Jia Hao Goh

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.

(E)-1-(4-Fluoro­phen­yl)ethan-1-one semicarbazone

In the title compound, C9H10BrN3O, the hydrazone portion and aliphatic chain are essentially coplanar [maximum deviation 0.057 (15) Å] and the mean plane makes a dihedral angle of 70.9 (6)° with the benzene ring. The main feature of the crystal structure is the intermolecular N—H⋯O hydrogen bond, which links molecules into zigzag chains along the a axis. These chains are further stacked along the b axis. The crystal structure features non-classical intermolecular C—H⋯O interactions. The crystal studied was a nonmerohedral twin, with a twin ratio of 0.505 (1):0.495 (1).

2,3-Diaminopyridinium 2-hydroxybenzoate

In the title compound, C5H8N3 +·C7H5O3 −, the pyridine N atom is protonated. In the 4-hydroxybenzoate anion, the carboxylate group is twisted slightly out of the benzene ring plane by an angle of 3.77 (5)°. The protonated N atom and one of the two amino groups are hydrogen-bonded to the 4-hydroxybenzoate anion through a pair of N—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. The crystal structure is further stabilized by O—H⋯O and C—H⋯O hydrogen bonds and π–π interactions involving the pyridinium rings [centroid–centroid distance of 3.6277 (5) Å], leading to the formation of a three-dimensional network.

Poly[[aquadi-μ3-malonato-hexaphenyl­ditin(IV)] acetone solvate]

The asymmetric unit of the title polymeric complex, {[Sn2=(C6H5)6(C3H2O4)(H2O)]·C3H6O}n, comprises of two Sn cations, one malonate anion and a non-coordinating acetone solvent molecule. Both crystallographically independent Sn cations are five-coordinated by two O and three C atoms in a distorted trigonal-bipyrimidal geometry. One of the Sn cations is bridged by the malonate units, affording polymeric chains which run along [001]. Weak intramolecular C—H⋯π interactions stabilize the molecular structure. In the crystal structure, adjacent chains are interconnected by intermolecular O—H⋯O and C—H⋯O hydrogen bonds into a three-dimensional supramolecular structure. A weak intermolecular C—H⋯π interaction is also observed.

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.

(E)-N′-(2-Hydroxy­benzyl­idene)-2-(4-isobutyl­phen­yl)propanohydrazide

The title hydrazide compound, C20H24N2O2, exists in a trans configuration with respect to the acyclic C=N bond and an intramolecular O—H⋯N hydrogen bond generates an S(6) ring motif. The mean plane through the formohydrazide unit is essentially planar [maximum deviation = 0.025 (2) Å], and forms dihedral angles of 24.45 (16) and 87.14 (16)° with the two benzene rings. In the crystal structure, intermolecular N—H⋯O and C—H⋯O hydrogen bonds link neighbouring molecules into extended chains along the c axis, which incorporate R 2 2(16) ring motifs. An intermolecular C—H⋯π interaction is also observed.

(E)-1-[1-(6-Bromo-2-oxo-2H-chromen-3-yl)ethyl­idene]thio­semicarbazide

The title compound, C12H10BrN3O2S, exists in an E configuration with respect to the C=N bond. The approximately planar 2H-chromene ring system [maximum deviation = 0.059 (1) Å] is inclined at a dihedral angle of 17.50 (5)° with respect to the mean plane through the thiosemicarbazide unit and an intramolecular N—H⋯N hydrogen bond generates an S(5) ring. In the crystal structure, adjacent molecules are linked by N—H⋯S hydrogen bonds, forming [010] chains built up from R 2 2(8) loops, such that each S atom accepts two such bonds. These chains are further interconnected into sheets parallel to the ab plane via short Br⋯O interactions [3.0732 (13) Å] and a π–π aromatic stacking interaction [3.7870 (8) Å] is also observed.

N-(2,4-Dioxo-1,3-thia­zolidin-3-yl)-2-(4-isobutyl­phen­yl)propanamide

In the title compound, C16H20N2O3S, the thiazolidine ring is approximately planar [maximum deviation = 0.020 (2) Å] and forms a dihedral angle of 86.20 (11)° with the benzene ring. The mean plane through the propanamide unit forms dihedral angles of 88.54 (12) and 76.36 (12)°, respectively, with the thiazolidine and benzene rings. In the crystal structure, molecules are linked into chains along the a axis by N—H⋯O interactions. These chains are interconnected into two-dimensional arrays parallel to the ab plane by three different C—H⋯O interactions. The crystal structure is further stabilized by weak intermolecular C—H⋯π and N⋯O [2.713 (2) Å] interactions.

3-{2-[2-(3-Hy­droxy­benzyl­idene)hydrazin-1-yl]-1,3-thia­zol-4-yl}-2H-chromen-2-one hemihydrate

In the title compound, C19H13N3O3S·0.5H2O, both organic molecules (A and B) exist in E configurations with respect to the acyclic C=N bond and have similar overall conformations. In molecule A, the essentially planar thiazole ring [maximum deviation = 0.010 (2) Å] is inclined at interplanar angles of 11.44 (10) and 32.50 (12)°, with the 2H-chromene ring system and the benzene ring, respectively. The equivalent values for molecule B are 0.002 (2) Å, 7.71 (9) and 12.51 (12)°. In the crystal structure, neighbouring molecules are interconnected into infinite layers lying parallel to (010) by O—H⋯O, O—H⋯N, N—H⋯O and C—H⋯O hydrogen bonds. Further stabilization of the crystal structure is provided by weak intermolecular C—H⋯π and π–π [centroid–centroid distance = 3.6380 (19) Å] interactions.

6-Meth-oxy-4-methyl-2H-chromen-2-one.

The whole molecule of the title coumarin derivative, C11H10O3, is approximately planar, with a maximum deviation of 0.116 (3) Å from the least-squares plane defined by all non-H atoms. In the crystal, adjacent molecules are linked into chains along [011] via intermolecular C—H⋯O hydrogen bonds.