁2₁) and a similar alignment of their phenyl‐substituted backbone with respect to the c axis. Similar C—H⋯O hydrogen‐bonding associations are listed for the carbonyl O atoms, while only one of the morpholine O atoms is involved in any such association.     

4‐Phenyl­butan‐2‐one semi­carbazone

The title compound, C₁₁H₁₅N₃O, crystallizes with two mol­ecules in the asymmetric unit, which are held together by an extended network of hydrogen bonds. It is remarkable that only five of the six theoretically possible hydrogen bonds are formed.     

The monohydrates of the four polar dipeptides l‐seryl‐l‐asparagine,l‐seryl‐l‐tyrosine,l‐tryptophanyl‐l‐serine and l‐tyrosyl‐l‐tryptophan

The crystal structures of the four dipeptides l ‐seryl‐l ‐asparagine monohydrate, C₇H₁₃N₃O₅·H₂O, l ‐seryl‐l ‐tyrosine monohydrate, C₁₂H₁₆N₂O₅·H₂O, l ‐tryptophanyl‐l ‐serine monohydrate, C₁₄H₁₇N₃O₄·H₂O, and l ‐tyrosyl‐l ‐tryptophan monohydrate, C₂₀H₂₁N₃O₄·H₂O, are dominated by extensive hydrogen‐bonding networks that include cocrystallized solvent water molecules. Side‐chain conformations are discussed on the basis of previous observations in dipeptides. These four dipeptide structures greatly expand our knowledge on dipeptides incorporating polar residues such as serine, asparagine, threonine, tyrosine and tryptophan.     

l‐Histidyl‐l‐serine 3.7‐hydrate: water channels in the crystal structure of a polar dipeptide

Dipeptides may form nanotubular structures with pore diameters in the range 3.2–10 Å. These compounds normally contain at least one and usually two hydrophobic residues, but l ‐His‐l ‐Ser hydrate, C₉H₁₄N₄O₄·3.7H₂O, with two hydrophilic residues, forms large polar channels filled with ordered as well as disordered water molecules.     

Conformation and structure of bis­(glycyl‐l‐aspartic acid) oxalate 0.4‐hydrate

The title bis­(glycyl‐l ‐aspartic acid) oxalate complex {systematic name: bis­[2‐(2‐ammonio­acetamido)butane­dioic acid] oxalate 0.4‐hydrate}, 2C₆H₁₁N₂O₅⁺·C₂O₄²⁻·4H₂O, crystallizes in a triclinic space group with the planar peptide unit in a trans conformation. The asymmetric unit consists of two glycyl‐l ‐aspartic acid mol­ecules with positively charged amino groups and neutral carboxyl groups, and an oxalate dianion. The twist around the C—Cα bond indicates that both the peptide mol­ecules adopt extended conformations, while the twist around the N—Cα bond shows that one has a folded and the other a semi‐extended state. The present complex can be described as an inclusion compound with the dipeptide mol­ecule as the host and the oxalate anion as the guest. The usual head‐to‐tail sequence of aggregation is not observed in this complex, as is also the case with the glycyl‐l ‐aspartic acid dihydrate mol­ecule. The study of aggregation and inter­action patterns in binary systems is the first step towards understanding more complex phenomena. This further leads to results that are of general interest in bimolecular aggregation.     

Alaninyl­tryptophan hydrate,glycyl­tryptophan dihydrate and tryptophyl­glycine hydrate

The crystal structures of the title tryptophan‐containing dipeptides, C₁₄H₁₇N₃O₃·H₂O, (I), C₁₃H₁₅N₃O₃·2H₂O, (II), and C₁₃H₁₅N₃O₃·H₂O, (III), respectively, contain at least one water mol­ecule of solvation. As a result, the crystal packing of these compounds is composed of regions of water‐mediated hydrogen bonding and tryptophan ring‐to‐ring stacking separated by the length of the mol­ecule. The tryptophan rings stack in a continuous layer that, when viewed edge‐on from the outermost part of the tryptophan ring, exhibits a herring‐bone motif. However, owing to the lack of direct overlap of adjacent rings, no degree of π contact or long‐range delocalization of ring systems is possible here. The overall molecular conformations of (I) and (III) contain a folding of one peptide over the other, such that a minimum in molecular volume occurs without any intramolecular hydrogen bonding. In these two dipeptides, extensive hydrogen bonding is observed to and from the single water mol­ecule of solvation. In the crystal structure of (II), however, an extended mol­ecule conformation complements a more extensive hydrogen‐bonding scheme involving two water mol­ecules of solvation per dipeptide.     

Strontium d‐glutamate hexa­hydrate and strontium di(hydrogen l‐glutamate) penta­hydrate

[Sr(C₅H₇NO₄)]·6H₂O, (I), and [Sr(C₅H₈NO₄)₂]·5H₂O, (II), both crystallize with similar strontium–glutamate–water layers. In (I), the neutral layers are connected through hydrogen bonds by water mol­ecules, while in (II), the positively charged layers are connected through hydrogen bonds and electrostatic inter­actions by inter­leaving layers of hydrogen glutamate anions and water mol­ecules.     

l‐Alanylglycyl‐l‐alanine monohydrate at 20 K

The X‐ray crystal structure of the title compound, C₈H₁₅N₃O₄·H₂O, at 20 K (space group P2₁) reveals that the mol­ecular conformation of the tripeptide is remarkably different from the water‐free form (space group P2₁2₁2₁) reported previously [Padiyar & Seshadri (1996), Acta Cryst. C 52 , 1693–1695].     

catena‐Poly[copper(II)‐μ‐l‐tyrosyl‐l‐leucinato]

In the title compound, [Cu(C₁₅H₂₀N₂O₄)]_n, the copper(II) coordination is square planar. The anionic l ‐tyrosyl‐l ‐leucinate ligand binds in an N,N′,O‐tridentate mode to one Cu^II cation on one side and in an O‐monodentate mode to a second Cu^II cation on the other side, thus defining –Cu—O—C—O—Cu′– chains which run along the a axis. These chains are held together by a strong hydrogen bond involving the hydroxy H atom.     

2‐(Phenyl­amino­methyl­idene)­cyclo­hexane‐1,3‐dione

In the title compound, C₁₃H₁₃NO₂, there is polarization of π‐electron density from the amine N atom to the acceptor carbonyl groups: as a result, the mol­ecule exists predominantly in an azomethino‐1,3‐diketone tautomeric form. There is crystallographic evidence that the phenyl ring, although roughly coplanar with the rest of the mol­ecule, is deconjugated with the adjacent π system of the mol­ecule. The cyclo­hexane ring adopts an unsymmetrical half‐chair conformation and converts between two inversion‐related conformers. The mol­ecule is stabilized by an intramolecular hydrogen bond, while the intermolecular packing is dominated by a number of short C—H⋯O contacts.