1. Two N-(2-phenylethyl)nitroaniline derivatives as precursors for slow and sustained nitric oxide release agents
Alec R Badour, John A Wisniewski, Dillip K Mohanty, Philip J Squattrito Acta Crystallogr C Struct Chem. 2016 May 1;72(Pt 5):405-10. doi: 10.1107/S2053229616005763. Epub 2016 Apr 13.
Notwithstanding its simple structure, the chemistry of nitric oxide (NO) is complex. As a radical, NO is highly reactive. NO also has profound effects on the cardiovascular system. In order to regulate NO levels, direct therapeutic interventions include the development of numerous NO donors. Most of these donors release NO in a single high-concentration burst, which is deleterious. N-Nitrosated secondary amines release NO in a slow, sustained, and rate-tunable manner. Two new precursors to sustained NO-releasing materials have been characterized. N-[2-(3,4-Dimethoxyphenyl)ethyl]-2,4-dinitroaniline, C16H17N3O6, (I), crystallizes with one independent molecule in the asymmetric unit. The adjacent amine and nitro groups form an intramolecular N-H...O hydrogen bond. The anti conformation about the phenylethyl-to-aniline C-N bond leads to the planes of the arene and aniline rings being approximately perpendicular. Molecules are linked into dimers by weak intermolecular N-H...O hydrogen bonds such that each amine H atom participates in a three-center interaction with two nitro O atoms. The dimers pack so that the arene rings of adjacent molecules are not parallel and π-π interactions do not appear to be favored. N-(4-Methylsulfonyl-2-nitrophenyl)-L-phenylalanine, C16H16N2O6S, (II), with an optically active center, also crystallizes with one unique molecule in the asymmetric unit. The L enantiomer was established via the configuration of the starting material and was confirmed by refinement of the Flack parameter. As in (I), there is an intramolecular N-H...O hydrogen bond between adjacent amine and nitro groups. The conformation of the molecule is such that the arene rings display a dihedral angle of ca 60°. Unlike (I), molecules are not linked via intermolecular N-H...O hydrogen bonds. Rather, the carboxylic acid H atom forms a classic, approximately linear, O-H...O hydrogen bond with a sulfone O atom. Pairs of molecules related by twofold rotation axes are linked into dimers by two such interactions. The packing pattern features a zigzag arrangement of the arene rings without apparent π-π interactions. These structures are compared with reported analogues, revealing significant differences in molecular conformation, intermolecular interactions, and packing that result from modest changes in functional groups. The structures are discussed in terms of potential NO-release capability.
2. Supramolecular architectures of N-acetyl-L-proline monohydrate and N-benzyl-L-proline
P Rajalakshmi, N Srinivasan, R V Krishnakumar, Ibrahim Abdul Razak, Mohd Mustaqim Rosli Acta Crystallogr C. 2013 Nov;69(Pt 11):1390-6. doi: 10.1107/S010827011302581X. Epub 2013 Oct 5.
The title compounds, N-acetyl-L-proline monohydrate, C7H11NO3·H2O, (I), and N-benzyl-L-proline, C12H15NO2, (II), crystallize in the monoclinic space group P21 with Z' = 1 and Z' = 2, respectively. The conformation of C(γ) with respect to the carboxylic acid group in (I) is C(γ)-exo or UP pucker, with the pyrrolidine ring twisted, while in (II), it is C(γ)-endo or DOWN, with the pyrrolidine ring assuming an envelope conformation. The crystal packing interactions in (I) are composed of two substructures, one characterized by an R6(6)(24) motif through O-H...O hydrogen bonds and the other by an R4(4)(23) ring through C-H...O interactions. In (II), the crystal packing interactions consist of N-H...O and C-H...O hydrogen bonds. Proline (Pro) exists in its neutral form in (I) and is zwitterionic in (II). This difference in the ionization states of Pro is manifested through the absence of N-H...O and presence of O-H...O interactions in (I), and the presence of N-H...O and absence of O-H...O hydrogen bonds in (II). While C-H...O interactions are present in both (I) and (II), the geometry of the synthons formed by them and their mode of participation in intermolecular interactions is different. Though the title compounds differ significantly in terms of modifications in the Pro skeleton, the differences in their supramolecular structures may also be viewed as a result of the molecular recognition facilitated by the presence of a solvent water molecule in (I) and the zwitterionic state of the amino acid in (II).
3. DL-3-aminoisobutyric acid monohydrate
A J Dobson, R E Gerkin Acta Crystallogr C. 1998 Jul 15;54 ( Pt 7):972-4. doi: 10.1107/s0108270198001310.
The title acid, 3-amino-2-methylpropanoic acid monohydrate, C4H9NO2.H2O, crystallized in the centrosymmetric space group Pbca in the zwitterionic form. The three H atoms on N, which are involved in hydrogen bonding, are ordered. The three intermolecular N-H...O hydrogen bonds have N...O distances ranging from 2.758 (2) to 2.809 (2) A and N-H...O angles ranging from 149 (2) to 171 (1) degrees. The two intermolecular O-H...O hydrogen bonds have O...O distances 2.739 (2) and 2.755 (2) A, and O-H...O angles 170 (2) and 175 (2) degrees. Each acid molecule and its associated water molecule are directly hydrogen bonded to five acid molecules and two water molecules; the structure comprises two subsets of molecules which are not cross-linked by these hydrogen bonds. Through basic second-level graphs, approximately two-thirds of the hydrogen-bonding patterns are finite and one-third are chains; there is a single ring pattern, which occurs about a center of symmetry.
