Mechanistic Insights into the Selective Synthesis of 4H-Pyran Derivatives On-Water Using Naturally Occurring Alginate from Sargassum muticum: Experimental and DFT Study.

The naturally occurring sodium alginate (SA) biopolymer from the Sargassum muticum (Yendo) Fensholt was employed as a green organocatalyst for the synthesis of 4H-pyran derivatives. The naturally extracted macromolecule was fully characterized using different analyses, including nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Energy Dispersive X-ray Analysis (EDX). The catalytic activity of SA was investigated in the one-pot reaction between aldehydes, malononitrile, and 1,3-dicarbonyl compounds in water at room temperature, and the corresponding 2-amino-3-cyano-4H-pyran derivatives were obtained with good to excellent yields. This organocatalyst was easily separated from the reaction mixture and reused for at least two consecutive cycles without a significant loss of its catalytic activity or selectivity. From the mechanistic point of view, density functional theory (DFT) and NCI analyses were performed for the first time to explain the regioselectivity outcomes for the synthesis of 2-amino-3-cyano-4H-pyran derivatives using SA as a green organocatalyst.

Crystal structure, spectroscopic characterization and Hirshfeld surface analysis of trans-di-aqua-[2,5-bis-(pyridin-4-yl)-1,3,4-oxa-diazole]di-thio-cyanato-nickel(II).

The reaction of 2,5-bis-(pyridin-4-yl)-1,3,4-oxa-diazole (4-pox) and thio-cyanate ions, used as co-ligand with nickel salt NiCl2·6H2O, produced the title complex, [Ni(NCS)2(C12H8N4O)2(H2O)2]. The NiII atom is located on an inversion centre and is octa-hedrally coordinated by four N atoms from two ligands and two pseudohalide ions, forming the equatorial plane. The axial positions are occupied by two O atoms of coordinated water mol-ecules. In the crystal, the mol-ecules are linked into a three-dimensional network through strong O-H⋯N hydrogen bonds. Hirshfeld surface analysis was used to investigate the inter-molecular inter-actions in the crystal packing.

Copper complexes of the 1,3,4-thiadiazole derivatives modulate antioxidant defense responses and resistance in tomato plants against fungal and bacterial diseases.

The metallic complexes µ-chloro-µ-[2,5-bis (2-pyridyl)-1,3,4-thiadiazole] aqua chlorocopper (II) dichlorocopper (II) (abbreviated 2PTH-Cu2-Cl4); aquabis [2,5-bis (2-pyridyl)-1,3,4-thiadiazole-κ2N2,N3] (trifluoromethane-sulfonato-κO) copper(II) trifluoro metrhanesulfonate (2PTH-Cu-tF) and bis[(2,5-bis(pyridine-2-yl)-1,3,4-thiadiazole-di-azido copper(II)] (2PTH-Cu-Az) were compared for their antimicrobial activities in vitro, and their aptitude to control Verticillium wilt and crown gall diseases development of tomato in the greenhouse. Results showed that the complex 2PTH-Cu-Az inhibited drastically the growth of V. dahliae in vitro. 2PTH-Cu2-Cl4 and 2PTH-Cu-tF did not display any noticeable antimicrobial activity in vitro against all of the pathogens tested. However, in planta evaluation revealed that the three complexes protected tomato against crown gall similarly. They also reduced Verticillium wilt disease severity, although the complex 2PTH-Cu-Az was the most efficient. When compared to other complexes, 2PTH-Cu-Az triggered only a weak oxidative burst as revealed by H2O2 measurement and the activity of ascorbate peroxidase and catalase. These results suggest that the superiority of 2PTH-Cu-Az against V. dahliae rely on its direct antifungal activity and its ability to modulate H2O2 accumulation.

The mononuclear nickel(II) complex bis(azido-κN)bis[2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole-κ2 N2 ,N3 ]nickel(II) protects tomato from Verticillium dahliae by inhibiting fungal growth and activating plant defences.

BACKGROUND: The antifungal properties of the nickel(II) complex bis(azido-κN)bis[2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole-κ2 N2 ,N3 ]nickel(II) [NiL2 (N3 )2 ] and its parental ligand 2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole were examined to evaluate their ability to protect tomato plants against Verticillium dahliae. Our main objectives were to determine their effects on the in vitro growth of the pathogen, and their aptitude for controlling verticillium wilt and activating plant defence responses in the greenhouse. RESULTS: NiL2 (N3 )2 exhibited in vitro an elevated inhibition of radial growth of three strains of the pathogen. According to the strain, the EC50 values ranged from 10 to 29 µg mL-1 for NiL2 (N3 )2 . In the greenhouse, it induced an elevated protection against V. dahliae when it was applied twice as foliar sprays at 50 µg mL-1 . It reduced the leaf alteration index by 85% and vessel browning by 96%. In addition, its protective ability was associated with the accumulation of H2 O2 and the activation of total phenolic content, as well as potentiation of the activity of peroxidase and polyphenol oxidase. CONCLUSION: These results demonstrated that the coordination of the ligand with Ni associated with the azide as a coligand resulted in an improvement in its biological activity by both inhibiting the growth of V. dahliae and activating plant defence responses. © 2016 Society of Chemical Industry.

Crystal structure of bis-[2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole-κ(2) N (2),N (3)]bis-(thio-cyanato-κS)copper(II).

