Anita Hazra

Recognition of Carboxylate Anions and Carboxylic Acids by Selenium-Based New Chromogenic Fluorescent Sensor: A Remarkable Fluorescence Enhancement of Hindered Carboxylates

A selenium metal-based new fluorescence sensor 5-pivaloylamino-1,2,5-selenodiazolo[3,4-d]pyrimidin-7-(6H)-one (receptor 1) has been reported for the recognition of monocarboxylic acids and carboxylate anions both by UV-vis and fluorescence methods. Receptor 1 recognizes carboxylate anions more than monocarboxylic acids and it is a selective sensor for carboxylates with specially hindered carboxylate anions. The changes of fluorescence intensity are remarkably enhanced with red shift in presence of bulky carboxylate anions. The X-ray crystal structure of receptor 1 with pivalic acid has been reported.

Recognition of creatinine by weak aromatic acids in solid phase along with their supramolecular network

Aromatic acids and creatinine, an important blood metabolite, form well-defined crystalline ionic complexes. Their supramolecular architecture is formed not only by simple proton transfer and ionic interaction but also by other very important noncovalent interactions, especially the hydrogen bonds. The supramolecular behavior of the complexes is varied with the acidity and structural difference of aromatic acids. Creatinine interestingly generated creatine monohydrate during crystallization of creatinine with glacial acetic acid and the supramolecular array of creatine monohydrate is also reported.

Non-covalent synthesis of ionic and molecular complexes of benzoic acid and substituted 2-aminopyrimidines by varying aryl/alkyl substituents and their supramolecular chemistry

The non-covalent synthesis of ionic and molecular complexes of substituted 2-aminopyrimidines with benzoic acid in crystalline solid phase is reported. The nature of supramolecular architecture varied with the substituents in the 2-aminopyrimidine ring. Two complexes have been synthesised from two differently substituted 2-aminopyrimidines and benzoic acid. In one case, proton transfer takes place and an ionic organic salt is formed, whereas in the other, there is no proton transfer and a hydrogen-bonded molecular complex is formed.

Anion recognition by a family of quinoline-functionalised bis-amide hosts in solid state and in solution

The interaction between a series of bidentate, amide-functionalised 8-oxyquinoline receptors and coordinating anions is investigated. Anion recognition properties and conformations were studied by solid-state structures, Hartree–Fock calculations and solution-phase 1H NMR investigations. Our findings suggest that the amide-oxyquinoline motif coordinates anions and water with a well-defined, consistent geometry involving multiple hydrogen bonds. Solution studies of the neutral receptors reveal the unprotonated oxyquinoline ring to indirectly contribute to anion binding by the adjacent amide NH groups despite being unable to directly participate through hydrogen bonding.

Sodium Cyanoborohydride–Mediated Direct Conversion of Some Heterocyclic Aldehydes to Esters

Abstract An exceptional oxidizing behavior of sodium cyanoborohydride is observed where electron-withdrawing heterocyclic aldehydes are directly converted to their corresponding esters on treatment of sodium cyanoborohydride in methanol. The spectral analysis and single-crystal structure confirm the formation of esters.

6-Amino-2,5-bis-(pivaloylamino)pyrimidin-4(3H)-one dihydrate.

The asymmetric unit of the title compound, C14H23N5O3·2H2O, contains two crystallographically independent 6-amino-2,5-bis(pivaloylamino)pyrimidin-4(3H)-one molecules (A and B) with similar geometry and four water molecules. In both independent molecules, one of the amide groups is almost coplanar with the pyrimidine ring [dihedral angle of 12.85 (9) in A and 12.30 (10)° in B], whereas the other amide group is significantly twisted away from it [dihedral angle is 72.18 (7) in A and 71.29 (7)° in B]. In each independent molecule, an intramolecular N—H⋯O hydrogen bond generates an S(6) ring motif. Molecules A and B are linked into chains along the a axis by N—H⋯O and C—H⋯O hydrogen bonds. Adjacent chains are linked into a two-dimensional network parallel to the ac plane by water molecules via N—H⋯O and O—H⋯O hydrogen bonds.

Methyl pyrido[2,3-b]pyrazine-3-carboxyl-ate.

The asymmetric unit of the title compound, C9H7N3O2, is composed of two independent molecules. The crystal structure is stabilized by C—H⋯O and C—H⋯N hydrogen bonds, forming a three-dimensional network. The crystal structure also features pyrazine–pyrazine π–π interactions [centroid–centroid distance = 3.6994 (5) Å] and also pyridine–pyrazine π–π interactions [centroid–centroid distance = 3.6374 (5) Å].

N,N'-Bis(pyrimidin-2-yl)terephthalamide dihydrate.

The organic molecule of the title compound, C16H12N6O2·2H2O, lies across a crystallographic inversion centre. The dihedral angle between the pyrimidine and benzene rings is 80.78 (6)°. The two pyrimidine rings are parallel by virtue of the centre of symmetry. The pyrimidine and benzene rings form dihedral angles of 41.41 (7) and 40.26 (7)°, respectively, with the amide plane. The molecules are linked by N—H⋯N and C—H⋯N hydrogen bonds into a two-dimensional network parallel to the (11) plane. O—H⋯O and C—H⋯O hydrogen bonds involving the water molecules link the adjacent layers into a three-dimensional network. In addition, a C—H⋯π interaction involving the benzene ring is observed.

Ethyl 7-pivaloyl-amino-1,8-naphthyridine-2-carboxyl-ate sesquihydrate.

In the title hydrate, C16H19N3O3·1.5H2O, both water molecules are disordered: one over two adjacent sites in a 0.498 (5):0.502 (5) ratio and one lying near a crystallographic twofold axis. The dihedral angle between the pyridine rings of the organic moleucle is 1.47 (6)°. In the crystal, the components are linked by N—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds, forming sheets lying parallel to the ac plane.

N-Butyl-4,6-diphenyl-pyrimidin-2-amine.

In the title compound, C20H21N3, the pyrimidine ring is inclined at dihedral angles of 51.57 (4) and 2.49 (4)° to the two phenyl rings. The dihedral angle between the two terminal phenyl rings is 50.44 (4)°. In the crystal, adjacent molecules are linked via a pair of N—H⋯N hydrogen bonds, forming an inversion dimer with an R 2 2(8) ring motif. Furthermore, the crystal structure is stabilized by a weak π–π interaction, with a centroid–centroid distance of 3.6065 (5) Å.