Nirmal Kumar Das

Recognition of acids involved in Krebs cycle by 9-anthrylmethyl-di(6-acetylamino-2-picolyl)amine: a case of selective fluorescence enhancement for maleic acid

Anthracene coupled di(6-acetylamino-2-picolyl)amine, 1 is designed and synthesized for selective sensing of maleic acid among the series of carboxylic acids involved in the Krebs cycle. The interaction of sensor 1 with acids is examined using 1H NMR, UV-vis and fluorescence spectroscopic methods. In UV-vis, 1 shows six isosbestic points on titration with maleic acid and this result is similar to the result obtained with trifluoroacetic acid (TFA). Sensor 1 shows significant fluorescence enhancement upon treatment with maleic acid with red shift (Δλ = 10 nm) in the λmax whereas other acids show very marginal change. Significant amide shifts in 1 : 1 1H NMR and appreciable binding constant values of sensor 1 with monotetrabutylamonium salts of guest acids and also with tetrabutylammonium salts of guest acids by fluorescence suggest the binding affinity towards the anions. In the solid state, 1 shows two polymorphs in the same space group and in co-crystal A (1 with fumaric acid), aliphatic tertiary nitrogen of 1 is protonated and this proton forms two intramolecular hydrogen bonds with nitrogen of pyridine rings. Thus pyridine rings of 1 remain inert towards intermolecular hydrogen bonding to fumaric acid and only amide hydrogens of the sensor 1 are available for intermolecular hydrogen bonding and form a polymeric supramolecular network.

Advanced reagent for thionation: Rapid synthesis of primary thioamides from nitriles at room temperature

A series of aliphatic, aromatic and heterocyclic nitriles is thionated to give the corresponding thioamides in excellent yield using a newly developed reagent system of phosphorus pentasulfide and sodium sulfite or sodium dithionite at room temperature in a very short time (5–25 minutes). The microwave procedure of the reactions also is reported to afford the same products.

Ethylene spacer-linked bis-acetamidopyridine for dicarboxylic acid recognition and polymeric new wave-like anti-perpendicular arrangement of a host–guest in the solid state

In this paper, 1,2-bis(2-acetamido-6-pyridyl)ethane, receptor 1, having an ethylene spacer is reported to recognise dicarboxylic acids. The binding study in the solution phase is carried out using 1H NMR (1:1) and UV–vis experiments and in the solid phase by single-crystal X-ray analysis. In 1H NMR, the downfield shifts of specific amide protons of receptor 1 in 1:1 complexes of receptor and guest diacids, and in the UV–vis experiment, the appearance of an isosbestic point as well as significant binding constants are observed, which thus unambiguously support the complexation of receptor 1 with dicarboxylic acids in solution. Receptor 2, simple 2-acetamido-6-methylpyridine, has lower binding constants than receptor 1 due to cooperative binding of two pyridine amide groups with two acid groups of diacids. In the solid phase, the ditopic receptor 1 shows a grid-like polymeric hydrogen-bonded network that changes to a polymeric wave-like 1:1 anti-perpendicular network instead of the syn–syn polymeric 1:1 (Goswami, S.; Dey, S.; Fun, H.-K.; Anjum, S.; Rahman, A.-U. Tetrahedron Lett. 2005, 46, 7187–7191), anti–anti polymeric 1:1 (Goswami, S.; Jana, S.; Dey, S.; Razak, I.A.; Fun, H.-K. Supramol. Chem. 2006 , 18, 571–574; Goswami, S.; Jana, S.; Fun, H.-K. Cryst. Eng. Comm. 2008, 10, 507–517; Goswami, S.; Jana, S.; Dey, S.; Sen, D.; Fun, H.-K.; Chantrapromma, S. Tetrahedron 2008, 64, 6426–6433), syn–syn 2:2 (Karle, I.L.; Ranganathan, D.; Haridas, V. J. Am. Chem. Soc. 1997 , 119, 2777–2783) or top–bottom-bound 1:1 (Garcia-Tellado, F.; Goswami, S.; Chang, S.K.; Geib, S.J.; Hamilton, A.D. J. Am. Chem. Soc. 1990 , 112, 7393–7394) co-crystals.

