Perumal Venkatesan

Crystal structure, Hirshfeld surfaces and DFT computation of NLO active (2E)-2-(ethoxycarbonyl)-3-[(1-methoxy-1-oxo-3-phenylpropan-2-yl)amino] prop-2-enoic acid

Nonlinear optical (NLO) activity of the compound (2E)-2-(ethoxycarbonyl)-3-[(1-methoxy-1-oxo-3-phenylpropan-2-yl)amino] prop-2-enoic acid is investigated experimentally and theoretically using X-ray crystallography and quantum chemical calculations. The NLO activity is confirmed by both powder Second Harmonic Generation (SHG) experiment and first hyper polarizability calculation. The title compound displays 8 fold excess of SHG activity when compared with the standard compound KDP. The gas phase geometry optimization and vibrational frequencies calculations are performed using density functional theory (DFT) incorporated in B3LYP with 6-311G++(d,p) basis set. The title compound crystallizes in non-centrosymmetric space group P21. Moreover, the crystal structure is primarily stabilized through intramolecular N-H···O and O-H···O hydrogen bonds and intermolecular C-H···O and C-H···π interactions. These intermolecular interactions are analyzed and quantified using Hirshfeld surface analysis and PIXEL method. The detailed vibrational assignments are performed on the basis of the potential energy distributions (PED) of the vibrational modes.

1-Alkyl-(N,N-dimethylamino)pyridinium bromides: inhibitory effect on virulence factors of Candida albicans and on the growth of bacterial pathogens

A homologous series of 1-alkyl-(N,N-dimethylamino)pyridinium bromides, termed compounds 1-11, was synthesized and studied for antibacterial and antifungal activity. Of these, compound 8, containing a ten-carbon alkyl chain, showed maximum inhibition against all the tested bacterial strains. The highest antibacterial activity using a disc diffusion method was recorded against Mycobacterium smegmatis [zone of inhibition (ZOI): 45.75±0.25 mm], followed by Escherichia coli, Proteus mirabilis, Vibrio cholerae, Staphylococcus aureus and Salmonella typhi. In addition to antibacterial activity, compounds 3-11 displayed good inhibitory action against the human opportunistic yeast pathogens Cryptococcus neoformans and various Candida spp. The maximum ZOI was observed against Cryptococcus neoformans (51.5±0.5 mm) using compound 8, with ZOIs of 23.5±0.5, 32.0±0.0, 27.75±0.25 and 41.5±0.5 mm against Candida albicans, Candida glabrata, Candida tropicalis and Candida krusei, respectively. Furthermore, compound 8 caused inhibition of the candidal yeast-hyphae transition at a concentration of 0.29 µM and also inhibited the secretion of extracellular hydrolytic enzyme such as secreted aspartyl proteinase at subinhibitory concentrations. Compound 8 showed very little haemolytic activity at a concentration of 0.58 µM (1.315±0.75 %), with its highest haemolytic activity (47.806±2.32 %) observed at a concentration of 2.9 µM.

Synthesis, characterization and antimicrobial activity of 4-amino-1-alkyl pyridinium salts

A series of 4-amino-1-alkyl pyridinium bromide salts (1–10) were synthesized and antimicrobial activity was evaluated by disc diffusion as well as broth macro-dilution method. 4-Amino-1-hexadecylpyridinium bromide (10) which showed good inhibition against Candida albicans and C. glabrata also displayed good germ tube inhibition against C. albicans. Compound 8 shows very low haemolytic activity against human red blood cells. Compound 10 exhibits excellent antibacterial activity against Escherichia coli and Staphylococcus aureus. Inhibition of phospholipase enzyme secretion was also observed against compound 8 to find the possible mode of action.

Invariant and variable intermolecular interactions in functionalized malonic acid half-esters: X-ray, Hirshfeld surface and PIXEL energy analyses

A series of functionalized malonic acid half-ester derivatives (parent compound MHE-1), with variations in functional groups at different positions on the aromatic ring, have been synthesized and crystal structures are determined at room temperature (296 K). The methyl (4-CH3, MHE-2) and chloro (4-Cl, MHE-3) derivatives are isomorphous with each other. The overall crystal packing of MHE-1–3 is similar. However, there are few differences observed between stacking of layers in these structures. Compounds with nitro (3-NO2, MHE-4) and ethyl ester (2-COOC2H5, MHE-5) substituents crystallize in different space groups and thus crystal packing is different when compared to MHE-1–3. In all the structures, intramolecular N–H⋯O and O–H⋯O hydrogen bonds generate a two fused S(6) ring motif. A detailed study is carried out to visualize intermolecular interactions observed in all five crystal structures (MHE-1–5) using Hirshfeld surface (HS) analysis with two dimensional fingerprint plots. The relative contribution of intermolecular H⋯H contacts in MHE-3 is substantially lower than that in MHE-1–2, though similar crystal packing arrangements of MHE-1–3 and MHE-2 and MHE-3 are isomorphous. From HS analysis it is clear that the observed H⋯H contact contribution (MHE-3) is a consequence of the presence of the chlorine substituent and growing contribution of Cl⋯H contacts. The relative contributions of other intermolecular contacts involving various atoms are comparable in MHE-1–3 structures. The intermolecular interaction energies are quantified using PIXEL for various molecular pairs extracted from respective crystal structures. Interestingly, there are some invariant and variable intermolecular contacts observed between different groups in all five structures.

4-Amino-(1-methyl­phen­yl)pyridinium bromide

In the cation of the title compound,

4-Amino-(1-ethoxycarbonylmethyl)pyridinium iodide

C-{12}H_{13}N2 {^+}Br{^-}

4‐Amino‐(1‐carboxy­meth­yl)pyridinium chloride

, the dihedral angle between the pyridine and benzene rings is

Crystal structure and Hirshfeld surface analysis of 1-carb­oxy-2-(3,4-di­hydroxy­phen­yl)ethan-1-aminium bromide 2-ammonio-3-(3,4-di­hydroxy­phen­yl)propano­ate

80.0(1){^o}

2-Amino-1-(4-nitro­benzyl)pyridinium bromide

. The anions and cations are connected by intermolecular N—H...Br hydrogen bonds, forming one-dimensional chains along [100].

Two new isatin derivatives: 1-benzyl-4,5,6-trimethoxyindoline-2,3-dione and 1-benzyl-5-fluoroindoline-2,3-dione

The crystal structure of the title compound,