The mononuclear title complex, [Cu(SCN)2(C12H8N4S)2], was obtained by the reaction of 2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole and potassium thio-cyanate with copper(II) chloride dihydrate. The copper cation lies on an inversion centre and displays an elongated octa-hedral coordination geometry. The equatorial positions are occupied by the N atoms of two 2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole ligands, whereas the axial positions are occupied by the S atoms of two thio-cyanate anions. The thia-diazole and the pyridyl rings linked to the metal are approximately coplanar, with a maximum deviation from the mean plane of 0.190 (2) Å. The cohesion of the crystal structure is ensured by weak C-H⋯N hydrogen bonds and π-π inter-actions between parallel pyridyl rings of neighbouring mol-ecules [centroid-to-centroid distance = 3.663 (2) Å], leading to a three-dimensional network.

Induced Resistance in Tomato Plants against Verticillium Wilt by the Binuclear Nickel Coordination Complex of the Ligand 2,5-Bis(pyridin-2-yl)-1,3,4-thiadiazole.

Verticillium wilt caused by Verticillium dahliae is a major limiting factor for tomato production. The objective of this study was to evaluate the effectiveness of ligand 2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole (L) and its complex bis[µ-2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole-κ(4)N(2),N(3):N(4),N(5)]bis[dihydrato-κO)nickel(II)] as activators of plant defenses in controlling Verticillium wilt. In the greenhouse, they protected tomato plants against V. dahliae when they were applied twice as foliar sprays at 100 µg mL(-1). A synergistic effect was observed between the ligand L and the transition metal Ni, with disease incidence reduced by 38% with L and 57% with Ni2L2. Verticillium wilt foliar symptoms and vascular browning index were reduced by 82% for L and 95% for Ni2L2. This protection ability was associated with the induction of an oxidative burst and the activation of the total phenolic content as well as potentiation of the activity of peroxidase and polyphenol oxidase. These results demonstrated that L and Ni2L2 can be considered as new activators of plant defense responses.

Crystal structure of (Z)-ethyl 3-[2-(5-methyl-7-nitro-1H-indole-2-carbon-yl)hydrazinyl-idene]butano-ate.

The reaction of 5-methyl-7-nitro-1H-indole-2-carbohydrazide with ethyl aceto-acetate yielded the title mol-ecule, C16H18N4O5, in which the indole ring is almost planar, with the greatest deviation from the mean plane being 0.006 (2) Å. The nine atoms of the indole ring are almost perpendicular to the mean plane through the ethyl acetate group, as indicated by the dihedral angle of 87.02 (4)° between them. In the crystal, centrosymmetric supra-molecular dimers are formed via N-H⋯O hydrogen bonds and eight-membered amide {⋯HNCO}2 synthons. These are consolidated into a three-dimensional architecture by C-H⋯O contacts, and by π-π inter-actions between six-membered rings [inter-centroid distance = 3.499 (2) Å].

Crystal structure of bis-(azido-κN)bis[2,5-bis(pyridin-2-yl)-1,3,4-thia-diazole-κ(2) N (2),N (3)]cobalt(II).

In the mononuclear title complex, [Co(N3)2(C12H8N4S)2], the cobalt(II) atom is located on an inversion centre and displays an axially weakly compressed octa-hedral coordination geometry. The equatorial positions are occupied by the N atoms of two 2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole ligands, whereas the axial positions are occupied by N atoms of the azide anions. The thia-diazole and pyridine rings linked to the metal are almost coplanar, with a maximum deviation from the mean plane of 0.0273 (16) Å. The cohesion of the crystal is ensured by weak C-H⋯N hydrogen bonds and by π-π inter-actions between pyridine rings [inter-centroid distance = 3.6356 (11) Å], forming a layered arrangement parallel to (001). The structure of the title compound is isotypic with that of the analogous nickel(II) complex [Laachir et al. (2013 ▶). Acta Cryst. E69, m351-m352].

Crystal structure of bis-(azido-κN)bis-[2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole-κ(2) N (2),N (3)]nickel(II).

Reaction of 2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole and sodium azide with nickel(II) triflate yielded the mononuclear title complex, [Ni(N3)2(C12H8N4S)2]. The Ni(II) ion is located on a centre of symmetry and is octa-hedrally coordinated by four N atoms of the two bidentate heterocyclic ligands in the equatorial plane. The axial positions are occupied by the N atoms of two almost linear azide ions [N-N-N = 178.8 (2)°]. The thia-diazole and pyridine rings of the heterocyclic ligand are almost coplanar, with a maximum deviation from the mean plane of 0.0802 (9) Å. The cohesion of the crystal structure is ensured by π-π inter-actions between parallel pyridine rings of neighbouring mol-ecules [centroid-to-centroid distance = 3.6413 (14) Å], leading to a layered arrangement of the mol-ecules parallel to (001).

Bis[µ-2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole-κ(4) N (2),N (3):N (4),N (5)]bis-[(nitrato-κO)silver(I)] tetra-hydrate.

The self-assembly of an angular 2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole ligand (L) with silver nitrate (AgNO3) produced a new dinuclear silver(I) coordination complex, [Ag2(C12H8N4S)2(NO3)2]·4H2O, which crystallizes with two Ag atoms bridged by two L ligands. The Ag atom is surrounded by four N atoms of L and by one O from the nitrate anion defining a distorted square pyramid. The atoms comprising the dication are nearly coplanar, with an r.m.s. deviation of 0.1997 Å. Mol-ecules are linked by C-H⋯O and O-H⋯O hydrogen bonds through nitrate anions and water mol-ecules, forming a two-dimensional porous network. The overall structure involves stacking of Ag complex layers along the b axis. The cohesion in the three-dimensional architecture is ensured by O⋯Ag inter-actions.