Triselenium Dicyanide (TSD) as a New Cyanation Reagent: Synthesis of Cyano Pterins and Quinoxalines Along with Library of Cyano N-Heterocyclic Compounds

Abstract Triselenium dicynide (TSD) has been reported for the first time to be a novel cyanation reagent for the microwave-assisted one-pot synthesis of a series of various types of cyano N-heterocycles such as pterin, deazapterin, quinoxaline, naphthyridine, and pyridine in good yields.

2-(Pyrene-1-yl)-1,3-dithiane

In the title compound, C20H16S2, the pyrene ring is planar [maximum deviation 0.0144 (15) Å] and the dithiane ring adopts a chair conformation. The crystal packing is stabilized by C—H⋯π interactions. An intramolecular C—H⋯S hydrogen bond generates an S(5) ring motif.

2,7-Dimethyl-1,8-naphthyridine.

The asymmetric unit of the title compound, C10H10N2, contains one half-molecule with the two shared C atoms lying on a twofold rotation axis. The 1,8-naphthyridine is almost planar with a dihedral angle of 0.42 (3)° between the fused pyridine rings. In the crystal, molecules are linked into infinite chains along the c axis by intermolecular C—H⋯N hydrogen bonds, generating R 2 2(8) ring motifs. In addition, the crystal structure is further stabilized by C—H⋯π interactions.

A case study of solid state inhibition lock opening of pyridine N-oxide in dicarboxylic acid recognition

An ethylene-linked mixed pyridine diamide receptor 1 is synthesised to study the binding with dicarboxylic acid in solid phase. In 1H NMR, the amide proton adjacent to pyridine N-oxide shows almost negligible shift, which suggests the non-participation of the amide proton for acid binding in solution. However, in solid phase (X-ray, IR), we have found significant role of this amide proton in binding.

N-(6-{2-[6-(2,2-Dimethyl-propanamido)-2-pyrid-yl]eth-yl}-2-pyrid-yl)-2,2-dimethyl-propanamide.

The title compound, C22H30N4O2, lies about a crystallographic inversion center. The whole molecule is disordered over two positions with a refined occupancy ratio of 0.636 (10):0.364 (10). The pyridine rings are approximately planar, with maximum deviations of 0.033 (10) and 0.063 (17) Å for the major and minor components, respectively. The mean planes of the pyridine rings form dihedral angles of 17 (2)° in the major component and 18 (2)° in the minor component with the respective formamide groups attached to them. In the crystal packing, intermolecular N—H⋯O and C—H⋯O hydrogen bonds link the molecules into two-dimensional networks parallel to the ab plane.

N-(6-Bromo­meth­yl-2-pyrid­yl)acetamide

The title acetamide compound, C8H9BrN2O, crystallizes with three crystallographically independent molecules (A, B and C) in the asymmetric unit. In molecule A, the mean plane through the acetamide unit is inclined at a dihedral angle of 4.40 (11)° with respect to the pyridine ring [10.31 (12) and 2.27 (11)°, respectively, for molecules B and C]. In the crystal structure, molecules are interconnected into sheets parallel to the ac plane by N—H⋯O, C—H⋯Br, C—H⋯O and C—H⋯N hydrogen bonds. The structure is further stabilized by weak intermolecular C—H⋯π interactions.

Quinoxaline-2-carbonitrile

In the title compound, C9H5N3, the quinoxaline ring is essentially planar, with a maximum deviation of 0.012 (1) Å. Short intermolecular distances between the centroids of the 2,3-dihydropyrazine and benzene rings [3.6490 (5) Å] indicate the existence of π⋯π interactions. In the crystal packing, the molecules are linked via two pairs of intermolecular C—H⋯N interactions, forming R 2 2 (8) and R 2 2 (10) ring motifs; these molecules are further linked into a two-dimensional network parallel to (1 0 2) via another C–H⋯N interaction.