Sulphur(lone pair)…π interactions with FAD in flavoenzymes

The interactions of π-systems with lone-pairs of electrons are known and have been described in biological systems, involving lone-pairs derived from metals, metalloids, sulphur, oxygen and nitrogen. This study describes a bibliographic survey of the disulphide-bound sulphur(lonepair) interactions with -systems residing in the flavin adenine dinucleotide (FAD) cofactor oxidoreductase enzymes (flavoenzymes). Thus, of the 172 oxidoreductase enzymes evaluated for gamma-S(lone pair)…π(FAD) interactions, 96 proteins (56%) exhibited these interactions corresponding; 61% of 350 the constituent monomers featured at least one gamma-S(lone pair)…π(FAD) interaction. Two main points of association between the S(lone pair) and the isoalloxazine moiety of FAD were identified, namely at the centroid of the bond linking the uracil and pyrazine rings (60% ), and the centroid of the uracil ring (37%). Reflecting the nature of the secondary structure in three prominent classes of oxidoreductase enzymes: glutathione disulphide reductases (GR; 21 proteins), trypanothione disulphide reductases (TR, 14) and sulfhydryl oxidases (SOX, 22), the approach of the gamma-S(lone-pair) to the FAD residue was to the si-face of the isoalloxazine ring system, i.e. to the opposite side as the carbonyl residue, for all GR and TR examples, and to the re-face for all SOX examples. Finally, the attractive nature of the gamma-S(lone pair)…π(FAD) interactions was confirmed qualitatively by an examination of the non-covalent interaction plots

N′-[(2E)-3-Phenyl­prop-2-eno­yl]benzo­hydrazide

In the title compound, C16H14N2O2, the conformation about the C=C bond is E, and the two amide groups are effectively orthogonal [the C—N—N—C torsion angle is 104.5 (2)°]. In the crystal structure, the amide groups groups associate via N–H⋯O hydrogen bonding, forming supra­molecular tapes with undulating topology along the c-axis direction

N-(2-Chloro­eth­yl)pyrazine-2-carboxamide

In the title mol­ecule, C7H8ClN3O, the pyrazine and amide groups are almost co-planar [N—C—C—N torsion angle = −2.4 (2) °], a conformation stabilized by an intra­molecular N—H⋯N hydrogen bond. The chloro­ethyl group lies out of the plane [N—C—C—Cl = −65.06 (17) °]. In the crystal, the presence of N—H⋯N hydrogen bonds leads to the formation of a C(6) supra­molecular chain along the b axis. The carbonyl-O atom accepts two C—H⋯O inter­actions. These, plus Cl⋯Cl short contacts [3.3653 (6) Å], consolidate the packing of the chains in the crystal

5-(3-Nitro­benz­yl)-1,3,4-thia­diazol-2-amine

In the title mol­ecule, C9H8N4O2S, the dihedral angle between the thia­diazole and benzene rings is 73.92 (8)° and the thia­diazole group S atom is orientated towards the benzene ring, the central S—C—C—C torsion angle being 45.44 (18)°. In the crystal, supra­molecular tapes mediated by N—H⋯N hydrogen bonds and comprising alternating eight-membered {⋯HNCN}2 and 10-membered {⋯HNH⋯NN}2 synthons are formed along [010]. The tapes are consolidated into a three-dimensional network by a combination of C—H⋯O, C—H⋯S and C—H⋯π inter­action

(2E)-N-(3,5-Dibromo-4-methoxy­phen­yl)-2-(hydroxy­imino)acetamide

The title compound, C9H8Br2N2O3, is planar (r.m.s. deviation = 0.030 Å) with the exception of the terminal methyl group which lies out of the plane [1.219 (3) Å]. The conformation about the C=N double bond [1.268 (3) Å] is E. An intra­molecular N—H⋯N hydrogen bond occurs. Linear supra­molecular chains along the b axis mediated by O—H⋯O hydrogen-bonding inter­actions feature in the crystal structure. These chains are also stabilized by weak C—H⋯N contacts

[(2R,3S,6S)-3-Acet­yloxy-6-(1-phenyl-1H-1,2,3-triazol-4-yl)-3,6-dihydro-2H-pyran-2-yl]methyl acetate

In the title compound, C18H19N3O5, the 3,6-dihydro-2H-pyran ring adopts a half-chair, distorted towards a half-boat, conformation with Q T = 0.5276(14) Å. The benzene ring is twisted out of the place of the triazole ring [dihedral angle = 23.54 (8)°]. In the crystal, supra­molecular layers in the ac plane are formed through C—H⋯O and C—H⋯π(triazole) inter­actions. These stack along the b axis being connected by C—H⋯N contacts

(2E)-N′-[(E)-4-Chloro­benzyl­idene]-3-phenyl­prop-2-enohydrazide monohydrate

The conformation about each of the imine and ethene bonds in the title hydrazide hydrate, C16H13ClN2O·H2O, is E. The hydrazide mol­ecule is approximately planar (r.m.s. deviation of the 20 non-H atoms = 0.172 Å). The most significant twist occurs about the ethene bond [C—C=C—C = 164.1 (5)°] and the dihedral angle formed between the benzene rings is 5.3 (2)°]. In the crystal, the presence of N—H⋯Ow and O—H⋯Oc (× 2; w = water and c = carbon­yl) hydrogen bonds leads to a supra­molecular array in the bc plane

2-Methyl-4-(4-nitrophenyl)but-3-yn-2-ol: crystal structure, Hirshfeld surface analysis and computational chemistry study

The di-substituted acetylene residue in the title compound, C11H11NO3, is capped at either end by di-methylhydroxy and 4-nitrobenzene groups; the nitro substituent is close to co-planar with the ring to which it is attached [dihedral angle = 9.4 (3)]. The most prominent feature of the molecular packing is the formation, via hydroxy-O—HO(hydroxy) hydrogen bonds, of hexameric clusters about a site of symmetry 3. The aggregates are sustained by 12- membered {OH}6 synthons and have the shape of a flattened chair. The clusters are connected into a three-dimensional architecture by benzene-C—HO(nitro) interactions, involving both nitro-O atoms. The aforementioned interactions are readily identified in the calculated Hirshfeld surface. Computational chemistry indicates there is a significant energy, primarily electrostatic in nature, associated with the hydroxy-O—HO(hydroxy) hydrogen bonds. Dispersion forces are more important in the other identified but, weaker intermolecular contacts

(2E)-N′-Benzoyl-3-(4-nitro­phen­yl)prop-2-enohydrazide

In the title compound, C16H13N3O4, the dihedral angle between the terminal benzene rings is 14.02 (7)°. The carbonyl groups are anti with respect to each other, which facilitates their participation in the formation of supra­molecular chains. Each side of the –C(=O)N(H)N(H)C(=O)– residue associates with a centrosymmetrically related mol­ecule, resulting in the formation of essentially flat ten-membered {⋯O=CNN(H)}2 synthons. The resultant chains are further consolidated in the crystal structure via C—H⋯O contacts